TEST OF CARBONYL COMPOUNDS_DNP/ DNPH Test

 

DNP test/ DNP test

What is DNP/ DNPH?

DNP/ DNPH is 2,4-dinitrophenyl hydrazine. Its structure is:

What is the DNP/ DNPH test?

When Aldehyde or Ketone is treated with 2,4-dinitrophenyl hydrazine, corresponding 2,4-dinitrophenyl hydrazine is formed which is yellow crystalline compound forms. This is called DNP/ DNPH test.

What is DNP reagent?

DNP reagent is the yellow-colored solution formed by dissolving 2,4-dinitrophenyl hydrazine powder into Concentrated sulphuric acid.

How is DNP/ DNPH test carried out?

1 ml of Organic sample is taken in a clean and dry test tube. Then a few drops of DNP/ DNPH reagent is added.

Formation of Yellow crystalline compound confirms the given compound is carbonyl compound (Aldehyde or Ketone).

What is the observation made during the DNP/ DNPH test?

DNP solution is Yellow colored liquid. When it is added to the carbonyl, yellow crystalline solid forms. This is an observation made.

Suggest Chemical test for the Carbonyl compound.

DNP/DNPH test is the test for the Carbonyl compound.

Can DNP test be used as a chemical to distinguish aldehyde from a ketone?

No, the DNP test cannot be used to distinguish aldehyde from ketone. For such distinction, Tollen’s test or Fehling test is suitable.

Distinguish Ethanal from ethanol.

Ethanal is distinguished from ethanol by using DNP/DNPH test. Ethanal is aldehyde which is a carbonyl compound so it gives DNP test. Whereas, Ethanol is not a carbonyl compound so it doesn’t give DNP test.

Give one example of the DNP test.

What is its significance?

DNP/ DNPH test is a chemical test for distinction of aldehyde and ketone from other organic compounds.

What is the mechanism behind reaction involved in the DNP test?

It involves two steps:

Step:1

Addition of 2,4-dinitrophenyl hydrazine across the C=O bond.

Step:2

Then intermediate eliminates water molecule to form corresponding 2,4-dinitrophenylhydrazone which is a yellow crystalline compound.

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This site provides notes on different chapters of Chemistry of Grade XI and XII (NEB Board). Also, it posts number of blogs on Collection of past questions and solution. Conversion chart, rules, Chemical test are some additional features.

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