Catalytic Synthesis of a sulfuric acid, butyl paraben

Sulfuric acid catalyzed esterification method is the classic method of synthetic esters, synthetic parabens, the hero Hasegawa, Atsushi Maekawa governance and Xie Wei Yang and has long been reported. Such a catalytic reaction for a long time, low yield, alcohol consumption, and improve the use of p-hydroxybenzoic acid, n-butanol, benzene and sulfuric acid molar ratio of 1: 3.5: 1: 0.015, refluxing 1 h , n-butyl paraben yield up to 99.12%, with an average yield of 97.58%.
Ming et al pipe coil in toluene as the solvent, when p-hydroxybenzoic acid, n-butanol and toluene molar ratio of 1: 4: 2, with sulfuric acid as a catalyst, refluxing 4 h, then the solvent was distilled off and 50% alcohol, cooling precipitation precipitation, filtration, n-butyl paraben was 89.3% yield. Zhengxue Zhong et without organic solvent with n-butanol as a dehydrating agent, p-hydroxybenzoic acid, n-butanol and sulfuric acid molar ratio of 1: 3.5: 0.15, refluxing 0.75 h, p-hydroxybenzoate n-butyl formate yield of 98.4%.
To improve the storage and ease of use, tubes and the like to the disc-ming sulfate SO4 2- / bentonite catalyst (mass fraction of about 5%), with toluene as the solvent, when p-hydroxybenzoic acid, n-butanol and toluene molar ratio of 1: 4 : 2, in the <110 ℃ stirred refluxing 5h, then steamed out 50 percent of solvents and alcohol, cooled to precipitate precipitation, filtration to obtain the product of n-butyl paraben, yield 88.6%.
To accelerate the reaction process under microwave irradiation synthesis of n-butyl paraben, when p-hydroxy benzoic acid, n-butanol molar ratio of 1: 4, the use of sulfuric acid as a catalyst in the working frequency of the microwave radiation source 2450MHz 30min, n-butyl paraben yield of 85.1%, rather than use the microwave, you need to refluxing 300min, product yield was 83.8%, so the reaction rate increased by 10-fold.
2 sulfonic acid catalytic synthesis of butyl paraben

2.1 p-toluenesulfonic acid
Since the sulfuric acid cause side reactions when heated organic etherification, oxidation, carbonization, sulfonation, while its corrosion resistance, operation, use and storage is not convenient and safe. Toluenesulfonic acid (p-CH3C6H4SO3H.H2O) is an organic acid, sulfuric acid can overcome many shortcomings, easy to use, is a good catalyst for esterification, can be synthesized in high yields of hydroxy esters. The author has used 0.05mol paraben, 0.30mol alcohol in 0.0052mol (1.0g) under refluxing toluene sulfonic acid catalysis 3h, n-butyl paraben yield of 95.9% . Since the p-toluenesulfonic acid dissolved in an organic reaction system, the reaction liquid after the reaction the acid is still strong, the need for treatment, there is a certain waste liquid, the catalyst can not be reused. Shi Lei, such as 10g of granular activated carbon immersed in 60mL mass fraction of 25% aqueous solution of toluene sulfonic acid 30h, drained after too 15.31g, immobilization rate of 53.10%, select this catalyst 0.6g, 0.1mol hydroxybenzoic acid, 0.3mol butanol refluxing 3h, n-butyl paraben yield of 98.02%, the catalyst can be reused five times, the yield was still up 97.65% [9 ]. This method is easy to operate, reducing environmental pollution, high ester yield, catalyst reuse performance, is a good catalyst.

2.2 amino acid
Sulfamic acid (H2N-SO2OH) with p-toluenesulfonic acid, as is also an inexpensive, readily available, stable solid. Transport, storage, easy to use, except that it is insoluble in organic reaction system, easy separation, can be reused, for small equipment corrosion, high yield synthesis products is a good catalyst for the synthesis of butyl paraben. When the right-hydroxy acid, n-butanol and the amino acid molar ratio of 1: 4: 0.41 refluxing 3h, n-butyl paraben yield of 97.9%. When converted to butanol isobutanol, p-hydroxybenzoic acid, isobutyl alcohol, an amino acid molar ratio of 1: 6: 0.52 refluxing 3h, p-hydroxybenzoic acid yield of 90.7 Isobutyl %.
2.3 strong acid cation exchange resin
Strong acid cation exchange resin is a polymer acid, cheap, no corrosion of equipment, do not pollute the environment, does not cause side effects, and the resin is insoluble in the reaction system, recyclable, recycled and reused, easy to operate , product yield, is an effective catalyst for industrial production. Using five kinds of models of the resin (D72, D61, dry hydrogen resin, HD-8 and JK008) catalytic synthesis of ethyl paraben, Discovery JK008 resin highest activity. When the p-hydroxybenzoic acid to the resin mass ratio of 1: 0.08, p-hydroxybenzoic acid with n-butanol molar ratio of 1: 5.5, refluxing 4.5h, obtained by gas chromatographic analysis of n-butyl p-hydroxybenzoate ester yield of 98.0%, JK008 resin has good reuse catalytic performance.
Introducing benzene sulfonic acid groups on the benzene ring zirconium, made ​​a similar strong acid cation exchange resin solid acid – acid sulfonated benzene zirconium (ZSPP), catalytic synthesis of n-butyl paraben. Specific conditions: 0.05mol paraben, 0.20mol n-butanol, 1g ZSPP catalyst at 117¯120 ℃ refluxing 8 h, n-butyl paraben yield of 92%, this catalyst can reuse reused 10 times, the yield is still about 90%, the catalyst has a high thermal stability (over 250 ℃ was released SO2) than the sulfonic acid resin, an organic substance at high temperature coking, no corrosion of equipment application prospect is a solid acid catalyst promising.

