SELECTIVE REDUCTION OF CONJUGATED NITROQLEFINS
DISSERTATION
Presented in Partial Fulfillment of the Requirements for the Degree Doctor of Philosophy in the Graduate School of The Ohio State University
By
DEAN EVERETT LEY, B.Sc., M.Sc.
The Ohio State University
1954
Approved by:
/ Adviser Department of Chemistry ACKNOWLEDGMENTS
The author wishes to express his gratitude to Doctor Harold Shechter, who suggested this problem, for his generous guidance and advice throughout this investigation and his assistance in the preparation of this dissertation.
He also acknowledges the generous spirit in which several graduate students and staff members contributed useful materials, equipment and information.
The author also wishes to express his appreciation to the Office of Naval Research, who generously supplied the funds that made this research possible. TABLE OF CONTENTS
Page A. STATEMENT OF PROBLEM...... 1 B. INTRODUCTION...... 2 C. HISTORICAL 1. Reduction of Conjugated Nitroolefins by Dissolving Metals...... 10 2. Catalytic Reduction of Conjugated and Unconjugated Nitroolefins...... 13 3. Reduction of Conjugated Nitroolefins With Complex Hydrides ...... 15 D. THE PRESENT INVESTIGATION, DISCUSSION OF RESULTS 1. Selective Reduction of Conjugated Nitroolefins by Sodium Trimethoxyboro- hydride...... 22 2. Selective Reduction of Conjugated Nitroolefins by Lithium Borohydride.... 34 3. Selective Reduction of Conjugated Nitroolefins by Lithium Aluminum Hydride 43 4. Selective Reduction of Conjugated Nitroolefins by Sodium Borohydride 4& E. EXPERIMENTAL TECHNIQUE 1. Apparatus...... 52 2. Solvents...... 52 3. Mode of Addition...... 54 4. Handling of Hydrides...... 54 5. Acidification of the Reaction Mixture.. 55 6. Identification of Products...... 55 F. REAGENTS...... 57 iii Page
G. EXPERIMENTAL 1. Selective Reduction of Conjugated Nitroolefins by Sodium Trimethoxyboro- hydride...... 65 a. Reduction of 1-nitropropene 65 b. Reduction of 2-methyl-l-nitro- propene...... 67 c. Reduction of 2-nitro-l-butene... 70 d. Reduction of 2-nitro-2-butene... 73 e. Reduction of 4-nitro-3-heptene.. 76 f. Reduction of 3,3>3-trichloro-l- nitropropene...... 79 g. Reduction of 4j45 5, 5,6,6,6-hIepta- fluoro-2-nitro-2-hexene...... 82 h. Reduction of 5,5,6,6,7>7, 7-Kepta- fluoro-3-nitro-3“heptene...... 83 i. Reduction of omega-nitrostyrene. 8k j. Reduction of 2-(2-nitrovinyl) furan...... 8 9 k. Attempted reduction of l-(nitro- methyl) cyclopentene...... 91 1. Reaction of Sodium trimethoxy- borohydride with 2-nitro-l-butyl acetate...... 92 2. Selective Reduction of Conjugated Nitroolefins by Lithium Borohydride a. Reduction of 1-nitropropene 93 b. Reduction of 2-methyl-l-nitro- propene...... 95 c. Reduction of 2-nitro-l-butene... 97 d. Reduction of 2-nitro-2-butene. 100 e. Reduction of 4-nitro-3-heptene.. 101 f. Reduction of 3j3>3-trichloro-l- nit r opropene...... 104 g. Reduction of 4,4,5j5,6,6 ,6-hepta- fluoro-2-nitro-2-heptene...... 10$ h. Reduction of 5,5,6 ,o,7>7>7-hepta- fluoro-3-nitro-3-heptene...... 106 i. Reduction of oraega-nitrostyrene. 10$ j. Reduction of 2-(2-nitrovinyl) furan...... 110 k. Reduction of D-arabo-tetra- acetoxy-l-nitrohexene...... 112 1. Reaction of Lithium borohydride with 2-nitro-l-butyl acetate.... 113
iv Page
3. Selective Reduction of Conjugated Nitro olefins With Lithium Aluminum Hydride a. Reduction of 2-nitro-2-butene 114 b. Reduction of 3>3j3-trichloro-l- nitropropene...... 115 c. Reduction of 3,3,3-trifluoro-l- nitropropene...... 116 d. Reduction of 5j5>6,6,7,7j7-hepta- fluoro-3-nitro-3-heptene...... 118 e. Reduction of omega-nitrostyrene... 119 f. Reduction of 2-nitro-l-phenyl- propene...... 122 g. Reduction of 2-(2-nitrovinyl)furan 124 4. Selective Reduction of Conjugated Nitroolefins With Sodium Borohydride a. Reduction of 2-nitro-2-butene 125 b. Reduction of 4-nitro-3-heptene..., 127 c. Reduction of omega-nitrostyrene... 128 d. Reduction of D-arabo-tetra- acetoxy-l-nitrohexene...... 131 e. Attempted heretrogeneous reduction of 5,5,6, 6,7,7j7-heptafluoro-3- nitro-3-heptene...... 131 5. Reaction of Omega-nitrostyrene in the Presence of Benzyltrirnethylammonium Hydroxide...... 132 6. Reaction of 2-(2-Nitrovinyl)furan in the Presence of Benzyltrirnethylammonium Hydroxide...... 133 7. Reaction of l-Nitro-2-phenylethane and Omega-nitrostyrene...... 133 8. Reaction of 2-Nitro-l-butene and 2- Nitrobutane...... 134 H. CONCLUSIONS...... 136 I. BIBLIOGRAPHY...... 139 J. AUTOBIOGRAPHY...... 144
o o SELECTIVE REDUCTION OF CONJUGATED NITROOLEFINS
A. STATEMENT OF PROBLEM
The present investigation is primarily a study of the reduction of conjugated nitroolefins with lithium borohydride, sodium borohydride, sodium trimethoxyborohydride and lithium aluminum hydride, respectively. It is the purpose of this study to develop satisfactory laboratory methods for synthesis of primary and secondary nitroalkanes from their corresponding conjugated nitroalkenes; it is also desirous that the methods developed be applicable for preparation of complex and highly functionally-substituted primary and secondary mononitroalkanes.
1 2 B. INTRODUCTION
During the past decade the chemistry of aliphatic nitro compounds has been a subject of renewed interest; excellent reviews of the earlier chemistry of nitroalkanes 1 2 have been written by Gabriel in 1939 and 1940 , Hass and Riley^ in 1943, Degering in 1945^, Levy and Rose'* in 194$> 6 7 Shechter and Kaplan in 1952, and Hass, Riley and Shechter' in 1953. Examination of the extensive literature of nitro- paraffin chemistry reveals, however, that there are very few methods for synthesis of pure nitroalkanes by satisfactory • methods. Most of the methods that have been developed suffer the limitations that they are not general, the yields of reaction product are poor, the processes are tedious and involve complex and unavailable reactants, and mixtures which are difficultly separated are obtained. A survey, appropriate for the present discussion, of laboratory methods, and their limitations, for preparing mononitro- alkanes will now be summarized. The most important method for preparation of lower nitroalkanes involves nitration of alkanes in the vapor- 8 phase with nitric acid. Vapor-phase nitration is usually conducted as a continuous process at temperatures ranging from 350-450° and exposure times up to one second. Under these conditions, any primary, secondary, or tertiary hydrogen atom or any alkyl group of an alkane may be 3 replaced by a nitro group to yield mononitroalkanes. Thus, nitration of propane, a process now being operated tech- 9 nically by the Commercial Solvents Corporation, yields nitromethane, nitroethane, 1-nitropropane, and 2-nitro- propane. The vapor-phase method, although quite satis factory for commercial adaptation, suffers from the facts: (1 ) the experimental conditions are either too drastic or are inaccessible for ready laboratory use, (2 ) the reactions are relatively non-specific in that oxidation is an important competitive process, and (3 ) the nitration products are those derived by all possible hydrogen and alkyl-substitu tion processes. At present, for the laboratory chemist, the most significant aspect of the vapor-phase method is that it offers large quantities of lower mononitroalkanes very economically; these lower mononitro compounds then serve as convenient reagents for synthesis of more complex mononitro compounds. Nitration of hydrocarbons in the liquid-phase has been widely studied"^’ ^ in an attempt to develop adequate methods for preparing mononitroalkanes. The principal liquid-phase nitration reaction is replacement of hydrogen atoms by nitro groups; a nitration reaction involving replacement of alkyl groups does not occur as in the vapor-phase process. The order of reactivity of hydrogen atoms of alkanes or cycloalkanes is tertiary >
O 4 secondary> primary. The liquid-phase method; offers the disadvantages that (1 ) most organic substances are in soluble in nitric acid or in nitrating mixtures, (2 ) mixtures of primary, secondary, and tertiary mononitro compounds which are separated with great difficulty are always obtained, (3 ) excessive oxidation-reduction usually accompanies nitration, (4 ) hydrolysis and oxidation of the primary and secondary nitroalkanes yield carboxylic acids and ketones, respectively, which then undergo further oxi dation, and (5) continued nitration of mononitroalkanes results in formation of polynitroalkanes. The principal laboratory uses for liquid-phase nitration are therefore usually limited to preparation of simple tertiary nitro compounds (separable from acidic nitro compounds by alkaline extraction), simple nitrocycloalkanes, and certain stable and unique primary and secondary mononitroalkanes. The most important general method for preparing unsubstituted mononitroalkanes has been reaction of alkyl halides with metallic nitrites. Reaction of silver nitrite with primary, secondary, or tertiary halides is known as the Victor Meyer method; the reaction may lead to the formation of alkyl nitrites and nitrates and various 11 12 oxygenated derivatives along with nitroalkanes, ’ This 13, 14 reaction is of greatest importance in preparation of primary mononitroalkanes (44-&3 per cent); yields of
Q 0 0 0 5 secondary nitroalkanes are greatly diminished ( 15 per cent); formation of tertiary nitroalkanes from tertiary alkyl halides is almost negligible (0-5 per cent). The yield of undesirable esters and various oxygenated products may be minimized by effecting reaction of the primary halides at temperatures below that at which silver nitrite decomposes into silver nitrate and nitric oxide. Improvements have also been made in the procedures for isolating the nitro alkanes from their various contaminants. A recent advantageous adaptation of the Victor Meyer reaction involves displacement of primary and secondary alkyl bromides and iodides with electrovalent metal nitrites (NaNC^) KNC^j and LiNOg) in homogeneous media. The solvents which may be used are dimethylformamide,^ ethylene glycol- 16 17 water-tetrahydrofurfuryl alcohol, and pyrocatechol; in such systems displacement involving oxygen-alkylation become less important, and formation of nitroalkanes becomes practicable. The solvent of choice is dimethylformamide; thus, reactions of 1-iodoctane, 2-iodooctane, 2-bromooctane and benzyl bromide with sodium nitrite at room temperature give 1-nitrooctane (60 per cent), 2-nitrooctane (60 per cent), 2-nitrooctane (59 per cent), and phenylnitromethane(55 per cent), respectively."^ In similar reactions involving displacement by nitrite ion, sodium nitrite reacts, respec- 1$ tively, with (1 ) alkyl sodium sulfates or dialkyl sulfates
0 o
6 or (2 ) salts of cc -halo acids to give nitromethane and its 3 homologs. Displacement reactions of salts of mononitro com- . pounds with alkyl halides involving carbon-alkylationlhave often been attempted for preparation of substituted raono- 6 19 nitroalkanes. ' A competitive reaction involving oxygen- alkylation may result in formation of the isomeric nitronic esters; nitronic esters are unstable and decompose into 6 ,1 9 > 20 oximes and aldehydes or ketones. Carbon-alkylation may be enhanced by using silver salts of the nitroalkanes and methyl iodide. Benzyl halides, substituted in the para and/or ortho positions with nitro groups, react with alkanenitronates to give substituted mononitroalkanes; benzyl halides, either unsubstituted or containing electro negative or electropositive groups other than nitro groups, usually yield oxygen-alkylated products upon reaction with 20 21 22 2 ^ salts of mononitroalkanes. ’ * ’ 5-Nitrofurfuryl chloride and sodium 2-propanenitronate have been found to give 5-nitro-2-(2 ’-nitro-2 ’-methylpropyl)-furan in low yield. Oxidation of functional groups containing nitrogen attached to carbon may be used for preparation of certain nitroalkanes. Oxidation of primary and secondary amines may yield nitroalkanes; however, these reactions suffer the complications that the primary and secondary nitro “compounds
o O 7 e • 0 0 * formed undergo further oxidation. This method therefore has had little applicability,0 Oxidation of tertiary * A carbinamines to tertiary nitro compounds may be effected in high yields by oxidation with potassium permanganate or alkaline hydrogen peroxide; at present, this method appears to be the most applicable for efficient and convenient 25 laboratory synthesis of pure tertiary nitroalkanes. Oximes may be converted to nitro compounds if the nitro products are sufficiently stable to withstand further oxida tion by the oxidant; oximinomalonic esters are converted to * * 26 nitromalonic esters by the action of manganese dioxide. An improved general method for conversion of ketoximes to secondary nitro compounds has been developed 27 28 29 by Iffland and associates. y 7 By this method ketoximes are converted to oc-bromonitroso compounds by reaction with N-bromosuccinimide; oc-bromonitro compounds are prepared by oxidation of the oc-bromonitroso compounds with nitric acid; reduction of the oc-bromonitro compounds to nitro compounds is effected by sodium borohydride in aqueous medium. This 4- method has proved to be of considerable importance for the
preparation of strained" nitrocycloalkanes and highly branched mononitroalkanes; however, the sequence is labor- ious, it is not applicable for synthesis of primary nitro compounds, it requires synthesis of complex ketones or 0 ketoximes, and the hydrocarbon structures on which successful O »o 0 o !> o @ @ >
3 reaction may be accomplished must be inert to the actions of nitric acid or N-bromosuccinimide. Reaction of alkyl magnesium bromides with primary 29A and secondary oc -nitroolefins 7 has been studied as a preparation for certain nitroalkanes. The initial step is a rapid 1:4 addition of the Grignard reagent to the conjugated system to give a complex which may be decomposed by water to give a nitroparaffin. The product may react with more Grignard reagent to give another complex which on treatment with water yields an oxime. Some 1:2 addition to the nitroolefin occurs to give a complex that results in basic products upon treatment with water. The general applicability of this reaction has not been studied and the yields are rather low. Since an examination of 'die literature revealed a deficiency in adequate methods (other methods shall be described in the Historical section) for synthesis of primary and secondary mononitroalkanes and of functionally- substituted primary and secondary nitro compounds, the author became concerned with developing new or improved general reactions for preparation of acidic mononitroalkanes. * It appeared that a convenient and efficient route to satu rated mononitro compounds might be derived from conjugated nitroolefins; conjugated nitroalkenes may be readily pre pared in the laboratory by dehydration of vicinal
O 0 9 nitroalcohols,^ dehydroacylation of vicinal nitroesters, ^ or by elimination of nitrous and nitric acids from the vicinal addition products derived from alkenes or cyclo- 32 alkenes and oxides of nitrogen. The reduction of con jugated nitroalkenes has been the subject of many previous studies, as is described in the following Historical section however, useful general procedures for selective reduction of the carbon-carbon double bond have not been evolved. It was therefore the purpose of this research to examine the selective reduction of appropriate nitroolefins to their corresponding saturated nitro compounds. c HISTORICAL
1. REDUCTION OF CONJUGATED NITROOLEFINS BY DISSOLVING METALS.
Controlled reduction of conjugated nitroolefins by various metals and acids usually results in formation of aldoximes and ketoximes. Thus W a l l a c h ^ reduced 1-anisyl- 2-nitropropene and 2-nitro-l-piperonylpropene to 1-anisyl- 2-propanone oxime and l-piperonyl-2-propanone oxime, respectively, with zinc and acetic acid at 0°; hydrolysis of the oximes with sulfuric acid yielded the corresponding OJ ketones. Similarly Bouveault and Wahl reduced omega- nitrostyrene to phenylacetaldehyde with zinc or aluminum amalgam and glacial acetic acid. The poor yields in re duction of p-raethoxy-omega-nitrostyrene by the methods of oc Bouveault and Wahl have been found by Rosenmund"^ to arise from the ease with which the substituted nitrostyrene polymerizes, Alexejew,^ Priebs^? and Alles-^ experienced con siderable difficulty in reducing conjugated arylnitro- alkenes to the corresponding oximes with dissolving metals or their amalgams; Alles has found, however, that 2-nitro- 1-phenylpropene and similar derivatives are reduced to 2-amino-l-phenylpropane and its analogs by electrochemical methods. The reduction of simple conjugated nitroolefins with 10 11 iron and hydrochloric acid has been studied by Hass, Susie, og and Heider. It was found that the corresponding oximes or carbonyl compounds were produced in excellent (70 per cent) yields; there is very little polymerization of the conjugated aliphatic nitroolefins under these reducing conditions. An examination of the literature on the reducing action of dissolving metals on conjugated nitroolefins does not reveal an example of controlled reduction to the satu rated nitroalkane. The reduction of conjugated nitroolefins to nitroalkanes appears to be complicated by possible re duction of the nitroalkane as formed to the corresponding oxime, hydroxylamine, or amine. As yet, there has been no study of the effect of reducing potential on the paths of reduction of nitroolefins; the mechanisms of reduction of conjugated nitroolefins to oximes have also not been established. In the absence of any specific information, it is assumed that there are at least four general paths for conversion of nitroalkenes to oximes: (1 ) 1 ,2-addition to the conjugated nitroalkene to give the saturated nitro alkane, subsequent reduction of which yields the corre sponding oxime (Equation,1), (2) 1,4-addition to the nitro alkene to produce the nitronic acid, reduction of which gives the oxime (Equation 2 ), (3 ) initial reduction of the nitro compound to the unsaturated hydroxylamine, tautomeri- zation of which will be expected to yield the oxime
o o 12 (Equation 3)> and. (4) initial reduction to the unsaturated nitroso compound, subsequent reduction and tautomerization of which may give the oxime (Equation 4). In view of the fact that aliphatic and 0 0 RCH~CH-N_ + / r>+ 2 k ■> RCH2-CH2-N^^ 7 > RCH2-CH=N0H (1) 0 0 0 OH + '// -r + / RCH=CH-N -> RCH0-CH=N Zn > RCHo-CH=N0H (2) \ H+ \ H+ X 2 0 0 0 RCH'CH-N RCH^CH-NHOH RCH2-CH=NOH (3) N> 0 RCH=CH-rt/ — -j, RCH^CH-fPO RCH2-CH2-N=0 -a^RCH2 -(4) 0 CH=NOH aromatic nitro groups are readily reduced by metals and acids, it appears quite likely that sequences 3 or 4 may be preferred routes, thus preventing formation of inter mediate saturated mononitro compounds. If the reducing actions of metal on nitroalkenes to yield nitroalkanes is to be investigated, it is of importance to consider the possibilities of reduction in alkaline media or at control led potentials in an effort to effect reduction via paths 1 and 2 .
o 0 O 13 2. CATALYTIC REDUCTION OF CONJUGATED AND UNCONJUGATED NITROOLEFINS.
