Organic 2 Review Problem 405

Organic 2 Review Problem 405 - limate on the cooler parts...

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REACTIONS AND IDENTIFICATION 389 Section 24. Purines. Uric acid or 2,6,8-trihydroxypurine, C 6 H 4 N 4 O 8 . HN C:O N==C-OH I l I l O:C C NH HO.C C N I I >C:0 ^ Il Il >C.OH HN C NH N C NH (A) Keto or lactam form. (B) Enol or lactim form. Physical Properties. White solid almost insoluble in water and in ethanol. It is a weak acid and exists in the tautomeric forms (A) and (B) above. It dissolves in alkali hydroxide solutions, giving salts of the type C 6 H 2 Na 2 N 4 O 3 , the free acid being reprecipitated from such solutions on the addition of HCl or acetic acid: it is also soluble in solutions of borates, phosphates, carbonates and acetates of the alkali metals. It dissolves in cone. H 2 SO 4 , and is reprecipitated on addition of water. REACTIONS. 1. Chars on being heated. 2. Gives murexide on treatment with cone. HNO 8 and then ammonia. 3. Solution in aqueous Na 2 CO 3 reduces silver nitrate (Scruff's test). 4. Reduces Fehling's solution. 5. Reduces alkaline KMnO 4 in the cold. 1. Action of heat. Heat about 0-2 g. of uric acid in a hard-glass test-tube. Note the charring and also the formation of a white sub-
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Unformatted text preview: limate on the cooler parts of the tube. 2. Murexide test. Place about o-1 g. of uric acid in a small evapor-ating-basin and moisten with 2-3 drops of cone. HNO 3 . Heat very gently to dryness, and then add i drop of aqueous NH 8 from a glass rod: a purple coloration is produced due to the formation of ammonium purpurate or murexide.* Now add a drop of NaOH solution: the coloration changes to blue. 3. Schiff's test. Dissolve about oi g. of uric acid in Na 2 CO 8 solution and pour some of this solution on to a filter-paper which has been moistened with AgNO 8 solution: a black stain of metallic silver results. 4. Reduction of Fehling's solution. Dissolve o-i g. of uric acid in Na 2 CO 3 solution, and to the clear solution add Fehling's solution drop by drop. Note the formation of a white precipitate of copper * Murexide is probably...
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