What is Acetylation?
Acetylation is a chemical reaction in which a hydrogen atom is exchanged for an acetyl group (CH3C=O group) in a molecule. This exchange occurs during the acetylation process. Acetylation is an organic esterification reaction using acetic acid in organic chemistry. It incorporates an acetyl group into a molecule. These substances are known as acetate esters or simply acetates.
The reverse of acetylation, deacetylation is the removal of an acetyl group from a chemical molecule.
The reaction of acetylation of salicylic acid
In this step, salicylic acid is acetylated with the aid of acetic anhydride to produce acetylsalicylic acid (commonly known as aspirin) and acetic acid. Note that acetic anhydride is also applied as an acetylating agent in the production of THC acetate ester and diacetylmorphine.
Mechanism of Acetylation of Salicylic Acid
Salicylic acid acetylation happens in an acidic environment. In this instance, the acidic media (often concentrated sulfuric acid) facilitates the separation of the acetate ion from the acetic anhydride. This acetate ion then binds to the proton released by the phenolic OH group (hydroxy group) of the salicylic acid molecule, producing acetic acid (CH3COOH).
The mechanism of the acetylation reaction that salicylic acid undergoes to produce aspirin and acetic acid is depicted below.
First, the acid protonates an oxygen atom of the acetic anhydride. The resultant positive charge is transferred to the neighboring carbonyl carbon, which attaches to the phenolic hydroxy group. This intermediate is now deprotonated, and one molecule of acetic acid separates from it. Thus, the required products are generated (aspirin and acetic acid).
Acetylation of cellulose
As a polyol, cellulose is sensitive to acetylation, which is accomplished with acetic anhydride. Hydrogen bonding, which otherwise dominates the characteristics of cellulose, is disrupted by acetylation. The cellulose esters are therefore soluble in organic solvents and can be molded into fibers and films.
Organic synthesis
Generally speaking, acetylations are used to create acetate esters and acetamides. In Friedel-Crafts processes, acetylations are commonly employed to form C-acetyl linkages. Carbanions and their analogs are amenable to acetylation.
Acetylation reagents
These three reagents facilitate several acetylations:
- Acetic anhydride: This is a typical laboratory reagent that creates acetic acid.
- Acetyl chloride: This is a common laboratory reagent, however, its use can produce hydrogen chloride, which can be undesired.
- Ketene: Historically, acetic anhydride was produced by combining ketene and acetic acid:
H2C=C=O + CH3COOH → (CH3CO)2O ΔH = −63 kJ mol−1
This is a typical laboratory reagent that creates acetic acid. It is also possible to perform acetylations with less electrophilic reagents, such as esters of thioacetic acid.
Frequently Asked Questions – FAQs
Q.1 What do you mean by acetylation?
Acetylation refers to the organic chemical reactions in which a compound’s hydrogen atom is replaced by an acetyl group (a functional group with the generic formula CH3C=O). Typically, acetylation processes produce compounds with acetoxy functional groups. The ultimate product of an acetylation reaction in which the hydrogen of alcohol is replaced by an acetyl group is an ester.
The acetylation of salicylic acid with acetic anhydride to produce acetic acid and acetylsalicylic acid is one of the most widespread instances of an acetylation reaction. Note that acetylsalicylic acid is generally referred to as aspirin.
Q.2 What are some examples of acetylation reactions?
Below are some examples of acetylation reactions.
*Salicylic acid is acetylated with acetic anhydride to produce aspirin alongside acetic acid.
*For the synthesis of acetanilide, aniline is acetylated with acetic anhydride in an atmosphere including glacial acetic acid.
*During gene regulation, lysine residues in histones are acetylated.
The N-terminal acetylation of proteins is a typical form of covalent transitional modification.
Q.3 How does acetylation happen?
The transfer of acetyl groups from acetyl coenzyme A (acetyl CoA) to lysine residues by acetyltransferase neutralizes the positive charge of the lysine residues.
