Addition reactions of conjugated double bonds. Part III. The kinetics of pyrazoline ring formation from αβ-unsaturated phenylhydrazones

H. Ferres, M. S. Hamdam, W. R. Jackson

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Abstract

The kinetics of cyclisation of a series of 4-arylbut-3-en-2-one arylhydrazones with differing substituents in the aryl rings have been studied in acetic acid solution. Values of log k56• are discussed in terms of Hammett σ+ values and the F and R constants of Swain and Lupton. Rearrangements of 4-phenylbut-3-en-2-one phenylhydrazone in deuterioacetic acid showed no significant kinetic isotope effects. The ratio kHOAc/kDOAc varied from 1.036 to 1.053 for kinetic runs at three temperatures. The rates of cyclisation of 4-phenylbut-3-en-2-one phenylhydrazone have been determined in a series of water-acetic acid mixtures. A mechanism for the reaction is proposed. The work of Raiford and his co-workers on the acid-catalysed cyclisation of phenylhydrazones from unsymmetrically substituted dibenzylideneacetones has been confirmed and the products have been shown to be thermodynamically controlled.

Original languageEnglish
Pages (from-to)1892-1898
Number of pages7
JournalJournal of the Chemical Society B: Physical Organic
DOIs
Publication statusPublished - 1 Jan 1971
Externally publishedYes

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