Aldonic acid
Encyclopedia
An aldonic acid is any of a family of sugar acids obtained by oxidation of the aldehyde
functional group
of an aldose
to form a carboxylic acid
functional group. Thus, their general chemical formula is HOOC-(CHOH)n-CH2OH. Oxidation of the terminal hydroxyl
group instead of the terminal aldehyde yields a uronic acid
, while oxidation of both terminal ends yields an aldaric acid
.
Aldonic acids are typically prepared by oxidation of the sugar with bromine
. They are generally found in their lactone
form, with the ring structure essentially the same as in the original sugar's cyclic
hemiacetal
form, which is the form the sugar is usually found in. However, unlike hemiacetals, lactones do not have a chiral
anomer
ic carbon, and they cannot form glycosidic linkages.
Aldonic acids are found in many biological systems, and are the products of the oxidation of aldose
s by Benedict's
or Fehling's
reagents. Their lactones are key intermediates in the Kiliani-Fischer synthesis
of sugars.
Nomenclature of aldonic acids and their lactones is based on replacing the suffix "-ose" with "onic acid" or "onolactone" respectively; hence D-glucose
is oxidized to D-gluconic acid
and D-gluconolactone.
Aldehyde
An aldehyde is an organic compound containing a formyl group. This functional group, with the structure R-CHO, consists of a carbonyl center bonded to hydrogen and an R group....
functional group
Functional group
In organic chemistry, functional groups are specific groups of atoms within molecules that are responsible for the characteristic chemical reactions of those molecules. The same functional group will undergo the same or similar chemical reaction regardless of the size of the molecule it is a part of...
of an aldose
Aldose
An aldose is a monosaccharide that contains only one aldehyde group per molecule. The chemical formula takes the form Cnn. The simplest possible aldose is the diose glycolaldehyde, which only contains two carbon atoms....
to form a carboxylic acid
Carboxylic acid
Carboxylic acids are organic acids characterized by the presence of at least one carboxyl group. The general formula of a carboxylic acid is R-COOH, where R is some monovalent functional group...
functional group. Thus, their general chemical formula is HOOC-(CHOH)n-CH2OH. Oxidation of the terminal hydroxyl
Hydroxyl
A hydroxyl is a chemical group containing an oxygen atom covalently bonded with a hydrogen atom. In inorganic chemistry, the hydroxyl group is known as the hydroxide ion, and scientists and reference works generally use these different terms though they refer to the same chemical structure in...
group instead of the terminal aldehyde yields a uronic acid
Uronic acid
thumb|300px|The [[Fischer projection]]s of [[glucose]] and [[glucuronic acid]]. Glucose's terminal carbon's hydroxyl group has been oxidized to a [[carboxylic acid]]....
, while oxidation of both terminal ends yields an aldaric acid
Aldaric acid
Aldaric acids are a group of sugar acids, where the terminal hydroxyl groups of the sugars have been replaced by terminal carboxylic acids, and are characterised by the formula HOOC-n-COOH....
.
Aldonic acids are typically prepared by oxidation of the sugar with bromine
Bromine
Bromine ") is a chemical element with the symbol Br, an atomic number of 35, and an atomic mass of 79.904. It is in the halogen element group. The element was isolated independently by two chemists, Carl Jacob Löwig and Antoine Jerome Balard, in 1825–1826...
. They are generally found in their lactone
Lactone
In chemistry, a lactone is a cyclic ester which can be seen as the condensation product of an alcohol group -OH and a carboxylic acid group -COOH in the same molecule...
form, with the ring structure essentially the same as in the original sugar's cyclic
Cyclic compound
In chemistry, a cyclic compound is a compound in which a series of atoms is connected to form a loop or ring.While the vast majority of cyclic compounds are organic, a few inorganic substances form cyclic compounds as well, including sulfur, silanes, phosphanes, phosphoric acid, and triboric acid. ...
hemiacetal
Hemiacetal
Hemiacetals and hemiketals are compounds that are derived from aldehydes and ketones respectively. The Greek word hèmi means half...
form, which is the form the sugar is usually found in. However, unlike hemiacetals, lactones do not have a chiral
Chirality (chemistry)
A chiral molecule is a type of molecule that lacks an internal plane of symmetry and thus has a non-superimposable mirror image. The feature that is most often the cause of chirality in molecules is the presence of an asymmetric carbon atom....
anomer
Anomer
In carbohydrate chemistry, an anomer is a special type of epimer. It is one of two stereoisomers of a cyclic saccharide that differs only in its configuration at the hemiacetal or hemiketal carbon, also called the anomeric carbon. Anomerization is the process of conversion of one anomer to the other...
ic carbon, and they cannot form glycosidic linkages.
Aldonic acids are found in many biological systems, and are the products of the oxidation of aldose
Aldose
An aldose is a monosaccharide that contains only one aldehyde group per molecule. The chemical formula takes the form Cnn. The simplest possible aldose is the diose glycolaldehyde, which only contains two carbon atoms....
s by Benedict's
Benedict's reagent
Benedict's reagent is a chemical reagent named after an American chemist, Stanley Rossiter Benedict....
or Fehling's
Fehling's solution
Fehling's solution is a chemical test used to differentiate between water-soluble aldehyde and ketone functional groups, and as a test for monosaccharides. The test was developed by German chemist Hermann von Fehling in 1849.-Laboratory preparation:...
reagents. Their lactones are key intermediates in the Kiliani-Fischer synthesis
Kiliani-Fischer synthesis
The Kiliani–Fischer synthesis, named for German chemists Heinrich Kiliani and Hermann Emil Fischer, is a method for synthesizing monosaccharides. It proceeds via synthesis and hydrolysis of a cyanohydrin, thus elongating the carbon chain of an aldose by one carbon atom while preserving...
of sugars.
Nomenclature of aldonic acids and their lactones is based on replacing the suffix "-ose" with "onic acid" or "onolactone" respectively; hence D-glucose
Glucose
Glucose is a simple sugar and an important carbohydrate in biology. Cells use it as the primary source of energy and a metabolic intermediate...
is oxidized to D-gluconic acid
Gluconic acid
Gluconic acid is an organic compound with molecular formula C6H12O7 and condensed structural formula HOCH24COOH. It is one of the 16 stereoisomers of 2,3,4,5,6-pentahydroxyhexanoic acid....
and D-gluconolactone.