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A condensation reaction is a class of an organic addition reaction that proceeds in a step-wise fashion to produce the addition product, usually in equilibrium, and a water molecule (hence the name condensation). The reaction may otherwise involve the formation of ammonia, ethanol, or acetic acid. It is a versatile class of reactions that can occur in acidic or basic conditions or in the presence of a catalyst. This class of reactions is a vital part of life as it is essential to the formation of peptide bonds between amino acids.

There are also copious variations of condensation reactions carried out in the lab, common examples include the Aldol Condensation, the Claisen Condensation, the Knoevenagel Reaction and the Dieckman Condensation (intramolecular Claisen Condensation).

1. "Condensation Reaction". IUPAC Copendium of Chemical Terminology (Gold Book). IUPAC. Retrieved 7 December 2017.
2. Voet, Donald; Voet, Judith; Pratt, Chriss (2008). Fundamentals of Biochemistry. Hoboken, NJ: John Wiley & Sons, Inc. p. 88. ISBN 978-0470-12930-2.
3. Bruckner, Reinhard (2002). Advanced Organic Chemistry (First ed.). San Diego, California: Harcourt Academic Press. pp. 414–427. ISBN 0-12-138110-2. {{cite book}}: |access-date= requires |url= (help)

The condensation reaction-speed can be catalyzed, by simply adding a concentrated acid to the reaction. It effects it by acidifying the environment whereas the reaction takes place the acid thereby binds with the water molecules and speed up the process. Also, an example of the condensation reaction is the dehydration synthesis.

Mechanisms

The numerous amount of condensation reactions correspond to numerous mechanisms but they all tend to follow a similar pathway.

Knoevenagel Reaction Mechanism

This reaction takes between a carbonyl compound and a activated methylene compound or with a nitromethane group, in mildly basic conditions. The final product of the reaction is an alkene with two geminal acceptor groups or one nitro group

Crossed Claisen Condensation Reaction Mechanism

The crossed claisen reaction results in the acylation of an ester enolate with another ester. These reactions are only possible when one ester has no alpha hydrogens. The reaction conditions call for a highly basic solution and a rapid acidic workup to achieve the final compound.

Applications

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Many artificial, man-made chemical reactions, and many biological transformations are condensation reactions. In the latter case (reactions in nature), phosphorylation and glycosylation reactions are generally all condensations, as are the key bond-forming reactions in all polypeptide and polynucleotide syntheses, and much of polyketide and terpene biosynthesis as well. Examples of the large number of condensation reactions are used in synthetic organic chemistry include:
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• Acyloin condensation
• Aldol condensation
• Claisen condensation
• Claisen–Schmidt condensation
• Darzens reaction (glycidic ester condensation)
• Dieckmann condensation
• Guareschi–Thorpe condensation
• Knoevenagel condensation
• Pechmann condensation
• Rap–Stoermer condensation
• Self-condensation or symmetrical aldol condensation
• Thorpe–Ziegler reaction

The reactions that form acid anhydrides from their constituent acids are also typically condensation reactions.

Condensation polymerization

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Condensation polymerization produces many important polymers, for example: nylon, polyester, and other condensation polymers and various epoxies. It is also the basis for the laboratory formation of silicates and polyphosphates. In condensation polymerization or "step-growth polymerization", multiple condensation reactions take place, joining monomers and monomer chains into long chains called polymers. It occurs for example in the synthesis of polyesters or nylons. It can be homopolymerization of a single monomer A-B with two different end groups that condense, or copolymerization of two co-monomers A-A and B-B.

Condensation polymerization releases multiple small molecules, in contrast to polyaddition reactions, which do not. In general, condensation polymers form more slowly than addition polymers, often requiring heat. They are generally lower in molecular weight. Monomers are consumed early in the reaction; the terminal functional groups remain active throughout; and short chains combine to form longer chains. A high conversion rate is required to achieve high molecular weights, per Carothers' equation.

Bifunctional monomers lead to linear chains, and therefore thermoplastic polymers, but, when the monomer functionality exceeds two, the product is a branched chain that may be a thermosetting polymer.

See also

• Anabolism
• Hydrolysis, the opposite of a condensation reaction
• Condensed tannins

References

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2. Bruckner, Reinhard (2002). Advanced Organic Chemistry. San Diego, California: Harcourt Academic Press. p. 418. ISBN 0-12-138110-2.

• Condensation reactions