Reactions of 4-Amino-3-penten-2-one and Its NSubstituted Derivatives with Diazonium Ions

Abstract

Azo coupling reactions of benzenediazonium salts with substituted 4-amino-3-penten-2-ones take place at the C-3 atom. 1H and 13C NMR spectroscopy has been used to study the structure of both the starting enaminones and coupling products. In CDCl3, 3-(4-chlorophenylhydrazono)-2-(4-methylphenylimino)-4-pentanone exists in hydrazo form whereas 4-amino-3-(4-chlorophenylazo)-3-penten-2-one is present as a mixture of two azo compounds differing probably in the arrangement of the intramolecular hydrogen bond. The azo coupling reaction kinetics have been studied in acetate buffers and methanol-water or tert-butyl alcohol-water mixtures. The coupling rate has been found independent of pH and buffer concentration. The reaction orders with respect to the starting compounds have been determined and the reaction mechanism is suggested. Linear dependence has been found between log kobs and substituent constants according to the Hammett or Yukawa-Tsuno equations.

15N,13C and1H NMR study of azo coupling products from diazonium salts and enaminones

“…It is obvious that such substances represent a rewarding subject of structural studies using multinuclear magnetic resonance. In spite of this fact, only a single paper 2 has been published so far dealing systematically with their structure. That study 2 made use of 1 H and 13 C NMR spectra to suggest the tautomeric form of two products of coupling reaction of enaminones, viz.…”

“…In spite of this fact, only a single paper 2 has been published so far dealing systematically with their structure. That study 2 made use of 1 H and 13 C NMR spectra to suggest the tautomeric form of two products of coupling reaction of enaminones, viz. 4-amino-3-phenylazopent-3-en-2-one and 4-(4-methylphenylimino)-3-(4-chlorophenylhydrazono)pentan-2-one.…”

“…The earlier paper 2 gives 1 H and 13 C NMR data for a series of substituted 4-aminopent-3-en-2-ones. It was proved that these substances exist exclusively in the tautomeric form of enaminones.…”

“…In the spectrum of pentane-2,3,4-trione 3-phenylhydrazone, the nitrogen atoms of the hydrazone group exhibit 7 11 (in the case of the azo compound, however, the structural similarity is far lower, and only the existence of an intramolecular hydrogen bond was taken for the similarity criterion) for the limiting values of corresponding nitrogen atoms in pure azo form, then according to earlier work 6,11 it is possible to calculate the proportion of the hydrazo form in the tautomeric mixture: 93. 6 2 The estimate of the proportion of azo form based on the coupling constants of 90 and 7.6 Hz is 8.4%. Three out of the four parameters given provide a consistent picture of the structure of 2a, which is present in CDCl 3 solution as a tautomeric mixture of about 90% hydrazo-imino compound and 10% azo-enaminone.…”

“…Structurally similar to the products of azo coupling reactions with enamines areˇ-amino-˛-nitro-˛,ˇ-unsaturated ketones, whose structure was studied by Chiara et al using 1 H NMR and IR spectra. 3 The aim of this work was both to verify earlier information 2 about tautomerism of the coupling products prepared from enaminones with the use of a larger set of models and to synthesize their selected 15 N isotopomers and, by means of 15 N NMR spectra (not yet studied) of isotopically labelled and unlabelled substances, to obtain further more detailed information about their tautomerism.…”