Herman Von Fehling: A Biography

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Herman von Fehling was a German chemist, who developed Fehling’s solution which was used for estimations of sugar. The Fehling’s solution is a chemical test used to differentiate between water-soluble carbohydrates and ketone functional groups, and as a test for monosaccharide. When working with Fehling’s solution, Fehling took extra precautionary measurements when working in the laboratory. He created two separate solutions known as Fehling’s A and Fehling’s B. Fehling’s A is a blue solution of Copper II, Sulfate, while Fehling’s B is a clear solution of potassium, sodium, tartrate (Rhochelle Salt) and a strong alkali (Sodium hydroxide). The volumes of the two mixtures are mixed to get the final Fehling’s solution. In this mixture, the aqueous tartrate ions from the dissolved Rochelle salt ions from the dissolved Copper II sulfate, as bidentate ligands giving bistartratocuprate II. The tartarate ions, by completing copper, prevent the formation of Cu(OH)2 from the reaction of CuSO42H2O and NaOH in the solution. Fehling’s solution is an oxidizing agent in the Bistartratocuprate II and the active reagent in the test. The compound being tested is added to Fehling’s solution and the mixture is heated. The aldehydes are oxideized, giving a positive result, but ketones do not reacte, unless they are alpha-hydroxy-ketones. The bistratratocuprate II is a complex oxidizes the aldehyde to the carboxylate anion, and in the process the copper II ions of the xomplex are reduced to Copper I ions. A negative result is the absence of the red precipitate; Fehling’s will NOT work with aromatic aldehydes; in that case Tollen’s reagent – a chermical reagent most commonly used to determine whether a known carbonyl contation compound is an aldehyde or a ketone, a positive test with Tollen’s reagent sults in elemental silver precipitation out of solution, occasionally outo the inner surface of the tube, productiona characteristic and memorable “silver mirror” on the inner serface -...
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