In Situ Monitoring of Selective Catalysts on Urethane Formation by FT-IR Spectroscopy

A number of tertiary amines and organotin catalysts for the phenyl isocyanate- 1,2-propylene glycol reaction were investigated by using in situ FT-IR. The reaction rate of each hydroxyl group, which is defined as the ratio between the rate constant of the secondary hydroxyl group and the rate constant of the primary hydroxyl group, is described with a second-order equation. The influence of different catalyst concentrations as well as the reaction temperature is discussed. It is observed that the selectivity depends on temperature but not on concentration, and stannous octoate is the most effective catalyst. The thermodynamic parameters were determined for the catalyzed reactions, primary and secondary hydroxyl groups being differentiated.