二氧化硫的循环与再利用

The recycling of sulfur dioxide

自然界的重要化石能源如煤、石油中普遍含有硫化物.因此,人类在利用这些能源的过程中,不可避免地会产生大量二氧化硫(SO_2)气体.据统计,全世界每年二氧化硫的排放量达到1.5亿吨.SO_2作为空气四大核心污染物之一(二氧化氮、臭氧、固体颗粒物为另外3种),它在空气中的含量直接影响生态环境和人类健康.与此同时,SO_2被广泛用作食品添加剂、漂白剂等化工原料,然而这个使用量只占排放量的1.6%.而在高附加值的药物结构和有机光电材料当中,含砜结构骨架广泛存在.如何将有害的SO_2气体高效转化成为高附加值化学产品成了一个亟待解决的科学问题.本文从SO_2背景出发,通过对其危害性和应用性介绍,阐述SO_2研究的重要意义.

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 Wu’s 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.