Carbonyl compounds - tests

Question 1

what reagent is used to detect the presence of a carbonyl group?

Answer 1

2,4-DNPH

Question 2

What is brady’s reagent?

Answer 2

a solution of 2,4-DNPH in a mixture of methanol and sulfuric acid

Question 3

What forms when brady’s reagent is added to an aldehyde or ketone?

Answer 3

a yellow/orange precipitate called a 2,4-DNPH derivative. This confirms the presence of an aldehyde or ketone.

Question 4

What is used to further classify a carbonyl compound as either an aldehyde or ketone?

Answer 4

Tollens reagent

Question 5

How can you tell if a carbonyl compound is a ketone or an aldehyde?

Answer 5

Aldehydes are easily oxidised to carboxylic acids (forming a silver/grey solid) by Tollens’ but ketones are not oxidised by Tollen’s reagent.

Question 6

After the carbonyl compound has been identified as an aldehyde/ketone, how can you positively identify what compound it is?

Answer 6

• identify it from the melting point of the derivative.
• purify the orange sold by recrystallisation
• measure its melting point
• compare the melting point with data table values.