Reagents Benedict

Which of the following would be expected to give a positiv test with Benedicts reagent Why ... 

Benedicts reagent (Section 25 19) A solution containing the citrate complex of CUSO4 It is used to test for the presence of reducing sugars... 

Coumarins Benedict reagent Fluorescent spots under long-wave 1... 

Fluorescamines Antimony (III) chloride (10% in chloroform) Benedict reagent Lead (IV) acetate (basic, 25%) p-Toluenesulfonic acid (20% in chloroform) Perchloric acid (70%)... 

Benedict reagent A solution that is 0.1 M in cupric sulfate, 1.0 M in sodium citrate, and 1.0 M in sodium carbonate is sprayed on the plate, which is then observed under long-wave UV light. 

H28. Hussain, Q. Z., Shah, N. S., and Chaudhuri, S. N., Estimation of serum or protein using qualitative Benedict reagent. Clin. Chim. Acta 6, 447-448 (1961). 

Benedicts reagent (an alkaline solution containing a cupric citrate complex ion) and Tollens solution [Ag (NH3)20H] oxidize and thus give positive tests with aldoses and ketoses. The tests are positive even though aldoses and ketoses exist primarily as cyclic hemiacetals. 

Acetobacter and Pseudomonas strains readily convert glucose to gluconate, and this substance is then oxidized to 2-ketogluconate or to 5-ketogluconate. These substances may be distinguished by the ability of 2-keto acids to form spectrophotometrically detectable quinoxalines. 5-Ketogluconate reduces Benedicts reagent at 25 C. The marked reactivity of the latter presumably... 

Aromatic aldehydes react with the dimedone reagent (Section 111,70,2). All aromatic aldehydes (i) reduce ammoniacal silver nitrate solution and (ii) restore the colour of SchifiF s reagent many react with sodium bisulphite solution. They do not, in general, reduce Fehling s solution or Benedict s solution. Unlike aliphatic aldehydes, they usually undergo the Cannizzaro reaction (see Section IV,123) under the influence of sodium hydroxide solution. For full experimental details of the above tests, see under Ali-phalic Aldehydes, Section 111,70. They are easily oxidised by dilute alkaline permanganate solution at the ordinary temperature after removal of the manganese dioxide by sulphur dioxide or by sodium bisulphite, the acid can be obtained by acidification of the solution. 

A characteristic property of an aldehyde function is its sensitivity to oxidation A solu tion of copper(II) sulfate as its citrate complex (Benedict s reagent) is capable of oxi dizing aliphatic aldehydes to the corresponding carboxylic acid... 

The formation of a red precipitate of copper(I) oxide by reduction of Cu(II) is taken as a positive test for an aldehyde Carbohydrates that give positive tests with Benedict s reagent are termed reducing sugars... 

Benedict s reagent is the key material in a test kit avail able from drugstores that permits individuals to mom tor the glucose levels in their urine... 

Oxidation with Benedict s reagent (Section 25 19) Sugars that con tain a free hemiacetal function are called reducing sugars They react with copper(ll) sulfate in a sodium citrate/sodium carbonate buffer (Benedict s reagent) to form a red precipitate of copper(l) oxide Used as a qualitative test for reducing sugars... 

Reducing sugar (Section 25 19) A carbohydrate that can be oxidized with substances such as Benedict s reagent In general a carbohydrate with a free hydroxyl group at the anomenc position... 

Benedict s qualitative reagent (for glucose) dissolve 173 g of sodium citrate and 100 g of anhydrous sodium carbonate in about 600 mL of water, and dilute to 850 mL dissolve 17.3 g of CUSO4 5H2O in 100 mL of water and dilute to 150 mL this solution is added to the citrate-carbonate solution with constant stirring. See also the quantitative reagent below. 

Benedict s quantitative reagent (sugar in urine) This solution contains 18 g copper sulfate, 100 g of anhydrous sodium carbonate, 200 g of potassium citrate, 125 g of potassium thiocyanate, and 0.25 g of potassium ferrocyanide per liter 1 mL of this solution = 0.002 g sugar. 

Fig. 1 Chromatograms of two natural product extracts and associated reference substances A. before and R after application of Benedict s reagent.

Fig. 2 Increase in fluorescence of the genuine fluorescence (A) by treatment with Benedict s reagent (B) and immersion in a paraffin solution (C) and reduction of emission intensities with time for the two cumarins umbelliferone and scopoletin (curves).

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