The kinetics of the chromic acid oxidation of diphenylmethane |
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Authors: | K B Wiberg and R J Evans |
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Institution: | The Department of Chemistry, University of Washington USA |
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Abstract: | The kinetics of the chromic acid oxidation of diphenylmethane in aqueous acetic acid solution has been studied. The rate law is v = kφCH2φ]CrO3]h0 a kinetic isotope effect, kH/kD = 6·4 at 30°, was noted, and electron releasing groups were found to moderately facilitate the reaction ( + = ?1·17). These, and related data, suggest that the initial reaction is the abstraction of a hydrogen atom forming a benzhydryl radical. The latter may then be further oxidized to give the product, benzphenone. It is noted that the chromic acid oxidations which must involve hydrogen abstraction all show a kinetic dependence on the total chromium (VI) concentration, whereas those which are believed to proceed via an ester mechanism have a kinetic dependence on only the acid chromate ion. This difference is suggested as a possible method of distinguishing between these two mechanisms. The effect of the water content of the solvent on the rate of the reaction is discussed, and a tentative, relative, H? scale for some of these solutions is suggested. This may permit one to determine the number of molecules of water which are involved in a reaction. |
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