tert-Butyllithium
tert-Butyllithium is a chemical compound with the formula (CH3)3CLi. As an organolithium compound, it has applications in organic synthesis since it is a strong base, capable of deprotonating many carbon molecules, including benzene. tert-Butyllithium is available commercially as solutions in hydrocarbons (such as pentane); it is not usually prepared in the laboratory.
Preparation
[edit ]tert-Butyllithium is produced commercially by treating tert-butyl chloride with lithium. Its synthesis was first reported by R. B. Woodward in 1941.[1]
Structure and bonding
[edit ]Like other organolithium compounds, tert-butyllithium is a cluster compound. Whereas n-butyllithium exists both as a hexamer and a tetramer, tert-butyllithium exists exclusively as a tetramer with a cubane structure. Bonding in organolithium clusters involves sigma delocalization and significant Li−Li bonding.[2] Despite its complicated structure, tert-butyllithium is usually depicted in equations as a monomer.
The lithium–carbon bond in tert-butyllithium is highly polarized, having about 40 percent ionic character. The molecule reacts like a carbanion, as is represented by these two resonance structures:[3]
Reactions
[edit ]tert-Butyllithium is renowned for deprotonation of carbon acids (C-H bonds). One example is the double deprotonation of allyl alcohol.[4] Other examples are the deprotonation of vinyl ethers.[5] [6] [7]
In combination with n-butyllithiium, tert-butylllithium monolithiates ferrocene.[8] tert-Butyllithium deprotonates dichloromethane:[9]
- H2CCl2 + RLi → HCCl2Li + RH
Similar to n-butyllithium, tert-butyllithium can be used for lithium–halogen exchange reactions.[10] [11]
Solvent compatibility
[edit ]To minimize degradation by solvents, reactions involving tert-butyllithium are often conducted at very low temperatures in special solvents, such as the Trapp solvent mixture.
More so than other alkyllithium compounds, tert-butyllithium reacts with ethers.[2] In diethyl ether, the half-life of tert-butyllithium is about 60 minutes at 0 °C. It is even more reactive toward tetrahydrofuran (THF); the half-life in THF solutions is about 40 minutes at −20 °C.[12] In dimethoxyethane, the half-life is about 11 minutes at −70 °C[13]
In this example, the reaction of tert-butyllithium with (THF) is shown:
Safety
[edit ]tert-butyllithium is a pyrophoric substance, meaning that it spontaneously ignites on exposure to air. Air-free techniques are important so as to prevent this compound from reacting violently with oxygen and moisture:
- t-BuLi + O2 → t-BuOOLi
- t-BuLi + H2O → t-BuH + LiOH
The solvents used in common commercial preparations are themselves flammable. While it is possible to work with this compound using cannula transfer, traces of tert-butyllithium at the tip of the needle or cannula may ignite and clog the cannula with lithium salts. While some researchers take this "pilot light" effect as a sign that the product is "fresh" and has not degraded due to time or improper storage/handling, others prefer to enclose the needle tip or cannula in a short glass tube, which is flushed with an inert gas and sealed at each end with septa.[14] Serious laboratory accidents involving tert-butyllithium have occurred. For example, in 2008 a staff research assistant, Sheharbano Sangji, in the lab of Patrick Harran [15] at the University of California, Los Angeles, died after being severely burned by a fire ignited by tert-butyllithium.[16] [17] [18]
Large-scale reactions may lead to runaway reactions, fires, and explosions when tert-butyllithium is mixed with ethers such as diethyl ether, and tetrahydrofuran. The use of hydrocarbon solvents may be preferred.
See also
[edit ]References
[edit ]- ^ Bartlett, Paul D.; C. Gardner Swain; Robert B. Woodward (1941). "t-Butyllithium". J. Am. Chem. Soc. 63 (11): 3229–3230. Bibcode:1941JAChS..63.3229B. doi:10.1021/ja01856a501.
- ^ a b Elschenbroich, C. (2006). Organometallics. Weinheim: Wiley-VCH. ISBN 978-3-527-29390-2.
