2 4 Dinitrophenylhydrazine - Structure, Preparation, Brady’s Reagent, FAQs

Edited By Team Careers360 | Updated on Jul 02, 2025 04:49 PM IST

2,4-dinitrophenylhydrazine is generally abbreviated as 2,4-DNP also known by the Brady’s reagent. This is generally present in solid form and orange-red in color. It is very reactive in nature so to avoid the risk of explosion we keep it in water or we can say it is stable in wet conditions as compared to dry one.

This Story also Contains

2,4-Dinitrophenylhydrazine Structure
Preparation of 2 4 Dinitrophenylhydrazine from Chlorobenzene
Mechanism of Synthesis of 2,4-DNP
Brady’s Reagent
2,4-Diphenylhydrazine Laboratory test
Reaction of 2,4-DNP with Ethanal

2,4-Dinitrophenylhydrazine Structure

2,4-DNP structure can be shown as follows where DNP full form is dinitrophenylhydrazine

2,4-dinitrophenylhydrazine structure

As the name suggests 2,4-dinitro i.e. presence of two nitrogen groups and phenyl hydrazine is represented by benzene ring with This group is called phenyl hydrazine.

The main use of 2,4-DNP and its derivatives gives us a method of separating the components of compounds containing aldehydes and ketones mixture. Aldehyde and ketone can easily separate out with the help of fractional distillation but we can easily separate 2,4-DNP and its derivatives with the help of column chromatography. One more advantage of this is that formation from aldehydes and ketones is reversible in nature and separated derivatives will be regenerated easily to their original carbonyl compounds with the help of hydrolysis of those derivatives.

Also read -

Preparation of 2 4 Dinitrophenylhydrazine from Chlorobenzene

2,4-DNP is not said to be commonly known substituted hydrazine but it can be prepare with the help of resonating phenomenon with this we can easily make a reasonable inference which suggests that hydrazine represented by the molecular formula acts as a good nucleophile. We can prepare the 2,4-DNP with the reaction of hydrazine with 2,4-dinitrochlorobenzene. Presence of two nitro groups makes the compound available for electron-accepting which makes it easy to displace these two chloride ions. The reaction can be shown as follows:

Synthesis of 2,4-dinitrophenylhydrazine

In this reaction we can see that 2,4-dinitrochlorobenzene reacts with hydrazine and one chloro group replaces it with hydrazine group.

Mechanism of Synthesis of 2,4-DNP

Mechanism can be explained by the following three steps:

1. Chlorobenzene is prepared from benzene by chlorination where the chlorine group is said to be ortho and para directing group and deactivating in nature.

2. After that we nitrate chlorobenzene with sulphuric and nitric acid. As chlorine is para or ortho directing then first para position is already blocked then two nitro groups will attack on ortho and para positions as nitro is also said to be ortho para directing group.

3. After this 2,4-dinitrochlorobenzene reacts with hydrazine which replaces the chlorine group with hydrazine and gives us the desired product.

The mechanism can be shown as follows:

Mechanism of synthesis of 2,4-DNP

Brady’s Reagent

Aqueous solution of 2,4-dintrophenyl hydrazine or 2,4-DNP is known as Brady’s reagent or borsches reagent. This reagent reacts with carbonyl compounds where carbonyl compounds are those which contain carbonyl group like aldehyde and ketone and carbonyl group is represent as while in aldehyde carbonyl group is present as while in ketone is there and gives colored precipitate with them. These precipitates generally show sharp melting points and these sharp melting points will confirm the presence of carbonyl compounds in them.

2,4-DNP test is given by only those compounds which are aldehyde and ketones in nature as when aldehyde and ketones reacts with 2,4-DNP then it forms yellow, orange or reddish orange precipitates with 2,4-DNP but when alcohols which do not have carbonyl compound gets react with 2,4-DNP the reaction will not get succeed or we can say no reaction takes place. This test is also used to check the presence of alcohol in the body. Benzaldehyde and acetone can be distinguished by this test.

How can we Identify Carbonyl Compounds with the help 2,4-DNP?

