The kinetics of hydrogen‐deuterium exchange of methylisothiazoles

The rates of hydrogen‐deuterium exchange of 3‐methyl, 4‐methyl, 5‐methyI and 3,5‐dimethyl‐isothiazole were determined and compared with the rate of exchange of 2‐methylpyridine. The rates were measured in dimethylsulfoxide‐d6 ‐deuterium oxide (90:10), using sodium deuteroxide as catalyst. The relative rates for exchange of both ring protons and methyl protons were 5 > 3 > 4. For exchange of methyl hydrogens, the approximate ratio of rate constants is 100:1:< 10−4 for positions 5,3, and 4, respectively. Activation parameters are reported for 5‐methylisothiazole.