Study On Improvement Of Preparation Technology Of Para-ester As Dyestuff Intermediate

Acetamidobenzenesulfonyl chloride(ASC)is a key intermediate for the synthesis of para-ester used as an important raw material for the synthesis of reactive dyes.The improved synthetic process of ASC was mainly discussed in this thesis.In the traditional synthetic process of ASC,excess chlorosulfonic acid is necessary for the reaction with acetanilide.The molar ratio of chlorosulfonic acid to acetanilide is4.9:1,but the yield is only 74%.This method has disadvantages of low yield,low utilization rate of chlorosulfonic acid,and also generates a large amount of waste acid,resulting in difficult post-processing and increased production costs.In order to solve these problems,we has made improvements to the traditional process.In the presence of different solvents,acetoaniline is chlorosulfonated to synthesize ASC with chlorosulfonic acid as the sulfonating agent and chlorinated sulfoxide as the chlorinating agent.The higher yield of ASC could be achieved by optimalization of crucial reaction factors of this process.The developed process exhibited significant improvements with reduced amount of chlorosulfonic acid and waste acid.Hence,this new process is highly valuable for the industrial application.CCl₄,tetrachloroethylene,the mixture of tetrachloroethylene and CCl₄were used respectively as the solvent to investigate the effect of solvent on the synthesis of ASC.The effects of solvent amount,reaction temperature,reaction time,amount of chlorinating agent and ratio of the reactants on the yield were also investigated.Taking into account the problem of solvent recovery,tetrachloroethylene is the best choice as favorable solvent for chlorosulfonation.The optimal process conditions were obtained through a series of controlled experiments.The reaction system with the molecular ratio of acetanilide:chlorosulfonic acid:dichlorosulfoxide:tetrachloroethylene=1:2.5:1.1:3,firstly reacted at 45^oC for 1h,then reacted for another 1.5h at 65^oC.Under this process condition,the yield of ASC is 97%,the purity is 98%,and the recovery rate of solvent is 90%.About 1%of p-chloroacetanilide is produced in the synthesized ASC as byproduct.Due to the stricter national regulations on the content of p-chloroacetanilide,it is necessary to reduce the amount of p-chloroacetanilide in the commercial product.The difference in the solubility of p-chloroacetanilide and ASC in the solvent were used to purify the crude product by solvent.Various solvents have been tried,among which solvents such as chloroform,chlorobenzene and benzene can remove p-chloroacetanilide efficiently.The influence of stirring temperature,stirring time,and the amount of solvent on removing chloroacetanilide were studied.Chloroform was found to be the best solvent to reduce the content of p-chloroacetanilide.The optimal conditions are:Stirring temperature 55^oC,stirring time 1h,mass ratio of crude product to solvent 1:4,ice water cooling for 2h.After purification with chloroform extraction,the content of p-chloroacetanilide in ASC has been reduced from about 1%to 0.049%,which meets the relevant standards set by the state,and the yield of ASC after purification is also 91%.Therefore,the process conditions are feasible,which not only reduces the content of p-chloroacetanilide,but also ensures a higher yield of ASC.