Tin oxide surfaces. Part VI.—An infrared study of the reactions of ethyl isocyanate and phenyl isocyanate with tin(IV) oxide and methylsilylated tin(IV) oxide

Abstract

Ethyl isocyanate reacts at 320 K with single hydroxyl groups on a trimethylsilylated tin(IV) oxide surface to form a urethane. The adsorption is reversed by evacuation at higher temperatures. Adjacent hydroxyl groups and water on tin(IV) oxide react to give 1,3-diethylurea which is adsorbed on the oxide as a perturbed “carboxylate-type complex”. The 1,3-diethylurea complex decomposes to ammonia and an acetate on evacuation at elevated temperatures. The stability of the surface urethanes to evacuation increases in the series SnO₂ < MgO < SiO₂. Phenyl isocyanate also forms a urea and a urethane, the urethane desorbing by evacuation at 320 K. The highly oxidising nature of the tin(IV) oxide surface prevented study of reactions at elevated temperatures.