Intramolecular catalysis. Part 7. The Smiles rearrangement of substituted 2-hydroxy-2′-nitro- and -2′,4′-dinitro-diphenyl sulphones, as well as 2-amino-2′,4′-dinitrodiphenyl sulphide, 2-[(2-aminophenyl)thio]-3-nitropyridine and 2-hydroxy-2′,4′-dinitrodiphenyl ether

Abstract

Rate coefficients have been measured for the Smiles rearrangement of a series of 4- and 5-substituted 2-hydroxy-2′-nitrodiphenyl sulphones in 70%(v/v) dioxane–water at 60.0 °C, and for three substrates at several temperatures. The activation parameters for these substrates have been evaluated, as has the dependence on solvent composition [aqueous dioxane and dimethyl sulphoxide (DMSO)] of the rates for these substrates. The effects of substitution have been assessed by means of the Hammett equation using meta- and para-σ values for the 4- and 5-substituents, respectively, to give ρca.–2.0. All the evidence indicates reaction via a spiro Meisenheimer intermediate with the formation of the intermediate being rate determining. Rate coefficients have been also measured for the Smiles rearrangement of a series of 5-substituted 2-hydroxy-2′,4′-dinitrodiphenyl sulphones in 70%(v/v) dioxane–water at 24.8 °C and for three typical substrates at several temperatures. The activation parameters for these substrates have been evaluated, as has the dependence of rate on aqueous dioxane and aqueous DMSO solvent composition. In aqueous DMSO spiro Meisenheimer complexes are observed as the DMSO content increases. Above 50 mol% DMSO these intermediates are very rapidly and completely formed. The effects of substitution in 70%(v/v) dioxane–water have been assessed by means of the Hammett equation using meta-σ values to give ρca. 1.7. The evidence indicates that, in aqueous dioxane, reaction occurs via the spiro intermediate, with rate-determining decomposition of the Meisenheimer intermediate, and, in aqueous DMSO, the spiro intermediate becomes effectively the ‘initial’ state. The rate coefficients for the formation of the symmetrical spiro complex from 2-hydroxy-2′,4′-dinitrodiphenyl ether in DMSO–water and DMSO-tert-butyl alcohol containing base have been measured. The rate coefficients for the rearrangements of 2-amino-2′,4′-dinitrodiphenyl sulphide and 2-[(2-aminophenyl)thio]-3-nitropyridine have been measured in the same systems. Under these conditions, the ‘initial’ state is the spiro complex and the rate-determining step is the decomposition of the intermediate to form the product.