Mechanism of hydrolysis of imidoyl chlorides

Abstract

The rates of solvolysis of substituted imidoyl chlorides (1a), chloroimidates (1b), chlorothioimidates (1c), and chloroformamidines (1d) have been investigated in aqueous dioxan. The initial products of solvolysis are the corresponding amides (3). Studies at varying pH indicate that all solvolyse by a unimolecular mechanism over the pH range 0–14 except the chloroimidates which also show acid and base catalysed reactions. In neutral solution the stabilized carbonium ion species (2) are formed as shown by salt and common ion effects, and also by large solvent effects (m 1·0–1·4). The ease of carbonium ion formation varies as follows: (1a) > (1d) > (1c) > (1b). In all cases the N-aryl ring (Ar¹) bears a larger fraction of the charge in the transition state for formation of (2)(reflecting the importance of the ‘octet-stabilized’ resonance structure) and the magnitude of ρ value for substituent variation (ρ_Ar¹–3·0 ± 0·15) is relatively independent of the heteroatom attached to carbon. Substituents attached to carbon in (1)[Ar, ArO, ArS, ArN(Me)] have a relatively smaller effect with ρ–2·0.