17.1.4—2,4-DNPH carbonyl test
- Syllabus
- 9701–2028–2029
- Objective
- 17.1.4
- Level
- AS
2,4-DNPH detects aldehydes and ketones by forming an orange carbonyl derivative
2,4-dinitrophenylhydrazine reacts with aldehydes and ketones, which contain a C=O group, to form a yellow/orange precipitate of a 2,4-dinitrophenylhydrazone.
The test confirms a carbonyl compound but does not distinguish aldehyde from ketone. Use it alongside an oxidation test or spectroscopy when the structure is unknown.
An unknown gives an orange precipitate with 2,4-DNPH, showing it contains an aldehyde or ketone. Tollens’ reagent can then distinguish which one.
2,4-DNPH is not a general alcohol test and a positive result does not identify the exact carbon chain.
ConceptA-Level CAIE Chemistry AS