Kinetics of hydrolysis and rearrangements of S-acylthiouronium salts

Abstract

Kinetics of transformation of S-acetyl- and S-benzoylisothiouronium chlorides have been followed, and its reaction products in dilute hydrochloric acid media and aqueous buffers have been identified. In dilute hydrochloric acid the reaction rate is pH-independent, and the acetyl derivative reacts 8 times as rapidly as the benzoyl derivative. In acetate and phosphate buffers the decomposition rate of the both derivatives increases linearly with the buffer concentration. In acetate buffers the reaction rate is pH-independent, and acetate ion reacts as a nucleophile. In phosphate buffers the rate increases with increasing pH. The reaction catalyzed by the basic buffer component produces thiourea and carboxylic acid, that catalyzed by hydroxyl ion produces N-acetyl- or N-benzoylthiourea. The solvolysis rates of both S-acyl derivatives depend on percent composition of water-methanol solvent. The maximum solvolysis rate is reached in methanol with 25% (v/v) water.