Tert-Butyllithium Solution: A Strong, Pyrophoric Organolithium Reagent

Tert-butyllithium (t-BuLi) is a highly reactive organolithium compound widely used in organic synthesis as an exceptionally strong base and nucleophile. Typically supplied as a solution in hydrocarbon solvents like hexanes or pentane, it is known for its extreme reactivity—particularly its pyrophoric nature, meaning it ignites spontaneously in air.

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Chemical Identity

• Chemical Formula: C₄H₉Li

• Molecular Weight: 64.06 g/mol

• CAS Number: 594-19-4

• Common Name: tert-Butyllithium

• Structure: (CH₃)₃CLi

Tert-butyllithium contains a lithium atom bonded to a tertiary butyl group, forming a highly polar covalent bond that gives it powerful reactivity in both proton abstraction and carbon–carbon bond formation.

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Physical and Chemical Properties

• Appearance: Colorless to pale yellow solution

• Solvent: Usually hexanes or pentane

• Reactivity: Extremely pyrophoric and highly basic

• Boiling Point: Dependent on the solvent used

• Basicity: Very high (pKa of conjugate acid ~53)

• Solubility: Soluble in hydrocarbon solvents, reacts violently with water and alcohols

Tert-butyllithium is more reactive and less stable than other organolithium reagents due to the steric bulk of the tert-butyl group.

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Applications in Organic Synthesis

1. Superbase for Deprotonation

• Used to deprotonate weakly acidic C–H bonds, especially in aromatic and heterocyclic systems

• Common in directed ortho-lithiation reactions

2. Metalation Reactions

• Reacts with a wide variety of substrates to generate carbanions or lithium intermediates

• Serves as a precursor in transmetalation processes

3. Initiator in Polymerization

• Acts as an anionic initiator in the polymerization of dienes and other monomers

4. Synthesis of Organometallic Compounds

• Involved in the preparation of organolithium intermediates for complex synthesis pathways

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Handling and Safety Considerations

Hazards:

• Extremely pyrophoric — ignites on exposure to air

• Reacts violently with water, acids, and alcohols

• Can cause severe burns on skin and damage to eyes or mucous membranes

• Toxic by inhalation or ingestion

Precautions:

• Must be handled under strict inert atmosphere (glovebox or Schlenk techniques)

• Use dry, air-free solvents and equipment

• Wear full protective gear: gloves, face shield or goggles, flame-resistant lab coat

• Keep Class D fire extinguisher nearby for metal fires

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Storage

• Store in sealed containers under an inert gas like nitrogen or argon

• Keep away from heat, air, and moisture

• Store at low temperatures in a designated chemical storage area for pyrophoric reagents

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Waste Disposal

Tert-butyllithium must be carefully quenched before disposal. This typically involves slow addition to an alcohol (e.g., isopropanol) under an inert atmosphere, followed by water and neutralization. All disposal steps should follow institutional hazardous waste protocols.

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Conclusion

Tert-butyllithium solution is a cornerstone reagent in modern synthetic organic chemistry, providing unmatched strength as a base and nucleophile. Its effectiveness in complex molecule construction and metalation chemistry is counterbalanced by its extreme pyrophoricity and toxicity. When handled correctly under rigorously controlled conditions, t-BuLi is a powerful tool for the skilled synthetic chemist, enabling high-precision transformations that few other reagents can achieve.

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