Catalytic hydrogenation of nitroolefins has been ‘the subject of many studies. A wide variety of products is produced in these reactions; the nature of these products appears to depend on the type of nitroolefin reduced, the reducing catalyst, and the experimental conditions. With careful control of the experimental environment it is possible to direct the paths of reduction so that specific types of derivatives may be prepared in satisfactory yields. Sonn and Schellenberg^ have found that the principal product of reduction of omega-nitrostyrene with platinum and hydrogen is the dimer, 1 ,4-dinitro-2 ,3-diphenylbutane; the minor product of reduction is phenylacetaldoxime. Similar results were obtained with 3>4-methylenedioxy-omega- nitrostyrene. In an extension of this study, Kohler and Drake^- have reported that reductions of omega-nitrostyrene in various solvents and in the presence of palladium black, platinum black of different degrees of activity, colloidal' platinum, or nickel, give constant yields of 1 ,4-dinitro- 2,3-diphenylbutane. Reductions of nitrostilbene and 2-nitro- 1 ,1-diphenylethene was attempted; however, no saturated mononitro or dimeric nitro products were obtained. Smith and Bedoit^ have recently duplicated the results of Sonn and Schellenberg. p * o O * 3 • o © 3. REDUCTION OF CONJUGATED NITROOLEFINS WITH COMPLEX HYDRIDES. Principally from efforts of Schlesinger and his associates, complex hydrides of elements of the third periodic group have become available; these hydrides have found extensive general use in reduction of organic com pounds. The hydrides function as nucleophilic reductants; they, thus, find wide application in reduction of the un saturated groups in esters, aldehydes, ketones, acids, amides, nitriles, etc. The hydrides often offer advantage in that side reactions, polymerizations, condensations and cleavage may be avoided. Reduction products are often obtained in nearly quantitative yields and of. purity difficult to ob tain by other methods. Lithium aluminum hydride has become one of the most useful and convenient reagents for selective reduction of various unsaturated groups;^2 aldehydes, ketones, acids, esters, and acid chlorides are reduced to corresponding alcohols, amides to corresponding amines, aromatic nitro compounds to azo compounds, nitroalkanes to amines53 at room temperature, etc. The hydride is usually used in diethyl ether solution, less commonly in high boiling ethers. The reduction reactions usually give rise to intermediate metal aluminoalkoxides or other complexes from which the desired products are liberated by hydrolysis. The principal limita tions in use of lithium aluminum hydride are the hazard, costs, and the losses entailed in isolation of the product. Reduction of carbon-carbon double bonds by lithium aluminum hydride was first discovered by Hochstein and Brown.^ In reduction of cinnamaldehyde, reaction occurs 17 in two stages; (1 ) reduction of cinnamaldehyde, to cinnamyl alcohol (Equation 5)> and (2) addition of the metal hydride to the double bond, followed by hydrolysis to LiAlHj. C6H5-CH=CH-CH=0 J LiAl (O-CHg-CPPCH-^H^ (5) LiAlHj i LiAl(0-CH2-CH=CH-C6H5)4 I* LiAl( ^ (6) ' v HpO LiAl(0-CH2-CH2-CH-G6H5)4 C6H5-CH2-CH2-CH20H hydrocinnamyl alcohol (Equations 6 ). The reduction can be stopped at the first stage by reverse addition of the hydride at low temperatures. Snyder^’^ and coworkers have selectively reduced the carbon-carbon double bond of unsaturated amides to saturated amides; reverse addition was used. The mechanism of this reduction was postulated to involve hydride ion transfer from the aluminohydride ion to the more positive carbon atom of the olefinic bond (Equation 7); hydrolysis of the anion ■ produced yields the saturated amide (Equation 8). rVc-CR^-CONI^ + AlHj" --- ». R1R2CH-CR3-CONR2 + AIH3 (7) R1R2CH-QR3-C0NR2 + HOH --- > R1R2CH-CHR3-C0NR2 + 0H“ (3) In this work it was noted that higher molecular weight products were formed; these products were probably formed by Michael addition of the reduction product ( a basic anion) o o o 0 18 to the unsaturated amide. Recently, evidence for reduction of the carbon-carbon double bond of acrylonitrile by lithium aluminum hydride has been found, by Soffer and Parrota;^? ap high dilutions in ethyl ether, n-propylamine (low yields) is formed. As a result of the fact that the carbon-carbon double bond in cinnamyl alcohol can be reduced by lithium aluminum hydride, a study of the reduction of conjugated nitroolefins with complex hydrides was planned. Concurrent with this ci study Nord and Gilsdorf? published the results of the reverse addition of lithium aluminum hydride to nitroolefins. In their study of the reduction of 2-nitro-l-phenylpropene and omega-nitrostyrene, it was found that different products could be obtained by varying the reaction temperature and the ratio of the reactants. Their studies demonstrated that the reduction of conjugated nitroolefins occurs stepxvise and is capable of such control that amines, hydroxylamines, oximes, or nitroalkanes are produced. At temperatures of -40 to -50°, 2-nitro-l-phenylpropene was reduced to 2-nitro- 1-phenylpropane in 56 per cent yield, thereby demonstrating the stability of aliphatic nitro groups in the presence of lithium aluminum hydride at low temperatures. The procedures developed in this research were, in general, inadequate for the synthesis of saturated nitro compounds. D o m o w and B a r t s c h ^ have since suggested that reaction of lithium aluminum hydride with omega-nitrostyrene involves o 19 actual 1,4-addition of lithium aluminum hydride to the conjugated nitroolefin system. Simultaneous with (and as a result of) the work of the present author, Cook, Pierce and McBee^ reported the reduction of 3>3 j4 ,4,5,5,5-hepta- fluoro-l-nitropentene, 4 j 4} 5> 5,6 ,6 ,6-heptofluoro-2-nitro- 2-hexene and 5,5,6,6,7>7>7-heptafluoro-3-nitro-3-heptene to the corresponding fluorinated nitroalkanes in yields of 51 per cent, 51 per cent and 69 per cent, respectively. Aliphatic and aromatic nitro groups are not reduced by sodium borohydride. Meta-nitrobenzaldehyde is reduced by sodium borohydride to m-nitrobenzyl alcohol; aliphatic nitrocarbonyl compounds are rapidly converted to the £\0 0 corresponding nitrocarbinols at 0-25 over the pH range 3-10.5. Iffland and associates^ have recently further illustrated the stability of aliphatic nitro groups to borohydrides by reducing oc-bromonitro compounds to the corresponding nitro compounds with sodium borohydride. These results and the fact that sodium borohydride is a mild re ducing agent having nucleophilic properties have led to the present study of the reducing action of sodium borohydride on conjugated nitroolefins. Sodium borohydride may be somewhat limited in its use because of its insolubility in ethyl ether; it may be used to reduce carbonyl compounds in alcohol or alcohol-water mixtures. O o 20 Sodium trimethoxyborohydride may be prepared con veniently from sodium hydride and trimethylborate. It is an excellent reducing agent; it is a more powerful reductant than sodium borohydride but less powerful than lithium aluminum hydride or lithium borohydride. This hydride readily reduces aldehydes, ketones, acid chlorides, and anhydrides, but esters and nitriles are only slowly reduced at elevated temperatures. The nitro group in nitrobenzene is not reduced by sodium trimethoxyborohydride at lower temperatures but undergoes reaction at 140°. Double bonds proved stable even when conjugated with a carbonyl group. Since sodium trimethoxyborohydride is readily prepared, since nitro groups are not rapidly attacked by this hydride and since it is predicted that the hydride has greater nucleophilic or reductive properties than sodium borohydride, a study was planned of its selectivity for reducing ‘ conjugated nitroolefins. Lithium borohydride shares with lithium aluminum hydride the property of solubility in ethyl ether and other organic solvents. In ether it is a more powerful reducing agent than sodium borohydride or sodium trimethoxyborohydride but less powerful than lithium aluminum hydride. It reduces acid chlorides, aldehydes, and ketones very easily but reduces esters and carboxylic acids to alcohols only on refluxing for several hours.^ The stability of nitro o 0 o groups to this reagent has been previously determined by reduction of m-nitroacetophenone to cc-(m-nitrophenyl)- ethanol; however, nitrobenzene, upon being refluxed with lithium borohydride for IS hours in ether-tetrahydrofuran, gave aniline (22 per cent), an unidentified product (30 per cent), and :unchanged nitrobenzene (30 per cent). It thus appeared that lithium borohydride shows promise for selective reduction of conjugated nitroolefins by a reaction of the Michael type. A study of its use and a comparison with lithium aluminum hydride, sodium borohydride and sodium trimethoxyborohydrlde for preparation of saturated nitro compounds is to be made in the present research. o o O O o 22 D. THE PRESENT INVESTIGATION, DISCUSSION RESULTS 1. SELECTIVE REDUCTION OF CONJUGATED NITRQQLEFINS BY SODIUM TRIMETHOXYBOROHYDRIDE. An investigation has been made of selective reduction of conjugated and unconjugated nitroolefins with sodium trimethoxyborohydride. It has been found that sodium trimethoxyborohydride is an excellent reducing agent for the carbon-carbon double of conjugated nitroolefins; the reduction reaction is of the Michael type (Equations 9) RR'C=CR»N02 + NaBH(OCH3)3_____ > RR’CH-CR"N02Na + (OCH^)B RR»CH-CR»N02Na + H+ ____ „ RR'CH-CHR"N02 + Na+ (9) and results in a satisfactory general method for preparing primary and secondary mononitroalkanes. The reduction reaction is conducted in tetrahydrofuran-ethyl ether and occurs rapidly over a temperature range of -70 to 0°. The reductions may be effected with stoichiometric quantities of sodium trimethoxyborohydride and nitroolefin; however, incomplete reduction usually occurs, resulting in formation of mixtures of nitroalkene and nitroalkane. The nitro- alkene may be selectively removed by reaction with aqueous sodium bisulfite; it is more practical, however, to use 50 per cent excess sodium trimethoxyborohydride and drive the reduction reaction to completion. The reduction products, initially the sodium salts ofprimary and secondary nitroalkanes, are isolated upon acidifying the reduction mixtures with solutions of acetic acid and urea at 0°. A summary of the results of reduction of various oc , p-unsatu- rated nitro compounds is included in Table 1. The aliphatic conjugated nitroalkenes: 1-nitropropene, 2-nitro-l-butene, 2-nitro-2-butene, 2-methyl-l-nitropropene, and 4-nitro-3-heptene were studied to determine the scope and the efficiency of this reaction for preparing saturated aliphatic nitro compounds. Yields of 1-nitropropane, 2- nitrobutane, and 2-methyl-l-nitropropane of Sl.7> 45.0-62.6 , and 5^.7 per cent, respectively, (Table 1) were obtained with little difficulty at 0 to -70°. It was thus established that sodium trimethoxyborohydride will function effectively as a reducing agent for conjugated nitroolefins containing a primary nitro group and a terminal carbon-carbon double bond, a secondary nitro group and a terminal double bond, or a secondary nitro group and a internal (secondary) double bond. In general, the yields obtained from reduction of these lower nitroolefins can not be correlated with differences in electrical effects in the nitro compounds. The relatively hindered nitroolefin, 4-nitro-3- heptene, undergoes very slow reduction by sodium trimethoxy borohydride. Reaction proceeds slowly at -40°, and, even after prolonged periods at 0° (6 hours, Table 2), reduction is not complete. The relative resistance of 4-nitro-3- 24 TABLE 1 REDUCTION OF CONJUGATED NITROOLEFINS WITH SODIUM TRIMETHOXYBOROHYDRIDE" Per cent Conjugated Nitroalkene Reaction Products Conversion 1-Nitropropene 1-Nitropropane; 61.7 2-Methyl-1,3- 11.4 dini tropentane 2-Methyl-l-nitropropene 2-Methyl-l-nitro- 56.7 propane 2-Nitro-l-butene 2-Nitrobutane; 45.0 3-Methyl-3, 5- 35.0 dinitroheptane 2-Nitro-2-butene 2-Nitrobutane; 62.6 3,4-Dimethyl-2,4- 11.4 dinitrohexane 4-Nitro-3-heptene 4-Nitroheptane 55.0 3,3,3-Trichloro-l- 1,1,l-Trichloro-3- 44.2 nitropropene nitropropane; 1,1, l-Trichloro-3, 5- 32.1 dinitro-4-tri chloro- methylpentane 5,5,6,6,7,7,7-Heptafluoro-1,1,1,2, 2,3, 3-Hepta- 91.0 3-nitro-3-heptene fluoro-5-nitroheptane 4,4,5,5,6,6 ,6-Heptafluoro- 1,1,1,2,2,3,3-Hepta- 64.0 2-nitro-2-hexene fluoro-5-nitrohexane Omega-nitrostyrene 1-Nit ro-2-phenylethane; 36.6 1 ,3-dinitro-2,4- 23.6 diphenylbutane; Polymer 19.6 2-(2-Nitrovinyl)furan 2-(2-Nitroethyl)furan; 26.3 Polymer 46.6 25 heptene to reduction may be attributed to steric factors involved in attack of the hindered nitroolefin by the hindered trimethoxyborohydride ion. A further aspect of reducing hindered nitroolefins (particularly at higher temperatures [0°]) is that reduction of the aliphatic nitro group may become of competitive significance. The reductive attack on the nitro group of 4-nitro-3-heptene may arise as TABLE 2 EFFECT OF TIME AND TEMPERATURE ON REDUCTION OF 4-NITRO-3-ITEPTME' WITH SODIUM I^TME^HQXYBOROHYDRIDE Per cent Per cent Time Conversion to Recovery of Temperature Hours 4-Nitroheptane 4-Nitro-3-heptene o - 3 - o r 1.66 40.5 27.9 0° 1.66 50.5 31.0 0° 6.00 55.0 2.9 a resultant of default in reduction of the carbon-carbon double bond. Evidence (infrared) was obtained in reduction of 4 -nitro-3-heptene that minor attack on the nitro group was occurring; the reduction product was isolated in low yield but could not be completely characterized. (See Experimental) The reduction of conjugated nitroolefins by sodium trimethoxyborohydride is complicated by consecutive reactions 26 of the Michael type in which the reduction product, the salt of the nitroalkane, adds to the initial conjugated nitroolefin to yield the corresponding 1,3-dinitroalkanes (Equation 10). Thus reduction of 1-nitropropene also yields RR’CH-CR"(N0o)“ + RR»C=CR"N0? ____ => (10) RR tCH-CR"(N02)-CRR*-CR"N02~ 2-methyl-1,3-dinitropropane (11.4 per cent); 2-nitro-l- butene also gives 3-methyl-3, 5-dinitrobutane (35.0 per cent), and 2-nitro-2-butene affords 3,4-dimethyl-2,4-dinitrohexane (11.4 per cent). The 1,3-dinitroalkanes were isolated and then identified by infrared and quantitative analyses. 3-Methyl-3,5-dinitroheptane, obtained from reduction of 2- nitro-l-butene, was converted to 3-methyl-3-nitro-5-heptanone and its 2,4-dinitrophenylhydrazone via its sodium salt, the Nef reaction^ (41 per cent) and subsequent reaction with 2.4-dinitrophenylhydrazine. The 3-methyl-3-nitro-5-heptanone 2.4-dinitrophenylhydrazone was identical with that obtained from authentic 3-*nethyl-3, 5-dinitroheptane prepared by Michael reaction (59 per cent) of 2-nitro-l-butene and 2- nitrobutane. Products derivable from consecutive Michael typej . reactions were absent in several systems. In compounds having high steric requirements such as 4-nitro-3-heptene, the Michael reaction may be sterically hindered. Also, stable salts of nitro compounds, such as the salt of o 27 1,1,1,2,2,3,3-heptafluoro-5-nitroheptane, probably do not tend to undergo these further condensations, thus higher molecular weight products are absent. In reduction of 2-nitro-l-butene ■ (Table 3)> a non-distillable residue was obtained at 0° which suggests that the competing Michael type reaction may advance beyond 1:1 addition to produce higher molecular weight products. The reduction reactions of sodium trimethoxyboro hydride and 3»3>3-trichloro-l-nitropropene (Table 1) were investigated to determine if (1) a conjugated carbon-carbon double bond can be selectively reduced in the presence of allylic chlorine, and (2) a highly electron deficient (and hindered) conjugated nitroolefin will undergo Michael re duction. It is to be expected that nucleophilic attack on the p-carbon atom of 3>3>3-trichloro-l-nitropropene (A) will be enhanced by the inductive effect (electron withdrawing) of the trichloromethyl group. 3>3>3-Trichloro- 1-nitropropene undergoes rapid reduction to give 1,1,1- C1 l S+ + /0 Cl-C-eCH=CH-N^ s- (A) ci tri chi or o-3-nitro pro pane (44.2 per cent) and 1,1,1-t rich loro- 3,5-dinitro-4-trichloromethylpentane (32.1 per cent). It thus appears that hydride reduction of halogen-containing conjugated nitroolefins is a very promising method for preparing sensitive mono and polyhalonitroalkanes. The selective reduction of conjugated nitroalkenes has been extended to 4,4,5,5,6,6,6-heptafluoro-2-nitro-2- hexene and 5,5, 6,6,7,7,7-heptafluoro-3-nitro-3-heptene, Reduction of these polyfluoronitroalkenes occurs very rapidly and in excellent yields to give 1,1,1,2,2,3,3- heptafluoro-5-nitrohexane (34 per cent) and 1,1,1,2,2,3,3- heptafluoro-5-nitroheptane (91 per cent), respectively. There was no evidence in these two systems for Michael addition of the reduction products to the initial polyfluoro nitroalkenes. The greater rate of reduction of polyfluoro nitroalkenes as compared to alkylnitroalkenes may be at tributed to the electron withdrawing properties of perfluoro- alkyl groups. The much more rapid reduction of 5,5,6,6,7,7,7- heptafluoro-3-nitro-3-heptene at -70° than of 4-nitro-3- heptene, a relatively hindered and unreactive nitroolefin, at 0° illustrates clearly the influence of electron with drawing groups in nitroolefins on the rate of nucleophilic reduction with sodium trimethoxyborohydride. * Omega-nitrostyrene and 2-(2-nitrovinyl)furan (Table 1) are selectively reduced, in fair conversions, by sodium trimethoxyborohydride to the corresponding saturated nitro compounds; the aromatic and heterocyclic nuclei are not affected. Thus, omega-nitrostyrene gives l-nitro-2-phenyl- ethane (3^.6 per cent) and 1,3-dinitro-2,4-diphenylbutane (23.6 per cent); 2-(2-nitrovinyl)furan yields 2-(2-nitro- ethyl)furan (23.3 per cent). In reduction of omega-nitro- 29 styrene and 2-(2-nitrovinylJfuran, there are also obtained (19.6 and 46.6 per cent, respectively) high melting, insoluble products which are believed to be polymers of the nitrostyrene and the nitrovinylfuran. The unidentified product derived from omega-nitrostyrene is a saturated nitro compound (see Experimental for chemical studies) containing benzene rings; its analysis is in agreement with that for poly-omega-nitrostyrene. The high molecular weight product may be obtained in the absence of sodium trimethoxyboro hydride by reaction of benzyltrimethylammonium hydroxide and omega-nitrostyrene. Similarly, the unidentified product obtained from 2-(2-nitrovinyl)furan contains furan nuclei and may be obtained in the absence of sodium trimethoxyboro hydride by the action of bases. It is suggested that sodium trimethoxyborohydride is sufficiently basic to effect anionic polymerization of omega-nitrostyrene and 2-(2-nitrovinyl) furan. The polymers are thus believed to contain 1,3-dinitro- alkane units as derived by continued Michael-type additions (Equations 11). RRtCH-CR"(N02)“ + r r »c =c r »n o 2 ---- > RR * CH-CR"(N02)-CRR'-CR"(N02)" (ID RR»CH-CR"(N02)-CRR’-CR»(N02)- + RR’C=CR"N02_____^ RR »CH-CR,f (N02) -CRRT -CR” (N02) - CRR»-CR” (N02)" 30 The effects of time and temperature on the reduction of 2-nitro-l-butene and omega-nitrostyrene have been studied. At 0° reduction of 2-nitro-l-butene (Table 3) results mainly in polymeric material (66 per cent) but at -55 to -60° the amount of polymer is reduced (7 per cent conversion), and the yields of 2-nitrobutane (29.7 per cent) and 3-methyl-3,5-dinitroheptane (46.2 per cent) are increased. Temperature is also important in the reduction of omega- nitrostyrene (Table 4); at 0° only polymeric material was TABLE 3 EFFECT OF TEMPERATURE AND HYDRIDE-NITROOLEFIN RATIO ON REDUCTION OF 2-NITR0-1-BUTENE WITH SODIUM TRIMETHOXYBOROHYDRIDE Per Cent Conversion Moles 3-Methyl- Time NaBH(0CHo)V 2-Nitro- 2-Nitro 3,5-dinitro- Poly- Temp. Min. moles Oleffn 1 -but en e -butane heptane mer -1 to 160 1/1 $ 9.2 5.03 66.0 -2° ■ o o -55 to —i 1/1 * 29.7 46.2 7.2 -60° -60 to 100 1.5/1 Non e 45.0 35.0 6.5 -65° ^Extracted from the reaction product with sodium sodium bisulfite solution. produced, while at -40° the polymer (19.6 per cent) yield decreased, and l-nitro-2-phenylethane (3^.6 per cent) and l,3-dinitro-2,4-diptenylbutane (23.6 per cent) were obtained. Optimum reaction conditions include a low temperature of reaction. TABLE 4 EFFECT OF TEMPERATURE AND HYDRIDE-NITROOLEFIN RATIO ON REDUCTION OF OMEGA-NT®S'fYRENE WITH SODIUM TRIMETHOXYBOROHYDRIDE Moles 1,3-Dinitro- Time NaBH(0CHo)o/ 2,4-diphenyl- l-Nitro-2- Temp. Hours moles Olefrin Polymer butane______phenylethane 0 to 3 1/1 S3.6 -3° -40 to 2 1.5/1 19.6 23.6 33.6 -42° The reactions of 2-nitro-l-butyl acetate with excess sodium trimethoxyborohydride was investigated as a method for preparing saturated nitro compounds. Since sodium trimethoxyborohydride is a base, it was deemed possible that it would eliminate acetic acid from 2-nitro-l-butyl acetate to give 2-nitro-l-butene (Equation 12). Subsequent reduction of 2-nitro-l-butene by sodium trimethoxyborohydride, and acidification (Equations 13 and 14) would be expected to yield 2-nitrobutane. 32 CH3-CH2-C(N02)=CH2 + NaBH(OCH3)3 >CH3-CH2-C(N02Na)-CH3 + (OCH3)B (13) GH3-CH2-C(N02Na)-CH3 + H+ y CH3-CH2-CH(N02 )-CH3 + Na+ (14) A successful reduction sequence of this type will eliminate one step in the preparation of nitroalkanes from vicinal nitroalcohols since nitroolefins are usually obtained by elimination of carboxylic acids (or its homologs) from vicinal acyloxynitroalkanes. Reaction of 2-nitro-l- butyl acetate with sodium trimethoxyborohydride at 3-5° and at 40° resulted in reduction of the carboxylate ester to 2-nitro-1-butanol (40 per cent yields); there was no evidence for the formation of 2-nitro-l-butene or 2-nitrobutane. It was therefore apparent that normal reduction of the ester to carbinol occurs more rapidly than does elimination of acetic acid from the nitrobutyl ester; sodium trimethoxyborohydride apparently is not a sufficiently strong base to effect rapid elimination of carboxylic acids from vicinal nitroesters. The reduction of l-(nitromethyl)cyclopentene, a non conjugated nitroolefin (Equation 15), was attempted with sodium trimethoxyborohydride. No reduction of the unconju gated nitro compound could be detected under conditions which were quite satisfactory for reduction of conjugated nitroolefins. Attempts were made under the reducing conditions o 33 to isomerize (base-catalyzed) the nitromethylcyclopentene to its conjugated exocyclic isomer (Equation 16) and then ch2-n o 2 ch2-n °2 (15) NaBH(0CH,), oh2no2 Ach-n o 2 c h 2-n o 2 effect reduction of the nitro compound. It is to be ex pected that the exocyclic isomer should be more stable than the endocyclic isomer because of the general stability of 66 exo double bonds in cyclopentane ring systems and the resonance stabilization resulting from conjugation of the nitro group with the carbon-carbon double bond. In all experiments, however, it was found that cyclopentylnitro- methane was not formed; the unisomerized nitrocyclopentene, l-(nitromethyl) cyclopentene, was recovered essentially unchanged in all experiments. Normal addition, addition of the nitroolefin to the sodium trimethoxyborohydride solution, was used in all reduction experiments to minimize competing Michael addition 34 reactions leading to polynitroalkanes. Inverse addition was not studied as experiments with lithium aluminum hydride demonstrated that it offered no advantages. 