Abstract
The kinetics of the electron transfer reaction of methylene blue and titanium trichloride was studied in water and aqueousalcoholic solvents at various temperatures by spectrophotometry. The rate of reaction was observed by taking change inabsorbance as a function of time at λmax 660 nm. The reaction is pseudo-first order, dependent on concentration of titaniumtrichloride at fixed concentration of methylene blue.The effect of solvent was studied in the pH/Ho range from 4 to 7. It was observed that the rate of reaction increased withincrease in polarity of the reaction medium. The rate of reaction was high in acidic condition and decreased with furtherincrease in hydrogen ions activity. The increase in temperature increased the rate of electron transfer reaction of methyleneblue and titanium trichloride. Activation energy (Ea) was calculated by Arrhenius relation. The absence of any reactionintermediate was confirmed by spectroscopic and kinetic investigations. A plausible mechanism for the reaction in line withouter-sphere reaction pathway has been proposed. Thermodynamic parameters such as activation energy (Ea), enthalpychange (∆H), free energy change (∆G) and entropy change (∆S) were also evaluated.
Highlights
The methylene blue (3,7-Bis-dimethylamino phenazo-thionium chloride) is a water soluble organic, polyaromatic and heterocyclic compound and is chemically named as methylthioninium chloride
The pH in 942 | P a g e water was measured by Orion pH meter while the hydrogen ion activity in aqueous alcoholic solvents was determined in terms of Hammet acidity function (Ho) by measuring the absorbance of acridine orange solutions
The spectral analysis of methylene blue was done in different solvents in the presence and absence of titanium trichloride to determine the effect of different solvents and titanium trichloride on the absorption spectrum
Summary
The methylene blue (3,7-Bis-dimethylamino phenazo-thionium chloride) is a water soluble organic, polyaromatic and heterocyclic compound and is chemically named as methylthioninium chloride. It is a powerfull cationic dye having λmax at 660 nm. The structure of methylene blue is shown below. The phenothiazine dyes have a variety of applications such as in dyeing of clothes, coloring of paper, manufacturing of colored plastics, optical data storage devices, data recording holographic industries, in pharmaceutical preparations as an antiseptic and in food industry but on the other hand; they are toxic and carcinogenic in nature. The colorimetric indicators of oxygen used in food industry are based upon a chemical reaction between methylene blue and glucose present in the food [1]. Methylene blue can be used in photodynamic therapy of tumors and RNA viruses can be inactivated by treatment with methylene blue molecules [2]
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