SIDE REACTIONS OF PHENYLISOCYANATE DURING AMINE-CATALYZED CARBANILATION OF CELLULOSE

Reactions of phenylisocyanate under conditions used for the carbanilation of cellulose were studied, and the products were analysed by reversed phase HPLC. The reactions were carried out in pyridine, DMF or N,N-dimethylacetamide (DMAc) at 80°, or in DMSO at 70°, typically for 72 hr; residual phenylisocyanate was quenched with methanol. Products included methyl carbanilate, phenylisocyanurate (phenylisocyanate trimer) and 1,3-diphenylurea (from reaction with water). The phenylisocyanate dimer was not found as a product. The ability of the solvents to promote trimerization increased in the order pyridine < DMAc < DMSO < DMF. Amines catalysed the trimerizations, especially DABCO and 4-dimethylaminopyridine. The trimer is stable under the carbanilation conditions, and the trimerization competes with carbanilation. In contrast, the phenylisocyanate dimer dissociates to the monomer under carbanilation conditions. No evidence was obtained for the intermediacy of the dimer during carbanilation. The dimer is suggested as an alternative reagent to phenylisocyanate for carbanilation. © 1990.