2. SELECTIVE REDUCTION OF CONJUGATED AND UNCONJUGATED NITROOLEFINS BY LITHIUM BOROHYDRIDE. In the present investigation, lithium borohydride has been found to be an excellent reducing agent for conjugated carbon-carbon double bonds in nitroolefins; the reaction developed serves as a valuable method for synthesis of complex primary and secondary nitroalkanes (Table 5). The reductions are effected conveniently in mixtures of ethyl ether and tetrahydrofuran at -40 to -70°. The stoichiometry of the reduction reaction is (Equation 17): 4 RR’C=CR,'N02 + LiBH^ ____(RR»CH-CRw»N02)ifBLi (17) (RR»CH-CRn«N02 )^BLi + H-Ac + 3H20 _____ * 4RR»CH-HCR"N02 + H^BO^ + LiAc (Id) Acidification of the reaction mixture with acetic acid and urea results in decomposition of the reduction inter mediates and liberation of the nitroalkanes (Equation IS). 35 TABLE 5 REDUCTION OF CONJUGATED NITROOLEFINS WITH LITHIUM HUr o h Y d r i d E Reaction Initial Nitroolefin Products Per Cent Conversion 1-Nitropropene 1-Nitropropane; 49.9 2-Methyl-l,3- dinitropentane 2-Methyl-1-nitro- 2-Methyl-l-nitropropane 4$.4 propene 2-Nitro-l-butene 2-Nitrobutane; 59.3 3-Methyl-3 > 5- dinitroheptane 14.2 2-Nitro-2-butene 2-Nitrobutane 60. & 4-Nitro-3-heptene 4-Nitroheptane 65.0 3> 3> 3-Trichloro-l- 1,1,1-Trichloro-3- &5.0 nitropropene nitropropane 4.4.5.5.6.6.6-Hepta- 1,1?1,2,2,3,3-Heptafluoro- &7.# fluoro-2-nitro- 5-nitrohexane 2-hexene 5.5.6.6.7.7.7-Hepta- 1,1,1,2,2,3>3-Heptafluoro- 91.0 fluoro-3-nitro- 5-nitroheptane 3-heptene Omega-nitrostyrene 1-Nitro-2-phenylethane; 55.3 Polymers 3&. 2-(2-Nitrovinyl) 2-(2-Nitroethyl)furan 31.4 furan Polymers 54.2 D-arabo-tetraacetoxy- 1-Nitro-l,2-dideoxy-D- 1-nitrohexene arabo-hexitol tetraacetate 54.2 X-ray analysis of crystalline lithium borohydride indicates that the salt is electrovalent and is composed of lithium and (tetrahedral) borohydride ions. In ether solution it is probable that lithium borohydride exists largely as aggregates of strongly solvated lithium and borohydride (BH^”) ions. The mechanism of reduction of conjugated nitroalkenes by lithium borohydride has not been established in this research. It is expected however, that the driving force of the reduction is derived from the nucleophilic attack of the borohydride ion (possibly attenuated by the solvating properties of the lithium ion) on the conjugated nitroolefin. A conjugated nitroolefin is an electronegatively substituted unsaturated compound and, as a resultant of inductive and resonance effects, should be polarized in the following manner: »0 s_ *»+ - R' N— 0 wc=c / \ R" R,f» The most plausible mechanism of reduction involves attack of the borohydride ion at the relatively positive end of a polarized carbon-carbon double bond (Equation 19); the addition reaction is of the Michael type and possibly involves formation of a borohydride complex of the 37 alkanenitronate anion. The intermediate monoalkanenitro- natoborohydride ion may undergo further reductive attack on the conjugated nitroolefin to give first the dialkanenitronatoborohydride (Equation 20); further reduc tive reaction give the trialkanenitronatoborohydride (Equation 21) and then finally the tetraalkanenitronato- borohydride (Equation 22). Li+BH^“ + R2C=CR-N02 v (R2CH-CR=N02)BH3”Li+ (19) (R2CH-CR=N02)BH3-Li+ + R2C=CR-N02 ►- (20) (H2CH-CR=N02)2BH2"Li+ (R2CH-CR=N02 )2BH2~Li+ + R2C=CR-N02 v (21) (R2GH-CR=N02)3BH”Li+ (R2CH-CR=N02)3BH"Li+ + R2C=CR-N02 ____^ (22) (R2CH-CR=N02)^B“Li+ (R2CH-CR=N02)4B"Li+ + HAc + H20 -----> (23) 4R2CH-CH2N02 + LiAc + H3B03 Hydrolytic decomposition of the tetraalkanenitronatoboro- hydride with aqueous acetic acid gives four equivalents of the nitroalkane (Equation 23). The evidence for the stepwise sequence of addition processes is the overall stoichiometry of reaction (Equation 17). The reductions are often incomplete; however; they are thus usually conducted best by adding the nitroolefin to 100 per cent excess lithium borohydride. On the basis of the usual need for excess lithium borohydride to effect rapid and complete reduction, it is suggested that steric factors become greatly increased as each nitronate ion becomes incorporated in the borohydride ion; the effective reducing activity of the hindered di-and trialkanenitronato- borohydride ions may thus be less than that of the boro hydride and the monoalkanenitronatoborohydride ions. Selective reduction of the carbon-carbon double bond has been accomplished in satisfactory yield in {Table 5) 1-nitropropene, 2-nitro-l-butene, 2-nitro-2-butene, 2- methyl-l-nitropropene, 4-nitro-3-heptene, 3>3>3-trichloro- l-nitropropene, 4,4,5,5j 6,6, 6-heptafluoro-2-nitro-2-hexene, 5,5,6,6,7,7,7~heptafluoro-3-nitro-3-heptene, omega- nitrostyrene, and 2-(2-nitrovinyl)furan. Lithium borohydride is thus an effective reductant for (1) terminal or internal double bonds attached to primary or secondary nitro groups, (2) conjugated nitroalkenes having allylic halogen, and (3) conjugated aryl and heteronitroolefins. A competing Michael addition reaction between the initial reduction product and the nitroolefin to yield 1,3-dinitroalkanes (Equation 24) occurs with RR»CH-CR»N02“ + r r ,g =c r »n o 2 --- RR' CH-CR" (N02) -CRR ’ -CR,tN02“ {24) 39 1-nitropropene and 2-nitro-l-butene; these products are 2-methyl-1,3-dinitropentane and 3-methyl-3,5-dinitroheptane, respectively. Further Michael addition to give trimers and higher polymers may occur with very reactive (and unhindered) nitroolefins such as (1) 1-nitropropene, 2- nitro-l-butene, omega-nitrostyrene, and 2-(2-nitrovinyl) furan, etc. The competitive yield-lowering Michael addition or polymerization reactions may be minimized by lowering the reaction temperatures and adding the conjugated nitro olefin to excess reducing agent. TABLE 6 EFFECT OF TIME AND TEMPERATURE ON REDUCTION OF 3» 3, 3-TRIC'HLORtPI^NITROPROVENE WITH LITHIUM BQ~ROHYDRIDE Per cent Conversion to 1,1,1-Trichloro- Temperature Reaction Time (Hrs.) 1-nitropropane -70- 2° 7 35 -40° 5.5 43.3 The relationship of conversion to reaction time and temperature have been studied with 3»3j3-trichloro- l-nitropropene (Table 6), 2-nitro-l-butene (Table 7) and 4-nitro-3-heptene (Table B). In general, reduction occurs slowly over the temperature range-40 to -70°; the yield of nitroalkane is usually best when effecting reduction at 40 TABLE 7 EFFECT OF TIME AND TEMPERATURE ON REDUCTION OF 2-NITR0-1-BUTENE WITH LITHIUM BOROHYDRIDE Per Cent Conversion Reaction 3-Methyl- Time Moles LiBH/j./ 2-Nitro- 2-Nitro 3>5-dinitro Poly* 1 1 O P —1 1 0 1 16.2 22.& H 2.5 1/4 20.3 15.7 -50 to 1 . 1 1/4 * 24.0 5.76 3.27 -55° -6B to 5.5 1/4 23.7 39.0 9.2 11. S -70° VO -co i>- ■PO 0 1 1/2 None 59.3 14.2 9.15 0 5.5 1 $ Per cent recovery * 2-Nitro-1-butene was removed with sodium bisulfite solution. TABLE S EFFECT OF TIME AND TEMPERATURE ON REDUCTION OF 4-NITRO^FHEPTENEITi TH LITHIUM BOROHYDRIDE Reaction Per Cent Conversion Time Unidentified Temp. Hours 4-Nitro3-heptene* 4-Nitroheptane Product* -65 to $. 11.3 6$. 9.2 -70° 0° 5.5 Trace 44.7 19.6 +Per cent recovery * Infrared data show the presence of hydroxyl and amine groups possibly formed by further reduction of the nitro group, see Experimental 41 relatively low temperatures and for long reaction times rather than at elevated temperatures and shorter reaction periods. In reduction of 4-nitro-3-heptene, a relatively inert and hindered nitroolefin, at 0°, there are obtained 4-nitroSheptane (45 per cent) and an unidentified mixture ( 20 per cent) derived by reductive attack on the nitro group of the nitroolefin. The attack on the nitro group is probably the resultant of steric manifestations in the initial nitroolefin; these complications may be minimized by effecting reduction at -65 to -70° and for extended reaction periods. The reaction of 2-nitro-l-butyl acetate with excess lithium borohydride was investigated as a one-step method for preparing mononitroalkanes. The requirement for success of this method is that lithium borohydride function as a base and effect elimination of acetic acid from the nitro- butyl ester at a rate greater than it will function as a reducing agent for carboxylic esters. It was found however, that reaction at 3-4° gives 2-nitro-l-butanol (40 per cent) rather than 2-nitrobutane. It thus appears that lithium borohydride is mot a sufficiently strong base to effect elimination in competition with its nucleophilic activity as a reducing agent (see also part 1, Section D). Selective reduction of the carbohydrate derivative, D-arabo-tetraacetoxy-l-nitrohexene, ^ was studied in an 42 attempt to develop a satisfactory method for preparing carbohydrate deoxynitroalkanes (Equation 25). Such a method will be of considerable importance for use in synthesis of deoxy carbohydrates. Reaction of (I) with lithium borohydride at 0° occurs readily; reductions CH-NO?II 2 CHp-NOr, | 2 2 CH CH2 , AcO-CH1 AcO-CH 1 ,(25) * I l)LiBH4 | HCOAc ^ HC-OAc HCOAc 2)H0Ac HC-OAc I 3)Ac20,H+ I H2C-Ac H2G-0Ac (I) (II) of the carbon-carbon double bond and (a portion of) the acetoxy groups are effected. The resulting crude acetoxy- hydroxy nitroalkane (unidentified) was acetylated with acetic anhydride and sulfuric acid; the desired reduction product, 1-nitro-1,2-dideoxy-D-arabo-hexitol tetraacetate (II), was obtained in 54.2 per cent overall conversion. It thus appears that reduction of conjugated nitroolefins with lithium borohydride will be of interest in preparation of various deoxynitro sugars and their derivatives; the method is adaptable for large scale preparative purposes. 43 3. SELECTIVE REDUCTION OF CONJUGATED NITROOLEFINS BY LITHIUM ALUMINUM HYDRIDE. Gilsdorf and Nord^ have reported preparation of 2- nitro-l-phenylpropane by inverse addition of lithium aluminum hydride to 2-nitro-l-phenylpropene at -40°. The reaction procedure given is unsatisfactory for use in synthesis of nitroalkanes from nitroalkenes; the general applicability of the method Was not determined. Lithium aluminum hydride is a more powerful nucleophilic reducing agent than are sodium trimethoxyborohydride and lithium borohydride; its reactivity may often be controlled by proper choice of temperature and solvent. Since lithium aluminum hydride is cheaper and usually more readily avail able than sodium trimethoxyborohydride and lithium borohydride, a study of its efficiency for selective reduction of conju gated nitroolefins has been made. Conjugated nitroolefins are conveniently and rapidly reduced to saturated nitro compounds (Table 9) by lithium aluminum hydride at -40° and below in ethyl ether; under these conditions, reductions of nitroalkenes to oximes, hydroxylamines and amines are minimized. The stoichiometry of reduction and subsequent hydrolysis is expressed by the following equations (Equations 25 and 26); the reduction is usually effected with 100 per cent excess lithium aluminum 44- TABLE 9 REDUCTION OF CONJUGATED NITROOLEFINS WITH LITHIUM ALUMINUM HYDRIDE Per Cent Nitroolefin Reaction Products Conversion 2-Nitro-2-butene 2-Nitrobutane 52.9 3.3.3-Trichloro-l- 1.1.1-Tri chloro-3- 43. & nitropropene nitropropane 3.3.3-Trifluoro-1- 1.1.1-Trifluoro-3- 24.3 nitropropene nitropropane; 1.3-Dinitro-2,4-ditri- fluoromethylbutane 5,5,6,6,7,7,7-Hepta- 1.1.1.2.2.3.3-Heptafluoro- £5.3 fluoro-3-nitro- 5-nitroheptane heptene Omega-nitrostyrene l-Nitro-2-phenylethane; 50a, 47? 1.3--Dinitro-2,4- o.0a, 1.7 diphenylbutane 2-Nitro-l-phenyl- 2-Nitro-l- 43a , 31b propene phenylpropane 2-(2-Nitrovinyl)furan 2-(2-Nitroethyl)furan 16.1 a Normal addition b Inverse addition 45 4 E2C=CRN02 + LiAlH^ >. (R2CH-CR=N02) ifAl’Li+ (25) ( R2CH-CRssN02 ) ^AlLi + HAc + 3H20 __ 4 R2CH-CRH-N02 + LiAc + H-jAlO^ (26) hydride. The mechanism of reduction appears analogous to that of conjugated nitroolefins with lithium borohydride (See Section D, Part 2) in that intermediates such as lithium monoalkanenitronatotrihydroalurainate, lithium dialkanenitro- natodihydroaluminate, lithium trialkanenitronatohydroalurainate, and lithium tetraalkanenitronatoaluminate are probably formed. The resulting nitroalkanes are liberated from their inter mediate lithium alkanenitronatohydroaluminate complexes by the action of acetic acid and urea. Competitive Michael processes involving addition of the reduction product (prob ably as an aluminohydride complex) to the nitroalkene giving substituted 1,3-dinitroalkanes also occur (Equation 26 A). This reaction is thus similar to that observed when sodium trimethoxyborohydride and lithium borohydride are used as reductants. r 2ch -c r =n o 2" + r 2c=c h n o 2 ____ >r2c h -c r (n o 2)-cr 2-c h =n o 2-(26a ) The reducing actions of lithium aluminum hydride were studied on (Table 9) 2-nitro-2-butene,3,3j3-trichloro-l- nitropropene, 3>3»3-trifluoro-l-nitropropene, 5>5>6,6,7>7>7- o heptafluoro-3-nitro-3-heptene, omega-nitrostyrene, 2-nitro- 1-phenylpropene, and 2-(2-nitrovinyl)furan. The conversion of these nitroolefins to the saturated nitro compound without affecting other functional groups range from 25 to 53 per cent; the actual reductive conversion is usually much higher since a considerable portion of the initial reduction product is converted to 1,3-dinitroalkanes and higher derivatives by competing Michael processes. It is of interest that in reduction of 3,3}3-trichloro-l-nitropropene with lithium aluminum hydride, 1,1,1-trichloro-3-nitropropane is obtained in satisfactory conversion (43.& per cent); even with such a powerful reducing agent, the reaction may be controlled so that there is no effective reduction of allylic chlorine. Considerable difficulty was experienced in reduction of 3j3>3-trifluoro-l-nitropropene; the reaction is complicated by the ease with which 1,1,l-trifluoro-3- nitropropane reacts with 3>3>3-trifluoro-l~nitropropene to give 1,3-dinitro-2,4-ditrifluoromethylbutane (See Experi mental) . Gilsdorf and Nor d ^ and Cook, McBee, and Pierce^ have effected reduction of 2-nitro-l-phenylpropene^ and perfluoroalkylnitroalkenes^ by inverse addition of lithium hydride to the nitroolefins. Since it has been found in the present study that a major yield-lowering competitive process is Michael addition of the reduction product to the initial nitroolefin, it would be predicted that a better general procedure might involve addition of the nitroolefin to the (excess) hydride; it is to be expected that such a procedure will minimize formation of the undesired 1,3- dinitroalkanes. A study has thus been made of the effect of normal and of inverse addition under comparable conditions on the efficiency of reduction of nitroolefins by lithium aluminum hydride (Table 9). It has been found that normal addition of omega-nitrostyrene to lithium aluminum hydride produces 1-nitro-2-phenylethane in 49.$ per cent conversion; inverse addition gives 47.3 per cent conversion. Normal addition to 2-nitro-l-phenylpropene results in 43.4 per cent conversion; inverse addition gives 31.0 per cent conversion. Inverse reduction of 5>5»6,6,7j7>7-heptafluoro-3-nitro-3-heptene results in 69 per cent conversion to l,l,l,2,2>3>3-hepta- fluoro-5-nitroheptane; in the present study it has been found that normal addition gave the reduction product in #5.3 per cent conversion. It can thus be concluded that normal addition is the better method for selective reduction of conjugated nitroolefins; this method is also superior for reduction of readily polymerizable nitro olefins. 4. REDUCTION OF CONJUGATED NITROOLEFINS BY SODIUM BOROHYDRIDE. Selective reduction of conjugated nitroolefins to saturated nitro compounds may be effected in excellent yields (Table 10) by sodium borohydride. The reduction reaction is believed to proceed according to Equation 27; the intimate mechanism of the reduction processes possibly involves formation of intermediate alkanenitronatoborohydrides by nucleophilic attack of the Michael type on the nitroolefin. These reactions are thus analogous to those of lithium borohydride and lithium hydride (See Section D, Parts 2 and 3). Hydrolytic decomposition of the intermediate and final alkanenitronatoboron complexes is afforded by reaction with aqueous acetic acid. As in previous reductions of conjugated nitroolefins with sodium trimethoxyborohydride, lithium 4R2C=CR-N02 + NaBH^ _ ~ (R2CH-CR=N02)^B-Na+ (27) (R2CH-CR=N02)Z}B-Na+ + HAc + 3H20 ---- 4R2CH-CRH-N02+ NaAc + H^BO^ borohydride, and lithium aluminum hydride, addition of the reduction product to the initial conjugated nitroalkene ocdurs competitively to give 1,3-dinitroalkanes (Equation 2$) and similar higher molecular weight polynitro compounds. t 49 r2CH-CR=N02“ + R2C=CRN02 ___ ^R2GH-CR(N02)-GR2-CR=N02" (28) TABLE 10 REDUCTION OF CONJUGATED NITROOLEFINS VTITH SODIUM BOROHYDRIDE Per Cent Initial Nitroolefin Reduction Products Conversion 2-Nitro-2-butene 2-Nitrobutane 63.5 4-Nitro-3-heptene 4-Nitroheptane 21.7 Omega-nitrostyrene l-Nitro-2-phenylethane; 14.4 1,3-Dinitro-2,4- 24.4 diphenylbutane; Polymer 29.3 D-arabo-tetraacetoxy-1- 1-Nitro-l,2-dideoxy- 63.9 nitrohexene D-arabo-hexitol tetraacetate The reductionsof 2-nitro-2-butene, 4-nitro-3-heptene, omega-nitrostyrene and D-arabo-tetraacetoxy-l^nitrohexene (Table 10) were investigated. The simple reduction products obtained were 2-nitrobutane (63.5 per cent), 4-nitroheptane (21.7 per cent), l-nitro-2-phenylethane (14.4 per cent) and 1-nitro-l,2-dideoxy-D-arabo-hexitol tetraacetate (63.9 per cent); 1,3-dinitro-2,4-diphenylbutane (24.4 per cent) and 50 polymers also resulted from reduction of omega-nitrostyrene. Sodium borohydride was arbitrarily used in 100 per cent excess in all reductions; the operating stoichiometry for this borohydride is thus similar to that used with lithium borohydride and lithium aluminum hydride. Absolute ethanol was used as solvent in all of the successful re ductions. Attempts were made to use ethyl ether-tetrahydro- furan as a solvent mixture; however, reduction does not occur because of the insolubility of sodium borohydride in these solvents. It was found that the maximum concentration of sodium bobohydride that could be used in ethanol was 2.$4 g. per 50 ml.; if more concentrated solutions of sodium borohydride in ethanol were used, complete decom position of the hydride occurred in a few seconds with liberation of gases (presumably hydrogen) upon introduction of the nitroolefin (even as little as one drop). When using more dilute solutions of the hydride, gases are evolved slowly throughout the reduction reaction; the reduction of nitroolefins occurs so rapidly, however, that the competi tive destruction of the borohydride is of minor importance in the method. Reduction of lower nitroalkenes by sodium borohydride occurs rapidly and efficiently; the method is not particu larly valuable, however, for synthesizing very volatile nitroalkanes because of the difficulty in effecting ° o o a 51 efficient separation of the product from ethanol. The most important use of sodium borohydride as developed in this study involves preparation of dideoxynitro-acetoxy carbohy drates, Sodium borohydride is the reagent of choice because it reduces conjugated carbon-carbon double bonds in nitro olefins, but does not :rapidly reduce carboxylic esters. Thus, sodium borohydride reduces D-arabo-tetraacetoxy-1- nitrohexene to 1-nitro-l,2-dieoxy-D-arabo-hexitol tetraacetate conveniently and efficiently; the conversion in this reduction is 63.9 per cent. 52 E. EXPERIMENTAL TECHNIQUE 1. APPARATUS The reduction experiments were usually conducted in a 300 ml., three-neck, round-bottomed flask equipped with a glass mechanical stirrer, a dropping funnel, a thermometer and a drying tube. No special precautions were taken to exclude moisture because an excess of the hydride was always employed. Upon acidifying the reaction mixture at the end of each reduction period, provision was made for exit of the hydrogen and possible boron hydrides resulting from de composition of the excess hydride. It was advisable to use sparkless stirring motors for the stirring operations since ether solutions were being used and hydrogen was being evolved. 2. SOLVENTS In reductions using sodium trimethoxyborohydride and lithium borohydride, mixtures, of ethyl ether and tetrahydro- furan were employed as solvent. The hydrides are much more soluble in tetrahydrofuran than in ethyl ether; however, they are sufficiently soluble in ethyl ether (4 parts) and tetra hydrofuran (1 part) to allow satisfactory use. Tetrahydro furan may be used as a single solvent. This solvent is some what unsatisfactory since the reaction mixture is acidified 52 53 with aqueous acetic acid and urea; in such a system- the reduction product can not be conveniently ether-extracted. In the reduction reactions using lithium aluminum hydride ethyl ether was used as the solvent; the solubility of lithium aluminum hydride in ethyl ether is 25-30 g. in 100 g. of ethyl ether at 25°. The solubility is not known at -40° but is expected to be lower. Absolute ethanol was used as the solvent for reduc tions using sodium borohydride; the hydride is practically insoluble in ethyl ether and tetrahydrofuran. An attempt was made to effect heterogeneous reduction of 5, 5> 6, 6, 7, 7, 7- heptafluoro-3-nitro-3-heptene in a mixture of tetrahydro furan (3 parts) and ethyl ether (7 parts); since no reduction occurred, it was concluded that the solubility of the hydride was too small to allow satisfactory reaction. Ethanol has the disadvantage that it is difficulty separated from lower nitroalkanes. It was impractical to separate 2-nitrobutane from ethanol in a 2.5 foot column packed glass helides; separation of 4-nitroIheptane from ethanol was satisfactorily effected, however, in a Claisen flask. It is suggested that ethanol not be used as a solvent in reductions using sodium borohydride when the reduction product boils below l60-l30°. There appears to be a maximum concentration of sodium borohydride in ethanol that can be used satisfactorily for reduction. Traces of nitro compounds catalyze the evolution of hydrogen from sodium borohydride-ethanol solutions; if the concentration was greater than 2.34 g. of sodium boro hydride per 50 ml. of ethanol, complete evolution of hydrogen occurred in a few seconds. Lesser concentrated solutions evolve hydrogen slowly; if the reduction time is not in excess of approximately three hours, the amount of hydrogen evolved is negligable. 