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 hydrocarbon solutions; it is not usually prepared in the laboratory. Its synthesis was first reported by R. B. Woodward in 1941.[1]

tert-Butyllithium
Names
Preferred IUPAC name
tert-Butyllithium
Identifiers
3D model (JSmol)
3587204
ChemSpider
ECHA InfoCard 100.008.939
EC Number
  • 209-831-5
UN number 3394
  • InChI=1S/C4H9.Li/c1-4(2)3;/h1-3H3; Y
    Key: BKDLGMUIXWPYGD-UHFFFAOYSA-N Y
  • [Li]C(C)(C)C
Properties
LiC
4H
9
Molar mass 64.055 g mol−1
Appearance Colorless solid
Density 660 mg cm−3
Boiling point 36 to 40 °C (97 to 104 °F; 309 to 313 K)
Reacts
Acidity (pKa) 45–53
Hazards
GHS labelling:
Danger
H225, H250, H260, H300, H304, H310, H314, H330, H336, H411
P210, P222, P223, P231+P232, P370+P378, P422
NFPA 704 (fire diamond)
4
4
4
Flash point −6.6 °C (20.1 °F; 266.5 K)
Related compounds
Related compounds
 n-Butyllithium

sec-Butyllithium

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

Structure and bonding

Like other organolithium compounds, tert-butyllithium is a cluster. Whereas n-butyllithium exists both as a hexamer and a tetramer, tert-butyllithium exists as tetramer with a cubane structure. Bonding in organolithium clusters involves sigma delocalization and significant Li−Li bonding.[2]

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] (Given the polarity calculations on the C−Li bond, the "real" structure of a single molecule of t-butyllithium is likely a near-average of the two resonance contributors shown, in which the central carbon atom has a ~50% partial negative charge while the lithium atom has a ~50% partial positive charge.)

Chemical properties

Similar to n-butyllithium, tert-butyllithium can be used for the exchange of lithium with halogens and for the deprotonation of amines and activated C−H compounds.

This compound and other alkyllithium compounds are known to react with ether solvents; the half-life of tert-butyllithium is 60 minutes at 0 °C in diethyl ether, 40 minutes at −20 °C in tetrahydrofuran (THF),[4] and about 11 minutes at −70 °C in dimethoxyethane.[5] In this example, the reaction of tert-butyllithium with (THF) is shown:

To minimize degradation by these solvents, reactions involving tert-butyllithium are often conducted at very low temperatures in special solvents, such as the Trapp solvent mixture.

Safety

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 catch fire 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.[6] Serious laboratory accidents involving tert-butyllithium have occurred. For example, in 2008 a staff research assistant, Sheharbano Sangji, in the lab of Patrick Harran[7] at the University of California, Los Angeles, died after being severely burned by a fire ignited by tert-butyllithium.[8][9][10]

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.

References
  1. Bartlett, Paul D.; C. Gardner Swain; Robert B. Woodward (1941). "t-Butyllithium". J. Am. Chem. Soc. 63 (11): 3229–3230. doi:10.1021/ja01856a501.
  2. Elschenbroich, C. "Organometallics" (2006) Wiley-VCH: Weinheim. ISBN 978-3-527-29390-2
  3. Organometallic reagents: sources of nucleophilic carbon for alcohol synthesis. K. P. C. Vollhardt, N. E. Schore: Organic Chemistry : Structure And Function. 3rd edition, 1999, §8.7.
  4. 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.
  5. 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.
  6. 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.
  7. "Harran Lab: UCLA".
  8. Jyllian Kemsley (2009-01-22). "Researcher Dies After Lab Fire". Chemical & Engineering News.
  9. Jyllian Kemsley (2009-04-03). "Learning From UCLA: Details of the experiment that led to a researcher's death prompt evaluations of academic safety practices". Chemical & Engineering News.
  10. Los Angeles Times, 2009-03-01
This article is issued from Wikipedia. The text is licensed under Creative Commons - Attribution - Sharealike. Additional terms may apply for the media files.