Acetic anhydride

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Acetic anhydride

Acetic anhydride is the chemical compound

Chemical compound

A chemical compound is a Chemical substance consisting of two or more different chemical element Chemical bond together in a fixed mass ratio that can be split into simpler substances....
with the formula

Chemical formula

A chemical formula is a way of expressing information about the atoms that constitute a particular chemical compound, and how the relationship between those atoms changes in chemical reactions....
(CH₃CO)₂O. Commonly abbreviated Ac

Acetyl

In organic chemistry, acetyl , is a functional group, the acyl of acetic acid, with chemical formula -CarbonOxygenCarbonHydrogen3. It is sometimes abbreviated as Ac ....
₂O, it is one of the simplest acid anhydrides and is a widely used reagent

Reagent

A reagent or reactant is a substance or compound consumed during a chemical reaction. Solvents and catalysts, although they are involved in the reaction, are usually not referred to as reactants....
in organic synthesis

Organic synthesis

Organic synthesis is a special branch of chemical synthesis and is concerned with the construction of organic compounds via organic reactions. Organic_chemistry molecules can often contain a higher level of complexity compared to purely Inorganic_chemistry compounds, so the synthesis of organic compounds has developed into one of the most im...
. It is a colorless liquid that smells strongly of acetic acid

Acetic acid

Acetic acid, CH3COOH, also known as ethanoic acid, is an organic acid which gives vinegar its sour taste and pungent smell. Pure, water-free acetic acid is a colourless liquid that absorbs water from the environment , and freezes at 16.7 Celsius to a colourless crystalline solid....
, which is formed by its reaction with the moisture in the air.

ic anhydride is produced by carbonylation

Carbonylation

Carbonylation refers to Chemical_reactions that introduce carbon monoxide into Organic_compound and inorganic compound substrates. Carbon monoxide is abundantly available and conveniently reactive, so it is widely used as a reactant in industrial chemistry....
of methyl acetate

Methyl acetate

Methyl acetate, also known as acetic acid methyl ester or methyl ethanoate, is a clear, flammable liquid with a characteristic, not unpleasant smell like certain glues or nail polish removers....
:

CH₃CO₂CH₃ + CO ? (CH₃CO)₂O

This process involves the conversion of methyl acetate to methyl iodide and an acetate salt.

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Production

Acetic anhydride is produced by carbonylation

Carbonylation

Methyl acetate

CH₃CO₂CH₃ + CO ? (CH₃CO)₂O

This process involves the conversion of methyl acetate to methyl iodide and an acetate salt. Carbonylation of the methyl iodide in turn affords acetyl iodide, which reacts with acetate salts or acetic acid to give the product. Rhodium and lithium iodides are employed as catalysts. Because acetic anhydride is not stable in water, the conversion is conducted under anhydrous conditions. In contrast, the Monsanto acetic acid synthesis

Monsanto process

The Monsanto process is an important method for the manufacture of acetic acid. This process operates at a pressure of 30-60 atmosphere and a temperature of 150-200 ?C and gives a selectivity greater than 99%....
, which also involves a rhodium catalyzed carbonylation of methyl iodide, is at least partially aqueous.

To a decreasing extent, acetic anhydride is also prepared by the reaction of ketene

Ketene

A ketene is an organic compound of the form R2C=C=O. Hermann Staudinger pioneered the research of ketenes. Ketene also refers to ethenone, the specific compound of this class in which both Rs are hydrogen....
with acetic acid. Ketene is generated by dehydrating acetic acid at elevated temperatures. This production method was developed by Wacker Chemie

Wacker Chemie

Wacker Chemie AG is a worldwide operating company in the chemical business. The product ranges vary from silicones, polymer products like dispersible polymer powder, chemical materials, polysilicon to wafers for semiconductor industry....
in 1922, when the demand for acetic anhydride increased due to the production of acetic fibre.

Due to its low cost, acetic anhydride is purchased, not prepared, for use in research laboratories.

