The recycling of sulfur dioxide

Abstract

Sulfur-containing compounds are commonly found in important fossil fuels, such as coal and petroleum etc. Therefore, in the process of utilizing these energy sources, we will inevitably produce a large amount of sulfur dioxide gas. According to statistics, the annual emission of sulphur dioxide is 1.5 billion tons worldwide. Sulfur dioxide is one of the four core pollutants in air (nitrogen dioxide, ozone and solid particles are other three core pollutants), its content in the air directly affects the ecological environment and human healt. Meanwhile, sulfur dioxide is widely used as food additives, bleaching agents and other chemical raw materials, and this usage accounts is only 1.6% of its emissions. Sulfonyl-containing compounds exist widely in the drug and organic photoelectric material molecules. How to convert harmful sulfur dioxide into useful chemical products has become a scientific problem demanding prompt solution. In 1957, Meerwein et al. developed the synthesis of arylsulfonyl chlorides from aryl diazonium salts and SO2 gas in the presence of a catalytic amount of CuCl. Afterwards, some CuCl-catalyzed strategies were developed and applied to preparations of aryl sulfonyl chlorides from different organometallic reagent and SO2 gas. Sulfur dioxide, as a toxic gas, is not easy to handle and store in the process of its use. Therefore, the development of sulfur dioxide gas surrogates has become an important research direction in organic chemistry. In 2010, the Willis group employed the known complex DABSO DABCO·(SO2)2 (DABCO=1,4-diazabicyclo [2.2.2] octane) to synthesize aryl N -aminosulfonamides via the palladium- catalyzed three-component coupling of aryl iodides, hydrazines and DABSO. Subsequently, the Wu group described a palladium-catalyzed three-component coupling of arylboronic acids, DABSO and hydrazines in the presence of dioxygen. Inorganic sulfites also can be used as the source of sulfur dioxide. In 2012, the Wus group disclosed a palladium-catalyzed coupling of aryl halides, potassium metabisulfite (K2S2O5), and hydrazines for the synthesis of aryl N -aminosulfonamides. The Toste group developed a gold(I)-catalyzed sulfination of aryl boronic acids via the three-component coupling of aryl boronic acids, potassium metabisulfite and alkyl bromides. Shavnya et al. explored the palladium-catalyzed one-step synthesis of (hetero)aryl-alkyl sulfones via the three-component coupling of (hetero)arylboronic acids, potassium metabisulfite, and unactivated or activated alkylhalides. In 2017, our group reported a straightforward sulfur dioxide-iodine exchange protocol for the construction of diarylannulated sulfone employing the readily available inorganic sodium metabisulfite as a safe and convenient sulfur dioxide surrogate. Some structural novel π-conjugated molecules, which give great potentials as organic light emitting diodes (OLEDs) materials molecules, were successfully established through our strategy, Despite the great attention of direct introduction of sulfur dioxide into organic frameworks have been paid, there is still necessary to develop more stable, green, cheap and easy to handle sulfur dioxide surrogates.