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The Na-NH3 reaction, or the reaction between sodium metal (Na) and liquid ammonia (NH3), is a powerful chemical process with diverse applications in organic chemistry. Just as with other reactions involving sodium, the outcome of the Na-NH3 reaction is profoundly influenced by the surface area of the sodium metal. Sodium (Na), being a soft metal, exhibits heightened catalytic activity when it is fashioned into thin strips or wires.
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Key Terms: NaNH₃, Soft Metal, Birch Reduction, Alkyne Reduction, Catalytic Activity
Reaction of Sodium and Ammonia
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The sodium-ammonia reaction yields sodamide (NaNH2) as the primary product, with hydrogen gas (H2) as a byproduct. Unlike ammonium gas, this reaction employs liquefied ammonia. The balanced chemical equation for this reaction is as follows:
2Na + 2NH3 → NaNH2 + 2H2
This reaction represents a redox process in which sodium undergoes oxidation, transitioning from an oxidation state of 0 to +1, while the hydrogen in ammonia undergoes reduction, moving from an oxidation state of +1 to 0..
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Properties of Ammonia and sodium reaction
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The properties of the reaction are as follows:
- Sodium amide (NaNH2) serves as a potent base in various chemical reactions.
- Ammonia exhibits acidic properties during this reaction, attributed to the release of hydrogen gas as sodium reacts with it.
- It's essential to note that sodium amide reacts vigorously with water, producing ammonia and sodium hydroxide.
Alkynes Reduction
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Alkynes have the general formula C∏H∏∏∏∏, and they can be effectively reduced to alkanes and alkenes by the addition of hydrogen atoms. Alkynes can be selectively reduced to both cis and trans alkenes, depending on the catalyst employed.
Alkynes Reduction
Cis Alkene Formation: To convert alkynes into cis alkenes, a lindlar catalyst is employed. This catalyst is often referred to as a "poisoned catalyst."
Trans Alkene Formation: The transformation of alkynes into trans alkenes is achieved using NaNH3. This reaction proceeds through a radical mechanism, with hydrogen being added in an anti-fashion manner.
Trans Alkene Formation
To convert alkynes into trans alkenes, NaNH3 is used. The reaction takes place through a radical mechanism and the hydrogen is added in an anti-fashion mechanism.
Hydrogenation (Reduction) of Alkyne by Metal
Do Check Out:
| Important Concepts | ||
|---|---|---|
| Ammonium Nitrate | Solution | Homogenous equilibrium |
| Ammonium Nitrite Formula | Hydrides | Types of Titration |
| Zero order reaction | Half Life formula | Oxides of Nitrogen |
Birch Reduction
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In the Birch reduction, aromatic compounds undergo a transformation into 1,4-cyclohexadienes. This reaction introduces two hydrogen atoms at opposite ends of the aromatic ring. The reduction process occurs in the presence of liquid ammonia and sodium (Na), leading to the formation of radical anions when solvated electrons are introduced to the aromatic ring.
Birch Reduction
Things to Remember
- Sodium (Na) is a highly reactive metal, especially when shaped into thin strips or wires.
- The sodium-ammonia reaction results in the formation of sodium amide (NaNH2).
- NaNH3 can be employed for the reduction of alkynes, yielding either cis or trans alkenes, depending on the catalyst used.
- For trans alkene formation, NaNH3 is the catalyst of choice.
- NaNH3 also plays a crucial role in the Birch reduction of aromatic compounds.
Read More: Mass Percent Formula
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Sample Questions
Ques: What type of reaction is Birch reduction? (1 mark)
Ans: The Birch reduction is an organic redox reaction. It involves the reduction of aromatic rings in the presence of liquid ammonia and sodium, with the formation of radical anions as intermediates.
Ques: How can trans and cis alkenes obtained? (2 marks)
Ans: Alkynes can be selectively reduced to cis alkenes using a lindlar catalyst, often referred to as a poisoned catalyst. For the formation of trans alkenes, NaNH3 in liquid ammonia is the catalyst of choice, and the reaction proceeds via a radical mechanism.
Hydrogenation (Reduction) of Alkyne by Metal
Ques: Write the reaction of Sodium with ammonia. (1 mark)
Ans: 2Na + 2NH3 → NaNH2 + 2H2
Sodamide is the product of the reaction. It is a redox reaction, sodium is getting oxidized and ammonia is getting reduced.
Ques: What are the uses of sodium amide? (3 marks)
Ans: Sodamide is an inorganic compound. The compound has an anion of azanide and sodium cation.
- It is used as a strong base, in the presence of liquid ammonia.
- It is used for drying ammonia. It has a low nucleophilicity.
- It is highly used in the production of indigo.
- It is also used during the crystallisation of N-phenylglycine and dehydrogenation.
- Other reactions are birch reduction and alkyne reduction.
Ques: How will NaNH3 react with the aromatic compound? (1 mark)
Ans: The reaction is called Birch reduction. During the reaction, the aromatic compounds are converted into 1,4 cyclohexadiene. It is a redox reaction and a radical anion is created.
Birch reduction
Ques: What is the mechanism for the preparation of alkynes with NaNH3? (3 marks)
Ans: The C-C bond in alkynes is cleaved by sodium (Na), forming an anion with radicals. This radical intermediate can be transformed into both cis and trans forms, with trans alkenes being more stable due to steric factors. Ammonium then protonates the anion, leading to the formation of a vinyl radical and a second anion. Subsequent protonation results in the production of alkenes, with the predominant formation of trans alkenes and the generation of two NaNH2 molecules.
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