SiO2-H2SO4 catalysed, microwave-assisted cyclization cum acetylation of 2-propenones under solvent-free condition: Synthesis and spectral correlations of some 1-acetyl pyrazolines

Some 1N-acetyl pyrazoles, including 3-phenyl-(5-(substituted phenyl)-4,5-dihydro-1H-pyrazole-1-yl)ethanones, were synthesized by solvent-free cyclization cum acetylation of chalcones of substituted styryl phenyl ketones with hydrazine hydrate and acetic anhydride in the presence of a SiO2-H2SO4 catalyst. The yield of these N-acetyl pyrazole derivatives was greater than 80%. The synthesized derivatives were characterized by their physical constants and spectral data. The infrared spectral νCN and CO (cm−1) frequencies, nuclear magnetic resonance chemical shifts (δ, ppm) of Ha, Hb, Hc, CH3 protons, CN, CO and CH3 carbons of 3-phenyl-(5-(substituted phenyl)-4,5-dihydro-1H-pyrazole-1-yl)ethanones were assigned and correlated with Hammett substituent constants and Swain–Lupton parameters by single and multiple regression analyses. The results of the statistical analyses indicated that the substituents affect the frequencies and chemical shifts of acetylated pyrazoles.