Etherification of cellulose is of significant importance to construct cellulose-based materials. However, the homogeneous and controllable etherification of cellulose is difficult to achieve. Herein, we systematically demonstrated that mild, rapid and efficient etherification of cellulose was realized in tetra-n-butylphosphonium hydroxide ([P_4,4,4,4]OH) aqueous solution, including Williamson etherification reaction, Michael addition reaction, and hydroxyalkylation reaction. A series of cellulose ethers with different substituents and degrees of substitution (DS) were easily and controllably synthesized, including ethyl cellulose, cyanoethyl cellulose, hydroxypropyl cellulose and quaternized cellulose. More interestingly, both the Williamson etherification and hydroxyalkylation reaction were conducted in 15 min at 25–60 °C which are rapid and efficient. The DS and performance of the resultant cellulose ethers were regulated over a wide range by changing the reaction conditions. The solvent [P_4,4,4,4]OH aqueous solution could be successfully recovered after a three-steps process of extraction with CHCl₃, anion exchange and concentration.

Graphical abstract