Thermal studies of some biological active oxadiazoles Non-isothermal kinetic study of potent antibacterial 2-(4-chlorophenyl)-5-(thiophen-2-yl)-1,3,4-oxadiazole Sanjiv Arora • Deepak K. Aneja • Mahesh Kumar • Chetan Sharma • Om Prakash Received: 6 September 2011 / Accepted: 4 April 2012 / Published online: 26 May 2012 Ó Akade ´miai Kiado ´, Budapest, Hungary 2012 Abstract A series of new unsymmetrical 2,5-disubstituted 1,3,4-oxadiazoles (3a–d) has been synthesized to evaluate their antibacterial and thermal properties. All compounds have been tested for their in vitro antibacterial activity against two Gram-positive bacteria namely, Staphylococcus aureus and Bacillus subtilis. Among the tested compounds, com- pound 2-(4-chlorophenyl)-5-(thiophen-2-yl)-1,3,4-oxadiaz- ole (3c) has been found to be most potent member having minimum inhibitory concentration. Thermal stability and melting point of compounds have been studied by TG and DSC analysis in air atmosphere at heating rate of 10 °C min -1 . Thermal degradation kinetics of the most potent antibacterial compound 3c has been carried out by multiple heating rate model free kinetic methods namely, Ozawa–Flynn–Wall, modified Coats-Redfern, and Kissinger. Keywords 2,5-Disubstituted 1,3,4-oxadiazole  Antibacterial activity  TG  DSC  Kinetics Introduction 1,3,4-Oxadiazoles are of significant interest in polymer and material science, because of their chemical/thermal sta- bilities and their high photoluminescence quantum yields. Since oxadiazoles groups are known as one of the most extensively investigated class of electron-accepting spe- cies, oxadiazoles-based compounds have been used as electron transport materials in organic light emitting diodes [1–8]. 1,3,4-Oxadiazoles constitute an important class of het- erocyclic compounds as they have attracted significant interest in medicinal chemistry. Among the 1,3,4-oxadi- azoles, 2,5-unsymmetrical disubstituted derivatives have attracted considerable attention because of their biological activity, their synthesis, and transformation for a long time. Biological activity associated with this class of compounds are antibacterial and antifungal [9, 10], anticancer [11], anti-inflammatory and analgesic [12, 13], anticonvulsant, neurotoxicity [14, 15], etc. Thermal analysis of pharmaceutical/medicinal com- pounds is a reliable method for purity control, and it is a necessary part of the characterization of new compounds with potential bioactivity. The thermal analysis methods are widely used for the study of the stability, and decom- position of the substances used in medicine. The evaluation of the stability of biologically active compound in solid dosage form is realized especially by analyzing its decomposition behavior in isothermal and non isothermal conditions [16]. There are many applications of thermal analysis in pharmaceutical industry and is summarized by Electronic supplementary material The online version of this article (doi:10.1007/s10973-012-2439-7) contains supplementary material, which is available to authorized users. S. Arora (&)  D. K. Aneja  M. Kumar Department of Chemistry, Kurukshetra University, Kurukshetra 136119, Haryana, India e-mail: sanjivkuk@yahoo.co.in D. K. Aneja e-mail: dk_aneja@rediffmail.com M. Kumar e-mail: mahesh.attri@yahoo.co.in C. Sharma Department of Microbiology, Kurukshetra University, Kurukshetra 136119, Haryana, India e-mail: chetanmicro147@gmail.com O. Prakash Institute of Pharmaceutical Sciences, Kurukshetra University, Kurukshetra 136119, Haryana, India e-mail: dromprakash50@rediffmail.com 123 J Therm Anal Calorim (2013) 111:17–25 DOI 10.1007/s10973-012-2439-7