Periodate-chlorite sequence of oxidation of cellulose is widely used for its remarkable selectivity. Periodate oxidizes cellulose on C2-C3 position into dialdehyde cellulose (DAC); and further, chlorite oxidizes aldehydes into carboxyls. Cellulose degradation is limited due to high reaction selectivity, compared to the use of other oxidants. In literature, different methods were reported to measure the carbonyl content of the substrate after periodate oxidation. Measures are commonly performed by specific group titration after derivatization, e.g. carboxyls after chlorite oxidation. Assessments can also be done from the amount of consumed periodate during oxidation or from the degradation of DAC through β-alkoxydegradation in mild alkaline medium. Only few papers compared these methods and attribute eventual differences in carbonyl contents to hemiacetal formation or to periodate-induced degradation. In the present study, we studied the differences between these methods for various conditions (temperature, NaIO4/AGU ratios, DPV). Periodate consumption was measured by UV-HPLC, degradation of DAC was measured by alkali back-titration and carboxyl content after chlorite over-oxidation was measured by conductometric titration. Regardless the conditions, results showed an important but constant difference between periodate consumption and carboxyl content, except for varying NaIO4/AGU ratio. Carbonyl assessments from DAC β-alkoxydegradation confirmed that this difference comes from a limitation of the chlorite reaction rather than side-reactions with periodate. Although chlorite oxidation is a very selective reaction, side-reactions such as hypochlorite formation affect reaction efficiency. Oxidation is then commonly carried out with a large excess of chlorite and for long time. Previous works on hypochlorite scavengers, as DMSO, hydrogen peroxide or sulfamic acid, have proved interesting, although a strong degradation was observed with sulfamic acid. Therefore, as a next step, we aimed at reaching full chlorite reaction by varying pH or hypochlorite scavengers. Scavengers impact on cellulose DPv was also measured, in order to ensure the high oxidation selectivity.

New insight in the cellulose oxidation by the periodate-chlorite sequence: Side reactions comprehension and limitations

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