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Schotten-Baumann Reaction
Schotten-Baumann Conditions:
The use of added base to drive the equilibrium in the formation of amides from amines and acid chlorides.
The acylation of amines with carboxylic acid chlorides leads to the production of one equivalent acid, which will form a salt with unreacted amine and diminish the yield. The addition of an additional equivalent of base to neutralise this acid is a way to optimise the conditions. Normally, aqueous base is slowly added to the reaction mixture.
In general, the use of biphasic aqueous basic conditions is often named "Schotten-Baumann conditions".
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Schotten Baumann Reaction
Schotten Baumann reaction refers to the method of chemically synthesizing amides from acyl chlorides and amines. This organic chemical reaction is named after the German chemists Carl Schotten and Eugen Baumann, who discovered this method of synthesizing amides.
Features of Schotten Baumann Reaction
The Schotten Baumann reaction can also refer to the benzoylation of active hydrogen-containing compounds with the help of benzyl chloride and aqueous sodium hydroxide. Pyridine can also be used as an alternative to the sodium hydroxide base.
This reaction can be generalized as follows.
Schotten Baumann Reaction
Some key features of the Schotten Baumann Reaction are:
It is a base-catalyzed reaction. The base is necessary to encourage an equilibrium shift towards the formation of amides.
The base also neutralizes the hydrochloric acid which is formed in the process, thereby preventing the further protonation of the amide product formed.
Usually, aqueous sodium hydroxide is used as the base catalyst, but pyridine also can be used in this reaction.
It is generally observed that the acyl chlorides are converted into acylating agents of superior power when pyridine is used as the base catalyst.
The ‘Schotten Baumann conditions’ maintained in this reaction refer to the aqueous basic environment which is biphasic in nature.
Schotten Baumann Reaction Mechanism
The mechanism of this reaction can be broken down into three steps in order to easily understand it. These steps are:
Step 1
The formation of a protonated compound from the reaction between the acyl chloride and the amine. First, the nitrogen atom puts forth a lone pair of electrons towards the formation of a carbon-nitrogen bond
The positive and negative charges on the nitrogen and oxygen atoms are neutralized by the exchange of a proton between them.
Step 2
The catalyst of the reaction (i.e. the base) proceeds to absorb the acidic proton which is formed when oxygen attempts to reform a double bond with the carbonyl carbon (which is favorable as the electronegative chlorine atom can easily break its bond with carbon and be liberated as a chloride ion).
Step 3
In the final step of the Schotten Baumann reaction mechanism, the required amide product is formed along with hydrochloric acid now that the base catalyst has absorbed the acidic proton. This HCl is neutralized by the base catalyst as well.
Schotten Baumann Reaction Mechanism
The entire mechanism of the Schotten Baumann Reaction is illustrated above.
Applications of Schotten Baumann Reaction
Some important applications of this reaction are listed below.
The reaction and its conditions are used in the synthesis of synthetic capsaicin and phenethylamine.
The acylation of benzylamines can be done using this process with the help of either acetyl chloride or acetic anhydride.
Some of the concepts used in the Schotten Baumann reaction are also used in the Fischer synthesis of peptides.
Thus, it can be noted that the Schotten Baumann reaction is a very important named reaction in organic chemistry, having numerous applications
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