The Rates of Gas-Phase Reactions of Solvated Anions With Acetone and Methyl Acetate. A Flowing Afterglow Study

Abstract

The gas-phase reactions of MeO ^---- HOMe with acetone and methyl acetate to form solvated enolate anions have rates of 2.0×10^-9 and 4.8×10^-11 cm³ molecule^-1 s^-1. It is proposed that the latter reaction is slow because internal barriers (transition states more negative in energy than reactants) cause the reactants to be entropy- favoured. Rates of reaction decrease dramatically as the extent of solvation of the nucleophile is increased; e.g., for the reactions of MeO ^-( HOMe )_n(n = 1- 3) with acetone, the rates for n = 1-3 are 2.0×10^-9, 1.5×10^-10 and 1.6×10^-12 cm³ molecule^-1 s^-1, respectively.