Study On Green Synthesis Of CLT Acid

5-amino-2-chlorotoluene-4-sulfonic acid,also known as CLT acid,is an important intermediate of red organic pigment.This paper uses toluene sulfonation to produce CLT acid.Using toluene as raw material,5-nitro-2-chlorotoluene-4-sulfonic acid is synthesized by sulfonation,chlorination and nitration in turn.Then the nitration liquid is neutralized and prepared by direct hydrogenation reduction to obtain the final product CLT acid.According to the existing problems in the preparation process,such as the serious side effects of sulfonation,the over chlorination,the low utilization rate of the nitrating agent,and the hydrogenation dechlorination,the sulfonation process of recycling mother liquor with excessive toluene coupling,the sequential chlorination,the high water and low nitrate nitration method and the application of electron rich organic amine dechlorination inhibitor in liquid phase catalytic hydrogenation are used to solve the problem.By using the above methods,the reaction selectivity and the yield of CLT acid are improved.Based on the single factor experiment of three stages which include sulfonation,chlorination and nitrification,the yield of 5-nitro-2-chlorotoluene-4-sulfonic acid is calculated at 89% under the optimum conditions.The liquid phase catalytic hydrogenation of CLT acid is studied by using Raney nickel catalyst.The optimum hydrogenation conditions are determined by single factor experiment.50 g nitration solution is prepared with NaOH solution containing 10%mass fraction methanol to 300 ml,PH is 7,2.5g wet catalyst,4.0mg dicyandiamide(premixed with the catalyst),the reaction temperature is 80?,the reaction pressure is3.0MPa,the stirring speed is 400 rpm.Under the optimal process conditions,the conversion rate of raw material is 100% and the yield is 99.18%.The catalyst reusing experiment is carried out using the optimized preparing conditions.The catalyst uses 42 times altogether,with new catalyst adding 6 times.During the whole experiment,the reaction system is stable,the content of CLT acid is kept above 88%,and the yield remaines above 98.6%.The fresh and used catalysts are analyzed by characterizations such as BET,ICP and DTA,we conclude that the main reason of catalyst deactivation is that the surface of catalyst is adhered by impurities during the process of application,which blockes the pore of catalyst,reduces the specific surface area of catalyst,and reduces the catalytic activity.For the deactivation of Raney nickel catalyst,organic solvent and NaOH aqueous solution are used for regeneration treatment.The results show that the thermal washing of 5% NaOH solution can restore the activity of the catalyst,which is similar to that fresh catalyst.