The rearrangement of benzoin to diphenylacetic acid was discovered by Lachman.1 By long heating in sealed tubes in the presence of aqueous solutions of phosphoric or sulfuric acids at temperatures up to 230°he was able to convert as high as 9 per cent, of the benzoin to diphenylacetic acid. Considerable decomposition to diphenylmethane and carbon dioxide occurred, however. , (C6H6)2CHCOOH
CeHsCHOHCOCeHs ( x (C6H6)2CH2 + co2This reaction is of interest from a theoretical standpoint because the alpha-hydroxy ketone benzoin is intermediate structurally between the diketone benzil and the glycols hydrobenzoin and pinacol. The benzil and glycolic rearrangements are usually almost quantitative under suitable conditions, and have attracted repeated consideration.2 3 The benzoin rearrangement is closely related also to the rearrangement of other alpha-hydroxy ketones and alpha-hydroxy aldehydes. Danilov and Venus Danilova4 found that alpha-hydroxyisobutyraldehyde could be changed to isobutyric acid in alkaline solution in the presence of hydroxides of heavy metals such as copper and lead. Heating the same aldehyde with very dilute mineral acid brought about a reaction of another type. , (CH3)2CHCOOH (CH3)2COHCHO ( x CHsCHOHCOCHs Other examples of this second type of rearrangement have been discussedrecently as "interconversion of mixed benzoins"6 where R'CHOHCOR" R'OHOHCOR'.* Compiled from a thesis submitted by Floyd L. James in partial fulfillment of the requirements for the degree Doctor of Philosophy.
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