Catalysis-free green synthesis of thiophenes and thioketones by one-pot method based on the resource utilization of SO2 in flue gas

Thiophenes and thioketones possess significant synthetic value due to their extensive pharmacological activities. However, the sulfur sources used in traditional methods for synthesizing these compounds are not only costly but also highly toxic and corrosive. Furthermore, these methods heavily rely on efficient catalysts during the reaction process and are constrained by complex reaction conditions. This work presents a green, catalysis-free, and one-pot method for synthesizing thiophenes and thioketones by directly reacting natural amino acids with SO 2 in flue gas. By screening various natural amino acids, it was found that phenylalanine, valine, leucine, and alanine can react with SO 2 to synthesize 2,5-diphenylthiophene, 4-methyl-3H-1,2-dithiole-3-thione, 4,5-dimethyl-3H-1,2-dithiole-3-thione, and 3-acetyl-2,5-dimethylthiophene, respectively. The yields of these four target products were significantly improved by optimizing the reaction conditions. Based on the characterization analysis and theoretical calculation, the common mechanism of synthesizing these sulfur-containing organic compounds has been proposed, including deamination, hydrolysis, dehydrogenation, SO 2 reduction to sulfur, and the subsequent reaction with organic intermediates. This research not only expands the synthesis methods for organic sulfur-containing compounds but also aids in reducing SO 2 emissions and promoting its green resource utilization. We have developed a green, catalyst-free one-pot strategy for efficiently synthesizing thiophene and thioketone derivatives. Using natural amino acids as substrates and industrial flue gas-derived SO 2 as the sulfur source, this method enables the preparation of seven distinct organosulfur compounds. The approach not only expands synthetic pathways for such compounds but also supports SO 2 emission reduction and sustainable resource utilization. • Catalysis-free and green synthesis of thiophenes and thioketones by one-pot method. • The efficient resource utilization of SO 2 in flue gas is realized. • The optimal reaction conditions for the target product were determined. • The mechanism for the synthesis of thiophenes and thioketones was clarified.