The Influence of pH and Temperature on Tautomerism of Imines Derived from 2-hydroxy -1- napthaldehyde .

Abstract

The tautomerism reactions of one oxime molecule and seven Schiff bases
derived from 2- hydroxy-1- napthaldehyde with an appropriate aliphatic and aromatic
amines were studied .
The study is mainly concerned with the tautomerism reactions of the above
mentioned imines . This requires the measurements of UV absorption spectra of
imines 2-9 under the influence of different pH values in the range 4-10 and different
temperatures. This is accomplished by the evaluation of equilibrium constants K1 and
K2 for the tautomerism and isomerization reactions respectively and for imines 3-7
The remaining imines 2,8 and 9 undergo a tautomerism reaction only . The result
shows that the extent of keto and enol forms in these imines are altered by the
variation of both , pH and temperature .
The processes of tautomerism and isomerization reactions are proved by the
evaluation of thermodynamic parameters which were measured in ethanol and 1,2-
dichloroethane . The ΔH values calculated for both reactions indicate an exothermic
reactions type.Also these reactions being either spontaneous or nonspontaneous as
confirmed from the sign and value of ΔG estimated .Finally the calculated negative
entropies values ΔS , support these reactions stated above and are accompanied by
loss of keto entropy .Finally , a suitable explaination for the last behavior is given and
discussed .