Nucleophilic reactivities of tertiary alkylamines

摘要

The kinetics of the reactions of tertiary amines, triethylamine (1a), N-methylpyrrolidine (1b), N-methylpiperidine (1c), and N-methylmorpholine (1d) with benzhydrylium ions (Ar_2CH~+) have been studied in acetonitrile and dichloromethane. The benzhydryl cations were generated by laser flash photolysis of quaternary phosphonium and ammonium tetrafluoroborates. For most reactions, exponential decays of the absorbances of the benzhydryl cations were observed because the carbocations were generated in the presence of a high excess of the amines (pseudo-first-order conditions). From the linear plots of k_(obs) versus the amine concentrations, the second-order rate constants k were obtained, which allowed us to calculate N and s for these amines in CH_3CN and CH_2Cl_2. The linear free energy relationship log k = s(N + E) was thus used to integrate 1a-d into our comprehensive nucleophilicity scales.