Kinetic Study of the Reaction between Substituted Triphenylmethyl Perchlorates with Pyridines in Nitromethane and 1,2-Dichloroethane Solvents

Abstract

Second-order rate constants at 25 °C have been measured for the reaction of triphenylmethyl carbonium ion with pyridine and substituted pyridines in nitromethane and 1,2-dichloroethane solvent. The activation parameters are in the range 1 to 3 kcal mol⁻¹ for the enthalpies of activation and −20 to −45 cal mol⁻¹ deg⁻¹ for the entropies of activation. The results are compared to the analogous measurements for Menschutkin reactions and it is concluded that the enthalpy of activation of a Menschutkin reaction results mainly from the bond breaking process and solvation changes associated with it, since the carbon-nitrogen bond making process seems to be entropy controlled.Rate measurements have also been made for 2-methylpyridine reacting with a series of para-substituted triphenylmethyl carbonium ion substrates in 1,2-dichloroethane solvent. A plot of log k₂vs ∑σ⁺ is non-linear and the curvature is interpreted as a saturation effect.