This dissertation has been 62-829 microfilmed exactly as received

! ALTWICKER, Elmar Robert, 1930- j THE ALKYLATION OF THE BORON HYDRIDES; REACTION OF PENTABOlLANE-9 WITH 1-BUTENE AND SOME POLYHALOGENATED HYDROCARBONS.

The Ohio State University, Ph.D., 1957 Chemistry, organic

University Microfilms, Inc., Ann Arbor, Michigan THE ALKYLATION OF THE BORON HYDRIDES Reaction of Pentaborane-9 with 1-Butene and Some Polyhalogenated Hydrocarbons

DISSERTATION Presented in Partial Fulfillment of the Requirements for the Degree Doctor of Philosophy in the Graduate School of The Ohio State University

EIZvIAR RP'^TWIGKER, B.S.

The Ohio State University 1957

Approved by;

m Departme Ï Chemistry Acknowledgement

The author would like to thank Professor A.B, Garrett for the supervision of this research.

He would also lik e to thank Dr. John Norman of the Olin-Mathieson Chemical Corporation for the mass spectrographic analyses.

11 Table of Contents Page I. Purpose ...... 1 II. Historical ...... 2 III, Experimental ...... 5

A. Apparatus ...... $ 1. Main Vacuum System ...... ^ 2. Reaction-, Transfer-, and Storage A pparatus...... ^

3. Analytical Apparatus ...... Vy

5. Materials l 6 G. Reaction of Pentaborane-9 with 1-Butene . . . 18 1. Reaction and Separation of the Reaction Mixture ...... 19

2. Identification of Butylpentaborane . . . 2h

3. Results ...... 30 Ü. Summary ...... ill

D. Reaction of Pentaborane-9 with Triraethyl- borane ...... k2

E. Reaction of Pentaborane-9 v/ith Ethyl Magnesium Bromide ...... F. Reaction of Pentaborane-9 with Solvents . . . U9 1. Aromatic Compounds ...... « ...... $0

2. Methyl Cyanide ...... $ l 3. n-Heptane ......

i l l Table of Contents (Continued) Page G. Reaction of Pentaborane-9 vrLtb Some Polyhalogenated Hydrocarbons ...... $9 1. Introduction ...... $9 2. Reaction and Separation of the Reaction Mixture...... 6 l

3. Analysis ...... 68 U. Reaction of Pentaborane-9 with Diehloromethane, Dibromomethane, and Broraochloromethane ...... 71 a. Dichloromethane » ...... 73 b. Identification of 1,1’-Dipentaboiyl- methane ...... 7k c. Summary...... 63 d. Identification of 1-Pentaboryl- borondichloromethane ...... 8U e. Bromochloromethane ..... 85 f. Dibromomethane ...» 87 g. Summary ...... 87

5. Reactionrof Pentaborane-9 with Chloroform . 88

6 . Reaction of Pentaborane-9 with Dichloro- bromomethane ...... 97 7. Reaction of Pentaborane-9 with Carbon Tetrachloride ...... 103

8 . Reaction of Pentaborane-9 with 1,2-Dichloro- ethane and l-3romo-2-chloroethane ..... 105

9. a. 1,2-Dichloroethane ...... 106

b. l-Bromo-2-chloroethane ...... 110 IV. Discussion ...... 118 A. G e n e r a l...... 118

B. Reaction of Pentaborane-9 vrith l-Butene .... 120

iv Table of Contents (Continued) C. Reaction of Pentaborane-9 with Polyhalogenated hydrocarbons ...... ••••• 122 D, Reaction with Solvents ...... , . * 132

7. Sum m ary ...... 13U Bibliograpliy ...... 136 Autobiography ...... 138

A L is t of Tables

Table Page

I. Cooling baths ...... 14

II. Reaction of Pentaborane-9 with 1-butene ...... 31»32,33 I I I . Vapor pressure of 2-n-butylpentaborane-9 ...... 30,39 IV. Reaction of Pentaborane-9 with Trimethylborane . . . 43

V. Reaction of Pentaborane-9 with Solvents ...... 56,57 VI. Reaction of Pentaborane-9 with Methylene Halides ...... 75,7&,77 VII. Reaction of Pentaborane-9 with Chloroform ...... 90,91,92 VIII. Reaction of Pentaborane-9 with Dichlorobroiaomethane ...... 99 IX* Reaction.of Pentaborane-9 with Carbon Tetrachloride ...... 103

X. Reaction of Pentaborauie-9 with 1,2-Dichloroethane ...... 106

XI. Reaction of Pentaborane-9 with l-bromo-2- chloro ethane ...... 110

v i List of Illustrations Figure Page

1. Vacuum System ...... 6

2. Section of Fractionation Train •••.» ...... • 8 3* Reaction Vessels 10 U, Storage Tubes, Infrared Samples, and Tube Opener * • • . 12 Fractionation Scheme ••••• ...... ••• 22

6 . Vapor Pressures of Reaction Components •• •• 23 7. Infrared Spectrum of 2-n-3utylpentaborane-9 ......

8 . Infrared Spectrum of Pentaborane-9 ...... 35 9. Infrared Spectruin of Tri-n-Bu.tylborane (impure) ..... 37

10. Vapor Pressure of 2-n-Butylpentaborane-9 ...... UO 11. Infrared Spectmim of Solid Reaction Product ...... 52

12. Infrared Spectrum of Solid Reaction Product ...... 5U 13. Infrared Spectrum of Mixture ...... 58 lU. Vapor Pressures of Reactants ...... 60

15. U-Trap D istilla tio n ...... 66

16 . Transfer Arrangement ...... 69 17. Sublimator...... 69 18. Infrared Spectrum of 1 -Methylpentaboranc-9 ...... 79 19. Infrared Spectrum of 1,1'-Dipentaborylmethane ...... 80 20. Vapor Pressure of 1 ,1 '-Dipentaboiylmethane ...... 82

21. Infrared Spectnua of Fraction (v.p. 11 mm/o®) ...... 86 22. Infrared Spectrum of Mixture from Run 18-120 ...... 9U

23. Infrared Spectrum of 1-PentaborylborondichD.oromethane . . 96

v li List of Illustrations (Continued) Figure Page 2U. Infrai’sd Spectrum of Tars from Reaction of Pentaborane-9 with Chloroform (and AICI 3 ) in Carbon D isulfide ...... 98 2S« Infrared Spectrum of Gaseous Mixture 100

26 . Infrared Spectrum of Fi’action (v.p. 2 mm/25®) • • • • 102

27. Infrared Spectrum of l-Etbylpentaborane-9 ••**.• 100

28. Infrared Spectinun of l-Ethylpentaborane-9 .•••.• 109

29. Infrared Spectrum of l-Pentaboryl-2-chloroethane . . . Ill

3 0. Infrared Spectrum of 0°-Trap Fraction ...... 1])^ 31. Infrared Spectrum of -36“-Trap Fraction ...... Il5

3 2 . Pentaborane-9, Space Relationship ...... I I 9 33. Mechanism of Formation of l,l*-Dipentaborylmethane . . 12U

v i i i THE ALKXUTION OF THE BORON HIDRIDES

The Reaction of Pentaborane-9 with 1-Batene and with Some Poljdialogenated Hydrocarbons

I . Purpose

The purpose of th is research was to study reactions vdiich would lead to alkylation of pentaborane-9. A butyl derivative, 2-n-butylpentaborane-9, was prepared by the reaction of penta- borane-9 with 1-butene, Reactions of pentaborane-9 with a number of pol^alogenated hydrocarbons were investigated with the objective of preparing compounds containing more than one pentaboryl group per molecule. In connection with the latter reactions, the reaction of pentaborane-9 with a series of solvents was also briefly studied.

-1 - II. Historical Until recently, known reactions of boron hydrides with organic molecules were almost completely limited to the lowest member of the boron hydride series, diborane. Most of the reactions reported in the literature led to products resulting from breakdown of the diborane structure. Stock^ first reported on the reactions of boron hydrides.

1. A. Stock, The Hydrides of Boron and Silicon. Cornell University Press, Ithaca, New York, 1933* chiefly diborane and tetraborane, with substances such as ethane, ethylene, acetylene, and ethanol. Decomposition was invariably the main reaction. No substituted diboranes were obtained. An attendit to prepare ethyldiborane from chlorodiborane and zinc diethyl re­ sulted in the formation of a white solid which was not further identified^. The direct msthylation of diborane with zinc dimethyl

2. H. I. Sohiesinger and A. B. Burg, J. Am. Chem. Soc.. 53. 4331 (1931). ______

3 supposedly led to trace amounts of methyldiboranes .

3. H. I. Schlesinger and A. 0. Walker, J. Am. Chem. Soc.. 57. 621 (1935).

-2 - -3 - In the late thirties Sehlesinger and co-wrkera^*^ succeeded

4* H.8ohlesinger, L. Horvitz and A, B. Burg, J. Am. Chem. Soc.. 9B. 407 (1936). 5• ÜSehlesinger, N, W, Florin and A, B, Burg, J. Am. Chem. Soc.. 6 L 1078 (1939). in substituting up to four hydrogens in diborane by alkyl groups. The reactio n was based on the equilibrium between diborane and trialkylboranes. Reactions of diborane with saturated and un­ saturated hydrocarbons, and benzene at elevated temperatures led chiefly to trialkylboranes and polymeric products containing B-C bonds^. The main products obtained from reactions of boron

6 , D, T. Hurd, J . Ab u Obem. Soc.. ]&, 2053 (1948). ' ■ I ■ I II I w i —1111 — ■■ w 1 ■■■■■■■■ i i f ' ■ 1 1 '» ■■■■■ hydrides and alcohols and ether were di- and trialkoxyboranes^'^.

7. H. I. Sehlesinger and A. B, Burg, J. Am. Chem. Soc.. 55. 4020 (1933). 8 . A. B. Burg and F. G. A. Stone, J . Am. Chem. Soc.. 75. 228 (1953). 9. H. I. Sehlesinger and A. B, Burg, J. Am. Chem. Soc.. 296 (1938).

Dialkoxyboranes were the main reaction products from reactions of diborane with aldehydes, ketones, and esters^.

10. H. C. Brown, H. I. Sehlesinger, A. B. Borg, J. Am. Ohem. Soo.. 6 L 673 (1939). Reactions of diborane with ethylene oxide, acrylonitrile, and styrene have also been reported^.

11. F. A. G. Stone and H. J. Emeleus, J. Chem. Soc., 1950, 2755-9. ______

Alkyl derivatives of the higher boron hydrides were first prepared in this laboratory by two basic reactions. Mezey^

12. E. Mezey, Master's Thesis, The Ohio State University, Columbus, Ohio, 1954.

obtained 2-sec-butylpentaborane-9 from reaction of pentaborane-9 and cis-trans 2-butene at 150°. Harris^^ synthesized methyl and

1 3 . S. Harris, Ph.D. Thesis, The Ohio State University, 1956#

ethyl derivatives of pentaborane and dec abor ane by reaction of

these boron hydrides with the corresponding alkyl halides in the presence of aluminum chloride at teo^eratures between 25° and 100°. III. Experimental A. Apparatna

The sensitivity of pentaborane-9 to air and moisture made work in a high vacuum system mandatory. 1. Main Vacuum System. A flexible high vacuum system was constructed of Pyrex glass on both sides of a vacuum bench and consisted of the units shown in Fig. 1. For detailed information concerning the construction of a high vacuum system the reader is referred to the referenceslisted below^>^»^5. High vacuum stopcocks were used to make a l l

1 4 . E. T. Sanderson, Vacuum Manipulation of Volatile Congpounds, John Wiley and Sons, Inc., New lb:*, 1948« 1$. G. B. Ryschkewitsch, Ph.D. Thesis, The Ohio State University, Columbus, Ohio, 1955*

connections.

The intake manifold next to the fractionation train consisted of a horizontally mounted piece of 20 nm pyrex tubing and a closed end manometer. To the manifold were attached two stopcocks f itte d

w ith 1 IS/9 outer ball joints. The volume of the manifold and of one trap in the fractionation train was calibrated.

This manifold was similarly constructed and consisted of

several stopcocks equipped with 1 lS/9 outer ball Joints, a gas

-5 - Totplor pump

C O i train 1 Trop McLeod gouge Intoke a volume meosuring diffusion monifold pump

intake Froctionotion manifold troin Trop I Molting Vapor pt. opp preesure bulb Fore pump

VACUUM SYSTEM FI&VRE I -7 - condenslng bulb (isolable by means of a sbopcock), 1100 ml capacity, three removable and interchangeable spherical bulbs of 300,500 and 1000 ml capacity and a closed end manometer. A ll volumes in th is section of the system were calibrated, storage Manifold:

Tliis section consisted of seven bulbs and tubes of assorted sizes with attached cold fingers all connected individually through stopcocks to a manifold. It was used mainly to store gases and im­ pure fraction s from fractio n atio n s which were to be handled la te r . Fractionation Train; The original unit consisted of four U-traps with enlarged bottom sections connected by mercury float valves. The manipulation of the float vsüLves proved to be somewhat tedious and a train with

four traps was somewhat inflexible especially in the fractionation of the volatile products from the polyhalide reactions. This train was therefore replaced by one having six U-traps (three with en­ larged bottoms), and these traps were separated by high vacuum stop­ cocks of 4 mm bore. A section of the final arrangement is shown in Figure 2. For future use a train consisting of eight or even ten

U-traps would provide even greater ease of manipulation, especially when repeated fractionation of one impure fraction is required. All trap s were connected to a close-end manometer. Dow-Corning High vacuum Silicone grease as well as Apiezon K, L, H, and N were used to lubricate stopcocks and jo in ts . The Dow-Gorning grease was s a tis ­ factory in general but gave some difficulty with stopcocks that were From preceding To frcctionaticn ^ trap train manifold

& I

Manometer

Section of Fractionation Train

FIGURE 1 -9 - maniptil&ted only occasionally* In these latter cases the stopcock core tended to seat tight, and often considerable force was re­ quired to free it.

Vapor Pressure Apparatus* This apparatus permitted the measurement of vapor tension above room temperature and could also be used for molecular weight determination by attachment of a larger bulb. The design has been described by Sanderson^,

2, Reaction-. Transfer-, and Storage-Apparatus Reaction Vessels. The reaction vessels most frequently used were constructed from distillation flasks of various sizes, and provided with con­ striction for seal off and side arm with break off tip for inser­ tion into the tube opener. This type is shown in Fig, 3, design A, Designs B and G were tried with the object of obtaining a more uniform mixture by stirring. However, neither design permitted heating the reaction mixture at elevated temperature.

Design B was tried in the reaction of methylene chloride with

pentaborane-9 and aluminum chloride. I t was made from a 12$ ml Brlenmeyer flask around which a 1 liter Dewar containing a cooling mixture would just fit. The stirring bar was inserted before the

co n stric tio n was made.

Design G was fitted with a water-cooled condenser and attached directly to the high-vacuum manifold. In this type of reactor the 0 1

0

REACTION VESSELS

FIfrURE 3 -1 1 - total pressure inside the system could not be permitted to rise much above atmospheric. Considering the time and attention that had to be given to reactions run in and 3C, the results obtained did not encourage their extensive use.

Storage. and__Transfe« All liquids were kept in one of two types of weighing tubes. These are shown in Fig. type A and B. Liquids other than penta­ borane-9 and its derivatives were usually kept, weighed, and trans­ ferred in type B tube which consisted of two sections made from a

8 24/40 outer and inner joint. The size of these tubes (A and B) varied.

Tube Opener - described by Mezey^. (Fig. 4) IR Sampler (1.) - described by Ryschkewitsch^^. (Fig. 4) IR Sampler (gas) - This piece of apparatus was made by the glass blower. It consisted of a piece of Pyrex tubing of approximately

5 cm in diameter and 5 cm in length. The two open ends were flared and ground. Each opening was then sealed with a NaCl window using molten Apiezon W-100 which solidified on cooling. On the side of the c e ll a high vacuum stopcock equipped with 1 1Ô/9 b a ll Jo in t was provided. This permitted direct attachment to the vacuum line and consequently rapid san^ling. When not in use the cell was wrapped in a polyethylene bag and kept in a desiccator.

