AbstractThe kinetics of the gas‐phase decomposition of ethyl, isopropyl, andt‐butyl isocyanates have been studied in the temperature range of 380–530°C.t‐Butyl isocyanate decomposes almost exclusively by a unimolecular route to isobutene and HNCO, but in EtNCO andi‐PrNCO this route competes with a free‐radical chain which produces CO, CH4, and HCN or CH3CN. Ini‐PrNCO, however, the chain process is very rapidly inhibited by the propene formed in the parallel unimolecular route. A minor heterogeneous bimolecular decomposition in each case gives rise to carbon dioxide and a carbodiimide. Mechanisms and trends in the alkyl isocyanates from methyl throught‐but