Osazones are a class of
carbohydrate derivatives found in
organic chemistry formed when
reducing sugars
A reducing sugar is any sugar that is capable of acting as a reducing agent. In an alkaline solution, a reducing sugar forms some aldehyde or ketone, which allows it to act as a reducing agent, for example in Benedict's reagent. In such a reactio ...
are reacted with excess of
phenylhydrazine at boiling temperatures.
Formation
Osazone formation was developed by
Emil Fischer, who used the reaction as a test to identify
monosaccharide
Monosaccharides (from Greek ''monos'': single, '' sacchar'': sugar), also called simple sugars, are the simplest forms of sugar and the most basic units (monomers) from which all carbohydrates are built.
They are usually colorless, water-solub ...
s.
The formation of a pair of
hydrazone
Hydrazones are a class of organic compounds with the structure . They are related to ketones and aldehydes by the replacement of the oxygen =O with the = functional group. They are formed usually by the action of hydrazine on ketones or aldehydes. ...
functionalities involves both oxidation and condensation reactions. Since the reaction requires a free carbonyl group, only "reducing sugars" participate.
Sucrose
Sucrose, a disaccharide, is a sugar composed of glucose and fructose subunits. It is produced naturally in plants and is the main constituent of white sugar. It has the molecular formula .
For human consumption, sucrose is extracted and refined ...
, which is nonreducing, does not form an osazone.
:
:
Appearance
Osazones are highly coloured and crystalline compounds. Osazones are readily distinguished.
*Maltosazone (from
maltose
}
Maltose ( or ), also known as maltobiose or malt sugar, is a disaccharide formed from two units of glucose joined with an α(1→4) bond. In the isomer isomaltose, the two glucose molecules are joined with an α(1→6) bond. Maltose is the two- ...
) forms petal-shaped crystals.
*Lactosazone (from
lactose
Lactose is a disaccharide sugar synthesized by galactose and glucose subunits and has the molecular formula C12H22O11. Lactose makes up around 2–8% of milk (by mass). The name comes from ' (gen. '), the Latin word for milk, plus the suffix '' - ...
) forms powder puff-shaped crystals.
*Galactosazone (from
galactose) forms rhombic-plate shaped crystals.
*Glucosazone (from
glucose,
fructose
Fructose, or fruit sugar, is a Ketose, ketonic monosaccharide, simple sugar found in many plants, where it is often bonded to glucose to form the disaccharide sucrose. It is one of the three dietary monosaccharides, along with glucose and galacto ...
or
mannose) forms broomstick or needle-shaped crystals.
Historic references
*
*
*
References
{{Reflist
Carbohydrates
Hydrazones
Emil Fischer