Aldaric acid is a group of
sugar acids characterised by the formula HOOC-(CHOH)n-COOH.
Aldaric acids are usually synthesized by the
oxidationof aldoses with nitric acid. In this reaction it is the open-chain (polyhydroxyaldehyde) form of the sugar that reacts.
An aldaric acid is an
aldosein which both the hydroxylfunction of the terminal carbon and the aldehydefunction of the first carbon have been fully oxidized to carboxylic acidfunctions. (Oxidation of just the aldehyde yields an aldonic acidwhile oxidation of just the terminal hydroxyl group yields an uronic acid.) Aldaric acids cannot form cyclic hemiacetals like unoxidized sugars, but they can sometimes form lactones.
Nomenclature of the aldaric acids is based on the sugars from which they are derived; for example, glucose is oxidized to glucaric acid and xylose to xylaric acid.
Unlike their parent sugars, aldaric acids have the same
functional groupat both ends of their carbon chain; therefore, two different sugars can yield the same aldaric acid (this can be understood by looking at the Fischer projectionof a sugar upside down--with normal aldoses, this is a different compound due to the aldehydefunction at the top and the hydroxylfunction at the bottom, but with aldaric acids, there is a carboxylic acidfunction on both ends, so upside down and right side up do not matter). For example, D-glucaric acid and L-gularic acid are the same compound. A consequence of this is that some aldaric acids are meso forms with no optical activitydespite their multiple chiral centers--this occurs if a sugar and its enantiomeroxidize to the same aldaric acid. An example is D- mannose--it has four chiral centers, but D-mannaric and L-mannaric acids, which have the opposite configuration at each chiral center and therefore would be expected to be enantiomers, turn out to be the same compound; therefore, mannaric acid is an achiral meso formwith no optical activity. Again, this can be understood by taking the Fischer projection of either acid and looking at it upside down--the configuration is now switched at every carbon. Adipic acid, HOOC-(CH2)4-COOH, is not an aldaric acid, though it is structurally similar. In fact, six-carbon aldaric acids can be considered tetrahydroxyl derivatives of adipic acid.
* Carey, Francis A. (2006). Organic Chemistry, Sixth Edition, New York, NY: McGraw-Hill. ISBN 0-07-111562-5.
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Sugar acid — Sugar acids are monosaccharides that have had an OH group oxidized to a carboxyl group.Main classes of sugar acids include: * Aldonic acids, in which the aldehyde functional group of an aldose is oxidized * Uronic acids, in which the terminal… … Wikipedia
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xylaric acid — noun The aldaric acid derived from xylose … Wiktionary
tetraric acid — noun Any aldaric acid having four carbon atoms … Wiktionary