tert-Butyllithium

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tert-Butyllithium
Skeletal formula of tert-butyllithium with all implicit hydrogens shown, and partial charges added
Identifiers
CAS number 594-19-4 YesY
PubChem 638178
ChemSpider 10254347 YesY
EC number 209-831-5
UN number 3394
Beilstein Reference 3587204
Jmol-3D images Image 1
Properties
Molecular formula LiC
4
H
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)
Solubility in water Reacts
Acidity (pKa) 53
Hazards
GHS pictograms The flame pictogram in the Globally Harmonized System of Classification and Labelling of Chemicals (GHS) The corrosion pictogram in the Globally Harmonized System of Classification and Labelling of Chemicals (GHS) The exclamation-mark pictogram in the Globally Harmonized System of Classification and Labelling of Chemicals (GHS) The health hazard pictogram in the Globally Harmonized System of Classification and Labelling of Chemicals (GHS) The environment pictogram in the Globally Harmonized System of Classification and Labelling of Chemicals (GHS)
GHS signal word DANGER
GHS hazard statements H225, H250, H260, H304, H314, H336, H411
GHS precautionary statements P210, P222, P223, P231+232, P370+378, P422
EU classification Flammable F+ Corrosive C Dangerous for the Environment (Nature) N Very Toxic T+
R-phrases R11, R15, R17, R34, R51/53, R65, R66, R67, R50/53, R38
S-phrases S26, S36/37/39, S43, S45, S62, S61, S16, S33
NFPA 704
Flammability code 3: Liquids and solids that can be ignited under almost all ambient temperature conditions. Flash point between 23 and 38 °C (73 and 100 °F). E.g., gasoline) Health code 3: Short exposure could cause serious temporary or residual injury. E.g., chlorine gas Reactivity code 4: Readily capable of detonation or explosive decomposition at normal temperatures and pressures. E.g., nitroglycerin Special hazard W: Reacts with water in an unusual or dangerous manner. E.g., cesium, sodiumNFPA 704 four-colored diamond
Flash point −6.6 °C (20.1 °F; 266.5 K)
Related compounds
Related compounds n-Butyllithium

sec-Butyllithium

Except where noted otherwise, data are given for materials in their standard state (at 25 °C (77 °F), 100 kPa)
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Infobox references

tert-Butyllithium is a chemical compound with the formula (CH3)3CLi. As an organometallic compound, it has applications in organic synthesis (see also Grignard reaction) since it is a sufficiently strong base to deprotonate many carbon acids, including benzene. In regard to molecular aggregation state, the compound exists in clusters.

tert-Butyllithium is readily 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]

Chemical properties[edit]

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.[2] (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.)

Tert-Butyllithium, Mesomerie.svg

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 be unstable in ether solvents; the half-life of tert-butyllithium is 60 minutes at 0 °C in diethyl ether, 40 minutes at -20 °C in THF,[3] and about 11 minutes at -70 °C in dimethoxyethane.[4] In this example, the reaction of tert-butyllithium with tetrahydrofuran (THF) is shown:

Zersetzung THF tert-Butyllithium1.svg
Zersetzung THF tert-Butyllithium2.svg

Safety[edit]

tert-Butyllithium is a pyrophoric substance, meaning that it easily catches fire on exposure to air. (A precise definition of a pyrophoric material is one "that ignite[s] spontaneously in air at or below 54.55 °C (130.19 °F)".[5]) 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, some workers 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 when her synthetic sweater caught on fire while working with a syringe of this compound.[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, tetrahydrofuran, and glymes. The use of hydrocarbon solvents may be preferred.

Air-free techniques are important so as to prevent this compound from reacting violently with oxygen and moisture in the air:

t-BuLi + O2t-BuOOLi
t-BuLi + H2O → t-BuH + LiOH

References[edit]

  1. ^ Bartlett, Paul D.; C. Gardner Swain, Robert B. Woodward (1941). J. Am. Chem. Soc. 63 (11): 3229–3230. 
  2. ^ 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.
  3. ^ 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. 
  4. ^ 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. 
  5. ^ SEMI, standard F6-92, Guide for Secondary Containment of Hazardous Gas Piping Systems, as cited by ChemiCool.com
  6. ^ Errington, R. M. (1997). Advanced practical inorganic and metalorganic chemistry (Google Books excerpt). London: Blackie Academic & Professional. pp. 47–48. ISBN 0-7514-0225-7. 
  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