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Schmidt Reaction is one of the most important organic reactions in organic chemistry. Azide, a conjugate base of hydrazoic acid, reacts with a derivative of carbonyl like aldehyde, carboxylic acid, ketone, etc, to provide amine or amides alongside nitrogen under acidic conditions. This is known as a rearrangement reaction. Hence, it is also called the Schmidt Rearrangement reaction. This reaction closely resembles another reaction called Curtius rearrangement. When Schmidt reaction happens including carboxylic acid, then it provides amine, however, when it happens with a ketone, it provides amides. It is also found that in Schmidt reactions consisting of ketone and a carboxylic acid, nitrogen is released and hydrazoic acid is used.
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Key Terms: Schmidt Reaction, Schmidt Reaction Mechanism, Ketone, Carboxylic Acid, Amine, Amide, Curtius Rearrangement, Azide, Hydrazoic Acid
Schmidt Reaction For Carboxylic Acid
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An example of Schmidt Reaction is when a chemical reaction between a ketone and an azide produces an amide. The following diagram illustrates this reaction.
Schmidt Reaction For Carboxylic Acid
The Schmidt reaction uses benzophenone and hydrogen azide to produce benzanilide. This example consists of an amide’s preparation from an azide and a ketone.
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Schmidt Reaction For Ketones
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Schmidt Reaction is also utilised when a chemical reaction between a ketone and an azide produces an amide. The following image illustrates this reaction:
Schmidt Reaction For Ketones
The Schmidt reaction is used in the preparation of benzamide by using hydrogen azide and benzophenone. This is an example of how an amide is prepared from an azide and a ketone.
Schmidt Reaction Mechanism
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Schmidt reaction is used to produce either amides or amines as discussed earlier. For amides or amines, a different functional group is required (ketones and carboxylic acids respectively). The mechanisms for each of these reactions are elaborated in detail below:
Schmidt Reaction Mechanism for Producing Amines
- First Step: The mechanism starts off by forming an acylium ion by the protonation of the carboxylic acid after which the water is removed.
- Second Step: The acylium ion then reacts with hydrazoic acid, which leads to forming a protonated azido ketone.
- Third Step: The protonated azido ketone along with the R group goes through a reaction known as rearrangement, which results in the carbon-nitrogen bond’s migration alongside the dinitrogen’s removal which leads to the forming of a protonated isocyanate.
- Fourth Step: When the water is brought out to attack the protonated isocyanate, then a carbamate is formed.
- Fifth Step: The deprotonation of carbamate now occurs. Now the CO2 is finally removed and yields the required amine.
Schmidt Reaction Mechanism for Producing Amines
Schmidt Reaction Mechanism for Producing Amides
- Step 1: This Mechanism starts off with ketone’s protonation, which leads to the O-H bond formation.
- Step 2: The azide’s nucleophilic addition leads to an intermediate formation.
- Step 3: Now, the Water is removed from this intermediate with the help of an elimination reaction, which forms a temporary imine.
- Step 4: The migration of an alkyl group which was a part of the original ketone happens from the carbon to the imine’s nitrogen. This causes the elimination of dinitrogen.
- Step 5: Water is utilised to target the produced compound, and the deprotonation provides a tautomer of the amide that is required.
- Step 6: A proton’s relocation which belongs to the amide’s tautomer provides the final amide product.
Schmidt Reaction Mechanism for Producing Amides
Curtius Rearrangement
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Theodor Curtius was conducting many different experiments using acyl azides. During one of these experiments, he found out that when acyl azide goes through thermal decomposition, then it provides isocyanate while losing nitrogen gas. When the isocyanate is reacted with alcohols then it gives carbamate while using water and amines provides derives primary amine and urea. In this reaction, acyl azide can be made by reacting either acid anhydrides or acid chlorides with trimethyl azide or sodium azide or by direct reacting the carboxylic acid with diphenyl phosphoryl azide.
The reaction is given below as:
Curtius Rearrangement
Relation Between Schmidt Reaction and Curtius Rearrangement
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Schmidt reaction and Curtius rearrangement reaction are related closely. In Curtius rearrangement reaction, the production of acyl azide is done by reacting acid chloride with sodium azide and the formation of acid chloride is done by reacting the carboxylic acid with SOCl2. However, in Schmidt's reaction, the production of acyl azide is done by reacting the carboxylic acid with hydrazoic acid.
Things to Remember
- Azide, a conjugate base of hydrazoic acid, reacts with a derivative of carbonyl like aldehyde, carboxylic acid, ketone, etc, to provide amine or amides alongside nitrogen under acidic conditions.
- Hence, it is also called the Schmidt rearrangement reaction. This reaction closely resembles another reaction called Curtius rearrangement.
- The Schmidt reaction uses benzophenone and hydrogen azide to produce benzanilide. This example consists of an amide’s preparation from an azide and a ketone.
- The Schmidt reaction is used in the preparation of benzanilide by using hydrogen azide and benzophenone.
- This is an example of how an amide is prepared from an azide and a ketone.
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Sample Questions
Ques. What is Schmidt rearrangement? (3 Marks)
Ans. Schmidt reactions are the electrophile's acid-catalyzed hydrazoic acid reactions like tertiary alcohols, carbonyl compounds and alkenes. To include, amides, nitriles, amines, or imines, these substrates go through rearrangement and nitrogen’s extrusion.
Ques. What is reformatsky reaction? (3 Marks)
Ans. The Reformatsky reaction is a kind of organic reaction that utilises metallic zinc to make β-hydroxy-esters condense ketones or aldehydes with the help of al-halo esters. By using an alpha-halo ester on some zinc dust, a Reformatsky enolate, which is a kind of organozinc reagent is prepared.
Ques. Which reaction involves the migration of the group from carbon to nitrogen? (3 Marks)
Ans. The Schmidt reaction consists of the migration of alkyl with the expulsion of nitrogen over the chemical bond of carbon-nitrogen in an azide. A carboxylic acid’s Schmidt reaction starts with the acylium ion that is derived from water loss and protonation.
Ques. What is the Schmidt Claisen Reaction? (3 Marks)
Ans. Claisen-Schmidt condensation is the reply to a ketone or an aldehyde consisting of an alpha-hydrogen along with an aromatic carbonyl compound without any alpha hydrogen.
Ques. In which medium Favorskii rearrangement occurs? (3 Marks)
Ans. In cyclic α-halo ketones, the Favorskii rearrangement contains a ring contraction. This happens under the presence of a base, like a hydroxide, to obtain a carboxylic acid but mostly it’s either an amine or an alkoxide base to obtain an amide or an ester, respectively.
Ques. What kind of isomers are formed in the rearrangement reactions? (3 Marks)
Ans. The kinds of products formed contain identical molecular formulas but have different bonds or structures between their atoms. For instance, Isobutane and Butane have the same number of carbon atoms and hydrogen atoms, so their chemical formulas are identical.
Ques. In Schmidt's reaction, what is the reagent? Give some examples of Schmidt's Reaction. (3 Marks)
Ans. Hydrazoic acid is an important reagent that utilises this azide group, and the products from the reaction depend on the existence of the substrate.
Some examples of Schmidt Reaction are:
- Obtaining amides by reacting the azide with a ketone.
- Obtaining an amine by reacting the azide with a carboxylic acid.
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