2,4-Dinitrophenylhydrazine(2,4-DNP Test) - Definition, Synthesis and Reaction - GeeksforGeeks (2024)

2,4-Dinitrophenylhydrazine is a chemical compound having the molecular formula C₆H₃(NO₂)₂NHNH₂. It is also called Brady’s Reagent. Another most popular name of 2,4-Dinitrophenylhydrazine is DNPH, which is most popular in the market. DNPH is a red and orange colored solid and is most commonly used as a reduction in shock, friction or explosion.

In this article on 2,4-Dinitrophenylhydrazine, we will learn about what is 2,4-Dinitrophenylhydrazine, the synthesis of DNPH, physical and chemical properties of DNPH and many more things in detail.

What is 2,4-dinitrophenylhydrazine?

2,4-Dinitrophenylhydrazine (DNPH) is a organic chemical compound widely used as a reagent in organic chemistry to detect and identify carbonyl molecules, particularly aldehydes and ketones. It has the molecular formula C6H3NHNHCONHNH2. It appears as yellow to orange crystalline solid sparingly soluble in water but soluble in organic solvents such as ethanol, acetone, and ether.

Structure of 2,4-Dinitrophenylhydrazine

2,4-Dinitrophenylhydrazine (2,4-DNPH) structure consists of a phenyl ring with two nitro groups attached at the ortho and meta positions with a hydrazine group attached to one of the carbon atoms in the phenyl group.

This reagent is useful in organic chemistry as it imparts a characteristic orange-to-red color and reacts with carbonyl compounds, allowing for qualitative identification of carbonyl functional groups.

Properties of 2,4-Dinitrophenylhydrazine

The properties of 2,4-Dinitrophenylhydrazine are mentioned below:

Physical Properties of 2,4-DNP

• Physical Properties: 2,4-Dinitrophenylhydrazine is a yellow-orange crystalline solid.
• DNPH is poorly soluble in water but soluble in organic solvents such as ethanol, acetone, and ether.
• The melting point of 2,4-dinitrophenylhydrazine is around 210-212°C.
• It has a mild odor, which is typical of aromatic substances.

Chemical Properties of 2,4-DNP

• Reactivity: DNPH is a powerful nucleophile that easily interacts with carbonyl compounds to produce hydrazones. This reaction is commonly used in analytical chemistry to conduct qualitative and quantitative analyses of aldehydes and ketones.

• Hydrazone Formation: In the presence of carbonyl molecules (such as aldehydes and ketones), DNPH undergoes a condensation process, resulting in orange-red or yellow-orange crystalline precipitates called hydrazones. These hydrazone derivatives are frequently insoluble in water and may be readily isolated and described.

• DNPH is sensitive to light, heat, and shock, thus treat with caution to avoid decomposition or explosion.

• Stability: While DNPH is stable under normal conditions, hydrazone derivatives generated by its interaction with carbonyl compounds may undergo further reactions or breakdown over time.

Synthesis of the 2,4-Dinitrophenylhydrazine

2,4-Dinitrophenylhydrazine is prepared by using chlorobenzene, due to Chlorobenzene is ortho and para directing groups.

Firstly, Benzene is converted into Chlorobenzene by the reaction of AlCl_2.

After, Chlorobenzene is synthesized by using conc.HNO₃ and conc.H₂SO₄, it gives 2,4-Dinitrochlorobenzene.

Then, 2,4-Dinitrochlorobenzene will be converted into with 2,4-Dinitrophenylhydrazine when reacts with hydrazine ( NH₂-NH₂).

Brady’s Reagent

The aqueous solution of the DNP is known as Brady’s reagent. Brady’s reagent used primarily for the detection of aldehydes and ketones (Carbonyl compounds). It reacts with carbonyl compounds (aldehydes & ketone) to produce a coloured precipitate which confirms the carbonyl compounds.

When an aldehyde or ketone reacts with Brady’s reagent, it produces a 2,4-dinitrophenylhydrazone derivative, which is a yellow to orange precipitate.

