Thermophysical study by DSC of several barbituric acid derivatives

M. Roux1, M. Temprado1, R. Notario1, F. Ros2, M. Segura3 and J. Chickos4

1Institute of Physical Chemistry Rocasolano, CSIC, Madrid, Spain
2Institute of Medical Chemistry, CSIC, Madrid, Spain
3PerkinElmer España S.L., Tres Cantos, Spain
4Department of Chemistry and Biochemistry, University of Missouri-St. Louis, St. Louis, Missouri, USA

Keywords: heat capacity
property: heat capacity, enthalpy of fusion
material: barbituric acid derivatives

The study of heat capacity as a function of temperature along with other phase changes plays an important role in identifying and understanding polymorphism in solids and the identification of liquid crystalline behaviour. The present study reports heat capacities as a function of temperature and fusion enthalpies and their associated temperatures for the following barbituric acid derivatives: 1,3-dimethylbarbituric acid [CAS 769-42-6]; 5,5-dimethylbarbituric acid [CAS 24448-94-0]; 1,3-diethylbarbituric acid [CAS 32479-73-5]; 1,3,5-trimethylbarbituric acid [CAS 7358-61-4]; 1,5,5-trimethylbarbituric acid [CAS 702-47-6]; and tetramethylbarbituric acid [CAS 13566-66-0] in the temperature interval from T = 268 K to their respective melting temperatures by differential scanning calorimetry (DSC).

Heat capacities at T = 298.15 K have also proven useful in algorithms developed to adjust vaporization, sublimation and fusion enthalpies with temperature. Experimental values are essential in the development of group additivity relationships. An additional objective of this work was to expand the database of available experimental heat capacities to provide reliable data that could be used to both generate additional group values or to refine existing values for the estimation of this property in cases hampered by the lack of sufficient data.

The support of the Spanish Ministry of Science and Innovation under Projects CTQ2007-60895 and CTQ2010-16402  is gratefully acknowledged. MT acknowledges the Spanish Ministry of Science and Innovation for a "Juan de la Cierva" contract.

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