Author(s)

Refaat I. Nessim¹, Imad E. Albalaa², Mona Abu Assi²

¹Department of Chemistry, Faculty of Science, University of Cairo, Giza, Egypt.
²Faculty of Basic Education, Public Authority of Applied Education and Training, Kuwait City, Kuwait.

Acid dissociation constants, pKa, of 2-pyrrolaldehyde phenylsulphonyl hydrazone, 1, and 2-thiophenealdehyde phenylsulphonyl hydrazone, 2, have been determined spectrophotometrically in ethanol-water media of various compositions over the temperature range 25℃ - 45℃. The obtained results were used in the calculation of the enthalpy, △H°, and the entropy, △S°, of the ionization processes. The slight variations observed in the pKa values of the thiophene compound compared to the pyrrol analogue revealed that neither of the two hetero atoms in the pyrrol or thiophene rings, of the two compounds, is involved in a hydrogen bond chelation. This conclusion was also confirmed through measurements of the dipole moment, IR and NMR spectra.

Acid Dissociation Constant, Pyrrol, Thiophene

Nessim, R. , Albalaa, I. and Assi, M. (2016) Effect of Temperature and Solvent Composition on the Acid Dissociation Constants of 2-Pyrrol and 2-Thiophene Aldehyde Phenyl Sulphonyl Hydrazones. Natural Science, 8, 442-449. doi: 10.4236/ns.2016.810046.