Bond scission processes in sulphur compounds. Part IX. Nucleophilic catalysis in the methanolysis of methyl p-nitrophenyl sulphate

Abstract

Two consecutive processes are observed in the reaction of methyl p-nitrophenyl sulphate in methanol containing lithium perchlorate, as followed by u.v.–visible spectroscopy at 25°. In this solvolytic process, an initial conversion to p-nitrophenyl sulphate ion (carbon–oxygen scission) is followed by a further reaction to give p-nitrophenol (sulphur–oxygen scission). In reaction media containing perchloric acid the rate of the second stage is increased but the rate of the first stage remains unchanged. Therefore, there is no acid catalysis in the primary process yielding p-nitrophenyl sulphate ion. An apparent increase in the rate of this reaction which is observed in media containing hydrogen chloride can be ascribed to chloride ion catalysis. Similarly, nucleophilic catalysis is observed with bromide, fluoride, and azide ions. The reactivity order followed is typical of substitution at aliphatic carbon. A preference of alkyl aryl sulphates for reaction with nucleophiles at the alkyl carbon, rather than at aryl carbon or sulphonyl sulphur centres, is noted.