Perchlorate esters. Part 9. Correlation of the rates of solvolysis of methyl perchlorate using the extended Grunwald–Winstein equation

Abstract

The specific rates of solvolysis of methyl perchlorate in a wide variety of organic and aqueous-organic solvents have been measured and correlated by the extended Grunwald–Winstein equation. Each of the N_T and N_OTs scales of solvent nucleophilicity have been combined with each of the Y_OClO3 and Y_OTs scales of solvent ionizing power. The analysis shows the superiority of the Y_OCIO3, scale for correlating perchlorate esters and indicates a sensitivity to changes in solvent nucleophilicity about equal to that found previously for the S-methyldibenzothiophenium ion or methyl p-toluenesulphonate and a sensitivity to changes in solvent ionizing power slightly less than that for methyl p-toluenesulphonate; these sensitivities are consistent with a conventional S_N2 mechanism for the solvolyses. A claim for nucleophilic attack by the solvent at the chlorine of a secondary perchlorate ester is discussed and an alternative, involving attack at carbon, is proposed.