Journal of the Korean Chemical Society 2013, Vol. 57, No. 5 Printed in the Republic of Korea http://dx.doi.org/10.5012/jkcs.2013.57.5.599 -599- Solvent-Free Synthesis of Some1-Acetyl Pyrazoles Ganesamoorthy Thirunarayanan †, * and Krishnamoorthy Guna Sekar ‡ † Department of Chemistry, Annamalai University, Annamalainagar-608 002, India. * E-mail: drgtnarayanan@gmail.com ‡ Department of Chemistry, National College, Tiruchirappalli-620 001, India. (Received June 11, 2013; Accepted August 28, 2013) ABSTRACT. Some N-acetyl pyrazoles including 1-(3-(3,4-dichlorophenyl)-5-(substituted phenyl)-4,5-dihydro- 1 H-pyrazole- 1-yl) ethanones have been synthesised by solvent free cyclization cum acetylation of chalcones like substituted styryl 3,4- dichlorophenyl ketones using hydrazine hydrate and acetic anhydride in presence of catalytic amount of fly-ash: H2SO4 catalyst. The yield of these N-acetyl pyrazole derivatives are more than 75%. The synthesised N-acetyl pyrazoline derivatives were charac- terized by their physical constants and spectral data Key words: Solvent-free cyclization cum acetylation, N-acetyl pyrazoles, IR, NMR spectra INTRODUCTION N-acetyl pyrazole is one of the derivatives of 4, 5-dihy- dro- 1 H-pyrazoles. These N-acetyl pyrazole derivatives are important precursor for the synthesis of some other pyra- zoline based heterocycles such as cyanopyridine 1 indoxacarb 2 carbohydrazide hydrazine, 3 pyrimidine. 4 There are numerous solvent-free or solvent assisted acetylation methods avail- able for the synthesis of N-acetylated pyrazoline deriva- tives in literature. 5-8 Glacial acetic acid and acetic anhydride were employed with solvent assisted conventional heat- ing, solvent-free microwave and ultrasound wave irradi- ation for acetylation of pyrazolines. 5,6 The sulfated solid catalysts such as sulphated titania, 9 sulphated zirconia, 10 sulphated tinoxide 11 , sulphated and molybdated iron oxide 12 and sulphated and phosphate zirconia 13 were employed for solvent assisted and solvent-free synthesis of organics. Osman et al., 1 have synthesised 75% yield of 4,7-dimethoxy- 5-(5-aryl-N-acetylpyrazolin-3-yl)benzofuran-6-ols by reflux- ing of Khellinone chalcones, hydrazine hydrate and glacial acetic acid. The 5-(p-tolyl)-4,5-dihydro-1-acetyl-pyrazol- 3-yl-phenyl}-3H-quinazolin-4-ones were synthesised using refluxation method of corresponding chalcones with hydra- zine acetic acid in ethanol by Mosaad et al. 14 More than 84% yield of some series of new N 1 -cinnamoyl-3,5-diaryl- 2-pyrazolines have been synthesised using microwave as well as conventional heating by Srivastava et al. 6 Shah et al., have synthesised 75% yield and studied the IR and 1 H NMR spectra of some new series of 4-(4-hydroxyphenyl)- 3-chloro-1-{4-5-(substituted phenyl)-1-acetyl-4,5-dihydro- pyrazol-3-ylphenyl} azetidin-2-one with 3-chloro-1-{4-5- (substitutedphenyl)-4,5-dihydro-pyrazol-3-ylphenyl}-4-(4- hydroxyphenyl) azetidin-2-one in acetic acid. 15 N-acetyl-3- (2-naphthyl)-5-aryl pyrazoline derivatives were synthe- sised and studied their FTIR, NMR and HRMS data by Ethiraj et al. 16 Many N-acetyl pyrazole derivatives such as N-acetyl-3,5-diphenyl pyrazolines, 17 1-acetyl-4-5-(3-chloro- 4-fluorophenyl)-2-furyl-3-substituted phenyl-4,5-dihydro- 1H-pyrazoles, 18 2,4-bis-(tetrahydro-1,4-oxazine)-6-4''- {1''-acetyl-5''-(4'''-methoxyphenyl)-2''-pyrazoline-3''-yl} phenylamino-s-triazine 19 , fluorine containing arylfuryl N- acetylpyrazolines 7 and 4,6-dimethoxy-5-(1-acetyl-5-aryl-2- pyrazolin-3-yl)benzobfurans 20 were synthesised by syn- thetic organic chemists using conventional heating method and studied their spectral data. These 1-acetyl pyrazoline derivatives possess important biological activities such as antibacterial, 6,7,15,18 endogenous proteolysis, 17 cytotoxic- ity, 16 EGFR kinase 8 and anti-inflammatory activities. 14 The literature survey reveals that there is no information avail- able for solvent-free synthesis of some N-acetyl pyrazolines including 3-(3,4-dichlorophenyl)-5-(substitutedphenyl)- 4,5-dihydro- 1 H-pyrazole) derivatives by cyclization of the respective chalcones and acetic anhydride in the presence of solid fly-ash:H 2 SO 4 catalyst. Therefore the authors have taken efforts to synthesis some N-acetyl pyrazolines including 3-(3,4-dichlorophenyl)-5-(substitutedphenyl)- 4,5-dihydro- 1 H-pyrazole) derivatives by solvent free microwave assisted cyclization of chalcones with hydra- zine hydrate and acetic anhydride in presence of catalytic quantity of fly-ash:H 2 SO 4 . The purities of these pyrazo- lines were checked by their physical constants and spec- tral data with reference published earlier in literature.