Schotten Baumann Reaction: Characteristics, Mechanism, and Applications

The Schotten Baumann reaction is a common term in Organic Chemistry and was first described by two German chemists, Carl Schotten, and Eugen Baumann in 1883.

• The main objective of the reaction is to synthesize amides from amines and acid chlorides.
• This condensation reaction is utilized in the primary synthesis of many other fields and each of them serves unique purposes.
• This chemical relationship has been extensively investigated.
• Being dependent on a base to act as a catalyst, the reaction is used in Fischer’s synthesis of peptides too.

Key Terms: Amide, Amines, Acid, chloride, Dichloromethane, Condensation reaction, Pyridine, Nitrogen, Alcohol, Schotten–Baumann reaction, Catalyst, Acid, Base

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What is Schotten–Baumann Reaction?

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The chemical synthesis of amides, from amines and acyl chlorides is known as the Schotten Baumann reaction.

• The reaction is popularly named after one of the top German scientists, Carl Schotten and Eugen Baumann back in 1883.
• They observed that acid chloride reacts efficiently with amine and a suitable base in order to give an amide in the byproduct. 
• At times, the reaction may also indicate a reaction between acid chloride or anhydride with respect to alcohol and a suitable base.
• In this process, the ester is produced as a result.
• The reaction can be called a condensation reaction in Chemistry. 

The term "Schotten–Baumann reaction conditions", shows that it is a two-phase solvent system.

• This system actively consists of water and an organic solvent.
• Acid is produced in the reaction, the effect of which after some time is neutralized by the bae present inside water.
• On the other hand, the starting materials and the product remain undisturbed in their organic state, which is often dichloromethane. 

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Characteristics of Schotten–Baumann Reaction

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The following are the characteristics of Schotten–Baumann reaction

• The Schotten-Baumann reaction has a base acting as its catalyst.
• Besides providing support for speeding up the reaction, the base is responsible for stimulating a consistent shift in the equilibrium in the way in which amid is formed. 
• The base neutralizes the hydrochloric acid which is formed in the process.
• This prevents the amide from further going through protonation. 
• The base acting as the catalyst may usually be in the form of aqueous sodium hydroxide.
• It is said that pyridine may also play its part as the catalyst in the reaction. 
• When pyridine works as the base catalyst, acyl chlorides are transformed into acylating agents with more strength in comparison. 

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Schotten Baumann Reaction Mechanism

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There are three primary stages that the reaction goes through, before finally giving the end product. Each of them has a unique role to play in bringing the mechanism to an end. These are

Step 1 

In this step, the acyl chloride reacts with the amine. This results in the formation of a protonated compound.

• The Nitrogen atom belonging to the amine offers a single pair of electrons to the carbon of acyl halide.
• This results in a carbon-nitrogen bond.
• Later, by the exchange of a proton, the positive and negative charges on nitrogen and oxygen are neutralized. 

Step 2 

The base catalyst of the reaction moves forward to absorb acidic protons.

• The acidic proton is previously formed when oxygen tries to reform its double bond with carbonyl carbon.
• The situation provides very favorable conditions as the electronegative charge on chlorine atoms can crumble easily which will cause the bond to break with carbon.
• Then it will end up being released into the atmosphere as a chloride ion. 

Step 3 

In the final stage of this mechanism, the amide product starts to form along with the hydrochloric acid, after the basic catalyst has absorbed the acidic proton. The base catalyst also neutralizes the Hydrochloric acid.

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Applications of Schotten Baumann Reaction

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This reaction is widely used in synthesis in organic chemistry. A few applications of this reaction are given below.

• The reaction is used in the synthesis of N-vanillyl nonanamide, which also goes by the name synthetic capsaicin.
• It is also applicable in the synthesis of benzamide from benzoyl chloride and phenethylamine.
• The reaction is used in the process of acylation of benzylamine, which is further devised in Fischer's synthesis of peptides.
• Here, an a-chloro acid chloride is infused with esters of an amino acid.
• The ester undergoes the process of hydrolysation, where the acid gets transformed into acid chloride.
• This allows the peptide to extend by another unit. Later, the atom belonging to the chloride gets replaced by an amino group. 
• The resultant product of the Schotten Baumann reaction gives esters and amides, which are utilized in many food and medical industries.

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Examples of Schotten – Baumann Reaction 

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Some examples of the Schotten–Baumann reaction are given below

• Benzoylation of phenol
• The reaction of benzylamine with acetyl chloride
• The reaction of the acid chloride with primary amine
• Benzoylation of aniline - reaction of the acid chloride with primary amine (aromatic)

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Things to Remember 

• The chemical synthesis of amides from amines and acyl chloride is known as the Schotten Baumann reaction in Organic chemistry.
• It was started first in 1883 and was discovered by two German chemists, Carl Schotten and Eugen Baumann.
• The benzoylation of phenols with benzoyl chloride is the primary method, taking place in the reaction.
• The Schotten-Baumann reaction has a base acting as its catalyst.
• The Schotten Baumann reaction can also be defined as the benzoylation of active hydrogen-containing compounds using benzyl chloride and aqueous sodium hydroxide.
• The reaction and its conditions are used in the synthesis of synthetic capsaicin and phenethylamine.