Furfuryl mercaptan

Description

Furfuryl mercaptan has a characteristic unpleasant odor. It is prepared by reacting thiourea and furfuryl chloride with subsequent hydrolysis of the reaction product; also by reduction of difurfuryl disulfide in alcoholic solution using zinc dust and a small amount of acetic acid or using activated alumina. Furfuryl mercaptan tends to polymerize when heated in the presence of mineral acids.

Description

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.

Chemical properties

clear colorless to pale yellow liquid

Chemical properties

2-Furylmethanethiol is an important constituent of the aroma of roasted coffee. It is a liquid with an unpleasant odor, which becomes like coffee when diluted.

Chemical properties

Furfuryl mercaptan has a characteristic unpleasant odor.

Occurrence

Reported found in raw and roasted chicken, cooked beef, grilled pork, sesame seed oil, coffee and popcorn; tends to polymerize when heated in the presence of mineral acids

The Uses of Furfuryl mercaptan

Furfuryl Mercaptam is a volatile flavor component of corn tortilla chips.

Preparation

Furfuryl mercaptan is prepared from furfuryl alcohol, thiourea, and hydrogen chloride.The resulting S-furfurylisothiouronium chloride is cleaved with sodium hydroxide to give furfuryl mercaptan.

Definition

ChEBI: 2-Furanmethanethiol is a heteroarene.

Aroma threshold values

Detection: 0.005 to 0.01 ppb; aroma characteristics at 0.01%: intense sulfurous onion impact, lacrimator, slightly skunk-like with a dairy nuance and a hint of savory and coffee-like notes.

Taste threshold values

Taste characteristics at 0.2 to 1 ppb: sulfureous, roasted, onion, garlic and coffee.

General Description

Darkens on storage

Safety Profile

Poison by intraperitoneal route. Experimental reproductive effects. Used as a flavoring in chocolate, fruit, nuts, and coffee. When heated to decomposition it emits toxic fumes of SOx. See also MERCAPTANS.

Synthesis

Prepared by reacting thiourea and furfuryl chloride with subsequent hydrolysis of the reaction product; also by reduction of difurfuryl disulfde in alcoholic solution using zinc dust and a small amount of acetic acid or using activated alumina.