Mercaptan

They are preferred because, as alcohols, they burn quite cleanly and don't leave residue (much).

                                  H
       H                      H H S H
       |                      | | | |
     H-C-SH                 H-C-C-C-C-H
       |                      | | | |
       H                      H H H H

   Methanethiol             2-butanethiol

The most characteristic property of thiols are their odor. The human nose can detect the presence of these compounds at levels of about 0.02 ppb (that is parts per billion!). These compounds are found for instance in the spray of skunks, or as breakdown products during the digestion of asparagus. Mercaptans are also added to butane for domestic applications, so that consumers can smell whenever they have a gas leak (butane itself is odorless).

Mercaptans are known as thiols in modern chemical language. This more accurately describes them as alcohol analogs with sulfur replacing oxygen, and brings the nomenclature together (thioethers are R-S-R', thioesters are R(CO)SR'). No one ever said mercaptoether.

Mer*cap"tan (?), n. [F., fr. NL. mercurius mercury + L. captans, p. pr. of captare to seize, v. intens. fr. capere.] Chem.

Any one of series of compounds, hydrosulphides of alcohol radicals, in composition resembling the alcohols, but containing sulphur in place of oxygen, and hence called also the sulphur alcohols. In general, they are colorless liquids having a strong, repulsive, garlic odor. The name is specifically applied to ethyl mercaptan, C2H5SH. So called from its avidity for mercury, and other metals.

© Webster 1913.