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H2C=C=O + CH3COOH -> (CH3CO)2O
This reagent is common in the laboratory; its use cogenerates acetic acid.
Acetylations can also be achieved using less electrophilic reagents, such as esters of
In organic chemistry
Organic chemistry is a subdiscipline within chemistry involving the science, scientific study of the structure, properties, and reactions of organic compounds and organic materials, i.e., matter in its various forms that contain carbon atoms.Clay ...
, acetylation is an organic esterification
In chemistry, an ester is a compound derived from an oxoacid (organic or inorganic) in which at least one hydroxyl group () is replaced by an alkoxy group (), as in the substitution reaction of a carboxylic acid and an alcohol. Glyceride ...
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 componen ...
. It introduces an acetyl group
In organic chemistry, acetyl is a functional group with 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, acetyl is called ethanoyl ...
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 ele ...
. Such compounds are termed ''acetate ester
In chemistry, an ester is a compound derived from an oxoacid (organic or inorganic) in which at least one hydroxyl group () is replaced by an alkoxy group (), as in the substitution reaction of a carboxylic acid and an alcohol. Glycerides ...
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.
Organic synthesis
Acetate esters andacetamide
Acetamide (systematic name: ethanamide) is an organic compound with the formula CH3CONH2. It is the simplest amide derived from acetic acid. It finds some use as a plasticizer and as an industrial solvent. The related compound Dimethylacetamide, ...
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 formula (CH3CO)2O. Commonly abbreviated Ac2O, it is the simplest isolable anhydride of a carboxylic acid and is widely used as a reagent in organic synthesis. It is a c ...
. This reagent is common in the laboratory; its use cogenerates acetic acid.
*Acetyl chloride
Acetyl chloride (CH3COCl) 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 ...
. 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 monovalent chemical groups (or two separate substitution sites in the same molecule). The name may also refer to the specific compound eth ...
. At one time acetic anhydride was prepared by the reaction of ketene with acetic acid:
:thioacetic acid
Thioacetic acid is an organosulfur compound with the molecular formula . It is the sulfur analogue of acetic acid (), as implied by the ''thio-'' prefix. It is a yellow liquid with a strong thiol-like odor. It is used in organic synthesis for the ...
.
Acetylation of cellulose
Cellulose is apolyol
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, thre ...
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/deacetylation in biology
Acetylation is one type ofpost-translational modification
Post-translational modification (PTM) is the covalent and generally enzymatic modification of proteins following protein biosynthesis. This process occurs in the endoplasmic reticulum and the golgi apparatus. Proteins are synthesized by ribos ...
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. It contains an α-amino group (which is in the protonated form under biological conditions), an α-carboxylic acid group (which is in the deprotonated &minu ...
, 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 by which information from a gene is used in the synthesis of a functional gene product that enables it to produce end products, protein or non-coding RNA, and ultimately affect a phenotype, as the final effect. ...
and cancer
Cancer is a group of diseases involving abnormal cell growth with the potential to invade or spread to other parts of the body. These contrast with benign tumors, which do not spread. Possible signs and symptoms include a lump, abnormal bl ...
. These modifications are effected by enzymes called histone acetyltransferase
Histone acetyltransferases (HATs) are enzymes that acetylate conserved lysine amino acids on histone proteins by transferring an acetyl group from acetyl-CoA to form ε-''N''-acetyllysine. DNA is wrapped around histones, and, by transferring an ...
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 a histone, allowing the histones to wrap the DNA more tightly. This is important because DNA is wrapped around h ...
s (HDACs).
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 addition ...
*Acylation
In chemistry, acylation (or alkanoylation) is the chemical reaction in which an acyl group () is added to a compound. The compound providing the acyl group is called the acylating agent.
Because they form a strong electrophile when treated wit ...
*Amide
In organic chemistry, an amide, also known as an organic amide or a carboxamide, is a compound with the general formula , where R, R', and R″ represent organic groups or hydrogen atoms. The amide group is called a peptide bond when it is ...
*Ester
In chemistry, an ester is a compound derived from an oxoacid (organic or inorganic) in which at least one hydroxyl group () is replaced by an alkoxy group (), as in the substitution reaction of a carboxylic acid and an alcohol. Glycerides ...
*Organic synthesis
Organic synthesis is a special branch of chemical synthesis and is concerned with the intentional construction of organic compounds. Organic molecules are often more complex than inorganic compounds, and their synthesis has developed into one o ...
References
{{Reflist, 35em Organic reactions