Tert-Butylthiol Explained

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. It is considered a flavoring agent.^[1]

Preparation

It 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]

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

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. 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 -0.5C. 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 as 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)

Notes and References

1. Web site: tert-butyl mercaptan . thegoodscentscompany.com.
2. Dobbin, Leonard . 1890 . On tertiary Butyl Mercaptan. Journal of the Chemical Society, Transactions. 57 . 639–643 . 10.1039/ct8905700639.
3. 10.1002/prac.19321340901 . Tertiäres Butylmercaptan . 1932 . Rheinboldt, Heinrich . Mott, Friedrich . Motzkus, Erwin . A. D. McMaster . B. M. Mattson . S. T. Michel . Journal für Praktische Chemie . 134 . 257–281 . 9–12.
4. Schulze, W.A. . Lyon, J.P. . Short, G.H. . amp . 1948 . Synthesis of Tertiary Alkyl Mercaptans . Industrial and Engineering Chemistry. 40 . 2308–2313. American Chemical Society . 10.1021/ie50468a019 . 12.
5. 10.1002/9780471264194.fos06530 . Lithium 2-methylpropane-2-thiolate . 2006 . Ho, Tse-Lok . Fieser, Mary . Fieser, Louis . Fieser and Fieser's Reagents for Organic Synthesis . 0471264199.
6. Preparation of thiol esters: s-tert-butyl cyclohexanecarbothioate and s-tert-butyl 3α,7α,12α-trihydroxy-5β-cholane-24-thioate . 1990 . Spessard, Gary O. . Chan, Wan Kit . Masamune, S. . 7 . 87 . Organic Syntheses . 10.1002/0471264180.os061.28 . 0471264229.
7. 10.1021/ja00401a017 . A Novel Molybdenum Thiolato Compound, Tetrakis(tert-butylthiolato)molybdenum(IV). Preparation and Crystal and Molecular Structure . 1981 . Otsuka, Sei . Kamata, Masato . Hirotsu, Ken . Higuchi, Taiichi . 103 . 3011–3014 . Journal of the American Chemical Society. 11.
8. Web site: Scientific Opinion on Flavouring Group Evaluation 8, Revision 3 (FGE.08Rev3): Aliphatic and alicyclic mono-, di-, tri-, and polysulphides with or without additional oxygenated functional groups from chemical groups 20 and 30. 11 May 2011 . EFSA. 15 April 2013.
9. Food Flavors and Odors, Volatile Sulfur Compounds in Potatoes. 1964 . Gumbmann, M. R. . Burr, H. K. . Journal of Agricultural and Food Chemistry. 12 . 404–408 . 10.1021/jf60135a004 . 5.
10. Book: Devos, M. Standardized Human Olfactory Thresholds. 1990. IRL Press at Oxford University Press. Oxford. 0199631468. 118. Patte, F. . Rouault, J. . Lafort, P. . Van Gemert, L. J. .