3. MODE OF ADDITION In all of the reduction experiments, except those which allowed a special study of this effect, the nitroolefin solution was added to a homogeneous hydride solution or to a heterogeneous hydride slurry. In the present study it was found that approximately the same conversion to reduction products is obtained by either normal or inverse addition, however, this variable was not studied thoroughly. It is suggested that normal addition be used for nitroolefins that are to undergo reactions of the Michael-type very readily. The mode of addition is discussed more thoroughly in section D, Discussion of Results. 4. HANDLING OF HYDRIDES Sodium borohydride and sodium trimethoxyborohydride can be handled in the atmosphere without special fire pre cautions, however, sodium trimethoxyborohydride was handled rapidly because of its reaction with moisture in the atmosphere. Care was exercised when lithium borohydride was used since it may be ignited by moisture in the air. When using the hydrides they were weighed out rapidly into containers containg the cold solvent to be used for the reductions. The quantities of hydrides involved in the present research were small; it is suggested that the hydrides be handled in an inert atmosphere when larger quantities are involved. 5. ACIDIFICATION OF THE REACTION MIXTURE After reduction of nitroolefins by hydrides the re action products must be acidified to free the nitroalkanes from the various complexes. For these acidifications a solution 2.7# molal in urea and in acetic acid^ was used; the quantity used of this acidificant was 5-10 per cent in excess of that of theory. The urea-acetic acid minimizes the formation of ketones, aldehydes, nitrolic acids and pseudonitrols by various secondary processes. The excess acetic acid was removed by extracting an ethyl ether solution of the product with sodium bicarbonate solution. Caution must be exercised in this separation because certain nitro compounds such as 1,1,l-trifluoro-3-nitropropane are strong enough acids to react with sodium bicarbonate. 6. IDENTIFICATION OF PRODUCTS The products of reduction which were not new compounds were identified by (1) comparing their physical constants with those in the literature, (2) their infrared spectra, and (3) conversion to known derivatives. New compounds and their derivatives were analyzed for carbon, hydrogen, and nitrogen. The physical constants of all products were not accepted until their infrared spectra indicated the absence of impurities or by-products. When a reduction product was contaminated with initial nitroolefin, the nitrolefin was removed by extracting an ether solution of the product with a saturated solution of sodium bisulfite. Three extractions are necessary if products of high purity are desired; the wash period should exceed five minutes since a long contact time is usually necessary to remove the nitroolefin. F. REAGENTS Sodium borohydride, lithium borohydride, sodium trimethoxyborohydride and lithium aluminum hydride were purchased from Metal Hydrides, Inc., 12-24 Congress Street, Beverly, Massachusetts. Nitromethane and nitroethane were purchased from the Commercial Solvents Corporation. The nitroalkanes were washed with 10 per cent sodium bicarbonate solution, and rectified over boric acid in a column (4 foot) packed with glass helices, 2-Nitro-l-butanol was purchased from The Commercial Solvents Corporation. Distillation of the crude material gave colorless 2-nitro-l-butanol, b.p. 64° (0,7 mm.), n22 1.4334. 1-Nitropropene (b.p. 76-60° (66 mm.), n2^ 1.4535; lit. b.p. 37° (10 mm.), n2^ 1.4527) was prepared in 53.3 per cent conversion by dehydration of 1-nitro-2-propanol with ph^thalic anhydride.^ 1-Nitro-2-propanol (b.p. 73-74° (3.6-3.7 mm.), n2§ 1,4411) was obtained by condensation of nitro^methane 70 with acetaldehyde in JO per cent conversion.' 2-Methyl-l-nitropropene (b.p. 69-71° (23 mm.), n2^ 1.4660; lit,^1 b.p. 59-62° (15 mm.), n2§ 1.466.) was prepared in 75.7 per cent conversion by reaction of 2-methyl-1-nitro- 72 2-propyl acetate with hot sodium acetate! 2-Methyl-l-nitro- 2-propyl acetate (b.p. 63-64° (9 mm.), n2jj 1.4305) was 5a obtained in 35-30 per cent conversion from reaction of 2- 71 methyl-l-nitro-2-propanol with acetyl chloride. 2-Methyl- l-nitro-2-propanol (b.p. 73-30° (10 mm.), n2^ 1,4425) was synthesized in 16 per cent conversion by condensation of nitromethane with acetone.72 2-Nitro-l-butene (b.p. 70-70.3° (30 mm.), n 2§ 1.4392; 20 lit.b.p. 60° (50 mm.), n d 1.4360) was prepared in 74.3 per cent conversion by reaction of 2-nitro-l-butyl acetate with sodium acetate.7^ 2-Nitro-l-butyl acetate (b.p. 62-65° (0.5 mm.), n2p 1.4290) was obtained (33 per cent conversion) by acetylation of 2-nitro-1-butanol with acetic anhydride and sulfuric acid.7^ 2-Nitro-2-butene (b.p. 61-62° (20 mm.), 1.4613; lit.39 b.p. 70.4° (30 mm.), n ^ 1.4534) was prepared in 65.3 per cent conversion from 3-nitro-2-butyl acetate by 72 reaction with sodium acetate. 3-Nitro-2-butyl acetate (b.p. 76-77° (3.2-3.5 mm.), 1.4231) was obtained in 34.7 per cent conversion by acetylation of 3-nitro-2-butanol with acetic anhydride.7^ 3-Nitro-2-butanol (b.p. 63.5-70° 20 3.0-3.5 mm.), n p 1.4431) was synthesized (33 per cent conversion) from nitroethane and acetaldehyde.74- 4-Nitro-3-heptene was prepared by the following procedure: (a) 4-Nitro-3-Heptanol. Propanal (116.2 g., 2 moles) was added at 30-35° in ca. one hour to a solution of 1- nitrobutane (106.2 g., 2 moles) in 95 per cent ethanol (200 ml.) and 10 N sodium hydroxide (4 ml.). When approxi mately two thirds of the aldehyde had been added, additional 10 N sodium hydroxide (4 ml.) in water (15 ml.) was added. After 48 hours the mixture was neutralized with 2 N hydro chloric acid. After removal of all unreacted material and solvents at reduced pressure, distillation gave: 4-nitro- 3-heptanol (248,3 g., 1.54 moles, 77 per cent conversion) as a greenish-yellow liquid, b.p, 79.9-83.3° (0.7 mm.), n^§ 1.4460-1.4474. Redistillation of the compound gave a pure, light yellow product, b.p. 71t71.5° (0.5 mm.), n^§ 1.4475, djjg 1.0324; MRD (calcd.) 41.79, MRg (found) 41.76. Anal. Calcd. for CyH-^NO^: C, 52.15; H, 9.38; N, 8.69. Found: C, 52.62, 52.73; H, 9.42, 9.41; N, 8.45, 8.53. The infrared spectrum of 4-nitro-3-heptanol (sand wich cell) contained bands for the mononitro (6.4 and 7.2 microns) and hydroxyl (2.9 microns) groups. (b) 3-Acetoxy-4-Nitroheptane. Acetic anhydride (129 ml., 1.2 moles + 5 per cent excess) wqs added dropwise in SO minutes at 40-50° to 4-nitro-3- heptanol (193.4 g., 1.2 moles) containing sulfuric acid (1 ml.). After addition 60 was completed, the mixture was stirred for 2 hours. The mixture was diluted with ethyl ether (200 ml.), washed with water (2 x 100 ml.), neutralized with sodium bicarbonate, washed with saturated sodium bicarbonate solution (2 x 200 ml.), washed with sodium chloride solution (100 ml.) and dried over anhydrous sodium sulfate. After removal of the sodium sulfate by filtration and distillation of the solvents, distillation gave: 3-acetoxy-3~nitroheptane (216.9 g., 1.07 moles, $9 per cent conversion) as a light yellow liquid, b.p. 75.5-79° (1 mm.), n2® 1.4339-1.4362. Redistillation of the product gave pure, colorless 3-acetoxy-4- nitroheptane, b.p. 69° (0.1 mm.), n2° 1.4352, d2g 1.0409; MRD (calcd.) 51.12, MRd (found) 50.97. Anal. Calcd. for C^yNO^: C, 53.19; H, S.43; N, 6.69. Found: C, 53.32, 53.21; H, 6.27, 6.36; N, 6.66, 6.90. The infrared spectrum of 3-acetoxy-4-nitroheptane (sandwich cell) contained bands for carbonyl (5.7 microns), mononitro (6.4 and 7.2 microns), and acetate (6.1 microns) groups. (c) 4-Nitro-3-Heptene. 3-Acetoxy-4-nitroheptane (131.5 g., O.65 mole) and sodium acetate (6.6 g.) were heated at 115° (12 mm.) in a modified Claisen flask equipped 61 with a 20 cm. Vigreux column with downward condenser and iced receiver; the reaction product distilled at 75-&50 (12 mm.). The distillate, in ethyl ether (300 ml.), was washed with saturated sodium bicarbonate solution (2 x 200 ml.) and dried over anhydrous sodium sulfate. After removal of the sodium sulfate by filtration and separation of the solvents, distillation gave: 4-nitro-3-heptene (67.6 g., 0.473 mole, 72.3 per cent conversion) as a light green, lachrymatory liquid, b.p. 70-70.3° (5.2 mm.), n^j] 1.45$5. The infrared spectrum of 4-nitro-3-heptene (sandwich cell) contained a strong band for a nitro group attached to an unsaturated carbon atom and weak bands for a mononitro group (6.4 microns) attached to a saturated carbon atom and for a carbon-carbon double bond. The contaminant is prob ably 4-nitro-2-heptene produced during the elimination processes. 3,3,3-Trichloro-l-nitropropene (b.p, 69-70° (5.5 mm.), on n p 1.5177) was obtained (73 per cent conversion) by refluxing 1,1,l-trichloro-3-nitro-2-propyl acetate with sodium carbonate in benzene.^ 1,1, l-Trich.loro-3-nitro- 2-propyl acetate was synthesized by the following modified procedure of Chattaway and Witherington.^ Acetic anydride (153 g.> 1.5 mole) was added dropwise in 30 minutes to stirred l,l,l-trichloro-3-nitro-2-propanol 62 (143.7 g.} 0.69 mole; 156.3 g. of 92 per cent pure material was used). After the initial reaction had subsided the mixture was heated on a steam bath for one hour. Excess acetic anhydride and acetic acid were removed under reduced pressure on a steam bath. Ethanol (150 ml.) was added and the solution was kept at 0° for 13 hours. The precipitated 1.1.1-trichloro-3-nitro~2-propyl acetate was filtered; the filtrate was concentrated and placed in a refrigerator. This procedure gave the acetate in four crops: (1) 111.3 g., m.p. 57.5-59.5°; (2) 33.9 g., 56.0-59.5°, (3) 12.0 g., m.p. 55.5-58.5°; and (4) 6.1 g., 54-58°. The 1,1,1-trichloro- 3-nitro-2-propyl acetate (163.3 g., 0.616 mole, 39.3 per cent conversion) was re crystallized once from hot ethanol to give a purer product, m.p. 58-60° in slightly lower yield. This procedure eliminates distillation of the product. 1.1.1-Trichloro-3-nitro-2-propanol was obtained as a research sample from Westvaco Chemical Division, Food Machinery and Chemical Corporation, New York, New York. 3j3)3-Trifluoro-l-nitropropens was supplied by E. B. Roberson, Department of Chemistry, The Ohio State University, Columbus, Ohio, 4, 4> 5> 5j 6,6,6-Heptafluoro-2-nitro-2-hexene and 5,5,6,6,7,7,7-heptafluoro~3-nitro-3-heptene were the gifts of Dr. 0. R. Pierce, Chemistry Department, Purdue University, West Lafayette, Indiana. Omega-nitrostyrene (m.p. 57-5$°; lit.^ m.p. 57-58°) 77 was synthesized from benzaldehyde and nitromethane-. 2-Nitro-l-phenylpropene (m.p. 64.5-65.0°; lit.^ m.p. 65°) was prepared by condensation of nitroethane and Q ] benzaldehyde. ' 2-{2-Nitrovinyl)furan was prepared by the following procedure: A solution of sodium hydroxide (63.1 g., 1.5 mole + 5 per cent excess) in water (150 ml.) was added dropwise below 15° (Caution: the initial reaction is very exothermic) to a stirred mixture of nitromethane (91.56 g., 1.5 moles), furfural (144.1 g., 1.5 moles) and methyl alcohol (350 ml.). A white precipitate is formed; sufficient methanol is added such that stirring of the mixture is not difficult. The pasty mass was converted to a clear solution in 15 minutes upon adding one liter of crushed ice-ice water; the temperature of the mixture is maintained below 5°. The reaction mixture was then slowly poured into hydrochloric acid (300 ml.) and water (450 ml.). The yellow crystalline product was filtered and washed free of chloride ion. The product was recrystallized from Skellysolve B to give 2-(2-nitrovinyl)furan (96.35 g.i 0.692 mole, 46.1 O per cent conversion) as yellow needles, m.p. 74-75 ; lit. m.p. 74-75°. D-arabo-tetraacetoxy-l-nitrohexene (m,-. p. 115-116°; lit.^ m.p. 115-116°) was prepared by the condensation of D-arabinose with nitromethane, full acetylation of the 9 carbohydrate with acetic anhydride, and deacetylation in 64 the 1,2 position with sodium bicarbonate in hot benzene. 50 9 EXPERIMENTAL 1. SELECTIVE REDUCTION OF CONJUGATED NITROOLEFINS BY SODIUM TRIMETHOXYBOROHYDRIDE. a. Reduction of 1-Nitropropene With Sodium Tri methoxyborohydride; 1-Nitropropane, 2^Methyl-i, 3- d?initropentane~ “ A solution of 1-nitropropene (15.2 g., 0.175 mole) in ethyl ether (25 ml.) was added dropwise in 70 minutes to a stirred suspension of sodium trimethoxyborohydride (33.5# g.» 0.175 mole + 50 per cent excess) ?n ethyl ether (150 ml.) and tetrahydrofuran (50 ml.). During addition the reaction mixture was kept at -70° - 1°; after addition was completed the mixture was stirred for 30 minutes at n ° -72 . The mixture was then acidified in 1 hour at 0 with urea-acetic acid solution (100 ml.). The mixture was saturat ed with sodium chloride; the aqueous layer was separated and extracted with ethyl ether (100 ml.). The combined ether extract was washed with saturated sodium bicarbonate solution (2 x 200 ml) and dried over anhydrous sodium sulfate. After removal of the sodium sulfate by filtration, distillation gave, after removal of ether, the following fractions: (1) 1-nitropropane (12.73 g., 0.143 mole, Si.7 per cent conversion) o / 20 as a colorless liquid, b.p. 40-72 (100 mm.), np 1.4025- 20 1.4046, d20 1.0006; MRD (calcd.) 21.6S, (found) 21.96, and (2) 2-methyl-1,3-dinitropentane (1.75 g.» 0.00994 mole, 11.4 65 66 per cent conversion) as a yellow-liquid, b.p. 105-10$.5° 20 (2 mm.), n D 1.4563, and (3) a residue (0.9 g.). Redistillation of Fraction 1 gave purer 1-nitropropane in slightly lower yield, b.p. 129° (742.3 mm.), n2j) 1.4023; lit.^1 131.6° (760 mm.); lit.^2 b.p. 130.5 (761 mm.), d2^ 1.0009, 1.40130. The infrared spectrum of 1-nitro- propane (sandwich cell) contained strong bands for the mono- nitro (6.4 and 7.2 microns) group and no bands for a carbonyl group (5.7 microns), a mononitro group attached to an un saturated carbon atom (6.5 microns) or a carbon-carbon double bond (6.0 microns). The structure of 1-nitropropane was proven by its 65 conversion to propionaldehyde via the Nef reaction followed by preparation of propionaldehyde 2,4-dinitrophenylhydrazone in 62 per cent overall conversion, m.p. 153.5-155.5°; lit. 155°. The melting point of the derivative was not depressed when mixed with an authentic sample. Fraction 2, crude 2-methyl-l,3Riinitropentane, was re distilled twice to give a colorless product in only slightly lower yield, b.p. $6-$6.$° (0.$ run.), n2g 1.4553, d|o 1.1707; MRq (calcd.) 41.31, MRp (found) 40.$9. The infrared spectrum of 2-methyl-l,3-dinitropentane (sandwich cell) showed bands for a mononitro group (6,4 and 7.25 microns) but no bands for any other functional group. The following analysis was obtainedj&p 2-methyl-1,3-dinitropentane: Anal. Calcd, for G^H-j^NgO^: c> 40.90; H. 6.#7; N t 15.90 Found: C, 41.16, 41.IS; H, 6.89, 7.11; H, 15.83, 15.80 b. Reduction of 2-Methyl-l-Nitropropene With Sodium Trimethoxyborohydride; 2^Methyl-l^itropropane. Procedure 1. A solution of 2-methyl-l-nitropropene (15.2 g., 0.15 mole) in ethyl ether (25 ml.) was added dropwise in $5 minutes to a stirred suspension of sodium trimethoxyborohydride (21.1 g., 0.15 mole plus 10 per cent excess) in ethyl ether (125 ml.) and tetrahydrofuran (50 ml,). During addition the reaction mixture was kept at -2 to -5°; after addition was completed the mixture was stirred for 35 o minutes at 0 , The mixture was then acidified in one hour at 0° with urea-acetic acid solution (60 g.). The mixture was saturated with sodium chloride; the aqueous layer was separated and extracted with ether (100 ml.). The combined ether extract was washed with saturated sodium bicarbonate solution (2 x 150 ml.), saturated sodium bisulfite solution (2 x 150 ml.) and saturated sodium chloride solution (200 ml.). After drying the ether extract over anhydrous sodium sulfate and removal of the solvent, distillation of the product gave: 63 (a) crude 2-methyl-l-nitropropene, as a light yellow oil, b.p. 55-7$° (70 mm.), n2§ 1.4110-1.4137; (b) crude 2-methyl- l-nitropropene (1.33 g.), b.p. 67-71° (25 mm.), n2§ 1.4509- 1.4619; and (c) a brown residue (0.5 g.). The crude 2-raethyl-l-nitropropane was dissolved in ether (150 ml.) and washed with saturated sodium bisulfite solution (3x 150 ml., 5 minutes with each portion) to remove contaminating 2-methyl-l-nitropropene. Distillation of the product, after drying the ether solution and removing the ether, gave pure 2-methyl-1-nitropropane (5.13 g.,OjQ503 mole, 33.5 per cent conversion, 42.3 per cent min. yield) as a 20 colorless liquid, b.p. 69-70.7° (70 mm.), n d 1.4037-1.4093» d|o 0.9627; MRd (calcd.) 26.33, MRD (found) 26.46; lit.36 b.p. 140.5°, 4 1 0.9625, n2£ 1.4050. The structure of 2-methyl-1-nitropropane was proven by its conversion to 2-methyl-l-propanal via the Nef re action^ followed by preparation of 2-methyl-l-propanal 2, 4-dinitrophenylhydrazone in 55 per cent overall yield, m.p. 179-131°; lit.^ 132°. The melting point of the derivative ’.was not depressed when mixed with an authentic sample, m.p. 179-131°. The infrared spectrum of the 2-methyl-l-nitropropane (sandwich cell) contained a strong band for the mononitro (6.4 and 7.2 mi crons): group and no bands for a carbonyl group o O 69 (5.7 microns), a mononitro group attached to an unsaturated carbon atom (6.5 microns), a carbon-carbon double bond (6.0 microns), or any other functional group. Procedure 2. The experiement was conducted as previously except, after addition of the 2-methyl-l-nitro- propene was completed, the mixture was stirred for 30 minutes- at 34°. Distillation of the product gave: (a) 2-methyl-1- nitropropane (7.26 g.,0^Q706 mole, 47.1 per cent conversion, 56.1 per cent yield) and 2-methyl-l-nitropropene (2.69 g., 0.0266/mi^8 per cent recovery) as a mixture (analysis by refractive index), b.p. 55-60° (70 mm.) and 62-66° (25 mm.), n2j) 1,4146-1.4610; (b) unidentified high boiling material* (0.69 g.), b.p. 66-90° (0.6 ran.), n2§ 1.4663; and (c) residue (1.2 g.). Procedure 2. The experiment was conducted according to procedure 1, except, after addition of the 2-methyl-l- nitropropene was completed, the mixture was stirred for 16 hours at +2°. Distillation of the product gave: (a) 2-methyl-l-nitropropane (9.06 g.,0.0661 mole, 5^.7 per cent conversion, 72.1 per cent yield) and 2-methyl-l-nitropropene (2.79 g., 0.0276 mole, 16.6 per cent recovery) as a mixture (analysis by refractive index), b.p. 55-76.5° (70 mm.) and 60-71° (24 mm.), n2§ 1.4129-1.4622; (b) unidentified high $ Possibly 2,2,4-trimethyl-l, 3-dinitropentane formed by Michael addition of 2-methyl-l-nitropropane to 2-methyl-l- nitropropene. 70 boiling material* (1.21 g»), b.p. 60-90° (0.6 mm.), n28 1.4637; and (c) residue (0.5 g.). c. Reduction of 2-Nitro -l-b>ut ene With Sodium Tri methoxyborohydride ; 2-Hitrobutane, '3-Methyl-3. 5-dinitro- heptane" Procedure 1. A solution of 2-nitro-l-butene (15.2 g., 0.15 mole) in ethyl ether (25 ml.) was added dropwise in 70 minutes to a stirred suspension of sodium trimethoxyboro hydride (26.6 g., 0.15 mole plus 50 per cent excess) in ethyl ether (125 ml.) and tetrahydrofuran (50 ml.). During addition the reaction mixture was kept at -60 to -65°. The mixture was then acidified in one hour at 0° with a solution of urea- acetic acid (100 ml.). The mixture was saturated with sodium chloride; the aqueous layer was separated and extracted with ethyl ether (100 ml.). The combined ether extract was washed with saturated sodium bicarbonate solution (2 x 200 ml) and dried over anhydrous sodium sulfate. After removal of the sodium sulfate by filtration and evaporation of the solvent, distillation of the product gave the following fractions: (1) 2-nitrobutane (6.95 g.» 0.0675 mole, 45 per cent conver- O sion) as a colorless liquid, b.p. 60-70 (60 mm.), 137.5 (742.3 mm.) (capillary method), n2§ 1.4046-1.4050, 620 0.9652; MRp(calcd.) 26.33, MRD (found) 26.19; and (2) 3- methyl-3, 5-dinitroheptane (5.34g., 0.026 mole, 35 per cent £ Possibly 2,2,4-trimethyl-l,3-dinitropentane formed by Michael addition of 2-methyl-l-nitropropane to 2-methyl-l- nitropropene, O 71 conversion), b.p. 36-90° (0.5 mm.), n2jj 1.4563-1.4577, and (3) a residue (1.3 g.). Redistillation of Fraction 1 gave very pure, color less 2-nitrobutane, b.p. 133.5° (756.4 mm.) (capillary tube method), n2g 1.4044, d|° 0.9676; lit.3 b.p. 140°, n2p 1.4036, d|o 0.963; lit.83 b.p. 138-139° (747 mm.), Sp. Gr. 0.9377; lit.81, b.p. 139.6° (760 mm.); lit.67 n2§ 1.4042. The infrared spectrum of Fraction 1, 2-nitrobutane (sandwich cell), contained strong bands for an aliphatic mononitro group (6.4 and 7.2 microns); no other functional groups were evident. The structure of 2-nitrobutane was established by its conversion to methyl ethyl ketone via the 6*5 Nef reaction ' followed by preparation of methyl ethyl ketone 2,4-dinitrophenylhydrazone in 46 per cent overall conversion O A A m.p. 115-116.5 , lit. 115°. The melting point of the de rivative was not depressed when mixed with an authentic sample. Redistillation of Fraction 2 gave purer 3-methyl-3, 5-dinitroheptane in slightly lower yield, b.p. 79-31° 9 0 90 (0.7 mm.), n4g 1.4573, dg} 1.1125; MRD (calcd.) 50.61, MRD (found) 50.03. The infrared spectrum of the 3-methyl-3, 5-dinitroheptane contained strong bands for a mononitro group (6.4 and 7.2 microns). The following analysis was obtained for the 3-methyl-3,5-dinitroheptane: 72 Anal. Calcd. for C^H^l^O^: c , 47.05; H, 7.90; N, 13.70. Found: C, 47.95, 43.01; H, 7.90, 7.70; N, 13.50, 13.35. A derivative of 3-methyl-3, 5-dinitroheptane was prepared by its conversion to 3-m ethyl-3-nitro-5-heptanone 6*5 via the Nef reaction J followed b y preparation of 3-methyl-3- nitro-5-heptanone 2, 4-dinitrophenvlhydrazone in 41 per cent overall conversion,m .p. 131.5-132.