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Reactions of Hydrogen Peroxide. VII. Alkali-Catalyzed Epoxidation and Oxidation Using a Nitrile As Co-Reactant

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Reactions of Hydrogen Peroxide. VII. Alkali-Catalyzed Epoxidation and Oxidation Using a Nitrile As Co-Reactant MARCH 1961 EEACTIONS OF HYDROGEN PEROXIDE. VII 659 had been consumed, 0.03 mole of alkali utilized, and 0.005 tional 1-ml. portions were added at hourly intervals to main­ mole of oxygen evolved. After chilling thoroughly, the in­ tain the desired pS.. Oxygen was collected by means of an soluble solid was collected by filtration, washed with meth­ inverted graduate cylinder. At the end of 2 hr., 185 ml. of anol, and dried to a constant weight of 8.2 g., m.p. 202-203°. gas had been collected and iodometric titration showed that By diluting the filtrate with two volumes of water, there 0.020 mole of peroxide had been consumed. At the end of 4 was obtained an additional 7.3 g. of crude epoxy amide. hr., 245 ml. of gas had been evolved and 0.033 mole of per­ Recrystallization from chloroform afforded 1.9 g. of product, oxide consumed. m.p. 201-202°. Another crop of 0.4 g., m.p. 195-200°, Dilution of the stirred mixture with 150 ml. of water gave was secured by dilution with hexane. The total yield of crystalline material which was isolated by filtration. It epoxyamide was therefore 10.5 g., or 60%. No further weighed 4.2 g. and had m.p. 115-122°; a mixed m.p. with crystalline product was obtained by re-working the filtrate starting material was 122-127°. The infrared spectrum was from the last crop. virtually identical with that of the starting material. Lack Attempted epoxidation of a-phenyl-trans-cinnamamide by of absorption at 11.00 and 11.31/1 indicated the absence of acetonitrile-hydrogen peroxide. A solution of 5.0 g. (0.0224 any significant amount of epoxyamide. mole) of a-phenyWra?is-cinnamamide, 5 ml. of acetonitrile, A 2.0-g. sample of product was recrystallized from 100 and 3.4 g. (0.050 mole) of 50% hydrogen peroxide in 50 ml. ml. of ether to give 1.4 g. of recovered starting material, of methanol was stirred magnetically using a large tap water m.p. and mixed m.p. 126-128°. bath for cooling. One milliliter of N sodium hydroxide was added to bring the pH to 8 and initiate reaction. Three addi- EMERYVILLE, CALIF. [CONTRIBUTION FROM SHELL DEVELOPMENT CO., EMERYVILLE, CALIF.] Reactions of Hydrogen Peroxide. VII. Alkali-Catalyzed Epoxidation and Oxidation Using a Nitrile as Co-reactant GEORGE B. PAYNE, PHILIP H. DEMING, AND PAUL H. WILLIAMS Received April W, 1960 A new epoxidation and oxidation technique has been discovered in which dilute hydrogen peroxide (30-50%) is utilized under essentially neutral conditions. The procedure involves the initial reaction of an organic nitrile with hydrogen peroxide to produce what is most likely a peroxycarboximidic acid. This has been used to epoxidize cyclohexene, styrene, and acrolein diethyl acetal in 73, 70, and 62% yields, respectively, as well as to oxidize pyridine to its N-oxide in 79% yield and aniline to azoxybenzene in 62% yield. Hydrogen peroxide by itself is a relatively poor H2O2 + OH- —> H2O + OOH " oxidizing agent. For example, its use in organic II reactions has generally been limited to the conver­ A completely new method of achieving oxidation sion of tertiary amines to their oxides and sulfides to 1 by hydrogen peroxide was developed through con­ sulfoxides : sideration of possible mechanisms involved in the 4 R3N + H2O2 —*- R3N — O + H2O epoxidation of acrylonitrile. In this system, hydro­ gen peroxide reacts with a nitrile under controlled R—S—R' + H2O2 —> R—S—R' + H2O I pH conditions (usually pH 8) to generate what is O felt to be a peroxycarboximidic acid intermediate (III). The latter has not been isolated; it reacts For other oxidations, including epoxidation and NH hydroxylation, the hydrogen peroxide must be "ac­ OH- • Jl tivated" by conversion to another species, usually RCN + H2O2 >• R—C-OOH (1) a peroxy acid (I)2 or the perhydroxyl anion (II).8a,b pH8 III O O RCOOH + H2O2 -^-> RCOOH + H2O III + Reductant —>- RCNH2 + Oxidation product (2) I rapidly with any available reducing agent. In the absence of an added substrate (an olefin, for (1) Reactions of hydrogen peroxide in organic chemistry example), III reacts with hydrogen peroxide (now are summarized by W. C. Schumb, C. N. Satterfield, and R. L. Wentworth in Hydrogen Peroxide, Reinhold Publish­ acting as the reducing agent) to give amide and ing Corp., New York, 1955, p. 406. oxygen": (2) D. Swern, Org. Reactions, VII, 378 (1953). (3) (a) R. C. Elderfield, Heterocyclic Compounds, Vol. I, NH O John Wiley and Sons, Inc., New York, N. Y., 1950, p. 6. RC-OOH + H2O2 —>. RCNH2 + O2 + H2O (3) (b) See G. B. Payne, Hydrogen Peroxide: New Techniques for III Its Utilization, Fifth World Petroleum Congress, May 30- June 5, 1959, New York, N. Y., Section IV—Paper 16, for (4) G. B. Payne and P. H. Williams, J. Org. Chem., 26, a recent review with references. 