Urethanes. I. Organometallic catalysis of the reaction of alcohols with isocyanates

The catalysis of the reaction of n-butyl alcohol with isocyanates, using organometallic derivatives of lead, tin, and mercury, has been investigated. The rate of the reaction was measured by following the disappearance of the isocyanate absorption in the infrared. Phenyl, n-butyl, and cyclohexyl isocyanate were chosen to represent typical aromatic primary and secondary aliphatic isocyanates. Within the same series of catalysts, R_nMOAc, the catalytic effect decreases in the order RHg > R₃Sn > R₃Pb; and in all cases R = aryl > R = alkyl. The electronic effects of substituents on the aryl moiety are not pronounced. Changes in X of R_nMX greatly affect the catalytic activity. The mechanism of organometallic catalysis of the alcohol-isocyanate reaction occurs via a template-type mechanism whereby the catalyst acts to complex both reactants in a catalyst phase allowing the reaction to occur with greater facility.