Thiol

In organic chemistry, a thiol is a organosulfur compound that contains a carbon-bonded sulfhydryl (-C-SH or R-SH) group (where R represents an alkane, alkene, or other carbon-containing moiety). Thiols are the sulfur analogue of alcohols.

Many thiols have strong odours resembling that of garlic. The odours of thiols are often strong and repulsive, particularly for those of low molecular weight. Skunk spray is composed mainly of low molecular weight thiol compounds. These compounds are detectable by the human nose at concentrations of only 10 parts per billion.

Thiols are also responsible for a class of wine faults caused by an unintended reaction between sulfur and yeast and the "skunky" odour of beer that has been exposed to ultraviolet light.

However, not all thiols have unpleasant odours. For example, grapefruit mercaptan, a monoterpenoid thiol, is responsible for the characteristic scent of grapefruit. This effect is present only at low concentrations. The pure mercaptan has an unpleasant odour.

Natural gas distributors began adding thiols, originally ethanethiol, to natural gas, which is naturally odourless, after the deadly 1937 New London School explosion in New London, Texas. Most gas odourants utilized currently contain mixtures of mercaptans and sulfides, with t-butyl mercaptan as the main odour constituent. In situations where thiols are used in commercial industry, such as liquid petroleum gas tankers and bulk handling systems, the use of an oxidizing catalyst is used to destroy the odour. A copper-based oxidation catalyst neutralizes the volatile thiols and transforms them into inert products.

Thiols are often referred to as mercaptans. The term mercaptan is derived from the Latin mercurium captans (capturing mercury) because the thiolate group bonds so strongly with mercury compounds.