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chemistry Chemistry is the scientific study of the properties and behavior of matter. It is a physical science within the natural sciences that studies the chemical elements that make up matter and chemical compound, compounds made of atoms, molecules a ...
, acetylation is an organic
esterification In chemistry, an ester is a compound derived from an acid (either organic or inorganic) in which the hydrogen atom (H) of at least one acidic hydroxyl group () of that acid is replaced by an organyl group (R). These compounds contain a distin ...
reaction with
acetic acid Acetic acid , systematically named ethanoic acid , is an acidic, colourless liquid and organic compound with the chemical formula (also written as , , or ). Vinegar is at least 4% acetic acid by volume, making acetic acid the main compone ...
. It introduces an
acetyl group In organic chemistry, an acetyl group is a functional group denoted by the chemical formula and the structure . It is sometimes represented by the symbol Ac (not to be confused with the element actinium). In IUPAC nomenclature, an acetyl grou ...
into a
chemical compound A chemical compound is a chemical substance composed of many identical molecules (or molecular entities) containing atoms from more than one chemical element held together by chemical bonds. A molecule consisting of atoms of only one element ...
. Such compounds are termed ''acetate
ester In chemistry, an ester is a compound derived from an acid (either organic or inorganic) in which the hydrogen atom (H) of at least one acidic hydroxyl group () of that acid is replaced by an organyl group (R). These compounds contain a distin ...
s'' or simply ''
acetate An acetate is a salt formed by the combination of acetic acid with a base (e.g. alkaline, earthy, metallic, nonmetallic, or radical base). "Acetate" also describes the conjugate base or ion (specifically, the negatively charged ion called ...
s''. Deacetylation is the opposite reaction, the removal of an acetyl group from a chemical compound.


Acetylation/deacetylation in biology

Histone deacetylase Histone deacetylases (, HDAC) are a class of enzymes that remove acetyl groups (O=C-CH3) from an ε-N-acetyl lysine amino acid on both histone and non-histone proteins. HDACs allow histones to wrap the DNA more tightly. This is important becaus ...
s "play crucial roles in gene transcription and most likely in all eukaryotic biological processes that involve chromatin". Acetylation is one type of
post-translational modification In molecular biology, post-translational modification (PTM) is the covalent process of changing proteins following protein biosynthesis. PTMs may involve enzymes or occur spontaneously. Proteins are created by ribosomes, which translation (biolog ...
of proteins. The acetylation of the ε-amino group of
lysine Lysine (symbol Lys or K) is an α-amino acid that is a precursor to many proteins. Lysine contains an α-amino group (which is in the protonated form when the lysine is dissolved in water at physiological pH), an α-carboxylic acid group ( ...
, which is common, converts a charged side chain to a neutral one. Acetylation/deacetylation of histones also plays a role in
gene expression Gene expression is the process (including its Regulation of gene expression, regulation) by which information from a gene is used in the synthesis of a functional gene product that enables it to produce end products, proteins or non-coding RNA, ...
and
cancer Cancer is a group of diseases involving Cell growth#Disorders, abnormal cell growth with the potential to Invasion (cancer), invade or Metastasis, spread to other parts of the body. These contrast with benign tumors, which do not spread. Po ...
. These modifications are effected by enzymes called
histone acetyltransferase Histone acetyltransferases (HATs) are enzymes that acetylation, acetylate conserved lysine amino acids on histone proteins by transferring an acetyl group from acetyl-CoA to form ε-N-acetyllysine, ε-''N''-acetyllysine. DNA is wrapped around his ...
s (HATs) and
histone deacetylase Histone deacetylases (, HDAC) are a class of enzymes that remove acetyl groups (O=C-CH3) from an ε-N-acetyl lysine amino acid on both histone and non-histone proteins. HDACs allow histones to wrap the DNA more tightly. This is important becaus ...
s (HDACs). 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.


Organic synthesis

Acetate esters and
acetamide Acetamide (systematic name: ethanamide) is an organic compound with the formula CH3CONH2. It is an amide derived from ammonia and acetic acid. It finds some use as a plasticizer and as an industrial solvent. The related compound ''N'',''N''-dime ...
s are generally prepared by acetylations. Acetylations are often used in making C-acetyl bonds in Friedel-Crafts reactions. Carbanions and their equivalents are susceptible to acetylations.


