Stability of polyvinyl chloride in the presence of nitrating acid

Under the effect of sulfuric acid, oil of vitriol, or chlorosulfonic acid, with the simultaneous formation of sulfur dioxide, hydrochloric acid, and carbon dioxide, the polyvinyl chloride is transformed to a reticulated product which is insoluble in organic solvents and usable for ion‐exchange. The rate of reaction is dependent on the specific surface of polyvinyl chloride, the temperature, and the concentration of the sulfuric acid. In the presence of nitric acid, the reactivity of the polyvinyl chloride to the sulfuric acid changes fundamentally. Under duly chosen circumstances, and in the presence of several per cent of nitric acid, the polyvinyl chloride shows no appreciable change in composition in 100% sulfuric acid, even at 175°C., and it retains its thermoplastic properties and its solubility; only its molecular weight is decreased. At higher temperatures the polyvinyl chloride is slowly oxidized by the nitrating acid. On the basis of our investigations on the stabilizing effect of the nitric acid, conclusions can be reached concerning the rates of reactions initiating the decomposition of polyvinyl chloride and the subsequent reaction, the ratio of reaction rates, as well as the kinetics of the processes taking place in sulfonation and dehydrochlorination. The high stability of the polyvinyl chloride to the nitrating acid indicates that the zip reaction starts at one or two points of the individual molecules of polyvinyl chloride, and this reaction runs along the whole macromolecule. The strong stabilizing effect of the nitric acid can be attributed to the fact that it reacts with the double bond formed at the beginning of the decomposition at a higher rate than of the chain reaction of splitting off of hydrochloric acid from the allyl structure.