Bial's test

The Bial - sample (or orcinol test ) is a specific test for pentoses. The reaction goes back to Manfred Bial.

Implementation and response

The Bial 's reagent is a solution of orcinol and FeCl3 in concentrated HCl. The test is positive if it sets a green - blue color after addition of Bial 's reagent for carbohydrate and after heating. Pentoses such as ribose, formed under the action of strong mineral acids, furfural ( Furancarbaldehyd ). The color is produced by a forming iron complex in cooperation with orcinol. Hexoses enter only by prolonged exposure to heat a positive response.

Reaction with deoxyriboses

From 2 -deoxyribose forms in acidic medium 3- Acetylacrolein. This reacts with 3,5- dihydroxy toluene ( orcinol ) in the sense of an aldol- aldehyde - phenol condensation via an intermediate oxidation to a series of violet and blue dyes. The main components were as 9 - (2- Acetylvinyl ) -dimethyl- 3- hydroxy- isoxanthon and 1 - ( dimethyl-3- isoxanthonyl ) -2 - [ (dimethyl -dihydroxy -9 -methyl- xanthenyl ) -9 ] characterized ethene.