Ionic liquid is a kind of salt, new reaction medium and green solvent that melts at room temperature. It has a wide liquid range, wide dissolution range, 0 vapor pressure, good stability, adjustable acidity and alkalinity, and easy separation of products. A series of unique properties such as recyclability and recyclability are considered to be another large class of reaction media and new green solvents with good application prospects in modern organic synthesis after water and supercritical carbon dioxide. At present, some ionic liquids have been successfully applied. for the synthesis of ethyl p-hydroxybenzoate.
1) 1,3-Dialkylimidazolium ionic liquid
Four kinds of 1,3-dialkylimidazole ionic liquids were used to catalyze the synthesis of ethyl p-hydroxybenzoate. The effects of reaction temperature, reaction time, catalyst dosage, and the ratio of acid-alcohol substances on the reaction yield and the reusability of ionic liquids were investigated. . The research results show that using [BMIm]BF as catalyst, its dosage is 3 mL, the ratio of acid to alcohol substance is 1.0:2.5, the reaction time is 2.5 h, the reaction temperature is 80 cI=, the yield is 79.7%, the highest yield is 79.7%. , and the product and the ionic liquid catalytic system are insoluble and layered, which is convenient for separation, and the ionic liquid can be used stably for 5 times. The ionic liquid can be used as a new type of green solvent to effectively catalyze the synthesis of ethyl p-hydroxybenzoate and reduce environmental pollution.
2) Acidic ionic liquid
Ethyl p-hydroxybenzoate was synthesized by using acidic ionic liquids [C, SO, Hmim]HSO4, [C4SO3Hmim]HSO4 and [C3SO3Hnhm]HSO4 instead of concentrated sulfuric acid as catalysts. The effects of reaction temperature, reaction time, catalyst dosage, acid-alcohol substance ratio on the reaction yield and the reusability of ionic liquids were investigated.
3) Reaction-controlled phase transfer ionic liquids
Using SO3H-functionalized 1-(3-sulfonic acid)propyl-3-methylimidazolium phosphomolybdic acid ionic liquid as catalyst to catalyze the synthesis of paraben, the performance of the catalyst and the green synthesis process of paraben were investigated. . Experiments show that the catalytic system can realize the reaction-controlled phase transfer of the catalyst, the product is easy to separate, and the catalyst is easy to recycle. Alcohols of different polarities have a significant effect on the realization of the reaction-controlled phase transfer of the catalyst. The optimized paraben reaction conditions are: (catalyst): (alcohol): where (paraben) = 0.03: 3: 1, When the reaction time is 8 h and the reaction temperature is 120 ℃, the yield of ethyl paraben can reach 97.6%. In the green esterification system, the catalyst can be reused 6 times, and the product yield is stable.
4) Br6nsted acidic ionic liquid [Hmim]C1
Using Br+nsted acidic ionic liquid [Hmim]cl as catalyst to catalyze the synthesis of parabens, the effects of reaction time, alkyd substance ratio and ionic liquid dosage on the reaction were investigated, and the optimal reaction conditions were determined: p-hydroxybenzene The amount of formic acid was 0.04 mol, the reaction time was 2.5 h, the ratio of alkyd substances was 2:1, the amount of ionic liquid was 3 mL, and the yield was more than 82%. The ionic liquid can be recycled for 5 times, and the catalytic activity is basically unchanged.
5) New ionic liquid 1-(4-sulfonic acid)butyl-3-methylimidazolesulfonic acid [BSmim]HSO
A novel ionic liquid, 1-(4-sulfonyl)butyl-3-methylimidazolesulfonic acid [BSmim]HSO, was studied for the catalytic synthesis of ethyl paraben. The reaction time, reaction temperature, alkyd substance ratio and ionic Effect of liquid dosage on the yield of ethyl paraben. The experimental results show that the optimal reaction conditions for ethyl paraben are as follows: when the reaction time is 2.5 h, the reaction temperature is the reflux temperature, the ratio of alkyd substances is 2.5:1, and the amount of ionic liquid is 3 mL. Using the ionic liquid as a catalyst for synthesizing parabens has the advantages of high yield, simple operation, reusability and good application prospect.