2,4-DNPH (Brady's Reagent)

What is it a test for?

a C=O group (will give a positive result with either an aldehyde or ketone)

What are the observations?

forms orange precipitate as the hydrazine product is insoluble

What is another way to determine whether the sample is an aldehyde or ketone?

• solid purified by recrystallisation

• test the mpt of the hydrazine product (which is a solid)

• both aldehydes and ketones have different known mpts so can determine which is a ketone and which is an aldehyde

• (mpts determined experimentally and their values compared to a Databook to identify them)

What is special about carbonyl compounds that allows you to distinguish between them using their melting temperatures?

• carbonyl compounds are their derivatives have sharp melting points (they melt over a narrow range of temperatures)

Does it work for carboxylic acids?

No, it does not.

Is it quantitative or qualitative?

Qualitative