Diarylsulphides are popular motifs for the basis of drug design and materials, but their synthesis is usually dependant on inherently wasteful cross coupling reactions that require metals such as palladium, copper, and indium. Now iodine has been discovered to be an effective catalyst for the synthesis of diarylsulphides from thiophenols and cyclohexanone derivatives. Researchers from Xiangtan in China have shown that the desired reaction is achievable when an oxygen atmosphere is used to regenerate the catalyst. A large number of pendant functional groups are tolerated, with yields of up to 80% observed.
The use of iodine to replace metal containing catalysts is hugely beneficial in securing the long term sustainability of this synthetic protocol. The vulnerability of scarce metal resources is a vital consideration often overlooked when designing new organic syntheses supposedly within the remit of green chemistry. Unlike C-S cross coupling procedures that result in stoichiometric halide containing wastes, this new protocol produces only water as a by-product, whilst also circumventing the need for an auxiliary base or an expensive metal catalyst. Unfortunately the only satisfactory solvent that could be found was NMP, which will need to be improved upon if this procedure is to be considered as a green process. Otherwise this synthetic method is a welcome advance in the development of sustainable catalytic chemistries.
By James Sherwood
Iodine-catalyzed efficient 2-arylsulfanylphenol formation from thiols and cyclohexanones, Yunfeng Liao, Pengcheng Jiang, Shanping Chen, Hongrui Qi and Guo-Jun Deng, Green Chem., 2013, DOI: 10.1039/c3gc41671b