Mechanism of Hydrolysis of Hydroxy Thiolesters in the Presence of Boric Acid

Article abstract of DOI:10.1021/jo00320a021

The catalytic effect of boric acid on the hydrolysis of S-butyl 2-hydroxy-2-phenylthioacetate (thiomandelate, 1) and 3-hydroxy-3-phenylthiopropionate (2) has been investigated in aqueous solution.The catalytic constants increased sigmoidally with increasing pH, the pK_a of the curve being 9.2 for both 1 and 2.Approximate Hammett ρ values were 1.2 and 0.6 for the alkaline and borate-catalyzed hydrolyses of ring-substituted derivatives of 1, respectively.Boric acid did not show any specific influence on the hydrazinolysis of 1.Thise results lead to the conclusion that the borate catalysis occurs through an intramolecular transfer of the boron-coordinated hydroxide ion to the carbonyl carbon within a borate-substrate complex.