Synthesis Of Quaternary Ammonium Ionic Liquids Through Oxidation-reduction Method

Ionic liquids as a new type of green solvent and catalyst is expected to replace the traditional organic solvent and catalyst,realize green material,green catalyst in green chemistry.The ionic liquids play an important role,and ionic liquids are concentrated as green chemistry symbol in a sense.Ionic liquids have excellent physical and chemical properties such as extremely low volatility even under vacuum,present as liquid in a large range of temperatures,wide electrochemical window,and high thermal stability etc.In recent years,despite the growing applications of ionic liquids,their preparation and purification have taken on an air of ‘only need to know'.The synthesis methods of ionic liquids are divided into one step and two steps.Although the ionic liquids can be obtained by one step method,the types of cation and anion of ionic liquids are limited by the limited alkylation reagent,the two step is the main synthetic method of ionic liquids.However,the traditional two step method is faced with many problems,such as low yield,long synthesis time,high reaction temperature and high impurity content.In this paper,a series of quaternary ammonium ionic liquids was prepared through new type of synthesis route named oxidation-reduction method.The hydrogen peroxide reacted with quaternary ammonium bromide in the present of protonic acid containing desired anions with 1-hexene as bromine scavenger.A serious of room temperature ILs whose cations are tetramethyl ammonium,tetraethyl ammonium,tetrabutyl ammonium,and anions are methane sulfonate,hydrosulfate,nitrate,trifluoroacetic,p-toluene sulfonic were produced.The ionic liquids were characterized by 1H NMR and 13 C NMR,and the residual bromide and water content of the prepared ILs were measured by ion chromatography(IC)and Karl-Fischer test,respectively.The results showed that under the condition of room temperature and 3~4h,the yield of ionic liquid was up to 98%,and the bromine salt impurity content and water content were lower.This method not only produces ILs in high purity and high yield,but also simplifies the reaction conditions in comparison with previous routes.The advantage of the method used in this work is making the reaction condition milder than others in the previous literatures,reducing the reaction time,getting high purity and yield products at the same time.It was also found that ionic liquids containing olefinic bond functional groups and weak acid ionic liquid is not suited for the synthesis of this method.