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2,4-Dinitrophenylhydrazine

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2,4-Dinitrophenylhydrazine
Names
Preferred IUPAC name (2,4-Dinitrophenyl)hydrazine
Other names 2,4-DNPH
2,4-DNP
Brady's reagent
Borche's reagent
Identifiers
CAS Number
3D model (JSmol)
ChEBI
ChEMBL
ChemSpider
ECHA InfoCard 100.003.918 Edit this at Wikidata
EC Number
  • 204-309-3
KEGG
PubChem CID
UNII
CompTox Dashboard (EPA)
InChI
  • InChI=1S/C6H6N4O4/c7-8-5-2-1-4(9(11)12)3-6(5)10(13)14/h1-3,8H,7H2Key: HORQAOAYAYGIBM-UHFFFAOYSA-N
  • InChI=1/C6H6N4O4/c7-8-5-2-1-4(9(11)12)3-6(5)10(13)14/h1-3,8H,7H2Key: HORQAOAYAYGIBM-UHFFFAOYAM
SMILES
  • c1cc(c(cc1(=O))(=O))NN
Properties
Chemical formula C6H6N4O4
Molar mass 198.14 g/mol
Appearance Red or orange powder
Melting point 198 to 202 °C (388 to 396 °F; 471 to 475 K) dec.
Solubility in water Slight
Hazards
Occupational safety and health (OHS/OSH):
Main hazards Flammable, possibly carcinogenic
GHS labelling:
Pictograms GHS02: FlammableGHS07: Exclamation mark
Signal word Warning
Hazard statements H228, H302, H319
Precautionary statements P210, P240, P241, P264, P270, P280, P301+P312, P305+P351+P338, P330, P337+P313, P370+P378, P501
Safety data sheet (SDS) MSDS
Except where otherwise noted, data are given for materials in their standard state (at 25 °C , 100 kPa). ☒N verify (what is  ?) Infobox references
Chemical compound

2,4-Dinitrophenylhydrazine (DNPH, Brady's reagent, Borche's reagent) is the chemical compound C6H3(NO2)2NHNH2. Dinitrophenylhydrazine is a red to orange solid. It is a substituted hydrazine. The solid is relatively sensitive to shock and friction. DNPH is a precursor to the drug Sivifene.

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:

Brady's reagent is prepared by dissolving 2,4-dinitrophenylhydrazine in a solution containing methanol and some concentrated sulfuric acid. The medium should be slightly acidic.

DNP test

2,4-Dinitrophenylhydrazine is used to qualitatively detect ketones and aldehydes. A positive test is signalled by the formation of a yellow, orange or red precipitate of the dinitrophenylhydrazone. Aromatic carbonyls give red precipitates whereas aliphatic carbonyls give more yellow color. The reaction between 2,4-dinitrophenylhydrazine and a generic ketone to form a hydrazone is shown below:

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

This reaction is, overall, a condensation reaction as two molecules joining together with loss of water. Mechanistically, it is an example of addition-elimination reaction: nucleophilic addition of the -NH2 group to the C=O carbonyl group, followed by the elimination of a H2O molecule:

X-ray structure of DNP-derived hydrazone of benzophenone. Selected parameters: C=N, 128 pm; N-N, 1.38 pm, N-N-C(Ar), 119
When 3-heptanone is added to a solution of 2,4-DNPH and heated, an orange-red precipitate forms.

DNP-derived hydrazones have characteristic melting points, facilitating identification of the carbonyl. In particular, the use of 2,4-dinitrophenylhydrazine was developed by Brady and Elsmie. Modern spectroscopic and spectrometric techniques have superseded these techniques.

Dinitrophenylhydrazine does not react with other carbonyl-containing functional groups such as carboxylic acids, amides, and esters, for which 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. Also, with carboxylic acids, there is the effect of the compound acting as a base, leaving the resulting carboxylate negatively charged and hence no longer vulnerable to nucleophilic attack.

Safety

Explosions have resulted from the use of DNPH.

See also

References

  1. Allen, C. F. H. (1933). "2,4-Dinitrophenylhydrazine". Organic Syntheses. 13: 36. doi:10.15227/orgsyn.013.0036; Collected Volumes, vol. 2, p. 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. Tameem, Abdassalam Abdelhafiz; Salhin, Abdussalam; Saad, Bahruddin; Rahman, Ismail Ab.; Saleh, Muhammad Idiris; Ng, Shea-Lin; Fun, Hoong-Kun (2006). "Benzophenone 2,4-dinitrophenylhydrazone". Acta Crystallographica Section e Structure Reports Online. 62 (12): o5686–o5688. doi:10.1107/S1600536806048112.
  5. Brady, Oscar L.; Elsmie, Gladys V. (1926). "The use of 2:4-dinitrophenylhydrazine as a reagent for aldehydes and ketones". Analyst. 51 (599): 77–78. Bibcode:1926Ana....51...77B. doi:10.1039/AN9265100077.
  6. "Bomb disposal squads detonate chemical stocks in British schools". The Guardian. 2 November 2016. Retrieved 19 March 2018.
Hydrazines
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