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A study of the photodegradation kinetics of yohimbine in acid media using multivariate curve resolution alternate least square (MCR-ALS)

A.E.El Gendy, M.Farouk, L.Abd El Aziz, A.Ashour, E.S.Shokry

A multivariate curve resolution method based on combination of multivariate curve resolution and alternate least square (MCR-ALS) is presented. The proposed method was used to study the degradation kinetics of yohimbine sulphuric acid solution upon exposure to the light of an 8-watt UV lamp in the range of 254 nm. The spectra of YOH in different concentrations of acid solutions collected at different lighting times (5 minute interval) were subjected to factor analysis and three different components were detected in the reaction system. Pure spectra of the components involved and their concentration profiles were obtained. It was suggested that in the presence of light, the acid solutions ofYOH are sensitive to atmospheric oxygen and they oxidize to 3,4 dehydroyohimbine.Atwo step mechanism is proposed for this photochemical reaction. In the first step, excited YOH reacts with ground state oxygen to give hydroperoxoyohimbine. This intermediate slowly rearranges in a second acid catalyzed step to yield 3,4 dehydroyohimbine. The results revealed that the photodecomposition ofYOH and the formation of dehydroyohimbine (DH) follow first order kinetics whose rate constants increase linearly with the concentration of acid.