$°- For a proof of struc ture of this compound see page Anal. Calcd. for O ^ H ^ O g : C, 47.59; H, 5.42; N, 19.32. Found : C, 47.43; H, 5.29; N, 19.96. Procedure 2. The experiment was conducted as previous ly except 2-nitro-l-butene (12,1 g t,'0,12 mole) was added to sodium trimethoxyborohydride (16,9 g., 0,12 mole + 10 per cent) in 70 minutes at -55 to -60°• after addition was completed the mixture was stirred for 30 minutes at -60°. The ether extract was also washed with saturated sodium bisulfite solution (3 x 150 ml,). Distillation of the product gave: (a) 2-nitrobutane (3.67 g., 0,0357 mole, 29.7 per cent conversion) as a colorless liquid, b.p. 44-62° (60 mm.), \9 73 n D 1.4047-1.4055> (b) 3-methyl-3, 5-dinitroheptane(5.65g.> 0,0277 mole, 46,2 per cent conversion) as a yellow liquid, b.p. 99-100° (1 mm.), n2§ 1.4559-1.45#0, and (c) a residue (1.1 g.). Procedure 2. The experiment was conducted as pre viously (Procedure 1) except the 2-nitro-l-butene was added dropwise in 1.5 hours to sodium trimethoxyborohydride (21.1 g., 0.15 mole + 10 per cent excess). During addition the reaction mixture was kept at -1 to -2°; after addition was completed the mixture was stirred for 1.5 hours at 0°. The ether extract was also washed with sodium bisulfite solution (3 x 150 ml.). Distillation of the product gave: (a) 2-nitrobutane (1.42 g., 0.013# mole, 9.2 per cent con version) as a pale yellow liquid, b.p. 45-53° (50 mm.), n2§ 1.404#-1.406l, (b) 3-methyl-3,5-dinitroheptane (0.77 g.> 0,00377 mole, 5.03 par cent conversion) as an amber liquid, b.p. 40-90° (0,6 mm.), n2§ 1.4570 and (c) a residue (10,41 g.). The residue was not identified. d. Reduction of 2-Nitro-2-butene With Sodium Tri methoxyborohydride; 2^¥itrobutane, 3.4-Simethyl-2, 4-dinitro- he'xaine. “ *" *” Procedure 1. A solution of 2-nitro-2-butene (15.2 g., 0.15 mole) in ethyl ether (25 ml.) was added dropwise in 65 minutes to a stirred suspension of sodium trimethoxyborohydride (28.6 g., 0,15 mole, + 50 per cent excess) in ethyl ether 74 (150 ml.) and tetrahydrofdran (50 ml.). During addition the reaction mixture was kept at -70°; after addition was com pleted the mixture was stirred for 35 minutes at -70°. The mixture was then warmed to ca. -20°; suddenly a grey pre cipitate separated and the temperature rose to ca. +20°. The mixture was cooled to 0° and acidified in 1.5 hours at 0° with urea-acetic acid solution (100 ml.). The mixture was saturated with sodium chloride; the aqueous layer was separa ted and extracted with ethyl ether (100 ml.). The combined ether extract was washed with saturated sodium bicarbonate solution (2 x 200 ml.) and dried over anhydrous sodium sulfate. The sodium sulfate was removed by filtration; distillation gave: (1) 2-nitrobutane (9.49 g.» 0.0939 mole, o 62.6 per cent conversion) asa colorless liquid, b.p. 70-73 (go mm.), n 2g 1.4033-1.4057, d|g 0.9674; MHj, (calcd.) 26.33, MRd (found) 26.13; (2) 3,4-diraethyl-2, 4-dinitrohexane (1.74 g.» 0.00&5 mole, 11.4 percent conversion) as a green liquid, b.p. 111-112° (1.3 mm.), n2° 1.4642-1.4647, and (3) a residue (0.8 g.). Redistillation of Fraction 1 gave pure 2-nitrobutane, b.p. 138.5° (756.4 mm.) (capillary tube method), n2§ 1.4044, djto 0.9676; lit.3 b.p. 140°, nD 1.4036, dgo 0.968; lit.*3 b.p. 138-139° (747 mm.), Sp. Gr.° 0.9877; lit.31 139.6° (760 mm.); lit.^ n2^ 1.4042. 75 The infrared spectrum of the 2-nitrobutane (sandwich cell) contained strong bands for the mononitro (6.4 and 7.2 microns) group and no bands for a carbonyl group (5.7 microns), a mononitro group attached to an unsaturated carbon atom (6.5 microns) or a carbon-carbon double bond (6.0 microns). The structure of 2-nitrobutane was established upon its conversion to methyl ethyl ketone via the Nef reaction^ followed by preparation of methyl ethyl ketone 2.4-dinitro- phenylhydrazone in 55 per cent overall conversion, m.p. 115-116.5°; lit.*d 115°. The melting point of the deriva tive was not depressed when mixed with an authentic sample. Product 2 was redistilled twice to give 3»4-dimethyl-2, 4-dinitrohexane as a light yellow liquid in only slightly lower yield, b.p. 73-30° (0.1 mm.), n2§ 1.4657, d2§ 1.126; MRj) (calcd.) 50,61; MRp (found) 50.20. Its infrared analysis indicated the presence of an aliphatic mononitro group (6.4 and 7.2 microns). Anal. Calcd. for CgHl6N204 : C, 47.05; H, 7.90; N, 13.70. Found: C, 47.01, 47.17; H, 7.Si, S.00; N, 13.32, 13.66. Procedure 2. The experiment was conducted as pre viously except the sodium trimethoxyborohydride was suspended 76 in 200 ml. of ethyl ether. The same rapid rise in tempera ture was noted when the reaction mixture was warmed to -30°. Distillation of the product gave: (a) 2-nitro-2-butene (3.19 g.» 0.0316 mole, 21 per cent recovery) and 2-nitro butane (9.72 g., 0.0942 mole, 62.3 per cent conversion, 79.4 per cent yield) as a mixture (analysis by refractive index), b.p. 72.5-7#° (#0 mm.), and (b) a residue (0.5 g.). Procedure The experiment was conducted as pre viously (Procedure 1) except the sodium trimethoxyborohydride was suspended in 200 ml. of ethyl ether. The olefin was added in 75 minutes and, after addition was completed, the mixture was stirred for 125 minutes. The same rapid tempera ture rise was noted when the reaction mixture was warmed to -30°. Distillation of the product gave: (a) 2-nitrow2-butene (2.53 g., 0.0251 mole, 16.7 per cent recovery) and 2-nitro butane (9.56 g., 0.092# mole, 61.9 per cent conversion, 74.3 per cent yield) as a mixture (analysis by refractive index), b.p. 72-#0° (#0 mm.), and (b) a residue (0.6 g.). •• Reduction of 4-Nitro-3-fteptene With Sodium Tri- methoxyborohydrideT"4-Nitroheptane. Procedure 1. A solution of 4-aitro-3-heptene (15.75 g., 0.11 mole) in ethyl ether (25 ml.) was added dropwise in 3 hours to a stirred suspension of sodium trimethoxyboro hydride (21.11 g., 0.11 mole, plus 50 per cent excess) in 77 ethyl ether (125 ml.) and tetrahydrofuran (50 ml,). During addition the reaction mixture was kept at 0 - 1 ; after addition was completed the mixture was stirred for 3 hours at 0°. The mixture was then acidified below 0° in one hour with urea-acetic acid solution (75 ml., aqueous solution, 2.73 molal in urea and acetic acid). The mixture was satur ated with sodium chloride; the aqueous layer was separated and extracted with ethyl ether (100 ml.). The combined ether extract was washed with saturated sodium bicarbonate solution (2 x 150 ml.) and dried over anhydrous sodium sulfate. After separation of sodium sulfate by filtration and removal of the solvents, distillation gave: (a) 4-nitroheptane (3.30 g., O.O6O6 mole, 55 per cent conversion) as a light yellow liquid, b.p. 63-71° (3.3 mm.), h2^ 1.4236-1.4232; (b) a mixture of 4-nitroheptane (0.94 g.» 0.00647 mole, 5.9 per cent conversion) and 4-nitro-3-heptene (0.46 g., 0.00321 mole, 2.9 per cent recovery) (analysis by refractive index), b.p. 72° (3.3 mm.), n2§ 1,4330; and (c) an unidenti fied product (1.70 g.), b.p. 77-33° (1.1 mm.), n2§ 1.4465- 1.4499. Two redistillations of the 4-nitroheptane gave a very pure, colorless product in slightly lower yield, b.p. orj 70-71° (9 mm.), n2§ 1.4224-1.4236, d20 0.9269; MRD (calcd.) 40.27, MRd (found) 39.92; lit.29 b.p. 90° (25 mm.), n2fj 1.4200, d2^ 0.919. The total yield 4-nitroheptane was 62.7 per cent. 73 Anal. Calcd. for C^H^NC^: C, 57.90; H, 10.41; N, 9.65 Found: C, 53.32; H, 10.53; N, 9.40 The infrared spectrum of the 4-nitroheptane (sand wich cell) contained strong bands for the mononitro group (6.4 and 7.2 microns) but no bands for any other functional group. An infrared spectrum of the unidentified product (sandwich cell) contained a strong band for the. mononitro group (6.4 and 7.2 microns) and weak bands for a carbonyl group (5.3 microns) and amino group (2.95 and 6.1 microns). The structure of 4-nitroheptane was proven by its 65 conversion to 4-heptanone via the Nef ' reaction followed by preparation of 4-heptanone 2, 4-dinitrophenylhydrazone in 45 per cent overall conversion, m;p,' 74-75.5° lit .^ m.p. 75°. The melting point of the derivative was not depressed when mixed with an authentic sample. Procedure 2. The experiment was conducted as pre viously except the nitroolefin was added in 70 minutes at 0° and the mixture was stirred for 30 minutes at 0°. Distillation gave: 4-nitro-3-heptene(4.39 g., 0.0342 mole, 31 per cent recovery) and 4-nitroheptane ($.07 g., 0.0555 mole, 50.5 per cent conversion, 73.2 per cent yield) as a 20 mixture, b.p. 67-80° (9 mm.), n d 1.4215-1.4497. The re- 79 action time in this experiment was too short to effect complete reduction. Procedure 2* The experiment was conducted as previ ously except the nitroolefin was added in 70 minutes at -40° for 30 minutes. Distillation gave: 4-nitro-3-heptene (4.3& g.» 0.0306 mole, 27.9 per cent recovery) and 4-nitro heptane (6.43 g., 0.0446 mole, 40.5 per cent conversion, 56.1 per cent yield) as a mixture, b.p. 69-31° (9 mm.), 70 n Q 1.4259-1.4570. The reaction time in this experiment was too short for complete reduction. f. Reduction of 3. 3.3-Trichloro-l-hiitropropene With Sodium Trimethoxyborohydride; 1,1, l^TH\:hlbVo-3-nitrapropane; 1, l,l-T'rlchloro-3i f>-d'initro-4-£richloromethyIpentane. A solution of 3>3»3-trichloro-l-nitropropene (15.20 g., 0.03 mole) in ethyl ether (25 ml.) was added dropwise in 70 minutes to a stirred suspension of sodium trimethoxyboro hydride (15.3 g.> 0.06 mole + 50 per cent excess) in ethyl ether (125 ml.) and tetrahydrofuran (50 ml.). During addi tion the reaction mixture was kept at -40° t 2°; after addition was completed the mixture was stirred for 30 minutes at -40°. The mixture was then acidified in 45 minutes below 0° with urea-acetic acid solution (50 ml., aqueous solution, 2.73 molal in urea and acetic acid). The mixture was saturat ed with sodium chloride; the aqueous layer was separated and extracted with ethyl ether (100 ml.). The combined ether 30 extract was washed with saturated sodium bicarbonate solu tion (2 x 150 ml.) and dried over anhydrous sodium sulfate. After separation of the sodium sulfate by filtration and removal of the solvents, the mixture was set in a refrigera tor for 3 days. A crystalline solid separated from the re action mixture during this period. The solid was filtered and washed with methanol (5 ml.); the methanol washings were concentrated. The oily residue was placed in a refrigerator and allowed to crystallize. By repeating the previously described procedure, three crops of a crystalline solid were 0 obtained: (1) 2.53 g., ra.p. 150-151 ; (2) 1.33 g.» m.p. 149-150°; and (3) 0.62 g., m.p. 149-150°. The filtrates from the above crystallizations were distilled (I) and gave: 1,1,1-trichloro-3-nitropropane (6.77 g., 0.0354 mole, 44.2 per cent conversion) as a color less liquid, b.p. 91-92° (9 mm.), n2jj 1.4636-1.4900; and a residue. Redistillation of the reduction product gave a 1,1,1-trichloro-3-nitropropane of analytical purity, b.p. 70-71.3P (3 mm.), n2g 1.4399, d2§ 1.5347; MR^ (calcd.) 36.13, MRjj (found) 36.25. Anal. Calcd. for C^H^CljI^: C, 13.72; H, 2.10; N, 7.23. Found: C, 19.11, 19.10; H, 2.13, 2.30; N, 7.11, 7.14. $1 The residue (2.3 g.) from the initial distillation (I) of 1,l,l-trichloro-3-nitropropane was dissolved in hot methanol (10 ml.); the mixture was then cooled in a refriger ator and gave an additional crop (4; 0.3# g.) of the white crystalline solid, m.p. 147-14$°. The crops of solids were combined and recrystallized twice from hot carbon tetrachlo ride to give a product identified by analysis as 1,1,1-tri- chloro-3» 5-dinitro-4-trichloromethylpentane (4.0 g., 0.012$5 mole, 32.1 per cent conversion), a white fibrous material, m.p. 150-151°. Anal. Calcd. for C6H6C16N2Q^: C, IS,$2; H, 1.5$ N, 7.32. Found: C, 1S.79, 1$.76; H, 1.72, 1.71; N, 7.30, 7.26. The infrared spectrum of 1,1,1-trichloro-3-nitro- propane (sandwich cell) contained strong bands for a mononitro group (6.35 and 7.2 microns), a trichloromethyl group (12.5 microns) and a carbon-chlorine bond (14.4 microns), but no bands for any other functional group. The infrared spectrum of 1,1,1-trichloro-3,5-dinitro-4-trichloromethyl- pentane (0.2 molar in chloroform) contained strong bands for a mononitro group (6.35 an<^ 7.25 microns) and a trichloromethyl group (12.4 microns). 32 S. Reduction of 4»4.5» 5,6,6,6-Heptafluoro-2-nitro- 2-hexene With Sodium Trimethoxyporonydriae; 1,1.1,2,2,3, 3- IT e pt af luo ro-5-hitrohexane. A solution of 5,5,6,6,7,7,7-heptafluoro-2-nitro-2- hexene (7.50 g., 0,0294 mole) in ethyl ether (25 ml.) was added dropwise in 2 hours to a stirred suspension of sodium trimethoxyborohydride (5.76 g., 0.0294 mole + 50 per cent excess) in ethyl ether (75 ml.) and tetrahydrofuran (25 ml.). During addition the reaction mixture was kept at -65 to -70°; after addition was completed the mixture was stirred for one hour at -65 to -70°. The mixture was then acidified in 30 minutes below 0° with urea-acetic acid solution (25 ml., aqueous solution, 2.73 molal in urea and acetic acid). The mixture was saturated with sodium chloride; the aqueous layer was separated and extracted with ethyl ether (100 ml.). The combined ether extract was washed with saturated sodium bicarbonate solution (2 x 75 ml.) and dried over anhydrous sodium sulfate. After separating the sodium sulfate by filtration and removal of the solvents on a steam bath, dis tillation gave: l,l,l,2,2,3,3-heptafluoro-5-nitrohexane (6.34 g.» 0.0247 mole, 34 per cent conversion) as a color- o 20 less liquid, b.p. 77-7*.3 (39-40 inn.), n‘% 1.3405-1.3409, d^g 1.4*61; lit.60 b.p. 64° (23 mm.), n2g 1.3412. An infrared spectrum of the l,l,l,2,2,3,3-heptafluoro-5-nitro- hexane contained strong bands for the mononitro group (6.35 and 7.2 microns) and for carbon-fluorine bonds (3.0-3.4 microns), but no absorption for any other functional group. h. Reduction of 5.5.6,6,7.7,7-Heptafluoro-3-nitro- 3-Keptene With SodXum Trime tnoxyborohyride; 1,171,2,2,2>"1“ heptafluoro-5-Nitroheptane; 5.5.b,b,777, 7-HeptafTuoro-3- Keptanone.' " A solution of 5,5>6,6,7,7,7-hepta£luoro-3-nitro-3- heptene {15.34 g.» 0.057 mole) in ethyl ether (25 ml.) was added dropwise in 2 hours to a stirred suspension of sodium trimethoxyborohydride (10.94 g.» 0.057 mole + 50 per cent excess) in ethyl ether (125 ml.) and tetrahydrofuran (25 ml.). During addition the reaction mixture was kept at -60 to -65°; after addition was completed the mixture was stirred for 1 hour at -60 to -65°. The mixture was then acidified in 45 minutes below 0° with urea-acetic acid solution (75 ml., aqueous solution, 2.7# molal in urea and acetic acid). The mixture was saturated with sodium chloride; the aqueous layer was separated and extracted with ebhyl ether (100 ml.). The combined ether extract was washed with saturated sodium bicarbonate solution (2 x 150 ml.) and dried over anhydrous sodium sulfate. After removal of the sodium sulfate by filtration, distillation gave, after removal of the solvent 1.1.1.2.2.3.3-heptafluoro-5-nitroheptane (14.07 g., 0.052 mole, 91 per cent conversion) as a colorless liquid, b.p. 78.5-79° (23-25 r r n . ) , ^ 1.31*85-1.3491, df° 1.4286; lit.60 b.p. 60° (9 mm.), n2§ 1.3493. The infrared spectrum of 1.1.1.2.2.3.3-heptafluoro-5-nitroheptane (sandwich cell) contained strong bands for a mononitro group (6.34 and 7.2 microns) and for carbon-fluorine bonds (#.0-S.5 microns), 34 but no bands for any other functional group. A solution of 1,1,1,2,2,3,3-heptafluoro-5-nitroheptane (1 g., 0.00369 mole) in methanol (10 ml.) was added to a solution of sodium hydroxide (0.4 g., 0.01 mole) in water (10 ml.) and kept at 0° for IS hours. This solution was added dropwise at 0° to concentrated sulfuric acid (2,5 ml.) in water (12 ml.); a solution of 2,4-dinitrophenylhydrazine was added. An oil separated and was crystallized from hot ethanol; four recrystallizations from hot ethanol gave 5,5.6,6,7.7. 7-heptafluoro-3-heptanone 2,4-dinitrophenyl- hydrazone (0.71 g.j 0.00135 mole, 50 per cent overall conversion) as orange needles, m.p. 123-124°. Anal. Calcd. for ci2F7Hn ^ 4°4: 37.15; H, 2.64; N, 13.33 Found: C, 37.75, 37.62 H, 2.99, 2.35; N, 13.51, 13.56. 1 i. Reduction of Omega-hitrostyrene With Sodium Trimethoxyborohydride; l-Nitro-2-phenylethane; 173-Dintro- 2,4-^i phenylbutane. ~~ ~ Procedure 1. A solution of omega-nitrostyrene (14.9 g., 0.1 mole) in ethyl ether (50 ml.) and tetrahydrofuran (50 ml.) was added dropwise in 95 minutes to a stirred suspension of sodium trimethoxyborohydride (19.2 g., 0.1 mole + 50 per cent excess) in ethyl ether (125 ml.) and tetrahydrofuran (25 ml.). During addition the mixture was kept at -40^ 2°; after addition was completed the mixture was stirred for 25 min utes at -40°. The mixture was then acidified in 40 minutes below 0° with urea-acetic acid solution (70 ml., aqueous solution, 2.73 molal in urea and acetic acid). The mixture was saturated with sodium chloride; the aqueous layer was separated and extracted with ethyl ether (100 ml.). The combined ether extract was washed with saturated sodium bi carbonate solution (2 x 150 ml.). A solid (A) began to separate in the ether phase; the solid (A) was centrifuged, filtered and dried to give a milky-white material (2.96 g., O 19.6 per cent conversion) m.£. 255 (dec.) t unidentified. After drying the ether layer over anhydrous sodium sulfate and removal of the solvents, distillation gave: l-nitro-2- phenylethane (5.33 g., 0.0336 mole, 33.6 per cent conversion) as a colorless liquid, b.p. 73-74.5° (0.5 mm.), n ^ 1.5266- 1.5273, dlo 1.1314; MRD (calcd.) 41.37, MR,,!found), 41.08; lit.69 b.p. 128-135° (14 ora.); lit.90 b.p. 249-251° (763 mm.); lit.91 125-135° (mm.); lit.67 n2j> 1.5276, and (2) a distillation residue (5 g.). The infrared spectrum of 1-nitro-2-phenylethane (sandwich cell) contained bands for a mononitro group (6.35 and 7.2 microns) and a mono- ^See page 132; omega-nitrostyrene in the presence of benzyltrimethylammonium hydroxide forms this same solid. 36 substituted benzene ring (13.3 and 14.3 microns), but no bands for any other functional group. The distillation residue (5g.) crystallized to a pasty, amber solid; the residue was then dissolved in boiling ethanol. A white solid (B) separated from the ethanol solu tion on cooling; recrystallization from hot ethanol gave 1.3-dinitro-2,4-diphenylbutane (3.57 g., 0.0116 mole, 23.6 per cent conversion) as white plates, m.p. 120.5-121.0°. 1 .3-dinitro-2,4-diphenylbutane can exist in two racemic modifications but apparently only one form is produced or isolated from this reaction. Its infrared spectrum (0.2 molar in chloroform) contained bands for a mononitro group (6.4 and 7.3 microns) and a mono-substituted benzene ring (14.4 microns) but no other functional groups. Anal. Calcd. for c, 63.99; H, 5.37; N, 9.33. Found: C, 63.90, 63.#3; H, 5.22, 5.13; N. 9.53, 9.24. Procedure 2. A solution of omega-nitrostyrene (14.9 g., 0.1 mole) in ether (75 ml.) was added dropwise in 1.5 hours to a stirred suspension of sodium trimethoxyborohydride (14.1 g., 0.1 mole + 10 per cent excess) in ethyl ether (125 ml.) and tetrahydrofuran (50 ml.). During addition 0 O o the reaction mixture was kept at -2 to -3°; after addition was completed the mixture was stirred for 1.5 hours at 0°. The mixture was then acidified in one hour at 0° with urea- acetic acid solution (60 ml.). The ether phase contained a white solid. The mixture was saturated with sodium chloride the aqueous layer was separated and extracted with ethyl ether (100 ml.). The white solid (A), m.p. ca. 263 > was filtered from the combined ether extract and air dried to constant weight (13.2 g.); the filtrate was washed with saturated sodium bicarbonate solution (2 x 200 ml.) and saturated sodium bisulfite solution (3 x 150 ml.). The ether layer was dried over anhydrous sodium sulfate and then evapo rated; no residue was obtained. The following tests were made on the white solid isolated from the reduction reaction: (1) The white solid (1 g.) was refluxed for 2 hours with 1:1 hydrochloric acid (20 ml.); the solid was recovered unchanged. (2) A mixture of potassium hydroxide (2 g.) and the reduction product (1 g.) in ethyl alcohol (25 ml.) and water (25 ml.) was heated on a steam bath for 5 minutes. The white solid dissolved producing a dark red solution; a small amount of charred material settled from solution. Half of the solution was acidified at 0° with urea-acetic acid 33 solution and then extracted with ethyl ether (50 ml.). No residue was obtained upon evaporation of the ether ex tract. The second half of the basic solution was dropped slowly at 0° into 50 per cent sulfuric acid (excess) (Nef 65 reaction ). This solution was treated with 2,4-dinitro- phenylhydrazine solution; however, no derivative precipi tated. (3) An infrared spectrum of the white solid in Nujol contained strong bands for a mononitro group (6.4 and 7.25 microns) and a mono-substituted benzene ring (13.6 and 14.35 microns) but no bands for any other functional group. (4) The product was insoluble in the following sol vents at their boiling points: ether, Skellysolves, benzene, methanol, ethanol, water, carbon tetrachloride, chloroform, acetone and acetic acid. (5) The white solid (0.75 g.) was dissolved in hot aqueous sodium hydroxide (0.025 gram in 5 ml.). The red solution was cooled and added dropwise to aqueous sodium permanganate +3^0 (1.4 g. in 25 ml.). The mixture was heated on a steam bath until most of the permanganate color was gone. The mixture was then cooled in ice and made strongly acid; manganese dioxide was dissolved by adding sodium bisulfite (solid). (Note: Since sodium bisulfite is basic, sufficient acid must be present to generate -C00H from -COO" ion). The white solid present was contaminated with charred material. The mixture was filtered and the solid was dissolved in sodium hydroxide solution, filtered from charred material, and reprecipi tated by adding dilute hydro chloric acid. The solid, benzoic acid, was filtered and recrystallized from hot water, m.p. 113-120°, lit,^ 121.4°. No depression in melting point was observed when the oxidized product was mixed with an authentic sample of benzoic acid. (6) The white solid (A) was analyzed: Anal: C, 64.05, 64.21; H, 4.94, 5.01; N, 9.23, 9.24. A polymer of omega-nitrostyrene would analyze: C, 64.42; H, 4.73; N, 9.39. It has been found (See page ) that omega-nitrostyrene in presence of benzyltrimethylammonium hydroxide forms this same solid (A). J- Reduction' of 2- (2-Nitrovinyl) furan With Sodium Trimethoxyborohydride; £-(^-Nitroe'thyX) Furan. Procedure 1. A solution of 2-(2-nitrovinyl) furan (15.3 g.» 0.11 mole) in ethyl ether (75 ml.) and tetra- hydrofuran (25 ml.) was added dropwise in 110 minutes to a stirred suspension of sodium trimethoxyborohydride (21.1 g., 0.11 mole plus 50 per cent excess) in ethyl ether (125 ml.) and tetrahydrofuran (25 ml.). During addition the reaction was kept at -40 i 2°; after addition was completed the mixture was stirred for 55 minutes at -40°, The mixture was warmed to 0°, stirred at 0° for 15 minutes and acidified 9° in 45 minutes below 0 with urea-acetic acid, solution (75 ml.). The mixture was saturated with sodium chloride; the aqueous layer was separated and extracted with ethyl ether(100 ml,). The combined ether extract was washed with saturated sodium bicarbonate solution (2x200 ml.). The separations were difficult because the organic layer had a gelatinous material suspended in it. The organic layer was centrifuged; the decantate was dried over anhydrous sodium sulfate. The precipitate was dried to give a brown, glassy, unidentified material solid (A), (7.14 g.» 46.6 per cent conversion) m.p.