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a) Suggest a method of preparation of benzaldehyde from toluene.

b) Aldehydes and ketones differ in their chemical reactions. How do they react with the following?

i) Tollen’s reagent

ii) Alcohol.

c) How will you convert propanoic acid into the following compounds?

i) Ethane

ii) Butane.

1 Answer

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a) Toluene on treating with chromyl chloride give benzaldehyde.This reaction is called Etard reaction.

b) i) Tollens’ Test: on warming an aldehyde with freshly prepared ammonical silver nitrate solution (Tollens’ reagent), a bright silver mirror is produced due to the formation of silver metal.

RCHO+2[Ag(NH3)2]++3OH→RCOO+2Ag+2H2O+4NH3

Ketones, will not anwserTollens’ test.

ii) Aldehydes react with one equivalent of monohydric alcohol in the presence of dry hydrogen chloirde to yield alkoxy alcohol known as hemiacetalswhich further react with one more molecule of alcohol to give a gem-dialkoxy compound known as acetal.

Ketones react with ethylene glycol in presence of dry hydrogen chloride to form cyclic products known as ethylene glycol ketals.

c) Propanoic acid → Ethane

OR

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