Fehling’s reagent

Aubertein Rehling (Ref 15) have shown that treatment with water at approx 100° causes PETN to hydrolyze. At 125° and under pressure, hydrolysis proceeds quite quickly, and is considerably enhanced by the presence of 0.1% HNO3. Regardless of whether it occurs in water alone or in water acidified with nitric acid, the hydrolysis produces mainly Penta-erythritol Dinitrate. A dil NaOH soln causes PETN to hydrolyze.more rapidly than acidified water. PETN neither reduces Fehling s reagent nor enters into addition products with any aromatic nitro compd. In this respect it differs from both Erythritol Tetranitrate and Nitro-mannitol... 

Fehling s reagent analychem A solution of cupric sulfate, sodium potassium tartrate, and sodium hydroxide, used to test for the presence of reducing compounds such as sugars. fal-iijz re,a-j3nt ... 

Figure 2.37 Oxidation of lactose by alkaline copper sulphate (Fehling s reagent).

Given the structure of a sugar, write equations for its reaction with each of the following reagents acetic anhydride, bromine water, nitric acid, sodium borohydride, and Tollens or Fehling s reagent. 

Place 3 mL of 2% sucrose solution in each of two labeled test tubes. To the first test tube (no. 1), add 3 mL of water and 3 drops of dilute sulfuric acid solution (3 M H2S04). To the second test tube (no. 2), add 3 mL of water and 3 drops of dilute sodium hydroxide solution (3 M NaOH). Heat the test tubes in a boiling water bath for about 5 min. Cool both solutions to room temperature. To the contents of test tube no. 1, add dilute sodium hydroxide solution (3 M NaOH) (about 10 drops) until red litmus paper turns blue. Test a few drops of each of the two solutions (test tube nos. 1 and 2) with Fehling s reagent as described before. Record your results on your Report Sheet. 

When a reducing sugar reacts with Fehling s reagent, what will be the product besides Cu20 ... 

Sample Condition of hydrolysis Fehling s reagent (positive or negative)... 

Lake other aldehydes, aldoses are easily oxidized to yield the corresponding monocarboxylic acids, called aldomic acids. Aldoses react with Tollens reagent lAg in aqueous Fehling s reagent (Cu in aqueous sodium... 

Nonreducing sugar (Section 27.9B) A carbohydrate that cannot he oxidized by Tollens, Benedict s, or Fehling s reagent. 

Fehling s reagent contains complexed blue copper ions in the +2 oxidation state, and these are reduced when heated with aldehydes to a red precipitate of copper(I) oxide, CU2O. Ketones are not able to do these reactions. 

The typical aldehyde reactions of D-(-H)-glucose—osazone formation, and perhaps reduction of Tollens and Fehling s reagents—are presumably due to a small amount of open-chain compound, which is replenished as fast as it is consumed. The concentration of this open-chain structure is, however, too low (less than 0.5%) for certain easily reversible aldehyde reactions like bisulfite addition and the Schiff test. 

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