What is the Difference Between Acylation and Acetylation

Acylation and acetylation are both chemical reactions involving the addition of an acyl group to a molecule. Acetylation is a subset of acylation.

What is the difference between acylation and acetylation? Acylation can involve various acyl groups, while acetylation involves the addition of the acetyl group.

Key Areas Covered

1. What is Acylation  
      – Definition, Features 
2. What is Acetylation
      – Definition, Features 
3. Similarities Between Acylation and Acetylation
      – Outline of Common Features
4. Difference Between Acylation and Acetylation
      – Comparison of Key Differences
5. FAQ: Acylation and Acetylation
      – Answers to Frequently Asked Questions

Key Terms

Acylation, Acetylation

What is Acylation

Acylation is a chemical reaction in which an acyl group (RCO-) is introduced into a molecule.  The acyl group contains a carbonyl group (C=O) bonded to an alkyl or aryl group (R). There are several types of acylation reactions, such as alkylation of acyl compounds, Friedel-crafts acylation, and acylation of amino acids.

Alkylation of acyl compounds involves the reaction of an acyl compound (such as an acid chloride or anhydride) with a nucleophile (like an alcohol or amine). For example, the reaction of acetic anhydride with ethanol yields ethyl acetate.

Figure 1: Friedel-Crafts Acylation of Benzene by Ethanoyl Chloride

An acyl group is introduced into an aromatic ring using an acyl halide and a Lewis acid catalyst (like aluminum chloride) in Friedel-Crafts acylation. In protein synthesis, amino acids are bonded together by peptide bonds formed through acylation reactions.

Some of the common acylation reagents include acid chlorides, acid anhydrides, and esters. Acylation reactions are used in the production of various industrial products, such as pharmaceuticals, dyes, and polymers.

What is Acetylation

Acetylation is a chemical reaction that involves the addition of an acetyl group. Acetyl group consists of a functional group consisting of a carbonyl group (C=O) bonded to a methyl group (CH3). Modification of proteins is an example of acetylation. This process is catalyzed by enzymes called acetyltransferases, which transfer an acetyl group from a donor molecule, such as acetyl-coenzyme A (acetyl-CoA), to a specific amino acid residue within the protein. Acetylation can alter the conformation of a protein. It can also influence the protein’s susceptibility to degradation or its localization within the cell.

Figure 2: Salicylic Acid is Acetylated to Form Aspirin

Acylation can occur also in DNA, mainly on histone proteins. Histone acetylation involves the addition of acetyl groups to the lysine residues within histone tails. This modification neutralizes the positive charge of the lysine residues, reducing the electrostatic interaction between histones and the negatively charged DNA backbone. Histone acetylation is associated with increased gene expression. Acylation is also seen in many other biological roles, such as gene regulation, protein function, cell signaling, and metabolic pathways.

Similarities Between Acylation and Acetylation

1.  Acylation and acetylation are both chemical reactions that involve the addition of an acyl group to a molecule.
2. Both are electrophilic reactions.

Difference Between Acylation and Acetylation

Definition

• Acylation is a chemical reaction that adds any acyl group (RCO) to a molecule, while acetylation is a chemical reaction that adds an acetyl group (CH₃CO) to a molecule.

Esters and Amides

• Acylation forms esters or amides depending on the nucleophile (alcohol or amine), while acetylation always forms an ester or amide with an acetyl group.

Specificity

• Acylation is less specific and can add various acyl groups, whereas acetylation is more specific and always adds an acetyl group.

Conclusion

Acetylation is a subset of acylation seen in organic chemistry. The main difference between acylation and acetylation is that acylation can involve various acyl groups, while acetylation involves the addition of the acetyl group.

FAQ: Acylation and Acetylation

1. What is the difference between acylation and deacetylation?

The basic difference between acylation and deacetylation is that acylation adds an acyl group to a molecule, while deacetylation removes an acetyl group.

2. What is the difference between acyl chloride and acetyl chloride?

Acyl chloride is a general term for any organic compound with a carbonyl group bonded to a chlorine atom. Acetyl chloride is a specific type of acyl chloride where the carbonyl group is attached to a methyl group.

3. Is acetylation the same as acylation?

Acetylation is a specific type of acylation. Acylation involves adding an acyl group to a molecule, while acetylation specifically adds an acetyl group.

4. What is the difference between acetylation and esterification?

Acetylation involves the addition of an acetyl group, while esterification involves the formation of an ester from an alcohol and an acid. This is the main difference between acetylation and esterification.

5. What is the opposite of acetylation?

The opposite of acetylation is deacetylation. In acetylation, an acetyl group is added to a molecule, while in deacetylation, the acetyl group is removed from the molecule. This process is common in biological systems, especially in the regulation of proteins like histones.

Reference:

1. “Acetylation.” Wikipedia. Wikipedia Foundation.
2. “Acylation – An Overview.” Science Direct.

Image Courtesy:

1. “Benzen acylowany” By Arrowsmaster – Own work (Public Domain) via Commons Wikimedia
2. “Aspirin synthesis” By Edgar181 – Own work (Public Domain) via Commons Wikimedia