Abstract
The kinetics and mechanism of oxidation of 2,4-dinitrophenylhydrazine (DNPH), a widely used derivatization reagent for analysis of aldehydes, with copper(II) in aqueous solution have been studied spectrophotometrically as a function of Cu(II) and DNPH concentrations at ionic strength (I = 1M) of NaCl. Since the hydrazine group of DNPH would be easily oxidized by Cu(II), serious interference for determination of aldehydes with Cu(II) was needed to be examined. The rate of the reaction was followed by monitoring the disappearance of the DNPH at 360 nm. System parameters such as pH, ionic strength, temperature and concentrations of Cu(II) and DNPH are examined. The rate of oxidation of DNPH is first order with respect to Cu(II) and DNPH concentrations. The oxidation of DNPH was studied at different temperatures (T = 293 – 313 K), and the active parameters Ea, △H□ and △S□ were evaluated. And the rate law of the whole system was followed as: The oxidation occur via aryl radical intermediate, to produce 2,4-dinitrophenol as final product. In the oxidation 3-4 mol of Cu(I) are produced by each mol of DNPH.