Molish reaction is a qualitative reaction to the presence of carbohydrates in the solution .
Description
The message of the reaction discovered by him was published in 1886 by the Austrian botanist Hans Molish [1] . This is a very sensitive test for carbohydrates, based on the dehydration of carbohydrate with sulfuric acid to convert it into aldehyde , which reacts with two molecules of phenol - α-naphthol , resorcin or thymol - to form a red or purple compound.
To carry out the reaction, first the test solution (for example, 1 ml of water with several sugar crystals dissolved in it) is mixed in a test tube with a small amount of an alcohol solution of α-naphthol, resorcinol or thymol (for example, a few drops of an alcohol solution of resorcinol). After mixing, the tube is tilted slightly and a small amount (for example, 2 ml) of concentrated sulfuric acid is poured along its wall, and then returned to the vertical position. In this case, the acid, due to its greater density than that of water, falls to the bottom - it is located as a layer under the layer of the test solution. If the Molish reaction is positive, a red or purple ring forms between the layers of acid and the test substance [2] .
All carbohydrates - monosaccharides , disaccharides and polysaccharides - give a positive Molish reaction, as do nucleic acids and glycoproteins , since all these compounds undergo hydrolysis with a strong acid, turning into monosaccharides. Pentose is then dehydrated into furfural and hexose into 5-hydroxymethylfurfural. Both of these aldehydes, if present, condense with two molecules of phenol and form a red or purple compound.
Notes
- ↑ Molisch, Hans. Zwei neue Zuckerreactionen ( Neopr .) // Monatshefte für Chemie. - 1886. - V. 7 , № 1 . - p . 198-209 .
- ↑ Experiments with carbohydrates // Encyclopedic Dictionary of the young chemist. 2nd ed. / Comp. V. A. Kritzman, V. V. Stanzo. - M .: Pedagogy , 1990. - p . 247 . - ISBN 5-7155-0292-6 .