Nucleophilic heteroaromatic substitution-XXIV. Kinetics of piperidinodechlorination of 2- and 6- alkyl-4-chloropyrimidines in ethanol and toluene-evidence for a steric hindrance to solvation of the aza-group

Article abstract of DOI:10.1016/0040-4020(67)85028-2

The rate constants for the reaction of 2- and 6-alkyl-4-chloropyrimidines with piperidine in toluene and ethanol have been determined at 30.0°. The reactivity ratio k_Me/k_t-Bu increases considerably in passing from the reaction of 6-alkyl-4-chloropyrimidines in toluene (1.62) to the reaction of 2-alkyl-4-chloropyrimidines in ethanol (17.3). This remarkable increase (over a factor of ten) is ascribed to a steric hindrance to solvation of the aza-groups caused by the bulkier substituent.