Kinetics and Mechanism of Hydrolysis of 2-Methylthio-4, 5-diphenyl-1 ,3, 4-thiadiazolium Iodide

Research and Development Division, East India Pharmaceutical Works Ltd., Ottleuttra-31
Manuscript received 7 September 1973; accepted 23 March 1974

Kinetic runs with 2-methylthio-4, 5-diphenyl-1,3,4-thiadiazolium iodide (3) in 50% methanol (µ = 0.05) indicated that the rate constant (k_0b) of the hydrolysis of 3 is practically pH independent at pH>4 with first order dependence on [substrate]. Partial inhibition of the hydrolysis at pH<4 and the negative salt effect are attributed to specific cationanion interaction. Hydrolysis of 3 is also s Abject to general base catalysis with Br\(\phi\)nsted constant β\(\simeq\)0.2. Increase in rate with decreasing polarity of the medium and the small magnitude of ΔS* are consistent with unimolecular break­down of a nonpolar intermediate. Probable course of the degradation of 3 has been discussed in the light of experimental data.