Abstract

Background: We have developed a one-pot, simple and efficient protocol for the direct synthesis of symmetrical organic disulfides in high yields via domino reaction between aryl/alkyl halides and Sodium thiosulfate as the sulfur source, in the presence of copper/imidazole and K₂CO₃.

Methods: Owing to the importance seen in the synthesis disulfides, as is evident from the number of publications in the recent past, and our continuing interest in the synthesis of organosulfur compounds using direct synthesis and domino reaction. Herein we designed the synthesis of various disulfide using reaction of aryl/alkyl halides with sodium thiosulfate in presence CuI catalyst, K₂CO₃ and imidazol as ligand in solvent DMSO. The reaction of iodobenzene with sodium thiosulfate was studied under normal atmospheric conditions in order to optimize the reaction conditions in terms of temperature, amount of reagent and catalyst, and the type of ligand.

Results: Effect of solvent and ligand was perceptible, The reaction proceeded not well in the absence of a ligand. The best ligand for these reaction was imidazole. The various solvents tested in this investigation. It was observed that excellent yield of the product was obtained when the reaction was carried out by using DMSO as solvent. The reaction no proceeded in the absence of a base. K₂CO₃ was a good choice. We examined various amount of the copper salt. It was found to be the best choice in presence 0.7 mmol from copper salt. Also it was significantly found that the reaction yield and rate increased with temperature. The reaction favoured at 130ºC temperature. The 3 mmol Na₂S₂O₃•5H₂O concentration was sufficient to give maximum yield of the required product in comparison with other amounts. Diaryl/alkyl disulfides were synthesized in terms of the connecting and type position of the substituents on the aryl/alkyl groups, so that products with different substituents, both electron withdrawing and electron-donating substituent, were synthesized in the ortho, meta and para positions. The results show that iodobenzene and bromobenzene were effective for the reaction. Although it was seen that the reaction cannot progress with compound of aryl chloride. Symmetrical diheteroaryl disulfides were well synthesized from the corresponding heteroaryl iodides, bromides and chlorides.

Conclusion: In summary, we have developed a new and effective method for the direct synthesis of diaryl/ alkyl disulfides from various aryl/alkyl halides by domino reaction. In this work reports an effective and cheap metal catalyzed sulfur transfer reaction, which is more economic, and more environmentally friendly and more comprehensive than previous methods. As a novel sulfur source, Na₂S₂O₃ shows notable advantage in this system. This reaction functions under mild conditions, and various functional groups are well tolerated.

Keywords: Cu-mediated, domino reaction, disulfides, sodium thiosulfate, direct synthesis.

Graphical Abstract