Bial sample

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The bial probe (or orcin test ) is a specific test for pentoses . The reaction goes back to Manfred Bial (1869–1908).

Execution and response

The Bial reagent is a solution of orcin and FeCl 3 in concentrated hydrochloric acid . The test is positive if a green-blue color changes after adding Bial reagent to the carbohydrate and after heating. Pentoses, for example ribose, form furfural (furancarbaldehyde) under the action of strong mineral acids . The color is caused by an iron complex that forms in conjunction with orcin. Hexoses only give a positive reaction after prolonged exposure to heat.

The bial sample with ribose.

Reaction with deoxyriboses

From 2-deoxyribose, 3-acetylacrolein is formed in an acidic medium. This reacts with 3,5-dihydroxytoluene (orcin) in the sense of an aldol-like aldehyde-phenol condensation via an intermediate oxidation to a series of purple and blue dyes. The main components were characterized as 9- (2-acetylvinyl) -dimethyl-hydroxy-3-isoxanthone and 1- (dimethyl-3-isoxanthonyl) -2 - [(dimethyl-dihydroxy-9-methyl-xanthenyl) -9] -ethene .

See also

Individual evidence

  1. ↑ M. Bial: About the diagnosis of pentosuria with the reagent I have indicated. In: DMW - German Medical Weekly. 29, 1903, p. 477, doi : 10.1055 / s-0028-1138555 .
  2. ↑ Flörke / Wolff: Chemistry course topics , Volume 2, Organic Chemistry and Biochemistry, Bonn 1982, ISBN 3-427-43121-5 , pp. 6/10.
  3. ↑ K.-D. Flossmann, W. Erler: “On the mechanism of the color reaction of DNA and 2-deoxyribose with orcin”, in: Journal für Praktische Chemie , 1971 , 313  (2), pp. 314-330 ( doi : 10.1002 / prac.19713130217 ).

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