Equilibrium and Kinetic Studies of Some Reactions of 1-Anthraquinonesulfenic Acid and Its Methyl Ester

Article abstract of DOI:10.1021/jo00278a038

1-Anthraquinonesulfenic acid (2) is a stable arenesulfenic acid.Its pK_a, and the products and kinetics of its reactions, and those of its methyl ester (3), with both a thiol (n-BuSH) and m-chloroperoxybenzoic acid (MCPBA), have been determined.The results are compared with those for the corresponding reactions of two stable areneselenic acids (1a and 1b).The pK_a of 2 (7.51) shows it to be ca. 3 pK units stronger acid than o-O2NC6H4SeOH (1a).Reaction of 2 and 3 with n-BuSH occurs at comparable rates and gives n-butyl 1-antraquinonyl disulfide (5) via a reactionthat is acid catalyzed.The rate of reaction of 2 with the thiol is ca. 10⁴ slower than the rate of reaction of the structurally analogous areneselenenic acid, o-PhC(O)C6H4SeOH (1b).The probable reason for this large difference in rates is outlined.The difference in the rates of oxidation of 2 and 1b by MCPBA is much smaller, the selenenic acid being oxidized only 6 times faster than 2.Just as was found with selenenic acid 1a and its methyl ester, the rate of oxidation of sulfenic acid 2 by MCPBA is much faster than the rate of oxidation of its methyl ester.