Cooling Baths: For fractionation a number of cooling baths were used. These Figure 4 Storage Tubes, Infrared Saaçler, abd Tube Opener

C S -13- were prepared by cooling suitable pure liquids to their melting points with Dry Ice or liquid nitrogen (see Table I). To reproduce

a tençerature of -78.5*j a 49*4 I 50.6, CCLi, t GHClg (by weight) mixture was used^. This mixture, as well as carbon tetrachloride, chloroform, and l,l-dich3joroethane, were cooled with Dry Ice;

liquid nitrogen was used to prepare the other cooling baths. Polyethylene Bagt

For the transfer of sangles that could not be handled con­ veniently in the vacuum system a polyethylene bag was used. This was made from a sheet of polyethylene film and provided with a num­ ber of sleeve-like openings for attachment of transfer- and storage- tubes. Positive nitrogen pressure (o il punqped nitzx>gen passed through a PgOg - drying tower) was maintained at all times. The respective tubes or flasks were then attached by inserting their necks into the opening and making an airtight seal with a rubber band. The bag was so arranged that one or two flasks attached to the lower end rested on the bench in the hood, while the upper opening, which was clanqied on a ringstand held a hypodermic syringe or a vessel from which a solution was to be poured into one of the receivers below. Samples from the polyhalide reactions were readied for analysis in this fashion. The receiver to which the transfer was made was weighed before and after. Rubber stoppers were placed

inside the bag before a transfer was started. Thus the sanqple could be tightly stoppered before the receiver was again eaqposed to the

atmosphere. -14- Table I cg.oitos M^hg. Compoimd Temperature. *C

W ater-ice 0

Water-aalt -1 to -15 Et hyleneglycol -11

Carbon tetrachloride -24

1 f 1-dic hloroethane -36

Ghlorobenzene -45 Diethyl malonate -52

Chloroform 4 3

Carbon tetrachloride-chloroform (see page 15) -78.5 Methylene chloride -97 Diethyl ether -1 1 6

E thyl bromide -1 1 9 Me thylcyelohexane -126

Me thylcyclopentane -1 4 2 Liquid nitrogen -196 -15-

At various stages in this vrork a number of microdistillations were made. The apparatus consisted of a distillation flask attached to a Claissen head with nitrogen capillary inlet and a thermometer in the neck. To the side arm was attached a condenser (optional) and a cow with 5 receivers. This system was connected through a cold tra p to a Cenco high vacuum punqp. A manometer was also pro­ vided. With the exception of distillation flask and thermometer joints, all joints were either 1 12/5 ball joints or 1 7/25 joints. The d is tilla tio n flask was heated by means of a mineral o il bath. The receiver (s) was cooled by ice or ic e -s a lt mixtures and occasionally by Dry Ice. The apparatus gave few satisfactory results. When only one receiver was used} the product was usually inqpure even if d istil­ lation was interrupted to change receivers. The use of the cow led to considerable hold-up in the narrow diameter tubing, and also gave poor separation.

3. Analytical Apparatus. For analysis of products the following apparatus was used; Toepler pusqi, carbon dioxide train, Beckman Model G pH meter, olefin absorbent, Baird J. R. Spectrometer, Perkin-Elmer Infrared Spectro­ photometer.

Toepler pum p ! This was used to measure the hydrogen formed from a hydrolyzed —16— ^ * ni 8£uq>le. The design has been described by Sanderson^, Carbon dioxide trAini

In this apparatus which has been described in detail by Hezey^ carbon was determined as COg. The only modification was a three-way stopcock at the inlet, one way connected directly to the high vacuum line, the others to train and sanple, respectively.

Olefin Absorbent; Since it was impossible to determine by vapor pressure measure­ ments a HTnflii impurity of saturated hydrocarbon in the olefin the latter was absorbed in a solution of the following composition!

200 g Hg(N 03)2, 100 g AgNOa, 100 g KNOg, 25 ml cone, HgSOi,, 865 ml HgO,^^

1 6 , M. T, H artig, Standard O il of Ohio, Private Communication,

B. Pentaborane-9. This compound was supplied by the Olin-Mathieson

Chemical Corporation. Any residual pressure at -78.5" was pumped

o f f. Tr imethvlborane. Trimethylborane was kindly supplied by

James Coleman, The Ohio State U niversity, RF P roject 116-C, I t was

fractionated until tensiometrioally pure. 1-Butene. A Matheson C.P. grade was used directly from tank. Benzene. Merck Con;>any - Reagent Grade benzene was dried over

sodium. -1 7 - Toluene. Mathieson, Coleman and Bell. A constant boiling cut was taken. Chlorobenzene. Mathieson, Coleman and Bell. A constant boiling cut was taken.

Nitrobenzene. Eastman Kodak Reagent grade was used without further purification. Methyl cyanide. Union Carbide and Carbon. R ed istilled from PgOg. n-Heotane and cye^fi|^fl-ig|»>ne were supplied from the American Petroleum

Institute, Project The Ohio State University. Both conqpounds were dried over anhydrous magnesium sulfate. Their refractive

indices were in agreement with literature values. Carbon disulfide. Baker's Analyzed Reagent Grade. Redistilled and kept under nitrogen.

goljfaa3x>genated Hydrocarbons: methylene chloride, chlorobromo- methane. methylene dibromide. 1.2-dichloroethane. l-bromo-2-chloro- ethane. Eastman Kodak reagent grade, dtied over anhydrous magnesium su lfate.

Chloroform. Mallinckrodt Analytical grade was redistilled. A center cut was dried over anhydrous magnesium su lfate. Carbon tetrachloride. B & A grade, made by the General Chemical Division, Allied Chemical and Dye Corporation, was used. A center

cu t was dried over anhydrous magnesium su lfa te . Bromodichloromethane. Matheson, Coleman and Bell reagent grade was

washed with conc. dried over CaCl% and distilled. “13“ Aluminum chloride, B & A grade, made by General Chemical Division, Allied Chemical and Dye Corporation, was used. Unless otherwise stated, this material was resublimed and stored under dry nitrogen. Stannic chloride, Matheson, Coleman and Bell analytical grade was transferred under vacuum.

Aluminum bromide, Fisher Scientific C.P, grade was resublimed. Hydrogen chloride, Matheson Company product was used d ire c tly from tank,

C, Reaction of Pentaborane-9 with 1-butene

Mezey^ and Ryschkewitsch^^ have shown that pentabarane-9 could be alkylated by reaction with 2-butene and isobutene to give

2-sec-butylpentaborane-9 and 2-isobutylpentaborane-9 respectively, ^ y# A » .• It was desirable to extend this reaction to other olefins and for

this reason the reaction of pentaborane-9 with 1-butene was studied, A new butyl derivative, 2-n-butylpentaborane-9 was prepared. Other products of the reaction were: hydrogen, butane, tributyl- borane, and tars. The effect of Lewis acids such as aluminum chloride, stannic chloride, and zinc chloride was studied briefly, Polymerization of the olefin appeared to be the main reaction in the presence of these catalysts. In cases where the sûLkyl derivative

was formed i t was not ascertained whether sub stitu tio n had taken place at the base or the apex of the pentaborane pyramid. However, Me zey^^ has shown that under carefully controlled conditions Lewis

17, E. Mszey, Ph,D, Thesis, The Ohio State U niversity, Golurdaus, Ohio; 1957. -19- aclds such as ferric chloride catalyze the reaction of pentaborane-9 with olefins to give apically substituted alkyl derivatives* 1, Reaction and Separation of the Reaction Mixture. The reaction bulb was attached to the manifold, evacuated, tested for leaks, and degassed with a low flame*

Pentaborane-9 was weighed as a liquid and transferred from a storage tube* The amount of pentaborane-9 to be transferred could be estimated from a knowledge of the dimensions of the storage tube* Once 6ua exact amount of pentaborane-9 had been transferred, the stop­ cock to the reactor was closed and 1-butene was admitted to the calibrated manifold to a predetermined pressure* The 1-butene was then condensed in the gas condensing tube, any noncondensable was punqped off, and the pressure measured again* The stopcock to the reacto r was then opened and the o lefin was condensed at liq u id n itro ­ gen temperature* Stannic chloride was also introduced into the reaction bulb by vacuum transfer. Aluminum chloride, zinc chloride, and zinc dust were placed into the reactor before the volatile reactants were added* After evacuation, the reactor was filled in the dry nitrogen, removed from the manifold, and the solids were introduced* When condensation was consiste, the reactor was sealed off at

the constriction; the glass tip was annealed, allowed to cool, and

tested for leaks, while the contents of the reactor were held at

liquid nitrogen tenqperature* The reactor was then placed inside a screen made from Cu wire screen and was warmed to room temperature* “20- All reactions at elevated ten^erature were run in a Fisher IsotesQ) drying oven which was placed inside a 1/4 inch steel plate safety housing open on the side facing the window*

A small amount of clear liquid was always present at the be­ ginning of a run. As the reaction progressed formation of brown tars set in and the amount of liquid increased. After the com­ pletion of a run, the reactor was cooled to room temperature and stored in the deep freeze.

The reaction was worked up in the following way: the contents of the reactor were condensed with liquid nitrogen. The break-off c a p illary was then scored lig h tly and the break-off arm was sealed into the tube opener with Apiezon W-100. The tube opener was at­ tached to the intake manifold which was then evacuated. After the absence of leaks had been assured, the tip was broken off, any pressure due to noncondensable gas measured, and the gas pumped off.

The reactor was warmed slowly to room tenqperature (25-30*) while open to traps at -45*, -78* and -196*. In this way a rough fractionation of the mixture into three fractions consisting largely of 1-butene (-196*), pentaborane-9 (-78*), and alkyl derivative

(-45*) was effected. After a few hours the -45* trap was cooled to - 196*. If no further condensation from the reactor occurred, the

trap was closed off and the reactor was filled with dry nitrogen. Because of the low vapor pressure of tri-n-butylborane, there was no

guarantee that its removal from the reactor was quantitative. -21- e specially when the amount of non-volatile tar was large, A flow sheet for the fractionation of the products resulting from the reaction of isobutene with pentaborane-9 has been given by Ryschkewitsch^5, A sim ilar procedure was followed in th is work and i s shown in Figure 5» A graph showing th e vapor pressures of the reaction components is also given (Fig. 6), This flowsheet is not intended to indicate a rig id procedure. Minor m odifications were used occasionally depending on the re la tiv e amounts of each compon­ ent. Time was, of course, an important variable in these fraction­ ations, especially when the fractionation of two substances as close in vapor pressure as n-butylpentaborane-9 and tri-n-butylborane was involved. The progress of a fractionation was followed by periodi­ cally checking the vapor pressure of the fractions obtained. This was done by isolating the particular trap from the rest of the fractionatio n tra in and warming i t s contents to a temperature (O*, room temperature, -78*) at vrtiich a representative vapor pressure measurement could be made.

If further evaporation (ay increasing the volume above the liq u id ) produced no change in vapor pressure the frac tio n was assumed to be e sse n tia lly pure and removed from the tra p . Large liquid fractions were usually split into two parts and the vapor pressures of each part measured again. Due to their proximity in vapor pressure, it was not possible to separate 1-butene from butane by fractionation; the mixture instead was analyzed by absorption of the -22-

RT

-36 RT -97

C4 -froctlon

-196 -97

-196 -36 -78 -97

-3 6 - 4 5 -78

A ■36 - 4 5 - 196 RT RT ♦■10 Rintaboratw wii q I - ' f -3 6 -78 RmfobortiM I RT RT RT -196 -10

-45 -196 Alkyl- ptntoboront 0 -10

Triolkyl - boron# -23- Figure 6 1000 r— Vapor Pressures of Reaction Components

100

P mm. H g

20 * 0,1 2 5 3.0 35 4.0 4.5 5.0 “24“

16 * * olefin in the absorbent (page 16).

The fractionation scheme leading to the separation of the alkyl derivative from the trialkylborane was usually repeated several tim es. Vapor pressure was not a good c rite rio n of p u rity , since both substances were of low volatility. Fractionation was usually continued until the alkylpentaborane fraction showed no measurable change in vapor pressure at 27*. When tensiometrically pure fractions had been obtained, their amounts were determined. Pentaborane-9 and n-butylpentaborane-9

# . • « were condensed into small storage tubes (Fig. 4A) and weighed as liquids. The hydrocarbon fraction was measured as a gas and the amount of butane determined by analysis (see above). The tri-n- butylborane fraction was normally not determined quantitatively, but was estimated and subsequently destroyed with methanol.

2. Identification of Butylpentaborane. The following methods were employed to characterize the alkyl derivatives: 1) Hydrolysis 2) Oxidation 3) Infrared analysis

4) Vapor tension measurement and molecular weight determination

3) Degradation 1) Hydrolysis It has been shown by Schiesinger end co-workers^ that -25“ « alkyldiboranes reacted quantitatively with water to yield boric acid, alkyl boronic acid, and hydrogen. Butylpentaborane would therefore be expected to react according to the equation + 14 HgO ----► C/,H;B(OH)g + 4 B(OH)a + 11 Hg In to a 250 or 5OO ml reactor was introduced 1-2 ml of distilled water. The water was frozen out with liquid nitix>gen, the reactor was evacuated, and a known amount of sazple was condensed into it.

Samples were in the order of 30-70 mg. To minimize errors due to weighing, the storage tube was f i r s t weighed enpty. The sample was then transferred to the storage tube, which was reweighed. After the sample had been condensed in the reactor vessel, the storage

tube was weighed again. The reactor was now sealed, placed inside a wire mesh screen, warmed to room temperature, and heated for 2-3 days at 150*.

The boric acid (and the alkyl boronic acid) was washed into a beaker and the reactor was rinsed tlioroughly with distilled water,

to insure complete transfer of boric acid. The pH of the solution

was adjusted to about 5*0-6.0. Hannitol was then added to convert the boric acid into the strongly acidic monobasic complex. The ti­ tra tio n was carried out with 0.1 N NaOH solution and was followed by a Beckman pH meter. A titration curve was usually plotted and the endpoint read from the graph. Since alkyl boronic acid is partially titrable, values for boron from hydrolysis were usually

low. The volu#s of hydrogen was converted to standard conditions and the moles of hydrogen calou3^ted. From the equation “26- mole 8 hydrogen x 2.016 x x ■■■ - x 100 ■ hydrolyzable % 22 v t. sample the percentage of hydrolyzable hydrogen, i.e. hydrogen attached to boron, was obtained.

2) Oxidation Fuming nitric acid according to the procedure of Sohiesinger 3 and Walker was used to convez*t the alkyl derivative completely into boric acid and carbon dioxide. Also formed in the reaction were; water, nitrogen, nitrous oxide, nitric acid, and.nitrogen dioxide.

An excess of nitric acid was used based on the equations

+ 24[0] *• 4C0g + jHaBOj + H%0

2HNO3 ---- - N2O4, + HgO + [ 0] 48HNO3 — ► 24 [oj About 2-3 ml fuming nitric acid was placed into a 1 liter reactor. The amount of sample added varied from $0-100 mg. The procedure

followed was very similar to the one described under 1) hydrolysis. The sealed reactor was kept at room teiqperature for several hours. I t was then heated a t 200-220* fo r a t le a st 3 days. The reaction mixture was woi^ed up as follows# any noncon­ densable present (nitrogen) was pumped off. The reactor was then warmed slowly and the contents passed through a -119* trap into a - 196* trap . Only h^O and GOg «jdtisi^ed the la tte r ; NO was pumped o ff. The N3O-GO3 mixture was passed over the hot copper mesh and con­ densed at the outlet. Any nitrogen produced by reduction of NgO

was pun^d off. Reduction was repeated until no further nitrogen -27- liras produced. The -119* trap was then opened again to the -196* trap to Insure complete removal of all 00% from the former. When the material in the -196* trap showed a vapor pressure of 11 mm at -119* i t was taken as pure 00%. The amount of COg was then measured in the calibrated trap and the moles of 00% were calculated using the ideal gas law. The nonvolatile white solid in the reactor was dissolved in distilled water. The reactor was rinsed thoroughly several times. Any strong acid present was first neutralized to a pH of 5,1-5*5 with base. Hannitol was now added and the titration carried out as described under I).

Since the boron-carbon bond was broken by oxidation in this manner, results for boron were in better agreement with the calcu­ lated value than the results from hydrolysis.

3) Infrared Analysis The sampling tube shown in Fig. 4 was attached to the mani­ fo ld , evacuated, and thoroughly degassed. A liq u id sample was con­ densed into the tube, vMch was then filled with dry nitrogen and capped. The tube was now placed into a Incite dry box which had been flushed with dry hitrogen for at least 15 minutes. Infrared c e lls , syringe and hypodermic needle, and dry solvents had been placed into the dry box prior to that. The rubber cap of the sanpling tube was then punctured with a hypodermic syringe and

enough sample was withdrawn to fill the infrared cell. The spectrum was then scanned. The cell was returned to the dry box. As much —28— a 8 possible of the sample was withdrawn and returned to the sailing tub e. F inally, the c e ll was washed several times with methylene chloride followed by petroleum ether or benzene. It was then dried by blowing a slow stream of nitrogen through it. 4) Vapor Tension Measurement and Molecular Weight Deterfidnation The vapor pressure below room tenperature was measured by placing a cooling bath of known temperature around the trap contain­ ing the sançle and reading the pressure directly. For measurement of the vapor pressure above room teiqperature and for molecular weight determination the apparatus described by Sanderson was used^^. The vapor pressure bulb of the apparatus was baked out for 1 day by heating and punning. Since the vapor pres­ sure and molecular weight were to be determined in one run, a known weight of sample was condensed into the bulb and the mercury lev el was raised so as to cut off the teneimeter. A beaker containing glycerol was now raised around the apparatus until the latter was completely immersed. The glycerol was stirred magnetically and heated by means of an immersion heater. As the pressure inside the vapor pressure bulb rose, it was compensated for by admitting nitrogen to the manifold side of the system. A time-temperature curve was kept and pressure readings were taken by balancing the mercury columns in the cut off to the same lev el. The volume of the vapor pressure bulb was calibrated. This -29- was indicated by a mark on the bulb side of the cut off* Whenever readings were taken* it was attempted to keep the mercury columns at level with the mark.

The saicple was first heated to 95* and then cooled to 50* which gave the first heating and cooling curve. Upon condensation with liquid nitrogen* no noncondensable material was measured. The same sanple was heated again to 100* and then rapidly to 150*. It was held at that tençeratxire for 25 minutes. On cooling* the vapor- tension was measured again in the range from HO* to 50*. From the pressure (corrected for the vapor pressure of mercury at that temperature) the temperature* and the known volume of the vapor pressure bulb the molecular weight was calculated using the ideal gas law.

