The effect of a carboxyl substituent on the metabolism of aromatic aldehydes has been examined in several species of animals. 2. Phthalaldehydic acid was exclusively reduced to the corresponding alcohol in mice, rats, rabbits, dogs and man. The oxidized metabolite phthalic acid was not detected appreciably in any species. 3. Iso- and terephthalaldehydic acid were oxidized to the corresponding dicarboxylic acids in rats and dogs. The reduced metabolites were not detected. 4. The aldehyde group of o-formylphenoxyacetic acid and o-formylphenoxypropionic acid was largely reduced to the corresponding alcohol in rats, rabbits and dogs. In contrast, oxidation to the carboxylic acid predominant over the reduction in mice. In the former three species, the amount of the minor metabolite carboxylic acid was larger with o-formylphenoxypropionic acid than with o-formylphenoxyacetic acid. 5. 1,8-Naphthaldehydic acid, m- and p-formylphenoxyacetic acid were mainly oxidized to the corresponding carboxylic acids in rats. 6. It was concluded that aromatic aldehydes bearing a carboxyl group in the ortho position, attached either directly or indirectly to the benzene nucleus, tend to be reduced to the corresponding alcohols in animals.
