Clark, D. J. (1954)
Esterification by nitric and sulphuric acids.
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A method for the analysis of 2,4-dinitrobenzyl alcohol in the presence of Its acid sulphate ester has been developed and used in a kinetic investigation of the sulphuric esterification of this alcohol. Velocity constants for esterification of the alcohol and for hydrolysis of the ester have been determined at 25° in aqueous sulphuric acid media ranging in composition from 64.5-82.2% H2SO4 and at 0 for medium compositions H2SO4. The plot of log k for esterification at £0° against the acidity function H0 is a straight line of slope -0.96. this is satisfactorily explained by the hypothesis that in all media the alcohol exists practically entirely as a solvation complex and the rate-determining step in the esterification is a unimolecular decomposition of a protoneted form of this complex. For the hydrolysis the kinetic data are consistent with a mechanism involving an equilibria proton uptake by the ester followed by a rate-determining bimolecular reaction between the protonated ester and a water molecule. Rate constants have also been determined in deutero-aulphario acid media and are consistent with the mechanisms proposed. In the more acid media esterification is accompanied by a side-reaction. The effect of this side-reaction on the accuracy of the kinetic results is discussed. Methods have been developed for following the nitration of ethyl alcohol and of 2,4-dinltrobengyl alcohol in aqueous sulphuric acid media and some preliminary kinetic data obtained in media 60-96% H2SO4. Only In the more acid media is nitration at all extensive. Rates of nitration, however, are very rapid in these media and only become conveniently measurable in more aqueous media where the equilibrium is very much in favour of the free alcohol. A further complication in the case of ethyl alcohol is that in these more aqueous media oxidation of the alcohol occurs and prevents the determination of nitration rates. the oxidation is subject to an induction period and this can be prolonged by the addition of inhibitors, but only to a rather limited extent, 2,4-Dinitrobenzyl alcohol is resistant to oxidation.
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Institution: University of London, Royal Holloway College (United Kingdom).