SYNTHESIS OF 1-VINYL-3(5)-METHYL-4-NITROPYRAZOLE AND STUDY OF THE EFFECT OF METHYL SUBSTITUTES IN THE PYRAZOLE RING DURING RADICAL POLYMERIZATION
Authors: Bichakhchyan Lilit A. , Markosyan Anna J. , Shakhatuni Aleksan G. , Badalyan Karine S. , Attaryan Hovhannes S. , Khachatryan Hasmik N. 
Published: December 2024

The aim of this work was to develop a convenient preparative method for the direct N-alkylation of 3(5)-methyl-4-nitropyrazole under conditions of phase-transfer catalysis (PTC). The need for development was also dictated by the fact that the reaction products are simultaneously intermediates in the synthesis of an important class of compounds - vinylpyrazoles. Alkylation of 3(5)-methyl-4-nitropyrazole under standard conditions of PTC (benzene-water-KOH-TEBACH (triethylbexylammonium chloride)) did not lead to the desired result. Apparently, benzene interrupts the transfer of the nitropyrazole anion from the aqueous organic medium, as a result of which the yield of the control alkyl compound is only 50%. During alkylation in the absence of benzene, under the influence of potassium hydroxide in water, deprotonation easily proceeds and the corresponding potassium salt of 3(5)-methyl-4-nitropyrazole is formed, which blocks the dehydrochlorination of 1,2-dichloroethane and leads to the selective course of the process of alkylation of the taken nitropyrazole. At an equimolar ratio of nitropyrazole and potassium hydroxide, the yield of a mixture of the resulting 1-(2-chloroethyl)-3- and 1-(2-chloroethyl)-5-methyl-4-nitropyrazoles reaches 80%. The dehydrochlorination of the obtained substituted chloroethylpyrazoles in a methanol solution, under conditions of PTC, and in an aqueous solution of N-methylmorpholine-N-oxide (NMO/H2O), in the presence of potassium hydroxide was also studied. Although the homogeneous method of dehydrochlorination is technologically imperfect, however, it makes it possible to obtain a mixture of 1-vinyl-3- and 1-vinyl-5-methyl-4-nitropyrazole isomers with a yield of 45%. Dehydrochlorination under PTC conditions is an alternative to a homogeneous process; however, it is not able to provide a high yield of the expected compounds - 20%. It has been established that the dehydrochlorination of the studied 1-(2̕'-chloroethyl)-3(5)-methyl-4-nitropyrazoles proceeds significantly successfully in the presence of KOH in the NMO/H2O system, leading to the total yield of 1-vinyl-3- and 1-vinyl -5-methyl-4-nitropyrazoles up to 60%. The effects of methyl substituents of the pyrazole ring during radical polymerization have been studied. The identified monomers exhibit different activities under the same conditions. Thus, in the process of radical polymerization, the isomer in which the methyl group is in the fifth position of the pyrazole ring polymerizes at a higher rate than the isomer in which the methyl group is in the third position.
For citation:
Bichakhchyan L.A., Markosyan A.J., Shakhatuni A.G., Badalyan K.S., Attaryan O.S., Khachatryan A.N. Synthesis of 1-vinyl-3(5)-methyl-4-nitropyrazole and study of the effect of methyl substitutes in the pyrazole ring during radical polymerization. ChemChemTech [Izv. Vyssh. Uchebn. Zaved. Khim. Khim. Tekhnol.]. 2024. V. 67. N 12. P. 39-46. DOI: 10.6060/ivkkt.20246712.7065.