What is the preparation method of benzyl alcohol_Industrial additives

Overview

Benzyl alcohol, also known as benzyl alcohol, the English name is Benzylalcohol. Benzyl alcohol mostly exists in the form of esters in essential oils in nature. For example, jasmine oil, hyacinth oil and Peru balsam contain this ingredient. Benzyl alcohol is a very active alcohol. It is an intermediate for preparing benzyl esters or ethers. It reacts with hydrohalic acid and phosphorus halide to form benzyl halide. This product and benzyl alcohol are both benzyl methylation reagents and can react with benzene. The reaction produces diphenylmethane. In addition, benzyl alcohol is also easily oxidized to benzoic acid by various oxidants. If oxidized with nitric acid, aldehydes or acids can be generated depending on the concentration and temperature. As an aromatic alcohol, benzyl alcohol has been used as a fixative in cosmetics, as a preservative, solvent and viscosity reducer in industrial chemicals. Benzyl alcohol is selectively oxidized to produce benzaldehyde, which is widely used in medicine, spices, pesticides, dyes and other industries.

Physical and chemical properties

Benzyl alcohol, also known as benzyl alcohol, is a colorless liquid with an aromatic odor at normal temperature and pressure. The molecular formula is C7H8O, the melting point is -15.3oC, the boiling point is 205.7oC, and the density relative to water is 1.0419. It is slightly soluble in water and easily soluble in organic reagents such as alcohols, ethers, and aromatic hydrocarbons. The substance is toxic, flammable and irritating. Benzyl alcohol has the chemical properties of primary alcohol. Under the action of catalysts such as boron trifluoride and catalpa chloride, it is esterified to generate organic acid esters. When catalyzed by acid, it reacts with excess acetaldehyde to obtain acetal. Benzyl alcohol can be oxidized to form Benzaldehyde can be further oxidized to generate benzoic acid, and benzyl alcohol can also undergo sulfonation, chlorination, and slight oxidation reactions.

Preparation method

1. Benzyl chloride hydrolysis method This method is currently the main method for industrialization at home and abroad. Benzyl alcohol is obtained through azeotropic hydrolysis of an aqueous solution of benzyl chloride and alkali. At the same time, the product benzyl ether is generated, up to 10%. Pressure, high temperature, and increasing alkali concentration are all conducive to the formation of by-products. This method is divided into intermittent method and continuous method.

Figure 1 is the reaction equation of benzyl chloride hydrolysis method

The batch method is to add water, soda ash and benzyl chloride to a steel reactor equipped with a reflux condenser and a jacket, stir and heat, reflux until no more carbon dioxide escapes, cool the reactants, and add The salt is stratified until it is saturated, and the upper layer is carefully separated to obtain crude alcohol. The crude alcohol can be distilled under reduced pressure to obtain industrial-grade benzyl alcohol, with a yield of 70% to 72%, as shown in Figure 2.

Figure 2 is the flow chart of the intermittent method

Use a tertiary amine such as methenamine (hexamethylenetetramine) to treat the benzyl chloride remaining in the hydrolysis to avoid its formation of benzyl ether during the subsequent distillation process. Add an inert solvent to the hydrolysis. For example, chlorobenzene can also inhibit the formation of benzyl ether and obtain a purer finished product. In the continuous method, the aqueous solution of benzyl chloride and alkali is fully mixed under high temperature (180~275℃) and high pressure (1~6.8MPa), and then introduced into the hydrolysis zone. The hydrolysis time only takes a few minutes. The advantage of the continuous method is that there are very few by-products and it can be carried out in a tower reactor, as shown in Figure 3. Under appropriate conditions, the yield of benzyl alcohol with a purity of 99.8% is 98%, and a series of stirred reactors can also be used for continuous reaction.

Figure 3 is a schematic diagram of the continuous production of benzyl alcohol

2. Toluene oxidation method is to oxidize toluene in liquid phase (170~220℃, 1~1.5MPa) into benzyl hydroperoxide in the absence of catalyst. After benzyl hydroperoxide is separated, it can be used at ≤ 20℃. It can be treated with an aqueous solution of sodium sulfite to obtain benzyl alcohol with a yield of 92.6%, or hydrogenated in the presence of a catalyst (such as palladium, skeleton nickel) to obtain benzyl alcohol.

Figure 4 is the reaction equation of toluene oxidation method

3. Preparation of benzyl alcohol from benzaldehyde. Benzyl alcohol can be prepared by adding benzaldehyde, zinc powder and benzyltriethylamine chloride to methanol. The reaction rate can reach 90%. The use of heterogeneous catalytic reaction is conducive to the separation of reaction products. The solid-supported rhodium atom cluster can reduce benzaldehyde in the presence of CO and H2O, with a yield of 96%.

