Structure–activity relations. Part 6. The alkaline hydrolysis of 3-methyl-5-methylidene- and 3,5-dimethylthiazolidine-2,4-diones. The addition of thiols to 3-methyl-5-methylidenethiazolidine-2,4-dione
The rate-coefficients for the alkaline hydrolysis of 3-methyl-5-methylidene- and 3,5-dimethyl-thiazolidine-2,4-diones in water at 25.0 °C have been measured. The reaction of the 5-methylidene substrate is first order in both substrate and hydroxide ion. The reaction of the 5-methyl substrate is two-phase. The first and more rapid reaction of this substrate is 1.4 times faster than the only observed reaction of the former substrate. The second reaction is the hydrolysis of an intermediate, which is first order in substrate and has two components, one first and the other second order in hydroxide ion. The rate coefficients for the addition of a series of thiols to the 5-methylidene substrate in water at pH 7.40 have been measured. A Brønsted coefficient of ca. 0.37 has been found. The detailed reaction pathway and relation to Marcus and related theories are discussed.