REACTION OF ACETONE WITH DIETHYL OXALATE FOLLOWED BY AZOCOUPLING

Abstract

Condensation of acetone with diethyl oxalate in presence of sodium hydride followed by the action of a mixture of arylamine, hydrochloric acid and sodium nitrite in neutral medium in an equimolar ratio yields 3-arylhydrazono-2,4-dioxopentanoates. The method proposed is simple and convenient, it makes possible to obtain a variety of previously unknown 3-arylhydrazono-2,4-dioxoalkanoates. The target compounds are obtained with the yield of more than 35%, and it favours to produce single crystals for study of the crystal structure of the synthesized compounds by X-ray diffraction analysis. It was found that in the crystalline state synthesized compounds form the E-isomer. The structural features of 3-arylhydrazono-2,4-dioxopentanoates obtained are established by IR and NMR 1H spectroscopy. In the NMR 1H spectra, the signals of the proton-containing groups of 3-arylhydrazono-2,4-dioxopentanoates with comparable integral intensity values are detected in the expected region. In a weak field (15.00 - 15.08 ppm) signals of NH-protons are observed, which indicates the intramolecular hydrogen bond. It is shown that the ratio of reagents and pH of the medium affects the direction of further azocoupling by diazonium salts after acetone treated with diethyl oxalate. Thus, 1,5-diaryl-3-acetylformazanes were isolated in the alkaline medium with double excess of aryldiazonium chlorides by 35 – 37% yield. The identity of synthesized compounds is confirmed by thin layer chromatography, and their structure is proved by IR and NMR 1H spectroscopy data. The proposed structure of the isolated 1,5-diaryl-3-acetylformazans is the most preferred and characteristic of most formazans. NH-proton signals are observed in a weak field at 15.87 ppm. and 16.0 ppm the resulting 1,5-diaryl-3-acetylformazans, which indicates the formation of the hydrogen bond -NH ... N = N-type in the six-membered chelate cycle with the possibility of proton transfer.