2-Furfurylthiol

2-Furfurylthiol, which also goes by 2-furanmethanethiol, furfuryl mercaptan, and many other names, is an oily organic liquid that is best known as the principal odor component of roasting and brewing coffee.

In the late 1920s, a series of patents, primarily by noted organic chemist Hermann Staudinger¹ at the University of Freiburg (Germany), described syntheses of 2-furfurylthiol. In a 1928 Canadian patent, Staudinger and co-inventor Thadeus Reichstein treated furfural with ammonium hydrogen sulfide (NH₄HS) to make bis(furylmethyl) disulfide, which they then then reduced to the thiol. In a Swiss patent the same year, these inventors cited sodium sulfide and elemental zinc, aluminum, and sodium as useful reducing agents.

In a 1955 article in Organic Syntheses, Helmer Kofod at the Danish Pharmaceutical College (Copenhagen) described a synthesis of 2-furfurylthiol via the acid-catalyzed reaction of furfuryl alcohol and thiourea to produce an isothiouronium intermediate, which liberates the free thiol upon base hydrolysis.

In 1944, José Giral and Aureliano García Fernández at the University of Nuevo León (Monterrey, Mexico) were likely the first to identify 2-furfurylthiol with coffee aroma. Six years later, Staudinger and Reichstein, along with Staudinger’s son Hansjürgen, published a review of patents that covered the use of the thiol as a coffee-flavoring agent.

The Food and Agriculture Organization of the United Nations describes 2-furfurylthiol thus: “colourless oily liquid; extremely powerful and diffusive odour which on dilution becomes agreeable, coffee-like, caramellic-burnt, sweet”. In other words, the seemingly nasty compound described in the hazard information table becomes appealing when sniffed in small quantities.

Happy new year from the Molecule of the Week team—and we hope that smelling the aroma of 2-furfurylthiol on January 1 helped you wake up to the brand-new year.

1. Staudinger was awarded the 1953 Nobel Prize in Chemistry for his pioneering work on polymers.