12 - Chemical Tests On Carbonyl Compounds Flashcards
How do you form Brady’s reagent?
2,4 -DNP + Sulphuric Acid + Methanol -> Brady’s reagent.
What is 2, 4 -DNP?
2, 4 -Dinitrophenylhydrazine.
What happens with you mix Brady’s reagent wit an Aldehyde/Ketone?
It detects the presence of a carbonyl compound (Aldehyde/Ketone). It turns yellow/orange in the presence of either an aldehyde or ketone.
Wha is the name of the orange precipitate that forms? What happens with a carboxylic acid and ester?
The orange precipitate is a derivative of 2,4 -Dinitrophenylhydrazone - there’s no precipitate with a Carboxylic acid or an Ester.
What does Tollens’ reagent do?
Tollens’ is an oxidising agent which can be used to distinguish between aldehydes and ketones. Aldehydes can be oxidised to carboxylic acids, whereas ketones cannot be further oxidised.
How do you form Tollens’ reagent?
NaOH(aq) + AgNO3(aq) -> Brown silver oxide precipitate. Then dilute aqueous ammonia is added until the precipitate dissolves (AKA Ammonical silver nitrate).
What does an Aldehyde produce? What does a ketone produce with Tollens’?
Aldehydes produce a silver-grey solid. Whereas ketones don’t react with Tollens’.
What’s Oxidised and reduced using Tollens’?
The aldehyde is oxidised to a carboxylic acid. The silver ions are reduced to silver metal, Ag+(aq) + e- -> Ag(s).
What happens to the impure 2,4-Dinitrophenylhydrazone derivative?
The impure 2,4-Dinitrophenylhydrazone is filtered and recrystallised. This purifies the product 2,4-Dinitrophenylhydrazone derivative that is now purified. This is then filled and dried. The melting point is them measured and recorded. This melting point is then compared to a database, where a match can be found, and so it can be identified.
