Tert-Butylthiol

tert-Butylthiol, also known as tert-butyl mercaptan (TBM), and abbreviated t-BuSH, is an organosulfur compound with the formula (CH₃)₃CSH. This thiol has a strong odor. It is considered a flavoring agent.^[1]

tert-Butylthiol

Names
Preferred IUPAC name 2-Methylpropane-2-thiol
Other names t-BuSH 2-Methylpropane-2-thiol 2-Methyl-2-propanethiol tert-Butyl mercaptan
Identifiers
CAS Number	75-66-1 Y
3D model (JSmol)	Interactive image
Abbreviations	TBM
ChemSpider	6147 Y
ECHA InfoCard	100.000.810
PubChem CID	6387
UNII	489PW92WIV Y
CompTox Dashboard (EPA)	DTXSID0026418
InChI InChI=1S/C4H10S/c1-4(2,3)5/h5H,1-3H3 Y Key: WMXCDAVJEZZYLT-UHFFFAOYSA-N Y InChI=1/C4H10S/c1-4(2,3)5/h5H,1-3H3 Key: WMXCDAVJEZZYLT-UHFFFAOYAT
SMILES SC(C)(C)C
Properties
Chemical formula	C4H10S
Molar mass	90.18 g·mol−1
Appearance	Colorless liquid
Density	0.8 g/mL
Melting point	−0.50 °C (31.10 °F; 272.65 K)
Boiling point	62 to 65 °C (144 to 149 °F; 335 to 338 K)
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa). Y verify (what is YN ?) Infobox references

Preparation

tert-Butylthiol was first prepared in 1890 by Leonard Dobbin^[2] 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.^[3] 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 over a clay (silica alumina) catalyst.^[4]

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.^[5]

tert-Butylthiol reacts with thallium(I) ethoxide to give the thallium thiolate:^[6]

(CH₃)₃CSH + TlOC₂H₅ → (CH₃)₃CSTl + HOC₂H₅

This thallium thiolate can be used to convert acyl chlorides to the thioester:

(CH₃)₃CSTl + RCOCl → RCOSC(CH₃)₃ + TlCl

tert-BuSLi reacts with MoCl₄ with to give the tetrathiolate complex:^[7]

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.^{[citation needed]} 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 −0.5 °C (31.1 °F). 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 (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.^[8]

tert-Butylthiol is a very minor component of cooked potatoes.^[9]

Safety

The Threshold limit value (TLV) is 0.5 ppm. tert-butylthiol has an odor threshold of <0.33 ppb.^[10]

See also

• Butanethiol (butyl mercaptan)
• Ethanethiol (ethyl mercaptan)