Abstract
Reduction kinetics of the methylene green (MG) with ascorbic acid (AA) in acidic medium at λmax 660 nm was monitored through visible spectrophotomtry in absence and presence of sodium carbonate. CO2 release through reaction of sodium carbonate and oxalic acid, created deoxygenated atmosphere for reduction of dye which greatly boosted the reaction rate. Initially slow reaction in presence of atmospheric oxygen proceeded rapidly when sodium carbonate was added. The reaction followed fractional order kinetics with AA and zero order kinetics with MG. The rate of reaction shows no linear dependence on [H+] concentration as an acidic medium. The rate of reaction is directly related with the elevated concentration of salt, which suggests that the two same charged species are involved in the rate determining step. Secondary reactions at elevated temperature showed complex kinetics.
Highlights
Ascorbic acid (AA),a form of Vitamin C and water soluble which comes primarily from fruit and vegetables is an important micronutrient and plays many physiological roles
Strizhak [4] propose a kinetic scheme for reduction of methylene blue by ascorbic acid, characterized by the existence of two pathways: outersphere reduction of methylene blue according to a second-order reaction, and reduction through formation of a 1:1 complex with ascorbic acid
Yusuf and Giirel [6] used methylene blue (MB), incorporated into titanium phosphate for determination of ascorbic acid (AA) and showed that reaction can be helpful in some pharmaceutical products and are for the detection of AA as the procedure involving the reaction between triiodide and AA
Summary
Ascorbic acid (AA),a form of Vitamin C and water soluble which comes primarily from fruit and vegetables is an important micronutrient and plays many physiological roles. Cooper et al [3] reported the photo electrochemical analysis of ascorbic acid in aqueous solution at a platinum channel electrode, using the dissolved phenothiazine dyes methylene blue and methylene green. This is achieved by measuring the current produced by immediate electro-oxidation of the reduced form of the dyes produced during the 1:1 photoreaction between the dyes and ascorbic acid induced by visible light of a wavelength of 620 - 625 nm. Cooper et al, [9] discussed the photoelectrochemical analysis of AA and decolorizing efficiency of AA to different synthetic dyes using Co/ H2O2 system [10]
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