Abstract
Reaction of amines and phosgene at low temp, for conversion of the amino group into carbamyl chloride and amine hydrochloride, and further reaction of this at high temp, with phosgene is known so-called Cold-Hot Method for synthesis of isocyanate. In case diamine such as TDA is used, a high molecular urea compound is formed by the wrong procedure of reacting condition and precipitated, so that the reaction with phosgene becomes difficult, resulting considerable decrease in the reaction velocity and yield. For successful operation of this reaction, it is necessary to make sufficient contact of phosgene with TDA in low temp. reacction in order to decrease the amount of unreacted TDA in the product and sufficient supply of phosgene in high temp, reaction. It is desirable to use solvents, such as ketones, esters and ethers, having high solubilizing power of low temp. reaction product. Also, chlorobenzene, dichlorobenzene, etc. could be used as the solvents by adding TDA solution into phosgene solution with vigorous stirring, in order to give finely dispersed particles of low temp, reaction product. The high temp, reaction is completed in 30 min at 130°c by sufficient introduction of phosgene in the low temp, reaction product thus obtained and the yield is high.
