Bial's reagent
Bial's reagent is a reagent used to test for pentoses. It is a solution of 3,5-dihydroxytoluene (orcinol) in concentrated hydrochloric acid with a catalytic amount of iron(III) chloride.
Reagent
The reagent is prepared by dissolving 2 g of 3,5-dihydroxytoluene (orcinol) in concentrated hydrochloric acid with 1.5 cm3 of 370 mmol dm−3 iron(III) chloride solution,[note 1] and diluting to 1 litre with concentrated hydrochloric acid.[1][note 2] The final solution is 16 mmol dm−3 in 3,5-dihydroxytoluene and 550 µmol dm−3 in iron(III). The reagent should be stored in dark glass bottles away from direct light.
Test
A few drops of the solution to be tested are added to about 1 cm3 of the reagent in a test tube. The mixture is heated to 100 °C and kept at that temperature for three to five minutes, then allowed to cool. The appearance of a green-blue colouration indicates the presence of pentoses (including nucleosides), while hexoses can give a greenish-yellow colouration.
Notes and references
Notes
- ↑ The iron(III) chloride solution is prepared by dissolving 100 g of iron(III) chloride hexahydrate and 20 cm3 of concentrated hydrochloric acid in water and diluting to one litre.
- ↑ An alternative preparation dissoves the 3,5-dihydroxytoluene in 500 cm3 of concentrated hydrochloric acid with the iron(III) chloride solution, the dilutes to one litre with water. The final acid concentration is approximately 6 mol dm−3.
References
- ↑ CRC Handbook of Chemistry and Physics, 62nd ed.; Weast, Robert C., Ed.; CRC Press: Boca Raton, FL, 1981; p D-111. ISBN 0-8493-0462-8.
External links
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