acetaldehyde

acetaldehyde

acetaldehyde (ăsˌĭtălˈdəhīd) or ethanal (ĕthˈənălˌ), CH₃CHO, colorless liquid aldehyde, sometimes simply called aldehyde. It melts at −123℃, boils at 20.8℃, and is soluble in water and ethanol. It is formed by the partial oxidation of ethanol; oxidation of acetaldehyde forms acetic acid. Acetaldehyde is made commercially by the oxidation of ethylene with a palladium catalyst (see Wacker process). It is used as a reducing agent (e.g., for silvering mirrors), in the manufacture of synthetic resins and dyestuffs, and as a preservative. When treated with a small amount of sulfuric acid it forms paraldehyde, (CH₃CHO)₃, a trimer, which is used as a hypnotic drug.

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The following article is from The Great Soviet Encyclopedia (1979). It might be outdated or ideologically biased.

Acetaldehyde

 

acetic aldehyde, CH₃CHO, an organic compound; a colorless liquid with a sharp odor. Its boiling point is 20.8°C; its melting point, - 124°C. Its density is 783 kg/m³, and it is miscible in all proportions with water, alcohol, and ether. Acetaldehyde possesses all the properties characteristic of the aldehydes. In the presence of mineral acids it polymerizes into liquid trimeric paraldehyde (CH₃CHO)₃ and the crystalline tetrameric metaldehyde (CH₃CHO)₄. When both polymers are heated in the presence of sulfuric acid, acetaldehyde is liberated.

One of the long-known, basic methods for the preparation of acetaldehyde consists in combining water with acetylene in the presence of mercuric salts at a temperature of about 95°C (Kucherov’s reaction):

Because of the high cost and toxicity of mercury, another method for the direct catalytic hydration of acetylene has been worked out. A variant of indirect hydration is also possible; it consists in combining alcohol with acetylene in the presence of solid KOH, followed by saponification of the vinyl ether:

Acetaldehyde is also produced from ethyl alcohol by catalytic dehydrogenation at approximately 400°C. When acted upon by aluminum alkoxides, the acetaldehyde is transformed into ethylacetate (Tishchenko’s reaction):

This method has industrial significance. The oxidation of acetaldehyde by atmospheric oxygen over a catalyst is an industrial method for obtaining acetic anhydride. Acetaldehyde participates easily in aldol condensation:

2CH₃CHO → CH₃—CH(OH)—CH₂—CHO

Acetaldehyde is used in huge quantities in the production of acetic acid and acetic anhydride, in the preparation of various pharmaceuticals, and so on.

The Great Soviet Encyclopedia, 3rd Edition (1970-1979). © 2010 The Gale Group, Inc. All rights reserved.

acetaldehyde

[‚as·əd′al·də‚hīd]

(organic chemistry)

C₂H₄O A colorless, flammable liquid used chiefly to manufacture acetic acid.

McGraw-Hill Dictionary of Scientific & Technical Terms, 6E, Copyright © 2003 by The McGraw-Hill Companies, Inc.

acetaldehyde

a colourless volatile pungent liquid, miscible with water, used in the manufacture of organic compounds and as a solvent and reducing agent. Formula: CH₃CHO

Collins Discovery Encyclopedia, 1st edition © HarperCollins Publishers 2005