Reactions

Acetic anhydride is a versatile reagent for acetylation

Acetylation

Acetylation describes a reaction that introduces an acetyl functional group into an organic compound. Deacetylation is the removal of the acetyl group....
s, the introduction of acetyl groups to organic substrates. In these conversions, acetic anhydride is viewed as a source of CH₃CO⁺. Alcohol

Alcohol

In chemistry, an alcohol is any organic compound in which a hydroxyl Functional group is bound to a carbon atom of an alkyl or substituted alkyl group....
s and amine

Amine

Amines are organic compounds and functional groups that contain a base nitrogen atom with a lone pair. Amines are derivative s of ammonia, wherein one or more hydrogen atoms are replaced by organic substituents such as alkyl and aryl groups....
s are readily acetylated. For example, the reaction of acetic anhydride with ethanol

Ethanol

Ethanol, also called ethyl alcohol, pure alcohol, grain alcohol, or drinking alcohol, is a volatility , flammable, colorless liquid....
is:

(CH₃CO)₂O + CH₃CH₂OH ? CH₃CO₂CH₂CH₃

Ethyl acetate

Ethyl acetate is the organic compound with the formula CH3COOCH2CH3. This colorless liquid has a characteristic sweet smell like certain glues or nail polish removers, in which it is used....
+ CH₃CO₂H

Often a base such as pyridine

Pyridine

Pyridine is a simple and important heterocyclic aromatic organic compound with the formula CarbonHydrogenNitrogen. This colorless liquid with a distinctive fish-like odor is structurally related to benzene, wherein one CH group in the six-membered ring is replaced by a nitrogen atom....
is added to function as catalyst. In specialized applications, Lewis acid

Lewis acid

A Lewis acid is a chemical compound, A, that can accept a pair of electrons from a Lewis base, B, that acts as an electron-pair donor, forming an adduct, AB.Gilbert N....
ic scandium salts have also proven effective catalysts.

Aromatic rings are acetylated, usually in the presence of an acid catalyst. Illustrative is the conversion of benzene to acetophenone

Acetophenone

Acetophenone is the organic compound with the chemical formula C6H5CCH3. It is the simplest aromatic ketone. This colourless, viscous liquid is a precursor to useful resins and fragrances....
:

(CH₃CO)₂O + C₆H₆ ? CH₃COC₆H₅ + CH₃CO₂H

Ferrocene

Ferrocene is the organometallic compound with the formula Fe2. It is the prototypical metallocene, a type of organometallic chemistry chemistry compound consisting of two cyclopentadienyl complex rings bound on opposite sides of a central metal atom....
may be acetylated too:

Cp₂Fe → CpFe(C₅H₄COCH₃)

Hydrolysis

Acetic anhydride dissolves in water to approximately 2.6% by weight. Aqueous solutions have limited stability because, like most acid anhydrides, acetic anhydride hydrolyses to give acetic acid:

(CH₃CO)₂O + H₂O ? 2 CH₃CO₂H

Applications

As indicated by its organic chemistry, Ac₂O is mainly used for acetylations leading to commercially significant materials. Its largest application is for the conversion of cellulose to cellulose acetate

Cellulose acetate

Cellulose acetate, first prepared in 1865, is the acetate ester of cellulose. Cellulose acetate is used as a film base in photography, and as a component in some adhesives; it is also used as a synthetic fiber....
, which is a component of photographic film and other coated materials. Similarly it is used in the production of aspirin

Aspirin

Aspirin , also known as acetylsalicylic acid , is a salicylate medication, often used as an analgesic to relieve minor aches and pains, as an antipyretic to reduce fever, and as an anti-inflammatory medication....
, acetyl salicylic acid, which is prepared by the acetylation of salicylic acid

Salicylic acid

Salicylic acid is a beta hydroxy acid with the chemical formula C6H4COOH, where the OH group is adjacent to the carboxylic acid....
. It is also used as a wood preservative via autoclave impregnation to make a longer lasting timber. Because of its use for the synthesis of heroin

Heroin

Heroin is a opioid synthesized from morphine, a derivative of the opium poppy. It is the 3,6-acetate ester of morphine . The white crystalline form is commonly the hydrochloride salt diacetylmorphine hydrochloride, however heroin Freebase may also appear as a white powder....
by the diacetylation of morphine

Morphine

Morphine is a highly potent opiate analgesic Medication, is the principal active agent in opium, and is considered to be the prototypical opioid....
, acetic anhydride (known as 'AA' in clandestine chemistry

Clandestine chemistry

Clandestine chemistry is to chemistry carried out in secret, and particularly in illegal drug trade laboratories. Larger labs are usually run by gangs or organized crime intending to produce for distribution on the black market....
circles) is listed as a U.S. DEA List II Precursor, and restricted in many other countries. The largest markets for diverted acetic anhydride continue to be heroin laboratories in Afghanistan.

Safety

Acetic anhydride is an irritant and flammable. Because of its reactivity toward water, alcohol foam or carbon dioxide are preferred for fire suppression. The vapour of acetic anhydride is harmful.

Acetic anhydride

Production

Reactions

Hydrolysis

Applications

Safety

See also