Study On The Synthesis Of Benzothiazolone By Reaction Of COS With Disulfide

Benzothiazolone derivatives are a class of bicyclic compounds containing S and N heterocycles,which are widely used in pesticides,medicines and other fields.Therefore,the synthesis of benzothiazolone compounds has attracted much attention of scientists.Benzothiazolone derivatives are usually synthesized by the reaction of o-aminothiophenol and carbonyl reagent.Disulfide,the dimer of o-aminothiophenol,is odorless,low-cost and stable in the air,which is a more desirable raw material.The carbonyl reagent is another raw material for the synthesis of benzothiazolone,however,the traditional carbonyl reagent produces some by-products,which makes a low atomic utilization of the reactions.In recent years,with the proposal of"green chemistry",CO₂ has been used as a highly economical and renewable carbonyl source in the synthesis of carbonyl compounds.However,due to the high chemical stability,CO₂ is converted into high-value chemicals often requires more harsh conditions.Carbonyl sulfide?COS?,the molecular structure is similar to CO₂,could be used as an ideal carbonyl sourse due to its high chemical activity.However,in the participating carbonylation reactions,COS usually produces by-product H₂S,which show a low atom utilization.In order to utilize the by-product H₂S,a coupling reaction that the benzothiazolone derivative was synthesized by reacting disulfide with COS was designed under mild condition.In this reaction,The H₂S produced by the reaction of COS with the intermediate o-aminothiophenol can undergo a dynamic exchange reaction with the disulfide to break the S-S bond to form o-aminothiophenol.Through the coupling reaction of COS and disulfide,the C=O of COS is converted to benzothiazolone,and the S element of COS is converted into sulfur?S₈?by dynamic exchange reaction with disulfide.By investigating the reaction pressure,solvent and the type and amount of promoter,the optimal reaction conditions are obtained,which the ratio of disulfide and NaOH was1:0.3,the reaction solvent is DMF,stirred for 1.5 h under 0.5 MPa pressure of COS in the room temperature.The test experiment of different reaction substrates and the gram-scale experiment were carried out under the optimal conditions,which demonstrated that the reaction system has good versatility and practicability.In this paper,LCMS was used to capture the reaction intermediates,such as polysulfide,produced by the reaction of carbonyl sulfide with o-aminodisulfide,and the¹HNMR was used to prove that H₂S can break the S-S bond of o-aminodisulfide to form o-aminothiophenol.Hence,the proposed coupling reaction mechanism was verified through the above LCMS and ¹HNMR experimental data.Through the discussion of the reaction conditions,it was found that the system can be carried out smoothly under alkaline conditions.Subsequently,¹HNMR on-line monitoring and a series of comparative experiments were carried out to explore the reaction mechanism under alkaline conditions,and further explore the role of alkali,which demonstrated that the inorganic alkali NaOH can not only accelerate the reaction rate of H₂S-disulfide dynamic exchange,but also activate the reaction intermediate.