Testing for aldehydes and ketones Flashcards
What are the 2 tests for carbonyls?
Tollens and 2,4- DNPH
What does Tollens test for?
Aldehydes
What are the reagents/conditions for Tollen’s test?
Warm ammoniacal silver nitrate
What is the positive result for Tollen’s test?
Silver mirror forms
What is the negative result for Tollen’s?
Solution remains colourless
What does 2,4 - DNPH test for?
Aldehydes and ketones
What is the positive result for 2,4-DNPH?
An orange precipitate forms
What type of reaction is 2,4-DNPH?
Condensation
Why does the acidified potassium dichromate test require the carbonyl to be in excess?
Otherwise it would be difficult to see the colour change
Why does Tollen’s not react with ketones?
Ketones cannot be easily oxidised
Why does Tollen’s not react with primary or secondary alcohols?
It is not a powerful enough oxidising agent
What happens to silver ions in Tollen’s test?
They are reduced to silver
How can 2,4 DNPH used to identify compounds?
2,4-DNPH derivatives have characteristic melting points which can be compared to known values
