Differential electrolytic potentiometry with periodic polarisation. Part XXVII. Direct and mark-space biased periodic polarisation in substitution, addition and oxidation titrimetry with dibromine in anhydrous acetic acid

Abstract

Applications of direct current and mark-space biased square wave differential electrolytic potentiometry to bromination and oxidation reactions in anhydrous acetic acid have been examined. A few oxidation reactions, e.g., of iodine and ascorbic acid, are fast enough to permit direct titration. Other reactions, such as nuclear bromination of aromatic hydroxy and amino compounds, addition to unsaturated aliphatic moieties and oxidation of covalent group 5B compounds, require double excess back-titration. Of the three electrolytes examined, perchloric acid, lithium chloride and sodium acetate, the last gives the best results for aromatic substitution, being alkaline enough to allow the phenoxide ion intermediate to form. Certain oxidation indicators of the diphenylamine and benzidine classes and aminotriphenylmethanes are not oxidised, but react by substitution, by nuclear bromination, and are cleanly determined without interference from unstable oxidation products. Addition to double bonds is slow but complete.