4. Preparation of benzyl alcohol by benzoic acid and ester reduction method

(1) Benzoic acid reduction method: Benzoic acid cannot be reduced directly by NaBH4, but can only be reduced indirectly or by adding other reagents, such as adding AlCl3 or I2. However, when Zn(BH4)2 is refluxed in THF solvent, benzoic acid can be reduced to benzyl alcohol with a yield of 90%.

Figure 5 shows the reaction equation of benzoic acid reduction method

(2) Reduction from the corresponding ester NaBH4 cannot be used to reduce esters, so NaBH4 is often exchanged for cations so that it can reduce esters. LiBH4 was reported earlier in the literature, and it can reduce esters by refluxing in the presence of THF and diethyl ether. The preparation requires expensive lithium chloride, which limits the application of lithium tetrahydroborate. Zn(BH4)2 was also developed in recent years and can be used to directly reduce esters. Methyl benzoate, Zn(BH4)2 and cyclohexene were refluxed for 4 hours under nitrogen protection, and the yield could reach 75%.

5. Other methods At 200℃, in the presence of HZSM-5 catalyst (Al2O3:SiO2 is 80), benzene and formaldehyde are stirred for 4 hours to obtain benzyl alcohol and benzyl methyl ether. A simulated enzyme was constructed using β-cyclodextrin to catalyze the synthesis of benzyl alcohol from benzene and formaldehyde. High pressure oxidation and reductionThis method can produce high-purity benzyl alcohol from toluene, air and hydrogen.

Application

1. In the field of epoxy resin and coatings, benzyl alcohol is an excellent additive. It is mainly used as a diluent, accelerator, and curing agent for epoxy resin. It covers almost every application field of epoxy resin, such as epoxy resin coatings. , composite light-emitting diode (LED) packaging materials, adhesive epoxy AB glue, etc. Benzyl alcohol is used as a diluent for epoxy resin coatings, and the effect is very significant. It can avoid the disadvantages of reactive diluents such as high price, high volatility, and high toxicity, as well as the high VOC emissions or migration of non-reactive diluents. In recent years, the consumption scale of benzyl alcohol in the coating field has continued to expand, and the types of application products have continued to increase. In addition to traditional epoxy resin coating applications, it has also developed into film-forming additives for water-based coatings, marine paint stripper solvents, etc.

2. In the field of flavors and fragrances, benzyl alcohol is a very useful fixative in flavors. It is an indispensable spice when formulating flavors such as jasmine, moonflower, and ylang-ylang. It is used in the preparation of soaps and daily cosmetics. Fragrance is also commonly used as a fragrance solvent to dissolve artificial musk and other fragrances. Benzyl alcohol is a food flavoring allowed in my country’s “Hygienic Standards for the Use of Food Additives” and is mainly used in fruit flavors such as almonds, sweet oranges, cherries, grapes, and strawberries. The dosage is based on normal production needs, generally 1200mg/kg in chewing gum; 220mg/kg in baked goods; 160mg/kg in cold drinks; 47mg/kg in candies; and 15mg/kg in soft drinks.

3. In the medical field, benzyl alcohol is also known as “painless water” because of its anesthetic and analgesic effects. It is often used as a drug solvent in medical injections, such as the solvent of vitamin B injection and the solvent of spectinomycin hydrochloride. Solvent. At the same time, benzyl alcohol can also be used as a preservative for ointments or liquids, and an important intermediate in pharmaceutical synthesis.

4. Ink field: Benzyl alcohol is mainly used as an ink solvent and is used to produce ballpoint pen oil, meat and food printing oil and some special ink products. In recent years, consumption in this field has increased significantly. 5. Other fields In addition to the above fields, benzyl alcohol can also be used as a dye accelerator in textile printing and dyeing auxiliaries, a desiccant for nylon filaments, fibers and plastic films, etc. At the same time, as an excellent solvent, it is also widely used in organic glass solvents, polyvinyl chloride stabilizers, carpet degreasing agents, welding joint cleaners, and silicone solvent stabilizers.

Main reference materials

[1]Sun Zhansong. Analysis of domestic benzyl alcohol production and application[J]. Fine and Specialty Chemicals, 2012, 20(12):12-14.

[2] Peng Ling. Performance study of cobalt-based metal organic framework catalysts in benzyl alcohol oxidation reaction [D]. Jilin University, 2017.

[3]Nie Shaochun. Simulation and optimization of continuous preparation process of benzyl alcohol[D]. Wuhan University of Technology, 2014.

[4]Wu Xingqian, Li Linglan. Manufacturing method of benzyl alcohol [J]. Industrial Catalysis, 2002(02):26-32.