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Effect of Temperature and Solvent Composition on the Acid Dissociation Constants of 2-Pyrrol and 2-Thiophene Aldehyde Phenyl Sulphonyl Hydrazones |
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PP: 33-36 |
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doi:10.18576/ijnc/020201
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Author(s) |
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Refaat I. Nessim,
Emad E. Albalaa,
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Abstract |
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| 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
composition over the temperature range 25-45oC. The obtained results were used in the calculation of the enthalpy, ΔHo,
and the entropy, ΔSo, 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. |
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