Methanolyses of para-substituted benzoyl chlorides in isodielectric binary mixtures

Abstract

The kinetics and mechanism of solvolysis of p-substituted benzoyl chlorides have been investigated in three isodielectric systems: methanol–acetonitrile, methanol–nitrobenzene, and methanol–nitromethane mixtures. Only S_N1–S_N2 processes are favoured by electron-donating substituents in all binary systems, but carbonyl addition processes become dominant in the low basicity (β) region of binary mixtures, especially in methanol–nitromethane for compounds with electron-withdrawing substituents. The rates for unsubstituted substrates as well as those substitutes with electron-withdrawing groups are higher than those for p-methyl substituted substrates, suggesting the contribution of a combined S_N1–S_N2 and carbonyl addition pathway, rather than the involvement of a concerted displacement with variable transition state.