| The ionic liquid is widely used in various fields because of its unique physical and chemical properties.In this paper,according to three different synthetic route,2-picoline was as raw material to synthesis three types of 14 kinds of ionic liquids under solvent-free conditions.These ionic liquids include 2-methyl pyridine,2-picoline in the introduction of an alkyl carbon chain salt,the 2-picoline in the introduction of an alkyl sulfonic acid group chain salt.Since the synthesis yield of the ionic liquid is mainly decided by the first step,the optimum process conditions of the first step of the preparation of ionic liquids were obtained through the single factor experiment of reaction temperature and reaction time.The acidity of each ionic liquid was characterized by UV-vis,the relationship between the structure of ionic liquids and their acidity was researched.Then the ionic liquids were used as catalyst to synthesis polyglycerol ester of decanoic acid,and the relationship between the influence factors such as ionic liquid acid and its catalytic activity was studied.The single factor experiment of reaction temperature and reaction time showed that the optimum process conditions of the first step of the preparation of ionic liquids were:[2-MPy]HSO4:60?,20min;[2-MPy]H2P04:60?,40min;[EMPy]Br:70?,10h;[BMPy]Br:140?,10h;[2-MPy-PS]:40?,1.5h;[2-MPy-BS]:120?,4h.The UV-vis characterization results of ionic liquids showed that the ionic liquids had a close relationship with its structure.When the cation was same,the polarity of the anion raw material was stronger,the anion was more easily ionized protons H+,thus the acidity of the ionic liquid was stronger.When the anion was same,the negative inductive effect of alkyl carbon chain based on the cation resulted in the electron clouds of the pyridine ring to the alkyl carbon chain,H+ in the Pyridine ring was more easily ionized,thus the acidity was stronger.The longer the alkyl carbon chain,the less the negative inductive effect and the more difficult the pyridine ring proton ionization,thus the acidity of the alkyl carbon chain was weaker.When the anion was same,the alkyl sulfonic acid group based on the cation increased acid active sites of molecules,so that the acid density increased thus making an increase in acidity.The negative inductive effect of cationic pyridine ring made electronic shift along the direction of the ring carbon chain,the negative charge of Sulfonic acid anion dispersed and became stable,the growth of sulfonic acid base carbon chain weakened the induced effect,thus the longer alkyl sulfonic acid group,the weaker the acidity.The experimental results of ionic liquids used in the esterification reaction showed that the acidity of ionic liquids was the main factor of their catalytic activity,and the acidity played full in the esterification reaction affected by its structure to some extent.When the cation was same,the polarity of the anion raw material was stronger,the acidity of ionic liquid was stronger,thus the catalytic activity was stronger.When the anion was HSO4-,the alkyl carbon chain and alkyl sulfonic acid group based on the cation increased the acidity,thus the catalytic activity was stronger.When the alkyl carbon chain and alkyl sulfonic acid group was longer,the acidity decreased,while the hydrophobicity increased,dispersion effect in reaction phase was better,so the acidity played full and the catalytic activity increased.When the anion was H2PO4-,the alkyl carbon chain and alkyl sulfonic acid group based on the cation increased the acidity and Increased the viscosity,dispersion effect in reaction phase was worse,so the acidity did not play full and the catalytic activity decreased.When the alkyl carbon chain and alkyl sulfonic acid group was longer,the acidity decreased,while the viscosity increased,dispersion effect in reaction phase was worse,so the catalytic activity decreased.The viscosity and the hydrophobicity of the ionic liquid had close relationship with its structure,in the final analysis,its structure affect the full play of the acidity,thus affecting the catalytic activity.Ionic liquids in the synthesis of polyglycerol ester of decanoic acid showed high catalytic activity and the advantages of easy separation,so ionic liquids can be used to replace traditional catalysts in the esterification reaction. |
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