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Slide 1

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Test for Carbonyls
Brady's Reagent
2,4-dinitrophenylhydrazine (2,4-DNPH)
Dissolved in methanol and conc. sulphuric acid
Forms bright orange precipitate if carbonyl
group is present
Only with C=O groups not COOH. Therefore
only aldehydes and ketones.
Melting Point Technique
Orange precipitate is derivative of the carbonyl
Different carbonyl compound will produce a
different derivative with a different melting point
Therefore the melting point of the derivative
can be compared against the known melting
points of the derivatives so the carbonyl
compound can be identified.…read more

Slide 2

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Tollens' Reagent
AgNO3 dissolved in aqueous ammonia
Used to distinguish between an aldehyde and a ketone
Aldehydes can be easily oxidised whereas ketones
When aldehydes are oxidised, the oxidising agent is
Therefore Tollens' reagent can be used to oxidise the
aldehyde which changes colour when it is reduced
Tollens' reagent is colourless but forms a silver mirror
when reduced
Ag+(aq) + e- -------> Ag (s)
Silver ions in the Tollens' reagent are reduced from the
electrons which come from the oxidation of the aldehyde.
Ag forms the silver mirror
Ketones aren't oxidised and won't react with Tollens'
reagent. Therefore no colour change…read more


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