Methylglyoxal bis-(N,N-dimethylhydrazone): Synthesis and some reactions

Abstract

Methods were proposed for the synthesis of the methylglyoxal 1,2-bis-(N,N-dimethylhydrazone). A possibility was shown for the first time of its participation in the Diels-Alder reaction with maleic anhydride as an electron-rich diene. The second reaction of these reagents, which is observed in a wet media, is the formation of the hydrazinium salt of the initial diene with maleic acid. The most probable structure of the protonated diene among the four possible forms was revealed by the quantum-chemical calculations of the energy of the molecules and by the analysis of the 13 C NMR chemical shifts.The methylglyoxal bishydrazones, in particular, substituted bisguanylhydrazones and bisthiosemicarbazones, show pronounced biological activity, and some of them are used as drugs [1][2][3][4][5]. Earlier [6] by the reaction of 2-ethoxypropenal with equimolar amount of 1,1-dimethylhydrazine we obtained in a yield of 8% the previously poorly studied methylglyoxal bis-(N,Ndimethylhydrazone) (II) potentially possessing a pharmacological action.The aim of this work was an optimization of the methods for the synthesis of this compound in diverse ways and the study its properties.By the reaction of 50% aqueous solution of methylglyoxal (I) (commercial reagent) with dimethylhydrazine (molar ratio 1:4) the methylglyoxal bis-(N,N-dimethylhydrazone) (II) was produced. Depending on the experimental conditions and the method of binding water, the yield of bishydrazone II before distillation (according to 1 H NMR spectra) was 37-54%. A by-product of the reaction is methylglyoxal mono-N,N-dimethylhydrazone (III). Molar content of this compound in the reaction mixture was 13-22% depending on the experimental conditions. The formation of monohydrazone III is due to the reversible equilibrium in the water medium of the bishydrazone II and the related product of the hydrolysis at the ketone imine group.To eliminate the water medium we performed the synthesis of methylglyoxal from 2-ethoxypropenal in acetonitrile by the method of [7]. In the subsequent reaction of methylglyoxal with dimethylhydrazine MgSO 4 or molecular sieves 4 Å were used for binding the water formed at the condensation.