Study On Transition Metal Catalyst-free Synthesis Of Phenothiazines And Organic Disulfides

With the development of science and technology and the progress of society,people pay attention not only to production and efficiency,but also to environmental and energy issues.Transition metal catalysis is an important approaches to construct C-N,C-C and C-S bonds in the field of organic synthesis.The transition metal elements contain Pd,Pt,Cu and so on.These transition metal catalysts are generally expensive and not recyclable.In the point of production benefits,the use of transition metals will increase the cost of the products.In the point of atomic economy,the nonreusable transition metal catalysts does not meet the green chemical merit.At the same time,the adding of transition metal in the organic reaction will cause the postprocessing more complicated.In this paper,transition metal catalyst-free synthesis processes are described to prepare phenothiazine compounds and organic disulfides.Compared with the synthetic process using transition metal catalysts,the new processes have some advantages in economic efficiency and purification of product.In this paper,two non-transition metal catalytic routes were expored to synthesis the phenothiazines and organic disulfides.The main contents of experiment study are divided into two parts:The first part is the study on preparation process of phenothiazines without transition metal catalyst.After a number of experimantal trials,we found that the non-catalytic synthesis process can be carried out smoothly by S-2-acetamidophenyl ethanethioates and ortho-dihaloarenes.In order to optimize the process,we screened variousreaction conditions.The optimized condition was as follows: A reaction mixture of S-2-acetamidophenyl ethanethioates(1 mmol),ortho-dihaloarenes(1.2 mmol),Cs2CO3(4 equiv.)and DMF(3 mL)was stirred at130 °C for 10 hours.With the optimized reaction conditions at hand,reaction of various ortho-dihaloarenes and S-2-acetamidophenyl ethanethioates were performed to determine the scope of the substrates.The results show that all the reaction proceed smoothly,and the highest yield of phenothiazine was up to 91%.When the ortho-dihaloarenes with an electron-withdrawing group,the reaction yields increased;when more complex substrates were used in the reaction,the yields decreased due to side reactions.The second part is the study of preparation process of disulfides without transition metal catalyst.The copper-catalyzed reaction of t-butanesulfinamide and 2-mercaptoimidazole were investigated.We conducted two comparative experiments to further explore the impact of the presence of catalyst and inorganic base on the disulfide synthesis,and found that the use of the inorganic base did not benifit the reaction,whereas the catalyst experiment reduce the yield.As the result,we found that this type of catalyst and base had adverse effect on the reaction.After discovery of the transition metal catalyst-free and base-free synthetic method of the disulfide,we screened the solvents and found that the best yield was obtained when toluene was used as solvent.We finally determined obtained the optimized synthetic process of the disulfides: a mixture of tert-butanesulfinamide(1 mmol),2-mercapto heterocyclic(1 mmol),and toluene was stirred at 100 ? for 24 hours.Finally,in order to examine the scope of this reaction process,tert-butanesulfinamides with various kinds of 2-mercapto nitrogen-containing heterocycles(imidazole,pyrimidine,pyridine)were screened.And it is found that the reactions were all carried out.The 2-mercapto nitrogen-containing heterocycles with an electron-withdrawing group got higher yields.When the heterocycles are tetrazole,pyridine,pyrimidine,the yields were lower than that of the corresponding imidazole substrates.