Brady’s reagent is produced by dissolving 2,4-dinitrophenylhydrazine in a suitable solvent, typically a mixture of sulfuric acid and ethanol. The reagent solution must be freshly prepared before use to ensure accurate results.

What is 2,4-DNP Test?

The 2,4-dinitrophenylhydrazine (2,4-DNP) test is commonly used in organic chemistry labs to detect the presence of carbonyl groups (aldehydes and ketones) i.e., (C=O) functional group in organic compounds. Basically, the aqueous solution of the 2,4-Dinitrophenylhydrazine is used for the Identification of the carbonyl compounds.

Identification of a Carbonyl Compound

Brady’s reagent will be used for Identification of a Carbonyl Compounds. The carbonyl compound is simply mixed with an acid solution of Brady’s reagent in methanol.

DNPH reacts with the carbonyl group (C=O) of aldehydes and ketones to form a 2,4-dinitrophenylhydrazone derivative. This reaction is a classic method for identifying the presence of carbonyl compounds.

Reaction with Ethanal

2,4-Dinitrophenylhydrazine (2,4-DNP) interacts with aldehydes and ketones to produce compounds called 2,4-dinitrophenylhydrazones.

• The water is eliminated and reaction is a condensation reaction. The product is named using the name of the aldehyde or ketone followed by 2,4-dinitrophenylhydrazone, like ethanal 2,4-dinitrophenylhydrazone.
• The formed 2,4-dinitrophenylhydrazone is a solid that is purified, and the melting point is determined. The comparison of a melting point with a table of known values could identify the compound as aldehyde or ketone.
• All the derivatives of 2,4-dinitrophenylhydrazone are orange or yellow colored solids.

Laboratory Test for DNP

• To conduct the 2,4-dinitrophenylhydrazine test, take a test tube and add 5ml of the reagent.
• Next, add 10 drops of the unknown compound to the test tube and mix vigorously by tapping the test tube with a stick or finger. If the crystals do not form immediately, gently heat the test tube in a water bath at 65^oC for 5 minutes.
• Now, cool the test tube in an ice bath until crystals form. Then, collect the crystals by vacuum filtration using a Hirsch funnel. Allow the crystals to dry on the Hirsch funnel by drawing air through them. Take note of the melting point on the Report sheet.
• Generally, the crystals obtained are pure enough to produce an accurate melting point. However, if the melting point range is too wide, recrystallization can be performed from a minimum volume of ethanol.

Conclusion

It’s interesting to learn that 2,4-Dinitrophenylhydrazine (2,4-DNP) has a significant role in organic chemistry, especially in identifying carbonyl compounds like aldehydes and ketones. However, it’s important to handle it with care as it is a potentially hazardous material, being both flammable and explosive. Proper storage and handling precautions should be taken to ensure safety.

Also, Check

• Oxidation of Aldehydes, Ketones and Carboxylic Acids
• TollensTest
• Fehling’s Solution

Frequently Asked Questions on 2,4-Dinitrophenylhydrazine

What is 2,4-Dinitrophenylhydrazine?

2,4-Dinitrophenylhydrazine is a chemical compound having the molecular formula C6H3(NO2)2NHNH2. It is also called Brady’s Reagent and 2, 4 DNPH. DNPH is a red and orange color solid and is most commonly used as a reduction in shock and friction or explosion.

What is the chemical formula of DNPH?

The chemical formula of DNPH is C₆H₃(NO₂)₂NHNH₂.

What is Brady’s reagent?

The aqueous solution of the DNP is known as Brady’s reagent. Brady’s reagent used primarily for the detection of aldehydes and ketones (Carbonyl compounds).

What is DNPH used for?

It is used for identifying aldehydes and ketones. It reacts with the carbonyl compounds to form a solid derivative called a “hydrazone,” which can be used to confirm the presence of aldehydes and ketones in the chemical compound.

How does DNPH reacts with ethanal?

2,4-Dinitrophenylhydrazine (2,4-DNP) interacts with aldehydes and ketones to produce compounds called 2,4-dinitrophenylhydrazones.

What is the molecular weight of 2,4-DNPH?

The molecular weight of DNPH is 198.14 g/mol.