Acetylation reagents

Many acetylations are achieved using these three reagents: *
Acetic anhydride Acetic anhydride, or ethanoic anhydride, is the chemical compound with the chemical formula, formula . Commonly abbreviated , it is one the simplest organic acid anhydride, anhydrides of a carboxylic acid and is widely used in the production of c ...
. This reagent is common in the laboratory; its use cogenerates acetic acid. *
Acetyl chloride Acetyl chloride () is an acyl chloride derived from acetic acid (). It belongs to the class of organic compounds called acid halides. It is a colorless, corrosive, volatile liquid. Its formula is commonly abbreviated to AcCl. Synthesis On an ...
. This reagent is also common in the laboratory, but its use cogenerates hydrogen chloride, which can be undesirable. *
Ketene In organic chemistry, a ketene is an organic compound of the form , where R and R' are two arbitrary valence (chemistry), monovalent functional group, chemical groups (or two separate Substituent, substitution sites in the same molecule). The na ...
. At one time acetic anhydride was prepared by the reaction of ketene with acetic acid: : \Delta H = -63 \text


Acetylation of cellulose

Cellulose is a
polyol In organic chemistry, a polyol is an organic compound containing multiple hydroxyl groups (). The term "polyol" can have slightly different meanings depending on whether it is used in food science or polymer chemistry. Polyols containing two, th ...
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.


Acetylation of wood

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. The process involves the chemical reaction of
acetic anhydride Acetic anhydride, or ethanoic anhydride, is the chemical compound with the chemical formula, formula . Commonly abbreviated , it is one the simplest organic acid anhydride, anhydrides of a carboxylic acid and is widely used in the production of c ...
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 Wood science is the scientific field which predominantly studies and investigates elements associated with the formation, the physical and chemical composition, and the macro- and microstructure of wood as a bio-based and lignocellulosic materi ...
.


Transacetylation

Transacetylation uses
vinyl acetate Vinyl acetate is an organic compound with the Chemical formula, formula CH3CO2CH=CH2. This colorless liquid is the precursor to polyvinyl acetate, ethylene-vinyl acetate copolymers, polyvinyl alcohol, and other important industrial polymers. Prod ...
as an acetyl donor and
lipase In biochemistry, lipase ( ) refers to a class of enzymes that catalyzes the hydrolysis of fats. Some lipases display broad substrate scope including esters of cholesterol, phospholipids, and of lipid-soluble vitamins and sphingomyelinases; howe ...
as a catalyst. This methodology allows the preparation of enantio-enriched alcohols and acetates.


See also

*
Acetoxy group In organic chemistry, the acetoxy group (abbr. AcO– or –OAc; IUPAC name: acetyloxy), is a functional group with the formula and the structure . As the ''-oxy'' suffix implies, it differs from the acetyl group () by the presence of an addit ...
*
Acylation In chemistry, acylation is a broad class of chemical reactions in which an acyl group () is added to a substrate. The compound providing the acyl group is called the acylating agent. The substrate to be acylated and the product include the foll ...
*
Amide In organic chemistry, an amide, also known as an organic amide or a carboxamide, is a chemical compound, compound with the general formula , where R, R', and R″ represent any group, typically organyl functional group, groups or hydrogen at ...
*
Ester In chemistry, an ester is a compound derived from an acid (either organic or inorganic) in which the hydrogen atom (H) of at least one acidic hydroxyl group () of that acid is replaced by an organyl group (R). These compounds contain a distin ...
*
N-terminal acetylation N-terminal acetylation is the protein modification that occurs on the α-amino acid group at the N-termini of proteins. The backbone amino group on the first amino acid (α-amino group) on a protein N-terminus gets an acetyl group (-COCH3) via ac ...
*
Organic synthesis Organic synthesis is a branch of chemical synthesis concerned with the construction of organic compounds. Organic compounds are molecules consisting of combinations of covalently-linked hydrogen, carbon, oxygen, and nitrogen atoms. Within the gen ...


References

{{Reflist, 35em Organic reactions