In chemistry, a condensation reaction is an organic chemical reaction in which two or more reactants combine to form a single product, accompanied by the loss of a small molecule such as water, an alcohol, or an acid. It is a synthesis reaction and substitution reaction. The name “condensation” comes from the characteristic release of a condensed molecule. Less commonly, the term applies to a reaction where water (or other small molecule) formation does not occur, such as in a benzoin condensation.
Condensation Reaction Importance
Condensation reactions underpin several essential biological, chemical, and industrial processes. They contribute to the synthesis of significant biological polymers, including proteins, nucleic acids, and carbohydrates. The reaction also plays a crucial role in the formation of esters and amides, which are key substances in various chemical industries.
In everyday life, these reactions are at the core of the production of many materials, such as plastics, textiles, and resins. For instance, polyesters and polyamides, used extensively in the textile and plastics industries, form by condensation polymerization reactions.
Specific Types of Condensation Reactions
There are several specific types of condensation reactions, including esterification, dehydration synthesis, saponification, glycosylation, phosphorylation, polypeptide synthesis, and polynucleotide synthesis.
Dehydration Synthesis (Dehydration Reaction)
Dehydration synthesis is a type of condensation reaction where the small molecule that is lost is water. This reaction is significant in the formation of many important polymers. For example, the formation of disaccharides, like sucrose, from monosaccharides is a dehydration synthesis reaction.
As another example, two glucose monosaccharides condense and form a disaccharide like maltose and water:
C6H12O6 + C6H12O6 → C12H22O11 + H2O
Sometimes people use the terms “dehydration synthesis” and “condensation” interchangeably. But, while a dehydration is a type of condensation reaction, not all condensations are dehydration reactions.
Esterification
Esterification is a condensation reaction between a carboxylic acid and an alcohol, forming an ester and water. It’s an essential process in the production of a wide variety of compounds, from simple esters used as solvents to complex esters employed in pharmaceutical industries.
For example, carboxylic acid (RCOOH) and an alcohol (R’OH) combine to form an ester (RCOO-R’) and water:
RCOOH + R’OH → RCOO-R’ + H2O
As another example, acetic acid (CH3COOH) and ethanol (C2H5OH) can react to form ethyl acetate (CH3COOC2H5) and water:
CH3COOH + C2H5OH → CH3COOC2H5 + H2O
Saponification
Saponification is a condensation reaction between a fat or oil (triglyceride) and a strong base, typically sodium or potassium hydroxide, producing soap and glycerol. This reaction has practical importance in the soap industry and is an example of how condensation reactions contributes to everyday life.
A triglyceride (glyceryl tristearate, for example) and sodium hydroxide react to form soap (sodium stearate) and glycerol:
C57H110O6 + 3NaOH → 3C18H35O2Na + C3H8O3
Glycosylation
Glycosylation is a condensation reaction that attaches a carbohydrate (glycosyl donor) to a functional group of another molecule (glycosyl acceptor). It is critical for protein function in cells and is a significant reaction in biological systems and the pharmaceutical industry.
An example of a glycosylation reaction is the formation of a glycosidic bond between two glucose molecules to form maltose:
Glucose-1-Phosphate + Glucose → Maltose + Phosphate
Phosphorylation
Phosphorylation is a condensation reaction where a phosphate group is added to an organic molecule. It plays a key role in the regulation of cellular processes and the production of ATP, the main energy currency in cells.
An ATP molecule can phosphorylate glucose to form glucose-6-phosphate and ADP:
Glucose + ATP → Glucose-6-Phosphate + ADP
Polypeptide Synthesis
Polypeptide synthesis involves the formation of peptide bonds between amino acids to produce proteins. It is a condensation reaction as a molecule of water is released when a peptide bond is formed. This reaction is fundamental to life, as proteins are necessary for nearly all biological functions.
Two amino acids, such as glycine (NH2-CH2-COOH) and alanine (CH3-CH(NH2)-COOH), can react to form a dipeptide:
NH2-CH2-COOH + H2N-CH(CH3)-COOH → NH2-CH2-CO-NH-CH(CH3)-COOH + H2O
Polynucleotide Synthesis
Polynucleotide synthesis is another critical condensation reaction that occurs in biological systems. Nucleotides condense to form the backbone of DNA and RNA, releasing water in the process. This reaction is critical to the propagation of genetic information in living organisms.
The formation of a dinucleotide from two nucleotides (represented by NMP, where M stands for the monophosphate group) involves the release of pyrophosphate (PPi):
NMP + NMP → NMP-NMP + PPi
Please note that these are generalized equations, and actual biological reactions often involve enzymatic catalysts and may proceed through multiple steps.
How to Recognize a Condensation Reaction
Recognizing condensation reactions is straightforward once you know what to look for. Here are some pointers for identifying these reactions:
1. Formation of a Larger Molecule: In a condensation reaction, two or more molecules combine to form a larger molecule. So, if you notice that the products include a molecule that is larger than the reactants, it’s a clue that a condensation reaction might have taken place.
2. Loss of a Small Molecule: Condensation reactions involve the loss of a small molecule. This is often water (H2O), but it can also be other small molecules like hydrogen chloride (HCl), methanol (CH3OH), or acetic acid (CH3COOH).
3. Formation of a New Bond: In a condensation reaction, a new bond forms between the reactants. This bond could be an ester linkage (-COO-), an amide linkage (-CONH-), a glycosidic linkage (-O-), or a phosphodiester linkage (-OPO32-), among others.
4. Presence of Specific Functional Groups: Reactants in a condensation reaction often have certain functional groups, such as -OH (hydroxyl), -COOH (carboxyl), or -NH2 (amino) groups. These functional groups react and lead to the formation of water or other small molecules.
Remember, context is also crucial when identifying condensation reactions, particularly in biological systems. For example, if the reaction involves the formation of polymers like proteins or nucleic acids, it is almost certainly a condensation reaction.
Condensation Reaction – Conclusion
Condensation reactions are a fundamental and diverse group of chemical reactions that enable a myriad of biological, chemical, and industrial processes. From the formation of complex biological polymers to the synthesis of everyday materials, these reactions are an integral part of the chemical landscape. A thorough understanding of condensation reactions and their different types is vital for chemists and chemistry students alike as they navigate the vast and fascinating world of chemistry.
References
- Bruckner, Reinhard (2002). Advanced Organic Chemistry (1st ed.). San Diego, California: Harcourt Academic Press. ISBN 0-12-138110-2.
- Fakirov, S. (2019). “Condensation Polymers: Their Chemical Peculiarities Offer Great Opportunities”. Progress in Polymer Science. 89: 1–18. doi:10.1016/j.progpolymsci.2018.09.003
- IUPAC (1997). “Condensation reaction.” Compendium of Chemical Terminology (2nd ed.) (the “Gold Book”). Oxford: Blackwell Scientific Publications. ISBN:0-9678550-9-8. doi:10.1351/goldbook
- Zhang, Minhua; Yu, Yingzhe (2013). “Dehydration of Ethanol to Ethylene”. Industrial & Engineering Chemistry Research. 52 (28): 9505–9514. doi:10.1021/ie401157c