ALKYLATION OF 3(5)-METHYLPYRAZOLE WITH PROPARGYL BROMIDE AND STUDY OF THERMAL AND CATALYTIC POLYMERIZATION OF THE PRODUCTS OBTAINED

Field: Chemistry (Physical Sciences)

It is known that almost all reactions involving the nitrogen atom of 3(5)-methylpyrazole inevitably lead to the formation of N-substituted 3-methyl and 5-methyl pyrazoles. This also applies to 1-propargyl 3(5)-methylpyrazole. In this work, we succeeded in separating these isomers from each other and identifying them using 1H and 13C NMR spectroscopy methods. To synthesize individual isomers of 3-methyl-1-(prop-2-yl)-1H- and 5-methyl-1-(prop-2-yl)-1H-pyrazoles, we studied the alkylation of 3(5)-methylpyrazole with propargyl bromide under conditions of interphase catalysis in a liquid-liquid system of isopropyl alcohol-water at a temperature of 0-5°C, which provides a 75-80% yield of propargyl pyrazoles. For the first time, we were able to identify the obtained isomers. In the alkylation products, the 3-methyl isomer always predominates, but this does not complicate their separation from each other. It was of interest to determine the influence of the position of the methyl group in the pyrazole ring during the process of thermal catalytic polymerization. The data obtained from the thermal polymerization of the individual isomers showed that the isomer with the methyl substituent in the third position of the pyrazole ring does not polymerize practically at a temperature of 120-130 °C over 20 h, whereas the isomer with the methyl substituent in the fifth position of the pyrazole ring has a yield of 40.0% in the polymerization of pyrazoles. A completely different picture is observed during catalytic polymerization. At a temperature of 120-130 °C over 20 h, in the presence of a catalytic amount of PdCl2, both isomers polymerize at a rate of 50.0%. Since the alkylation of 3(5)-methylpyrazole yields mixtures of the 3-methyl-1(prop-2-yl)-1H-pyrazole (2a) and 5-methyl-1(prop-2-yl)-1H-pyrazole (2b) isomers, it is advisable to study their behavior during thermal and catalytic polymerizations together. The results of thermal polymerization showed that the 3-methyl-1(prop-2-yl)-1H-pyrazole (2a) isomer almost completely suppresses the polymerization process, with a polymer yield of only 8.0%, and in the presence of PdCl2 during polymerization of a 3(5)-methyl-1-(prop-2-yl)-1H-pyrazole (2a, 2b) isomer mixture, the polymer yield is ~40%. Thermogravimetric analysis (TGA) of the obtained polymers was carried out under dynamic heating conditions and it was shown that intensive weight loss of samples 3, 4 and 5 begins at a temperature of about 195 °C, 200 °C and 215 °C, respectively. The specific conductivity values of polypropargyl pyrazoles (10-3-10-5 Ohm-1.cm-1) indicate that they can find application as organic polymer semiconductors. For citation: Sukoyan A.H., Bichakhchyan L.A., Movsisyan T.G., Shakhatuni A.G., Hakobyan R.M., Attaryan O.S. Alkylation of 3(5)-methylpyrazole with propargyl bromide and study of thermal and catalytic polymerization of the products obtained. ChemChemTech [Izv. Vyssh. Uchebn. Zaved. Khim. Khim. Tekhnol.]. 2025. V. 68. N 4. P. 91-99. DOI: 10.6060/ivkkt.20256804.7168.