Acetylation

Salicylic acid is acetylated to form aspirin

In chemistry, acetylation is an organic esterification reaction with acetic acid. It introduces an acetyl group into a chemical compound. Such compounds are termed acetate esters or simply acetates. Deacetylation is the opposite reaction, the removal of an acetyl group from a chemical compound.

Acetylation/deacetylation in biologyEdit

Histone deacetylases "play crucial roles in gene transcription and most likely in all eukaryotic biological processes that involve chromatin".<ref name= Erasers/>

Acetylation is one type of post-translational modification of proteins. The acetylation of the ε-amino group of lysine, which is common, converts a charged side chain to a neutral one.<ref>Template:Cite journal</ref> Acetylation/deacetylation of histones also plays a role in gene expression and cancer.<ref>Template:Cite journal</ref> These modifications are effected by enzymes called histone acetyltransferases (HATs) and histone deacetylases (HDACs).<ref>Template:Cite journal</ref>

Two general mechanisms are known for deacetylation. One mechanism involves zinc binding to the acetyl oxygen. Another family of deacetylases require NAD⁺, which transfers an ribosyl group to the acetyl oxygen.<ref name= Erasers>Template:Cite journal</ref>

Organic synthesisEdit

Acetate esters<ref>Template:Cite journal</ref> and acetamides<ref>Template:Cite journal</ref> are generally prepared by acetylations. Acetylations are often used in making C-acetyl bonds in Friedel-Crafts reactions.<ref name=acetylfluorene>Template:Cite journal</ref><ref name=AcAnth>Template:Cite journal</ref> Carbanions and their equivalents are susceptible to acetylations.<ref name = denoon>Template:OrgSynth</ref>

Acetylation reagentsEdit

Many acetylations are achieved using these three reagents:

Acetic anhydride. This reagent is common in the laboratory; its use cogenerates acetic acid.<ref name=acetylfluorene /><ref>Template:Cite journal</ref>
Acetyl chloride. This reagent is also common in the laboratory, but its use cogenerates hydrogen chloride, which can be undesirable.<ref name=AcAnth />
Ketene. At one time acetic anhydride was prepared by the reaction of ketene with acetic acid:<ref name="Arpe">Template:Citation Template:Dead link</ref>

Template:Chem2 <math>\Delta H = -63 \text{ kJ/mol}</math>

Acetylation of celluloseEdit

Template:See also Cellulose is a polyol and thus susceptible to acetylation, which is achieved using acetic anhydride. Acetylation disrupts hydrogen bonding, which otherwise dominates the properties of cellulose. Consequently, the cellulose esters are soluble in organic solvents and can be cast into fibers and films.<ref>Template:Ullmann</ref>

Acetylation of woodEdit

Template:See also Acetylation of wood is a chemical modification process that enhances the properties of wood by making it highly resistant to fungi and insects, as well as very durable against moisture and environmental parameters.<ref>Template:Cite book</ref><ref>Holger Militz: Übersichtsbericht - Acetyliertes Holz - (Naturwissenschaftliche und technologische Grundlagen, materialtechnische und ökonomische Möglichkeiten und Grenzen, aktueller Stand der Umsetzung). SGD Süd-Forstliche Versuchsanstalt Rheinland-Pfalz, 2011, accessed in December 2024.</ref>

The process involves the chemical reaction of acetic anhydride with the free hydroxyl groups in wood polymers, mostly of lignin and hemicelluloses, without requiring a catalyst. The modification results in bonds between the structural polymeric components, significantly reducing the ability of the -OH groups to form hydrogen bonds with water molecules. This effectively "locks" the cellular walls, minimizing the capacity of wood to absorb water and enhancing its dimensional stability. Approximately 80-90% of the hydroxyl groups of wood are modified during the process. The whole process is an environmentally friendly treatment, and has emerged, in the 21st century, as a significant innovation in the scientific area of wood science.<ref>Template:Cite journal</ref><ref>Template:Cite journal</ref>

TransacetylationEdit

Transacetylation uses vinyl acetate as an acetyl donor and lipase as a catalyst. This methodology allows the preparation of enantio-enriched alcohols and acetates.<ref>Template:Cite book</ref>

ReferencesEdit

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