1. Solid super acid
1) S2O82-/ZrO2-Al2O3
Prepare the solid superacid catalyst S2O82-/ZrO2-Al2O3 by impregnation and precipitation methods. The optimum conditions for catalyst preparation are determined by orthogonal experiments, that is, the mass ratio of ZrO12 8H2O and macroporous A1O is 25.0:14.2, and the concentration of ammonium thiosulfate is 0.8 mol/L, the activation temperature is 650°C, and the activation time is 3 h. Using solid superacid S2O82-/ZrO2-Al2O3 as catalyst, p-Ethylparaben was synthesized from p-hydroxybenzoic acid and absolute ethanol.
2) SO4-/TiO2-attapulgite
Ethylparaben was synthesized with solid superacid SO4-/TiO2-attapulgite as catalyst, p-hydroxybenzoic acid and ethanol as raw materials, and the factors affecting the reaction were investigated. Under the optimal reaction conditions, the molar ratio of acid to alcohol is 1:4, the amount of catalyst is 3%, and the reaction time is 4 h, the product yield is 93.2%. Compared with the single-component solid superacid SO4-/TiO2, the catalyst has the advantages of lower cost, easy separation from products, reusability, and no environmental pollution. It is an environmentally friendly and green catalyst with application prospects.
3) Cerium-improved solid superacid
Using p-hydroxybenzoic acid and ethanol as raw materials, a new type of solid superacid SO4-/Sb2O3/Ce4+ catalyst was used to catalyze the synthesis of ethylparaben. The amount of benzyl alcohol added is 100 mL, the amount of acetic acid added is 2.80 mL, and the optimal process conditions are determined as: r/, (p-hydroxybenzoic acid): n (ethanol) = 1.0: 4.0, the temperature is about 350 ° C, and the catalyst dosage is 0.6 g , the reaction time was 4 h, and the ester yield was 93.8%.
4) SO4/La2O3-TiO2
A new catalyst SO4/La2O3-TiO2 was prepared by loading lanthanum on SO4/TiO2, and the effect of different preparation conditions on the performance of the catalyst was investigated using the esterification reaction of p-hydroxybenzoic acid and ethanol as a probe. The results show that the highest esterification rate can reach 94.5%. Moreover, the catalyst has good reusability and regeneration ability, and is very suitable for synthesizing Ethylparaben.
2. Copper p-toluenesulfonate
It has been reported recently that copper methanesulfonate has a good catalytic effect on the esterification of organic acids. Considering the complicated synthesis conditions of methanesulfonic acid, copper p-toluenesulfonate was prepared from p-toluenesulfonic acid, which was used to catalyze the synthesis of ethyl p-hydroxybenzoate. Ethyl p-hydroxybenzoate was synthesized with p-hydroxybenzoic acid and ethanol as raw materials and copper p-toluenesulfonate as catalyst, and the influencing factors of catalytic esterification were discussed. The optimized reaction conditions were as follows: the amount of p-hydroxybenzoic acid was 0.10 mol, the molar ratio of alkyd to acid was 4:1, the amount of copper toluenesulfonate was 2.2 g, and the reaction time was 4.0 h at reflux temperature. In this experiment, the esterification rate could reach Up to 94.3%. The product was characterized by a Fourier transform infrared spectrometer and a melting point instrument, and it was confirmed that it was completely consistent with the target product.
3. Ionic liquid: As a salt that melts at room temperature, a new type of reaction medium and a green solvent, ionic liquid has a wide range of liquid state, a wide range of dissolution, zero 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. In the synthesis of Ethylparaben.
1) 1,3-dialkylimidazolium ionic liquid
Four kinds of 1,3-dialkylimidazolium ionic liquids catalyzed the synthesis of ethyl p-hydroxybenzoate, and investigated the effects of reaction temperature, reaction time, catalyst dosage, and acid-alcohol ratio on the reaction yield and the reusability of ionic liquids . The research results show that [BMIm]BF is used as catalyst, the dosage is 3 mL, the ratio of acid to alcohol is 1.0:2.5, the reaction time is 2.5 h, the reaction temperature is 80 cI=, and the yield is 79.7%, which is the highest. , and the product is insoluble and separated from the ionic liquid catalytic system, which is easy to separate, and the ionic liquid can be stably reused 5 times. Ionic liquid can be used as a new type of green solvent to effectively catalyze the synthesis of Ethylparaben reaction and reduce environmental pollution.