^) 350°. After separation of the sodium sulfate from the decantate and removal of the solvents on a steam bath, distillation gave: (a) 2-(2-nitroethyl)- furan (4.39 g., 0.0311 mole, 23.3 per cent conversion) as a colorless liquid, b.p. 67-63,5° (1 .4-2.0 mm.), n^Q 1.4344- 1.4&43; and (b), a brown residue (3.1 g.). One redistil lation of the 2-(2-nitroethyl)furan gave a product of ana lytical purity, b.p. 61.5-63° (2 mm.), n^^ 1.4&42-1;,4345 d|8 1 .2052. Anal. Calcd. for C ^ N O ^ : C, 51.06; H, 5.00; N, 9.93. Found : C, 51.10, 51.25; H, 5.03, 4.93; N, 10.02, 10.13. The infrared spectrum of the 2-(2-nitroethyl)furan See page 133 ; 2-(2-nitrovinyl)furan forms this compound in the presence of benzyltrimethylammonium hydroxide. 91 (sandwich cell) contained strong bands for a mononitro group (6.35 and 7.15 microns) and a furan ring (13.5 microns). Procedure 2. The experiment was conducted as previously except 2-(2-nitrovinyl) furan (10.15 g.> 0.073 mole) in ethyl ether (50 ml.) and tetrahydrofuran (20 ml.) was added in 5 hours to sodium trimethoxyborohydride (14.0 g., 0.11 mole) in ethyl ether (75 ml.) and tetrahydrofuran (15 ml.); the mixture was then stirred for 4 hours. The solid (A) (4.17 g.» 27.6 per cent conversion), m.p, > 350° was filtered from the ethyl ether-tetrahydrofuran mixture. After removal of the solvent, distillation of the product gave; (a), 2- (2-nitroethyl) furan (2,50 g., 0,0177 mole, 16.1 per cent conversion) as a colorless liquid, b.p. 66-69° (2.0-2.1 mm.), 1.4637-1.4647; and (b), a brown residue (4.0 g.). k. Attempted Reduction of l-(Nitromethyl) dyclo- pentene With Sodium TrimethoxyForohydride. Procedure 1. A solution of l-(nitromethyl) cyclopen- tene (6.36 g., 0.05 mole) in ethyl ether (25 ml.) was added dropwise in 2.2 hours to a stirred suspension of sodium trimethoxyborohydride (9.59 g.» 0,05 mole + 50 per cent excess) in ethyl ether (75 ml.) and tetrahydrofuran (25 ml,). During addition the mixture was kept at -30 to -40°; after addition was completed the mixture was stirred for 3 hours at -35 to '40°. The mixture was then acidified below 0° in 30 minutes with urea-acetic acid solution (35 ml.). 92 The mixture was saturated with sodium chloride; the aqueous layer was separated and extracted with ethyl ether (50 ml.). The combined ether extract was washed with saturated sodium bicarbonate solution (2 x 75 ml.) and dried over anhydrous sodium sulfate. After separation of the sodium sulfate by filtration and removal of the solvents, distillation gave the starting material l-(nitromethyl) cyclopentene ( #5 per cent recovery) b.p. 70-70.5° (7.0-7.2 mm.), n2§ 1.4752. The infrared spectrum of the recovered material was identical with that of the starting material. Procedure 2. The procedure above was followed except the l-(nitromethyl) cyclopentene was added at 0° in 2 hours, and then the mixture was heated at 35 to 40° for 3.5 hours. The starting material was recovered unchanged (S3 per cent recovery). 1. Reaction of Sodium Trimethoxyborohydride With 2-Nitro-l-butyl Acetate. A solution of 2-nitro-1-butyl acetate (16.1 g., 0,1 mole) in ethyl ether (25 ml.) was added dropwise in two hours to a stirred suspension of sodium trimethoxyborohydride (2S.0 g., 0,2 mole plus 10 per cent excess) in ethyl ether (125 ml.) and tetrahydrofuran (50 ml.). During addition the reaction mixture was kept at 3-4°: after addition was complete, the mixture was stirred for IS hours at 3-4°, The reaction mixture was acidified in one hour at 0° with 93 urea-acetic acid solution (100 g), and saturated with sodium chloride; the aqueous layer was separated and extracted with ethyl ether (100 ml.). The combined ether extract was washed with saturated sodium bicarbonate solution (2 x 150 ml.), saturated sodium chloride solution (200 ml.) and then dried over anhydrous sodium sulfate. Distillation of the product, after removal of solvent, gave the following frac tions which are mixtures of 2-nitro-1-butanol and 2-nitro- 1-butyl acetate: Fraction Boiling Pressure Weight n 20« Per cent Range°C 2-Nitro- * ______1-butanol 1 50-66.5 1 mm. 0.37 g. 1.431$ 49 2 66.5-64 1-0.7 5.26 1.4339 52 3 64-65 0.7 2.B6 1.4347 61 4 65 0.7 0.37 1.4357 71 Residue 0.5 The infrared spectra of all fractions (sandwich cell) contained strong bands for a mononitro group (6.4 and 7.2 microns), a hydroxyl group (2.0 microns) and a carbonyl group (5.75 microns). 2. SELECTIVE REDUCTION OF CONJUGATED NITRQOLEFINS BY LITHIUM BQROHIDRIDE. a. Reduction of 1-Nitropropene With Lithium Boro- hydride; 1-Nitropropane, 2-Methyl-l,3-^iaitropentane. A solution of 1-nitropropene (15.2 g., 0.175 mole) in t Analysis made by refractive index. n 94 ethyl ether (25 ml.) was added dropwise in 3 hours to a stirred suspension of lithium borohydride (1.92 g., 0,088 mole) in ethyl ether (175 ml.). During addition the re- O i r\ action mixture was kept at -70 - 1 ; after addition was completed the mixture was stirred for 2 hours at -70°. The mixture was then acidified in 1 hour at 0° with urea- acetic acid solution (140 ml.). The mixture was saturated with sodium chloride; the aqueous layer was separated and extracted with ethyl ether (100 ml.). The .combined ether extract was washed with saturated sodium bicarbonate solu tion (2 x 200 ml.) and dried over anhydrous sodium sulfate. After removal of the sodium sulfate by filtration and con centration of the filtrate, distillation gave: (a) 1-nitro- propane (7.77 g., 0.0373 mole, 49.9 per cent conversion) as a colorless liquid, b.p. 65-69.5° (100 mm.), n2g 1.4035- 1.4045, d|o 0.9939; MRD (calcd.) 21.63, MRD (found) 22.12, (b) crude 2-methyl-1,3-dinitropentane (0.37 g.» 0.0021 mole, 2.4 per cent conversion) as a yellow liquid, b.p. ca. 105° (1 mm.), n2§ 1.4577 and (c) a brown residue (0.9 g.). Redistillation of fraction (a) gave purer 1-nitropropane, b.p. 129° (742.3 mm.), n2§ 1.4023; lit.79 b.p. 130.5, d2£*3 1.40027; lit.*0 b.p. 132°, d^g 1.003, nD 1.4015; lit.*1 131.6° (760 mm.); lit.*2 130.5° (761 mm.), d20 1.0009 n2§ 1.40130. ■)\ 95 The structure of 1-nitropropane was proven by con- 65 version to propionaldehyde via the Nef reaction followed by preparation of propionaldehyde 2,4-dinitrophenylhydrazone o in 61 per cent overall conversion, m.p. 153.5-155.5 ; lit. 155°. The melting point of the derivative was not depressed when mixed with an authentic sample. The infrared spectrum of the 1-nitropropane (sandwich cell) contained a strong band for a mononitro (6.4 and 7.2 microns) group and no bands for a carbonyl group (5.7 microns), a mononitro group attached to an unsaturated carbon atom (6.5 microns) or a carbon-carbon double bond (6.0 microns). b. Reduction of 2-Methyl-1-h'itropropene With Lithium Borohydride; 2-MethyT^l-hitropropane. A solution of-lithium borohydride (3.1 g., 0.0125 mole plus 10 per cent excess) in tetrahydrofuran (15 ml.) and ethyl ether (30 ml.) was added in small portions to 2-methyl- 1-nitropropene (5.05 g., 0.05 mole) in ethyl ether (10 ml.). After the initial reaction had subsided the reaction mixture was allowed to stand at room temperature for 3 hours and then refluxed for one hour. The mixture was cooled to 0° and acidified in 60 minutes with urea-acetic acid solution (25 ml.); the temperature of the mixture was maintained at -3 bo -5°. The mixture was diluted with ethyl ether (100 ml.), and saturated sodium bicarbonate (100 ml.) was added. After shaking the mixture vigorously, the mixture was saturated with sodium chloride; the aqueous phase was separated and extracted with ethyl ether (100 ml.). The combined ether extract was dried over anhydrous sodium sulfate, evaporated, and then distilled to give: (a) crude 2-methyl-l-nitropropane (2,5 g., 0.0242 mole, 46.4 per cent conversion), b.p. 45-73°, n2§ 1 .4137-1 .4212, dfo 0 .9666; MRd (calcd.) 26.33 MRD (found) 26.61; and (b) unidentified 20 material (1,03 g.), b.p. 63-39° (7-9 mm.), n D 1 .4402- 1.4517. Redistillation of fraction (a) gives pure 2-methyl- 1-nitropropane, b.p. 69-70.7° (70 mm.), n^jj 1 .4090, d|8 0.9627; MRd (calcd.) 26.33, MRd (found) 26.46; lit.^6 b.p. 140.5° d|| 0.9625, n2S 1.4050. The infrared spectrum of 2-methyl-l-nitropropane (sandwich cell) contained strong bands for the mononitro (6.4 and 7.2 microns) group but no bands for any other functional group. The infrared spectrum of high boiling product (b) contains only a band for the mononitro group (6.4 and 7.2 microns) and is probably a product resulting from Michael condensation of 2-methyl-l-nitropropane and 2-methyl-1-nit ropropene. 97 c* Reduction of 2-Nitro-l-butene With Lithium Borohydride; 2-Nitrobutane, 3-Methyl-375-di'n'itroheptane. Procedure 1. A solution of 2-nitro-l-butene (15.2 g., 0.15 mole) in ethyl ether (25 ml.) was added dropwise in 3 hours to a stirred suspension of lithium borohydride (1.72 g., 0.075 mole + 5 per cent) in ethyl ether (125 ml) and tetrahydrofuran (50 ml.) During addition the reaction mixture was kept at -6# to -70°; after addition was completed o the mixture was stirred for 2.5 hours at -70 . The mixture was then acidified in one hour at 0° with urea-acetic acid solution (75 ml.). The mixture was saturated with sodium chloride; the aqueous layer was separated and extracted with ethyl ether (100 ml.). The ether extract was washed with saturated sodium bicarbonate solution (2 x 200 ml.) and dried over anhydrous sodium sulfate. After separation of the sodium sulfate by filtration and removal of the solvent, distillation of product gave: (1) 2-nitrobutane (9.17 g., 0.089 mole, 59.3 per cent conversion) as a color less liquid, b.p. 67-70° (80 mm.), n^§ 1.4098, d^Q 0.968; MRD (calcd.) 26.33» MRp (found) 26.30, (2 ) 3-methyl-3} 5- dinitroheptane (2.16 g., 0.0106 mole, 14.2 per cent), b.p. 72-92° (1.4 mm.), n2§ 1.4564* and (3 ) a brown residue (1.4 g.). Redistillation of Fraction 1 gave very pure colorless 2-nitrobutane, b.p. 138.5° (756.4 mm.) (capillary tube 93 method), n2£ 1.4044, d2g O.9676; lit.3 b.p. 140°, nD 1.4036. d|§ 0.963; lit.33 b.p. 133-139° (747 mm.), Sp. Gr.° 0.9377; lit.Sl b.p. 139.6° (760 mm.); lit.67 n2° 1.4042. Its infrared spectrum (sandwich cell) contained strong bands for the mononitro (6.4 and 7.2 microns) group and no bands for a carbonyl group (5.7 microns), a mononitro group at tached to an unsaturated carbon atom (6.5 microns) or a carbon-carbon double bond (6.0 microns). The structure of 2-nitrobutane was proven by its 65 conversion to methyl ethyl ketone via the Nef reaction followed by preparation of methyl ethyl ketone 2,4-dinitro- phenylhydrazone, in 65 per cent overall conversion m.p. 115-116.5°; lit.33 115°. The melting point of the deriva tive was not depressed when mixed with an authentic sample. For a proof of structure of 3-methyl-3,5-dinitroheptane see page 134. Procedure 2. The experiment was conducted as previ ously except 0.36 g., 0.0375 mole of lithium borohydride was used. Distillation of the product gave: (a) 2-nitro- 1-butene (3.60 g., 0.0356 m., 23.7 per cent recovery) and 2-nitrobutane (6.03 g., 0,0535 mole, 39 per cent conversion, 51.1 per cent yield) as a mixture (analyzed by refractive index), b.p. 53-70° (32-33 mm.), (b) crude 3-methy1-3,5- dinitroheptane (1.41 g., 0.0069 mole, 9.2 per cent con version), b.p. 55-92° (1.3 mm.), n2p 1.4525, and 99 (c) a brown residue (1.3 g.). Procedure 2* The experiment was conducted as before (Procedure 1) except the 2-nitro-l-butene solution was added to lithium borohydride (0.36 g., 0,0375 mole) in 1.5 hours. During addition the mixture was kept at -1 to + 1°; after addition was completed the mixture was stirred for 1 hour at 0°. Distillation of the product gave: (a) 2-nitro-l-butene (3.07 g., 0.0304 mole, 20,3 per cent re covery) and 2-nitrobutane (2.50 g., 0.0243 mole, 16.2 per cent conversion, 20.3 per cent yield) as a mixture (analy sis by refractive index), b.p. 60-70° (30 mm.), (b) 3- methyl-3,5-dinitroheptane (3.49 g.> 0.0171 mole, 22.3 per 2Q cent conversion), b.p. 96-93° (1.3 mm.), n ^ 1.4594, and (c) a brown residue (2.4 g.). Procedure The experiment was conducted as previously (Procedure 1) except the 2-nitro-l-butene solu tion was added to the lithium borohydride (0.36 g., 0.0375 mole) in 50 minutes. During addition the reaction mixture was kept at -50 to -55°; after addition was completed the mixture was stirred for 15 min.at -55°. The combined ether extract was also washed with saturated sodium bisulfite solution (3 x 200 ml., 5 minutes with each portion). Distil lation of the product gave: (a) 2-nitro-l-butene (0.73 g., 0.0077 mole, 5.13 per cent recovery) and 2-nitrobutane Vfi I 100 (3.72 g., 0.0361 mole, 24 per cent conversion, 25.3 per cent yield) as a mixture (analysis by refractive index), b.p. 63-70° (SO mm.), (b) 3-methyl-3, 5 dinitroheptane (0 .8S g., 0.00432 mole, 5.76 per cent conversion), b.p. #9-91.5° (1.2 mm.), n2§ 1 .4503* and (c) a black residue (0.5 g.). d. Reduction of 2-Nitro-2-butene With Lithium Borohydride; 2-NitroFutane. “ Procedure 1. A solution of 2-nitro-2-butene (15.2 g., 0.15 mole) in ethyl ether (25 ml.) was added dropwise in 2.5 hours to a stirred suspension of lithium borohydride (1.72 g., 0.075 mole plus 5 per cent) in ethyl ether (125 ml.) and tetrahydrofuran (25 ml.). During addition the mixture was kept at -35 to -40°; after addition was completed the mixture was stirred for 2.5 hours at -35 to -40°. The mixture was then acidified below 0° in 35 minutes with urea- acetic acid solution (60 ml,). The mixture was saturated with sodium chloride; the aqueous layer was separated and extracted with ethyl ether (100 ml.). The combined ether extract was washed with saturated sodium bicarbonate solu tion (2 x 200 ml.) and dried over anhydrous sodium sulfate. After separation of the sodium sulfate by filtration and removal of the solvents, distillation gave: (a) 2-nitro butane (9.03 g.) contaminated with a trace of 2-nitro-2- butene, b.p. 73-7#.5° (7#-&0 mm.), n^jj 1 .40^5; and (b), a residue (4.33 g.). The residue was not investigated. Fraction (c£) in ethyl ether (100 ml.) was washed with saturated sodium bisulfite solution (3 x 75 ml,) 5 minutes with each portion) and dried over anhydrous sodium sulfate. After removal of the sodium sulfate by filtration and volitization of the solvents, distillation gave: 2-nitro- butane (7.13 g.» 0.0692 mole, 46.1 per cent conversion) as a colorless liquid, b.p. 70-71.3° (75-76 mm.), n2g 1.4051- 1.4056, djjQ 0.9660. Redistillation gave a very pure product b.p. 13$.5° (756.4 mm.) (capillary tube method), n2g 1.4044> d2g 0.9676; lit.3 b.p. 140°, nD 1 .4036, Sp. Or.20 0 .968; lit.33 b.p. 138-139° (747 mm.), Sp. Gr.° 0.9377; lit.*1 b.p. 139.6° (760 mm.); lit.67 n2g 1.4042. The infrared spectrum of the 2-nitrobutane (sandwich cell) contained strong bands for a mononitro group (6.4 and 7.2 microns), but no bands for any other functional group. Procedure 2. The experiment was conducted as previ ously except the nitroolefin was added in 3 hours and then the mixture was stirred for 2 hours. Distillation gave: 2-nitrobutane (9.40 g., 0.00912 mole, 60.8 per cent con- n 90 version) as a colorless liquid, b.p. 68-73 (30 mm.), n ^ 1.4053-1.4073, d11 0.9621. e. Reduction of 4-Nitro-3-heptene With Lithium Boro hydride ; 4-Nitroheptane. Procedure 1. A solution of 4-nitro-3-heptene (15.75 g 0.11 mole) in ethyl ether (25 ml.) was added dropwise in 4 o 102 hours to a stirred suspension of lithium borohydride (1.13 g,, 0.055 mole) in ethyl ether (125 ml.) and tetra- hydrofuran (25 ml.). During addition the reaction mixture was kept at -65 to -70°; after addition was completed the mixture was stirred for 4 hours at -65 to -70°. The mix ture was then acidified in 45 minutes below 0° with urea- acetic acid solution (100 ml., aqueous solution, 2,73 molal in urea and in acetic acid). The mixture was saturated with sodium chloride; the aqueous layer was separated and extract ed with ethyl ether (100 ml.). The combined ether extract was washed with saturated sodium bicarbonate solution (2 x 150 ml.) and dried over anhydrous sodium sulfate. After filtering the sodium sulfate and removing the solvents, dis tillation gave: (a) a mixture of 4-nitroheptane and 4-nitro- 3-heptene (12.16 g.) as a light yellow liquid, b.p. 69.3- 71.3° (8-8.2 mm.), n2p 1.4217-1.4319; and (b) a light yellow liquid (1.55 g.), b.p. 53-75° (1 mm.), n2g 1.4450-1.4520, unidentified. 4-Nitro-3-heptene was separated from 4- nitro- heptane upon solution in ethyl ether (100 ml.) by extraction with saturated sodium bisulfite solution (3 x 75 ml., 5 minutes with each portion); the ether layer was then dried over anhydrous sodium sulfate. After filtering the sodium sulfate and removing the solvents on a steam bath, distillation gave: 4-nitroheptane (10.39 g.» 0.0715 mole, 20 65 per cent conversion, 74.1 per yield) n q 1.4223-1.4234, 103 20 dgQ 0.9249; MRq (calcd.) 40.27, MR^ (found) 39.99. Redistil lation gave analytically pure material, b.p. 70-71° (9 mm.), n2o 1.4224-1.4236; d§g 0.9269; lit.29 b.p. 90° (25 mm.) n2p 1.4200, d2l 0.919. The infrared spectrum of the 4-nitroheptane (sandwich cell) contained bands for the mononitro group (6.4 and 7.2 microns)but no bands for any other functional group. In frared spectra of the high boiling product (b; collected in 4 fractions) showed the presence of a mononitro group (6.4 microns), a nitro group attached to a carbon atom of a carbon-carbon double bond (6.5 microns), a carbonyl group (5.7 microns) and possibly an amino group (3.0 and 6.2 microns). Procedure 2. The experiment was conducted as previ ously except the nitroolefin was added in 3.5 hours at 0° and then the mixture was stirred at 0° for 2 hours. Distillation gave: (a) crude 4-nitroheptane (6.57 g., 0.0452 mole, 44.7 per cent conversion) as a colorless liquid, b.p. 63.3-71° (3.1-3.3 mm.), n2§ 1.4250-1.4273; (b) an unidentified liquid (2.3 g.), b.p. 71-75° (4.1- 20 5,2 mm.), n D 1.4419-1.4473; and (c) an unidentified liquid (l.Og.), b.p. 60-64° (0.2-0.3 nm.), n2g 1.4492-1.4507. The infrared spectrum of the 4-nitroheptane (sandwich cell) contained strong bands for the mononitro group (6.4 104 7.2 microns) but no bands for any other functional group. An infrared spectrum of product (b) contained a very weak band for a mononitro group (6.4 microns) and a medium strong band for a hydroxyl group. An infrared spectrum of product (c) contained a band for an amino group (3.1 and 6.2 microns), but no band for a mononitro group (6.4 microns). On the basis of infrared results it is suggested that products b and c were formed by further reduction of the nitro group. f. Reduction of 3, 3, 3-Trichloro-l-nitropropene With Lithium Borohydride; 1,1,1-Trichloro-3-nitropropane. Procedure 1. A solution of 3,3>3-trichloro-l-nitro- propene (30.4 g., 0.16 mole) in ethyl ether (50 ml.) was added dropwise in 3.5 hours to a stirred suspension of lithium borohydride (1.74 g.» 0.0& mole) in ethyl ether (250 ml.) and tetrahydrofuran (50 ml.). During addition the reaction mixture was kept at -70° - 2°; after addition was completed, the mixture was stirred for 3.5 hours at -70°. The mixture was then acidified below 0° in one hour with urea-acetic acid solution (150 ml., aqueous solution 2.7# molal in urea and acetic acid). The mixture was saturated with sodium chloride; the aqueous layer was extracted with ethyl ether ( 2 x 100 ml.). The combined ether extract was washed with saturated sodium bicarbonate and dried with sodium sulfate. After separation of the I sodium sulfate by filtration and removal of the solvents, distillation gave: 1,1,l-trichloro-3-nitropropane (26.09 g., 0,136 mole, #5 per cent conversion) as a colorless liquid, b.p. 66.7-66.3° (2.1-2.3 mm.), n2g 1.4905-1.4910. The infrared spectrum of the 3>3>3-trichloro-l-nitro- propane (sandwich cell) contained strong bands for a mono nitro group (6.35 and 7.25 microns), a trichloromethyl group (12.5 microns) and a carbon-chlorine bond (14.4 mi crons) but no bands for any other functional group. Procedure 2. The experiment was conducted as previ ously except one-half of all materials was used, and the 3i3»3-trichloro-l-nitropropene was added in 3.5 hours at -40° and then stirred for 2 hours at -40°. Distillation gave: 1,1,l-trichloro-3-nitropropane (7.3$ g.> 0.0336 mole, 43.3 per cent conversion) as a colorless liquid, b.p. 67- 63° (2,3 mm.), n2§ 1.4914-1.4939. Redistillation gave a 0n very pure product, b.p. 67-67.7° (2.3 mm.), n p 1.4905, dfo 1.5375; MRp (calcd.) 36.13, MRD (found) 36.22. g. Reduction of 4,4,5.5.6,6,6-Heptafluoro-2-nitro- 2-hexene With LitHTum Borohydride; X, 1, 1 , 2,2,3,3-Hepta- riuoro-5-nitroKexane. A solution of 4,4,5,5,6,6,6-heptafluoro-2-nitro-2- hexene (7.50 g., 0.0294 mole) in ethyl ether (25 ml.) was added dropwise in 4 hours to a stirred suspension of lithium borohydride (0.33 g., 0.015 mole) in ethyl ether 106 (75 ml.) and tetrahydrofuran (25 ml.). During addition the reaction mixture was kept at -65° - 2°; after addition was completed the mixture was stirred for 4 hours at -65 to -70°. The mixture was then acidified in 30 minutes below 0° with urea-acetic acid solution (35 ml., aqueous solution, 2.7$ molal in urea and acetic acid). The mixture was saturated with sodium chloride; the aqueous layer was separated and extracted with ethyl ether (100 ml.). The combined ether extract was washed with saturated sodium bicarbonate solution (2 x 100 ml.) and dried over anhydrous sodium sulfate. After f fremovin'g : the sodium sulfate by filtration and removing the solvents, distillation gave: l,l,l,2,2,3,3-heptafluoro-5-nitrohexane (6.64 g., 0.025$ mole, $7 .