Standard enthalpies of formation of 2-aminobenzothiazoles in the crystalline phase by rotating-bomb combustion calorimetry E. Adriana Camarillo a,⇑ , Juan Mentado b , Henoc Flores a , Julio M. Hernández-Pérez a a Facultad de Ciencias Químicas de la Benemérita Universidad Autónoma de Puebla, 14 Sur y Av. San Claudio, C.P. 72570 Puebla, Puebla, Mexico b Instituto de Industrias, Universidad del Mar, Puerto Ángel, Distrito de San Pedro Pochutla, C.P. 70902 Oaxaca, Mexico article info Article history: Received 18 December 2013 Received in revised form 21 January 2014 Accepted 22 January 2014 Available online 31 January 2014 This paper is a contribution in honour to Prof. Manuel Ribeiro da Silva. We were fortunate to have met and learned from him. Dedicated to the memory of the late Professor Manuel Ribeiro da Silva. Keywords: Standard molar enthalpies of combustion 2-Aminobenzothiazole 2-Amino-4-methyl-benzothiazole 2-Amino-6-methyl-benzothiazole Enthalpies of formation in the gas phase Gausian-4 theory abstract The standard molar enthalpies of combustion of 2-aminobenzothiazole (2AB), 2-amino-4-methyl-benzo- thiazole (2A4MB), and 2-amino-6-methyl-benzothiazole (2A6MB) were determined in the crystalline phase at T = 298.15 K using a rotating-bomb combustion calorimeter. The molar energies of combustion of these compounds were found to be: (4273.6 ± 0.9), (4896.9 ± 1.1), and (4906.9 ± 1.2) kJ  mol 1 , respectively. From these values, the corresponding standard molar enthalpies of formation in the solid phase were obtained as: (59.55 ± 1.28), (2.71 ± 1.50), and (13.53 ± 1.53) kJ  mol 1 , respectively. The enthalpies of formation in the gas phase were determined using the experimental enthalpies of formation in the solid phase and predicted values of the enthalpies of sublimation. Additionally, the enthalpies of formation in the gas phase were calculated by means of the Gausian-4 theory, using several gas-phase working reactions, and were compared with those found using the predicted enthalpies of sublimation. Ó 2014 Elsevier Ltd. All rights reserved. 1. Introduction Benzothiazole derivatives possess a rather broad spectrum of applications. 2-aminobenzothiazole (2AB) is used as a precursor of compounds with anti-parasitic, anti-viral, and anti-tuberculosis activity. This compound has been investigated also for its use as an herbicide in agriculture [1,2]. 2-Amino-4-methylbenzothiazole (2A4MB) and 2-amino-6-methylbenzothiazole (2A6MB) have been researched for their properties as rust inhibitors of steel [3]. Recently, the heat of combustion of some nitrogen- and sulfur- containing compounds has been determined in our laboratory with high reproducibility and accuracy by using the rotating bomb com- bustion technique [4]. The aim of the present work is to contribute to better knowl- edge of the thermodynamics and thermochemical properties of 2-aminobenzothiazole (2AB), 2-amino-4-methylbenzothiazole (2A4MB), and 2-amino-6-methylbenzothiazole (2A6MB) as well as to establish some relationships between their molecular struc- ture and their energetics and reactivity. We have therefore conducted a detailed experimental study of the energetics of these compounds, whose structural formulas are depicted in figure 1. 2. Experimental 2.1. Materials and purity control The compounds were obtained from Fluka and Aldrich Com- pany with a mass fraction of less than 0.98. The samples were puri- fied by repeated re-crystallization from ethanol. The provenance and mass fraction purity are shown in table 1a. The purities, molar heat capacities, fusion temperatures and enthalpies of the compounds were determined using a TA Instru- ments 2010 differential scanning calorimeter. The calorimeter cal- ibration constant and the value of the thermal resistance for the temperature corrections were obtained by the fusion of high purity indium [5]. Sample purities were determined using the fractional fusion technique and performing the respective corrections for thermal lag and undetermined pre-melting [6]. The heating rates used were of 1 °C  min 1 and the masses of the samples were of ca. 3 mg. No sample weight loss was detected at run end in any of the differen- tial scanning calorimetry (DSC) measurements. http://dx.doi.org/10.1016/j.jct.2014.01.018 0021-9614/Ó 2014 Elsevier Ltd. All rights reserved. ⇑ Corresponding author. Tel.: +52 222 2295500x7533; fax: +52 222 2295584. E-mail address: elsa.camarillo@correo.buap.mx (E.A. Camarillo). J. Chem. Thermodynamics 73 (2014) 269–273 Contents lists available at ScienceDirect J. Chem. Thermodynamics journal homepage: www.elsevier.com/locate/jct