An organic compound (A) with molecular formula C8H8O forms an orange-red precipitate with 2,4-DNP reagent and gives yellow precipitate on heating with iodine in the presence of sodium hydroxide. It neither reduces tollens' or fehlings' reagent, nor does it decolourise bromine water or Baeyer's reagent. On drastic oxidation with chromic acid, it gives a carboxylic acids (B) having molecular formula C7H6O2. Identify the compounds (A) and (B) and explain the reactions involved.
 

  1. ‘A’ forms an orange colour precipitate with 2,4-DNP so it is an aldehyde or a ketone and also gives iodoform test so it must be having CH3-CO- group.
  2. Since ‘A’ does not reduce Tollen’s or Fehling’s reagent, it must be a ketone.
  3. The molecular formula shows that there should be unsaturation in the compound but ‘A’ does not decolourise bromine water or Bayer’s reagent which shows that the presence of unsaturation is due to benzene ring.
  4. On drastic conditions of oxidation, ’A’ which is a ketone changes to carboxylic acid ‘B’ containing one carbon less which is true for C6H5-CO-CH3.
  5. The molecular formula of ’B’ shows that it should be benzoic acid.
  6. Since total number of carbon atoms are eight in ‘A’[C8H8O], therefore, compound ‘A  should be phenyl methyl ketone or acetophenone [C6H5-CO-CH3].

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 A=acetophenone

B=benzoic acid

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how? elaborate it............

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