Synthesis of some substituted pyrazole-1- carbothioamides and spectral correlations in 3-(2,4-dibromophenyl)-5-(substituted phenyl)-4,5-dihydro-1H-pyrazole-1- carbothioamides

Background: This study aims to synthesise a series of 1-thiocarbomyl pyrazolines, including 3-(2,4-dibromophenyl)-5-(substituted phenyl)-4,5-dihydro-1H-pyrazole-1-carbothioamides, using solvent-free fly-ash:PTS catalyzed cyclization between chalcones and thiosemicarbazide, under microwave irradiation. Then to characterize them using analytical, physical and spectroscopic data. Methods: Solvent-free microwave assisted cyclization was adopted for the synthesis of 1-thiocarbomyl, including 3-(2,4-dibromophenyl)-5-(substituted phenyl)-4,5-dihydro-1Hpyrazole-1-carbothioamides, using fly-ash:PTS as the catalyst. They were characterised by IR, NMR and mass spectroscopic data. The infrared (IR) and nuclear magnetic resonance (NMR) spectral data was correlated with substituent constants, F and R parameters, using Hammett equation, to study the effect of substituents. Results: The yields of the synthesised chalcones were more than 85%. The spectral data of these 3-(2,4-dibromophenyl)-5-(substituted phenyl)-4,5-dihydro-1H-pyrazole-1- carbothioamides had been correlated, using single and multi-linear regression analysis. These gave a satisfactory or fair degree of correlation with some parameters. Conclusion: Easy handling, non-hazardous and environmentally benign cyclization method had been adopted for the synthesis of 1-thiocarbomyl pyrazolines using fly-ash:PTS as catalyst, with better yields. Some of the Hammett spectral correlations were found to be satisfactory, with the observed spectroscopic data. Keywords: 3-(2,4-dibromophenyl)-5-(substituted phenyl)-4,5-dihydro-1H-pyrazole-1- carbothioamides, fly-ash:PTS, Solvent-free synthesis, Hammett correlations.