Radiation-Induced Decoloration of Dyestuffs in Aqueous Solution

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Abstract
The radiation-induced decoloration of bromphenol blue, crystal violet and eosin Y in dilute aqueous solution was studied with and without the addition of second solutes. These compounds are thiourea, benzoic acid and its derivatives with gradually changing structure. As in the case of radiation-induced deactivation of some enzymes and vitamins, the concentration of dyestuff was found to decrease exponentially with radiation dose, whether a second solute is present or not. This finding was explained in terms of the competition reaction of dyestuff and the second solute for free radicals produced in water. Of these compounds tested, thiourea which is known as protector for enzyme deactivation was found effective for dyestuff. From a kinetic treatment of the data, protection quotients of the second solutes were determined. It was shown that the protection quotient of benzoic acid or its derivatives with gradually changing structure is a linear function of substitution constant in Hammett's law, which correlates the reactivity of substituted benzoic acid with their chemical structure.

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