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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.

The reversible reaction between the 1,3,5-trinitrobenzene-methoxide u complex (TNB.OMe-K+) and aniline in dimethyl sulfoxide-methanol solutions, yielding the 1,3,5-trinitrobenzene-aniIide u complex (TNB.NHPh-K+), has been studied spectrophotometrically and found to obey a rate law which is of first order with respect to aniline, but of complex order with respect to TNB.OMe-K+. An additional feature of this system is that whereas TNB and aniline alone undergo no reaction in MezSO-methanol, in the presence of methoxide ion a rapid reaction occurs to give the TNB-OMe-complex, which then undergoes a slow reversible conversion to the TNB-NHPh-complex. In both cases the kinetic data for the conversion of the methoxide complex (S) to the anilide complex (P) require a dissociative mechanism (Scheme IV) in which the interconversion of free T N B (I) and the protonated anilide complex (PH) constitutes the rate-determining step. Although the kinetic data do not rule against the intermediacy of the protonated methoxide complex (SH), the presence of this intermediate along the reaction pathway is considered unlikely. Further variations on the proposed dissociation mechanism (Scheme 11), as well as displacement mechanisms (Scheme I) and a mechanism involving anilide ion (Scheme 111), can be eliminated on kinetic grounds (cf. Table V and Figure 3). On the basis of the results of the present study, it is proposed that the lack of u-complex formation between T N B and aniline in the absence of strong base is due to a thermodynamic, rather than kinetic, factor.

Illustrating Consecutive ReactionsThe methanolysis of methyl p-nitrophenyl sulfate The student of chemical kinetics soon realizes that many reacting systems do not fit within the framework of a simple transformation, A -* B. Indeed he may even find intellectually stimulating the fact that the apparent simplicity of chemical dynamics does not hold in general.From eqn. ( 11), a plot of ln(OD--OD)n, versus time, from ti to t2, gives Volume 51, Number 12.

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