Abstract
Hydroxylamine reacts with aspirin in aqueous solution at 25 °C predominantly through oxygen, to give O-acetylhydroxylamine as the initial product (Scheme 3). The reaction is much faster than the intramolecular general base catalysed hydrolysis of the carboxylate anion, as it is also for the CO2H form of aspirin. Both reactions are faster than expected, consistent with moderate activation and/or proton transfer catalysis of hydroxylaminolysis by both CO2 – and CO2H groups. Calculations support oxygen attack as the preferred reaction, but do not permit a clear choice between mechanisms involving NH2OH and + NH3–O – as the effective nucleophile.
Highlights
Reactions involving nucleophilic attack by hydroxylamine are of special interest because of its remarkably high reactivity in nucleophilic substitutions at carboxylic acyl and phosphoryl centers: which has been accounted for in terms of a unique ambident α-nucleophilicity
We report a study of the reactions of hydroxylamine with substituted aspirins, designed to identify the reactive nucleophile(s) involved – and possible further interesting mechanistic variations
Reaction with hydroxylamine Reactions of hydroxylamine with substituted aspirins were investigated at pH 6.00, where only the anionic form of the substrate is present: the kobs values obtained are plotted in Figure 1 as a function of neutral [NH2OH] concentration
Summary
Reactions involving nucleophilic attack by hydroxylamine are of special interest because of its remarkably high reactivity in nucleophilic substitutions at carboxylic acyl and phosphoryl centers: which has been accounted for in terms of a unique ambident α-nucleophilicity. Reaction with hydroxylamine Reactions of hydroxylamine with substituted aspirins were investigated at pH 6.00, where only the anionic form of the substrate is present: the kobs values obtained are plotted in Figure 1 as a function of neutral [NH2OH] concentration.
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