6Sl (1961). 660 PAYNE, DEMING, AND WILLIAMS VOL. 26 By adding together equations (1) and (3) one in a similar manner, crystalline benzamide was arrives at the classical expression for the hydrolysis also secured in 82% yield. of an organic nitrile by alkaline hydrogen peroxide As a check on the accuracy of measurement of ("Radziszewski reaction")6: oxygen evolution by the wet test meter, equimolar quantities of benzonitrile and hydrogen peroxide O OH- Il were allowed to react in the absence of cyclohexene. RCN + 2H2O2 —>• RCNH2 + H2O + O2 (4) Benzamide was obtained in 94% yield based on peroxide charged, and the amount of oxygen In the presence of a better reducing agent (the evolved was 97% of theoretical for the quantity of olefin, for example), reaction of III with hydrogen amide isolated. peroxide may often be eliminated and epoxidation Epoxidation using trichloroacetonitrile. In order of the olefin accomplished instead. to determine the effect of a-electronegative atoms NH 0 on the reactivity of the cyano group toward alka­ line hydrogen peroxide, trichloroacetonitrile was I! \/ Jl \/ selected for reaction with cyclohexene. As was ex­ R—C—OOH + C —>• RCNH2 + Cv (5) pected, the reaction proceeded rapidly at a pH 111 /N approximately 2-3 units lower than usual to give 1,2-epoxycyclohexane in a titrated yield of 52% A based on peroxide charged. It will be noted, of course, that regardless of how Relative rates of epoxidation of 1-hexene and 2- III reacts (path 3 or path 5), it is always converted methyl-2-butene. The rate of reaction of a peroxy- to amide. carboxylic acid with an ethylenic compound is The reaction is not limited to epoxidation of highly dependent upon the degree of substitution at ethylenic compounds. Using acetonitrile, for ex­ the double bond. For example, 2-methyl-2-butene ample, aniline was oxidized to azoxybenzene and is epoxidized by peroxyacetic acid at a mte 290 pyridine to its iV-oxide. times that of l-hexene.7a In contrast to the above Epoxidation of cyclohexene by acetonitrile-hydrogen result, the rate of disappearance of hydrogen per­ peroxide. Cyclohexene was chosen as a model com­ oxide in a mixture of acetonitrile, hydrogen per­ pound with which to study briefly the new epoxida­ oxide, and olefins is essentially independent of ole­ tion procedure. Acetonitrile, because of its moder­ fin structure. This means that the slow step in -the ate reactivity and general availability, was selected process has to be the formation of the peroxy car- as the appropriate co-reactant for hydrogen per­ boximidic acid intermediate (III); this species must oxide. All reactions were carried out in methanol; react rapidly with any available reducing agent. this is an excellent solubilizing agent for water- soluble and water-insoluble materials. On the basis of results obtained, certain conclu­ V NH i O \/ sions were drawn regarding method of operation: OH J) A J C. (a) Optimum pH is 7.5-8. At higher pH, oxygen RCN + H2O2 —>• R—C—OOH —*• RCNH2 + I )0 evolution (measured by wet test meter) increased, slow fast C indicating an increase in hydrogen peroxide oxida­ HI /\ tion (Equation 3). Needless to say, this led to a Reaction of hydrogen peroxide with acetonitrile in lower yield of epoxide. the absence of base. In order to test the reactivity of (b) Method of addition. Hydrogen peroxide was hydrogen peroxide with acetonitrile in the absence best added slowly to an excess of both nitrile and of any added alkali, a solution of the former olefin. This led to higher yields of epoxide, since in the latter was allowed to reflux (68°) for 24 hours reaction 2 was promoted at the expense of reac­ in the presence of added cyclohexene. Less than tion 3. 5% of the peroxide reacted during that extended (c) Temperature. This was not critical as long as period. proper pH, method of addition, and ratios of reac- Epoxidation of other ethylenic compounds. Styrene tants were observed. Thus, equivalent yields (80- was epoxidized using acetonitrile in methanol solu­ 85% by titration of reaction mixtures for oxirane tion at 50° for seven hours. The yield of distilled oxygen) were secured at 60° as well as at 35°. styrene oxide was 74% based on unrecovered Epoxidation of cyclohexene using benzonitrile. styrene or 70% on the basis of hydrogen peroxide Benzonitrile was used in place of acetonitrile for charged. the epoxidation of cyclohexene. It was found to be It was hoped that by operating under almost approximately ten times as reactive, and provided neutral conditions with the nitrile-peroxide system an 80% (titrated) yield of 1,2-epoxycyclohexene in it would be possible to obtain certain epoxides six hours at 35°.
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