Temperature and pH stability of cellouronic acid

Cellouronic acid (CUA), (1 → 4)-β-d-polyglucuronate sodium salt, was prepared from regenerated cellulose by 2,2,6,6-tetramethylpiperidine-1-oxyl radical (TEMPO)-mediated oxidation in water at pH 10. Changes in chemical structure and degree of polymerization (DP) of CUA by treatment in water under various pH and temperature conditions were studied to evaluate the stability of CUA. No depolymerization occurred on CUA in water at pH 1.0–7.0 and room temperature, while clear depolymerization took place at pH 10 and 13 by β-elimination. When heated in water at >50 °C, CUA was depolymerized by hydrolysis at pH 1.0 and 4.8, and by both hydrolysis and β-elimination at pH 7.0. Kinetic studies showed that CUA depolymerization rate constant was roughly increased with increasing the pH or temperature. Especially, the depolymerization rate constant at pH 13 was approximately 128 and 55 times greater than those at pH 1.0 and 10, respectively, at 60 °C. Activation energies of hydrolysis and β-elimination of CUA were approximately 100 and 20 kJ mol⁻¹, respectively.