engleski

Intriguing Salt Effects in the Formation of Hydroxamic Acids from Aldehydes and Nitroso Compounds.

The addition of inorganic chlorides and perchlorates into the reaction mixture in water lead to the significant increase of the rate constants observed for the formation of N-phenyl hydroxamic acids from nitrosobenzene and formaldehyde or acetaldehyde. The rate enhancements (relative to the reaction rate constant in the “pure water”) vary from 7.4-fold increase observed on addition of 2.0M Mg(ClO4)2 into the reaction mixture, to the 230.0-fold increase in the case of 2.0M of MgCl2 added. Linear correlation between log kobs for the formation of the N-phenylformohydroxamic acid from nitrosobenzene and formaldehyde and the concentration of the anion of the salt added has been observed for MgCl2, CaCl2, LiCl, Mg(ClO4)2 and NaClO4, but different correlations were obtained for NaCl, HCl and HClO4. The observations are discussed in terms of the ion pairing between the unstable cation reaction intermediates and anion of the salt. The results obtained suggest that the stabilization of unstable cationic reaction intermediate by the formation of an ion pair with anion of the salt is of key importance for the formation of hydroxamate from aldehydes and nitrosobenzenes in the more concentrated inert salt water solutions.

salt-effects; ion-pairs; hydroxamic acids; hydroxamates; kinetics

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