Experimental and theoretical study of the structures and enthalpies of formation of the synthetic reagents l,3-thiazolidine-2-thione and l,3-oxazolidine-2-thione

This paper reports an experimental and a theoretical study of the structures and standard (po = 0.1 MPa) molar enthalpies of formation of the synthetic reagents 1,3-thiazolidine-2-thione [CAS 96-53-7] and 1,3-oxazolidine-2-thione [CAS 5840-81-3]. The enthalpies of combustion and sublimation were measured by rotary bomb combustion calorimetry, and the Knudsen effusion technique and gas-phase enthalpies of formation values at T = 298.15 K of (97.1 ± 4.0) and −(74.4 ± 4.6) kJ·mol−1 for 1,3-thiazolidine-2-thione and 1,3-oxazolidine-2-thione, respectively, were determined. G3-calculated enthalpies of formation are in reasonable agreement with the experimental values. In the solid state, 1,3-thiazolidine-2-thione exists in two polymorphic forms (monoclinic and triclinic) and 1,3-oxazolidine-2-thione exits in the triclinic form. The isostructural nature of these compounds and comparison of their molecular and crystal structures have been analyzed. The experimental X-ray powder diffractograms have been compared with the calculated patterns from their structures for identification of the polymorphic samples used in this study. A comparison of our results with literature thermochemical and structural data for related compounds is also reported.M.T. would like to thank MEC/SEUI, FPU AP2002-0603, Spain, for financial support. A.V.D. thanks the National Science Foundation (CHE-0547566) and the American Heart Association (0855743G) for financial support of this research. The support of the Spanish Ministerio de Educación y Ciencia under Projects CTQ2007-60895/BQU and CTQ2006-10178/BQU is gratefully acknowledged