$ per cent conversion) as a colorless liquid, b.p. 76.5-77.5° (38 nun.), n2§ 1.3405-1.3410, d§g 1 .4861; lit.60 b.p. 64° (23 mm.), n2§ 1.3412. The infrared spectrum of the 1,1,1 ,2,2,3,3-heptafluoro-5-nitrohexane contained a strong band for a mononitro group (6.35 and 7.2 microns) and for carbon-fluorine bonds ($.2 microns) but no bands for any other functional group. h. Reduction of 5.5.6,6.7.7.7-Heptafluoro-3-nitro-^^3- heptene With Lithium Borohydride; 171,I.2 , 3 , 3-Hepta?luoro- 5-nitroheptane; 5 , 5, 6.6.7.7.^-HeptafXuoro-3-heptanone 2 , 4 ^ Dinitrophenylhydrazone. A solution of 5j5j6 ,6,7,7>7-heptafluoro-3-nitro-3- heptene (15.34 g., 0.057 mole) in ethyl ether (25 ml.) was 107 added dropwise in 4 hours to a stirred suspension of lithium borohydride (0.62 g., 0,0285 mole) in ethyl ether (125 ml.) and tetrahydrofuran (50 ml.). During addition the reaction mixture was kept at -60° - 2°; after addition was completed the mixture was stirred for 4 hours at -60°. The mixture was acidified in 45 minutes below 0° with urea-acetic acid solution (75 ml., an aqueous solution, 2.7& molal in urea and acetic acid). The mixture was saturated with sodium chloride; the aqueous layer was separated and extracted with ethyl ether (100 ml.). The combined ether extract was wash ed with saturated sodium bicarbonate solution (2 x 150 ml.) and dried over anhydrous sodium sulfate. After removing the sodium sulfate by filtration and volatilizing the solvents, distillation gave: 1,1.1.2,2,3.3-heptafluoro-5- nitroheptane (14.08 g., 0.052 mole, 91 per cent conversion) as a colorless liquid, b.p. 79-79.3° (24.5-25 mm.), n2§ 1.3494. The infrared spectrum of the 1,1,1,2,2,3,3-hepta- fluoro-5-nitroheptane (sandwich cell) contained strong bands for the mononitro group (6.35 and 7.2 microns) and carbon- fluorine bonds (8.0-8,5 microns) but no bands for any other functional group. A solution of l,l,l,2,2,3,3-heptafluoro-5-nitro- heptane (1 g., 0.00369 mole) in methanol (10 ipl.) was added to a solution of sodium hydroxide (0,4 g., 0.01 mole) in it 103 water (10 ml.) and kept at 0° for 13 hours. This solution was added dropwise at 0° to concentrated sulfuric acid (2.5 ml.) in water (12 ml.); a solution of 2,4-dinitro- phenylhydrazine was then added. An oil separated which was crystallized from hot ethanol; four recrystallizations gave 5.5.6.6.7,7.7-heptafluoro-3-heptanone 2,4-dinitrophenylhydra- zone (0.33 g.» 0.00216 mole, 5&. 5 per cent conversion) as orange needles, m.p. 123-124°. The melting point was not depressed when mixed with a sample prepared in a previous experiment (see page 33 ). Reduction of Omega-nitrostyrene With Lithium Borohydride';' T-Ni'tro^-phenylethane. A solution of omega-nitrostyrene (14.9 g.» 0.1 mole) in ethyl ether (75 ml.) and tetrahydrofuran (25 ml.) was added dropwise in 3 hours to a stirred suspension of lithium borohydride (1.1 g., 0.05 mole) in ethyl ether (125 ml.) and tetrahydrofuran (50 ml.). During addition the reaction mixture was kept at -70 to -72°; after addition was com pleted the mixture was warmed to -15°; suddenly the temp erature rose to +13° and the mixture turned from an opaque yellow to a white color. The mixture was then cooled to 0° and acidified in 55 minutes at 0° with urea-acetic acid solution (90 ml.). The mixture was saturated with sodium chloride; the aqueous layer was separated and extracted with ethyl ether (100 ml.). The combined ether extract was o 109 washed with saturated sodium bicarbonate solution (2 x 200 ml.) and dried over anhydrous sodium sulfate. After re moval of the sodium sulfate by filtration and concentration of the filtrate, distillation gave: (a) 1-nitro-2-phenyl- ethane (S.36 g., 0.0553 mole, 55.3 per cent conversion) as a colorless liquid, b.p. 30-35.5° (0.3-1.2 mm.), n2§ 1,5291-1.5296; two redistillations of this fraction gave very pure l-nitro-2-phenylethane in slightly lower yield, b.p. 73-74.5° (0.5 mm.), n2° 1.5275, d|g 1.1314; MRD (calcd.) 41.37, MRd (found) 41.52; lit.91 125-135° (14 mm.); lit.^ n^p 1.5276, and (b) a yellow residue (5.7 g.). The l-nitro-2-phenylethane was analyzed. Anal. Calcd. for CgH9N02 : C, 63.56; H, 6.00; N, 9.27. Found: C, 63.49, 63.55; H, 5.94, 6.12; N, 9.39, 9.37. The structure of l-nitro-2-phenylethane was established by its conversion to phenylacetaldehyde via the Nef re action^ followed by preparation of phenylacetaldehyde 2,4- dinitrophenylhydrazone in 55 per cent overall conversion, m.p. 123.5-124.5°; lit.^ 121-121.5°. The melting point of the derivative was not depressed when mixed with an authentic sample. j. Reduction of 2-(2-Nitrovinyl)furan With Lithium Borohydride; 2-(NitroetfiylTfuran. Procedure 1. A solution of 2-{2-nitrovinyl)furan (15.3 g.> 0.11 mole) in ethyl ether (75 ml.) and tetra hydrofuran (25 ml.) was added dropwise in 5 hours to a stirred suspension of lithium borohydride (1.20 g., 0.055 mole) in ethyl ether (125 ml.) and tetrahydrofuran (25 ml.). During addition the reaction mixture was kept at -60 to . 0 Q '65 . The mixture was wanned to 0 ; a slightly exothermic reaction rasied the temperature of the mixt to +5° thus indicating incomplete reaction at -60°. The mixture was stirred for 30 minutes at -2°. The mixture was then acidi fied in 45 minutes at 0° with urea-acetic acid solution. The mixture was saturated with sodium chloride; the aqueous layer was separated and extracted with ethyl ether (100 ml.). The combined ether extract was washed with saturated sodium bicarbonate solution (2 x 150 ml.) and dried over anhydrous sodium sulfate. After removal of the sodium sulfate by filtration and separation of the solvents, distillation gave: (a) 2-(2-nitrovinyl)furan and 2-(2-nitroethyl)furan as a mixture (5.74 g.), b.p. 60-62.2° (1 mm.), n2§ 1.4944- 1.5231; and (b) a brown residue (3.3 g.). Fraction (a) in ethyl ether (50 ml.) was washed with saturated sodium bisulfite solution (3 x 75 ml., 5 minutes with each portion) and dried over anhydrous sodium sulfate. After removing the sodium sulfate by filtration and sepa rating the solvent on a steam bath, distillation gave 2-(2-nitroethyl)furan (4.^7 g.» 0.0345 mole, 31.4 per cent conversion) as a colorless liquid, b.p, 65.5-67.5° (2 mm.), n2° 1.1^41-1.4S«, dlo 1.2067. The infrared spectrum of the 2-(2-nitroethyl)furan (sandwich cell) contained strong bands for a mononitro group (6.35 and 7.25 microns) and a furan ring (13.5 mi crons) but no bands for any other functional group. Procedure 2. The experiment was conducted as previ ously except 2-(2-nitrovinyl)furan (10.15 g., 0.073 mole) in ethyl ether (50 ml.) and tetrahydrofuran (20 ml.) was added in 6 hours at -40° to lithium borohydride (0.61 g., 0.037 mole) in ether (75 ml.) and tetrahydrofuran (15 ml.); the mixture was then stirred for 1 hour;. Distillation gave: (a) 2-(2-nitrovinyl)furan and 2-(2-nitroethyl)furan as a mixture (3.66 g.), b.p. 72-76.3° (2.3 mm.), n2Jj 1.5019- 1.5279; (b) a residue (3.66 g.). The starting material comprised over 50 per cent of fraction (a). Procedure 2* The experiment was conducted as in procedure (2) except the nitroolefin was added in 5 hours at 0° and the mixture was stirred for 4.5 hours at 0°. Distillation gave: (k) 2-(2-nitrovinyl)furan and 2-(2- nitroethyl)furan as a mixture (2.20 g.) b.p. ca. 70-75° 20 (2.3 mm.), n d 1.4915-1.5300; and (b) a residue (6.5 g.). 112 Fraction (a) contained over 50 per cent starting material. k. Reduction of D-arabo Tetraacetoxy-l-nitrohexene With Lithium Borohydride; 1-Nitro-l,2-dideoxy-D-arabo-hexitol fetraacetate. A solution of D-arabo-tetraacetoxy-l-nitro-l-hexene (1.31 g., 0.005 mole) in ethyl ether (10 ml.) and tetra hydrofuran (4 ml.) was added dropwise in 70 minutes to a stirred suspension of lithium borohydride (0,11 g., 0.005 mole) in ethyl ether(15 ml.) and tetrahydrofuran (5 ml.). During addition the mixture was kept at 0°; after addition was completed the mixture was stirred for 2 hours at 0°. The mixture was then acidified below 0° in 15 minutes with urea- acetic acid solution (10 ml.). The mixture was saturated with sodium chloride; the aqueous layer was separated and extracted with saturated sodium bicarbonate solution ( 2 x 25 ml.), then dried over anhydrous sodium sulfate. After re moval of the sodium sulfate by filtration and distillation of-the solvent on a steam bath, ethyl ether (5 ml.) was added and the solution was cooled; crude 1-nitro-l,2-dideoxy- D-arabo-hexitol tetraacetate (1.37 g.) separated, m.p. 63- 73°. One recrystallization from ethyl ether did not raise the melting point,^ The crude material was heated on a steam bath with - Lithium borohydride is known to reduce esters to alcohols, from this fact and the experimental results it is suggested that possibly one or more of the acetyl groups were reduced completely to the alcohol during reduction of the conjugated nitroolefin. 113 acetic anhydride (15 ml.) and conc. sulfuric acid (1 drop) for one hour. The acetic anhydride and acetic acid were removed at reduced pressures; ethyl ether (5 ml.) was added and the mixture was cooled. A yellow solid (1.08 g.) separated, m.p. 86-91°. Two recrystallizations from ethyl ether gave pure 1-nitro-l,2-dideoxy-D-arabo-hexitol tetra acetate (0.9$6 g., 0.00271 mole, 54.2 per cent conversion) as a white solid, m.p. 90-92; lit.^ m.p. 91-92°. !• Reaction of Lithium Borohydride With 2-Nitro-l- butyl Acetate. A solution of 2-nitro-l-butyl acetate (16.1 g., 0,1 mole) in ethyl ether (25 ml.) was added dropwise in one hour to a stirred suspension of lithium borohydride (1.20 g., 0.05 mole plus. 10 per cent excess) in ethyl ether (125 ml.) and tetrahydrofuran (50 ml.). During addition the reaction mixture was kept at 4-5°; after addition was complete the mixture was stirred for 18 hours at 3-4°. The reaction mix ture was acidified in one hour at 0° with urea-acetic acid solution (40 g.), and saturated with sodium chloride; the aqueous layer was separated and extracted with ether (100 ml.). The combined ether extract was washed with saturated sodium bicarbonate solution (2 x 150 ml.), saturated sodium chloride solution (200 ml.) and then dried over anhydrous sodium sulfate. Distillation of the product, after removal of solvent, gave the following fractions which are mixtures of 2-nitro-l-butanol and 2-nitro1-1-butyl acetate. 114 20 Fraction Boiling Range Pressure Weight n ^ Per cent 2-Nitro- ______l-butanol+ 1 45-66° 1.3-1.0 nun. 0.10 g. 1.4306 19 2 66-65.5 1.0-0.6 5.19 1.4359 73 3 65.5-65.0 0.8 4.65 1.4370 85 4 65 0.8 0.53 1.4382 98 An infrared spectrum of Fraction 2 (sandwich cell) contained strong bands for a mononitro group (6.4 and 7.2 microns), a carbonyl group (5.7 microns) and a hydroxyl group (2.9 microns). 3. SELECTIVE REDUCTION OF CONJUGATED NITROOLEFINS WITH LITHIUlTliljUllNUM HYDRIDE. a. Reduction of 2-Nitro-2-butene With Lithium Aluminum Hydride; 2-Iitrobutane. A solution of 2-nitro-2-butene (15.2 g., 0.15 mole) in ethyl ether (50 ml.) was added dropwise in 2.5 hours to a solution of lithium aluminum hydride (2.&5 g., 0.075 mole) in ethyl ether (250 ml.). (Note: When less than this amount of solvent is used the reaction is too vigorous and thus hard to control). During addition the mixture was kept at -65°; after addition was completed the mixture was stirred for 3.5 hours at -65°. The mixture was then acidified in 1 hour below 0° with urea-acetic acid solution (125 ml.). The mixture was saturated with sodium chloride; the aqueous layer was separated and extracted with ethyl ether (100 ml.). "^Analysis by refractive index. 0 115 The combined ether extract was washed with saturated sodium bicarbonate solution (2 x 150 ml.) and dried over anhydrous sodium sulfate. After filtering the sodium sulfate and removing the solvent, distillation gave: 2-nitro -butane (3.IS g., 0.0793 mole, 52.9 per cent conversion) as a o 20 colorless liquid, b.p. 70-71.5 (75.7# mm.h n d 1.4040- 1.4075, dj?8 O.9669. Redistillation gives very pure 2-nitro- butane, b.p. 13*.5° (756.4 mm.) (capillary tube method), n2g 1.4044, d?8 0.9676; lit.3 b.p. 140°, nD 1.4036, d2° 0.96*; lit.S3 b.p. 133-139° (747 ran.), Sp. Or. 0.9*77; lit.61 b.p. 139.6 (760 mm.); lit.^7 n2§ 1.4042. The infrared spectrum of the 2-nitrobutane (sandwich cell) contained strong bands for a mononitro group (6.4 and 7.2 microns) but no bands for any other functional group. b.Reduction of 313.3»-Trichloro-l-nitropropene With Lithium AluminumlTydride; 1.1,l-TrTcEloro-3-nitropropane. A solution of 3,3, 3-trichloro-l-nitropropene (19.0 g., 0,1 mole) in ethyl ether (25 ml.) was added dropwise in 3.5 hours to a suspension of lithium aluminum hydride (1.0 g., 0.025 mole, plus 5 per cent excess) in ethyl ether (125 ml.) and tetrahydrofuran (25 ml.). During addition the reaction mixture was kept at -70°; after addition was . completed the mixture was stirred for 3.5 hours at -70°. The mixture was acidified in 45 minutes below 0° with urea-acetic acid 116 solution (50 ml., 0.27# molal in urea and in acetic acid). The mixture was saturated with sodium chloride; the aqueous layer was separated and extracted with ethyl ether (100 ml.). The combined ether extract was washed with saturated sodium bicarbonate (2 x 150 ml.) and dried over anhydrous sodium sulfate. After removal of the sodium sulfate by filtration and separation of the solvents, distillation gave; 1,1,1- trichloro-3-nitropropane and 3,3,3-trichloro-l-nitropropene as a mixture (13.24 g.), b.p. 61-63° (2.3 mm.), n ^ 1,4929- 1.5034* The above mixture in ethyl ether (150 ml.) was washed with saturated sodium bisulfite solution (3 x 150 ml., 5 minutes with each portion) and dried over anhydrous sodium sulfate. After removal of the sodium sulfate by filtration and elimination of the solvents, distillation gave 1,1»1- trichloro-3-nitropropane (3.43 g.» 0.043& mole, 43.# per cent conversion) as a colorless liquid, b.p. 65-66,5° (2.2 mm.), n2g 1.4911-1.4923, d|8 1.5375; MRp (calcd.) 36.13; MRD (found) 36.28. c. Reduction of 3.3.3-Trifluoro-l-nitropropene With Lithium Aluminum hydride; l,l.l-Trifluoro-3-nitropropane; r, 3-Dinitro-^,4-ditrifluoromethylbutane7~ A solution of 3,3,3-trifluoro-l-nitropropene (14.11 g.» 0.1 mole) in ethyl ether (50 ml.) was added dropwise in 2 hours to a solution of lithium aluminum hydride (1.90 g., 0.05 mole) in ethyl ether (125 ml.). During addition the 117 mixture was kept at -40 to -45°; after addition was completed the mixture was stirred for 3 hours at -40 to -45°. The mixture was then acidified below 0° in 45 minutes with urea-acetic acid solution (72 ml.). The mixture was saturated with sodium chloride; the aqueous layer was separated and extracted with ethyl ether (100 ml.). The combined ether extract was washed with saturated sodium chloride solution (2 x 150 ml.) and dried over anhydrous sodium sulfate. After filtering the sodium sulfate and removing the solvents, distillation gave: (a) 1,1,1-tri- fluoro-3-nitropropane and acetic acid as a mixture (6.60 g.), b.p. 60-82° (147-150 mm.), n2g 1.3539-1.3607; (b) 1,3-dintro- 2,4-ditrifluoromethyl butane (3.49 g o 0.0123 mole, 24.6 per cent conversion) as a yellow liquid, b.p. 73.5-79.5° (0.9 mm.), n2g 1.3397-1.3903. The mixture (a) in ethyl ether (25 ml.) was washed with water (2 x 25 ml.) and dried over anhydrous sodium sulfate. Removal of the sodium sulfate and solvents followed by distillation gave: 1,1,l-trifluoro-3-nitropropane (3.53 g., 0.0248 mole, 24.3 per cent conversion) as a color less liquid, b.p. 132° (750.6 mm., capillary tube method), n2g 1.3549-1.3555, d|o 1.4203; lit.92 b.p. 134-134.3° (743 mm.), n2g 1.3553, d2g 1.4220; lit.93 b.p. 135.5°, n2D 1.3525, d2g 1.4259. 116 The infrared spectrum of the l,l,l-trifluoro-3- nitropropane exhibited bands for a mononitro group (6,4 and 7.2 microns) and carbon-fluorine bands (6.6 microns). The infrared spectrum of the l,3-dinitro-2,4-ditrifluoromethyl- butane (sandwich cell) showed absorption for a mononitro group (6.35 and 7.25 microns) and carbon-fluorine bands (6.6 microns). Two redistillations of product (b) gives very pure l,3-dinitro-2,4-ditrifluoromethylbutane, in slightly lower yield, as a colorless liquid, b.p. 76.6-77° (0,9 mm.), n2g 1.3910, d2° 1.6161. Anal. Calcd. for C6H604F6: C, 25.36; H, 2.13; N, 9.66. Found: C, 25.62, 25.66; H, 2.39, 2.43; N, 9.SO, 9.73. d. Reduction of 5. 5.6,6.7.7.ft-Heptafluoro-3-nitro- 3-heptene With Lithium Aluminum Hydride; 1,1,1,2,2,3,3- fT e pta f l’uor o 5 -nit ro h e pt an e. A solution of 5,5,6,6,7,7,7“heptafluoro-3-nitro-3- heptene (15.34 g., 0.057 mole) in ethyl ether (25 ml.) was added dropwise in 3 hours to a stirred suspension of lithium aluminum hydride (0.65 g., 0.01625 mole + 20 per cent excess).in ethyl ether (125 ml.) and tetrahydrofuran (25 ml.). During addition the mixture was kept at -65 to o -70 ; after addition was completed the mixture was stirred c J 119 o at -60 to -70 for 3.5 hours. The mixture was then acidi fied in 35 minutes below 0° with urea-acetic acid solution (35 ml., aqueous solution, 2.73 molal in urea and in acetic acid). The mixture was saturated with sodium chloride; the aqueous layer was separated and extracted with ethyl ether (100 ml.). The combined ether extract was washed with saturated sodium bicarbonate solution (2 x 150 ml.) and dried over anhydrous sodium sulfate. Filtration, removal of solvents, and distillation gave: 1,1,1,2,2,3.3-hepta- fluoro-5-nitroheptane (13.7 g.> 0.Q4&6 mole, 35.3 per cent conversion) as a colorless liquid, b.p. 7&.5-7#.7° (23 mm.), n2g 1.3490-1.3497, d20 1.4277; lit.60 b.p. 60° (9mm.), n2g 1.3493. The infrared spectrum of 1,1,1,2,2,3,3-heptafluoro- 5-nitroheptane (sandwich cell) contained strong bands for the mononitro group (6.35 and 7.2 microns) and carbon- fluorine bonds (3.0-3.6 microns) but no bands for any other functional group. e» Reduction of Omega-nitrostyrene With Lithium Aluminum Hydride; l-Nitro-2-phehylethane7 1,3-Dinitro- 2V4-dipfieriyibutane. ~ Normal Addition: A solution of omega-nitrostyrene (14,9 g., 0.1 mole) in ethyl ether (125 ml.) and tetra hydrofuran (25 ml.) was added dropwise in 2.2 hours to a stirred mixture of lithium aluminum hydride (1.90 g., 4 ’ 120 0.05 mole) in ethyl ether (100 ml.). During addition the mixture was kept at -40 to -45°; after addition was com pleted the mixture was stirred at -40° for 3 hours. The mixture was then acidified below 0° in 45 minutes with urea-acetic acid solution (SO ml.). The mixture was satu rated with sodium chloride; the aqueous layer was separated and extracted with ethyl ether (100 ml.). The combined ether extract was washed with saturated sodium bicarbonate solution (2 x 150 ml.) and dried over anhydrous sodium sulfate. After removal of the sodium sulfate by filtration and separation of the solvents on a steam bath, distillation gave: (a) l-nitro-2-phenylethane (7.53 g.» 0.049# mole, 49.# per cent conversion) as a colorless liquid, b.p. #2- #3.5° (O.S mm.), n2§ 1.5310-1.5350; and (b) a residue (6.9 g.)» Redistillation of product (a) gave very pure l-nitro-2-phenylethane, b.p. $3° (0.9 mm.), n^§ 1 .530#, d|g 1.1234; lit.89 b.p. 12#-135° (14 mm.); lit.90 b.p. 249- 251° (763 mm.); lit.91 125-135°(14 mm.); lit.67 n2g 1.5276. Residue (b) was dissolved in hot ethanol. On cooling, crude 1,3-dinitro-2,4-diphenylbutane (0.9 g., 0.0030 mole, 6.0 per cent conversion) separated, m.p, 112-115°. Two recrystallizations from hot ethanol gave the product as white plates, m.p, 120-121°. The melting point is not depressed when mixed with a sample of 1,3-dinitro-2,4- diphenylbutane obtained in previous reductions. o 121 The infrared spectrum of the l-nitro-2-phenylethane (sandwich cell) contained bands for a mononitro group (6.4 and 7.2 microns) and a mono-substituted benzene ring (13,3 and 14.3 microns) but no bands for any other func tional group. inverse Addition: The experiment was conducted as before except the lithium aluminum hydride solution was added to the omega-nitro^styrene solution. Distillation gave: (a) l-nitro-Z-phenylethane (7.15 g., 0.0473 mole, 47.3 per cent conversion) as a colorless liquid, b.p. 79.5- 30° (0.7 mm.), n2£ 1.5303-1.5325; and (b) a residue (6.0 g.). Redistillation of product (a) gave very pure l-nitro-2- phenylethane, b.p. 33° (0.9 ran.), ri2§ 1 .530#, d2§ 1.1234. Crude 1,3-dinitro-2,4-diphenylbutane (0.25 g.j 0,000#3 mole, 1.7 per cent conversion) was isolated from the residue, m.p. 114-115°. Recrystallization gave the product as white plates, m.p. 120-121°. The infrared spectrum of the l-nitro-2-phenylethane (sandwich cell) contained bands for a mononitro group (6.4 and 7.2 microns) and a mono-substituted benzene ring (13.3 and 14.3 microns) but no bands for any other func tional group. 122 f . Reduction of 2-Nitro-l-phenylpropene With Lithium Aluminum Hydride; 2-Nitro-1-phenylpropane. Normal Addition: A solution of 2-nitro-l-phenylpropene (16.32 g., 0.1 mole) in ethyl ether (150 ml.) and tetrahydro- furan (20 ml.) was added dropwise in 2 hours to a stirred solution of lithium aluminum hydride (1.14 g., 0.025 mole + 20 per cent excess) in ethyl ether (100 ml.) and tetra- hydrofuran (20 ml.). During addition the mixture was kept at -40 to -45°; after addition was completed the mixture o was stirred for 3 hours at -40 to -50 . The mixture was then acidified in 45 minutes at 0° with urea-acetic acid solution (50 ml.). The mixture was saturated with sodium chloride; the aqueous layer was separated and extracted with ethyl ether (100 ml.). The combined ether extract was washed with saturated sodium bicarbonate solution (2 x 150 ml.) and dried over anhydrous sodium sulfate. After removal of the sodium sulfate by filtration and separation of the solvents, distillation gave: 2-nitro-l-phenylpropane and 2-nitro-l-phenylpropene as a mixture (10.77 g), b.p. 81.5- 89° (0.8 mm.), n2§ 1.5200-1.5405; crystals of 2-nitro-l- phenylpropene separated from the last fraction. The re action product in ethyl ether (100 ml.) was washed with saturated sodium bisulfite solution (3 x 100 ml., 5 minutes with each portion) and dried over anhydrous sodium sulfate. After removal of the sodium sulfate and solvents, distilla tion gave: (a) 2-nitro-l-phenylpropane (7.17 g.