Methoxy-P-Benzoquinone and Methoxyhydroquinone As Models for Chromophore Changes in the Bleaching of Softwood mechanical pulps. II. The Effect of Peroxide Charge, Reaction Ph, and Transition Metal Ions

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Abstract
Methoxy-p-benzoquinone and methoxyhydroquinone were reacted with-hydrogen peroxide in the presence of either Na5 DTPA/Mg2+ or silicate/Mg2+ stabilization systems. The conditions used approximated those in the technical bleaching process, and the resulting effect on color was ascertained by monitoring the absorbance at 457 nm. The results revealed that the initial color of solutions of the quinone and hydroquinone increased dramatically with the application of relatively small amounts of alkaline peroxide and was “bleached” to its original level only after application of excessively large amounts of this oxidant. Subsequent experimentation, in which the pH of the of the reaction mixture, order of reagent addition and mixing regimen were varied, provided evidence suggesting that the observed increase in “color” on alkaline peroxide treatment of the quinone was attributable to alkali-promoted condensation reactions, the products of which were only partly decolorized through action of the peroxide. The effect on “color” produced by the addition of transition metal ions was found to depend on the particular metal and the peroxide stabilization system employed. The responses of the quinone/hydroquinone and mechanical pulps toward alkaline peroxide in terms of optical properties are compared.

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