Schotten–Baumann reaction

The Schotten- Baumann method is a named reaction in the field of organic chemistry, which was published for the first time in 1883 by the German chemists Carl Scots ( 1853-1910 ) and Eugen Baumann ( 1846-1896 ). Comprising the reaction of amines, alcohols or phenols with carbonyl halides - usually carboxylic acid chlorides - in the presence of at least stoichiometric amounts of aqueous solutions of alkali metal hydroxide into the corresponding amides or esters, respectively.

Survey

A carboxylic acid, this acid chloride is reacted with an alcohol to form an ester:

The reaction proceeds only by adding aqueous alkali metal hydroxide solution, in this case aqueous sodium hydroxide solution.

Alternatively, a carboxylic acid, this acid chloride can be reacted by reaction with a primary or secondary amine to form an amide.

The reaction proceeds only by adding aqueous alkali metal hydroxide solution, in this case aqueous sodium hydroxide solution.

Reaction mechanism

The following proposal for the reaction mechanism takes place exemplified by the reaction of a carboxylic acid chloride with a primary alcohol. The reaction course for all other points raised in the section Overview variants is analogous:

The primary alcohol is added to the carboxylic acid chloride 1. After subsequent proton transfer the hemiacetal formed by a second deprotonation of the hydroxide group and the elimination of the chlorine atom as chloride ion of the ester produced 3

Application Examples

An application example is the reaction of benzylamine with benzoyl chloride to give N- Benzylbenzoesäureamid:

According to the principle of the Schotten- Baumann reaction, the trivalent alcohol can also glycerol by reaction with benzoyl chloride in the presence of sodium hydroxide implement targeted to diesters, the two primary hydroxy groups are esterified, the secondary hydroxyl group is not responding.

Unicorn variant

In this variant of the Schotten- Baumann reaction of pyridine is used as the base and often at the same time as the solvent. It first reacts with the acid chlorides to give highly reactive pyridinium compounds. They are then attacked by Alkolhol or amines to form esters or amides nucleophilic. The hydrogen chloride formed is bound as pyridine hydrochloride. In contrast to the Schotten- Baumann reaction here the hydrolysis of the ester is avoided when working with dry alcohol. Pyridine acts as acid acceptor.

The variant is named after its discoverer, Alfred Einhorn.