TOLLENS’ TEST CHEMICAL TEST :
Purpose : Reagent and condition: Used to differentiate aldehydes from ketones. [Ag(NH3 )2 ] + , −OH Tollens’ reagent is a solution containing silver diamine ion complex, [Ag(NH3 )2 ] + . It is prepared by titrating aqueous ammonia to alkaline solution of silver nitrate until the precipitate formed just dissolves.
Tollens’ reagent oxidises aldehydes to carboxylate salts and it is reduced to metallic silver which appear as silver mirror on the walls of the test tube or a grey precipitate. Tollens’ reagent gives a negative result with all ketones except with α−hydroxyketones.
R C O + | H [Ag(NH3 )2 ] + + −OH O− Ag General equation : aldehyde ||| ||| R C O + | silver mirror Observation: Silver mirror or grey precipitate formed.
EXERCISE: C O H State what would be observed if the compound is reacted with Tollens’ reagent. Give the structure of the organic products formed. C O O - Silver mirror formed. ANSWER : Referring to the following compound,