Depolymerization of Cellulose in Water Catalyzed by Phenylboronic Acid Derivatives

Based on the knowledge that o-aminomethylphenylboronic acids reversibly bind to carbohydrates, relevant water-soluble derivatives of the former were prepared by appending hydrophilic tethers. In this way the phenylboronic acid derivatives were used to hydrolytically dissolve, i.e. depolymerize cellulose in water at nearly neutral pH values. Some of these hydrophilic tethers consisted of moieties that were surmised to be able to promote hydrolysis of the glycosidic bonds such as a carboxylic acid, phosphonic acid as weak Bronsted acids, or an imidazole functionality as a nucelophilic catalyst; water-soluble polyethylene glycol and polyethyenelimine appendages were also used. The results show that at around 120 °C efficient hydrolysis of cellulose to form water-soluble oligosaccharides could be attained in a period of 24 h. Importantly preimpregnation of a morpholine substituted o-aminomethylphenylboronic acid led to the very selective formation of glucose.