5) Degradation. Reaction of 2-n-butylpentaborane-9 and tri-n-butylborane with alkaline hydrogen peroxide was used to break the B-C bond. A 1 ml sample was injected slowly under the liq u id lev el of a saturated sodium hydroxide solution ( 15-20 ml) in a small flask equipped with reflux condenser. The system had been flushed with nitrogen. The condenser top was connected to a mercury outlet. The solution was refluxed gently until gas evolution became very slow. Thirty per cent hydrogen peroxide was then added dropwise

from a funnel and the solution was refluxed until further addition of peroxide produced no rapid gas evolution. The cooled solution -30- vas extracted with chloroform, the chloroform extract was washed w ith water, and dried over anhydrous magnesium su lfa te . After filtration it was concentrated until the odor of alcohol became quite noticeable.

An infrared curve was taken on that solution using chloroform, prepared by shaking with water and drying over anhydrous magnesium sulfate, as a blank,

3* Results, The experimental re s u lts are summarized in Table I I ,

1) Hydrolysis and 2) Oxidation For a butyl derivative, the calculated and ob­

served percentages are listed below# $ Hydrolyzable ^ G B H B/C Ratio

Theory 40.25 45.30 6.75 5/4 Hydrolysis ------43.7 6.76 — Oxidation 40,1 44.Ô — 4.97/4

The agreement with the theoreticsuL values can be considered good.

This leads to a formula 97^4.0^ 04 * 3) Infrared Analysis Inspection of the infrared curve taken on a liq u id sample

of 2-n-butylpentaborane-9, Fig, 7, shows characteristic absorptions

for pentaborane (Fig, B) at 3.95 a » 5.5/*^» 6.8-6.9 a # 7 .1 /^ , 11. 25yw/. The strong band at 9*6 is missing. There is at present Table II Beaction of Pept«bQr«ne-9 with 1-Butene REACTANTS. mmoles Volume of Time, Tenp., Reaction No. B5H5 1-butene C atalyst Reactor, 1 . hrs •c

B i-2 2 44.2 47.2 — .56 21 146-153 B2-23 61.5 62.7 — 1.06 15.5 Li8-152 63-^24 68.6 63.6 1.06 63.5 150 Bf^**26 44.0 42.3 .56 96 150 B5-27 30.6 31.3 smaUjZnClg .66 88.5 150 B6**36 47.4 47.2 small, Zn-dust .56 108 150 Bt !*45 43.7 47.8 — - .56 102 150 Ba-Jiâ 118.5 55.7 1.06 92 150 B,,74 36.8 38.9 r anh. -S11CI4 1 .56 68 days 25 I Bicr75 27.6 29.8 1 8.55 -» .56 50 150 B n “98 67.1 67.1 10.0 AICI3 .13%) 6 10-20 I B ia^57 49.3 50.1 ------.3 1 30 150 B13J .57 39.7 4 6 .1 .3 1 14.5 150

30 54.0 53.8 — .31 7.5 150 31 47.4 54.0 — .3 1 7.5 150

x) 125 ml Erlenmeyer flask Table II (conbixnied)

PRODUCT»*^, nymmlAg Reaction No. B5H0R ER3 RH Ha Tar Others

Bi-22 1 1. 1B small N.O. f .085 some Ba-23 ; .. I nmnll some — B3924 3.10 .31 aome — By26 3.05 .33 some — B5-27 .6 7 1.20 small — B®^36 3.82 .40 considerable —— 87-45 5.51 .10 considerable — 4.75 ’ .14 some — B;-74 V. small none .20 white solid 3.91 HOI Bi,t 75 2.44 none 3.0 V. large 2.64 HOI Bn-9Ô none none trace considerable trace HOI B|2-157 2.35 1.04 e99 .06 small — B, 3-157 .85 small #94 .18 trace 30 2.90 1.44 ** .3 ——— — 31 1.27 .48 0 .0 - .1 — Table II (conbixmed)

REACTANTS USB). m o les used ^ conv. 55 y ield Reaction No. B5H9 1-butene C atalyst BgHy 1-butene BsHgR of BgHg B,-22 0.2 4.6 .45 9.75 11 1.11 45.2 2.4 2.9 —. 3.9 4 .63 J' . • ' 3.7 7.0 5.4 14.2 4.56 83.6 " B u s S h 4.8 17.1 10.9 40.4 6.94 63.6 2.0 6.5 none 6.7 20.8 2.19 33.5 B6-36 4.7 27.3 none 20.5 57.9 8.09 39.4 Br-45 8.6 23.8 — 19.5 49.8 12.6 64.1 B$?«4B 32.8 28.6 10.8 51.4 4.01 37.1 Bg î»74 — 9.7 «man — 26.4 Bie-75 4*5 26.95 small 16.3 90.5 8.82 54.0 Bn»90 6.1 60.3 small 9.1 89.9 —— B u îJ.57 10.9 8.2 — 22.1 16.4 4r77 21.6 B,yJ.57 1.44 3.1 —. 3.63 6.73 2.1 58.5 30 4.75 11.3 ___ 8.8 21.0 5.36 61.0 31 3.26 5.1 6.9 9.44 2.07 38.9 PERCENT TRANSMITTANCE

I 8. en

mI I a T) W

H % z s ôs 5 !

VOtI

-"%- Figure 8

Infrared Spectrum of Pentaborane-9

100 100

5 80 80

60

40 40

20

WAVE LENGTH IN MICRONS

I

I -36- no certainty as to the position of the B-C frequency^. The band at

IB. G. N. Tyson, Jr., Olin Mat hie son Chemical Corporation, Pasadena, C alifornia, Private Communication.

7.AO ^ could be assigned to B-C absorption. Conparison with the spectrum of the trialkylborane (Fig. 9) shows peaks for the alkyl group at 8.1, 8.75, 9.1 and 9.75/^. Inspection of the trialkyl­ borane spectrum alone, would make a decision as to the nature of the alkyl group (n-butyl or sec-butyl) difficult. The peaks at 3.95# 5.&

11.25 and 11.85 ^ can be assigned to 2-n-butylpentaborane-9 present as an impurity, however.

a ) Vapor Tension Measurement and Molecular Weight Determination The vapor pressure data are reproduced in Table No. III. Comparison of heating and cooling curves shows, however, tirnt equi­ librium was not always attained. Some of the points from both runs are plotted in Figure IX). This plot fitted the equation

log P - -2.3A X lo3 I + 8.3A

Extrapolation of this plot gave a normal boiling point of 15A.5*. The heat of vaporisation was calculated to be 10.71 kcal/mole, the

Trouton constant 25.0 e.u. The molecular weight, calculated from the ideal gas law, was in

fair agreement with the theoretical value (119.25). Calculated;

117.A . Figure 9 Infrared Spectrum of Tri-n-Butylborane (ijjçure)

oo

80 oUi

h - 60

40 z LUD w(T Q. 20

W A V E l e n g t h in m i c r o n s

I t -38- Table III

F ir s t Run Temperature, 'K l/r x 10^ Pressure, m Hg Heating Curve 302.0 3.310 3.8 304.4 3.,290 4 .7 307.5 3.,254 5.6 312.0 3.,207 6.9 318.3 3.,141 8.8 328.5 3,.045 17.9 337.2 2.966 25.3 340.6 2.936 29.8 343.4 2.912 32.7 345.2 2.897 36.8 347.3 2.880 40.1 349.2 2.864 43.6 351.4 2.846 48.1 353.4 2.830 52.4 355.3 2.815 57.2 357.1 2.800 61.9 358.8 2.787 65.8 361.0 2.770 72.7 362.8 2.756 78.1 364.4 2.744 83.0 366.2 2.731 89.0 368.0 2.718 95.1 Cooling Curve 364.5 2.744 85.1 361.7 2.765 76.0 359.9 2.779 70.5 358.1 2.793 6 5.6 354.4 2.822 56.7 352.5 2.837 52.1 350.2 2.856 47.6 348.1 2,873 43.7 345.0 2.898 37.8 342.4 2.922 33.9 338.0 2.958 28.0 337.0 2.967 26.3 332.4 3 .0 1 0 21.5 -39- Table III (continued)

Second Run Temperature, *K l/U x 10^ Pressure, mm Hg Heating Curve 307.2 3.255 5.4 316.4 3.165 8.7 322.0 3.105 12.1 327.5 3.050 15.1 331.5 3.015 19.8 336.Ô 2.970 24.3 339.3 2.947 27.7 344.0 2.907 35.1 348.0 2.875 41.3 352.0 2.841 49.0 354.6 2.820 56.0 358.0 2.795 63.7 362.0 2.765 75.4 364.7 2.745 83.8 366.1 2.732 88.0 369.5 2.705 100.4 422.0 2.372 470.0 423.0 2.367 471.9 Cooling Curve 383.0 2.610 160.5 375.9 2.660 129.2 369.4 2.705 1 0 1 .2 366.0 2.730 89.0 363.0 2.755 79.5 348.5 2.870 44.4 337.5 2.963 26.3 - 4 0 “

1000 ^ I 1191 i w i i i A First run, coolinrJ iin g 9 Second ain, ti e a t i n g ^ Second run, cooling

100

P m m . H g

2.7 2 B 2.9 30 3.1 3.3 Ÿ N ID ,* *K - I

Figure 10

Vapor Pressure of 2-n-Butylpentaborane-9 -41- 5) Degradation

Gonç»arison of the infrared spectrum obtained from peroxide cleavage with an authentic sample of n-butanol showed the two to be identical. An iodoform test was negative. This further showed the absence of sec-butanol.

6) Tri-n-butylborane

This compound was identified by its vapor pressure, its infrared spectrum (Fig. 9)> and degradation by peroxide cleavage to n-butanol.

4 . Summary: The results listed above together with the evidence obtained from nuclear magnetic resonance studies^^ for 2-sec-butylpenta-

19* Shoolery, T., Varian Associates, Palo Alto, California, Private Communication. borane-9 left no doubt that the product was 2-n-butylpentaborane-9, i.e ., the base substituted product. Conparison of runs and B)3"^57 and 30 and 31^^, Table I I

illustrates that isobutene is more reactive than 1-butene. Under th e conditions tr ie d , Lewis acids such as aluminum chloride and stannic chloride led chiefly to olefin polymerization. -42- D. Reaction of Pentaborane-9 with Trinethylborane This reaction had previously been reported by Burg^* Alkyl

20. A. B. Burg, in Boronhydrldes and Related Conpounds, Second Edition, May, 1954, Gallery Chemical Cong)any« derivatives of diborane and a golden-brown solid polymeric material were obtained. Since trialkylboranes were produced by reactions of olefins with pentaborane-9 along with considerable amount of tars, it was of interest to investigate if reaction of the trialkylborane

with pentaborane-9 led to large decomposition of the latter, or if alkylation could take place by this route. The sample of trimethyl- borane was contained in a glass ang)ule and was introduced into the vacuum manifold by means of the tube opener. The sample was re - fractionatéd from a -78.5* trap through a -116* tr«Q) several times, u n til the vapor pressure of the frac tio n held a t -116* was in agree­ ment with the literature value (29 mm/-78.5*). The procedure followed was essentially that described for the 1-butene reaction. Because of the large difference in vapor

pressure between trimethylborane and pentaborane-9, separation was

re a d ily acconQ>lished. The reactions have been summarized in Table No. IV. Reactions II and III did not give any noncondensable gas; trace amounts of a

pale yellow non-volatile glassy solid were present. Pentaborane-9

and trimethylborane were recovered, but not quantitatively. Trace Table IV Reaction of Pentaborane-9 with Trimethylborane Volume of Theoretical Reactants Reactor Pressure Time Tenp. R eaction B5H9 nmoles 6 (0113)3 nmoles liters atm. hrs •C

11-15 1.5 5.0 .0 7 3.7 1 100 IH ,1 6 10.8 11.0 .61 1.3 1 75 51.2 42.3 1.06 3.2 48 150 V,36 132.5 42.0 1.06 6.0 92 150

I ■p- Reactants Used Y Reaction B5H9 nmoles 8 (083)3 nmoles Volatile Products Tars

U -15 N.D. N.D. Only trace amounts of Trace fractions other than B5H9 and 6 (083)3 U I-1 6 N.D. N.D. Same as 11-15 Trace IV-29 0.5 0.4 Trace» 5 m ^-78.5“ Small Trace# 7.5 W33" V-36 3.0 3.2 Small amount» 9 Small

N.D, " not determined -44“ amounts of intermediate volatile fractions were not further characterized, but could conceivably be due to methyldiboranes, which have the vapor pressures listed below*

Pmm T, 'G

CH3B2H5 55 -78.5 (CH3)2BHBH3 10 -78.5

(CH3BH2)2 7 -78.5

(ch3)2BHbh2CH3 123 ' 0

(CH3)2BH2 48 0

Reactions XV and V produced noncondensable material, which could have been either hydrogen and/or methane. Run IV also gave a mmaii amount of a pale yellow powdery solid which coated the inside of the reactor. Run V produced a brown-yellow glassy nonvolatile fra c tio n , as well as some amorphous so lid . Although the v o la tile mixtures were fractionated until pentaborane-9 and trimethylborane were teneiometrie ally pure, it should be remembered that trace amounts of methyldiboranes could have been included in those fra c tio n s.

Conclusion# From the results obtained it can be concluded that reaction of pentaborane with trimethylborane does not give an appreciable amount of decomposition, nor does it lead to formation of an alkyl- pent aborane. It seems probable therefore that the trialkylborane obtained in the olefin reaction is formed by successive alkylation -45“ and breakdown of the pentaborane skeleton*

E* Reaction of Pentaborane-9 with Ethyl Magnesium Bromide. Theoretical considerations of the pentaborane molecule have led to a charge distribution of about -*3 unit at the apex and the balancing positive charge spread evenly over the four base borons* It would therefore be conceivable that a Grignard reagent with an apparent polarity R“^-MgX'*^ could react with pentaborane-9 in two ways as shown below:

(1) Reaction on the apical boron atom

" S ' + R"^ R-H +

(2) Reaction on a base boron atom

R"^— -----► B-R ♦ MgK"^'+ H“ H*

In reaction 2 , i f hydride ion was actually formed, i t would be ex­ pected to act as a reducing agent on the Grignard reagent, forming hydrocarbon. The compound indicated by the formula, BgH@MgI, might react with alkyl halide, Rl, and hydrogen halide, HI, as shown below!

(3) BjHaMgl + RX ---- #" BsHjR ♦ (4) BjHgMgl ♦ HX — » BgH) + Mj^Ca ■•46“ Reaction 3 would be a coupling reaction with excess alkyl halide, leading to the formation of an alkyl derivative, while reaction 4 would result in regeneration of pentaborane. The literature reports no studies on the reaction of penta­ borane with Grignard reagents. Cohen^^ has reported on the

21. Olin Mathieson Chemical Company, MCC-1023-TR-125, A pril 29, 1955. ______' ^______

alk y latio n of decaborane with methyl magnesium iodide and ethyl

magnesium bromide. Large yields of hydrocarbon were obtained in both cases. Reaction of the methyl magnesium iodide - decaborane product with diethyl sulfate yielded ethyldecaborane. However,

when the ethyl magnesium bromide-decaborane product was treated with dimethyl sulfate, a liquid product was obtained which proved to be a mixture of methyl- and ethyldecaborane, with the former predominat&%

It was postulated that substitution of hydrogen by ethyl resulted from direct interaction of dec aborane with the Grignard reagent, whereas methyldecaborane was formed by attack of dimethyl sulfate on the metallated intermediate. More complete work on reactions

with organe lithium compounds (vdiich cannot be cited here) has indi- cated further that two possible reaction paths exist. Since dimethyl sulfate is a fairly reactive alkylating agent, one would probably expect the formation of methylpentaborane upon addition of dimethyl sulfate to the product from interaction of the Grignard reagent with pentaborane. One would also expect the -47- coupling reaction to occur with a more reactive halide, such as benzyl-, a lk y l-, or t-b u ty l-, i f an ionic mechanism is in operation.

Preparation of Ethyl Magnesium Bromide and Reaction with Pentaborane-9 The reaction was carried out in a 125 ml Erlenmeyer flask equipped with a reflux condenser and a dropping funnel with bypass.

The condenser and funnel were attached to the flask in the 1 18/9

ball joints. The condenser was tapped by a CaClg drying tube. A stirring bar was placed into the flask. The system was flushed for

about 5 min. with dry nitrogen. Magnesium turnings, 2.7 g (0,111 moles), were placed into the flask. A solution of ethyl bromide,

1 2 ,1 g ( 0,111 moles) in 35 ml n-butyl ether was slowly added from the separatory funnel over a period of 1 hour; positive nitrogen pressure was maintained during the reaction. Stirring was continued

for a little while. After the reaction appeared to be complete, the separatory funnel in le t was capped, the condenser was removed and the flask was attached to the manifold. Five ( 5) ml of the solution was titrated with standard acid; this indicated a conversion of over 90)G

to the Grignard reagent, Pentaborane (0,099 moles) was transferred to the reactor. The mixture was warmed slowly and stirred for about 2 hours at 0*. The mixture was then cooled to - 196." and 4 mm noncondensable gas was pumped off. The reactor was warmed to about 20*• The pressure

slowly increased from 232 mm to 573 mm. The reactor was then held -43- a t -110* and any gas noncondensable a t th a t tençerature was con­ densed at - 196* in a gas condensing tube.