> 0.0434 mole, 123 43.4 per cent conversion), as a light yellow liquid, b.p. 79-33° (0.7 nun.), n2§ 1.5200-1,5250; and (b) 2-nitro-l- phenylpropane and 2-nitro-l-phenylpropene as a mixture (1.62 g.), b.p. 33-35° (0.7 mm.). Product (a) was washed again with sodium bisulfite; distillation gave pure 2-nitro-1-phenylpropane, b.p. 81.5- 32° (0.3 mm.), n2g 1.5214, d|g 1.0916. The infrared spectrum of the 2-nitro-1-phenylpropane (sandwich cell) contained bands for a mononitro group (6.4 and 7.2 microns) and a mono-substituted benzene ring (13.3 and 14.3 microns) but no bands for any other functional group. Inverse Addition: The experiment was conducted as before except the lithium aluminum hydride solution was added to the 2-nitro-l-phenylpropene solution in 2 hours. Distillation gave: 2-nitro-l-phenylpropane and 2-nitro- l-phenylpropene as a mixture (13.43 g.), b.p. 83-91.5° (0.8-1.0 mm.). The above mixture in ethyl ether (100 ml.) was washed with saturated sodium bisulfite solution ( 3 x 100 ml., 5 minutes with each portion) and dried over anhy drous sodium sulfate. After removal of the solvents and sodium sulfate, distillation gave: (a) 2-nitro-1-pheny-1- propane (5.12 g., 0,031 mole, 31.0 per cent conversion), or\ as a light yellow liquid, b.p. 81.5-84° (0.8 mm.), n ^ 124 1.5196-1.5244; and (b) 2-nitro-l-phenylpropane and 2-nitro- l-phenylpropene as a mixture (2.02 g.), b.p. #4-36° (O.&mm.), n2g 1,5305-1.5454. Product (a) was washed again with sodium bisulfite; distillation gave pure l-phenyl-2-nitro pro pane in slightly lower yield, b.p, Si.5-&20 (O.SS ran.), n ^ 1.5214, d|g 1 .0916. The infrared spectrum of the 2-nitro-l-phenylpropane (sandwich cell) illustrated bands for a mononitro group (6.4 and 7.2 microns) and a mono-substituted benzene ring (13.3 and 14.3 microns) but no bands for any other func tional group. g. Reduction of 2-(2-Nitro vinyl)furan With Lithium Aluminum Hydride; 2-T?-Nitro ethyl)furan. A solution of 2-(2-nitrovinyl)furan (15.3 g., 0.11 mole) in ethyl ether (75 ml.) and tetrahydrofuran (25 ml.) was added dropwise in 3 hours to a solution of lithium aluminum hydride (2.1 g., 0.055 mole) in ethyl ether (125 ml.) and tet rahydrofuran (50 ml.). During addition the mixture was kept at -55 * 2°; after addition was completed the mixture was stirred at -55 to -65° for 3.5 hours. The mixture was acidified in 1 hour below 0° with urea-acetic acid solution (100 ml.). The mixture was saturated with sodium chloride; the aqueous layer was separated and extracted with ethyl ether (100 ml.). The combined ether extract was washed with saturated sodium bicarbonate solution (2 x 200 ml.), and dried over anhydrous sodium sulfate. After remov ing the sodium sulfate and the solvents, distillation gave: (a) 2-(2-nitroethyl)furan and 2-(2-nitrovinyl)furan as a mixture (4.78 g.), b.p. 63-74 (2.5-2.9 mm.), n2§ 1 .4908- 1.4996; and (b) a black residue (8.2 g.). Product (a) in ethyl ether (50 ml.) was washed with saturated sodium bisulfite solution (3 x 50 ml.j 5 minutes with each portion) and dried over anhydrous sodium sulfate. After removing the sodium sulfate and the solvent, distil lation gave: 2-(2-nitroethyl)furan (2.50 g., 0.0177 mole, 16,1 per cent conversion) as a colorless liquid, b.p. 65- 66° (2 mm.), n2§ 1.4837-1.4839, d§8 1.2061. The infrared spectrum of the 2-(2-nitroethyl)furan (sandwich cell) contained strong bands for a mononitro group (6.35 and 7.2 microns) and a furan ring (13.5 microns) but no bands for any other functional group. 4. SELECTIVE REDUCTION OF CONJUGATED NITRQQLEFINS WITH SODIUM BOROHYDRIDE. a» Reduction of 2-Nitro-2-butene With Sodium Boro- hydride; 2-Nitrob~utaneT A solution of 2-nitro-2-butene (15.2 g., 0.15 mole) in absolute ethanol (150 ml.) was added dropwise in 3 hours v 126 to a mixture of sodium borohydride (2.#4 g., 0.075 mole) in absolute ethanol (50 ml.). Note: if the concentrations of the reactants are higher, liberation of hydrogen is catalyzed and the hydride decomposes in a few seconds; there was slow liberation of hydrogen through this experiment. During addition the mixture was kept at 0°; after addition was completed the mixture was stirred for 4 hours at 0°. The mixture was then acidified in 1 hour below 0° with urea- acetic acid solution (125 ml,). The alcohol was distilled from the reaction mixture using a modified Claisen flask with a Vigreux neck. The residue was diluted with ethyl ether (50 ml.); two layers separated. The mixture was saturated with sodium chloride; the aqueous layer was sepa rated and extracted with ethyl ether (25 ml.). The combined ether extract was washed with saturated sodium bicarbonate solution (2 x 35 ml.) and dried over anhydrous sodium sulfate. After removal of the sodium sulfate and the sol vent, distillation gave an amber residue, ca. 2 g. The ethanol that was distilled from the reaction mixture gave a positive (blue) pseudonitrole test. The pseudonitrole test (blub) is characteristic of secondary nitro compounds upon treatment with alkali, sodium nitrite and subsequent acidification. Rectification of the ethanol in a 40 cm. column © packed with glass helices did not separate the 2-nitrobutane from the ethanol. An aliquot (15 ml.) of the ethanol mix ture.. (235 ml.) was added dropwise to sodium hydroxide (0.4 g.) in water (10 ml.) at 0-5°. This solution was added dropwise to conc. sulfuric acid (2.5 ml.) in water (12 mL) at 0-5°; upon adding 2,4-dinitrophenylhydrazine solution a derivative was precipitated. The methyl ethyl ketone 2,4- dinitrophenylhydrazone was recrystallized once from ethanol to give bright orange needles (0.46 g.), m.p. 113-114°. A control was run using 2-nitrobutane (1 g.)j 0.92 g. of derivative was isolated, the quantity of 2-nitrobutane in the ethanol distillate is thus estimated as 9.5 g. (0.0952 mole, 63.5 per cent conversion.) b. Reduction of 4-Nitro-3-heptene With Sodium Borohydride; 4-Nitro5eptane. A solution of 4-nitro-3-heptene (6.01 g., 0.042 mole) in absolute ethanol (75 ml.) was added dropwise in 2 hours to a stirred solution of sodium borohydride (O.BO g., 0.02i mole) in absolute ethanol (50 ml.). During addition the mixture was kept at 0°; after addition was completed the mixture was stirred for 7 hours at 0°. The mixture was then acidified in 30 minutes below 0° with urea-acetic acid solution (40 ml.). The ethanol was dis tilled from the reaction mixture using a modified Claisen head having a Vigreux neck. Ethyl ether (60 ml.) was added 128 to the residue and two layers separated, The mixture was saturated with sodium chloride; the aqueous layer was separated and extracted with ethyl ether (50 ml.). The combined ether extract was washed with saturated sodium bicarbonate solution (2 x 50 ml.) and dried over anhydrous sodium sulfate. After removing the sodium sulfate and the solvent, distillation gave: (a) crude 4-nitroheptane (1.84 g.) as a light yellow liquid, b.p. 65-70° (9 mm.), n2§ 1.4255-1.4350; and (b) a distillation residue (2.6 g.). Product (a) in ethyl ether (25 ml.) was washed with saturated sodium bisulfite solution (3 x 15 ml., 5 minutes with each portion) and dried over anhydrous sodium sulfate. After removing the sodium sulfate and the solvent, distil lation gave: pure 4-nitroheptane (1.32 g., 0.0091 mole, 21.7 per cent conversion) as a colorless liquid, b.p. 69- 70° (8.5 mm.), n2p 1.4223-1.4227, d|§ 0.9258; lit.29 b.p. 90° (25 mm.), n25 1.4200, d2£ 0.919. The infrared spectrum of the 4-nitroheptane (sand wich cell) contained bands for the mononitro group (6.4 and 7.2 microns) but no bands for any other functional group. c. Reduction of Qmega-nitrostyrene With Sodium Borohydride; l-Mitro^S-phenylethane; l,3T-Dinitro-214 diphenylbutane. ~ Procedure 1. A solution of omega-nitrostyrene (14.9 g., 0.1 mole) in absolute ethanol (150 ml.) was 129 added dropwise in 5 hours to a stirred mixture of sodium borohydride (1.9 g.> 0.05 mole) in absolute ethanol (50 ml.). During addition the mixture kept at 0°; after addition was completed the mixture was stirred at 0° for 1 hour. The o mixture was then acidified below 0 in 45 minutes with urea-acetic acid solution (75 ml.). The tan solid (A, 5.56 g.) that separated was filtered and washed with ethyl ether (15 ml,). The ethanol was removed on a steam bath at reduced pressure until a pasty-mass remained;this >semi-solid was dissolved in ethyl ether (125 ml.) and water (50 ml.). The mixture was saturated with sodium chloride; the aqueous layer was separated and extracted with ethyl ether (100 ml,). The combined ether extract was washed with saturated sodium bicarbonate solution (2 x 150 ml.) and dried over anhydrous sodium sulfate. After removing the sodium sulfate and the solvent, distillation gave: (a) l-nitro-2-phenylethane (2.1# g., 0.0144 mole, 14.4 per cent conversion) as a colorless liquid, b.p. 76.5-7#.5° (0.7 mm.), n ^ 1.5266- 1.5273j 1.1229; and (b) a distillation residue (4.2g.). Solid (A) was stirred with acetone (50 ml.) and filtered; an.' unidentified, tan solid* (4.37 g.) remained, m.p. 22S-2320. The filtrate was evaporated on a steam bath; crude 1,3-dinitro-2,4-diphenylbutane (1.19 g.) was obtained, m.p. 106-109°. "^See page 132 ; omega-nitro styrene forms this solid in the presence of benzyltrimethylammonium hydroxide. \ Y r o o c © O 130 « o The distillation residue was dissolved in hot ethanol. From this solution crude 1,3-dinitro-2,4-diphenylbutane (2.47 g.) was crystallized, m.p. 113-114°. Both crops 1,3- dinitro-2,4-diphenylbutane (3.66 g., 0.0122 mole, 24.4 per cent conversion) were combined and re crystallized twice from hot ethanol to give pure 1,3-dinitro-2,4-diphenylbutane as white plates, m.p. 120-121°. The melting point was not depressed when mixed with a sample identified in a previous experiment. The infrared spectrum of the 1-nitro-2-phenylethane (sandwich cell) contained strong bands for a mononitro group (6.4 and 7.2 microns) and a mono-substituted benzene ring (13.3 and 14.4 microns) but no bands for any other functional group. Procedure 2. The experiment was conducted as previ ously except the nitroolefin was added in 3.5 hours at -40 ± 2° and then the mixture was stirred for 2,5 hours at -40°. l-Nitro-2-phenylethane (1.67 g., 0.011 mole, 11.0 per.;cent conversion) was obtained as a colorless liquid, b.p. 76-77° (0.6 mm.), n2§ 1,5272-1.5278. 1,3-Dinitro-2,4-diphenyl butane (3.25 g., 0.010$ mole, 21.6 per cent conversion) was obtained as white plates. An unidentified solid (A) 2.92 g., 19.3 per cent conversion) was also isolated, 91.p. 232-235°. o o o 131 d. Reduction of D-arabo-tetraacetoxy-l-nitrohexene; 1-Nitro-1,2-dideoxy-P-arabo-hexitol Tetraacetate. A solution of D-arabo-tetraacetoxy-l-nitro-l-hexene (0.1 g., 0,0028 mole) in absolute ethanol (10 ml.) was added dropwise in 45 minutes to a stirred suspension of sodium borohydride (0.12 g., 0.0014 mole) in absolute ethanol (10 ml.). During addition the mixture was kept at 0°; after addition was completed the mixture was stirred for 2 hours at 0°. The mixture was then acidified below 0° in 10 minutes with urea-acetic acid solution (3 ml., 0.278 molal in acetic acid and in urea). The reaction mixture was reduced to a volume of about 5 ml. on a steam bath and under vacuum. This mixture was dissolved in ethyl ether (40 ml.) and dried over anhydrous sodium sulfate. After removing the sodium sulfate and all but 2-3 ml. of solvent, 1-nitro-1,2-dideoxy-D-arabo-hexitol tetraacetate (0.65 g., 0.00179 mole, 63.9 per* cent conversion) crystal lized as a white solid, m.p. 82-84°. One recrystallization from absolute ether gave only a slightly lower yield of highly pure product, m.p. 91-92°; lit.^ m.p, 91-92°. e. Attempted Heterogeneous Reduction of £,£,6,6,7,7,7- Heptafluoro-3-nitro-'J-heptene With Sodium BorohydricTeT ~ A solution of 5>5»6,6,7,7,7-heptafluoro-3-nitro-3- heptene (6.72 g., 0.023 mole) in ethyl ether (20 ml.) o was added dropwise in 3 hours to a suspension of sodium borohydride (0.47 g., 0.0125 mole) in ethyl ether (65 ml.) and tetrahydrofuran (20 ml.). During addition the reaction mixture was kept at -65°; after addition was completed the mixture was stirred at -65° for 3.5 hours. The mixture was then acidified in 20 minutes below 0° with urea-acetic acid solution (25 ml., aqueous solution, 2.7$ molal in urea and in acetic acid). The mixture was saturated with sodium chloride; the aqueous layer was separated and ex tracted with ethyl ether (50 ml.). The ether extracts were combined and washed with saturated sodium bicarbonate solution (2 x 100 ml.) and dried over anhydrous sodium sulfate. After removing the sodium sulfate and the solvents, distillation gave: 5j5>6,6,7»7,7-heptafluoro-3-nitro-3- heptene (5.3$ S.} $0 per cent recovery), the initial olefin, as a light green liquid, b.p. 77-7$° (79 mm.), n2§ 1.3590- 1.3597. The physical constants of the initial material, 5,5,6,6,7i7,7-heptafluoro-3-nitro-3-heptene, are: b.p. 7$.5-79.5° (75 mm.), n2° 1,3596. 5. REACTION OF QMEGA-NITROSTYRENE IN THE PRESENCE OF BENZYLTRIMETHYLAMMONIUM HYDROXIDE. A solution of omega-nitrostyrene ( 1 g.) in ethyl ether ( 5 ml.) was added dropwise at 25° to a solution of benzyltrimethylammonium hydroxide ($ drops of a 40 per cent solution in methanol) in ethyl ether (5 ml.) and methanol (1 ml.). A yellow solid separated; the solid was filtered \£\ e O 133 and washed with acetone to give a tan solid (0.87 g.» 87 per cent), m.p. 205-210°. An infrared spectrum (mulled in Nujol) exhibited bands for a mononitro group (6,4 and 7.2 microns) and a mono-substituted benzene ring (13.6 and 14.35 microns) but no bands for any other functional group. 6. REACTION OF 2-(2-NITR0VINYL)FURAN IN THE PRESENCE OF BENZYLTRIMETHYLAMMONIUM HYDROXIDE A solution of 2-(2-nitrovinyl)furan (l.g.) in ethyl ether (10 ml.) was added at 25° to a solution of benzyl trimethylammonium hydroxide (4 drops of a 40 per cent solu tion in methanol). A brown solid immediately separated. The solid was filtered and washed with methanol and ethyl ether to give an unidentified brown powder (0.95 g.» 95 per cent), m.p. > 350.° 7. REACTION OF 1-NITR0-2-FHENYLETHANE AND 0MEGA- NITROSTYRENE; 1,3-DINITRQ-2,4-DIPHENYLBUTANE A solution of oraega-nitrostyrene (2.98 g., 0.02 mole) in ethyl ether (20 ml.) was added dropwise in 30 minutes to a solution of 1-nitro-2-phenylethane (3.02 g., 0.02 mole) and Triton B (1 ml.) in ethyl ether (20 ml.) and methanol (5 ml., enough to make the reaction mixture homogeneous). During addition the mixture was kept at 0°; after addition 134 was completed the mixture was stirred at 5° for 1.5 hours. The mixture was acidified with 2 N hydrochloric acid (3 ml.) During reaction a white solid formed; this solid (2.71 g.) was filtered and air dried. The filtrate was saved. The white solid isolated is insoluble in all common organic solvents. Its melting point, ca. 255-260°, is not depressed when it is mixed with a sample of substance A isolated from reduction of omega-nitrostyrene with sodium trimethoxyborohydride. The filtrate that had been saved was reduced to a volume of 3-4 ml. and then dissolved in ethyl ether (50 ml.) The ether solution was washed with saturated sodium bicar bonate solution (50 ml.) and dried over anhydrous sodium sulfate. After removal of the sodium sulfate by filtration and removal of the solvent on a steam bath, distillation gave: (1) l-nitro-2-phenylethane (1.62 g., 0.0107 mole, 53.5 per cent recovery), b.p. #4-#5° (1.2 mm.), n^§ 1.5270; and (2) a residue (1.5 g.). S. REACTION OF 2-NITR0-2-BUTENE AND 2-NITROBUTANE; 3-MSTHYL-3,5-DINITROHEPTANE. 2-Nitrobutane (4.54 g.> 0.044 mole) was added at 15° to potassium hydroxide (2.91 g., 0.044 mole) in ethanol (20 ml.). Then 2-nitro-l-butene (4.45 g.> 0.044 mole) was added dropwise in 35 minutes at 15°. The mixture was then 135 acidified below 0° in 10 minutes with urea-acetic acid solution (20 ml.). The mixture was then continuously extracted for 13 hours with ethyl ether; the ether extract was dried over anhydrous sodium sulfate; after removing the sodium sulfate and the ether, distillation gave 3-methyl-* 3,5-dinitroheptane (2.64 g.» 0.0156 mole, 35.5 per cent conversion) as a colorless liquid, b.p. 30-&5° (1 mm.), n2g 1.4565, d|g 1.1132. A derivative of 3-methyl-3,5-dinitroheptane was prepared by its conversion to 3-methyl-3-nitrb-5-heptanone t via the Nef reaction ^ followed by preparation of 3-methyl- 3-nitro-5-heptanone 2,4-dinitrophenylhydrazone in 52'per cent overall conversion, m.p. 131.5-132.5°. This product is identical with the 3-methyl-3,5-dinitroheptane isolated in the reduction reactions ( see page 72 ). o H. CONCLUSIONS In the present investigation it has been found that sodium trimethoxyborohydride, lithium borohydride, lithium aluminum hydride and sodium borohydride are effective reducing agents for the selective reduction of the carbon- carbon double bond of conjugated nitroolefins. The reduction reaction proceeds readily with terminal (primary) or internal (secondary) olefins containing either primary or secondary nitro groups. The reduction of nitroolefins by hydrides may be carried out without affecting the following substituents: chlorine, fluorine, and furyl and aryl nuclei. (See Table 11). Reduction of nitroolefins to nitroalkanes may be accompanied by secondary competitive processes; the nitro- olefin and the reduction product, a salt of a' nitroalkane, undergo Michael addition to yield 1,3-d-initroalkanes. .In most instances this secondary reaction can be minimized by effecting reduction at low temperatures and by adding the nitroolefin to the hydride reductant. The reduction of 4-nitro-3-heptene, a relatively hindered nitroalkene, demonstrated the importance of steric factors on reduction and that with unreactive nitroolefins, reductive attack on the nitro group of the plefin might occur. Reductions proceeded very slowly at -40° and even © TABLE 11 REDUCTION OF CONJUGATED NITROOLEFINS WITH -COMPLEX HYDRIDES Per Cent Conversion Nitroalkene Nitroalkane* NaBH (OCH^), ; LiBH^; LiAlHjflaBH^ 1-Nitropropene 1-Nit.ropropane si.7 49.9 2-Methyl-l-nitropropene 2-Methyl-l-nitropropane 53.7 43.4 2-Nitro-l-butene 2-Nitrobutane 45.0 59.3 2-Nitro-2-butene 2-Nitrobutane 62.6 60.3 52.9 63.5 4-Nitro-3-heptene 4-Nitroheptane 55.0 65.0 21.7 3,3, 3-Trichloro-l-nitropro- 1.1.1-Trichloro-3-nitro- pene propane 44.2 35.0 43.3 3,3,3-Trifluoro-l-nitro- 1.1.1-Trifluoro-3-nitro- 24.3 propene propane 4.4.5.5.6.6.6-Heptafluoro- 1.1.1.2.2.3.3-Heptafluoro- 34.0 37.3 2-nitro-2-hexene 5-nitrohexane 5.5.6.6.7.7.7-Heptafluoro- 1.1.1.2.2.3.3-Heptafluoro- 91.0 91.0 35.3 3-nitro-3-heptene 5-nitroheptane Omega-nitrostyrene 1-Nitro-2-phenylethane 33.6 55.3 49 J 14.4 2 -Ni t ro -1 -ph enyl pro pen e 2-Nitro-l-phenylpropane 43.4 2-{2-Nitrovinyl)furan 2-(2-Nitroethyl)furan 23.3 31.4 • 16.1 D-arabo-tetraacetoxy- 1-Nitro-1,2-dideoxy-D’ 1-nitrohexene arabo-hexitol tetraacetate 64.2 63.9 i' * Only the conversion to the parent nitroalkane is recorded; the conversions to Michael addition products are thus not considered, even though they are part of the reduction processes. VjJ - 0 133 prolonged reaction times at 0° did not result in complete . reduction to 4-nitroheptane. The relative resistance of 4-nitro-3-heptene to reduction was attributed to steric factors involved in attack. Sodium borohydride is unique among the reductants studied in that it may be used on compounds containing acyl groups without effecting their reduction; sodium trimethoxyborohydride, lithium borohydride,, and lithium aluminum hydride reduce vi cinal nitrocarboxylic esters to the corresponding nitroalcohol. Therefore, D-arabo-tetra- acetoxy-l-nitrohexene was reduced to 1-nitro-1,2-dideoxy- D-arabo-hexitol tetraacetate with sodium borohydride as it is specific for the carbon-carbon double bond. In the present reduction studies the yields of products from the series of nitroolefins vary greatly and no reducing agent was found to be universally better than the others. Good yields are obtained with all of the complex hydrides studied; if yield or conversion is of great importance in- an investigation it is suggested that all of the reducing agents be tried. 139 I. BIBLIOGRAPHY e 1. G. L. Gabriel, Chem. Ind., 45, 664(1939). 2. C. L. Gabriel, Ind. Eng. Chem., y i, £37(1940). '3. H. B. Hass and E. F. Riley, Chem. Revs., 32, 373(1943). 4. E. F. Degering, "An Outline of Organic Nitrogen Compounds," University Litboprinters, Ypsilanti, Mich., 1945, PP. 61-106. 5. N. Levy and J. D. Rose, Quart. Rev., 2, 353(1943). 6.■ H, Shechter and R. B. Kaplan, "Encyclopedia of Chemical Technology," The Interscience Encyclopedia Inc., New York,1952, Vol. 9, PP. 423-455. 7. H. B. Hass, E. F. Riley, and H. Shechter, "The Science of Petroleum," Oxford Univ. Press, London, 1953, Vol. V, Pt. II, pp. 70-73. 3. H. B. Hass, E. B. Hodge, and B. M. Vanderbilt, U. S. Pat 1 ,967,067 (July 24, 1934); assigned to Purdue Research Foundation. 9. 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Vogel, J. Chem. Soc., 1943, 1333. 33. I. Bevad, J. prakt. Chem., (2), 43, 345-33(1393). 34. I. M. Heilbron, "Dictionary of Organic Compounds," Oxford University Press, New York, N. Y., 1953. 35. E. H, Huntress and S. P. Mulliken, "Identification of Pure Organic Compounds Order I," John Wiley and Sons, Inc., New York, N. Y., 1949. 36. H, B. Hass, E. B. Hodge and B. M. Vanderbilt, Ind. Eng. Chem., 23, 339(1936). 37. W. M. D. Bryant, J. Am. Chem. Soc., 54, 3760(1932). S3. C. F. H. Allen, ibid., 52, 2957(1930). 39. W. Borsche and F. Sinn, Ann., 553, 265(1942). 90. S. Kaneo, J. Pharm. Soc. Japan, 5j3, 256-60(1933). 91. J. W, Baker and I. S. Wilson, J. Chem. Soc., 1947, 342. 92. H. Shechter and F. Conrad, J. Am. Chem. Soc., 72, 3371(1950). 93. E. T. McBee, H. B. Hass and I. M. Robinson, ibid., 72, 3579(1950). AUTOBIOGRAPHY I, Dean E. Ley, was born in Middle Point, Van Wert County, Ohio, on February 4, 1925. My primary and secondary schooling was received in the public schools of Middle Point, e Ohio. I graduated from the Middle Point High School in May, 1943. After serving in the United States Army for 32 months, I entered The Ohio State University in the Autumn Quarter of 1946. I received the degree Bachelor of Science in December, 1949> and the degree Master of Science in August, 1951. .1 continued my research in the Department of Chemistry as a Research Fellow on Project 396 of The Ohio State University Research Foundation while completing the require ments for the degree of Doctor of Philosophy.