''tert''-Butylthiol, also known as ''tert''-butyl mercaptan (TBM), and abbreciated ''t''-BuSH, is an organosulfur compound with the formula (CH₃)₃CSH. This thiol has a strong

odor An odor (American English) or odour ( Commonwealth English; see spelling differences) is a smell or a scent caused by one or more volatilized chemical compounds generally found in low concentrations that humans and many animals can perceive ...

. It is considered a flavoring agent.

Preparation

''tert''-Butylthiol was first prepared in 1890 by Leonard Dobbin by the reaction of zinc sulfide and ''t''-butyl chloride. The compound was later prepared by the reaction of the Grignard reagent, ''t''-BuMgCl, with sulfur to give the corresponding thiolate, followed by

hydrolysis Hydrolysis (; ) is any chemical reaction in which a molecule of water breaks one or more chemical bonds. The term is used broadly for substitution reaction, substitution, elimination reaction, elimination, and solvation reactions in which water ...

. This preparation is shown below: :''t''-BuMgCl + S → ''t''-BuSMgCl :''t''-BuSMgCl + H₂O → ''t''-BuSH + Mg(OH)Cl It is made industrially by the reaction of isobutylene with

hydrogen sulfide Hydrogen sulfide is a chemical compound with the formula . It is a colorless chalcogen-hydride gas, and is toxic, corrosive, and flammable. Trace amounts in ambient atmosphere have a characteristic foul odor of rotten eggs. Swedish chemist ...

over a clay (silica alumina) catalyst.

Reactions

''tert''-Butylthiol is deprotonated by lithium hydride in an aprotic solvent such as hexamethylphosphoramide (HMPA). The resulting lithium thiolate salt has been used as demethylating reagent. For example, treatment with 7-methylguanosine gives guanosine. Other ''N''-methylated nucleosides in tRNA are not demethylated by this reagent. ''tert''-Butylthiol reacts with thallium(I) ethoxide to give the thallium thiolate: : This thallium thiolate can be used to convert acyl chlorides to the

thioester In organic chemistry, thioesters are organosulfur compounds with the molecular structure . They are analogous to carboxylate esters () with the sulfur in the thioester replacing oxygen in the carboxylate ester, as implied by the thio- prefix ...

: : ''tert''-BuSLi reacts with MoCl₄ with to give the tetra thiolate complex: :MoCl₄ + 4 ''t''-BuSLi → Mo(''t''-BuS)₄ + 4 LiCl

Commercial use and occurrence

''tert''-Butylthiol is the main ingredient in many gas odorant blends. It is always utilized as a blend of other compounds, typically dimethyl sulfide, methyl ethyl sulfide, tetrahydrothiophene or other mercaptans such as isopropyl mercaptan, ''sec''-butyl mercaptan and/or ''n''-butyl mercaptan, due to its rather high melting point of . These blends are used only with natural gas and not propane, as the boiling points of these blends and propane are quite different. Because propane is delivered as a liquid and vaporizes to gas when it is delivered to the appliance, the vapor liquid equilibrium would substantially reduce the amount of odorant blend in the vapor.

Food and flavor

''tert''-Butylthiol had been listed on the

European Food Safety Authority The European Food Safety Authority (EFSA) is the agency of the European Union (EU) that provides independent scientific advice and communicates on existing and emerging risks associated with the food chain. EFSA was established in February 2002 ...

(FL-no: 12.174) as a flavor additive. There is no indication of what flavor(s) it may have been used in. It has been removed from this list. ''tert''-Butylthiol is a very minor component of cooked potatoes.

Safety

The Threshold limit value (TLV) is 0.5 ppm. ''tert''-butylthiol has an odor threshold of <0.33 ppb.

References