Engineering cellulose into water soluble poly(protic ionic liquids) electrolytes in DBU/CO2/DMSO solvent system as organocatalyst for Knoevenagel condensation reaction

The facile design and preparation of polyelectrolytes is a frontier topic both in the fields of polymer science, energy storage devices and catalysis. Herein, a linear water soluble cellulosic poly(protic ionic liquids) (CPILs ) electrolytes was facile and atom economically prepared after the dissolution of cellulose in the newly developed DBU/CO2/DMSO solvent system, followed by the simply addition of succinic acid under mild conditions. The DBU not only participated the dissolution of cellulose as solvent component, but also acted as an organocatalyst for the acylation reaction of cellulose with succinic anhydride, as well as a cation component in the targeted CPILs electrolytes. The reaction was optimized, and the effect of the reaction conditions on the chemical physical properties of the CPILs was investigated. And then, as a proof of concept, the CPILs electrolyte aqueous solution was successfully used as a catalytic reaction media for the Knoevenagel condensation reaction. It was found that the reaction was homogenous at the beginning, and the products could precipitated out from the media with the proceeding of the reaction, thus achieving with satisfactory filtration yields ranging from 56.7% to 92.2%. The solution properties of the CPILs aqueous solution was primary investigated towards an in-depth understanding the catalytic mechanism, by which a synergetic catalytic mechanism by the CPILs was proposed, and the reaction started with a nucleophilic addition reaction, and then followed by a fast dehydration reaction. Finally, the direct reusability potential of the CPILs aqueous solution for the after the products filtration was also primary investigated for the Knoevenagel condensation reaction.