Green Synthesis Process Of Thioanisole

Thioaniosle is an important organic sulfur compound,which has important applications as a fine chemical raw material and organic intermediate in different fields.The traditional thioaniosle synthesis process has the problems of excessive discharge of alkaline wastewater,high cost,and environmental pollution.Therefore,the innovation and optimization of the green,economic,and efficient thioaniosle synthesis process cannot be delayed.This topic uses thiophenol（Ph SH）and dimethyl carbonate（DMC）as raw materials to synthesize anisole through Ph SH S-methylation reaction under homogeneous and heterogeneous catalysis,DMC is a cheap and easily available green methylation reagent.Using DMC as a methylation reagent for Ph SH S-methylation reaction,the by-products are CH₃OH and H₂O,which is harmless to the environment and pollution,and provides a green synthesis process of anisole.The main research results of the thesis are as follows:（1）From the perspective of basic research,using a homogeneous catalytic experiment method,through a series of organic tertiary amine catalytic catalytic performance inspection,found that the organic bicyclic amidine base 1,5-Diazabicyclo[4.3.0]non-5-ene（DBN）and 1,8-Diazabicyclo[5,4,0]-undec-7-ene（DBU）have excellent catalytic activity.Due to the strong basicity of DBN and DBU,Ph SH is easily activated to produce phenylsulfide anions（Ph Sˉ）with strong nucleophilic attack ability.By cultivating Ph SH and DBN salt-forming crystals and analyzing them,the existence of Ph Sˉwas finally confirmed.For this reaction,only when Ph SH is fully activated to Ph Sˉcan the reaction occur efficiently.Through the investigation of the S-methylation reaction of DMC with different substituted thiophenol compounds and the reaction of Ph SH with different carbonates and according to the theory of Hard-Soft-Acid-Base,it was determined that Ph Sˉonly attacked the methyl group of DMC but not the carbonyl group.Finally,a reasonable Ph SH S-methylated nucleophilic substitution reaction mechanism was proposed.Through the investigation of the catalytic performance of DBN and DBU,the appropriate reaction conditions under homogeneous catalysis were finally determined:using DBN or DBU as the catalyst,without solvent,DMC/Ph SH=2:1（molar ratio）,the reaction temperature was 100℃and the reaction time was 2hours.The conversion rate of thiophenol was 100%,and the selectivity of thioanisole was 100%.（2）Based on fully understanding the mechanism of S-methylation of DMC and Ph SH,from the perspective of engineering technology,in order to achieve continuous production and ensure that the entire process from material addition to product output is carried out under closed conditions,a fixed-bed reactor was used to conduct heterogeneous catalytic reaction experiments,under the conditions of heterogeneous catalysis,using activated alumina supported alkali metal salt as a catalyst,in a fixed bed reactor,under the conditions of three phases of gas-liquid-solid,catalyze the S-methylation of DMC and Ph SH to synthesize thioanisole.By examining the catalytic performance of a variety of different activated alumina supported alkali metal salt catalysts,the activated alumina supported K₂CO₃ catalyst has great advantages in terms of catalytic activity and economy.Based on the homogeneous catalytic reaction mechanism,the heterogeneous catalytic reaction mechanism was discussed,and it was found that the activation of Lewis basic sites on the surface of alumina plays a key role in the activation of Ph SH.Through the investigation of the catalytic performance of the catalyst,the appropriate reaction conditions under heterogeneous catalysis are finally determined:Using activated alumina supported K₂CO₃ as a catalyst（the mass fraction of supported K₂CO₃ is 10%,and the calcination temperature is 500℃）,in the fixed bed reactor,the mixed solution of Ph SH and DMC（molar ratio=1.0）,the airspeed is 0.75 h^-1,the reaction temperature is 120℃,under the conditions of gas-liquid-solid three-phase synthesis of anisole,the conversion rate of thiophenol is 100%,and the selectivity of anisole is 100%.The catalyst did not deactivate after continuous operation for 168 h.In terms of process safety,due to the reaction under closed conditions,Ph SH can be effectively prevented from leaking into the air during intermittent operation,thereby effectively avoiding the harm of Ph SH steam to the environment and human body,and has industrial application prospects.