Acid dissociation constants and the conformations of 2-furfural and 2-thiophene aldehyde benzenesulphonylhydrazones

Abstract EN

Acid dissociation constants, pKa, of 2-furfural benzene-sulpho-nylhydrazone, (1) and 2-thiophene aldehyde benzenesulphonylhydrazone, (2) have been determined spectrophotometrically in ethanol-water media of various composition over the temperature range 15-40°C.

The results were used to calculate the enthalpy AH and the entropy AS for the ionization process.

The slight difference observed between the pKa values of the studied compounds (1) and (2) revealed that the ring heteroatom is not involved in the formation of hydrogen-bonded chelate ring.

This was confirmed by dipole moment, IR, and NMR spectral measurements.