Steric effects in quaternizations. Alkylation of pyridine, thiazole, isothiazole and some benzologues with methyl, ethyl and isopropyl iodides

Abstract

Results of quaternization reactions in sulpholane at 65º are reported. A large steric hindrance is noted for quinoline relative to pyridine. A much smaller variation in rate with change in alkyl halide is seen in the benzothiazole/thiazole pair. Steric effects are very small and the rate retardation resulting from benzofusion is ascribed largely to an electronic effect. 2,l-Benzisothiazole reacts at essentially the same rate as isothiazole under these conditions.