3.10 Thiols or Mercaptans

Thiols are sulfur analogues of alcohols. They tend to be very smelly, even at low concentrations. They are variously gases or oily liquids, and are not soluble in water.

Methanethiol CH₃SH occurs naturally in living tissues and some foods, and contributes to the stink of halitosis as well as flatulence.

Methanethiol, ethanethiol CH₃CH₂SH, and tert-butanethiol (CH₃)₃CSH are used to foul otherwise odorless fuels such as propane and natural gas. They impart a rotten vegetable stench that serves as a signal for the danger of a gas leak.

Skunk spray contains butenethiol CH₃CH=CHCH₂SH, isopentanethiol (CH₃)₂CHCH₂CH₂SH, and a more complex thiol, all of which are potent stench odorants. Butanethiol CH₃CH₂CH₂CH₂SH is also notorious for smelling like skunk.

The skunky note in cannabis smoke is due to prenyl thiol, whose formula is (CH₃)₂C=CHCH₂SH. You might recognize the prenyl group as being similar in structure to isoprene.

Thiols are also called mercaptans, not beacuse they command boats at sea, but because these compounds are reactive towards mercury compounds; mercaptans "capture" mercury. So ethanethiol is the same thing as ethyl mercaptan; prenyl thiol is also called prenyl mercaptan, etc.

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