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 a t aliphatic carbon. A preference of alkyl aryl sulphates for reaction with nucleophiles a t the alkyl carbon, rather than at aryl carbon or sulphonyl sulphur centres, is noted.

Intramolecular catalysis of sulphate diester hydrolysis by one and two carboxy groups. The hydrolysis of aryl 2-carboxyphenyl sulphates

“…No significant amounts of salicylate could be detected on hydrolysis of phenyl salicyl sulphate, for which the route via (4) would be most favourable. We conclude that the hydrolyses of (la, b, and c) proceed through the common intermediate (3). This could be formed by a concerted, 'in-line' displacement,I2 or by way of a pentaco-ordinate intermediate (5).…”

“…The nucleophilic mechanism requires at least one, acyl sulphate, intermediate. This could be the cyclic mixed anhydride (3) or the open-chain derivative (4), and evidence that the carboxylate group becomes an acylating agent in the course of the reaction was obtained by carrying out the hydrolysis in the presence of hydroxylamine. Increasing concentrations of hydroxamic acid, detected by the characteristic ferric hydroxamate absorption at 530 nm, were formed as the reaction proceeded.…”

The acidolysis of p-nitrophenyl sulfate. A kinetic spectrophotometric method for evaluation of pKa

“…The pK, range can be extended somewhat by performing the rate measurements at temperatures other than 25 0C. 2 The method for pK, determination which we have described should be capable of application to media other than methan01.~ Preliminary experiments in ethanol have been performed. We 'In the previous work (3) the common ion effect of added hydrazinium chloride was not taken into account.…”

“…We reported recently on the kinetic study of o methyl p-nitrophenyl sulfate with some nucleo- [I] o ,~ philic reagents in methanol (1)(2)(3). It was found that a reagent HNu causes two reaction stages to rates was given (4) for the case that kA and kB (+SO>) are comparable in magnitude.…”

Morpholinolysis of Esters Analogous to Flutamide in 90% Methanol-water

“…Competition between the two electrophillic centers in the ester substrate is well documented for reactions of nitrophenylsulfonates, sulfates and phosphates with nucleophiles (Feuer, Patai, 1969& Buncel et al, 1975& Kirby, Jencks, 1965. On the other hand, most carboxylic esters undergo acyl-oxygen scission (Feuer et al, 1969& Kirby et al, 1965 partial Ar-oxygen scission was also reported attributable to the strong activation of the 1-position (ipso) of the phenolic group by the nitro groups (Guanti et al, 1975).…”