2,4-Dinitrophenylhydrazine
1919588
215621683
2008-05-29T00:05:38Z
Naidevinci
7045825
/* See also */
{{Chembox new
| ImageFileL1 = 2,4-Dinitrophenylhydrazine.png
| ImageSizeL1 = 110px
| ImageFileR1 = 24dnp3d.png
| ImageSizeR1 = 110px
| IUPACName = (2,4-dinitrophenyl)hydrazine
| OtherNames = 2,4-DNPH; 2,4-DNP; Brady's reagent
| Section1 = {{Chembox Identifiers
| CASNo = 119-26-6
| PubChem =
| SMILES = NNc1ccc(cc1[N+]([O-])=O)[N+]([O-])=O
}}
| Section2 = {{Chembox Properties
| Formula = C<sub>6</sub>H<sub>6</sub>N<sub>4</sub>O<sub>4</sub>
| MolarMass = 198.14
| Appearance = Red or orange powder
| Density =
| MeltingPt = 198 - 202 °C dec.
| BoilingPt =
| Solubility = Slight
}}
| Section7 = {{Chembox Hazards
| MainHazards = Flammable, possible carcinogen
| FlashPt =
| Autoignition =
}}
}}
'''2,4-Dinitrophenylhydrazine''' ('''DNPH''', '''Brady's reagent''') is the [[chemical compound]] C<sub>6</sub>H<sub>3</sub>(NO<sub>2</sub>)<sub>2</sub>NHNH<sub>2</sub>. Dinitrophenylhydrazine is relatively sensitive to [[Shock (mechanics)|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 group]]s associated with aldehydes and ketones. The hydrazone [[Derivative (chemistry)|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]] with 2,4-dinitrochlorobenzene.<ref>{{OrgSynth | author = Allen, C. F. H. | prep = cv2p0228 | title = 2,4-Dinitrophenylhydrazine | collvol = 2 | collvolpages = 228 | year = 1943}}</ref>
==Brady's test==
2,4-Dinitrophenylhydrazine can be used to qualitatively [[chemical test|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]]):
:RR'C=O + C<sub>6</sub>H<sub>3</sub>(NO<sub>2</sub>)<sub>2</sub>NHNH<sub>2</sub> → C<sub>6</sub>H<sub>3</sub>(NO<sub>2</sub>)<sub>2</sub>NHNCRR' + H<sub>2</sub>O
This reaction can be described as a condensation reaction, with two molecules joining together with loss of water. It is also called addition-elimination reaction: nucleophilic addition of the -NH<sub>2</sub> group to the C=O carbonyl group, followed by the removal of a H<sub>2</sub>O molecule.
:The mechanism for the reaction between 2,4-dinitrophenylhydrazine and an aldehyde or ketone is shown:<ref>Adapted from ''Chemistry in Context'', 4th Edition, 2000, Graham Hill and John Holman</ref>
:[[Image:Brady's-reagent-mechanism.png|480px|Reaction mechanism]]
Crystals of different hydrazones have characteristic melting and boiling points, hence 2,4-dinitrophenylhydrazine can be used to distinguish between various compounds containing carbonyl groups. The method was particularly important because melting point determinations require only low-cost instrumentation. This application in analytical chemistry was developed by Brady and Elsmie.<ref>{{cite journal | author = Brady, O. L.; Elsmie, G. V. | title = The use of 2:4-dinitrophenylhydrazine as a reagent for aldehydes and ketones | journal = [[Analyst (journal)|Analyst]] | volume = 51 | pages = 77–78 | year = 1926 | doi = 10.1039/AN9265100077}}</ref>
[[Image:24-dinitrophenylhydrazonederiv.jpg|thumb|right|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 delocalisation 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==
<references/>
==External links==
*[http://www.jtbaker.com/msds/englishhtml/d7464.htm MSDS for 2,4-Dinitrophenylhydrazine]
{{DEFAULTSORT:Dinitrophenylhydrazine, 2,4-}}
[[Category:Aromatic compounds]]
[[Category:Reagents for organic chemistry]]
[[Category:Hydrazines]]
[[de:2,4-Dinitrophenylhydrazin]]
[[es:2,4-dinitrofenilhidracina]]
[[fr:2,4-dinitrophénylhydrazine]]
[[it:2,4-dinitrofenilidrazina]]
[[pl:2,4-dinitrofenylohydrazyna]]
[[zh:2,4-二硝基苯肼]]