Sulfonamides
Sulfonamides are used in many drugs, including antibiotics and Viagra, as well as in agrochemicals and dyes. While to date it has been necessary to use corrosive chemicals, high temperatures and expensive metal catalysts to produce sulfonamides, a new electrochemical method — developed by a research team at Johannes Gutenberg University Mainz (JGU; Germany; www.uni-mainz.de) — requires only cheaper starting materials, electrical current and relatively safe solvents. The researchers recently reported their findings in Angewandte Chemie International Edition.
“The conventional procedure requires three reaction stages, with each stage driving up manufacturing costs by a factor of two to five. With the new method, just one reaction stage is needed. That makes it readily scalable and it can thus be applied on a technical scale,” says professor Siegfried Waldvogel, head of the research team.
The starting materials for the new reaction are amines, aromatics and SO2, which is a waste product of many industrial processes. In effect, the new method makes it possible to convert this unwanted material into valuable products. The amines react with the SO2 in solution, producing amidosulfinate as an intermediate product. This makes oxygen and sulfur available to react with the aromatic molecules that have already been oxidized using an electrical current. To prevent oxygen from bonding during this process, a suitable solvent was selected — “that is the really clever bit,” Waldvogel points out. The solvent forms strong hydrogen bonds with the oxygen atoms, thereby rendering them inactive — and clearing the way for the formation of the desired S–C bonds. After the reaction, the solvent can be redistilled and used again.