Carbonyl compound in methanol gets easily or we can say simply mixed with an acid solution of Brady’s reagent. The derivatives or product formed by this reaction is of orange color and crystalline solids which are further known by the name 2,4-dinitrophenylhydrazones. Crystals of 2,4-dintrophenylhydrazone are further filtered and purified by the process called re-crystallisation.

After drying, the melting point of the crystal has to be noted and compare the melting point with 2,4-dinitrophenyl hydrazines. If it got matched or we can say it gives colored precipitates then the carbonyl group gets confirmed.

Related Topics Link,

The reaction can be shown as:

2,4-dintrophenylhydrazone

The main advantage of Brady’s test is that it is used to test whether the carbonyl compound is present or not and the presence of carbonyl compound in the form of aldehyde or ketone will give orange colored precipitates.

Also read :

NEET Highest Scoring Chapters & Topics

This ebook serves as a valuable study guide for NEET exams, specifically designed to assist students in light of recent changes and the removal of certain topics from the NEET exam.

Download EBook

2,4-Diphenylhydrazine Laboratory test

This test is generally known by its abbreviation called 2,4-DNP test. The full form 2 4 DNP test is 2,4-diphenylhydrazine laboratory test. Let us consider the test by first showing its image

2,4 DNP Laboratory Test

This test can be explained by the following points:

1. Put 5 ml of 2,4-dinitrrophenylhydrazine in a test tube.

2. Now in this add 10 drops of any unknown compound and shake the test tube vigorously to mix them well and it will form crystals. If crystals were not formed then heat the test tube gently in a water bath about C for just 5-10 minutes.

3. After heating, cool the solution in an ice bath until you find the crystals. When crystals appear, wait some time to settle it down and then filter it through a Hirsch funnel like the funnel showing in image.

4. Now allow the crystals to dry with the help of Hirsch funnel by drawing air through crystals. Now after drying the crystals note down the melting point.

5. Take care that the crystals are dried properly and pure to note the accurate melting point. If you find the range of melting point is large then recrystallize the crystal with ethanol.

Reaction of 2,4-DNP with Ethanal

2,4-DNP is able to react with aldehydes as well as ketones which further produces 2,4-dinitrophenylhydrazone as a product. The reaction between 2,4-DNP and ethanal which is an aldehyde can be known as elimination reaction as in this reaction water molecules get eliminated and these reactions generally give orange and yellow colored solid compounds or precipitates of yellow/orange color. The melting point of these types of compounds is quietly sharp and the solution of 2,4-diphenylhydrazine is known by the name Brady’s reagent.

Also check-

NCERT Chemistry Notes :

Frequently Asked Questions (FAQs)

1. What are the positive results for 2,4-DNP test?

2,4-DNP stands for 2,4-dipheylhydrazine which is used to identify whether any aldehydic or ketonic group is present in any compound or not. The positive result for this test is the formation of precipitates of dinitrophenylhydrazone which is of yellow, orange or red in color.

2. 2,4-dintrophenylhydrazones are said to be better derivatives as compared to phenyl hydrazones. Explain.

2,4-Dinitrophenylhydrazones are said to be better derivatives as compared to phenyl hydrazones this can be explained by many different reasons. At first we can say that 2,4-dinitrophenylhydrazones and its derivatives contain higher molecular masses as compared to phenylhydrazones which increase the volume of substance and we know that those substances which are heavier in masses contain a greater tendency of becoming a solid.

3. Define Brady’s reagent.

Aqueous solution of 2,4-dinitrophenylhydrazone is generally known as Brady’s reagent which when react with those compounds which have carbonyl group inside them are able to give colored precipitates and in presence of alcohol it will not get reacted. So this reagent is basically used to test the presence of alcohol in the body.

4. 2,4-DNP stands for?

2,4-dinitrophenylhydrazone.

5. The reagent with which both acetaldehyde and acetone react is?

Grignard reagent.

