Ethenone

• Ketene
• Carbomethen
• Ketoethylen

Highly flammable, colorless gas with a pungent odor

Gaseous

1.93 g · m-3

-151 ° C

-56 ° C

Hydrolyzed in water

-47.5 KJ / mol

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Ethenon or ketene ( stress on the second syllable ketene ) is the simplest chemical compound from the group of ketenes and can be regarded as an internal anhydride of acetic acid.

Production and representation

Ketene is formed by dehydration of acetic acid or in the pyrolysis of acetone. Thus, in the acetone vapors by passing heated or electrically heated tubes, metal wires at 500-600 ° C in the presence of a small amount of carbon disulfide Ethenon addition to methane in yields of up to 95% of theory formed. The Ketonpyrrolyse has since been largely replaced in industrial chemistry from the dehydration of acetic acid ( Schmidlin Bergman Wilsmore reaction).

Ethenon was about the same time by Hermann Staudinger - by reaction of bromoacetyl bromide with metallic zinc - and NTM Wilsmore - by thermal decomposition of acetic anhydride - found.

Properties

Ethenon is chemically unstable. The gas is reasonably resistant only at low temperatures (-80 ° C). There must always be re-established and the same processed, otherwise an dimerization to diketene done, or polymerized further to intractable polymers. The proportion of polymer in the production of diketene is therefore also reduced, for example by addition of sulfur dioxide to the ketene gas or the reaction medium. Because of its cumulative double bonds Ethenon is highly reactive and adds nucleophilically H -acidic compounds to the corresponding acetic acid derivatives; it is hydrolyzed, for example with water to form acetic acid or reacted with prim. or sec. Amines to the corresponding acetamides.

Ketene is highly toxic; toxicity is about eight times of phosgene.

Use

Ethenon used for the production of acetic anhydride from acetic acid. Generally, it is used for the acetylation of chemical compounds.

Ethenon reacts with formaldehyde in the presence of Lewis acids such as AlCl3, ZnCl2 and BF3 as a catalyst to β -propiolactone. The industrially most important use of Ethenon the synthesis of sorbic acid from the reaction of crotonaldehyde (2- butenal ) with ketene in toluene at about 50 ° C in the presence of zinc salts of long chain carboxylic acids. This results in a polyester of 3-hydroxy -4- hexenoic acid, which is thermally or hydrolytically depolymerised to sorbic acid.

Safety

Ethenon prone to spontaneous polymerization. The contact with hydrogen peroxide leads to an explosive reaction. The vapors of ketene can combine with air to form an explosive mixture.