Benedict reagent

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The Benedict reagent is a reagent that is used in organic chemistry under the name " Benedict reaction " for the detection of reducing sugars , flavonoids and coumarins . It was invented in 1908 by the American chemist Stanley Benedict (1884–1936).

Composition and manufacture

The reagent consists of two solutions. The first solution contains sodium citrate (sodium salt of citric acid ) and sodium carbonate , which are dissolved in water . A second solution of copper (II) sulfate in water is added. By replacing hydroxide with carbonate, the reagent is less corrosive, and by using citrate instead of tartrate it is more stable than Fehling's reagent . The Benedict reagent can be z. B. in a school chemistry laboratory with simple means: You need four 250 mL bottles (similar to Fehling's reagent I and II) and four Benedict labels, a heating plate with magnetic stirrer, a stirring magnet, and a 1000 mL beaker , 173 g sodium citrate, 100 g anhydrous sodium carbonate (or 270 g sodium carbonate decahydrate) and approx. 600 mL demineralized water (tip: the sodium carbonate dissolves better when heated). In a second vessel, 17.3 g copper sulphate pentahydrate are dissolved in approx. 100 mL demineralized water. Then both solutions are combined with stirring, after cooling in the volumetric flask, the volume is made up to 1000 mL and divided between the four bottles and given the correct labels.

proof

Like the Fehling's reagent, the Benedict reagent is used to detect reducing sugars , flavonoids and coumarins . A precipitate then separates out in the solution, which is red, yellow or green depending on the sugar concentration. In school chemistry lessons, it is preferable to use Fehling's reagent for risk assessment , as sodium carbonate is used instead of sodium hydroxide and therefore there is less risk with the same effect.

Reaction scheme

The organic compound is formally oxidized by the copper ions. A precipitate of copper (I) oxide and the corresponding organic compound is formed, using the example of an aldehyde:

The reaction must take place in the alkaline range.

Individual evidence

  1. ↑ a b c d Stanley Benedict: A reagent for the detection of reducing sugars . In: J. Biol. Chem. , 1909, 5, pp. 485-487.
  2. ^ Robert D. Simoni, Robert L. Hill, Martha Vaughan: Benedict's Solution, a Reagent for Measuring Reducing Sugars: the Clinical Chemistry of Stanley R. Benedict . In: J. Biol. Chem. , 2002, 277, 16, 5, pp. 10-11.
  3. ↑ Klaus Ruppersberg: Benedict instead of Fehling: safer, easier, more durable! In: Science in Class: Chemistry . tape 27 , no. 156 . Friedrich-Verlag, 2016, p. 49-50 .
  4. ↑ Entry on Benedict's reagent. In: Römpp Online . Georg Thieme Verlag, accessed on January 3, 2015.

See also