The reaction of nitrile with α-hydrogens at high pressure III : pressure effects on the rates of the iminoether formation and proton/deuteron transfer reactions of substituted phenylacetonitriles in methanol

Abstract

The rates of the addition of methoxide ion to the CN bond and the proton/deuteron transfer reactions between methoxide ion and substituted phenylacetonitriles (XC_6H_4CY_1Y_2 CN: X=CH_3O, CH_3, Cl, Y_1=H, D, Y_2=H, D; X=H, Y_1=CH_3, Y_2=H, D) have been determined at high pressures, The rate constant at each pressure is fitted to the previously derived formula which permits the distinction between the structural volume change and the electrostatic volume change. The activation volume varies with the substituent from -(9.5±2.5) to -(13.7±1.8)cm^3/mol for the iminoether formation, and from +(18.2±2.9) to +(7.7±2.7) cm^3/mol for the deuteron transfer. The activation volume of the proton transfer reaction coincides with the value of the deuteron transfer reaction within experimental error. In the iminoether formation, the activation volume is more contributed from the structural term which does not vary so much with the substituent than the electrostatic one. And volume profile for that reaction suggests a product-like transition state. On the other hand, in the deuteron transfer reaction, the electrostatic term which varies considerably with the substituents, contributes to the activation volume much mare than the covalent one. It is also suggested from the fractionation theory that the solvation number does not change remarkably with pressure.