Synthesis Of P-chlorotoluene By Selective Chlorination From Toluene

Para-Chlorotoluene（abbreviated as PCT) was an important organic syntheticraw material, widely used in pharmaceuticals, pesticides, dyes, organic synthesisintermediates and rubber, synthetic resin as solvent. Its market demand increasedyear by year. The synthetic method of P-chlorotoluene included diazotization anddirect chlorination from toluene. Current industrial production methods essentiallyused the direct chlorination of toluene, which used chlorine as the source ofchlorine and Lewis acid as catalyst. Through this traditional method, the selectivityfor p-chlorotoluene was rather low and a large amount of o-chlorotoluene wasproduced. As known for all, the application and market demand of p-chlorotolueneis far greater than o-chlorotoluene. So how to improve the content of para-productsbecome one of the key technology research and development in toluene directchlorination, which focuses on selecting a chlorine source and catalyst.This paper studied the synthesis of p-chlorotoluene using oxidativechlorination of toluene. Being different with traditional direct chlorination of tolueneusing chlorine as the source, oxidative chlorination used hydrogen chloride orchloride ions as the chlorine source. This method has the advantages in higher atomutilization, more safe in use and storage, and environment-friendly. The workincluded the following two parts:(1) The oxidative chlorination of toluene used bismuth sodium and oxone asthe oxidant and metal chlorides as a chlorinating agent. The effect of variousconditions on the reaction, such as chloride species, the impact factor of molar,temperature, time and reaction solvent was studied. In optimal conditions, tolueneconversion rate could reach85%, in which the content ratio ofp-chlorotoluenes:o-chlorotoluenes reached3:2in the NaBiO3/ZnCl2/AcOH system;In the Oxone/KCl/CH3CN system, toluene conversion rate could reach100%, theratio of para-chlorotoluenes: ortho-chlorotoluenes reached7:3. The results showedthat the oxidative chlorination from toluene in this systems had high efficiency and high selectivity.(2) The oxidation chlorination of toluene used hydrochloric acid as a source ofchlorine and hydrogen peroxide as the oxidant. The influence of different effectssuch as reactant ratio, reaction temperature, reaction time and other factors wereinvestigated at this part in the absence or present of a catalyst. The results showedthat the hydrochloric acid-hydrogen peroxide system could achieve efficientoxidative chlorination, but the selectivity of para-product is not high in the absenceof a catalyst; in the present of L-type zeolite catalyst, and1,2-dichloroethane assolvent, the toluene conversion rate obtained96%, in which the content ratio ofp-chlorotoluenes:o-chlorotoluenes reached5:5. Compared to traditionalchlorination, this process showed better selectivity of para-product.Based on above results and conclusions, a new synthetic technology oftoluene chlorination which had higher para-product selectivity formed initially.