Abstract
Comparative analysis of the nucleophilicity of inorganic oxygen-containing α-nucleophiles (hydroxylamine and ClO-, BrO--, HOO--, NH2O-, and F- ions) covering the pKa range from -2 to 13.81 toward 4-nitrophenyl esters (4-nitrophenyl acetate, 4-nitrophenyl p-toluenesulfonate, diethyl 4-nitrophenyl phosphate, ethyl 4-nitrophenyl ethylphosphonate, and 4-nitrophenyl dimethylcarbamate) in water at 25°C (ionic strength μ 1.0, KCl) was performed in terms of the extrathermodynamic Bronsted relation. It was found for the first time that hydroxylamine anion ranks first among the series of α-nucleophiles. It is more reactive than HOO- ion with respect to 4-nitrophenyl acetate (by a factor of ∼8), 4-nitrophenyl p-toluenesulfonate (by a factor of ∼4) and 4-nitrophenyl dimethylcarbamate (by a factor of ∼10). The nucleophilicities of HOO- and NH2O- ions toward diethyl 4-nitrophenyl phosphate and ethyl 4-nitrophenyl ethylphosphonate are comparable. Taking into account that neutral hydroxylamine exhibits an anomalously high reactivity, as compared to not only common organic but also inorganic α-nucleophiles, it may be regarded as a unique α-nucleophile. Both neutral hydroxylamine and its anion as O-nucleophiles ensure high rates of acyl group transfer throughout a wide range of pH.
Published Version
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