Brady's Test
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Brady's Test
2,4-Dinitrophenylhydrazine
2,4-Dinitrophenylhydrazin.svg
2,4-dinitrophenylhydrazine-from-xtal-3D-balls.png
24dnp3d.png
Names
Preferred IUPAC name
(2,4-Dinitrophenyl)hydrazine
Other names
2,4-DNPH
2,4-DNP
Brady's reagent
Borche's reagent
Identifiers
3D model (JSmol)
ChEBI
ChEMBL
ChemSpider
ECHA InfoCard 100.003.918 Edit this at Wikidata
EC Number
  • 204-309-3
KEGG
UNII
  • InChI=1S/C6H6N4O4/c7-8-5-2-1-4(9(11)12)3-6(5)10(13)14/h1-3,8H,7H2 checkY
    Key: HORQAOAYAYGIBM-UHFFFAOYSA-N checkY
  • 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
  • c1cc(c(cc1[N+](=O)[O-])[N+](=O)[O-])NN
Properties
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.
Slight
Hazards
Main hazards Flammable, possibly carcinogenic
Safety data sheet MSDS
GHS pictograms GHS02: FlammableGHS07: Harmful
GHS Signal word Warning
H228, H302, H319
P210, P240, P241, P264, P270, P280, P301+312, P305+351+338, P330, P337+313, P370+378, P501
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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Infobox references

2,4-Dinitrophenylhydrazine (DNPH) is the organic 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. For this reason dinitrophenylhydrazine is usually handled as a wet powder. DNPH is a precursor to the drug Sivifene.

Synthesis

It can be prepared by the reaction of hydrazine sulfate with 2,4-dinitrochlorobenzene:[1]

Preparation of 2,4-DNPH.png

DNP test

DNPH is a reagent in instructional laboratories on qualitative organic analysis. Brady's reagent or Borche's reagent, is prepared by dissolving 2,4-dinitrophenylhydrazine in a solution containing methanol and some concentrated sulfuric acid. This solution is used to 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.[2] 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:[3]

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[4]
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.[5] 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.[6]

See also

References

  1. ^ Allen, C. F. H. (1933). "2,4-Dinitrophenylhydrazine". Organic Syntheses. 13: 36. doi:10.15227/orgsyn.013.0036.
  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. 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 2018.

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