In this study, 26 solvents belonging, respectively, to protic aliphatics, aprotic aliphatics, protic aromatics and aprotic aromatics were used to investigate the solvent effect on the quaternization of tributylamine with butyl iodide. The effect of the solubility parameter (delta) on the reactivity was correlated as In (k) = 1.28 delta - 23.8, R-2 = 0.943 for aprotic aliphatics; In (k) = 2.27 delta - 34.2, R-2 = 0.898 for aprotic aromatics; and In (k) = 0.102 delta - 12.6, R-2 = 0.671 for protic aliphatics. The deviation of some solvents was due to their abnormal behaviors with respect to the dipole moment (mu), dielectric constant (epsilon) and solubility parameter (delta). The activation energy (Ea), Gibbs free energy (DeltaG(not equal,0)), entropy (DeltaS(not equal,0)), and enthalpy (DeltaH(not equal,0)) in the 12 solvents used were also obtained. The values of [(Ea-DeltaH(not equal,0)) / RT] varyed from -0.632 in I-octanol to 1.164 in ethyl lactate. On the other hand, the structural effect of the tertiary amines, Me3N, Me2EtN, Me2BuN, Me(2)OctN, MeEt2N, Me(2)BzN, Me-2(OHEt)N, Et3N, Me2PhN, Pr3N, and Bu3N, on their quaternizations with BuI in acetonitrile at 40degreesC were demonstrated by the following relative reactivities k(Me3N) / k(Bu3N) = 584/1, k(Me(2)BzN / k(Me2PhN) = 33.9/1 and k(Pr3N) / k(Bu3N = 1.30/1. The Taft equation for the series of alkylamines is expressed as In(k/k(Me3N)) = -19.2 Sigmasigma + 5.73 Es, R-2 = 0.996. This equation can be used to predict the rate constants of the reactions of other alkylamines with butyl iodide.