3 Catalytic Synthesis of inorganic salts and oxides of butyl paraben
Catalytic and catalytic sulfuric acid were discussed earlier proton acid catalysis, catalytic inorganic salts and oxides vary due to different compounds. There are a large class of inorganic materials is cheap and easy to get the Lewis acid, the metal atom has with the carboxylic acid carbonyl oxygen ligands empty track, which has catalyzed esterification, while their small equipment corrosion, pollution reduction, catalyst with less, is a good catalyst for the synthesis of certain esters. Iron (Ⅲ) electronegativity strong, Fe3 + in outer space orbit with the carboxylic acid carbonyl oxygen ligands. Liu Yong, etc. using Fe2 (SO4) 3 · xH2O catalytic synthesis of n-butyl paraben: 0.1mol paraben, 0.4mol n-butanol, 0.5g of the catalyst under refluxing 4h, acid conversion rate of 91.6%, after going alcohol, after recrystallization paraben, n-butyl ester yield of 85% fine. Acetate Catalyzed, who used hydroxybenzoic acid and n-butanol molar ratio of 1: 4 to 4% of the mass fraction (based on the total reactant meter) chloride as catalyst different refluxing 5 h, then the catalyst was filtered off, the alcohol is recovered by distillation, the crude ester are precipitated by the water, an alkali, washed with water, then ethanol – n-butyl p-hydroxybenzoate may, after finishing the water of crystallization yield of an ester, respectively:
Catalyst CaCL2 ZnCL2 FeCL3 · 6H2O ALCL3 · 6H2O
Ester yield /% 30307883
Thus, chloride has a catalytic role, especially FeCl3 · 6H2O and AlCl3 · 6H2O is a good catalyst for the synthesis of the esters. Previously, Zhang Jing Qing, who have also been reported: When right-hydroxy acid with n-butanol molar ratio of 1: 3.5, FeCl3 · 6H2O mass fraction (the total mass of reactants) of 5%, in 139¯ under 140 ℃ reaction 1.5h, 84.6% of the available yield of n-butyl paraben [17]. Wang Mingxing, etc. have also been studied: when hydroxybenzoic acid, n-butanol and FeCl3 · 6H2O molar ratio of 1: 2: 0.12 refluxing 3h, the yield of n-butyl paraben 95 .1% ¯96.3% [18]. Yao spring, also reported the catalytic effect of FeCl3 · 6H2O, in its optimum conditions, product yield was 98.9%.
Tin (II) is also high negative elements, such as the use of cost Prudential stannous oxide (SnO) as catalyst was successfully synthesized n-butyl paraben: 0.1mol paraben, 0.3mol n-butanol . 5gSnO, 140 ℃ refluxing 4h, acid conversion rate of 96%.
Since most of the inorganic chlorides hygroscopic and difficult to use and accurate storage, and they were dissolved in the reaction system, to the product separation and purification inconvenience. Ammonium ferric sulfate is a stable crystal, in addition to having the chloride advantages, it is not easy to absorb moisture, insoluble in the reaction system, the reaction to form a loose spherical solid, non-corrosive reaction equipment, is a good ester catalyst. Deng Xuzhong such as the use of its catalytic synthesis of n-butyl paraben: 0.1mol paraben, 0.35mol n-butanol, 1.0g catalyst refluxing 4 h, the crude ester yield of 93.7% , after recrystallization from ethanol the yield was 90.1% fine ester.
Li Xiaoli, such as the use of rare earth oxide, neodymium oxide (Nd2O3) catalytic synthesis of n-butyl paraben, its optimal reaction conditions: When right-hydroxy acid, n-butanol molar ratio of 1: 4, the amount of catalyst of 5% by mass of p-hydroxybenzoic acid, refluxing 4h, yield of the ester was 81.2% and the good catalytic effect is repeated, the method to reduce the corrosion of equipment and environmental pollution, has certain industrial value.
Catalytic inorganic discussed above is part of Lewis acid catalysis. The authors note monohydrate sodium bisulfate (NaHSO4 · H2O) is also a good esterification catalyst, inexpensive, readily available, and stable crystal properties, and its solution is strongly acidic, due to ionizing HSO4- have H + exists, belongs to the proton acid catalysis, capable of catalyzing the synthesis of butyl paraben: When hydroxybenzoic acid, n-butanol and sodium hydrogen sulfate monohydrate molar ratio of 1: 2: 0.072 when refluxing 5h, n-butyl paraben ester yield of 92.8%; when paraben, isobutyl alcohol and sodium hydrogen sulfate monohydrate molar ratio of 1: 3: 0.036 refluxing 7h, isobutyl paraben yield can also be 99%. Of microwave radiation sodium bisulfate next catalytic synthesis of butyl paraben work, the optimization of reaction conditions: when n (alcohol): n (acid): n (NaHSO4 · H2O) = 0.15: 0 .05: 0.058, using the power of 210W microwave radiation 28min, product yield was 93.6%. The catalyst and the reaction time is shortened, the remaining sodium bisulfite and has a repetitive catalytic performance due to their insoluble in the reaction system, the corrosion of the equipment is greatly reduced, there is a catalyst for industrial application.