BRAINCAKE2,4-DNPH Test
2,4-dinitrophenylhydrazine (2,4-DNPH, also called Brady's reagent) is used to test for the carbonyl group, C=O, in aldehydes and ketones. It is usually used as a solution in methanol and sulfuric acid.
Add a few drops of the compound to the 2,4-DNPH solution. A positive result is a yellow or orange precipitate of a 2,4-dinitrophenylhydrazone. Both aldehydes and ketones give a positive result, so this test shows that a carbonyl group is present but not which type. Fehling's, Benedict's or Tollens' reagent is then used to decide.
Carboxylic acids and esters also contain C=O, but they do not give a precipitate, because their C=O group is less reactive.
Sign in free to see the rest of this lesson, the R.E.C.I.P.E. recall steps and the quiz
BrainCake is free. Make an account in seconds and pick up where this page stops.
More in Carbonyl Compounds
- Physical Properties of Carbonyls
- Oxidation of Aldehydes
- Tollens' Reagent
- Fehling's and Benedict's Solutions
- Iodoform Reaction
- Reduction with LiAlH4
- Reaction with HCN
- Nucleophilic Addition Mechanism
All 11 lessons in Carbonyl Compounds · All Edexcel A-level Chemistry topics