Organic 2 Review Problem 359

Organic 2 Review Problem 359 - REACTIONS A ND I...

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REACTIONS AND IDENTIFICATION 343 frequently fail to reduce Fehling's solution, since the alkali of the latter is neutralised by the acid present. On the other hand, an excess of Fehling's solution is not recommended, as the blue colour may then mask the ensuing reduction. Therefore proceed thus: To i ml. of the aldehyde or aldehyde solution, add about i ml. of 10% Na 2 CO 3 solution and then a few drops of Fehling's solution, and boil the mixture gently for i minute: the solution usually turns green and on standing a fine yellow or red precipitate* of cuprous oxide slowly separates. A control experiment using Fehling's solution alone should always be carried out to ensure that no reduction takes place on boiling. Aliphatic aldehydes reduce Fehling's solution rapidly, benzaldehyde very slowly and indecisively, salicylaldehyde does not reduce it. 6. Oxidation to acids. Warm together in a small conical flask on a water-bath for io minutes a mixture of 0-5 ml. of benzaldehyde or salicylaldehyde, 15 ml. of saturated KMnO
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