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Spectrophotometric and Chromatographic Investigation of Hydrolysis of Aromatic Aroylhydrazones Derived from Nicotinic Acid Hydrazide

Compounds 1–5 (scheme 1) were screened for their hydrolytic stability in acidic and basic solutions (methanol/water 1/1) by means of UV-Vis spectrophotometry. Hydrolytic stabilities of 4 and 5 were also studied by HPLC. It was observed that the hydrolysis was much faster in acidic than in basic solutions. Electron-withdrawing substituents were shown to accelerate hydrolysis in basic, whereas electron-donating substituents accelerated hydrolysis in acidic media. The rate-determining step of the hydrolysis reaction in acidic solutions is the attack of a water molecule on the protonated azomethine group, whereas in the basic medium it is the attack of water on completely deprotonated hydrazone.1 Hydrolysis of 4 and 5 does not proceed to completion, as evidenced by HPLC measurements. The formation of hydrazones 4 and 5 during time was observed when corresponding aldehyde and hydrazide were mixed at same experimental conditions (0.01 mol dm–3 HCl). The plots of kobs vs [H+] were not linear for compounds 4 and 5 suggesting different mechanisms regarding acidity and R substituent of investigated compounds. The results obtained by spectrophotometric and HPLC measurements were in agreement.

aroylhydrazones ; hydrolysis ; UV-Vis ; HPLC

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