37—Periodate Oxidation of Cellulose and Formaldehyde-Treated Cellulose

Experiments have been performed on the kinetics of the periodate oxidation of viscose rayon cellulose and formaldehyde-treated cellulose. There was no positive evidence that the Malaprade stage of the oxidation could be resolved into faster and slower reactions corresponding to the oxidation of more and less accessible regions, respectively. The extent of “Malaprade oxidation” of the formaldehyde-treated samples is considerably lower than the theoretical minimum value, indicating that all the “free” glycol groups are not accessible to the periodate.The diffusion constant of the periodate ion has been calculated, assuming the rate of reaction between the glycol groups and the periodate ion to be much faster than the diffusion rate of the periodate ion, and applying a method worked out by Olofsson for diffusion in fibres coupled with irreversible absorption or rapid reaction. A diffusion constant of about 12.7 Χ 10-10 cm2/min at 23°C is obtained, which is of the same order of magnitude a the constants reported for comparatively fast-diffusing direct dyes. Formaldehyde treatment decreases the rate of diffusion. The diffusion constant for the periodate ion in cellulose containing 2.7% of “fixed” formaldehyde is about 1.7 Χ 10-10 cm2/min.