Synthetic Pathways of Regioselectively Substituting Cellulose Derivatives: A Review

The nature of cellulose from renewable biomass contains a special chemical structure of showing C2-OH and C3-OH on one side while C6-OH on the other side along the anhydroglucose units. The difference between reactivity of hydroxyl groups located respectively on C2, C3 and C6 makes it possible to functionalize a great variety of cellulose derivatives through regioselective substitution pathways. This paper summarizes the synthetic pathways of regioselectively functionalized cellulose derivatives like 6-O-, 2,3-O-, 3-O-, 2,6-O, 6-O-2,3-O-cellulose esters with or without protecting methods. In regioselectively blocking hydroxyl groups of cellulose, mechanism and routes of functionalizing celluloses by using protecting reagents of Trityl Chloride, Tosyl Chloride, Triphenylmethyl Chloride, Halogenating, and Isocyanate are discussed. It is considerable that no uses of protecting routes regioselectively substituting cellulose can be realized directly on cellulose by the methods of nucleophilic substitution reaction, isocyanate substitution reaction, halogenate substitution reaction, ring-opening copolymerization. The facing problems and suggestions for preparing these functionalized cellulose ethers are pointed out.