The Measurement of Transfer Enthalpy in Mixed Solvent (Part 2) Solvent Effects on Nucleophilic Substitution Reactions of Ethyl and 2-Phenylethyl Benzenesulfonates

摘要

Heats of solution of aniline (AN), benzylamine (BA), ethyl-(EBS) and 2-phenylethyl benzenesulfonates (PEB) are calorimetrically measured in acetonitrile-methanol mixtures at 25.0 ∩. The activation parameters, ツH×, ツS× and ツ G×, are determined for the reactions of EBS and PEB with AN and BA using the kinetic data at three temperatures. Calorimetric transfer enthalpies of initial state, ヤHt0℃x(IS), and kinetically derived activation enthalpies, ヤツH×, in the MeCN-MeOH mixtures are combined to determine the transfer enthalpies of transition state, ヤ Ht0℃x(TS); ヤHt0℃x(TS) = ヤツH× + ヤHt0℃x(IS) The preferential solvation of anionic charge in the TS predicts a loose TS with a greater degree of bond cleavage for the reactions of PEB than for EBS, and also for the reactions with BA compared to the reactions with AN.