Electroanalytical studies of arsinic and arsonic acids

Abstract

Electroanalytical studies have been made on the dialkylarsinic acids (C[subscript n]H[subscript 2n+1])₂ AsOOH (n = 2-4; c[underscore]-C₆H₁₁), the alkylarsonic acids, C[subscript n]H[subscript 2n+1]AsO₃H₂ (n = 1-8), the aromatic arsinic acids (diphenyl, dibenzyl, and di-2-phenyethyl), and the aromatic arsonic acids (phenyl, benzyl, and 2-phenyethyl). Several buffer systems were used. The best results were obtained in HCl-KCl buffers in the range 1.10[less than or equal to]pH[less than or equal to]3.10. The polarographic results in HCl-KCl buffers have shown that all of the acids can be determined quantitatively by differential pulse polarography within a specified range. The aliphatic arsonic and arsinic acids with C[greater than or equal to]6 exhibited strong adsorption effects. Cyclic voltammetric studies revealed that adsorption of product and reactant were occurring on some of the aliphatic acids. All of the aromatic acids exhibited some adsorption effects. The surfactant Triton-X 100 was used to minimize adsorption phenomena. Solutions of 0.002% and 0.003% Triton-X 100 proved useful. The variation of the peak potential versus pH was found to be non-linear for the dialkylarsinic acids. It was linear for all other acids in HCl-KCl buffers. The peak current, in most cases, was found to be pH dependent indicating that the reduction current is not entirely diffusion controlled. Cyclic voltammetric studies indicated that all reductions at the mercury electrode were totally irreversible and dependent on a coupled protonation step. Constant potential electrolysis on dimethylarsinic acid gave an electron reduction number of 2.89 which was consistent with a three electron reduction to the product cacodyl.