The solvent effect and the structural effect of halides on the quaternization Et3N+RX → Et3RNX

In this study, the solvent effect on the rate constant of the quaternization Et3N + BzCl --> Et(3)BzNCl was studied. The used 20 solvents are, respectively, protic aliphatics, aprotic aliphatics, protic aromatics, and aprotic aromatics. The rate constant at 50 degreesC ranges from 0.23 x 10(-5) M-1 s(-1) in benzene to 31.74 x 10(-5) M-1 s(-1) in DMSO. For the solvents which possess normal characteristics among dipole moment (mu), solubility parameter (delta), and dielectric constant (epsilon), In k is shown to be proportional to delta. The activation energy (E-a), Gibbs free energy (DeltaG(not equal)), entropy (DeltaS(not equal)), and enthalpy (DeltaH(not equal)) in the various solvents were also obtained, and E-a - DeltaH(not equal) = RT was proved. On the. other hand, the structural effect of the halides on the rate constants of the quarternization Et3N + RX --> Et3RNX is shown by the two sequences k(RI)/k(BuI) = 2193, 1170, 522, 5.3, 1.3, 1.1, and I when R = Bz, Me, allyl, Et, Pr, and Hex, respectively, where k(BuI) = 3.37 x 10(-5) M-1 s(-1) in acetonitrile at 30 degreesC; and k(Bzl):k(BzBr):k(BzCl) = 2200:243: 1, where k(BzCl) = 3.36 x 10(-5) M-1 s(-1) in the same solvent and at the same temperature. (C) 2002 Elsevier Science B.V. All rights reserved.