Sodium tert-Butoxide: An Overview
Sodium tert-butoxide (NaOtBu or Na⁺[CH₃]₃CO⁻) is a strong, non-nucleophilic base widely used in organic synthesis. As a solid white powder or granule, it is known for its high basicity and bulkiness, making it ideal for promoting elimination reactions, generating enolates, and facilitating metalation processes in both academic and industrial chemistry.
Chemical Identity
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Chemical Formula: C₄H₉ONa
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Molecular Weight: 96.10 g/mol
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CAS Number: 865-48-5
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IUPAC Name: Sodium 2-methylpropan-2-olate
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Synonyms: Sodium tert-butylate, Sodium t-butoxide, NaOtBu
Physical and Chemical Properties
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Appearance: White to off-white powder or crystalline solid
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Odor: Slight alcohol-like odor
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Melting Point: ~230–250°C (decomposes)
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Solubility: Soluble in organic solvents such as THF, DMSO, and tert-butanol; reacts with water
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Basicity: Strong base (conjugate acid pKa ~17)
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Stability: Air- and moisture-sensitive; decomposes in humid conditions
The tert-butoxide ion is sterically hindered, which limits its nucleophilicity but maintains high basic strength. This makes it useful for reactions where selective deprotonation is preferred over nucleophilic substitution.
Applications in Organic Synthesis
1. Elimination Reactions (E2 Mechanism)
Sodium tert-butoxide is a preferred base in E2 eliminations, especially for producing less substituted or hindered alkenes. Its bulk favors Hofmann product formation (the less substituted alkene) over the Zaitsev product.
2. Enolate Formation
It is commonly used to form enolates from esters, ketones, and nitriles, which are intermediates in aldol, Claisen, and other condensation reactions.
3. Cross-Coupling Catalysis
In transition metal catalysis (such as Suzuki, Heck, or Buchwald–Hartwig reactions), sodium tert-butoxide acts as a strong, non-coordinating base, enabling efficient metal-ligand activation.
4. Metalation and Deprotonation
It assists in metalation of sensitive compounds or heterocycles where proton abstraction is required. It's often used in the preparation of organometallic intermediates.
5. Solubilizing Agent
Due to its solubility in organic solvents, sodium tert-butoxide is also used to enhance the solubility and reactivity of reactants in homogeneous reaction media.
Safety and Handling
Sodium tert-butoxide is highly reactive, especially toward moisture and protic solvents.
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Reacts violently with water, forming sodium hydroxide and tert-butanol
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Can cause severe skin, eye, and respiratory irritation
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Combustible in fine powder form and may cause fire hazard when exposed to air
Precautions:
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Handle under inert atmosphere (nitrogen or argon)
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Use dry, sealed containers and anhydrous conditions
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Wear gloves, safety goggles, and protective clothing
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Avoid inhalation of dust or vapors
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Use fume hood when weighing or transferring
Storage and Stability
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Store in tightly sealed, moisture-free containers
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Keep in a cool, dry area away from water, acids, and oxidizers
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Handle in an inert environment for maximum stability
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Use desiccators or sealed bottles with inert gas padding
Environmental and Waste Considerations
Sodium tert-butoxide should be carefully quenched with a protic solvent (typically alcohol) under controlled conditions before disposal. Neutralized waste should be disposed of as hazardous chemical waste per environmental regulations.
Conclusion
Sodium tert-butoxide is a highly versatile reagent valued for its strong basicity, low nucleophilicity, and steric bulk, making it particularly useful in elimination reactions, enolate chemistry, and catalytic cross-coupling. While powerful, it must be handled with care under anhydrous conditions due to its moisture sensitivity and reactivity. Properly managed, it remains a cornerstone reagent in synthetic organic chemistry.
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