Photochemical Stability, Chemical Kinetics, and Electrical Characterization Studies as well as Some Theoretical Studies of Some Cyclic Hydrazones

The kinetic and thermodynamic properties of six Schiff bases (M1-M4) derived from 4-Pyridinecarboxylic acid hydrazide, and various aromatic aldehydes were studied. The aldehyde rings contained both electron-withdrawing and electron-donating substituents, as well as benzaldehyde itself. Hydrolysis kinetics showed minimal variation in rate constant values, with M2 exhibiting the fastest hydrolysis. The effect of pH indicated that acidic and basic environments accelerated the reaction compared to neutral conditions. Temperature dependence revealed low activation energy values for all compounds, indicating rapid reactions. Thermodynamic analysis showed that the hydrolysis processes were non-spontaneous (ΔG > 0), facilitated by hydrogen and hydroxyl ions. The significance of enthalpy (ΔH) and entropy (ΔS) in controlling reaction rates was also observed, with a negative entropy value suggesting the formation of an activated complex. A Density Functional Theory (DFT) study using ORCA software examined the electronic structures of para-substituted benzaldehyde derivatives, highlighting the impact of substituents on hydrazone formation. Imines, key intermediates in organic synthesis, were produced through the acid-catalyzed condensation of the Schiff bases (M1-M4) and aromatic aldehyde derivatives.