No satisfactory mechanism has been devised for the production of 2,3-butanedione by the acid oxidation of 3-methyltetronic acid (I). Wolff proposed (1) an intermediate 3-hydroxytetronic acid (II) whose hydroxylic hydrogen atom was assumed to rearrange to the 5-position with simultaneous loss of carbon dioxide. This hypothesis was based upon his observation that 3-bromo-3methyltetronic acid (III) was slowly hydrolyzed by base to form a solution from which 2,3-butanedione and carbon dioxide were liberated on acidification. To date no further work has appeared on this remarkable reaction.In order to explore the limits of the oxidation reaction, and at the same time to gain information regarding its nature, we have prepared and studied various types of tetronic acids from which -diketones might arise. These fall into three structural classes. In class (a) are acids carrying only 5-substituents, while in (b) the substitution is entirely on the 3-carbon atom, and in (c) both 3-and 5-substitution are present. These compounds and the results of their oxidation are shown in Fig. 2 where, for the sake of uniformity, non-enolic structures are used.It is apparent that the formation of -diketones is not a general reaction, but is dependent upon certain structural features in the parent tetronic acid. The first and most important of these is the presence of methylene hydrogen to permit enolization. Second, if the 3-carbon is monosubstituted, -diketones are produced regardless of substitution on the 5-carbon atom. On the other hand, if the 3-carbon is unsubstituted, the 5-carbon must carry one and only one substituent group. Significant differences also appear with respect to the natu e of the diketones produced. Thus, if the tetronic acid carries one 3-substituent, then regardless of 5-substitution, the over-all oxidation process results in decarboxylation with reduction of the 5-and oxidation of the 3-carbon atoms.3 However, in the case of monosubstitution on the 5-carbon, this rule is exactly reversed. These cases, and also that of tetronic acid itself, will be considered later
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.