engleski

Acid-base Properties and Kinetics of Hydrolysis of Aroylhydrazones Derived from Nicotinic Acid Hydrazide

A series of aroylhydrazones were synthesized from nicotinic acid hydrazide and differently substituted benzaldehydes. The protonation constants of hydrazones 1 to 12, as well as of starting compounds, were determined in methanol/water 1/1 mixture by spectrophotometric-potentiometric batch titrations. In order to determine the effect of substituent on the stability of C=N bond, the kinetics of hydrolysis of hydrazones was studied spectrophotometrically in acidic and basic media. HPLC method was used for investigation of hydrolysis of selected compounds, for which equilibrium between hydrolysis and condensation reaction was noticed. The observed rate constants, calculated from chromatographic and spectrophotometric data were in good agreement. Electrospray mass spectrometry was used for determination of reaction products. The oxidation and formation of quinones in basic media were observed for 2, 3- and 2, 5-dihydroxy substituted benzaldehyde derivatives. On the other hand, the 2, 4-dihydroxy derivative showed higher stability compared to Nʹ-salicylidene-3- pyridinecarbohydrazide.

aromatic hydrazones ; HPLC ; hydrolysis ; mass spectrometry ; protonation constants ; UV spectrometry

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