Aldehyde
Any of a class of organic compounds containing the CHO group, ncluding formaldehyde and acetaldehyde
[90]
Aldehydes are carbonyl compounds with the general formula R CH O, where R is a hydrocarbon radical. The carbonyl functional group > C O is bonded in aldehydes to a hydrogen atom and a carbon atom. Several naming procedures are used for aldehydes. A standard procedure starts with the name of the longest carbon chain containing the aldehyde group and replacing the suffix -e with -al (e.g., methanal, ethanal, etc.). It is also common to name the aldehyde starting with the name of the acid from which the aldehyde derives (by the replacement of the COOH group with the CHO group). This is done by changing the suffix -ic acid or -oic acid with -aldehyde (e.g., formaldehyde from formic acid, acetaldehyde from acetic acid, etc.) In other procedures, the CHO group is indicated by the suffix carboxaldehyde or by the prefix oxo-.[91]
Aldehydes, ketones, carboxylic acids, and carboxylic acid derivatives can be reduced to alcohols. Historically, catalytic reduction with hydrogen and a catalyst such as platinum oxide or Raney nickel was employed to form the hydroxylic product in high yields.[92]
Aldehydes usually must be kept from contactwith air and under certain circumstances must bestabilized during distillation, subsequent storage ,and transportation. This applies particularly tounsaturated aldehydes, which have a tendency topolymerize (e.g., on contact with alkali). Forcommerical purposes aldehydes often are pro-tected by the addition of stabilizers and antiox-idants and by a nitrogen atmosphere. Whenhandling aldehydes, care must be taken to pre-vent either the liquids or their vapors from com-ing into contact with respiratory organs, eyes, and skin. Gloves and safety glasses are absolutelynecessary. Aldehydes are obtained mainly via the oxosynthesis, by mild oxidation (dehydrogenation)of primary alcohols, and by special olefin oxida-tion processes. Low concentrations of aldehydesoccur naturally in essential oils of various plants. Acetaldehyde is an intermediate product of alco-hol fermentation; it is formed by decarboxylationof the intermediate pyruvic acid. Aldehydes alsofulfill some important biological functions, e.g.,11-cis-retinal in the sight process or as pyridoxalin the transamination of amino acids. Their iso-lation from natural substances is of commercialsignificance only in a few cases, e.g., in theproduction of longer-chain fragrance aldehydes.[93]
Webster’s New World College Dictionary, 4th Edition. 2010 by Houghton Mifflin Harcourt. All rights reserved.
Serban C. Moldoveanu, Pyrolysis of Organic Molecules (Second Edition), 2019.
John Welch, Encyclopedia of Physical Science and Technology (Third Edition), 2003.
Kohlpaintner, C.; Schulte, M.; Falbe, J.; Lappe, P. and Weber, J. (2008) "Aldehydes, Aliphatic" in Ullmann's Encyclopedia of Industrial Chemistry. Wiley-VCH, Weinheim.