Condensation Reactions

In a condensation reaction, two molecules join to form a larger molecule and a small, stable molecule such as H2O or HCl. For example, ethyl acetate, CH3COOCH2CH3, is formed when acetic acid reacts with ethanol in the presence of an acid catalyst:

A chemical reaction is shown. On the left, a C H subscript 3 group bonded to a red C atom. The C atom forms a double bond with an O atom which is also in red. The C atom is also bonded to an O atom which is bonded to an H atom, also in red. A plus sign is shown, which is followed by H O C H subscript 2 C H subscript 3. The H O group is in red. Following a reaction arrow with H-plus above the arrow, a C H subscript 3 group is shown which is bonded to a red C atom with a double bonded O atom and a single bonded O. To the right of this single bonded O atom, a C H subscript 2 C H subscript 3 group is attached and shown in black. This structure is followed by a plus sign and red H subscript 2 O. The O atoms in the first structure on the left and the structure following the reaction arrow have two pairs of electron dots.

In general, condensation of a carboxylic acid and an alcohol produces an ester.

Condensation reactions are reversible: not all reactant molecules are converted to product molecules and, if product molecules are mixed, some reactant molecules form. The reverse reaction of a condensation that produces water is called a hydrolysis reaction. In hydrolysis, water breaks apart into H and OH with H attaching to one part the larger molecule and OH to another: hydrolysis comes from hydro, “water” and lysis, “breaking apart”.

Ethers can be obtained from condensation reactions involving two alcohol molecules. If the two alcohol molecules are the same, a symmetric ether forms. For example, when ethanol is treated with a limited quantity of sulfuric acid and heated to 140 °C, diethyl ether and water are formed:

This figure shows a reaction. The first molecule, which is labeled, “ethanol,” is a two C atom chain with the second C atom is bonded to a OH group. The H in the OH group is highlighted blue. There is a plus sign. The next molecule, which is labeled, “ethanol,” is also a two C atom chain with the second C atom is bonded to a OH group. The OH group is highlighted in blue. To the right of the second molecule there is an arrow labeled H subscript 2 S O subscript 4 above and Greek capital delta below. The resulting molecules is labeled, “diethyl ether.” It has two ethyl groups on either side of O atom. There is a plus sign and a blue water molecule.

If the condensation reaction involves two different alcohols, an asymmetric ethers can form. For example:

Alternatively, addition reactions between alkenes and alcohols can form ethers. For example:


Amides can be produced from carboxylic acids and primary or secondary amines (or ammonia) via condensation reactions:

It is through this reaction that amino acids (molecules containing both an amine and a carboxylic acid functional group) link together in a polymer to form peptides and proteins.

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Chemistry 109 Fall 2021 by John Moore, Jia Zhou, and Etienne Garand is licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 4.0 International License, except where otherwise noted.