Thiohydantoins. X. Kinetic Studies of the Acid Hydrolysis of 1-Acyl-2-thiohydantoins

The rates of hydrolysis of 22 1-acyl-2-thiohydantoins in aqueous sulfuric acid to give 2-thiohydantoin and a carboxylic acid have been determined. In 0-90% sulfuric acid, hydrolysis takes place by an A-2 mechanism, and the rate reaches a maximum in about 70% acid. In acid more concentrated than about 90%, hydrolysis takes place by an A-1 mechanism, and the rate increases monotonically. Evidence for the two mechanisms comes from Yates r and Bunnett-Olsen parameters; from entropies of activation; from pσ and pσ + relations; and from steric effects.