The water-soluble carboxylic acid-functionalized aromatic disulfides, 3,3′-dithiodibenzoic acid and 5,5′-dithiodiisophthalic acid (5,5′-dithiodi(1,3-benzenedicarboxylic acid)) were prepared and their rates of periodate oxidation to the sulfonic acids were determined. The reaction is first order in each of the reactants which indicates that the slow step is the initial oxidative cleavage step. These aromatic disulfides are oxidized to the sulfonic acids 4–8 times more slowly than a typical aliphatic disulfide. In all cases, water solubility of the disulfide is of prime importance. The periodate oxidation of two aliphatic carboxylic acid analogs were also examined, however, in these cases, the reactions were multiphasic and intermediate thiosulfinates were observed by1H NMR along with the sulfonic acids.