Profile
Settings
Refer your friends
Sign out
Acylation, which is also known as alkanoylation, is a process by which an acyl group is added to any compound. The acyl group is a functional group in organic chemistry that has the formula –RCO with a single bond between R and C. The substance from which the acyl group is transferred is known as the acylating agent. Acyl halides are the commonly used acylating agent as they form strong electrophiles in reaction with metal catalysts. Friedel-crafts acylation is the most common example of acylation reaction. Acylation reaction usually involves an electrophilic aromatic substitution mechanism to carry out the reactions. These reactions are of great importance in organic chemistry as well as in biology.
Acylation Basics
- It is the most important reaction involving primary and secondary amines.
- The acyl group mostly replaces the hydrogen atom from the compound and occupies its place.
- The acylating agent, the compound that donates the acyl group, can be acid chlorides, anhydrides, esters and most commonly, acyl halides.
- The product of an acylation reaction is the amide of the corresponding acid.
- Acylation converts compounds with active hydrogen into esters, thioesters and amides, along with converting primary amine to an amide.
- Acylation reaction usually takes place for aromatic compounds, mostly aromatic amines.
- One of the most common acylation reactions is the Friedel-Crafts Acylation reaction.
- In the case of amines and alcohols, acylation reactions take place on nitrogen and oxygen atoms.
- The most commonly used acyl group is the ethanoyl group CH3CO.
Example
A reaction of benzene with acetyl chloride in the presence of aluminium chloride (catalyst) yields a methyl phenyl ketone and a hydrogen chloride gas.
Friedel-Crafts Acylation
- Friedel-Crafts Acylation reaction was discovered in 1877 by Charles Friedel and James Crafts.
- In this reaction, an acyl group is added to an aromatic ring with the help of acid chloride and a lewis acid catalyst.
- Through this process, an aromatic ring is changed into a ketone.
- In this reaction, the halogen of acyl halide group complexes with a lewis acid in order to form an electrophilic acylium ion (RCO+).
Friedel-Craft Acylation Reaction Process
- 1st part is the reaction between the catalyst aluminium chloride and acyl halide. This reaction leads to the formation of acylium ions.
- The acylium ion RCO+ acts as an electrophile and attacks the aromatic ring, and an intermediate complex is formed.
- The complex undergoes deprotonation to replace the aromaticity of the ring. The proton then forms a bond with chloride ions to yield hydrogen chloride and aluminium chloride.
- The aluminium chloride then attacks the oxygen of the carbonyl compound, releasing a ketone.
Shortcomings of the acylation reaction
- Acylation reactions can only form ketones.
- Any aromatic compound less reactive than mono-halobenzene cannot participate in the acylation reaction.
- Aryl amine forms a highly unreactive complex with lewis acid catalysts, and hence, they do not take part in acylation reactions.
Applications of the Acylation reaction
- Acylation reactions can be used to prevent rearrangement reactions.
- Acylation of proteins during post-translational modification takes place through acyl linkages and plays a very important role.
- Protein acylation is a controlling mechanism in cell signalling via fatty acylation, which is the addition of acyl groups to fatty acids.
- Palmitoylation is a type of acylation where monounsaturated fatty acid (palmitoleic acid) is added to the serine or threonine residues of the proteins. This process plays an important role in protein targeting and functioning of Wnt proteins.
- The reaction of phosgene COCl2 yields urea which is of great industrial importance.
- Friedel-crafts acylation reaction is used to produce aryl ketones from Beta-lactams.
- Friedel-Crafts acylation is used in the preparation of chemical feedstock and chemicals in the chemical industry.
- It is often used in biology to form DNA.
Conclusion
Acylation is a process by which an acyl group is added to any compound. The acyl group is a functional group in organic chemistry that has the formula –RCO with a single bond between R and C. The substance from which the acyl group is transferred is known as an acylating agent. Acyl halides are the commonly used acylating agent as they form strong electrophiles in reaction with metal catalysts. It is the most important reaction involving primary and secondary amines. The acyl group mostly replaces the hydrogen atom from the compound and occupies its place. The acylating agent, the compound that donates the acyl group, can include acid chlorides, anhydrides, esters and acyl halides. The product of an acylation reaction is the amide of the corresponding acid. One of the most common acylation reactions is the Friedel-Crafts Acylation reaction, where the acyl group is added to the aromatic ring. The Acylation process also has great importance in the fields of chemistry and biology.
