Pakistan Research Repository


Azmat, Rafia (2004) KINETICS OF METHYLENE BLUE WITH ORGANIC REDUCTANTS. PhD thesis, University of Karachi, Karachi.



The photobleaching of methylene blue with reducing in 50% aqueous methanol using acetate buffer has been investigated with steady-illumination of monochromatic radiations of 661 mm on specially designed optical bench in a dark room. The dye reduction processes were studied at various parameters i) concentrations of dye, ii) concentrations of reductants such as Galactose, D-Mannose, D-(+)-Ribose, Maltose and Lactose, iii) acidity (Ho) of reaction solution iv) temperature as a function of quantum yield (0). Hammett acidity function (Ho) was used to determine acidity of the reaction solution. The optical method was adopted to evaluate the values of Ho. Bleaching of the dye simultaneously with demethylation has been observed upon irradiation, color recover as the source of irradiation turned off or exposure to air. Reaction follows second order kinetics with respect to dye concentration and reductant and first order with respect to triplet transient with life time of 10.1 us. A general mechanism has been proposed. Mathematical expressions were established and rations of rate constants were determined from experimental evidences. The tests were put forward to justify the mechanism. The mechanism was also supported by analysis of reaction mixture by TLC and column chromatic graphic techniques. Visible, Infra red and Mass spectrum of isolated product of the triplet transient showed the high reactivity of the dye triplet species towards different reagents present in the mixture The values of ratios of rate constant appearing in general mechanism were verified and it was found that quantum yield was the consequence of triplet

Item Type:Thesis (PhD)
Uncontrolled Keywords:methylene blue, organic reductants, monochromatic radiations, dye reduction, dye, photochemical reaction, laser photolysis, photobleaching
Subjects:Physical Sciences (f) > Chemistry(f2)
ID Code:1102
Deposited By:Mr. Muhammad Asif
Deposited On:20 Dec 2006
Last Modified:04 Oct 2007 21:04

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