Intermediates in wet oxidation of cellulose: identification of hydroxyl radical and characterization of hydrogen peroxide.

Some intermediates were identified during the course of non-catalytic wet air oxidation (WAO) of cellulose. Concentrations of by-products were determined in function of temperature and reaction time. This study also showed that hydroxyl radicals (HO*) and hydrogen peroxide (H2O2) play the role of intermediates in the initial phase of the oxidation reactions. Hydroxyl radicals were detected by the electron spin resonance spectroscopy coupled to the spin trapping technique using the 5,5-dimethyl 1-pyrroline N-oxide (DMPO) as spin trap agent. The spin adduct (DMPO/ HO*), resulting from the trapping of HO* with DMPO, showed a characteristic electron spin resonance signal which was inhibited when catalase was added, indicating that HO* was provided from H2O2. These transient species were only observed at the beginning of the reaction and were not oxygen dependent.