Which of the following describes the reaction where a monosaccharide reacts with a mild oxidizing agent ? a) Reduction to form a sugar alcohol b) Oxidation to form an aldonic acid c) Esterification to form a glycoside d) Condensation to form a disaccharide
The correct answer and explanation is:
The correct answer is b) Oxidation to form an aldonic acid.
When a monosaccharide reacts with a mild oxidizing agent, the aldehyde group of the sugar is typically oxidized. This oxidation results in the formation of an aldonic acid. Aldonic acids are derived from aldoses (monosaccharides with an aldehyde group) through oxidation of the aldehyde into a carboxylic acid group, while the rest of the molecule remains unchanged.
Monosaccharides such as glucose or galactose, when subjected to a mild oxidizing agent like bromine water or mild nitric acid, undergo oxidation. In the case of glucose, for example, the aldehyde group at the carbon-1 position is oxidized to form a carboxyl group, converting glucose into gluconic acid, which is an aldonic acid.
Aldonic acids are important intermediates in carbohydrate metabolism and are also used in various industrial processes, such as the production of sweeteners and in certain pharmaceuticals. The reaction is not a complete oxidation that would yield an aldaric acid (which would require a stronger oxidizing agent), but rather a mild oxidation that targets only the aldehyde group.
The other options provided are not correct for the following reasons:
- a) Reduction to form a sugar alcohol: This refers to the process where a monosaccharide is reduced, typically using a reducing agent like hydrogen or sodium borohydride, converting the aldehyde group into a hydroxyl group, forming a sugar alcohol like sorbitol.
- c) Esterification to form a glycoside: Glycoside formation occurs through a condensation reaction between a monosaccharide and an alcohol, not through oxidation.
- d) Condensation to form a disaccharide: This refers to the glycosidic bond formation between two monosaccharides, typically requiring the removal of a water molecule, not an oxidation reaction.
Thus, oxidation of a monosaccharide with a mild oxidizing agent leads to the formation of an aldonic acid.