Publications

ARO p-ISSN: 2410-9355, e-ISSN: 2307-549Xhttp://dx.doi.org/10.14500/aro.10508 5Abstract—A new series of novel pyrazoline compounds were synthesized by addition of thiosemicarbazide to the 2,6-dibenzylidenecyclohexanone (Chalcone) and its parasubstituted derivatives. This study was conducted for four purposes. First, a series of five-membered ring pyrazoline compounds were synthesized, and the structure of all new products obtained is supported by spectral data (1H-NMR, 13CNMR, infrared, and ultraviolet [UV]-visible), and the effect of substituents was studied. Second, the reaction kinetics of the newly synthesized compounds was studied to investigate the reaction mechanism pathway and order of the reaction; it was found that the reaction undergoes through Claisen route of mechanism with first-order reaction. Third, the thermodynamics of the reaction were studied, the rate of the reaction, Arrhenius parameters (A), and thermodynamic parameters for activation includes free energies (Ea), entropies (ΔS#), and Gibbs free energy (ΔG#) were estimated. Finally, the compensation effect was also studied and found the same pathway for all of the synthesized pyrazolicompounds.Index Terms—Pyrazolines, Kinetics, Mechanism, Chalcones, Compensation effect, Thiosemicarbazide, Claisen and Michael Pathway.I. IntroductionNucleophilic addition to α, β-unsaturated carbonyl compound as aldehydes, ketones carboxylic acids, and esters is one of the common reactions in organic synthesis. The presence of two conjugated functional groups C=C and C=O in the structure of α, β-unsaturated carbonyl compounds ease the nucleophilic addition reaction to occur frequently (Esmaeel, 1988). Moreover, α, β-unsaturated enones are important intermediate in many addition reactions of nucleophiles due to inductive polarization of carbonyl group at the β position (Ebenezer and Wight, 1995, Hamad et al., 2016). Furthermore, electrophilic addition (McCrae, 1973), Claisen addition (Carey, 1996), and Michael addition (Gutsche, 1967) are the most known types of such kind of reactions, and the use of heterocyclic compounds is the most common, due to their interesting biological activities.Pyrazoline is a heterocyclic compound that contains two adjacent nitrogen atoms; it can be synthesized using variety of methods. Pyrazoline compounds are not stable; readily convert to cyclopropane derivatives in the presence of heat or base catalyst (Qiu et al., 2008; Ramage et al., 1957). Pyrazoline and its derivatives are important compounds which constitute the basic framework of certain drug (Patel et al., 2011); also they are important precursors for pharmaceuticals and pesticides (Sloop et al., 2008).Pyrazoline compounds show a variety of biological activates such as anticonvulsant (Beyhan et al., 2017), antimicrobial (Joshi et al., 2012, Pandya et al., 2017, Kendre and Baseer, 2013, Hassan, 2011) antituberculosis, antileishmanial (Monga et al., 2014), and antifungal properties (Hassan, 2011).There are several works that have been published for the synthesis of pyrazolines. Mainly, the pyrazoline synthesis is based on the cyclization reaction of different chalcones with hydrazine compounds (Li et al., 2007, Lévai, 2005, Powers et al., 1998, Joshi et al., 2012, Pandya et al., 2017, Monga et al., 2014, Ethiraj et al., 2013, Kendre and Baseer, 2013, Hassan, 2011, Fazaeli et al., 2010), as shown in Scheme 1.Beyhan et al. reported a different method for the synthesis of pyrazoline compounds from the reaction of chalcones (prepared from methyl aryl ketones with substituted aldehydes) with thiosemicarbazide and N-(4-chlorophenyl) semicarbazide in alkaline medium (Beyhan et al., 2017). Another method for the synthesis of pyrazoline is through the reaction of substituted hydrazonoyl and N-phenylmaleimide in good yield (Abdelhamid et al., 2000), Scheme 2.The kinetic studies of pyrazoline formation from reaction of different chalcones with different compounds such as Schiff base, hydrazine, and thiourea in dimethylformamide and dimethylsulfoxide (DMSO) have been measured spectrophotometerically. The reaction is first order with respect to each reactant undergoes one or two steps to produce pyrazolines or pyrimidine thiones (Al-Khayat, 2010, Kaka et al., 2016). The kinetics of the reaction for the substituted chalcones have been also studied and found first-order reaction (Upadhyay, 2007).Synthesis of Novel Series of Pyrazoline, and Study their Kinetics and Reaction MechanismKosrat N. Kaka, Salam G. Taher, Wali M. Hamad and Aram H. IbrahimDepartment of Chemistry, Faculty of Science and Health, Koya University, Koya KOY45, Kurdistan Region – F.R. IraqARO-The Scientific Journal of Koya University Volume VII, No.2(2019), Article ID: ARO.10508, 9 pages DOI: 10.14500/aro.10508 Received 06 March 2019; Accepted: 18 August 2019 Regular research paper: Published 10 December 2019 Corresponding author’s e-mail: Kosrat.nazad@koyauniversity.orgCopyright © 2019 Kosrat N. Kaka, Salam G. Taher, Wali M. Hamad and Aram H. Ibrahim. This is an open-access article distributed under the Creative Commons Attribution License.