Combustion energies and formation enthalpies of 2-SH-benzazoles

doi:10.1016/j.jct.2008.02.018

The Journal of Chemical Thermodynamics

Volume 40, Issue 7, July 2008, Pages 1106-1109

https://doi.org/10.1016/j.jct.2008.02.018 Get rights and content

Abstract

The experimental determinations of combustion energies and the standard molar enthalpies of formation of 2-mercaptobenzimidazole, 2-mercaptobenzothiazole, and 2-mercaptobenzoxazole are presented. The combustion energies of compounds were determined by using a rotating-bomb calorimeter. The calorimeter used in the present work has been assembled, calibrated, and tested recently in our laboratory with desired results. As combustion auxiliary material, polyethene was used and its combustion energy was determined by using a static-bomb calorimeter. The combustion energies of 2-SH-benzazoles were used to derive the correspondent formation enthalpies in condensate phase at T = 298.15 K. The values of $Δ_{f} H_{m}^{\circ}$ for the compounds are (48.6 ± 1.4) kJ · mol⁻¹, (85.3 ± 1.5) kJ · mol⁻¹, and (−112.7 ± 1.4) kJ · mol⁻¹, respectively.

Introduction

The 2-SH-benzazoles, with a vast variety of molecular structures, are chemical compounds known by their application in biology and their study as antibacterial, antiviral, and anti-inflammatory agents in medicine [1], [2], [3]. The 2-mercaptobenzimidazole, 2-mercaptobenzothiazole, and 2-mercaptobenzoxazole are used as inhibitors of metallic copper and copper alloys corrosion in archaeological artifacts. The compounds were tested for their effectiveness in preventing the conversion of copper (I) into copper (II) compounds, which causes major damage in archaeological copper artifacts [4]. The heterocyclic compounds studied in the present work play an important role in organic synthesis. The 2-mercaptobenzothiazole and its derivatives have been used since 1920 as a primary accelerator to speed up the rubber vulcanization process to improve features of natural rubber [5]. Despite the applications of 2-SH-benzazoles in chemical and industrial fields, no combustion and formation enthalpies were found in specialized literature.

The present work is focussed on the experimental determination of the standard (p^∘ = 0.1 MPa) combustion energies and formation enthalpies in condensate phase of 2-mercaptobenzimidazole (2MBN), 2-mercaptobenzothiazole (2MBS), and 2-mercaptobenzoxazole (2MBO) at T = 298.15 K by using a rotating-bomb calorimeter. The molecular structures of 2-SH benzazoles studied are shown in figure 1.

According to figure 1, the compounds studied here are derivatives of benzimidazole (BN), benzothiazole (BS), and benzoxazole (BO), respectively, for which their enthalpies of formation in condensate state are (79.5 ± 1.3) kJ · mol⁻¹, (144.03 ± 0.70) kJ · mol⁻¹, and (−24.20 ± 1.1) kJ · mol⁻¹, respectively [6], [7].

Section snippets

Experimental

The 2MBN (cr), 2MBS (cr), and 2MBO (cr) are Aldrich and Fluka compounds. Reported mass fraction purity for 2MBS was higher than 0.99 and it was used without additional purification. The mass fraction purities for 2MBN and 2MBO were less than 0.98 and they were purified by repeated recrystallizations from (methanol + ethanol) mixtures and (ethanol + water + acetone) mixtures, respectively (solvents were Aldrich, HPLC grade), and then dried at T = 373 K for 10 h in a furnace. The mass fractions determined

Results and discussion

When the 2-SH-benzazoles were burned, the products of combustion process in the bomb were a sulphuric and nitric acids aqueous solution and a gaseous phase. Typical results of combustion experiments of 2MBN, 2MBS, and 2MBO are given in table 2 and correspond to the reactions (1), (2), (3), respectively. $\begin{matrix} C_{7} H_{6} N_{2} S (cr) + 10 O_{2} (g) + 113 H_{2} O (l) = \\ 7 {CO}_{2} (g) + (H_{2} {SO}_{4} \cdot 115 H_{2} O) (aq) + N_{2} (g) \end{matrix}$ $\begin{matrix} C_{7} H_{5} {NS}_{2} (cr) + 11.25 O_{2} (g) + 229.5 H_{2} O (l) = \\ 7 {CO}_{2} (g) + 2 (H_{2} {SO}_{4} \cdot 115 H_{2} O) (aq) + 0.5 N_{2} (g) \end{matrix}$ $\begin{matrix} C_{7} H_{5} ONS (cr) + 9.25 O_{2} (g) + 113.5 H_{2} O (l) = \\ 7 {CO}_{2} (g) + (H_{2} {SO}_{4} \cdot 115 H_{2} O) (aq) + \end{matrix}$

Acknowledgements

The authors thank VIEP-BUAP for financial support through Project 22 NAT 06-G. J.M. thank CONACyT (México) for his scholarship (register number 182142).

References (24)

W.O. Foye et al.
J. Pharm. Sci.
(1972)
P. Jiménez et al.
J. Chem. Thermodyn.
(1987)
W.V. Steele et al.
J. Chem. Thermodyn.
(1992)
M.V. Roux et al.
J. Chem. Thermodyn.
(1999)
H. Flores et al.
J. Chem. Thermodyn.
(2006)
S.P. Verevkin
J. Chem. Thermodyn.
(1998)
H. Flores et al.
J. Chem. Thermodyn.
(2004)
R.L. Thompson
J. Immunol.
(1947)
R.R. Mohan et al.
Indian J. Chem. B
(1985)
R.B. Faltermeier
Stud. Conserv.
(1999)

M.M. Coleman et al.

Ind. Eng. Chem. Prod. Res. Develop.

(1974)

W.Wm. Wendlandt

Thermal Analysis

(1986)

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Combustion energies and formation enthalpies of 2-SH-benzazoles

Abstract

Introduction

Section snippets

Experimental

Results and discussion

Acknowledgements

J. Pharm. Sci.

J. Chem. Thermodyn.

J. Chem. Thermodyn.

J. Chem. Thermodyn.

J. Chem. Thermodyn.

J. Chem. Thermodyn.

J. Chem. Thermodyn.

J. Immunol.

Indian J. Chem. B

Stud. Conserv.

Ind. Eng. Chem. Prod. Res. Develop.

Thermal Analysis