Studies on DMSO-containing carbanilation mixtures: chemistry, oxidations and cellulose integrity

The oxidative effect of carbanilation mixtures containing dimethylsulfoxide (DMSO) was demonstrated by means of alcohol model substances in which competitive carbanilation was prevented due to steric hindrance of the hydroxyl function, rendering those compounds specific probes for oxidation effects. Dimethylsulfonium ions and derived ylide species were shown to be the actually oxidizing species according to trapping methodology using lipophilic olefins which were converted into the corresponding cyclopropane and epoxide derivatives. The experimental data were in good agreement with DFT computations carried out on the B3LYP/6-311+G(d,p) level of theory. The direct interaction of cellulose and sulfoxide solvent was proven by means of methyl-(2-naphthyl)sulfoxide (MNSO) as a model for DMSO, which caused introduction of UV-detectable methylthionaphthyl ether moieties into the cellulose, formed in Pummerer-type side reaction paralleling the chemical behavior of DMSO. A facile color test-responding to sulfoxide-derived oxidizing species-was developed to assess the suitability of carbanilation conditions with regard to cellulose oxidation and degradation. DMSO-based carbanilation systems have to be used with great caution for determination of molecular weight parameters and for similar purposes which require complete maintenance of the cellulose integrity. Cellulose oxidation/degradation by DMSO-derived intermediates upon carbanilation can be minimized but cannot be avoided completely. Thus, if cellulose integrity is an issue as it is in cellulose analytics, it is recommended to replace DMSO by solvent components of similar solution behavior but without the inherent danger of generating oxidants, such as pyridine or DMAc, whenever possible.