A study of tautomerism in diazonium coupling products of 4‐hydroxycoumarin

Abstract

The spectra (1H nmr, ir and uv) of a series of 3‐arylazo‐4‐hydroxycoumarins 1a‐m indicate that such compounds exist predominantly in the keto hydrazone form 1A both in solid state and in solution. The acid dissociation constants of the series studied were determined spectrophotometrically in 80 vol% ethanol‐water mixture at 27° and ionic strength of 0.1. The results of the correlations of these constants by Hammett and Yukawa‐Tsuno equations exclude the presence of the hydroxyazo form 1B in equilibrium with 1A in agreement with the spectral data. Also, the HMO method has been used to study tautomerism in such compounds. The results are also in full agreement with both the spectral and linear free energy correlations, the hydrazone form 1A being the most stable. It is further shown that both the intermolecular and intramolecular hydrogen bonding favor the hydrazone tautomer.

Synthesis, Structure Elucidation and Application of Some New Azo Disperse Dyes Derived from 4-Hydroxycoumarin for Dyeing Polyester Fabrics

“…One might thus expect that the ketone group would be preferentially involved in the intramolecularly H-bonded system to indicate that D (Z-isomer) is more stable than D (E-isomer), which is in agreement with the isomer ratio observed in the 1 HNMR spectra (Z:E ~ 84.5:15.5). This evidence is in agreement with those previous values reported by the computational study [11] or 15 NNMR spectroscopy [10].…”

“…Another interesting feature of this class lies on its tautomeric behavior which has been studied by several investigators for many years. They were originally regarded as azo-structure (A) [7,8], but others workers [9][10][11] tended to the view that they were keto-hydrazone structure (D). Recently, two groups of workers [12,13] proposed that compounds exist as a mixture of tautomeric forms(A) and (D) (Fig.…”

Synthesis, Tautomeric Structure, Dyeing Characteristics, and Antimicrobial Activity of Novel 4-(2-Arylazophenyl)-3-(2-hydroxyphenyl)-1-phenyl-2-pyrazolin-5-ones

“…25,26 Treatment of 2a-f with phenyl hydrazine in ethanol under reux afforded the respective 4-(2-arylazophenyl)-3-(2-hydroxyphenyl)-1-phenyl-2-pyrazolin-5-ones 4a-f in good yields (Scheme 1). The structures of the latter derivatives 4a-f Experimental).…”

“…4-hydroxycoumarin (1), 24 2,3,4-chromantrione-3-arylhydrazones 2a-f, 25,26 and 1-phenyl-3-(2-hydroxyphenyl)-2-pyrazolin-5-one (3) 16 were prepared according to literature procedure.…”

Solvent-Free Synthesis and Spectral Linearity of Some (E)-2-(substituted benzylideneamino)-N-(3-chloro-4-fluorophenyl)-hexahydro-2<i>H</i>-cyclopenta[b]thiophene-3-carboxamides

“…Schiff bases are bimolecular condensation products of primary amines with carbonyl compounds. Schiff bases are characterized by the -N=CH-(imine) group which finds importance in elucidating the mechanism of transamination and racemization reactions in biological systems [1,2]. Schiff bases of aliphatic aldehydes are relatively unstable which readily undergo polymerization while those of aromatic aldehydes having an effective conjugation system are found to be more stable.…”