The kinetic acidity of halomethyltrimethylammonium salts†
Abstract
The kinetic acidities of members of a series of halomethyltrimethylammonium salts (Me3N+CH2X, BF4−) have been measured under conditions of −OD/D2O at 50 °C, with the rate constants being found to increase X = Cl < Br < I. The observed trend is rationalized on the basis of the polarizabilities and electron repulsion factors of the respective halogen substituents. The observed rate constants indicate a lowering of the ΔG‡ for deuterium/hydrogen exchange of 12–13 kcal mol−1 due to the presence of the α-halo substituents. The kinetic acidity of chloromethyldimethylsulfonium BF4− was ≈106 that of the analogous chloromethylammonium salt.