The mixture was s tirre d a t about 40* until gas evolution virtually ceased (about 4 hrs). Any gas which «as noncondensable at -110* was %ain tran sferred to a -196* tra p . The gas was shown to be ethane by vapor pressure measurements and infrared analysis. Based on the amount of ethyl bromide used in making the Grignard reagent, the yield of ethane was about 36 ^ (O.O36 moles). Ethyl bromide

(0.025 moles) was now placed in contact with the reaction mixture at room tenç>erature. No absorption of ethyl bromide took place. Transfer of the ethyl bromide into the reaction vessel and stirring at room temperature likewise produced no visible reaction. The reactor was placed at 0* and all material volatile at that

temperature was fractionated. Fractionation failed to yield any

fraction of v.p. 8-9 nmy^O* (v.p, for ethylpentaborane). A small amount of ethane was formed. Some pentaborane and most of the ethyl bromide was recovered. A ««#11 n-butyl ether fraction was returned

to the reactor. Regeneration of pentaborane was next attempted by the addition of dry gaseous hydrogen chloride. The gas was added directly from

tank and condensed in the reaction mixture. The reaction mixture was then warmed to room temperature and stirred over night. Upon

condensation with liquid nitrogen, a noncondensable gas, presumably

hydrogen, remained. It was pumped off. More hydrogen chloride was -49- addedj stirring was continued, and the noncondensable gas was punçed off again. This procedure was repeated until od more noncon­ densable gas was formed. The total amount of hydrogen chloride added was 0.0328 moles; the total amount of noncondensable gas punçed off was 0.00738 moles. Excess hydrogen chloride (0*0057 moles) was now added. Stirring for an additional 3 hours produced more noncondensable gas. Fractionation of the reaction mixture led to the recovery of 0.0017 moles HCl. No pentaborane was recovered. Only a rough fractio n atio n was made, and i t i s possible th at penta­ borane was present in trace amounts. However, formation of incon­ densable gas indicated that a decomposition reaction was taking place. A considerable amount of grayish amorphous so lid remained in the reaction vessel.

Conclusion.

The formation of ethane would indicate that the reaction pro­ ceeded according to scheme 1 rather than 2,

F, Reaction of Pentaborane-9 with Solvents The following solvents were tested for their reactivity with

pentaborane-9 under a variety of conditions: benzene, toluene, chlorobenzene, n-heptane, and methyl cyanide. Benzene and n-heptane were considered as possible solvents in the F riedel-C rafts type reactions with aluminum chloride. n-Heptane was actually used, but without significant success. Chlorobenzene

and nitrobenzene were not further pursued, because their high -50- boiling point would have made separation of low volatile fractions more d if f ic u lt.

Methyl cyanide and nitrobenzene were primarily investigated be­ cause of their possible use as ionizing solvents in reactions of pentaborane -9 with alkyl halides without catalysts. Other solvents of high dielectric constant, such as dimethyl sulfate, hydrogen cyanide were ruled out either on the basis of their physical properties and/or their reactivity. All reactions were run in the reactors described previously.

Color changes, usually beginning with a pale yellow and becoming darker as the reaction progressed were observed with all compounds

investigated. Products always included noncondensable gas (hydroge%

dark colored glassy non-volatile residues, amorphous powderlike residues (usually lighter colored), and occasionally small inter­ mediate volatile fractions,

1, Reaction with Aromatic Compounds, Experiments with benzene showed, that the amount of hydrogen as well as the amount of solid orange-brown colored materials in­

creased with increasing reaction time. The brown solid from this reaction was readily soluble in methanol with very little gas evo­ lution. This might indicate a conparative lack of B-H bonds. The

results of oxidative analysis of this material are given below# C ^ B B/C ra tio

44.9 46.4, 47.4 1.2/1 A Nujol mull of this solid was prepared and analysed by infrared. -51- Fig# 11, While the powdert appeared to be stable to the atmosphere, examination of the mull showed that a gas was formed very slowly.

The spectrum is quite unsatisfactory, k weak B-H band at 3#92^ and a series of weak bands in the 6 -6 . 4 5 region, possibly due to an aromatic residue, can be distinguished. Run ^ B 3-IOO gave a con­ siderable amount of orange colored, non-volatile solid.

Runs 68 with benzene, toluene, and chlorobenzene were compari­ son runs. In terms of noncondensable gas and non-volatile solid formed the reactivity decreased in the order: chlorobenzene > toluene > benzene. At the end of the runs, the chlorobenzene reaction was dark wine red in color, the toluene reaction was reddish-brown colored, wtiile the benzene reaction was orange-yellow. Nitrobenzene and pentaborane-9 showed no visible reaction for 4 hours at room tençerature. Over a period of one day, only a small amount of solid formed. However, heating for 2 hours at 80* pro­ duced a large amount of gel-like, yellow solid, as well as yellow powdery material in small quantities, 2. Reaction with Methyl Cyanide,

A blank run with anhydrous aluminum chloride and methyl cyanide gave no visible reaction at room temperature nor upon repeated

heating in a test tube. Known amounts of pentaborane-9 and methyl cyanide were sealed in a reactor. After a few hours at room temperature a yellow solid

deposited on the walls of the reactor, 14ore solid formed until the reaction was discontinued after 24 hours by freezing the contents Figure 11 Infrared Spectrum of Solid Reaction Product

100

O 8 C - z < *- 60 - <%I »-(T 40 z wO Ul(T a

WAVE length in microns -5 3 - of the reactor. After the volatile contents of the reactor had been removed, a pale yellow powder remained. The powder ehowdd no visible reaction upon eoqwsure to the atmosphere for several hours. However, there were also trace amounts of a glassy yellow solid. A n u jo l mull of thp powder was examined by in frared , Fig. 12; the

4.43-4*47/^ region for -C=N is absent. However, the band at 6«22yw.

•* ; can be assigned to the -C"N- or «C-N-Csgrouping.

Sandies of the powder were oxidized with fuming nitric acid in the following fashion: with a narrow spatula part of the powder was scraped into a small dry, weighed glass vial. The vial was then weighed again and loosely stoppered with glass wool. The vial was dropped into a 1-liter Ng-filled reactor containing 2 ml fuming nitric acid (frozen out). The ball joint with constriction and side arm was sealed onto the flask. The oxidation was carried out at 220" for 8-10 days. The results are listed belowt

^ 0 ^ B % /s * ra tio

(1) 20.7 19.7 1.14/1 (2) 24.9 19.3 .86/1 (3) 25.0 — — This points towards a It 1 B to G polymer, which is difficult to p ic tu re . Fractionation of the volatile constituents yielded tensio-

metrically pure methyl cyanide and pentaborane-9. Figure 12 Infrared Spectrum of Solid Reaction Product

ICO

ÜJ O 80 z >-2 60

z 40 tuo t r ÜJ Û. 20

WAVE length in microns

I rVJX -5 5 - 3« Reaction with n-heptane.

Although n-heptane had been used as a solvent in the reaction of pentaborane -9 with methylene chloride catalyzed by anhydrous aluminum chloride, incomplete recovery of the n-heptane had shown that it reacted with the other components of the system.

A blank run between n-heptane and anhydrous aluminum chloride at room temperature for several days led to the formation of gas noncondensable (probably methane) at - 196" as well as dark brown polymeric material. IVhen fresh aluminum chloride was added, further reaction took place.

From Table V it can be seen that the reaction between penta­ borane-9 and n-heptane led to a small amount of decon^x>sition. Fractionation of the volatile mixture gave no evidence of a product having a vapor pressure below that of n-heptane. Only a AmalT amount of vAiite decomposition product was present.

Infrared spectra. Fig. I 3, taken on recovered fractions (solid lines chiefly pentaborane- 9) #ave no evidence of B-C bond

formation. The presence of a small amount of pentaborane-9 in the n-heptane fraction is evident. However, characteristic n-heptane

peaks a t 2. 3, 6 * 3# , 10. 8 , 13* 1 , and 13*8$ are absent (dotted line). That may have been due to the low concentration of saaple in the gas cell. The experiments with solvents are summarized in Table V. Table V

Beactions of Pentaborane-9 with Solvents

Ban No* and Notebook Solvent, B5H,, C atalyst, Time, Teqp. page Solvent nmoles nmoles nmoles hrs 0*

4> Bj—62 63.4 65.3 ------20 150»

^83-63 ( p s 71.9 75.2 ------7 150" 68 I9.Ô ------150" 16.4 4 vi, O'I 68 20.2 18.2 ------4 150"

68 < t > d I9.Ô 1 7.1 ““ 4 150*

<}> B3—100 4 > u 48.5 46.0 AICI3, 8.3 62 25-35° 1^-119 MaCN 196.0 55.5 24 25" 149 n^hQitane 6 .2 7.7 25.6 80-83°

n -4 1 <^NÛ2 21.0 27.5 —— 2 80°

(continued on next page) Table V (continued)

Reactants Used i » Used Noncon- Solid, Size densable Colored Reactor, BgH,, Solvent, B5H9, Solvent, gas, M aterial L ite r maoles m o les mole mole % nmoles g others

.5 6 2.5 3.4 3.8 5.4 10.0 .1200(min) ----- .5 6 — ----- 2.95^ of total wt. 1.9 ------.18 —— . 30^ of total wt. .15 .0090 None .18 ---- 1.1 .8%G of total wt. .59 .0226 None * I .18 1.0 .6 5.75 3.0 .81 .0445 None VJT Y . 125*^ — — 9.43 56 of total wt. 2.4 ----- HCl, trace

.56 Ô.3 28.8 14.95 14.7 .13 .7 ii) None .18 .l(m in) a8 (max) 1.3 13.0 .0 4 -----

.18 12.0 ----- 43.5 ----- 1.6 ----- ——

x) 125 ml Erlenmeyer flask Figure 13 Infrared Spectra of MLjcture

100

S 80 z ; Î GO t-I 40 w tro aUJ

WAVE l e n g t h in m i c r o n s

? -59- * .f Gr* Reaction of Pentaborane-9 with Some Pol^halogenated ^ydrooarbone 1. Introduction;

Since reaction of pentaborane-9 with monoaiUcyl halides in the presence of anhydrous aluminum chloride led to the formation of monoalkyl derivatives of pentaborane-9^^ it was of interest to investigate the reactions of polyhalogenated hydrocarbons under similar conditions* These reactions could lead conceivably to sub­ stitution of more than one halogen by the BgHg-radical and the re­ sulting products would have a relatively high boron to carbon ratio# In the course of this investigation, dichloromethane was found to be more reactive than dibromomethane. In order to gain some possible insight into the reactions and intermediate products, the

reactions with bromochloromethane and other "mixed" halogenated

hydrocarbons were studied* The reactions with chloroform and carbon tetrachloride appeared to be more complex than those with the dihalides. Decomposition, substitution, reduction, and dispropor­ tionation reactions were taking place. The complexity of the

reaction mixtures made separation a major problem in this work* From an inspection of Figure 14* >diich shows the vapor pressure curves of pentaborane-9 and the pure polyhalides, it can be seen

that separation of a two-component mixture consisting only of penta- borane-9 and a polyhalide is not readily accomplished* Pentaborane^ and chloroform and bromochloromethane, respectively, could not be

separated by fractional evaporations and condensations. With the “ 60 -

Figure 14 Vapor Pressures of Reactants 000

100

mm. Hg

2 0 " -334" -78.5 2.5 30 3.5 4.5 - 6 1 - other polyhalides, it was usually possible to obtain upper and lower cuts consisting of pure pentaborane-9 and pure polyhalide (vice versa in the case of dichloromethane). But a smAil inter­ mediate fraction was usually present; this fraction was the larger the closer the vapor pressures of pentaborane-9 and the polyhalide. 2* Reaction and Separation of the Reaction Mixture The procedure followed here was essentially that outlined under the 1-butene reaction.

After the reactor had been tested for leaks and degassed, it was filled with dry nitrogen, stoppered, and weighed. The Erlen­ meyer flask containing the resublimed aluminum chloride was then attached to the flask, and some aluminum chloride was poured into the cold finger of the flask. The flask was then reweighed and evacuated. Pentaborane-9 and the polyhalides were weighed as

liq u id s and added by vacuum tra n sfe r. After conqplete condensation, the reactor was sealed and allowed to reach room tençerature. Host reactions were run in the Fisher-Isotemp drying oven mentioned

previously. The progress of the reactions could be followed by observing the color changes of the liquid phase, which was always present. In

the beginning, a considerable amount of frothing and foaming usually took place. This subsided as the reaction proceeded, at the same time the solution turned from colorless to various shades of yellow,

and sometimes orange or orange-brown. However, following the reaction by visual inspection is probably inadvisable, as in at - 62 - least one Instance the oven vas coigiletely destroyed by a violent explosion. At the completion of a run, the reactor was removed from the oven. The contents were condensed with liquid nitrogen*

Since large amounts of noncondensable gas were produced in these rea ctio n s, the reactors were opened to a calibrated volume, so th a t the amount of noncondensable gas could be estimated. The reactor was then warmed slowly to room temperature and all volatile com­ ponents were tran sferred. After the higher v o la tile components had been removed, a - 36 * trap was inserted; this trapped most of the low volatile constituents. The yellow-colored viscous liquid remaining

in the reactor usually had higher volatile constituents dissolved in

it. Therefore, transfer was normally continued for several hours and sometimes overnight. A practice employed in the beginning,

namely warming the reactor to 4O-5O*, introduced fractions into the vacuum system vdiich vrere d iffic u lt or impossible to remove later* This practice was therefore abandoned.

The transfer was discontinued when no more ready condensation took place upon changing the - 36 * bath to a -196* bath. The rea cto r was f ille d with dry nitrogen and removed from the tube opener* The contents were dissolved in dry methylene chloride. The work up of the resulting solution is described later. The separation - at least partially - of the volatile reaction conpon- ents was accomplished by a series of fractional evaporations and

condensations* Fractionation was usually accompanied by a certain -63“ •* « amount of decon^sition and dii^roportionation, at least in part due to reaction with stopcock grease, which led to the formation of more noncondensable gas and grayish-white amorphous so lids. The la tte r were nonvolatile and could only be removed by cleaning the trap with a mixture of methanol and tetrahydrofuran. The low volatile fractions, those held in the - 36 * bath, decomposed slowly giving off gas and viscous, yellow colored liquids which could not be handled any further in the high vacuum system. Due to the multiplicity of consonants present, repetitions of one or more series of cooling baths at varying time intervals were much more common than for the olefin reaction. Fractionation was continued to a point where vapor pressure measurements showed a fraction to be substantially pure. However, vapor pressure was found to be a poor c rite rio n of pu rity indeed. The following exanq>le will illustrate this point: fractionation yielded a liquid fraction which had a vapor pressure of 137 mm at 0* (methylene chloride). Doubling the volume above the liquid and splitting the fraction into two parts produced no measurable change in vapor pressure. However, addition of methanol

produced hydrogen, which indicated the presence of a B-H containing

impurity. Though this ingiurity was present in small amounts only, this behavior further showed that quantitative separation by

fra c tio n a l condensation was impossible. When reasonably pure fractions had been obtained their amounts

were determined. Gaseous fractions were measured volumetrically “ 6 4 “ and destroyed by reaction with a water-methanol mixture contained in a tube which was attached to the manifold. Sometimes infrared spectra were taken on the gases. These gases were then reacted with water and the resulting solutions were titrated for hydrochloric and boric add. All fractions that were liquid at room temperature were transferred to small storage tubes and weighed as liquids. It was found advantageous to transfer material of low volatility (3 mm at room temperature or less) to a small tube made by attaching a 1 lS/9 ball joint to a piece of 10 mm glass closed end tubing (6-10 cm long). After complete transfer, the tube was filled with dry nitro­ gen, capped, and clançed. The reason for using these tubes was that transfer through small bore stopcocks was always slow and sometimes accompanied by decomposition. In this way the number of stopcocks through which the vapors had to pass was minimized.

The dichloromethane solution of the non-volatile residue was worked up in the following way: The neck of the reactor was in­ serted into one lower sleeve of the nitrogen-flushed polyethylene bag. Into the other lower opening was inserted a small distillation flask (1 18/9) containing a boiling chip and a funnel. The upper sleeve held a hypodermic syringe filled with dichloromethane. The reactor was then inverted and the solution poured through the funnel

into the distillation flask. Several small portions of solvent were injected into the reactor and the washings added to the flask.

