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Stephen reaction is the organic redox reaction, used in preparation of aldehydes. It is also known as Stephen Reduction or Stephen Aldehyde Synthesis. Stephen Reaction was invented by an English chemist Henry Stephen and that's how it got its name. It is also an important name reaction in organic chemistry. It is an organic redox reaction where nitriles are reduced to imine with tin chloride with the help of hydrochloric acid, which results in aldehydes on hydrolysis. On the side product we also get ammonia and ammonium chloride.
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Key Terms: Aldehydes, Organic reaction, Redox Reaction, Organic Chemistry, Hydrolysis, Ammonia, Ammonium chloride, Aldehyde Synthesis, Hydrochloric acid
Stephen Reaction
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In the presence of hydrochloric acid and tin chloride, methyl nitrite reacts and forms iminium salt. After further quenching of iminium salt with water, aldehyde is produced. As the side product to this reaction we also get some amount of ammonium chloride or ammonia. Further quenching is required because iminium salt produced is not stable as it is produced as an intermediate product.
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Stephen Reaction Mechanism
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Stephen reaction mechanism steps to follow:
Step 1
In the Stephen reaction first step hydrogen chloride gases are passed through nitrile, which results in formation of correlated salt.
Step 2
In the second step, single electron transfer takes place in Stannous(ll) chloride in the formation of salt.
Step 3
The obtained salt is precipitated in this step. The salt after precipitation is aldimine tin chloride.
Step 4
In the final step, we obtain amide formed by hydrolysis of the salt obtained from the previous step. This results in the end product of aldehyde.
In Stephen reaction mechanism the end product obtained is aldehyde. The use of aliphatic nitrile, aromatic nitrile is more efficient to be used, is the important point to remember. The use of substitutes added to improve electron density, improves the salt formation of tin chloride. Electron withdrawing substances such as Amide chloride formation can also be promoted.
Examples of Stephen Reaction
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- Formation of acetaldehyde from acetonitrile.
- Formation of benzaldehyde from benzonitrile.
Things to Remember
- Stephen Reaction is also known as Stephen Reduction or Stephen Aldehyde Synthesis.
- In the presence of hydrochloric acid and tin chloride, methyl nitrite reacts and forms iminium salt. After further quenching of iminium salt with water, aldehyde is produced.
- Examples of Stephen Reaction
- Formation of acetaldehyde from acetonitrile.
- Formation of benzaldehyde from benzonitrile.
- Substitutes used to improve electron density will aslo improve formation of aldimine tin chloride.
- Formation of amide chloride is promoted by electron withdrawing substance.
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Sample Questions
Ques: What is Stephen's reduction reaction? (1 Mark)
Ans: Stephen Reaction is also known as Stephen Reduction or Stephen Aldehyde Synthesis. In the presence of hydrochloric acid and tin chloride, methyl nitrite reacts and forms iminium salt. After further quenching of iminium salt with water, aldehyde is produced.
Ques: Stephen Reaction is the type of …… (1 Mark)
Ans: Stephen reaction is an organic redox reaction.
Ques: Explain Stephen Reaction Mechanism in steps? (3 Marks)
Ans:
- Hydrogen chloride (HCl) is passed through nitrile, which results in formation of corresponding salt.
- A single electron transfer from tin(ll) chloride reduces this salt.
- Aldimine tin chloride is precipitates salt formed in step 2
- Then amide is obtained from hydrolysis of aldimine tin chloride
- Aldehyde is formed from amide and ammonium chloride is formed as a side product.
Ques: Define Redox reaction? (2 Marks)
Ans: Redox reaction is defined as a chemical reaction in which transfer of electrons takes place between two reactants participating in it. By observing the charges in oxidation state, we can indicate transfer of electrons.
Ques: What is oxidation reaction? (2 Marks)
Ans: Oxidation reaction is removal of electropositive elements or hydrogen or addition of electronegative elements or oxygen from the substance. It is also defined as loss of electrons from a substance.
Ques: What is the reduction reaction? (2 Marks)
Ans: Reduction reaction is addition of electropositive reaction or hydrogen, or removal of electronegative reaction of oxygen from the substance. In other words, a reduction reaction is the gain of electrons.
Ques: What are aldehydes? (2 Marks)
Ans: Aldehydes are the organic compounds in which a carbon atom shares a single bond with hydrogen atom, double bond with oxygen atom and also single bond with another atom or group of atoms (‘R’ is used as the designation in general chemical formula). The main characteristics of aldehyde groups is the carbon and oxygen double bond. It is represented by R-CHO in general.
Ques: Give Examples of Stephen reaction? (2 Marks)
Ans:
- Formation of acetaldehyde from acetonitrile (CH3CHO).
- Formation of benzaldehyde from benzonitrile (C6H5CHO).
Ques: Explain the structure of Aldehydes? (3 Marks)
Ans: Aldehydes is a functional group that is characterized as a carbon atom sharing double bond with oxygen, single bond with hydrogen and a single bond with another atom or group of atoms.
Examples of Aldehydes
Ques: What are named reactions? (2 Marks)
Ans: Named reactions are the reactions from organic chemistry. The chemical reactions that have been given names of the scientists who discovered it. This trend was started in 1870 when scientist Adolf Lieben discovered an iodoform test. To honor his discovery the test is now called Lieben Haloform Test.
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