Solvent effects in the benzylation of aniline

Second-order rate constants for the reaction of benzyl chloride with aniline were measured in various solvents: methanol, ethanol, 1-propanol, 2-propanol, 1 -butanol, 2,2-methylpropanol, benzyl alcohol, ethylene glycol, water, N-methylformamide, dimethyl sulfoxide, and some mixtures of alcohols with acetonitrile. The kinetic results depend on the dielectric constant and on the electrophilic parameter ET of the reaction medium. The protic solvent acts also a reaction catalyst, by favoring the displacement of the chloride ion by hydrogen bonding. The reaction is third order overall depending on the concentrations of the substrate, of the nucleophile, and of the protic solvent (electrophile), in agreement with the “push-pull” termolecular mechanism.