In chemistry, thiols (formerly known as mercaptans) are those compounds which contain the thiol group -SH attached to a carbon atom.
Thiols are similar to alcohols, with the oxygen of the hydroxyl group -OH being replaced by a sulfur atom. (Oxygen and sulfur have similar chemical properties, as they belong to the same periodic table group.) Thiols form thioethers, thioacetals and thioesters, in which the alcohol-derived oxygen atom is replaced by a sulfur atom.
Many thiols are colorless liquids having an odor resembling that of garlic. The odor is strong and repulsive. Thiols bind strongly to skinproteins, and are responsible for the intolerable, persistent odor produced by the spraying of skunks.
Natural gas distributors began adding various forms of mercaptan to natural gas, which is naturally odorless, after the deadly explosion in 1937 at the high school in New London, Texas.
When a thiol group is a substituent in an alkane, there are several ways of naming the resulting thiol:
The suffix -thiol is added to the name of the alkane. Example: CH3SH would be methanethiol.
The word mercaptan replaces alcohol in the name of the equivalent alcohol compound. Example: CH3SH would be methyl mercaptan.
After looking at mercaptan's binding states for metals, particularly mercury, one can see the reason for the name mercaptan, from the Latinmercurius captans, laying hold of mercury.
External links
Mercaptan (http://www.factmonster.com/ce6/sci/A0832739.html), by The Columbia Electronic Encyclopedia
What is Mercaptan? (http://www.columbiagaspamd.com/community_outreach/mercaptan.htm), by Columbia Gas of Pennsylvania and Maryland
Mercaptans are found in crude petroleum, and methyl mercaptan is produced as a decay product of animal and vegetable matter.
They also are produced by certain plants and animals; e.g., allyl mercaptan is released when onions are cut, butanethiol (butyl mercaptan) derivatives are present in skunk secretion, and mercaptans are among the sulfur compounds causing the disagreeable odor of flatus.
T-butyl mercaptan blends are often added to the odorless natural gas used for cooking and serve to warn of gas leaks.
The mercaptans are reacted with the diolefins to form sulfides which are higher boiling than that portion of the naphtha which is used as feed to the etherification or alkylation unit.
These mercaptans are inhibitors for the hydrogenation catalyst used to hydrogenate dienes in the feed to an etherification unit or to an alkylation unit.
In the reaction distillation zone 12 substantially all of the mercaptans react with a portion of the diolefins to form higher boiling sulfides which are distilled downward into the stripping section 15 and removed.
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