Studies on the Trirnerization of Phenyl isocyanate Using an Imidazole-Epoxide Catalytic System

Abstract

Heating phenyl isocyanate [PI] with phenyl glycidyl ether [PGE] in dimethyl sulfoxide [DMS0] in the presence of 1-(2-cyanoethyl)-2-phenylimidazole [B] as a catalys t gives mainly 1, 3, 5-triphenyl isocyanurate [TPI]. At first, 1, 3-diphenylurea [DPU] is formed by the reaction of PI with a very small amount of water which is contained in DMSO, and then the trimerization reaction of PI proceeds. This reaction was kinetically investigated below 100°C. This trimerization reaction exhibits a definite induction period before the reaction starts, and is first-order in PI (fig.4, Table 1).
This trimerization mechanism would be expressed as follows;
The following suggests the possibility of the proposed mechanism.
( 1 ) Rate constants are linear with initial concentration of PGE or B (Figs.6 and 7).
( 2 ) When PGE is preheated with B in DMSO, a very small amount of PGE decr eases and electric conductivity of the mixture solution increases approximately by a factor of 4. And then both remain unchanged for several hours (Fig.9). This results suggest the possibility of the formation of ions.
( 3 ) In the trimerization of PI in the presence of the foregoing catalytic system, rate constants rem in unchanged but induction periods decreases (Table 3).