engleski

Spectrophotometric Determination of Protonation Constants of Aroylhydrazones Derived from Nicotinic Acid Hydrazide

Aroylhydrazones have been extensively studied due to their numerous applications: they can serve as chelating agents, particularly for transition-metal and lanthanide ions, they show biological activity (anticancer, antibacterial and antimicrobial), and have promising properties for various analytical applications. In this work we have determined the protonation constants of aroylhydrazones derived from nicotinic acid hydrazide. The compounds studied were prepared according to the procedures described elsewhere. The protonation constants were determined in methanol/water 1/1 mixture at 25 °C and ionic strength 0.1 mol dm–3 (NaCl). Owing to the fact that aroylhydrazones are prone to hydrolysis in solvents containing water, batch spectrophotometric titrations were carried out. The UV-Vis spectra were recorded within first 3 min after the preparation of solutions. Due to the fact that hydrolysis of arolyhydrazones below pH=2 was rather fast, equilibrium constants corresponding to the protonation of pyridine nitrogen were not determined. The logarithms of constants assigned to the protonation of amide nitrogen were in the range 10.5 to 12.9, whereas those corresponding to the hydroxyl group ranged from 7.1 to 8.9.

Aroylhydrazones ; protonation constants ; substituents effect

nije evidentirano