Acetic anhydride

• Acetic anhydride
• Ac2O
• Ethansäureanhydrid

Colorless, pungent -smelling fluid

Liquid

1.08 g · cm -3

-73 ° C

139.4 ° C

5 hPa (20 ° C)

• Soluble in water with hydrolysis. ( Violent reaction )
• Soluble in ethanol and diethyl ether

1.3901 (20 ° C)

Risk

5 ml · m -3, 21 mg · m-3

-624.4 KJ / mol

Template: Infobox chemical / molecular formula search available

Acetic anhydride ( acetic anhydride) is a chemical compound from the group of acid anhydrides having the empirical formula C4H6O3. It is an acetic acid derivative which is formed by the condensation of two molecules of acetic acid. Here, the carboxyl groups of two molecules of acetic acid combine with elimination of water.

Production

In the laboratory

Acetic anhydride can be synthesized in the laboratory by the reaction of acetyl chloride with sodium acetate with the elimination of the sodium chloride:

Instead of sodium acetate and other alkali metal salt of acetic acid can be used.

Industrial production

The industrial production is carried out by dehydration ( dehydration ) of acetic acid at 800 ° C:

In the synthesis of a rapid cooling and separation of the products is necessary, since otherwise the reaction may proceed back to acetic acid.

Another possibility is the carbonylation of methyl acetate according to the Tennessee Eastman process. A part of the product stream is reacted with methanol to methyl acetate and again returned to the process. The synthesis of the acetic anhydride therefore requires only CO and methanol. Catalysts used primarily rhodium and iridium complexes. The reaction takes place at 200 ° C under elevated CO pressure and temperatures.

Reactions

As with other anhydrides can also be acetic anhydride with alcohols to give the corresponding esters with ammonia or with amines to give the corresponding amide implement.

When placed in water, the compound is first dissolved and is then cleaved by hydrolysis to acetic acid. The cleavage is much faster than in cold water in hot water and is base- or acid-catalyzed. In cold water, the solubility is 13.6 %.

Use

Acetic anhydride is the commercially most important aliphatic anhydride. Around one million tonnes are produced per year. It is mainly used for the reaction with alcohols to acetates. Common applications include the manufacture of cellulose acetate and acetyl salicylic acid as well as the dehydration of acetic acid. It is also essential in the production of heroin, so an attempt is made in many countries to contain the control of access to acetic anhydride, the preparation of these semi-synthetic drug.

In synthetic chemistry acetic anhydride is often used for the construction of protective groups, which converts an alcohol to a less reactive ester.

Diacetyl peroxide, which is used as a radical polymerization at, can be prepared from acetic anhydride and sodium metaborate peroxidhydrat.

In admixture with sulfuric acid (9 parts to 1 part of acetic acid), it is used for acetolysis.

Further, acetic anhydride is used for the acetylation of wood, a wood modification for improving the properties ( moisture resistance, and others ) of softwoods.