tert-Butylthiol
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| Names | |
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| Preferred IUPAC name
2-Methylpropane-2-thiol | |
| Other names
t-BuSH
2-Methylpropane-2-thiol 2-Methyl-2-propanethiol tert-Butyl mercaptan | |
| Identifiers | |
3D model (JSmol)
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| Abbreviations | TBM |
| ChemSpider | |
| ECHA InfoCard | 100.000.810 |
PubChem CID
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| UNII | |
CompTox Dashboard (EPA)
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| Properties | |
| 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).
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tert-Butylthiol, also known as tert-butyl mercaptan (TBM), and abbreciated t-BuSH, is an organosulfur compound with the formula (CH3)3CSH. This thiol is used as an odorant for natural gas,[citation needed] which is otherwise odorless. It may also have been used as a flavoring agent.[1]
Preparation[edit]
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[edit]
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[edit]
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[edit]
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[edit]
The Threshold limit value (TLV) is 0.5 ppm. tert-butylthiol has an odor threshold of <0.33 ppb.[10]
See also[edit]
- Butanethiol (butyl mercaptan)
- Ethanethiol (ethyl mercaptan)
References[edit]
- ^ "tert-butyl mercaptan". thegoodscentscompany.com.
- ^ Dobbin, Leonard (1890). "On tertiary Butyl Mercaptan". Journal of the Chemical Society, Transactions. 57: 639–643. doi:10.1039/ct8905700639.
- ^ Rheinboldt, Heinrich; Mott, Friedrich; Motzkus, Erwin; A. D. McMaster; B. M. Mattson; S. T. Michel (1932). "Tertiäres Butylmercaptan". Journal für Praktische Chemie. 134 (9–12): 257–281. doi:10.1002/prac.19321340901.
- ^ Schulze, W.A.; Lyon, J.P. & Short, G.H. (1948). "Synthesis of Tertiary Alkyl Mercaptans". Industrial and Engineering Chemistry. 40 (12). American Chemical Society: 2308–2313. doi:10.1021/ie50468a019.
- ^ Ho, Tse-Lok; Fieser, Mary; Fieser, Louis (2006). "Lithium 2-methylpropane-2-thiolate". Fieser and Fieser's Reagents for Organic Synthesis. doi:10.1002/9780471264194.fos06530. ISBN 0471264199.
- ^ Spessard, Gary O.; Chan, Wan Kit; Masamune, S. (1990). "Preparation of thiol esters: s-tert-butyl cyclohexanecarbothioate and s-tert-butyl 3α,7α,12α-trihydroxy-5β-cholane-24-thioate". Organic Syntheses. 7: 87. doi:10.1002/0471264180.os061.28. ISBN 0471264229.
- ^ Otsuka, Sei; Kamata, Masato; Hirotsu, Ken; Higuchi, Taiichi (1981). "A Novel Molybdenum Thiolato Compound, Tetrakis(tert-butylthiolato)molybdenum(IV). Preparation and Crystal and Molecular Structure". Journal of the American Chemical Society. 103 (11): 3011–3014. doi:10.1021/ja00401a017.
- ^ "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". EFSA. 11 May 2011. Retrieved 15 April 2013.
- ^ Gumbmann, M. R.; Burr, H. K. (1964). "Food Flavors and Odors, Volatile Sulfur Compounds in Potatoes". Journal of Agricultural and Food Chemistry. 12 (5): 404–408. doi:10.1021/jf60135a004.
- ^ Devos, M; Patte, F.; Rouault, J.; Lafort, P.; Van Gemert, L. J. (1990). Standardized Human Olfactory Thresholds. Oxford: IRL Press at Oxford University Press. p. 118. ISBN 0199631468.