Maleate is an important active intermediate and organic synthesis intermediate, as well as a plasticizer for a variety of plastics. It can be used to synthesize synthetic resins, coatings, plastics, petrochemical and paper industry materials that are widely used through self polymerization or copolymerization. At present, sulfuric acid is used as catalyst in industry, which is made from maleic anhydride and alcohol. Due to the strong acidity and oxidation of sulfuric acid, the equipment is severely corroded, and side reactions (such as carbonization, oxidation, polymerization, etc.) are easily caused. With the deepening of environmental protection legislation, people are urged to conduct in-depth research on esterification catalyst. This paper discusses the application of sodium bisulfate monohydrate in the synthesis of diethyl maleate.
Maleic anhydride, 95% ethanol and sodium bisulfate monohydrate are chemically pure reagents.
PE22400 element analyzer, WQF2310 Fourier transform infrared spectrometer, WAY Abbe refractometer and conventional organic synthesis instrument.
Add 419g (0105mol) maleic anhydride, a certain amount of 95% ethanol, sodium bisulfate monohydrate and 15mL water carrying agent into a 100mL three neck flask, install a water separator, a reflux condenser tube and a thermometer, heat the flask for reflux water separation until no water drops appear, react for another 20min (to ensure complete reaction), discharge the water layer, steam out the water carrying agent and unreacted ethanol through the water separator, and use cyclohexane (10mL) after cooling × 2) Extract the product from the reaction flask It is then washed with water, sodium carbonate solution and water, dried and distilled First steam out cyclohexane, and then collect 217-220 ℃ distillate as product.
Adding water carrying agent which can form low azeotrope with water is an effective method to promote the dehydration reaction. 419g (0105mL) maleic anhydride and 1210mL (0120mol) 95% ethanol were used as raw materials, 015g sodium bisulfate monohydrate was added as catalyst, and common water carrying agents cyclohexane, benzene and toluene (15mL each) were selected for reaction. The results are listed in Table1.
Table 1 Influence of water carrying agent on the yield
| Water carrying agent | Reaction time (min) | Temperature (℃) | V(Layer of water) (ml) | m(Product) g | Yield (%) |
|---|---|---|---|---|---|
| Cyclohexane | 60 | 66~84 | 915 | 313 | 3814 |
| Benzene | 60 | 70~77 | 112 | 219 | 3318 |
| Toluene | 60 | 82~88 | 313 | 313 | 3814 |
It can be seen from Table 1 that cyclohexane and toluene are more favorable for the reaction, while cyclohexane is less toxic than toluene. Therefore, cyclohexane is more appropriate for the reaction.
419g (0105mL) maleic anhydride and 1210mL (0120mol) 95% ethanol were used as raw materials, 15mL cyclohexane was used as water carrying agent, and the reaction was carried out by changing the amount of catalyst. See Table 2 for the results.
Table2 Influence of catalyst amount on the yield
| m (NaHSO4•H2O) / g | Reaction time (min) | Temperature (℃) | V(Layer of water) (ml) | m(Product) g | Yield (%) |
|---|---|---|---|---|---|
| 0 | 70 | 70~83 | 815 | 014 | 4165 |
| 0125 | 70 | 66~84 | 914 | 313 | 3814 |
| 0150 | 60 | 66~84 | 915 | 313 | 3814 |
| 1100 | 5 | 68~84 | 913 | 412 | 4910 |
| 1150 | 50 | 68~86 | 918 | 417 | 5417 |
| 2100 | 45 | 66~86 | 818 | 416 | 5315 |
| 2150 | 40 | 66~86 | 816 | 614 | 7414 |
| 3100 | 35 | 66~88 | 816 | 515 | 6410 |
| 3150 | 30 | 66~88 | 816 | 511 | 5913 |
It can be seen from Table 2 that the dosage of sodium bisulfate monohydrate is 2150g (01018mol).
Using 419g (0105mol) maleic anhydride as raw material, 2150g (01018mol) NaHSO4 • H2O as catalyst, 15mL cyclohexane as water carrying agent, the reaction was carried out by changing the amount of ethanol. The results are listed in Table 3.
Table3 Influence of ethanol amount on the yield
| V (95% ethanol)/ml | Reaction time (min) | Temperature (℃) | V(Layer of water) (ml) | m(Product) g | Yield (%) |
|---|---|---|---|---|---|
| 6 | 40 | 72~82 | 218 | 218 | 3216 |
| 12 | 40 | 66~86 | 816 | 614 | 7414 |
| 18 | 60 | 64~87 | 1515 | 610 | 6918 |
| 24 | 65 | 66~92 | 2216 | 518 | 6714 |
| 30 | 80 | 68~120 | 3416 | 413 | 5010 |
It can be seen from Table 3 that the appropriate molar ratio of acid anhydride, ethanol and Na HSO4 • H2O in this reaction is 0105 ∶ 0120 ∶ 01018=1 ∶ 4 ∶ 0136.
As sodium bisulfate monohydrate is hardly soluble in the reaction system, sodium bisulfate in the reaction bottle is reused for 4 times under the above optimized reaction conditions. See Table 4 for the results.
Table4 Repeated use results of the catalyst
| Number of uses | Reaction time (min) | Temperature (℃) | V(Layer of water) (ml) | m(Product) g | Yield (%) |
|---|---|---|---|---|---|
| 1 | 40 | 66~86 | 816 | 614 | 7414 |
| 2 | 40 | 68~85 | 816 | 518 | 6714 |
| 3 | 60 | 66~85 | 918 | 412 | 4910 |
| 4 | 90 | 66~84 | 910 | 412 | 4910 |
It can be seen from Table 4 that the used sodium bisulfate monohydrate still has a certain repeated catalytic performance, but the reaction time is prolonged and the yield is reduced with the increase of use times.
The synthesized diethyl maleate is a colorless transparent liquid with slight aroma. The measured refractive index n20 is 114410.
The measured value (calculated value) of elemental analysis (C8H12O4) is: w (C)=55191% (55182%), w (H)=7103% (6198%) The infrared spectrum has the following main absorption peaks (cm – 1): 2985 (hydrocarbon C-H), 1735 (ester C=O), 1640 (C=C), 1210, 1170 and 1020 (C-O).
(1) Sodium bisulfate monohydrate is a cheap, easily available and stable acidic inorganic crystal, which has catalytic esterification performance, is insoluble in organic reaction system, and is easy to separate. The catalytic synthesis of diethyl maleate by using this catalyst has a good effect.
(2) The optimum conditions for the synthesis of diethyl maleate catalyzed by sodium bisulfate monohydrate were as follows: the molar ratio of maleic anhydride, ethanol and sodium bisulfate monohydrate was 1∶4∶0136, cyclohexane was used as solvent, water was separated by reflux for 40 min, and the ester yield was 7414%.