6. Why are two nitro groups present in the structure of 2,4-DNP?

The two nitro groups in 2,4-DNP serve multiple purposes:

7. Can 2,4-DNP be used to detect other functional groups besides carbonyls?

While 2,4-DNP is primarily used for carbonyl compounds, it can react with or detect some other functional groups:

8. What is Brady's reagent, and how is it related to 2,4-DNP?

Brady's reagent is a solution of 2,4-dinitrophenylhydrazine in methanol or ethanol, usually with a small amount of sulfuric acid as a catalyst. It's named after the chemist who developed it, and it's used specifically for detecting and characterizing carbonyl compounds. When Brady's reagent is added to a solution containing an aldehyde or ketone, it forms a yellow or orange precipitate, which is the 2,4-dinitrophenylhydrazone derivative.

9. What safety precautions should be taken when working with 2,4-DNP?

When working with 2,4-DNP, several safety precautions are essential:

10. How does the color of the 2,4-DNP derivative relate to the structure of the original carbonyl compound?

The color of the 2,4-DNP derivative (hydrazone) can provide information about the original carbonyl compound:

11. How does the melting point of a 2,4-DNP derivative relate to the purity of the original carbonyl compound?

The melting point of a 2,4-DNP derivative is often used to assess the purity of the original carbonyl compound:

12. Can 2,4-DNP be used to distinguish between aldehydes and ketones?

2,4-DNP alone cannot distinguish between aldehydes and ketones because it reacts similarly with both:

13. What are the limitations of using 2,4-DNP as a carbonyl detecting agent?

While 2,4-DNP is a powerful tool for detecting carbonyl compounds, it has some limitations:

14. How is 2,4-DNP prepared in the laboratory?

2,4-DNP is typically prepared through a two-step process:

15. How does the pH of the reaction medium affect the formation of 2,4-DNP derivatives?

The pH of the reaction medium significantly influences the formation of 2,4-DNP derivatives:

16. What is the role of the solvent in 2,4-DNP reactions?

The solvent plays several important roles in 2,4-DNP reactions:

17. How can 2,4-DNP derivatives be used for the purification of carbonyl compounds?

2,4-DNP derivatives are useful for purifying carbonyl compounds through the following steps:

18. What is the significance of the hydrazone formation in organic synthesis?

Hydrazone formation, including reactions with 2,4-DNP, is significant in organic synthesis for several reasons:

19. What is 2,4-dinitrophenylhydrazine (2,4-DNP) and why is it important in organic chemistry?

2,4-Dinitrophenylhydrazine (2,4-DNP) is an organic compound with the formula (O2N)2C6H3NHNH2. It's important in organic chemistry because it's a key reagent used to detect and characterize carbonyl compounds (aldehydes and ketones). When 2,4-DNP reacts with carbonyl compounds, it forms bright orange or yellow precipitates called hydrazones, making it a valuable tool for qualitative analysis and identification of these compounds.

20. How does the structure of 2,4-DNP contribute to its reactivity?

The structure of 2,4-DNP consists of a benzene ring with two nitro (NO2) groups at positions 2 and 4, and a hydrazine (NHNH2) group at position 1. The nitro groups are electron-withdrawing, which makes the hydrazine group more nucleophilic. This enhanced nucleophilicity allows 2,4-DNP to react readily with the electrophilic carbonyl groups of aldehydes and ketones, forming hydrazones.

21. What is the mechanism of the reaction between 2,4-DNP and carbonyl compounds?

The reaction mechanism involves:

22. Why is an acid catalyst often used in reactions involving 2,4-DNP?

An acid catalyst, typically sulfuric acid, is used in reactions involving 2,4-DNP for several reasons:

23. How does the reactivity of 2,4-DNP compare to other hydrazine derivatives?

2,4-DNP is generally more reactive than simple hydrazine or other hydrazine derivatives due to:

24. How does the presence of other functional groups in a molecule affect its reaction with 2,4-DNP?

The presence of other functional groups can influence the reaction with 2,4-DNP in several ways:

25. What are some alternatives to 2,4-DNP for detecting carbonyl compounds?

While 2,4-DNP is widely used, there are several alternatives for detecting carbonyl compounds:

26. How does the structure of the carbonyl compound affect the rate of reaction with 2,4-DNP?

The structure of the carbonyl compound influences its reaction rate with 2,4-DNP in several ways: