EFFECT OF AMINES ON THE CARBANILATION OF CELLULOSE WITH PHENYLISOCYANATE

Various amines were added to carbanilation reactions of cellulose samples with phenylisocynate in an effort to aid the preparation of cellulose tricabanilates (CTCs) for determining molecular weight distributions (MWDs). However, the amines catalyzed the conversion of phenylisocyanate to its trimer phenylisocyanurate, especially in dimethylsulfoxide (DMSO) and N,N-dimethylformamide (DMF) media. In some of the reactions to which amines were added, the CTC products had high-performance size exclusion chromatographic peaks that tailed badly. The tailing was not caused by incomplete carbanilation. The amines 1,4-diazabicyclo (2.2.2) octane (DABCO) and 4-N,N-dimethylaminopyridine (DMAP) accelerated the dissolution of cellulose during carbanilation, while others retarded the dissolution. DABCO in pyridine assisted the carbanilation of cellulose samples, which were otherwise unreactive in pyridine, although the reactions were slower than in uncatalyzed DMSO media. However, the reactions in DMSO with added amines gave CTCs with lower degree of polymerization (DP) values, and the DP reduction was particularly severe when N-methylimidazole was the added amine. The possible involvement of oxidation by DMSO in the depolymerization process is discussed. It was concluded that addition of amines to carbanilation reactions of cellulose has limited application for CTC preparation for MWDs.