Reactions of N-chlorobenzylalkylamines in which the alkyl group is Me, Et, i-Pr, t-Bu, and sec-Bu with MeONa-MeOH have been investigated kinetically. The eliminations are quantitative and regiospecific, producing only benzylidenealkylamines. The reactions are first order in base and first order in substrate, and an E2 mechanism is evident. The relative rates of elimination at 25 °C are 1/0.5/0.3/0.2/0.01 for Me/Et/i-Pr/sec-Bu/t-Bu alkyl substituents, respectively. The results are attributed to repulsive interaction between the alkyl group and the base in the transition state. Hammett ρ and kH/kDvalues decreased, but the ΔH*and ΔS* values increased with bulkier alkyl substituents. Changes in the transition-state parameters with the substrate steric effect are interpreted with variation in structure of the imine-forming transition states.
ASJC Scopus subject areas
- Organic Chemistry