The flask was stoppered tig h tly . I t was next removed from the bag and attached to a series (2 to 4) of small U-traps, These were -65“ constructed from 8 mm tubing (Pyrex) and were connected by means of 1 18/9 ball joints (Fig, I 5), On one end was attached the fla sk containing the mixture of products, while the other end was directly attached to the vacuum line. The solvent was removed slowly to avoid heavy foaming. Suitable cooling baths were placed around the U -traps and the contents of the flask were slowly warmed. All material passing through a -78* trap was discarded. The temperature of the flask was raised very slowly with an elec trie ally-heated oil bath. Slow heating was important. I t should be remembered th at the aluminum chloride was s t i l l present in th is mixture and reacted slowly with the compounds in the flask. (No suitable solvent could be found that permitted separation of the aluminum chloride from the viscous material without extensive decomposition.) This reaction was slow below 70*. However, above this temperature prolonged heating usually produced a darkening in color of the flask contents and the pressure of noncondensable gas (at -I 96*) rose noticeably, When the flask was heated above 70* the stopcock to the punç) was u su ally kept open and the gas formed was punned out continuously

through a -I 96* trap. Heating was discontinued when formation of noncondensable gas became more noticeable or when aluminum chloride was sublimed from the flask. These distillations were commonly

conducted over a period from 3-8 hours. Each trap was usually held a t 2-4 d iffe re n t temperatures sta rtin g with a low temperature and

then progressively warmer baths. The d is tilla tio n was followed closely by visual inspection. Over the final hour of distillation Figure 15 U-Trap D istillation

Te high vacuum pump

2 - 4 traps manifold f r in series /C I O' /C O' I I a 8 - 1 0 cm m »

f ÿ bail joints "67~ the relative amounts of material in each trap were constant, as far as one could Judge from observation* The stillpot was cooled and dry nitrogen was admitted. The traps were disconnected, stoppered tightly, and stored in the deep freeze until the contents were ready for sampling. Two other types of reactor vessels, (Figure 3, Designs B & C) were tried in some reactions. The main objective was to be able to stir the mixture magnetically. The sealed reactor did not permit reaction over extended periods of time due to the formation of gaseous decomposition products once the reaction had started, A high temperature could not be attained since the constant reflux occurred on the cold walls of the reactor.

In one run the side arm of the reactor was connected through a mercury bubbler to a trap. As the pressure inside the reactor rose, it was counterbalanced by dry nitrogen admitted from a balloon. Pressure in excess over atmospheric was bubbled through the mercury valve into the -78* trap which was open to the atmos­ phere, The reaction mixture was heated at an oil bath tenqperature

o f 70-76* fo r 6,5 hours. However, only a trace amount of product was obtained.

Success in using an Erlenmeyer flask equipped with reflux con­ denser and magnetic stirrer was not much greater. The reaction mix­ ture (with and without solvents) was heated so that rapid reflux

took place in the lower part of the condenser. Pressure in excess of atmospheric was vented into a large evacuated volume. Again, —68— however, only trace amounts of product were formed. A thermometer suspended in the neck of the condenser showed that the highest

reflux temperature obtained was about 60* (run involving penta- borane-9, methylene dibromide, and aluminum chloride).

3* Analysis

(l) Oxidations Oxidation of the products from these reactions was carried out

in essentially the same fashion as described under the 1-butene . reaction. However, the sampling procedure was different. Crystal­ line products such as 1,1'-dipentaborylmethane were transferred in a set-up as shown in Fig# 16. This procedure eliminated contact with

stopcock grease and slow transfer through small bore stopcock# If the crystals were obtained in one of the U-traps from distil­ lation as described on page 6^ the following procedure was used# The glass tubing was scored above and below the section of the trap where the crystals were held. The trap was then placed inside the poly­ ethylene bag# The tubing was broken at the two scored marks. The crystals were pushed with a narrow spatula into a weighed receiver#

These crystals were then purified further by either recrystalliza­ tion or sublimation, or part of the saoqple was transferred directly for analysis as shown in Fig. l6# Liquid fractions obtained in the U-traps were sampled as follows: the long vertical arm of the U-trs^

was inserted into one of the lower sleeves of the polyethylene bag#

Into the other lower sleeve a small weighed and dried vial was To manifold

coolant well

fr Througti U-trap I I to tiigtiI vacuum O' f-!| joints ? I line

Transfer Arrangement Sublimator -70- In se rte d . A hypodermic syringe vdth a needle long enough to reach the bottom of the trap vas clanged into one of the upper sleeves. A positive nitrogen pressure vas maintained. All or part of the liq u id sample was withdrawn and injected into the v ia l which was stoppered before removal from the sleeve (corks wrapped tightly in aluminum foil were found to be least subject to changes in weight).

After the sample had been weighed the vial was again inserted into the polyethylene bag. The reaction flask was thoroughly flushed with nitrogen and a measured amount of fuming nitric acid was frozen out at -76*. The reactor flask, which was equipped with a neck piece of

20 mm open end tubing (5-10 cm long) was then inserted into the other sleeve. The stopper was removed from the vial and a piece of glass wool held inside a piece of glass tubing was pushed into its place. The vial was then dropped slowly through the neck of the reactor onto the frozen nitric acid, \M le the reactor was held at an angle. After insuring th at the glass wool plug was held in place only loosely, the piece consisting of sidearm with breakoff tip, seal-off constriction, and f 16/9 inner ball joint was sealed into place. The reactor was evacuated, tested fo r leaks, and sealed. I f the glass wool plug was too tightly in place, warm-up usually produced an explosion which destroyed sample and reactor. Otherwise, the plug was simply blown o u t and the sanple could read ily "mix" with the n itr ic acid.

Carbon dioxide and boric acid were determined as described previously. In the titration of boric acid, the glass wool was washed into the beaker so as to insure complete solution of the -71- sample.

(2) Hydrolysis The sampling procedure was the same as used above. The samples were worked up as described previously.

(3) Chlorine-determination Various methods were tried to determine chlorine both by oxi­ dation and by hydrolysis. Any strong acid formed in the hydrolysis was titrated as hydrochloric acid. However, this could not account for chlorine bound to carbon, as was shown by blank runs with methylene chloride and chloroform.

Chlorine from oxidations appeared to be in the form of chlorine gas or hydrochloric acid. The evidence for the presence of chlorine gas was the fact that the gases from oxidation reacted with the mercury in the manometer before passage through the hot copper mesh tube. Since part of the chlorine was apparently lost in this fashion, gravimetric determination the remainder usually gave low results. Addition of silver nitrate crystals to the reaction mix­ ture led to extensive reduction to silver by the boron hydride part of the molecule. Reoxidation was incomplete. Thus, any figures given for per cent chlorine must at best be considered low, at worst worthless. 4 . Pentaborane-9 with Methylene Chloride, Methylene Bromide, and Bromoc hloromethane The - 36 * trap from the fractionation of the reaction mixtures usually contained a liquid-crystalline mixture of vapor pressure less -7 2 - than 0.$ mm at room ten^erature. The crystals were soluble in the liquid» Complete separation of this mixture by vacuum train fractionation could not be effected. A partial separation was ob­ tained by holding the liquid in the bottom of the trap at -20" to - 30® and connecting to a - I 96® receiver. This usually gave a small amount of pure c ry sta ls in the receiver. On standing a t room temperature, the liquid-crystalline mixture showed a slow increase in pressure. The gas formed was noncondensable at -78.$", but com­ pletely condensable at -I 96". It was shown to be hydrogen chloride by infrared analy sis. (However, titr a tio n showed the presence of

0*3 nmoles of boron in a 1.93 nmole sanple of this gas.) Passage of the mixture through a stopcock or other greased connection was always accompanied by frothing and formation of gas, condensable only at -196". However, crystals completely free of liquid trans­ ferred without deconqjosition. It was found advantageous to transfer the mixture out of the fractionation train into the distillation flask that contained the diehloromethane solution of the non-volatile mixture. By a U-trap distillation as desczdbed on page 6$ crystals which contained only trac e anx)unts of liq u id im purities were usually obtained. To remove th ese trace amounts of liquid the c ry sta ls were sublimed in the apparatus shown in Fig. 17, In a polyethylene bag flushed with dry nitrogen the crystals

were scraped into the sublimator which had been cleaned and dried -7 3 - c arefully. The collector tip which was constructed from a 1 24/40 drip tip was put into place. The system was then evacuated. An ice- salt mixture was used as coolant, while the sanQ)le was kept at room tenç)erature. If the temperature differential was too great, liquid also collected on the drip tip. The sublimation was continued until only a liquid residue remained. The system was then filled again with nitrogen and returned to the polyethylene bag, with the coolant well protruding through one sleeve. The coolant well was removed from the outer jo in t and brought into position above a weighed v ia l or storage tube containing a funnel. Hot water was poured into the coolant well. This dropped the crystals onto the funnel from which they were scraped into the receiver. Crystals of 1,1’-dipentaboryl­ methane prepared in this fashion gave a melting range of less than one degree and good analytical results. A melting point was taken ly

drawing one end of a piece of 3 mm tubing into a capilleury. The tubing was evacuated and filled with dry nitrogen. A sançle was

placed into the capillary in the polyethylene bag. The capillary was then sealed and the melting point determined,

a. Methylene chloride! The reaction of pentaborane-9 with methylene chloride pro­ duced hydrogen, hydrogen chloride, diborane, borontrichloride,

1,1’-dipentaborylmethane, and 1-pentaboryl boron'dichloromethane, BgHsCHgBClg. Inconclusive evidence also indicated the formation of

methane, methyldlohloroborane, and msthylpentaborane. The noncon­ densable gas was assumed to be hydrogen. Gas th a t passed through a -7 4 - -142* trap was taken as hydrogen chloride and diborane. The acids

resulting from hydrolysis were titrated. Titration of the hydrolysis product from the "BCl)" fraction usually gave a BiC ratio of 2-2,5 t

1, This could possibly be eixplained by assuming the presence of methyldichloroborane in the sançle. Yellow non-volatile tars were produced from all these reactions. The amount obtained in run 15- 104 (see Table VI) was slightly less than that usually designated as "large". This might have been due to the fact that the reaction was run in n-heptane. Usually, 15-20 ml of solvent were employed.

However, in run 15-104 11.9^ of n-heptane entered into the reaction in some way. Furthermore, separation of the reaction mixture became much more difficult. Mass spectrographic evidence indicated that n- heptane gave rise to higher hydrocarbon fractions, which contaminated the product, l,l* 7dipentaborylmethane.

Carbon disulfide was used in several runs (in apparatus as

shown in Fig. 3» design Q.) at generally lower tençeratures than those indicated in the table. Carbon disulfide also entered into the reaction; and while the yield of crystalline product was not signifi­ cantly increased, the separation problem became more complex.

The re s u lts from these reactions are summarized in Table VI.

b. Identification of 1.1’-dipentaborylmethane (l) Oxidation and hydrolysis gave the following results;

^ B ^ C i» Hydrolyzable H B/C Ratio

Theory 76.2 8.7 11.56 lO/l Hydrolysis 73*6 — 11.2 ---- Oxidation 77.5 6.5 — 10.1/1 Table 71 Reaction of Pentaborane-9 with Methylene Halides Volume Reactants, nmoles Reactor Time Tenp. No, B5H9 H a lid e G a ta ly s t S o lv e n t 1 h rs. »G CHgClg 1-46 76.0 3 5 .0 A lC l3 , 3 .0 ----- 1.06 4.25 100 2 - 5 0 4 9 .3 4 9 .0 ZnCl2 , 7 . 4 1.06 80 100 3 - 6 3 7 9 .4 3 9 .7 A lG l3 , 3 .7 n -h e p ta n e .56 3.15 85-92 1 4 * ^ 0 2 6 0 .5 7 1 .7 A lC l3 , 4 .5 . — .125 12 25 1 5 -1 0 4 69.9 2 6 .6 A lG l3 , 3 .7 n -h e p ta n e .56 6 78 34- 1 9 Ô 5 0 .9 3 6 .3 A lG l3 , 2 .2 .56 7 68-72 68-72 3 5 ^ 9 0 6 4 .4 2 6 .5 A1 0 l 3 , 4 . 3 — .56 5 5 - 7 Ô 1 1 3 .8 5 4 .8 A1BT3, 1 .8 n -h e p ta n e 1.06 2.5 80-85 \J% 5 0 - 4 1 6 1 .4 2 8 .7 BF3 , 5 .7 1.06 8 70-75 I ÔO.O 5 6 .1 A lC l3 , 3 .5 .56 3 70-75 5 4 - 5 1 100 4 - 6 9 3 1 .6 1 5 .7 — .31 5 ----- 68-72 GHgBrCl 3 6 ^ 1 9 9 8 3 .3 3 1 .2 A lG l3 , 2 .9 .56 7 8 1 .8 2 5 .6 A lC l3 , 3 .9 —- .56 10 75 4 0 - 1 9 6 4 1 -1 9 9 3 .0 2 7 .8 A lC l3 , 4 .5 — .56 75

GHgBrg 1 9 -1 2 1 9 1 .2 1 7 .7 AlGl3,3.0 — .15 5.5 50 2 0 -1 2 3 1 2 1 .0 3 6 .3 A lC l3 , 4 . 2 — ■ .56 4 75 Table VI (continued)

Products. nsnoles Bun No. Ha HI B2H6 BCI3 B5 HgCH2BCl2 (B5Hg)2CH2 CH2CI2 1—46 37.6 ___ N.D. none treice 2-50 23.3 2 J» • 0 7 - N.D. 3-^3 42.0 5 . 4 .1 1 1 0 .5 14r

x) contaminated with liquid Table VI (continued) Reactant 3 used Mol 9^ used --- Run No. ^ yield S& eonv. Tars B5H9 Halide B5H9 Halide CHzGlg 1—46 large 27.0 N.D. 35.5 2-.5O large 13.3 N.D. 27.0 87.2 3 ^ 3 3,1 1.2 large 32.0 34.6 40.3 1 4 ^ 2 1.6 small 11.156 - reaction 15-104 24,4 10.2 2.6 g 29.6 NJ1.T 4 2.3 34J.98 1 78.0 21.0 22^6 - reaction 35^98 J f 6.3 3.8 3-78 1.4 some N.D. N.D. 50-41 trace 1.4 .9 2.3 •3J. 54-51 4.0 f a ir N.D. N.D. 4-69 trace 1.8^ - reactio n I CHgBrCl 36^199 — — w. some N.D. N.D. — — f ^ a lr 1 40-19 1 2d.'d‘>) N.D. N.D. - 2 7 ^ - reaction 41-19 J 1 more than* in 40-19

CHgBPg 19-121 — fiBTlAll 13.556 - reaction 2.8 25.6 20-123 1 g 3 ^ 9.3

o) estimated -7 8 - This leads to a formula ** 15,6 No strong acid was present in the hydarolysis mixture and the silver nitrate test for chlorine was negative, A positive Schiff's test f o r formaldehyde was obtained on the hydrolysis mixture, compared to a blank,

(2) Infrared Analysis

Comparison of the spectra of 1-methylpentaborane and 1,1'- dipentaborylmethane (Figs. 1? and 18) shows the two to be similar in many respects. This is not unexpected. The spectra of toluene and diphenylmethane, for example, are almost identical, except that in the latter absorption is somewhat stronger and several weak peaks can be identified. The same can be said for the two substituted penta- boranes. The double peak at $,$ is assigned to apical substitution.

For 1,1 '-dipentaborylmethane, the peaks at 7«9, 8,8, 13,7, and 14#35/»- are due to the liquid inpurities present in the sample which is probably BgHgCH^BClg and a low volatile hydrocarbon. The band at

13»7 /t. i s due to C-Cl absorption. The infrared spectrum of 1,1 '-dipentaborylmethane was also run in dichloromethane solution. However, imperfect matching of the cells produced strong solvent bands at 8,0yU. and 13,2-14,2/*-, The

B-C absorption has been variously assigned to the 7*6/*^ region for

aIkyldiboranes and to 8,25 for alkylpentaborane^.

Therefore, the peak appearing at 8,0-8,l /*- for both 1-methyl-

pentaborane and 1,1'-dipentaborylmethane is assigned tentatively to

the B-C bond. Figure 18 Infrared Spectrum of l-Methylpentaborane-9

100

g Ia K wZ w

WAVE l e n g t h in m i c r o n s Figure 19 Vapor Pressure of 1 ,1 '-Dipentaborylmethane

DO

60

2 0

WAVE LENGTH IN MICRONS -81- (3) Molecular Weight

The molecular weight of the compound was determined by two methods*

(a) by use of the vapor tension apparatus used for the molecular weight determination of 2-butylpenta-

borane-9, (b) by freezing point depression. Method (a) gave unsatisfactory results} the sample proved to be thermally unstable. However, inspection of Fig, 20 showed that be­ tween a pressure of 30-40 mm the pressure-tenperature relationship followed a straight line. If it is assumed that all the sanple was vaporized before decomposition set in, the molecular weight over th a t range calculates to 144» as compared to the th eo retical value o f 138.2.

The decomposition of th is sample (O.OI 36 g) gave ris e to non­ condensable gas, 0.0066 g clear liquid, and a yellow non-volatile solid. No crystals remained.

(b) Molecular weight determination by freezing point depression

proved fairly successful. Cyclohexane was used as a solvent, A nitrogen atmosphere was maintained above the liq u id lev el. The

value obtained for the molecular weight was 139* (4) Mass spectrometric analysis of the liquid-crystalline mix­ tu re showed th at one constituent of the sample was l,l'- d ip e n ta -

22 ' borylmethane .

22, J, Norman, Olin-Mathieson Chemical Corporation, Niagara Falls, New York, Private Conmmication. - 8 2 -

Figure 20

Vapor Pressure of 1 ,1 ’-Dipentaborylmethane 100

90

60

70

60

50

40 Pmm P «36 mm,

30

2 0 -

22 2.3 2.4 2.5 26 2.7 2.8 -33" Physical Properties:

The melting point of the conçxjxind was determined as 52-53* in a thick-walled tube, and 50»Ô-51»Ô* in a thin-walled capillary tube. The thermal instability of the product has been mentioned above.

