Background and overview[1-2]
Benzotriazoles are white to light pink crystals, soluble in alcohol, benzene, toluene, chloroform, and slightly soluble in water. Oxidation in air gradually turns red. Can explode when distilled in vacuum. The preparation method of benzotriazole is usually to diazotize o-phenylenediamine to prepare o-aminobenzene diazonium salt, and then immediately cyclize it in one step to synthesize the crude benzotriazole, which is then recrystallized, filtered, and dried to obtain benzene. Pure triazole.
Apply[3]
Benzotriazole is an important fine chemical product. It has a wide range of uses, mainly used as corrosion inhibitors for copper and copper alloys, metal rust inhibitors, photographic antifogging agents and organic synthesis intermediates. It is also widely used in coating additives, synthetic detergent preservatives, anticoagulants, lubricant additives, synthetic dye intermediates, polymer material stabilizers, plant growth regulators, anti-discoloration agents, vapor phase corrosion inhibitors and ultraviolet light absorbers. agent. Benzotriazole can be used in conjunction with a variety of corrosion inhibitors to improve the corrosion inhibition effect. It can also be used in conjunction with a variety of scale inhibitors and bactericidal algaecides. It can produce better corrosion inhibition effects on closed circulating cooling water systems. Adding benzotriazole to automotive antifreeze and paint can protect materials. During the machining process, adding benzotriazole to cutting oil can prevent the processed copper from discoloring.
Preparation[3]
Many researchers at home and abroad have done a lot of research work on the synthesis of benzotriazole. So far, the reported synthetic routes include the o-phenylenediamine method, the benzimidazolone method, the o-nitrophenylhydrazine method, the o-nitrochlorobenzene method, and the preparation of benzotriazine from sodium benzotriazole. Azole method.
1. O-phenylenediamine method: The o-phenylenediamine method is the most classic method for synthesizing benzotriazole, which includes the o-phenylenediamine atmospheric pressure synthesis method and the improved o-phenylenediamine high-pressure method.
1) Ortho-phenylenediamine normal pressure method: First dissolve o-phenylenediamine in acetic acid aqueous solution, and prepare about 40% sodium nitrite aqueous solution; the two solutions are pre-cooled to 1~5°C and then mixed and reacted. And keep it in an ice bath, then quickly heat it to 80°C to close the ring to generate benzotriazole. After cooling, filter and wash with water to obtain the crude product; distill at an absolute pressure of 2000Pa, collect the fractions between 201 and 204°C, and crystallize with benzene to obtain The product has a yield of 70% to 80%. At present, most domestic manufacturers use this method. However, this method has the disadvantages of high toxicity of o-phenylenediamine, consumption of a large amount of acetic acid, difficulty in product refining, low yield, and harsh reaction conditions. From the 1950s to the 1970s, foreign countries made many improvements to the above process and increased the product yield. Later, Joseph in the United States switched to the method of dropping sodium nitrite aqueous solution. The initial reaction temperature was increased to 55-60°C, and the reaction mixture was mixed with Extract amyl alcohol, distill at a pressure of 266.6Pa, collect the 157-170°C fraction, and obtain nearly colorless benzotriazole after cooling, filtration, and drying, with a yield of up to 96%. This method is easy to control the temperature. The ice bath, which is not conducive to industrial production, is eliminated. The reaction mixture is extracted with hexanol, polyethylene glycol 200 is added to the extract, the hexanol is first recovered by distillation under reduced pressure, and then benzene is azeotropically distilled under a pressure of 266.6Pa. Polyethylene glycol solution of benzotriazole. This improvement not only increases the yield of benzotriazole to 95.1%, but also reduces the risk of benzotriazole decomposition and explosion in vacuum distillation. The former West German Rochat used Potassium nitrate replaces sodium nitrite. In the presence of xylene and acetic acid, the reaction temperature is 20-50°C, and the yield can reach 97%.
2) O-phenylenediamine high-pressure method: The o-phenylenediamine high-pressure method was invented by John from the United States. The molar ratio of o-phenylenediamine and sodium nitrite is 1:1~1.05, and the reaction temperature is 200~300 ℃, the pressure is 4.8×106~6.9×106Pa. After the reaction is completed, use acid to adjust the pH value to 6. Since no acid participates in the diazotization ring-closing reaction, the chance of producing dark-colored tar-like substances from diazo coupling is reduced, thus It improves the yield of the product and makes the purification of the product easier. For example, o-phenylenediamine reacts with 37% sodium nitrite aqueous solution at a temperature of 260°C and a pressure of 3.0×106 to 3.3×106Pa. After 3 hours, cool and adjust the pH value from 11.7 to 6 with concentrated sulfuric acid to obtain benzotriazole with a purity of 100% and a yield of 96.9%. This process does not require acetic acid, has fewer side reactions, less pollution, and a high yield. The reaction time is short and can be produced continuously. Chinese researchers have successfully synthesized benzotriazole using a one-step pressurized method. Benzotriazole sodium is synthesized from o-phenylenediamine and sodium nitrite in one step under pressure, and then acidified and crystallized to obtain the product. This method reduces the cost by 50% to 70% and fills two domestic gaps.
2. Benzimidazolone method
Benzimidazolone and sodium nitrite aqueous solution were reacted at 190°C under high pressure for 75 minutes. After acidification, washing and drying, the product yield was 85.3%. Since benzimidazolones are composed of o-phenylenediamine and urea It is prepared by reaction, so it is expensive, which restricts the application of this synthesis method.
3. O-Nitrophenylhydrazine method
O-Nitrophenylhydrazine reacts in a mixed aqueous solution of ammonia, isopropyl alcohol and hexylene glycol at 140°C and high pressure for 1.5 hours to generate 1-hydroxybenzotriazole (HBTA). Use copper-dioxide trioxide Chromium is used as a catalyst, hydrogen and nitrogen are introduced in a ratio of 92:8, and the deoxygenation and hydrogenation reaction is carried out at 160 to 170°C and high pressure for 1 hour. HBTA is deoxygenated and hydrogenated to generate BTA. The final yield of benzotriazole is 89%.
4. O-nitrochlorobenzene method
HBTA is directly synthesized from o-nitrochlorobenzene and hydrazine hydrate, and then deoxygenated and hydrogenated to generate BTA.The highest total yield can reach 98.6%. The advantages of this method are high yield and few intermediate links. It is a promising and very important method.
Main reference materials
[1] Concise Dictionary of Fine Chemicals
[2] CN201110204636.4 A synthesis method of benzotriazole
[3] Synthesis and application of benzotriazole
