Background and overview[1][2]
4-Bromo-1,2-xylene, also known as 3,4-dimethylbromobenzene; molecular formula: C8H9Br, molecular weight: 185.06, CAS NO: 583-71-1; melting point: -0.2℃; boiling point: 215℃. 4-Bromo-1,2-xylene is mainly used as a raw material for organic synthesis. It is an important monomer for the synthesis of super heat-resistant polyimide, biphenyltetracarboxylic dianhydride, and is also the main component for the synthesis of 5-bromobenzofuranone. raw material. The 4-bromo-1,2-xylene products currently on the market are produced using the following process. 1) Diazotization method of 3,4-dimethylaniline: After diazotization reaction of 3,4-dimethylaniline in 48% hydrobromic acid and a certain amount of sodium nitrite to obtain the diazonium salt, Then add copper powder and heat to 60-100°C for decomposition to obtain crude 4-bromo-1,2-xylene. The crude product is distilled to obtain 4-bromo-1,2-xylene. The content of 4-bromo-1,2-xylene produced by this process is as high as 98%, but the yield is low, there are a lot of three wastes, and the cost of raw materials is high. Not conducive to industrial production. 2) Ortho-xylene bromination method: In current production processes at home and abroad, most catalysts such as I2, FeBr3, FeCl3, iron powder, etc. are used. Due to the special chemical structure of o-xylene, the substitution reaction of bromine will generate 4-bromo-1 , 2-xylene, 3-bromo-1,2-xylene, and three isomeric dibromides. The best product content is about 75%. If the content needs to be increased, the molar ratio of bromine to o-xylene must be increased to 1.3-1.5:1 and sulfur dioxide should be used as the solvent, resulting in low product yield and the production of a large amount of three wastes, making it unsuitable for industrial production.
Apply[2]
4-Bromo-1,2-xylene can be used as a raw material for organic synthesis, such as the synthesis of silicon-containing aromatic dianhydrides. Silicon-containing polyphthalimide resin combines the excellent properties of polyphthalimide and silicone resin, especially in solubility, adhesion, hygroscopicity, electrical insulation properties, etc., so it is attracting more and more attention. . Bis-(3,4-phenylenedicarboxylic acid)dimethylsilane was first prepared by reacting 4-bromo-1,2-dimethylbenzene with dichlorodimethylsilane in an ether solution of n-butyllithium. Bis-(3, 4-dimethylphenyl)dimethylsilane is produced, and then synthesized through oxidation, ester formation and other reactions.
Preparation [1]
A method for preparing 4-bromo-1,2-xylene. The method uses o-xylene as raw material, and in the presence of methylene chloride solvent and catalyst, dripping at a temperature of -60°C to -20°C Bromine, the molar ratio of o-xylene and bromine is 1:1. After the dropwise addition, keep the temperature for reaction, then slowly raise the temperature to 10-20°C, remove the dissolved hydrogen bromide in the reaction solution, and add saturated sodium sulfite aqueous solution. Stir for 30 minutes, recover the dichloromethane-containing product by layer, then wash with 5% dilute alkali solution to pH=8-9, and finally wash with water until neutral to obtain colorless or light yellow 4-bromo-1,2- The crude xylene product is distilled under normal pressure to recover the solvent methylene chloride, and then rectified under reduced pressure to obtain the 4-bromo-1,2-xylene product. The catalyst is a mixture of ferric chloride and quaternary ammonium salt. Examples of quaternary ammonium salts are: tetrabutylammonium chloride, tetrabutylammonium bromide, tetrapropylammonium bromide, methyltrioctylammonium chloride, benzyltriethylammonium chloride, ferric chloride and The mass ratio of quaternary ammonium salt is 4-5:1. The content of the obtained 4-bromo-1,2-xylene is increased to 85-93%, while the content of by-products is reduced, and the product yield is increased to 95%. Time for dropping bromine: 3-4 hours. Insulation reaction time: 2 hours. Alkaline washing temperature: room temperature.
Main Reference Materials
[1] CN201010161510.9 A method for preparing 4-bromo-1,2-xylene
[2] Synthesis of silicon-containing aromatic dianhydride and its polyimide