Exposure to the atmosphere caused the crystals to fume; a white coating was developed rapidly. Occasionally, a sample ignited spontaneously. (This is believed to be due to liquid inpurities,) However, on long standing the samples decomposed even under vacuum, as shown by the formation of gas and of a w hite, amorphous, non-volatile solid. This solid was fluffy in appearance and ex­ trem ely lig h t. Analysis by oxidation gave 43*7# C and 35*3# B. The reliability of these values is questionable, but they do point to a 111 boron to carbon ratio. Gas formation upon the addition of water or methanol indicated the presence of B-H bonds. Perhaps the pro­ duct contained units of the type - CHj-BH - (46.5# C, 41*8# B), 1,1'-dipentaborylmethane was tested for its solubility in the following solvent; methylene chloride - very soluble chloroform - quite soluble carbon disulfide, cyclohexane - soluble

petroleum ether, skellysolve, benzene - slightly soluble e . Summary

The analytical data of the product as well as the probable mode of its formation (see under discussion) leave no doubt that the -84- compound is 1,1'-dipentaborylmethane, i.e. two apical boron atoms are substituted. Although 1,2-dipentaborylmethane cannot be ruled out absolutely, the probable mechanism as well as the infrared evi­ dence do not favor it. d. Identification of 1-pentaboryl borondichloromthane The id e n tific a tio n of th is product is based chiefly on mass spectrographic evidence and comparison with a similar product ob­ tained from the reaction of pentaborane-9 with chloroform. Conqpared to 1,1'-dipentaborylmethane, this product was usually formed in equal or larger amounts, (1) Analysis Oxidation gave the following results:

^ B < f,G 5&C1

Theory for BgHaCHgBCla 41.1 7.5 45.1 Actual 43.3 7.5 37.0 The high boron percentage is probably due to contamination with 1 ,1 '-dipentaborylmethane, while the low chlorine percentage is due to the same reason as well as for reasons mentioned previously. (2) Infrared analysis; The infrared analysis on a sample from th is reaction was in­ conclusive. The sasq>le appeared to be quite contaminated.

(3) Mass spectrographic analysis of the liquid - crystalline mix­ ture showed that the liquid portion of the product was 1-pentaboryl borondichloromethane. “85“ (4) A molecular weight determination by freezing point depression using cyclohexane as solvent gave a value of 16?> as conçared to the theoretical value of I 58.O. A small amount of decomposition took place.

Physical Properties; The compound was quite unstable; it burned with a pale blue- green flame on exposure to a ir . Sometimes combustion was spontanS“ ous. On standing, the compound slowly decomposed giving off gases and leaving grayish“\diite deposits, e. Chlorobromomethane i The reaction of pentaborane-9 with chlorobromomethane produced hydrogen, hydrogen chloride (probably hydrogen bromide, though not

identified), diborane, borontrichloride, 1,1'-dipentaborylmethane,

and 1-pentaboryl borondichloromethane. A fraction having a vapor

pressure of 35 m i / O * was probably raothylpentaborane, although the infrared did not show a pronounced double peak at 5. 5/*-. This com­ pound was formed in 6^ conversion, based on the total charge of

pent aborane. There was also a fraction having a v.p. 11 ntn/O^ which was only identified by infrared (Fig. 21). Some typical runs are listed in Table VI.

Identification of Products; 1,1'-dipentaborylmethane was identified by its behavior which was analogous to the product from the methylene chloride reaction,

as well as by melting point and analysis. The purified crystals melted at 50.6-51.8". Results from analysis are listed below; Figure 21 Infrared Spectrum of Fraction (v.p. 11 mm/0“)

Î

àI “Ô7“

B ^ C % hydrolyzable H B/C ratio Theory 70.2 8.7 11. $6 lO/l Hydrolysis 78.1 — 11.65

Oxidation 77.0 9.1 — 9.4/1 f . Methylene dibromides

Under the conditions tried (Table VI) only a gmflll amount of reaction took place and none of the volatile products from the reaction except hydrogen and hydrogen chloride were identified. Only small amounts of crystalline product as well as liquid were produced. The crystalline product had a melting point of 50-52® and its behavior suggested that this material was identical to the product previously described. Not enough material for analysis could be purified. g . SunmaryS

1,1 ' -dipentaborylmethane and 1-pentaboryl^ borondic hloromethane have been identified as products from the reaction of pentaborane with methylene halides. Both compounds were formed in low yields, 1-pentaborylx borondichloromethane generally in larger amounts than

1,1'-dipentaborylmethane. Deconpositlon appeared to be the major reaction. Too high a temperature produced only non-volatile tars. Borontrifluoride and zinc chloride were ineffective as catalysts, although the latter produced a trace of product. Aluminum bromide also served as catalyst. Solvents did not increase the yield of "Ô8“ the desired product, 1,1*-dipentaborylmethane, significantly, but increased the complexity of the reaction system and made separation more d if f ic u lt.

5 • Reaction of Pentaborane-9 with Chloroform. This reaction was of great conç)lexity. Considerable decompo­ sition took place. During fractionation of the volatile products, disproportionation occurred. Due to their closeness in vapor pres­ sure, i t was inç)08sible to separate chloroform and pentaborane by fractionation, and the two were usually recovered together. The following volatile products were obtained from the reaction* hydrogen, hydrogen chloride, diborane, chlorodiborane, boron tri­ chloride, methylpentaborane, and an unidentified liquid fraction of vapor pressure 3 mny^lO". In addition, there were always small amounts of injure fractions which resisted further purification. The volatile products were mainly identified by infrared analysis. The gas passing through a -142* trap was shown to be diborane. Ifydroly«lr sis showed the presence of a strong acid. i(ydrogen chloride was the

only other compound th a t would conceivably pass through a -142*

trap. The presence of chlorodiborane was inferred from inspection

of the infrared spectra of fractions consisting chiefly of boron trichloride. The spectra were conqpared to authentic spectra of diborane, boron trichloride, as well as a 5*2 molar mixture of di­

borane to boron trichloride. The double peaks at 9#0$ and 9*1$A

and at 11.1 and 11.3 appearing in that mixture have been assigned -89- to chlorodiborane^^. Furthermore, there was infrared evidence for

23* Dorothy Bobbins, Olin-Kathieson Chemical Corporation, Niagara F a lls, New York, Private Communication* the presence of methyldichloroborane, methylene chloride, methyl

chloride, and chloromethyldichloroborane. Methane and trim ethyl- borane could not be found, but were perhaps foimnd in trace amounts* Methylpentaborane was identified by its vapor pressure and conçari- son of the infrared spectrum with an authentic sançle. It was also sliown by infrared analysis that the so-called non­ condensable was not hydrogen alone. Although the contents of the reacto r were condensed for some time a t -19&* and then punped

slowly through another -196* trap, the exit gases still contained

diborane and possibly methane* Some ty p ical runs are summarized in Table No. VII. Only the predominant products have been shown. The per cent of reaction is

based on the total amount of pentaborane-9 and chloroform recovered as compared to the to ta l amount of reactants charged. The yield s ih

millimoles are only approximate, since separation was usually not complete. The non-volatile fractions were separated from the yellow

polymeric product by two methods* m icro d istillatio n and U-trap

distillation, both described previously* In the microdistillation, after removal of solvent distillation usually occurred in the 80-90*/l mm region and yielded a Table VII Reaction of Pentaborane-9 with Ghlorofom ^ Reaction Reactants, nmoles Size Time Tengp. Based Bun Bo. BjH, CHCI3 AICI3 Reactor, 1 hrs. »G on Recovery

29-lAS 24.5 7.8 ----- .18 4 .5 7 0 -7 3 4 .5

18-120 89.6 26.6 3.7 .5 6 4 68 68.8 5 days ET

22-135 78.8 24.7 3.4 .56 4 .5 7 0 -7 3 66.7

24-137 97.7 2 5 .4 7.7 .5 6 4 .3 3 70 85 I «I 2 5 - 1 3 8 77.4 2 7 .0 2 .3 .5 6 3 .7 5 7 0 -7 3 A 2 6 - 1 3 8 83.4 2 6 .1 3 .9 .5 6 3.75 7 0 -73 ) 79.6 27-146 82.0 22.9 6.1 .5 6 4.0 72 / 23-146 79.4 2 5 .8 4.2 .5 6 4.5 7 0 -7 2 Table VII (continued)

Products^ mmoles Distillation Sun No. Ha HCl BCI3 B2H5CI v.p. 3/10*0 product,g T ars,g

29-168 .29 — ----- — —--- .0333 18-120 -3 5 - . 5 2.9 some trace small .5924 3.43 22-135 35.2 - 4 3 4 1 .3847 .6620 — 3

24-137 40.0 - 4 3.5 4.5 1 .5893 1.28 - 7 25-138 — ) ] .9990 some I 26-133 56.8 ► 17 11.5 20.5 some 1.34 27-146 46.0 - . 6 larg e st from any run

28-146 34.4 1.319 — 4 Table VII (continued)

E u n No* i» Conversion to BsHeCHgBCIa Nature of Catalyst Remarks 29-Ui8 la-iao 4.0 B <& A grade, taken Cyclohexane used as directly from bottle solvent for colored residue, only partly soluble in it

22-135 4.8 B & A grade, resublimed and stored under Ng

24-137 7.7 B & A grade, resublimed D istillation product ? and stored under yellow colored

25-138 Baker Chenu Co. anh. CP 3.6 grade, resublimed from 26-138 ] thÉJgranular form. Poly­ meric reaction product . daxker than that from B&A.

27-146 4.3 Baker Chem. Co.,ground in D istillation product mortar while exposed to yellow colored atm o^here

2 8 —146 9.3 B& A grade, taken directly D istillation product from bottle yellow colored -93- crjstalU ne-llquid mbcbure» Aside from the considerable hold-up and the sensitivity of the product to atmospheric esqposures, redis­ tillation of the distillate, which was usually colorless, resulted in

further decomposition to yellow-orange polymeric product. The U-trap distillation permitted a lower temperature and less san^>le was lost.

However, a ll the y ield s lis te d in Table VII under the heading

”distillation product” are to be considered minimum yields. These products could be divided into three classes*

1. Liquids at 0® and at room tençserature. 2. Crystalline solids, melting point between 22® and 32®.

3. Crystalline solids, melting point 45* and above. An infrared (Fig. 22) and elemental analysis on the liquid crystalline mixture from run 18-120 gave the results shown in Fig. 22 and below, respectively*

9&B C 95 Cl J5H

Oxidation $2.6 4*7 — — Hydrolysis 51*1 — 25.8 7*4 By mass spectroscopic investigation it was shown that the mixture

consisted chiefly of 1,1'-dipentaborylmethane and 1-pentaborylboron- d ichloromethane^.

The crystalline solid which melted above 45* was also shown to be 1,1'-dipentaborylmethane.

I t was observed th a t the c ry stallin e solids vdiich melted between

22- 32* were formed in variable amounts. One sangle melted at 22-24* Figure 22 Infrared Spectrum of Mixture from Run 18-120

oo

Ui

40 l&jz

UJ O- 2 0

WAVE l e n g t h in m ic r o n s

f -95- and gave the following analytical results; ^ B 52.5» $ C 5*78, bhlorine was also present. These percentages are in excellent agree­ ment with the th e o re tic a l values fo r a compound, BgHa-CClg-BgHg

B 52. 25, ?5 C 5 .8 ). Another sample (nup. 29.5-32®) gave; ^ B

51. 7, I 0 C 6.2. The sançle th a t was analyzed by mass spectroscopy contained only a trace amount of material in that melting range. Furthermore, that sançle was kept for some time at room temperature. If 1,1’- dipentaboryldichloromethane were actually formed, one would eoqpect it to be quite unstable; the molecule might either break apart or, because of the presence of strong reducing groups the OrGl botld might be reduced. Therefore, by the time the spectrum was taken, this compound probably was no longer present. However, in the ab­ sence of other evidence, this point remains undecided.

The liquid product behaved similarly to the product obtained from the methylene chloride reaction. The elemental analysis is listed below;

56 B G ^ H i o Cl

Theory fo r BgHgCHgBClg 41.1 7.6 5.1 45.1 Oxidation 39.0 6.3 — Oxidation 41.2 5.6(partly lost)

Hydrolysis 38.9 ——— 5.2 30.5 The agreement with the theoretical values is not very good, probably

due to the fa c t th at an aly tically impure 8ang)le8 were analyzed. The infrared spectrum is shown in Fig. 23. An apically substituted Figure 23 Infrared Spectrum of 1-Pentaborylborondichloromethane

IS PB iBBL.» 1B Ei.irsBÆ.BÉk'OiiHH iBBBBBB m m m m m m BBBPBH g a a m m n B BBB9B, B B H a a e BBBVVH HBBBHB BBHBVH - s s s a à B sB B B 8»ai ! fi m m S :

vOI 01 -97- pentaborane derivative is indicated. The 1 0 -1 2 absorption is characteristic of strong B-Cl absoz*ption. In Table VII the per cent conversion of pentaborane to 1-pentaborylborondichloromethane has been shown. This figure has been based on the assungation that 90^ of the distillation product was that compound. Considerable amounts of yellow-orange ta rs were formed in these reactions. However, this material obviously still contained at least one apically substituted pentaborane con^und. This was shown by infrared analysis of the tar in carbon disulfide solution

(Fig. 24)* Characteristic solvent bands appear at 4»5> 4#75, 6,3-6.9, 9*2, and 12.2/u. The bands characteristic of the pehta- borane-skeleton as well as the 5. 5yu- double peaks for apical sub­ stitution are evident. It is possible that a compound such as 1,1'-^

1 ’'-tripentaborylmethane is still contained in this mixture. The presence of pentaborane groups could also account - at least in part - for the high reactivity of the tars towards water and alcohol. The only other catalyst tried was anhydrous stannic chloride. Very little reaction took place; apparently some reduction to stannous chloride occurred.

6. D ic hlorobromomethane This conqpound appeared to be quite reactive. Two runs, one at room temperature and one at elevated temperature resulted in

violent explosions. A third run was made over a period of 8 days a t 10-20* under exclusion of d ire c t lig h t. I t i s summarized in Figure 24 Infrared Spectrum of Tars from Reaction of Pentaborane-9 with Chloroform (and AIGI 3) Carbon Disulfide

JSL

JS. _2g.

1 ^

vOI ' W I - 9 9 - Table VIII.

Table VIII Reaction of Pentaborane-9 with Dichlorobromomethane Run No. 47-30 pentaborane-9, mmoles 73.2 halide, mmoles 45.1 aluminum chloride, mmoles 3.0 size reactor, liters .56

time, days 8 temperature, ®C 10-20*

pentaborane-9 recovered, mmoles 45*9 halide recovered, mmoles 5.9

mol pentaborane used 37*3

mol io halide used 87.0 Products (mmoles)

hydrogen 32.3 diborane 1.4 hydrogen chloride 2.2 boron trichloride 4.5

The following evidence for additional products should be considered: F ig . 25 shows the infrared spectrum of a gaseous mixture obtained

a fte r repeated fractio n atio n which removed most of the diborane and boron trichloride. Also, the presence of dichlorobromomethane and Figure 25 Infrared Spectrum of Gaseous Mixture

iSIB!: I!i Si1 lii

è ? -101- pentaborane is unlikely. The double peak at 9*2$yuu and the peak at

1 1 , 2 may be due to chlorodiborane, which would also account for the strong B-H absorption. The strong absorption in the 10,0-10.7y^ region indicates the presence of boron trichloride in the sanple.

On the other hand, the presence of a CH band at the 6 - 6 / ^ , the 11,2yU., and the 13,1-13,$/*' absorption compare favorably with dichloromethane, rather than bromodlchloromethane or bromochloro- methane. This spectinim is therefore considered as evidence for the presence of ClGHgBGlg, the intermediate that has been postulated to

account for the formation of BgH^GHgBGlg, However, since the assignment of the B-G absorption is indefinite^, a mixture of boron trichloride and diehloromethane cannot be ruled out, A small crystalline fraction, which was similar to material obtained in the chloroform reaction, was probably 1,1'-dipentaboryl­

methane. Another Rmall fraction, vapor pressure about 2 mn/2$* was ob­ tained and analyzed by infrared. Fig, 26, An apically substituted

pentaborane-9 compound is indicated. Peaks at 8,45 and 8,8/*• com­ pare well with similar peaks for bromodichloromethane. The leveling

observed in the 13-14*$/*- region is due to imperfect matching of cells (spectrum was run in GHaClg solution vs. blank). The yellow residue from this reaction was not very viscous. Upon U-trap dis­

tillation it yielded a liquid and a crystalline fraction. Infrared analysis showed this liquid fraction to be a substituted (apical) Figure 26 Infrared Spectrum of Fraction (v.p, 2 mm/25") -103- pentaborane derivative also, although the C-H band and the double peak a t 5.5 ^ were extremely weak.

7. Reaction of Pentaborane-9 with Carbon Tetrachloride This reaction was not studied in any detail. The reaction was more rapid than either the reaction \dth diehloromethane or chloro­ form ( i.e . comparable amounts of hydrogen and polymer were produced faster). The results from one run are given below in tabular form.