- ^ K. P. C. Vollhardt, N. E. Schore (1999). "Organometallic reagents: sources of nucleophilic carbon for alcohol synthesis". Organic Chemistry : Structure And Function, 3rd edition.
- ^ Danheiser, Rick L.; Fink, David M.; Okano, Kazuo; Tsai, Yeun-Min; Szczepanski, Steven W. (1988). "(1-Oxo-2-Propenyl)Trimethylsilane". Organic Syntheses. 66: 14. doi:10.15227/orgsyn.066.0014 . ISSN 2333-3553.
- ^ Soderquist, John A. (1990). "Acetyltrimethylsilane". Organic Syntheses. 68: 25. doi:10.15227/orgsyn.068.0025 . ISSN 2333-3553.
- ^ Tschantz, M. A.; Burgess, L. E.; Meyers, A. I. (1996). "4-Ketoundecanoic Acid". Organic Syntheses. 73: 215. doi:10.15227/orgsyn.073.0215 . ISSN 2333-3553.
- ^ Jarowicki, Krzysztof; Kocienski, Philip J.; Qun, Liu (2002). "1,2-Metallate Rearrangement: (Z)-4-(2-Propenyl)-3-Octen-1-Ol". Organic Syntheses. 79: 11. doi:10.15227/orgsyn.079.0011 . ISSN 2333-3553.
- ^ Busacca, Carl A.; Eriksson, Magnus C.; Haddad, Nizar; Han, Z. Steve; Lorenz, Jon C.; Qu, Bo; Zeng, Xingzhong; Senanayake, Chris H. (2013). "Practical Synthesis of Di-tert-Butylphosphinoferrocene". Organic Syntheses. 90: 316. doi:10.15227/orgsyn.090.0316 . ISSN 2333-3553.
- ^ Matteson, Donald S.; Majumdar, Debesh (1983). "Homologation of Boronic Esters to α-Chloro Boronic Esters". Organometallics. 2 (11): 1529–1535. doi:10.1021/om50005a008.
- ^ Smith, Adam P.; Savage, Scott A.; Love, J. Christopher; Fraser, Cassandra L. (2002). "Synthesis of 4-, 5-, and 6-Methyl-2,2'-bipyridine by a Negishi Cross-Coupling Strategy: 5-Methyl-2,2'-bipyridine". Organic Syntheses. 78: 51. doi:10.15227/orgsyn.078.0051 . ISSN 2333-3553.
- ^ Amat, Mercedes; Hadida, Sabine; Sathyanarayana, Swargam; Bosch, Joan (1997). "Regioselective Synthesis of 3-Substituted Indoles: 3-Ethylindole". Organic Syntheses. 74: 248. doi:10.15227/orgsyn.074.0248 . ISSN 2333-3553.
- ^ Stanetty, P; Koller, H.; Mihovilovic, M. (1992). "Directed ortho Lithiation of Phenylcarbamic acid 1,1-Dimethylethyl Ester (N-BOC-aniline). Revision and Improvements". Journal of Organic Chemistry. 57 (25): 6833–6837. doi:10.1021/jo00051a030.
- ^ Fitt, J. J.; Gschwend, H. E. (1984). "Reaction of n-, sec-, and tert-butyllithium with dimethoxyethane (DME): a correction". Journal of Organic Chemistry . 49: 209–210. doi:10.1021/jo00175a056.
- ^ Errington, R. M. (1997). Advanced practical inorganic and metalorganic chemistry (Google Books excerpt). London: Blackie Academic & Professional. pp. 47–48. ISBN 978-0-7514-0225-4.
- ^ "Harran Lab: UCLA". Archived from the original on 2012年10月13日. Retrieved 2011年09月21日.
- ^ Jyllian Kemsley (2009年01月22日). "Researcher Dies After Lab Fire". Chemical & Engineering News.
- ^ Jyllian Kemsley (2009年04月03日). "Learning From UCLA: Details of the experiment that led to a researcher's death prompt evaluations of academic safety practices". Chemical & Engineering News.
- ^ Los Angeles Times, 2009年03月01日