2) Acidic ionic liquid
Ethyl p-hydroxybenzoate was synthesized using acidic ionic liquids [C, SO, Hmim]HSO4, [C4SO3Hmim]HSO4 and [C3SO3Hnhm]HSO4 instead of concentrated sulfuric acid. The effects of reaction temperature, reaction time, catalyst dosage, acid-alcohol 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 a catalyst to catalyze the synthesis of paraben ester, the performance of the catalyst and the green synthesis process of paraben ester 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 with different polarities have a significant impact on the realization of the reaction-controlled phase transfer of the catalyst. The optimized reaction conditions for paraben esters are: (catalyst): (alcohol): where (paraben acid) = 0.03: 3: 1, When the reaction time was 8 h and the reaction temperature was 120°C, the yield of ethyl paraben could 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 a catalyst to catalyze the synthesis of paraben ester, the influence of reaction time, the ratio of alkyd substances and the amount of ionic liquid on the reaction was investigated, and the optimal reaction condition was determined: p-hydroxybenzene The amount of formic acid was 0.04 mol, the reaction time was 2.5 h, the molar ratio of alkyd to acid was 2:1, the amount of ionic liquid was 3 mL, and the yield was more than 82%. The ionic liquid can be recycled 5 times, and the catalytic activity remains basically unchanged.
5) Novel ionic liquid 1-(4-sulfonic acid) butyl-3-methylimidazole sulfonic acid [BSmim] HSO
Study on the synthesis of ethylparaben catalyzed by a new type of ionic liquid 1-(4-sulfo)butyl-3-methylimidazolesulfonic acid [BSmim]HSO, investigate the reaction time, reaction temperature, molar ratio of alkyd and acid species and ion Effect of liquid dosage on yield of ethylparaben. The experimental results showed that the optimal reaction conditions for ethylparaben were as follows: when the reaction time was 2.5 h, the reaction temperature was reflux temperature, the molar ratio of alkyd to acid was 2.5:1, and the amount of ionic liquid was 3 mL. Using the ionic liquid as a catalyst for synthesizing parabens has high yield, is easy to operate, can be used repeatedly, and has good application prospects.
4. Microwave radiation catalytic synthesis
Ethyl p-hydroxybenzoate was efficiently and greenly synthesized under microwave irradiation conditions using p-hydroxybenzoic acid and ethanol as raw materials and SnC1/C as a heterogeneous catalyst. The effects of catalyst dosage, alkyd ratio, reaction time, reaction temperature, microwave radiation power, etc. on the yield were studied respectively, and Fourier transform infrared spectroscopy (FT-IR) and hydrogen nuclear magnetic resonance (H NMR) and mass spectrometry (MS) to determine the structure of the product. The results show that the best conditions for the synthesis of Ethylparaben are (p-hydroxybenzoic acid): n (ethanol) = 4: 4, the reaction time is 25 min, the mass fraction of the catalyst is 10%, and the reaction temperature is 120 ℃, microwave radiation power 640w, the product yield is 95%; SnC1/C catalyst still shows good catalytic activity after being recycled 4 times, and the yield can reach 89%.
5. Ultrasonic Catalytic Synthesis
The use of ultrasonic waves can improve chemical reaction conditions and shorten the reaction time. Under ultrasonic radiation, p-hydroxybenzoic acid and ethanol are used as raw materials, and p-toluenesulfonic acid is used as a catalyst to synthesize ethyl p-hydroxybenzoate, and affect the yield. The optimal conditions were determined by orthogonal experiments: ultrasonic power 350 W, ultrasonic temperature 70-80 °C, ultrasonic time 70 min, the ratio of ethanol to p-hydroxybenzoic acid was 7:1, and the amount of catalyst was 8%. , the yield can reach 85.51%.
6. Chitosan Phosphotungstate
It has been reported in the literature that it can act as a solid Lewis acid to catalyze the synthesis of some esters. Ethylparaben was synthesized by using p-hydroxybenzoic acid and ethanol as raw materials and chitosan phosphotungstate as a catalyst. The optimal conditions for the reaction were determined: the molar ratio of alkyd to acid was 5:1, the amount of catalyst was 0.9 g, and the reaction time was 3 h , the product yield reaches 87.1%. Experiments have shown that the use of chitosan phosphotungstate as a catalyst not only has short reaction time, high activity, and high esterification rate, but also the catalyst can be reused, opening up a new field of ethyl paraben esterification catalysts.
7. Synthesis by Dehydration of Triethyl Orthoformate
Using methanesulfonic acid as a catalyst, adding triethyl orthoformate as a dehydrating agent to the reaction raw materials, ethylparaben can effectively improve the reaction conversion rate and shorten the reaction time. Lai Yaping used p-hydroxybenzoic acid and ethanol as the main raw materials and methanesulfonic acid as the catalyst to synthesize ethyl paraben by adding triethyl orthoformate to the reaction system and heating to reflux for dehydration. The reaction process was tracked by high-performance liquid chromatography. The influence of various factors on the product conversion rate was investigated. The experimental results show that the dehydration method of triethyl orthoformate can improve the conversion rate of the target product and reduce the reaction time compared with the traditional method.
