The Study On Selective Chlorination Of M-xylene

1,3-Bis（trichloromethyl）benzene plays an important role in fine chemical industry and is an important intermediate for medicines,pesticides and dyestuffs,especially as an intermediate of meta-aramid has become a research hotspot,and its purity has a significant impact on the properties of meta-aramid,therefore,it is of great significance to study the preparation process of 1,3-bis（trichloromethyl）benzene with high selectivity and high purity.The selective chlorination reaction of m-xylene is complex,involving the transformation of various intermediate components.The study found that the side-chain photochlorination process due to limited light depth,the reactor structure is complex,and the mass transfer is difficult to strengthen,which leads to long reaction time,high content of by-products and poor selectivity.In this paper,the kinetics of1,3-bis（trichloromethyl）benzene photocatalytic reaction,the influence of catalysts on the reaction process and the optimization of process were studied with cheap m-xylene as raw material.The target product,intermediate product and by-product were qualitatively and quantitatively analyzed by GC-MS,IR,~1H-NMR and other analytical methods.The kinetic model of the reaction was established by kinetic experiments,and the reaction rate constants and activation energies of each step of the reaction were obtained.Through the study on the mechanism of 1,3-bis（trichloromethyl）benzene photocatalytic reaction,the formation path of main by-products was identified and obtained by combining with characterization methods.The effects of catalyst type and dosage on the reaction activity and selectivity were studied,and it was found that catalyst M could improve the reaction rate constant and the selectivity of the main product,and significantly inhibit the occurrence of side reactions.The influence of light intensity,solvent dosage,circulation mode,reaction temperature,chlorine flow,raw material and chlorine purity on the reaction were studied,and the optimal reaction conditions were obtained as follows:15W blue light lamp was used as the light source,the mass ratio of solvent to m-xylene was 1:1,the method of external circulation was adopted,the amount of catalyst M was 0.75%of the mass of m-xylene,the reaction temperature was 130°C,the flow rate of chlorine gas was 20 m L/min,the raw material was purified by distillation,and chlorine was dehydrated and purified by concentrated sulfuric acid before the reaction.Under these conditions,the yield of the target product was 96.57%and the purity was 99.60%.In summary,the selective chlorination of 1,3-bis（trichloromethyl）benzene using m-xylene as raw material and catalyst M combined with photocatalysis has the advantages of short reaction cycle,high selectivity and yield of target products,and excellent product quality.