Condensation Reaction
A condensation reaction is a reaction where two molecules join together and in doing so create a complex molecule and a much simpler molecule that is a byproduct of the reaction. The simple molecule eliminated can be water, ammonia, or an alcohol. The two combining molecules each contribute a single moiety (a part of portion of a molecule having a characteristic chemical property) to the eliminated molecule.
The formation of a peptide bond between two amino acids is an example of a condensation reaction, as is the manufacture of an ester (esterification).
Certain types of condensation reactions have their own name, for example the Claisen condensation. In this reaction, an ester joins with another ester, a ketone, or a nitrile. This must be carried out in the presence of sodium ethoxide that acts as a catalyst for the reaction. This type of reaction gives as its product a beta ketonic ester, ketone, or nitrile (depending upon the starting compounds) and an alcohol. The Claisen reaction is important in cell biology as it is this reaction that starts the acetyl group of acetyl CoA into the citric acid cycle (the Krebs or tricarboxylic acid cycle). The Krebs cycle is part of the energy pathway in all living cells.
A catalyst is usually, but not always, required. Catalysts commonly encountered in condensation reactions include acids, bases, cyanide, and complex metal ions.
If the molecules reacting together are identical then the reaction is known as self condensation. A condensation reaction can also occur between two separate parts of the same molecule.
Aldehydes, ketones, esters, alkynes, amino acids, nucleic acids, and amines are examples of several organic compounds that are capable of combining with each other and, with the exception of amines, themselves. Many of these compounds are important intermediate steps in organic synthesis reactions and in the manufacture of biologically important molecules.
If the condensation reaction process is repeated many times a condensation polymerization reaction is said to be taking place. This is the type of reaction used to form polyesters such as terylene and nylon. Both of these molecules contain the results of approximately 100 separate condensation reactions. This multiple condensation reaction is sometimes called a polycondensation reaction. This is the type of reaction that is used to build large organic polymers.
The first synthetic polymer produced by a condensation reaction was Bakelite. Bakelite is produced from phenol and methanol and the eliminated product is water. Bakelite has been used extensively as an electrical insulator.
Condensation reactions occur with the general formula of: XOH + HOY = XOY + H2O, where X and Y may be the same or different. This example gives water as an elimination product, but as has been stated other small, simple molecules may be manufactured instead.
The opposite of a condensation reaction is hydrolysis. In hydrolysis water is added to a compound to break it down.
Condensation reactions are an important class of reactions. They are used extensively in the manufacture of many commercially important products as well as being the driving force behind many of the processes necessary for life itself.
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