Confirmation of the Presence of Formaldehyde and N(Methylene)morpholinium Cations as Reactive Species in the Cellulose/NMM/Water System by Trapping Reactions

摘要

The presence of formaldehyde (4) in solutions of cellulose in N-methylmorpholine-N-oxide (NMMO, 1) has been shown by trapping formaldehyde as dimedone adduct 8 in a two-phase system. o--Dichloroben- zene was used as an inert solvent to extract the trapping product as soon as it had formed. Morpholine is a degradation product of NMMO and is always present in systems containing NMMO. Formaldehyde can react with morpholine to form an intermediate carbenium--iminium ion, N-(methyl- ene)morpholinium (6). The occurrence of 6 in the system cellulose/NMMO was demonstrated by trap- ping this intermediate in a Mannich type reaction with 2-acetonaphthone (9). Both formaldehyde and N- (methylene)morpholinium cations are highly reactive species readily undergoing further reactions with nucleophiles. These processes might contribute to the observed discoloration of the reaction mixture. and might also be responsible for the decomposition of NMMO that is inducible by carbenium-iminium ions.