Table IX Reaction of Pentaborane-9 with Carbon Tetrachloride

Remarks Run No. 33-183

pentaborane-9, mmoles 5Ô.I carbon tetrachloride, mmoles 18.5 B ^ A Grade, AICI 3, aluminum chloride, mmoles 2.4 Used d ire c tly from b o ttle Size reacto r, ml 56 O Time, hours 2

Temperature, ®C 65-67 pentaborane used, mmoles 38.0

mole io used 65,4 Small amount of CCI4 present carbon tetraclriloride used, mmoles N.D. Products (mmoles)

hydrogen 26.4 hydrogen chloride 1,8 diborane 10,9 boron tric h lo rid e 9*5 Impure -104- The presence of BgHgCl was inferred from infrared analyses. The gaseous mixture which passed through a -97" trap was also analyzed by infrared. Reduction of the G-01 bond was shown by a rather strong C-H band in the 3, 5^ region. Parts of that spectrum com­ pared favorably with an authentic sample of CH 3BCI2,

The viscous, colored residue was dissolved in diehloromethane and worked up in the manner described previously, Ihe residue was distilled from a small stillpot through three U-traps in series, after the solvent had been removed. The temperatures along with the respective times are listed in the table below# Stillpot Trap 1 Trap 2 Trap 3 Time, h rs.

0 -45" - 78 ® - 1 9 6® 2

25 -45" -78® .25" 2 50® -45" -78® 25" 1

50" -15" -45" -78" .5 slowly to no® -10® -45" -78" 1

At about 9 0*, gas noncondensable at -I 9 6* was formed. The products shown below were obtained in the traps held at tençeratures of -10*,

-45"» and -?8" (last line in table) after 6,5 hours! -78" trap 1 trace of colorless liquid

-45" trap 1 0,05 g colorless liquid (liquid at -78")

-10® trap t 0,19 g pale yellow liquid (nup, -25") as well as a trace of crystalline material The fractions were analyzed and the results are listed in the

following table: -105“ Sample Size, Method of No. S Analysis ^ B % H B/C Ratio

-45* .0391 oxidation 41.5-42.9 8.8-9.0 —— 5.26/1

-10® .0730 oxidation 37.0 7.7 —— 5.34/1

-10® .0547 hydrolysis 39.7 4.5 ——— It is obvious that impure samples were analyzed. The results from oxidation and hydrolysis for the -10® sançile do not exclude the possibility of BgHaCHaBClg being one of the products in the

reaction. This product was identified as the main part of the low volatile mixture (not separated as above) by mass spectrographic analysis 22 • Both oxidation and hydrolysis gave low values for boron. Incompleteness of the hydrolysis was further indicated by the fact that a vile, penetrating odor was noticed in the reactor after it was opened. This odor persisted for quite some time.

Chloride bonded to boron should have been hydrolyzed easily. How­

ever, only about one-half of the theoretical amount (22.55&) could

be accounted fo r by titr a tio n (th eo retical fo r BgHaCHgBClg j A5»l)« The trace amount of crystalline material found in the -10®

trap was shown to be dipentaborylmethane by mass spectrometric analysis^^. Ô. Reaction of Pentaborane-9 with 1,2-dichloroethane and 1-bromo- 2-chloroethane. As in the case of the halogenated methanes, decomposition was

the major reaction. In addition reduction of the cai'bon-halogen bond apparently occurred with relatively greater ease in the case -106- of the halogenated ethanes) the yield of ethylpentaborane obtained from these reactions was greater than the amount of methylpenta- borane obtained from any of the reactions involving halogenated methanes. Other products, which were identified by infrared analysis

and/or hydrolysis to hydrogen halide and boric acid t diborane, ethane, boron trichloride, and ethyldichloroborane. The non-volatile fractio n s were worked up as described pre­

viously. However, no analytically pure products were obtained. a. Pentaborane-9 and 1,2-dichloroethane The re s u lts from one representative run are summarized in Table X. Table X Reaction of Pentaborane-9 with 1,2-Dichloroethane

Run No. 2 1 -1 3 4 Remarks p entaborane- 9,mmole s 79.7 1, 2-dichloroethane,mmoles 24.0

•luminum chloride,mmoles 5.0 B Â Grade AICI 3 re sublimed size reactor, ml 560

time, hours 4.5

temperature, ®0 70-73 pentaborane used,mmoles 48.2

mole % used 61.6 1,2 dichloroethane used, mmoles large

Products: (mmoles)

hydrogen 26.9 -1 0 7 - Table X (continued)

Run No. & -1 2 4 Remarks Productas (moles)

hydrogen chloride .9 diborane trace

boron trichloride 3.2 e thyldichloroborane 3.2 ethane trace

e thylpent aborane 15.4

ia conversion 19.4 Contaminated with trace amounts of CHgClGHgCl ^ yield 32.0 Based on BgHg tars (yellow) large The noncondensable formed was assumed to be hydrogen. The infrared spectrum of ethylpentaborane (Fig. 27) was compared to an authentic sample (Fig, 28). The peak at 8/^ is due to absorption by the halüefc. The U-trap distillation of the non-volatile fractions (3

U-traps, held at room temperature, -78.5“» and - 196“ fo r 10 hours) yielded 0,17 g liquid in the -78.5* trap. The analysis of this material is given below: B 28,0

1» 0 12.2 The presence of chlorine was indicated by the fact that the gases re­

sulting from the nitric acid oxidation attacked the mercury in the manometer. Figure 2? Infrared Spectrum of l-F,thylpentaborane-9

100

t- 2 60

40 o a 20

WAVE l e n g t h in m i c r o n s Figure 28

Infrared. Spectrum of l-Ethylpentaborane-9

DO

u 80

60

4 0 - oUJ

WAVE l e n g t h IN MICRONS I so I - 1 1 0 -

The flask containing the remainder of the nonvolatile fractions was then heated slowly to 1 1 0" fo r 8 hours while connected to a -196® trap. At 70-80® material collected in the receiver. This material was liquid at room temperature. A small amount of crystals was also observed. About 0,23 g of liquid product was collected. The analysis by hydrolysis of this pro­ duct is given below: ^ B % R hydrolyzable % Cl actual kO,h 5.5 21.1 theoretical for BgHgCHaCHaCl U3.0 6. >41 26.2

The infrared spectrum of this material methylene chloride solution (matched cells) is shown in Fig. 29. The spectrum suggests l-pentaboryl- 2-ohloroethane, although 1 -pentaboryl-

2-borondichloroethane, BgHgCHgCHaBCla, cannot be ruled out, especially since ready hydrolysis of the G-Cl bond would not be expected for the former compound.

b, Pentaborane-9 and l-Brorao-2-chloroethane Some typical experiments are shown in table No, XI below. Table XI Reaction of Pentaborane-9 and l-Bromo-2-chloroethane

Run No, U5-29 U6-29 5l-)t2 Remarks pentaborane-9 95.0 67,7 38.0 mmoles num chloride was used. halide, mmoles 2 1 ,6 In run U5-29 i t was 31. U 47.5 taken directly from aluminum chloride 2 .8 2 ,6 3.9 b o ttle ; in run U6-29: mmoles resublimed; in run 51-U2: freshly resub­ size reactor, ml 560 560 560 limed Figure 29 Infrared Spectrum of l-pentaboryl-2-chloroethane

£ Î m

V. -112;, Table XI (Continued) ■Run No, 45-29 46-29 51-42 Remarks time, hours 7 5 4 temperature, “C 70-75 70-75 1 0 -2 0 pentaborane-9 used, 74,6 ND mmoles mole # used 45,9 - halide, mmoles large large Products (mmoles) hydrogen 26,4 33.4 2 8 ,1 hydrogen chloride 1,3 ND ethane 2,4 ND diborane ,7 ND boron trichloride 4,0 ND ethyldichloroborane 3,9 ND ethylpentaborane 2 8 ,0 9,5 % conversion 17,2 25,1 % yield 37.6 based on B 5H9 ta rs f a ir more than from L5-29 The U-trap distillation of the nonvolatile fractions has been summarized in the tab le below: Run No. Stillpot Trap 1 Trap 2 Time, hrs. U5-29, 46-29 25.40“ -45“ - 1 9 6“ Several 51-42 25-100“ -50“ - 1 9 6“ Several Combined liq u id pro­ ducts from -4 5 “ and 0 “ - 3 6 “ -196“ 5 - 5 0“ traps (above) The trace amounts of m aterial collected in the -196' traps were d is- carded. The total weight of liquid product in the 0* trap was about 0,3 g. Analysis: 33,9# B, The total weight of liquid product in the - 3 6 “ trap was about 0, l 5 g. -113-

Analysis: 26.056 B 11.6# C

3$.2# Cl (if precipitate of silver halide is taken as pure silver chloride)

60 . 3# Br (if all silver bromide) Applicatlon of the test for bromine in the presence of chlorine 24 was pbsitive for bromine.

2ii,Shriner and Puson, Identification of Organic Compounds, p. S 6 .

The infrared spectra of the two eamples in methylene chloride (using matched cells) were obtained and were almost iden­

tical, figures 30 and 31. Both samples show absorptions character­ istic of an apically substituted pentaborane in the h.O, 3.^,

7-7.2$, 11.1 ^ regions. Comparison with the spectrum of 1-bromo-

2-chloroethane indicateds that the peaks at 7. 7$, 8 . 3$, 1 1 . 9, and 1$,1 are due to absorption the halide. The bands at 11.9

and 1 $ ,1 yuu are characteristic of the dichloro-, as well as the chlorobromo halide. However, the presence of free halide is ruled out, as it would have been detectable by its vapor pressure. Contamination by ethylpentaborane is likewise excluded. Lack of

broad bands in the 9-10 and 1 0 -1 1 region (characteristic of ethyldichloroborane and borontrichloride, respectively) does not necessarily rule out a compound such as BgHGCHaCHgBClg which would he a possible product in analogy; with the product from the poly- halomethane reactions, BsHgCHgBOlg. Figure 30

Infrared Spectrum of 0°-Trap Fraction

I

« 0 0 0 0

P

H Figure 31

Infrared Spectrum of - 3 6 “-Trap Fraction

id hi

JSL -116—

The analytical data were quite poor. Probably mixtures were analyzed and the oxidations were incomplete. However^ from the data at hand it is suggested that both samples consisted chiefly of l-pentaboryl- 2-chloroethane, l-pentaboryl- 2-borondichloro- ethane, and possibly l-pentaboryl- 2-bromoethane wi.th substitution

on the apical boron atom. From the fractionation of the volatile products of this re­ action a considerable amount of liquid material with a vapor

pressure of U-6 mm/2?“ was formed. This material was quite unstablej transfer from one trap into another was invariably

accompanied by gas formation. This liquid was a crystalline solid

at -78 .^“. Infrared analysis of two different samples (vapor

pressures ^ mm/20‘*G and 3 mm/20°C) showed the two to be very sim ilar. Furthermore, these spectra were in good agreement vrith those obtained above (figure 30 and 31). The r e lia b ility of the vapor pressure measurements, however, was questionable. The gas was not condensable at -76.^“. On prolonged standing at room temperature the pressure usually rose slowly. Since the samples had been

exhaustive].y fractionated, the presence of a high volatile impurity was not likely. Probably a slow decomposition was talcing place. The samples used for infrared analysis were therefore combined, the solvent was removed, and the combined sample d is tille d

(room temperature into a -196® receiver) for 6 hours. The distillation was accompanied by formation of a gas; this gas was completely condensable at -196® receiver. The residue was pale yellow in color. Infrared curves were taken on residue and - 1 1 7 - distîllate, on the latter after removal of the noncondensable gas. Both curves again indicated apically substituted pentaborane derivatives. An infrared spectrum of the noncondensable gas gave no clue that would have permitted its ready correlation to either distillate or residue. Undoubtedly, residue and distillate are essentially the same product. IV» Discussion

A. General The theoretical and experimental considerations that have led to the currently accepted structure of pentahorane-9 have been 12 reviewed by Ryschkewitsch. The electronic structure has been described in terms of normal covalent, or two center, orbitals and three center orbitals. The three center orbitals are formed by linear combinations of three single boron electron wave functions or of two boron and one hydrogen wave function. There are five covalent 3-IÎ bonds and four so called hydrogen bridges.

A total of 2i\ electrons are available for bond formation. Ten of these are u tiliz e d in making the covalent B-II bonds and eight

form the four hydrogen bridges. From the remaining xix electrons the boron framework is constructed using the seven atomic orbitals that remain (one from each base boron and three from the apical boron atom). These atomic orbitals give rise to seven molecular o rb ita ls, of which three are bonding, one non-bonding, and three anti-bonding. The three bonding orbitals are filled with the six remaining electrons. The resulting electron distribution

leads to a charge of, - .3 2 to - .3 7 on the apical boron atom, while the balancing positive charge is evenly distributed over the four base boron atoms. The resulting dipole is about 2 D. The

space relationship is shown in figure 32,

-1 1 8 - -1 1 9 -

B5H9 (Space Relotionship)

FIGURE 31 - 120 - B, Reaction of Pentaborane-9 with 1-Butene Based on the charge d istrib u tio n in pentaborane-9 and the product obtained, a mechanism for the reactio n of the boron hydride with olefins in the basence of catalysts has been suggested by IS Ryschke>ri.tsch. This mechanism is shown schem atically “below; H H apex g -/

+ CHg “ CH-R ..CHa - CH-R

CHa -"CH-R if B -CHg - CHa - R H -f

Several factors can be considered to account for the observed

product: repulsion of the approaching Ti -electron pair of the olefin by the relatively large partial negative charge on the apical boron atom. The presence of electron releasing alkyl groups in the olefin causes a polarization as indicated above. Thus, attack of the electron dense carbon atom of the double bond on the p a rtia lly positiv e base boron atom is favored.

Statistical considerations would also favor addition at the base boron by Utl. The final product would be formed by transfer of

the boron bonded hydrogen with its electron pair to the electron

deficient carbon of the olefin (a 1 , 3-hydride shift). -121-

The results of the reaction of 1-butene with pentaborane-9 are in accord i-rith the mechanism outlined. The product is

2-n-butylpentaborane-9. Although no nuclear magnetic resonance studies were made on this product, the infrared spectrum and comparison with the products from the reactions of pentaborane-9 with 2-butene and isobutene leaves no doubt that base substitu­ tion has taken place. Nuclear magnetic resonance studies on the latter two reaction products showed them to be base substi- 19 tuted. From the data shown in table II, 1-butene appears to be less reactive than isobutene. This would be expected from a comparison of induction effects in isobutene (two methyl groups) and 1-butene (one ethyl group), 2-Butene has two activated positions and therefore would also be expected to be more reac­ tive than 1-butene, Thus, the following qualitative sequence can 15 be given for olefin reactivity (see also Ryschkewitsch );

isobutene ^ 2-butene > 1 -butene > propene » ethylene It would be of interest to investigate olefins having larger

R-groups of the type RR'C-CHg, RR'C»CHR", and RR'C-CR»'Rmi ,

lYom the evidence at hand one would conclude that the relative reaction rate is controlled by the inductive effect; however, at some point steric control might be predominant.

The nature of the butyl group from the Lewis Acid catalyzed reaction product was not established. It is, however, believed that this product is l-sec-butylpentaborane-9, i.e. substitution -122- on the apical boron atom. This could be pictured as an electro - philic attack of an entity such as [RCH*" -CHg: MX 3] on the partially negative apical boron. Considerable data on this point 17 has been obtained by Mezey ; it will therefore not be discussed here. Olefin polymerization appeared to be the predominant reaction even under such mild conditions as were used in run

B ii-9 8 (table II). Although no evidence was obtained for polyallcylated penta­ borane derivatives, their formation is not unlilcely. The tars from these reactions were not worked up, but that is where these products would be i f they were formed,

C, Reactions of Pentaborane-9 with Polyhalogenated Hydro­

carbons. It is obvious that the reactions of pentaborane-9 with polyhalogenated liydrocarbons are quite complex. The chief reaction appears to be decomposition of the pentaborane-9 skeleton. This is apparent from the large amount of hydrogen that is produced, other gaseous products such as diborane and borontrichloride, as well as from the considerable quantity of colored tars which contain a substantial amount of boron. Other reactions observed are substitution and reduction. In addition, there is dispropor­ tionation taking place among several of the reaction products. Under comparable conditions, little or no reaction at all

took place between pentaborane-9 and aluminum chloride (there is, of course, some reaction of the halides with aluminum chloride which accounts for some of the yellow tars that are formed). - 1 2 3 - Therefore, the reacting system must involve pentaborane-9, the halide, and the Lewis acid c a ta ly st. Furthermore, Lewis acids such as boron trifluoride, stannic chloride, and zinc chloride did not catalyze the reactions. Only a small amount of decom­ position took place with stannic chloride, and considerably more drastic conditions were required to effect reaction in the presence of zinc chloride. Of the few compounds cited, alumi­ num chloride is generally considered as the strongest Lewis acid in Friedel-Crafts type reactions. Since a Lewis acid acts by virtue of its ability to accept an electron pair from a doner, thereby exerting a strong polar effect on the system, a rather strong acceptor is obviously needed to make the reaction proceed. On the other hand, considerable decomposition took place with aluminum chloride as catalyst. Aluminum bromide was not studied extensively but appeared to be of comparable reactivity. Perhaps more satisfactory results could be obtained with an "intermediate" catalyst such as ferric chloride. Among the products from the reaction of pentaborane-9 with methylene dihalides, the formation

of 1 , 1 '-dipentaborylmethane could be pictured as show in figure 33. This would involve electrophilic attack of a methylene dihalide-aluminum chloride adduct on the apical boron atom. In the transition state, the new B-C bond is partially formed, while B-H bond is partially broken. Decomposition of the transi­

tion state leads to the intermediate 1 -pentaborylhalomethane, BsHgCHgX. This intermediate could react again id.th aluminum chloride forming another adduct, which would give the product by -124-

Figure 33 Mechanism of Formation of 1,1'-Dipentaborylmetharie

1. XCHs - X + AICI3 [XCII^ AIXCI3 ]

-6 -*5 , " ^ apex B B ------CHgX AIXCI 3 2. + [XCHg AlXClg] base i S I H 1st Transition state

^ CHgX - s 4

CH,X CHg A IC I3X -

r + - r if] CHg AlGljX H H B-i1 r -f t«f ~s / B B - CHg..B /Ü.CI3X 5. ' \ B+-

of pentaborane-9 vrith bromochlororaethane, assuming that the C-Cl bond would be the more reactive bond. However, no evidence could be obtained for the presence of that compound, not even by mass spectroscopy. The observation that bromides react more slowly than chlorides 25 has. been made previously. Calloway reported the following

25. N.Û. Calloway, J. Am. Chem. Soc. 59, lU?U (1937).

reactivity of alkyl halides in aromatic substitutions catalyzed 13 by aluminum chloride: F > Cl > Br > I. H arris found th at the reactivity of methyl halides in the reaction with pentaborane-9 and aluminum chloride decreased in the order:

CHgCl) CHaBr ) CH3I —]. 2 6 — In the reaction discussed above, since no BgHgGHgBr could be isolated, it is apparent that steps 1|. and 5 . in the mechanism outlined must be faster than step 2. And furthermore, this must be true fo r a ll tliree methylene dihalides. This would not be unexpected in view of the following considerations : Step U» involves approach of the Lewis acid to the halogen end of the G-X bond in B5H8GH2X, GHg - X : ^ AICI 3 CHg AIXCI 3 - £ apex B base B + B ‘ I t H H This would be followed by the formation of the adduct. The partial negative charge on the apical boron atom could assist in the removal of Xj thus the formation of the adduct would be greatly facilitated.

