Sodium Hydride

Definition

Sodium hydride (NaH) is a chemical compound consisting of a sodium cation (Na+) and a hydride anion (H-). It is a strong reducing agent and a powerful nucleophile, making it a versatile reagent in organic chemistry.

5 Must Know Facts For Your Next Test

1. Sodium hydride is a commonly used reagent in the preparation of ethers, as it can deprotonate alcohols to generate alkoxide ions that can then undergo nucleophilic substitution reactions.
2. In the Wittig reaction, sodium hydride is often used to generate the phosphorus ylide, a key intermediate that reacts with an aldehyde or ketone to form an alkene.
3. Sodium hydride can be used as a base in mixed aldol reactions, where it deprotonates the carbonyl compound to generate an enolate intermediate that can then undergo a condensation reaction.
4. In mixed Claisen condensations, sodium hydride is employed to deprotonate the ester or ketone, forming an enolate that can then react with another carbonyl compound.
5. Sodium hydride is a highly reactive and pyrophoric compound, requiring careful handling and storage under an inert atmosphere to prevent dangerous reactions with water or other substances.

Review Questions

• Explain how sodium hydride is used in the preparation of ethers, and describe the key steps involved in this reaction.
  • Sodium hydride is a commonly used reagent in the preparation of ethers. It can deprotonate alcohols to generate alkoxide ions, which then undergo a nucleophilic substitution reaction with an alkyl halide. This two-step process involves the initial formation of the alkoxide ion by the reaction of sodium hydride with the alcohol, followed by the nucleophilic attack of the alkoxide on the alkyl halide to displace the halide and form the desired ether product.
• Describe the role of sodium hydride in the Wittig reaction, and discuss the importance of this reaction in organic synthesis.
  • In the Wittig reaction, sodium hydride is often used to generate the phosphorus ylide, a key intermediate in the formation of alkenes. The sodium hydride deprotonates a phosphonium salt, forming the reactive ylide, which then reacts with an aldehyde or ketone to form a new carbon-carbon double bond. The Wittig reaction is a powerful tool in organic synthesis, as it allows for the selective formation of alkenes from carbonyl compounds, making it useful in the synthesis of complex organic molecules.
• Analyze the use of sodium hydride in mixed aldol and Claisen condensation reactions, and explain how it facilitates these important carbon-carbon bond-forming processes.
  • Sodium hydride plays a crucial role in both mixed aldol and Claisen condensation reactions. In mixed aldol reactions, it is used as a base to deprotonate a carbonyl compound, generating an enolate intermediate that can then undergo a condensation reaction with another carbonyl compound. Similarly, in mixed Claisen condensations, sodium hydride is employed to deprotonate an ester or ketone, forming an enolate that can react with another carbonyl species. These carbon-carbon bond-forming reactions are essential in organic synthesis, as they allow for the construction of more complex molecules from simpler starting materials. The use of sodium hydride as a strong base is key to facilitating these important transformations.

Related terms

Hydride: A hydride is a chemical species that contains hydrogen in the -1 oxidation state, typically bonded to a more electropositive element such as a metal.

Nucleophile: A nucleophile is a species that donates an electron pair to form a new covalent bond, typically attacking electrophilic centers in organic reactions.

Reducing Agent: A reducing agent is a substance that has the ability to reduce other substances, typically by donating electrons in a chemical reaction.