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Reactions of potassium ethyl xanthate in aqueous solution Tipman, Norman Robert

Abstract

The reactions of potassium ethyl xanthate (KEtX) and its oxidation product diethyl dixanthogen (EtX)₂ were studied in neutral and mildly alkaline aqueous solution. Dissolved oxygen-was shown to be ineffective in oxidizing KEtX in homogeneous systems (solution), but (EtX)₂ was produced electrochemically at a platinum electrode by application of a small anodic overpotential. A slow hydrolysis reaction was proposed for the alkaline decomposition of aqueous ethyl xanthate in which carbon disulfide and ethyl alcohol were the decomposition products. The first order rate constant k₁ = 7.6 ± 1.0 x 10⁻⁴ hr⁻¹ (22°C) was independent of pH in the region pH 7 to 11. Low concentrations of (EtX)₂ (10⁻⁵ to 10⁻⁷ moles liter⁻¹) were determined by a new method based on extraction of the aqueous (EtX)₂ by hexane followed by ultraviolet spectrophotometric determination of the (EtX)₂ in the hexane extract. A sensitive technique for measuring saturation of (EtX)₂ in water using light scattering photometry; was also developed. The solubility of (EtX)₂ in water was found to be 1.27 x 10⁻⁵ moles/liter at 22°C from pH 2 to 8.5. At pH > 8.5, aqueous (EtX)₂ was shown to react with hydroxyl ion by a bimolecular displacement (SN[subscript omitted]2) mechanism which resulted in the formation of one mole of ethyl xanthate and one mole of an intermediate ethyl xanthate sulfenic acid. Decomposition of the intermediate compound resulted in carbon disulfide and other reaction products. The second order rate constant (k₂ = 13.5±0.5 liter mole⁻¹min⁻¹ at 22°C) was determined. Rest potential measurements using a platinum electrode in potassium ethyl xanthate-diethyl dixanthogen solutions showed that the Nernst equation for a one electron reaction was obeyed over a wide range of both KEtX and (EtX)₂ concentrations. Dissolved oxygen was found to generate mixed potentials to which no overall reaction could be assigned. It is expected that the rapid oxidation of ethyl xanthate to diethyl dixanthogen observed in mineral systems proceeds by a catalytic oxidation or electrochemical reaction at or near the mineral surface.

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