ABSTRACT

This paper reports an experimental and theoretical study on the structural and energetic characterization of the 2-mercaptoimidazole (2-MI) in the solid and in the gaseous phases. The single crystal X-ray diffraction determinations on the anhydrous and hemihydrate 2-MI forms were carried out at T = (296 +- 2) K and T = (150 +- 2) K, respectively, and suggest that in both forms the 2-MI molecule is closer to the thione conformation, albeit some single bond character is possible. The energy of combustion of the title compound was measured by rotating-bomb combustion calorimetry, being used to derive the corresponding enthalpy of formation in the crystalline-phase. The enthalpy of sublimation of 2-MI, at T = 298.15 K, was obtained from high temperature Calvet microcalorimetry measurements. These two parameters yielded the gas-phase enthalpy of formation, allowing the inherent energetic analysis of the molecule. This result was discussed together with the corresponding predictions for 2-MI and its tautomer, 1,3-dihydro-2H-imidazole-2-thione, by the G3 method. The dehydration reaction of 2-MI 0.5H2O(cr) was also investigated and the corresponding enthalpy of dehydration was determined by Calvet microcalorimetry.

Compounds

#	Formula	Name
1	H2O4S	sulfuric acid
2	CO2	carbon dioxide
3	N2	nitrogen
4	H2O	water
5	O2	oxygen
6	C3H4N2S	2-mercaptoimidazole
7	C6H10N4OS2	2-mercaptoimidazole hemihydrate

Datasets

The table above is generated from the ThermoML associated json file (link above). POMD and RXND refer to PureOrMixture and Reaction Datasets. The compound numbers are included in properties, variables, and phases, if specificied; the numbers refer to the table of compounds on the left.
Type	Compound-#	Property	Variable	Constraint	Phase	Method	#Points
POMD	6	Mass density, kg/m3 ; Crystal	Temperature, K; Crystal Pressure, kPa; Crystal		Crystal	X-ray diffraction	1
POMD	6	Triple point temperature, K ; Crystal			Crystal Liquid Air at 1 atmosphere	DSC	1
POMD	6	Molar enthalpy of transition or fusion, kJ/mol ; Crystal			Crystal Liquid Air at 1 atmosphere	DSC	1
POMD	6	Molar enthalpy of vaporization or sublimation, kJ/mol ; Crystal	Temperature, K; Crystal		Crystal Gas	Static calorimetry	1
POMD	6	Molar heat capacity at constant pressure, J/K/mol ; Crystal	Temperature, K; Crystal	Pressure, kPa; Crystal	Crystal	Small sample (50 mg) DSC	8
POMD	6	Molar enthalpy, kJ/mol ; Gas	Temperature, K; Gas Pressure, kPa; Gas		Gas	Drop calorimetry	1
POMD	7	Mass density, kg/m3 ; Crystal	Temperature, K; Crystal Pressure, kPa; Crystal		Crystal	X-ray diffraction	1
RXND	6 1 2 3 4 5	Specific internal energy of reaction at constant volume, J/g				Rotating bomb calorimetry	1
RXND	6 7 4	Molar enthalpy of reaction, kJ/mol				DSC	1
RXND	6 7 4	Molar enthalpy of reaction, kJ/mol				Calvet drop calorimeter	1

Thermodynamics Research Center / ThermoML | Journal of Chemical Thermodynamics

Structural and energetic characterization of anhydrous and hemihydrated 2-mercaptoimidazole: Calorimetric, X-ray diffraction, and computational studies

Silva, A. L. R.[Ana L.R.], Morais, V. M. F.[Victor M.F.], Ribeiro da Silva, M. D. M. C.[Maria D.M.C.], Simoes, R. G.[Ricardo G.], Bernardes, C. E. S.[Carlos E.S.], Piedade, M. F. M., Minas da Piedade, M. E.[Manuel E.]

ABSTRACT