Cleavage of disulfide polymers. II. By thiols

AbstractThe study of the interchange reaction of thiols with disulfides is extended to include additional thiols and conditions for redistribution. In aqueous suspension, polymeric disulfides are reduced in molecular weight to widely different extents by thiols of varying structures. Water‐soluble thiols as mercaptoethanol, and tertiary thiols as t‐butyl mercaptan, are relatively ineffective in cleaving. The presence of sodium disulfide with some of the thiols, particularly the thiophenols and 2‐mercaptobenzothiazole, retarded cleavage by the thiols. A study of the molecular weight of the polymer as the cleavage by thiols proceeded indicated that short chain lengths were gradually removed from the surface of the polymeric particles. The partial cleavage of a disulfide polymer by a mixture of sodium sulfite and sodium hydrosulfite produces a disulfide polymer of lower molecular weight and terminal thiol groups. This product should be capable of self‐redistribution to a random distribution. The liquid polymer resulting from the cleavage had a high heterogeneity index (M̄w/M̄n). Efforts to randomize in bulk to the theoretical index of 2.0 by heat, ultraviolet light, water, and amines were not successful. It was found possible to effect the reaction of the disulfide polymer with butyl mercaptan in solution in dioxane with sodium phenolate as catalyst. The conclusion is drawn that the reaction of a thiol with a disulfide, both in aqueous suspension and in dioxane, is ionic rather than radical.