A different mode of reaction for BgHgCHgX and/or the 1st tra n sitio n sta te has to be considered, however, which would at least in part account for the low yield of 1 , 1 '-dipentaborylmethane as well as for the large amount of decomposition observed. The

-CHgX-group exerts an electron-withdrawing effect on the penta­ borane skeleton. It is suggested that the resulting disturbance

of the electronic structure of pentaborane-9 is great enough to cause breakdown of the skeleton. The precise manner in which this breaJfdown would occur is, of course, unknown, but it is interesting to observe that one fragment obtained would be

[B-GHgX] or [BGHgXtAlCls], This fragment could conceivably give rise to ClGHgBGlg, which is considered as one of the intermediates - 1 2 7 - 1 3 in the formation of BsHeCHgBGla, Harris isolated methyldichloro- horane from the reaction of methyl halides with pentaborane-9. 22 Norman has suggested th a t formation of ClCHgBClg from CHgBClg and a subsequent Priedel-Crafts reaction by attack of [CHgBClg AICI 4 ] on pentaborane-9 would account for the product. The tars from the reactions involving methyl halides were not worked up. Therefore, at present it is not known if BgHeCHgBClg is one of the products from the reaction of pentaborane -9 with methyl chloride and aluminum chloride. However, in view of the fact that another important reaction in all polyhalide reactions was reduction of the carbon- halogen bond, as shown by the formation of such products as methyl- dichloroborane, ethyldichloroborane, methyl-, and ethyl^entaborane, it is not believed that formation of ClCHgBClg occurs via CHgBClg* Thus, the following sequence could lead to the formation of

BgHgCHgBCl 2 !

B5H9 + [CHgCf MC1% ] BeHsCHaCl + HCl + AICI3 BgHsCHgCl + AICI3 [BeHeCHjmClJ ] [BsHsCBa AlClJ ] -+ [B^He] + [BCHgCl] + AICI3 [BGHgCl] + 2 AICI4 -V CICH2BCI2 + 2 AICI3

CCHgBGlg + AICI3 H. [CHgBClg AlClJ ] BgHg + [CHgBClg AICI4 ] -*• BgHeCHgBClg + HCl + AICI3

The fragment [BGHgCl] would be electrophilic and could pick up

chlorine from a strong base such as AIGI4 . There is mass spectro­ scopic evidence for the formation of [84113] from BgHs under drastic 18 conditions. This fragment would incorporate four of the six electrons th a t co n stitu te the boron framework in pentaborane-9 and - 1 2 8 - resonance structures can be written for it. Further breakdown of

[B4Hg] could yield, among other fragments, BHg-groups. The BH3- groups give rise to some of the other observed products - such as diborane and/or enter into the tars. 26 Brown and Grayson have considered Friedel-Crafts reactions

26, H. C. Brovm and H. Grayson, J. Am. Chem. Soc., 75. 6285 (1953). involving benzyl halides as nucleophilic reactions according to the scheme; RCl + AICI3 ^ RClzAlClg Hi + ArH + RCltAlCla [Ar AlCl. R" ,/H + [Ar AICI4 ^ R-Ar + HCl + AlCl: ^ R The experimental facts were in agreement with a mechanism involv­ ing a rate-determ ining nucleophilic attack by the aromatic component on a polar benzyl halide-aluminum chloride adduct. Similarly, the reactions of pentaborane-9 with methyl and methylene halides could be regarded as a nucleophilic attack of pentaborane-9 on a halide- aluminum chloride adduct. Thus, the rate of the reaction would be dependent on the concentration of pentaborane-9, the halide, and aluminum chloride. From the q u alitativ e observations made, th is appeared to be the case. If the molratio of pentaborane-9 to methylene halide was increased much over 3:1, little or no disubstituted product was formed.

The methylene dihalides were also shown to be less reactive than the corresponding methyl halides, since little or no reaction - 1 2 9 - took place with the former at room terqjerature. In terms of overall reaction. I.e. hydrogen and tars produced, further substi­ tution of hydrogen by halogen seemed to increase the reactivity of the halogenated hydrocarbon. Thus CCI4 > CHCI3 > CH2CI2 While more 1 ,1 ’-dipentaborylmethane was formed from methylene chloride than from chloroform or carbon tetrachloride, chloroform gave a larger amount of 1-pentaborylborondichloromethane,

EgH^HaBClg, than methylene chloride. Reduction of carbon-halogen bonds is one of the reactions taking place in all these systems. As was stated previously, no reduction was observed in the absence of aluminum chloride. There­ fore, it is apparent that the latter must play an important part in facilitating that reaction, although boron hydrides are known to act as reducing agents. Products resulting from reduction have 27 also been reported in the aromatic series. Thus, Thomas reports

27. C. A. Thomas, Anhydrous Aluminum Chloride in Organic Chemistry, Reinhold Publishing Corp., p. 108, and other references listed therein ,

among other products toluene from benzene and methylene dicliloride, ethylbenzene from 1,2-dichloroethane and benzene, triphenylmethane and dlphenylmethane from benzene and carbon tetrachloride, and diphenylmethane from chloroform and benzene.

Again, one can only speculate as to how reduction is effected. It could occur by attack of a hydridic hydrogen in pentaborane-9 on the halide-aluminum chloride adduct. This would involve -130- nacleophüic displacement of by H". Also, decomposition of pentaborane-9 must account for a large portion of the hydrogen formed, which in turn could reduce the carbon-halogen bond. A somewhat larger yield of 1-ethylpentaborane was produced from the reaction of l-bromo-2-chloroethane than from 1,2-dichloroethane, This seems reasonable, since one would expect the carbon-bromine bond to be more reactive than the carbon-chlorine bond, ,in nucleophU.ic displacements. Insufficient data were obtained for the methylene ha].ides to permit a similar comparison. Apparently, reduction proceeds with considerable ease in the case of the ethylene halidesj no evidence was found for a disubstituted pro­ duct, 1,2-1-dipentaborylethane. On the other hand there is evidence for the presence of BsHgCHgCHaX; this is not unreason­ able, since the electron-withdrawing effect of• the chlorine in the ^-position would be greatly diminished over that in theoC^osition as in BgHgCHgX. Therefore, BgHoCHgCHgX would be expected to be more stable than BgHsCHgX.

Although only fragmentary evidence has been presented for a compound such as 1,1'-dipentaboryldichloromethane, (B5Ho)gCClg, its formation is not unreasonable. The comparison with the aromatic series is again interesting, though necessarily of doubtful

validity. For example, diphenyldichloromethane has been obtained from the reaction of chloroform and benzene, and triphenylchloro- methane and diphenyldichloromethane from carbon tetrach lo rid e and benzene. On the other hand, the chlorine would be expected to

exert an electron withdraifing effect, which would decrease the - 1 3 1 - stability of the pentaborj^l group, A size effect might also oppose • formation of that compound, since four large groups would be attached to one central carbon. The great reactivity of the structures containing chlorine, such as BgHgCHgX and BgHgCHgBClg, as compared to the alkylated products of similar molecular weight can probably be attributed to the destabilizing effect of the electronegative

chlorines on the whole structure. One way in which tar formation might occur has been outlined previously. Redistillation of the low - and nonvolatile fractions at 60-100“ at about 1 mm pressure - after the original yellow tars had been left behind in a first distillation - invariably led to

further formation of yellow tars. Since that reaction presumably occurred in the absence of aluminiun chloride, the substitution products themselves must undergo further degradation. Fi’om infra­

red analysis, figure it is evident, however, that the tars still contain an appreciable amount of apica].ly substituted pentaborane compound (s). These compounds are probably of high molecular weight, for this material did not distill at 100“C at 1 mm pressure. The nature of the aluminum chloride appeared to have a definite effect on these reactions. Usually freslily sublimed aluminim chloride kept under dry nitrogen was used. This material seemed

to lose some of its reactivity on standing. Reaction $l-k2 (table XI) illustrates that point. The aluminum chloride used in that run had been freshly resublimed, while the material used in the other two runs (same tab le) had been standing fo r several days. Most cîT* all of the aluminum chloride used usually dissolved once - 1 3 2 - reaction temperature was reached. Powdered aluminum chloride th a t was stored in a bottle and transferred without special precautions, dissolved only with difficulty and sometimes formed a cake. The reactions started slower in these cases, but sometimes only tars were obtained. On the other hand, the material used in run 27-lUô (table VII) produced a rapid reaction accompanied by a large

amount of tar formation. In general, it can be said that resublimed aluminum chloride from which moisture was excluded gave the most

satisfactory results. D. Reaction with Solvents The reactivity of pentaborane-9 with a number of different compounds was studied to investigate their possible use as solvents in some of the reactions discussed previously. Although it was known that aluminum chloride reacted slowly with n-heptane, the latter was used in several runs with the objective of reducing the amount of decomposition. This was partially accomplished, but the gains were offset by the increased difficulty in separation of

the reaction mixture. Also, as the reaction proceeded, the colored tars formed separated from the solution, which was uniform at the start of the reaction. Furthermore, the product, 1,1'-dipentaboryl­ methane, was shown to be contaminated with hydrocarbon fragments by mass spectrom etric analysis. The yield given in tab le VI (run l^-ldi) is misleading, because the product was thusly contami­ nated, Results from the use of carbon disulfide were similar. The reaction of pentaborane-9 with the aromatic compounds appeared to be slight enough, but these compounds were not further studied - 1 3 3 - because of the separation problems involved. No evidence for a substituted pentaborane derivative was obtained from any of these reactions. Unless an effective method for separation can be found, operation on a large scale seems to be the only alternative in obtaining information on effect of solvents on reactions such as the methylene halide reactions. It should be pointed out, that in the reactions studied, the amount of solvent used was not in large excess over the reactants. One other reaction of in te re st should be mentioned, namely the reaction of pentaborane-9 with t-butyl bromide (no catalyst). This reaction was run at room temperature and at elevated tempera­ ture, but gave no evidence for a t-butyl substituted pentaborane.

This is further indication that a strongly polar species is required to effect substitution at the apex. It would be of interest to

investigate this reaction further in the presence of catalysts such as boron trifluoride or zinc chloride, or a solvent of high dielectric constant, such as nitrobenzene. V. Summary

The reaction of pentaborane-9 with 1-butene gave a new alkyl derivative of pentaborane-9, namely 2-n-butyl- pentaborane-9. This compound was identified by elemental analysis, molecular weight, and infrared spectrum. The other products of the reaction were; hydrogen, butane, tri-n-butylborane, and brown, nonvolatile tars, which were not further identified, but which contained boron and carbon. Under the conditions used (l$0*C fo r several hours) Lewis acid mainly caused polymerization of the olefin. It was shown that reaction of pentaborane-9 with a trialkyIborane did not lead to an alkylated pentaborane derivative.

The reactions of pentaborane-9 with a number of polyhalogenated hydrocarbons in the presence of siluminum chloride were investigated. These reacting systems were quite complex, and products derived from decomposition, substitution, and reduction were identified. From the reactions with methylene halides, a crystalline derivative, 1,1'-dipentaborylmethane, was isolated in low yield. This compound was also identified in the chloroform and carbon tetrachloride reactions. In the last two reactions, the principal substitution product appeared to be 1-pentaborylborondichloromethane, BgHaCHaBClg, This product, a liquid, was also formed in the methylene halide-

reactions. The principal product from the ethane dihalide-reactions

was ethylpentaborane. Other evidence indicated the formation of

-13Ur - 1 3 5 -

BgHgCHgCHgCl ancUBgHgCHgCHgBClg, l-pentaboryl-2-chloroethane and l-pentaboryl-2-borondichloroethane, respectively. Handling of these conqpounds proved difficult due to their low volatility and instability. Among the decomposition products were hydrogen, diborane, hydrogen chloride, boron tric h lo rid e , and large amounts of yellow tars.

Boron triflu o rid e and stannic chloride did not act as effective catalysts in these systems. Carbon disulfide and n« heptane did not significantly affect the yield or conversion to substitution product in the case of the methylene halide reactions. Bibliography

1. Stock, A., The Hydrides of Boron and S ilicon. Cornell U niversity Press, Ithaca, N .Ï,, 1933* 2 . Sc hie singer and Burg, Chem. Soc. .53. 4331 (1931) «

3. Schlesinger and Walker, ^ Chem. Soc,., ^ 621-25 (1935)•

4. Schlesinger, Horvitz, and Burg, £, Chem. Soc.. 50. 40? (1936).

5. Schlesinger, F lo rin , and Burg, J , ^ Chem. Soc. . 61. 10?B (193°)*

6. Hurd, ^ Chem. Soc.. 70. 2053 (194&). 7» Schlesinger and Burg, J, Chem. Soc.. 55. 4020 (1933).

Ô. Burg and Stone, J, Agi. Chem. Soc. . 75. 228 (1953). 9. Schlesinger and Burg, J,. Chem. Soc.. 60. 296 (1938)« 10. Brown, Schlesinger, and Burg, Am. Chem. Soc.. 61. 673 (1939).

11. Stone.and Emeleus, J.. Chem. Soc.. 1950. 2755-9. 12. Mezey, M.S. Thesis, The Ohio State University , Columbus, Ohio; 1954. 13. H arris, Ph.D. Thesis, The Ohio State U niversity, Columbus, Ohio; 1956. 14." Sanderson, Vacuum Manipulation of Volatile Compounds. John Wiley and Sons, In c ., New York, 1948.

15. Ryschkewitsch, Ph.D. Thesis, The Ohio State U niversity, Columbus, Ohio; 1955. 16 . Hartig, Standard Oil of Ohio, Private Communication. 17. Mezey, Ph.D. Thesis, The Ohio State U niversity, Columbus, Ohio; 1957. 18. Tyson, Jr., Olin-Mathieson Chemical Corporation, Pasadena, C alifornia, Private Communication.

19. Shoolery, Varian Associates Palo Alto, California, Private Communieatio n .

- 1 3 6 - - 1 3 7 -

20. Burg, in Boron h j f à r l û ea and Related Compounds, Second Edition May 1954» G allery Chemical Company. 21. Cohen, Clin Mathieson Chemical Co., MCC-1023-TR-125, April 29, 1959. ' ' ‘ 22. Norman, Olin Llathieson Chemical Co., Niagara Falls, N.Y., Private Communication. 23. Robbins, Olin Mathieson Chemical Co., Niagara Falls, N.Y,, Private Communication. 24. Shriner and Fuson, Identifieation of Organic Compounds, p. $6.

25. Galloway, £• Chem. Soc.. 59. 1474 (1937), 26. Brown and (brayson, J. ^ Chem. Soc.. 75. 6205 (1953).

2 7 . Thomas. Anhydrous Aluminum Chloride in Organic Chemistry. Reinhold Publishing Co., p. lOB, and other references listed therein. Autobiography

I, Elmar Robert Alt^d.cker, was born in Wolf en near Bitterfeld,

Germany, on April 4» 1930. I received my secondary school education in the public schools of Bitterfeld, Dieburg, and

Landshut, Germany. In February, 1949* I entered the University of Dayton; from this institution I received the degree of Bachelor of Science in June, 1952. lo. October, 1952, I entered the

Graduate School of the Ohio State University, where I specialized in the Department of Chemistry. While coo^leting the requirements

for the degree of Doctor of Philosophy, I held appointments as research assistant, research associate, and research fellow with the Ohio State University Research Foundation.

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