Mechanism of cerium (IV) oxidation of glucose and cellulose

Cerium (IV) oxidations of model compounds for the hydroxylic functional groups of cellulose were conducted in 1.0 M perchloric acid. Glucose, the model selected for the reducing end group, was oxidized 360 times faster than Schardinger β‐dextrin, the model for anhydro‐ D ‐glucose repeating units. In the presence of a fourfold excess of glucose, stoichiometry indicated specific conversion to arabinose; the competitive oxidation of arabinose produced is insignificant. Specific C 1 –C 2 bond cleavage was also indicated for 2‐ O ‐methyl‐ D ‐glucose, galactose, 2‐ O ‐methyl‐ D ‐galactose, and cellobiose. Anhydro‐ D ‐glucose units were oxidized predominantly by C 2 –C 3 bond cleavage as shown by the identification of erythrose and glyoxal in hydrolyzates of cerium (IV) oxidized Schardinger β‐dextrin and cellulose. Kinetic studies showed that chelate complexes were involved in oxidations of glucose, methyl β‐ D ‐glucopyranoside, 1,5‐anhydro‐ D ‐glucitol, and Sahardinger β‐dextrin. The oxidations of glucose derivatives which differed with respect to substituents on C 1 and C 2 demonstrated the importance of the hemiacetal group and the presence of oxygen on C 2 . For example, the relative rates of oxidation at 15°C for methyl β‐ D ‐glucopyranoside, 1,5‐anhydro‐ D ‐glucitol, 2‐deoxy‐ D ‐glucose, glucose, and 2‐ O ‐methyl‐ D ‐glucose are 1:1:12:360:1860, respectively. The mechanism of glucose oxidation is thought to involve formation of a chelate complex, disproportionation of the complex to form a free radical at either C 1 or C 2 and further rapid oxidation to 4‐ O ‐formyl‐ D ‐arabinose which is hydrolyzed in the reaction medium. General implications of the experimental results pertaining to initiation of vinyl graft polymerization on cellulose are discussed.