Original scientific paper

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

Monika Lovrek ; Faculty of Pharmacy and Biochemistry, University of Zagreb, A. Kovačića 1, 10000 Zagreb, Croatia
Viktor Pilepić ; Faculty of Pharmacy and Biochemistry, University of Zagreb, A. Kovačića 1, 10000 Zagreb, Croatia
Stanko Uršić ; Faculty of Pharmacy and Biochemistry, University of Zagreb, A. Kovačića 1, 10000 Zagreb, Croatia

Abstract

Addition of inorganic chlorides and perchlorates into the reaction mixture in water leads to a 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 »pure water«) vary from the 7.4-fold increase observed on addition of 2.0 mol dm-3 Mg(ClO₄)₂ into the reaction mixture to the 230.0-fold increase in the case of 2.0 mol dm-3 of MgCl₂ added. Linear correlation between log k_obs 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 ion pairing between the unstable cation reaction intermediates and the anion of the salt. The results obtained suggest that stabilization of the unstable cationic reaction intermediate by the formation of an ion pair with the salt anion is of key importance for the formation of hydroxamate from aldehydes and nitrosobenzenes in more concentrated inert salt water Solutions.

Keywords

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

Hrčak ID:

132011

URI

https://hrcak.srce.hr/132011

Publication date:

4.9.2000.

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