Investigations of catalysis of urethane formation using organotin dicarboxylate

The reaction mechanism of the urethane formation for both aliphatic and aromatic isocyanates in the presence of organotin dicarboxylate as a catalyst is investigated theoretically and experimentally. Modelling on a dispersion corrected DFT level of theory (B3LYP-D3) shows that an alkoxide complex is formed between organotin dicarboxylate and alcohol. This complex is the dominant catalyst for the urethane formation reaction. In this study, the interaction between the alkoxide complex and isocyanate through N-coordination is considered. By using thermochemical data, it is possible to show that aliphatic isocyanates can be more sensitive to the carboxylic ligand content of the organotin compound as a catalyst in urethane formation in non-polar solvents compared to aromatic isocyanates. The interactions of carboxylic acid, which is formed as an intermediate in the catalysis process, with isocyanate and the effects on the catalytic process are also discussed.