Intriguing Salt Effects in the Formation of Hydroxamic Acids from Aldehydes and Nitroso CompoundsReport as inadecuate

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Croatica Chemica Acta, Vol.73 No.3 September 2000. -

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 MgClO42 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 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, MgClO42 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.

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

Author: Monika Lovrek - ; Faculty of Pharmacy and Biochemistry, University of Zagreb, A. Kovačića 1, 10000 Zagreb, Croatia Viktor Pilep



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