SOME OBSERVATIONS ON CYANIC ACID AND CYANATES

Abstract

Various reactions of cyanic acid and the cyanate ion have been examined. Cyanic acid, in the presence of added hydrochloric or nitric acid, decomposes quantitatively according to the equation: HNCO + H3O+ → CO2 + NH4+. The rate constant for this reaction was measured over a range of temperature and ionic strength, and was found to be 0.86 mole liter−1 min.−1 at unit ionic strength and 1.5 °C. The activation energy is [Formula: see text] The effect of ionic strength on the reaction with hydrochloric acid closely parallels that on the activity coefficients of the acid itself. Without added acid cyanic acid decomposes by a first order reaction: HNCO + 2H2O → NH4HCO3, followed by a rapid second stage: NH4HCO3 + HNCO → NH4NCO + H2CO3. This reaction has a rate constant of 0.011 min.−1 at 0 °C. and an activation energy of 16 kcal. There is also a few per cent of some side reaction. Cyanate ions in alkaline solution decompose thus: OCN− + 2H2O → NH4+ + CO3−−. This reaction was examined over a range of temperature and ionic strength: it is first order with k = 3.0 × 10−3 min.−1at 100 °C. (0.3 ionic strength) and [Formula: see text] activation energy. The rate is somewhat dependent on hydroxide concentration, when this is fairly low. The reaction is catalyzed by carbonate, but not by a number of other anions that were examined. The rate of the catalyzed reaction is proportional to the carbonate concentration, but independent of cyanate, at least over a considerable range. The ionization constant of cyanic acid has been measured by a method that avoids errors from hydrolysis; the value obtained was 2.0 × 10−4. The oxidation of cyanate by hypochlorite and by chlorine was examined more briefly.