Conversion of aromatic ketones into π-arylalkanoic acids. Oxidation by thallium(III) and by halogens

Abstract

The mechanism by which thallium(III) nitrate oxidises aromatic ketones to α-arylalkanoic acids has been investigated and the role of additives in the system elucidated. It is found that in the absence of additives an organothallium intermediate, most probably the phenacylthallium species BzCH₂Tl(NO₃)₂, persists and that the key to an efficient rearrangement is the ready conversion of this compound into its acetal. Thallium(III) is shown not to be a unique reagent for the oxidation. Other oxidants capable of acting initially as an electrophile and then as a leaving group are equally effective, provided that formation of an acetal is possible. Iodine-silver nitrate in particular offers considerable advantages as a reagent over thallium(III). Higher specificity is achieved, unwanted side-reactions can be avoided, and toxicity problems are eliminated. Bromine may be used instead of iodine, but chlorine proves unsatisfactory as an oxidant.