2,4-Dinitrophenylhydrazine

2,4-Dinitrophenylhydrazine
IUPAC name (2,4-dinitrophenyl)hydrazine
Other names 2,4-DNPH; 2,4-DNP; Brady's reagent
Identifiers
CAS number	119-26-6 Y
ChemSpider	3001507 Y
KEGG	C11283 Y
ChEMBL	CHEMBL352799 Y
Jmol-3D images	Image 1
SMILES c1cc(c(cc1[N+](=O)[O-])[N+](=O)[O-])NN
InChI InChI=1S/C6H6N4O4/c7-8-5-2-1-4(9(11)12)3-6(5)10(13)14/h1-3,8H,7H2 Y Key: HORQAOAYAYGIBM-UHFFFAOYSA-N Y InChI=1/C6H6N4O4/c7-8-5-2-1-4(9(11)12)3-6(5)10(13)14/h1-3,8H,7H2 Key: HORQAOAYAYGIBM-UHFFFAOYAM
Properties
Molecular formula	C6H6N4O4
Molar mass	198.14
Appearance	Red or orange powder
Melting point	198 - 202 °C dec.
Solubility in water	Slight
Hazards
MSDS	MSDS
Main hazards	Flammable, possible carcinogen
Y (verify) (what is: Y/N?) Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa)
Infobox references

2,4-Dinitrophenylhydrazine (DNPH, Brady's reagent) is the chemical compound C₆H₃(NO₂)₂NHNH₂. Dinitrophenylhydrazine is relatively sensitive to shock and friction; it is a shock explosive so care must be taken with its use. It is a red to orange solid, usually supplied wet to reduce its explosive hazard. It is a substituted hydrazine, and is often used to qualitatively test for carbonyl groups associated with aldehydes and ketones. The hydrazone derivatives can also be used as evidence toward the identity of the original compound.

Synthesis

2,4-Dinitrophenylhydrazine is commercially available usually as a wet powder. It can be prepared by the reaction of hydrazine sulfate with 2,4-dinitrochlorobenzene:^[1]

Brady’s reagent is prepared by dissolving 2,4-dinitrophenylhydrazine in a solution containing methanol and some concentrated sulfuric acid.

Brady's test

2,4-Dinitrophenylhydrazine can be used to qualitatively detect the carbonyl functionality of a ketone or aldehyde functional group. A positive test is signaled by a yellow or red precipitate (known as a dinitrophenylhydrazone.) If the carbonyl compound is aromatic, then the precipitate will be red; if aliphatic, then the precipitate will have a yellow color.^[2] The reaction between 2,4-Dinitrophenylhydrazine and a ketone is shown below:

RR'C=O + C₆H₃(NO₂)₂NHNH₂ → C₆H₃(NO₂)₂NHNCRR' + H₂O

This reaction can be described as a condensation reaction, with two molecules joining together with loss of water. It is also considered an addition-elimination reaction: nucleophilic addition of the -NH₂ group to the C=O carbonyl group, followed by the removal of a H₂O molecule.

The mechanism for the reaction between 2,4-dinitrophenylhydrazine and an aldehyde or ketone is shown below:^[3]

Crystals of different hydrazones have characteristic melting and boiling points, allowing the identity of a substance to be determined in a method known as derivatization. In particular, the use of 2,4-dinitrophenylhydrazine was developed by Brady and Elsmie.^[4] Modern spectroscopic and spectrometric techniques have since superseded these techniques.

2,4-DNP reacting with 2-heptanone

Dinitrophenylhydrazine does not react with other carbonyl-containing functional groups such as carboxylic acids, amides, and esters. For carboxylic acids, amides and esters, there is resonance associated stability as a lone-pair of electrons interacts with the p-orbital of the carbonyl carbon resulting in increased delocalization in the molecule. This stability would be lost by addition of a reagent to the carbonyl group. Hence, these compounds are more resistant to addition reactions.

See also

• Tollens' reagent
• Fehling's reagent

References

1. ^ Allen, C. F. H. (1943), "2,4-Dinitrophenylhydrazine", Org. Synth., http://www.orgsyn.org/orgsyn/orgsyn/prepContent.asp?prep=cv2p0228 ; Coll. Vol. 2: 228 
2. ^ http://wiki.colby.edu/download/attachments/110920618/Experiment+%232.pdf?version=1&modificationDate=1265312071267
3. ^ Adapted from Chemistry in Context, 4th Edition, 2000, Graham Hill and John Holman
4. ^ Brady, O. L.; Elsmie, G. V. (1926). "The use of 2:4-dinitrophenylhydrazine as a reagent for aldehydes and ketones". Analyst 51 (599): 77–78. doi:10.1039/AN9265100077.