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
