2,4-Dinitrophenylhydrazine (2,4-DNPH or DNPH) is the
organic compound
In chemistry, organic compounds are generally any chemical compounds that contain carbon-hydrogen or carbon-carbon bonds. Due to carbon's ability to catenate (form chains with other carbon atoms), millions of organic compounds are known. The ...
C
6H
3(NO
2)
2NHNH
2. DNPH is a red to orange solid. It is a substituted
hydrazine
Hydrazine is an inorganic compound with the chemical formula . It is a simple pnictogen hydride, and is a colourless flammable liquid with an ammonia-like odour. Hydrazine is highly toxic unless handled in solution as, for example, hydrazine ...
. The solid is relatively sensitive to
shock
Shock may refer to:
Common uses Collective noun
*Shock, a historic commercial term for a group of 60, see English numerals#Special names
* Stook, or shock of grain, stacked sheaves
Healthcare
* Shock (circulatory), circulatory medical emergen ...
and
friction
Friction is the force resisting the relative motion of solid surfaces, fluid layers, and material elements sliding against each other. There are several types of friction:
*Dry friction is a force that opposes the relative lateral motion of t ...
. For this reason DNPH 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
Hydrazine sulfate, more properly hydrazinium hydrogensulfate, is a salt (chemistry), salt of the cation hydrazinium and the anion bisulfate (hydrogensulfate), with the formula or more properly . It is a white, water-soluble solid at room temperat ...
with
2,4-dinitrochlorobenzene
2,4-Dinitrochlorobenzene (DNCB) is an organic compound with the chemical formula (O2N)2C6H3Cl. It is a yellow solid that is soluble in organic solvents. It is an important intermediate for the industrial production of other compounds.
DNCB is p ...
:
:
DNP test
DNPH is a reagent in instructional laboratories on
qualitative organic analysis
Analytical chemistry studies and uses instruments and methods to separate, identify, and quantify matter. In practice, separation, identification or quantification may constitute the entire analysis or be combined with another method. Separati ...
. Brady's reagent or Borche's reagent, is prepared by dissolving DNPH in a solution containing
methanol
Methanol (also called methyl alcohol and wood spirit, amongst other names) is an organic chemical and the simplest aliphatic alcohol, with the formula C H3 O H (a methyl group linked to a hydroxyl group, often abbreviated as MeOH). It is a ...
and some concentrated
sulfuric acid
Sulfuric acid (American spelling and the preferred IUPAC name) or sulphuric acid ( Commonwealth spelling), known in antiquity as oil of vitriol, is a mineral acid composed of the elements sulfur, oxygen and hydrogen, with the molecular formu ...
. This solution is used to
detect ketone
In organic chemistry, a ketone is a functional group with the structure R–C(=O)–R', where R and R' can be a variety of carbon-containing substituents. Ketones contain a carbonyl group –C(=O)– (which contains a carbon-oxygen double bo ...
s and
aldehyde
In organic chemistry, an aldehyde () is an organic compound containing a functional group with the structure . The functional group itself (without the "R" side chain) can be referred to as an aldehyde but can also be classified as a formyl grou ...
s. A positive test is signalled by the formation of a yellow, orange or red
precipitate
In an aqueous solution, precipitation is the process of transforming a dissolved substance into an insoluble solid from a super-saturated solution. The solid formed is called the precipitate. In case of an inorganic chemical reaction leading ...
of the dinitrophenylhydrazone. Aromatic carbonyls give red precipitates whereas
aliphatic
In organic chemistry, hydrocarbons ( compounds composed solely of carbon and hydrogen) are divided into two classes: aromatic compounds and aliphatic compounds (; G. ''aleiphar'', fat, oil). Aliphatic compounds can be saturated, like hexane, or ...
carbonyls give more yellow color. The reaction between DNPH and a generic ketone to form a
hydrazone
Hydrazones are a class of organic compounds with the structure . They are related to ketones and aldehydes by the replacement of the oxygen =O with the = functional group. They are formed usually by the action of hydrazine on ketones or aldehydes. ...
is shown below:
:RR'C=O + C
6H
3(NO
2)
2NHNH
2 → C
6H
3(NO
2)
2NHN=CRR' + H
2O
This reaction is, overall, a
condensation reaction
In organic chemistry, a condensation reaction is a type of chemical reaction in which two molecules are combined to form a single molecule, usually with the loss of a small molecule such as water. If water is lost, the reaction is also known as a ...
as two molecules joining together with loss of water. Mechanistically, it is an example of
addition-elimination reaction: nucleophilic addition of the -NH
2 group to the C=O carbonyl group, followed by the elimination of a H
2O molecule:
:
DNP-derived hydrazones have characteristic melting points, facilitating identification of the carbonyl. In particular, the use of DNPH was developed by Brady and Elsmie. Modern spectroscopic and spectrometric techniques have superseded these techniques.
DNPH does not react with other carbonyl-containing functional groups such as
carboxylic acids
In organic chemistry, a carboxylic acid is an organic acid that contains a carboxyl group () attached to an R-group. The general formula of a carboxylic acid is or , with R referring to the alkyl, alkenyl, aryl, or other group. Carboxylic ...
,
amide
In organic chemistry, an amide, also known as an organic amide or a carboxamide, is a compound with the general formula , where R, R', and R″ represent organic groups or hydrogen atoms. The amide group is called a peptide bond when it is ...
s, and
esters
In chemistry, an ester is a compound derived from an oxoacid (organic or inorganic) in which at least one hydroxyl group () is replaced by an alkoxy group (), as in the substitution reaction of a carboxylic acid and an alcohol. Glycerides are ...
, for which there is resonance-associated stability as a lone-pair of electrons interacts with the
p orbital
In atomic theory and quantum mechanics, an atomic orbital is a function describing the location and wave-like behavior of an electron in an atom. This function can be used to calculate the probability of finding any electron of an atom in any spe ...
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
Dry DNPH is friction and shock sensitive. For this reason, it’s supplied damp or ‘wetted’ when a school purchases it from a chemical supplier. If DNPH is stored improperly and left to dry out, it can become explosive.
It is artificial uncoupler of electron transport chain (ETC).
See also
*
Tollens' reagent
Tollens' reagent (chemical formula Ag(NH3)2OH) is a chemical reagent used to distinguish between aldehydes and ketones along with some alpha-hydroxy ketones which can tautomerize into aldehydes. The reagent consists of a solution of silver ni ...
*
Fehling's reagent
In organic chemistry, Fehling's solution is a chemical reagent used to differentiate between water-soluble carbohydrate and ketone () functional groups, and as a test for reducing sugars and non-reducing sugars, supplementary to the Tollens' reag ...
*
Schiff test
:
The Schiff test is an early organic chemistry named reaction developed by Hugo Schiff, and is a relatively general chemical test for detection of many organic aldehydes that has also found use in the staining of biological tissues. The Schiff ...
References
{{DEFAULTSORT:Dinitrophenylhydrazine, 2, 4-
Nitrobenzenes
Reagents for organic chemistry
Hydrazines