2.4- Dinitrophenylhydrazones aldehyde determination

Dinitrophenylhydrazones (DNP) aldehyde determination, 670 core aldehydes, 689 malondialdehyde determination, 669 ozonide reduction, 726... 

The aldehyde R"CHO liberated can be determined quantitatively by means of dinitrophenylhydrazine. In the case of formaldehyde (R" = H) being split in an alcoholic-acid medium, it has been found that the formation of a dinitrophenylhydrazone is a relatively slow process. This seems to suggest that formaldehyde is originally split off in the form of an acetal which gradually yields formaldehyde under action of dinitrophenylhydrazine. 

When present in macro quantities, aldehydes and ketones can be determined by conversion to the 2,4-dinitrophenylhydrazone which can be collected and weighed. When present in smaller quantities (10 3M or less), although hydrazone formation takes place, it does not separate from methanol solution, but if alkali is added an intense red coloration develops the reagent itself only produces a slight yellow colour. Measurement of the absorbance of the red solution thus provides a method for quantitative determination. 

Many organic chemicals are analyzed by RPC. These include various arylhydroxylamines as the N-hydroxyurea derivative with methyl isocyanate (614) alkyl- and alkoxy-disubstituted azoxybenzenes (6t5), n-alkyl-4-nitrophenylcarbonate esters ranging in length from methyl to octyl (616), 4-nitrophenol in the presence of 4-nitrophenyl phosphate (617), ben-zilic acid, and benactyzine-HCI using ion-pair chromatography (618), as well as aniline and its various metabolites (619), stereoisomers of 4,4 -dihydroxyhydrobenzoin (620), and aldehydes and ketones as the 2,4-dinitrophenylhydrazones (621). The technique has also been used to analyze propellants and hydrazine and 1,1-dimethylhydrazine were quantitita-vely determined (622, 623). 

Direct GC analysis of hydrazones is carried out only with special derivatives, e.g., if the sensitivity of the determination is to be increased. GC retention data have been reported for phenylhydrazones [107], dinitrophenylhydrazones [108], and trichloro-phenylhydrazones [109] of different aldehydes and ketones. Particularly the last two types can be used to advantage in trace analysis using the ECD. 

It can thus be seen that zwitterions IV and V would be stabilized by the interaction of the alcohol with them, and the ozonide would have no opportunity to form and decompose abnormally. Whether zwitterions IV and V are formed in equal amounts depends upon the groups which are attached to the double bond and the carbon atom to which the ozone molecule initially adds. The final products, VI and VII, may be considered as hemiperacetals or hemiperketals and could be isolated only under special conditions. However, they can be easily decomposed with either sulfurous acid or sodium bisulfite and the ketones or aldehydes formed determined quantitatively as their 2,4-dinitrophenylhydrazones. 

Kuwata, K., Uebori, M., and Yamaski, Y., Determination of aliphatic and aromatic aldehydes in polluted airs as their 2,4-dinitrophenylhydrazones by high performance hquid chromatography,... 

Y. Suzuki, Class Determination of Aliphatic Aldehydes and Ketones as Their 2,4-Dinitrophenylhydrazones by Flow Injection Analysis [in Japanese]. Bunseki Kagaku, 34 (1985) 414. 

S. Honda and K. Kakei, Periodate oxidation analysis of carbohydrates. Vn. High-performance liquid chromatographic determination of conjugated aldehydes in products of periodate oxidation of carbohydrates by dual-wavelength detection of their 2,4-dinitrophenylhydrazones, J. Chromatogr., 152 (1978) 405 11. 

Let us focus here on determining the various carbony compounds. Figure 4.46 shows a HPLC chromatogram for the separation and detection of the first six homologous series of aldehydes as their 2,4-dinitrophenylhydrazone derivatives accomplished in the author s laboratory. The reaction of aldehydes and ketones with 2,4-nitrophenylhydrazine under mildly acidic conditions in water to form stable hydrazones is a well-known reaction in organic chemistry. The homologous series with R representing Ci, C2, C3, C4, C5, and Cg react as follows ... 

Thiosemicarbazones are of special interest, as they form insoluble compounds with monovalent metals such as silver, copper and mercury, which may be an aid to their separation from mixtures and to their quantitative determination. The colour of the nitrated phenylhydrazine derivatives can be characteristic of the type of carbonyl group. p-Nitrophenylhydrazones of aliphatic compounds are yellow or brown, those of aromatic compounds red. 2,4-Dinitrophenylhydrazones of saturated aliphatic aldehydes and ketones are yellow or orange, those of a, -unsaturated carbonyls are red, and those of simple aromatic compounds are yellow, orange or red. They are usually formed in excellent yields. 

Several classification tests might also be of assistance in classifying this compound. Does the 2,4-dinitrophenylhydrazine test for an aldehyde or ketone give a positive result Isolate the 2,4-dinitrophenylhydrazone derivative and determine its melting point. Does it correspond to the literature value of 180 °C What further test could be run to determine whether the carbonyl is present as an aldehyde or ketone ... 

Transformation to 2,4-dinitrophenylhydrazones combined with the chromatopolarographic technique has also been used recently ) for the separation and determination of aliphatic aldehydes (cf. p. 183). The mixture of 2,4-dinitrophenylhydrazones of propionic, butyric, and valeric aldehydes is separated on a rubber column with isooctane and 70 per cent dimethylformamide containing 0-2 M potassium chloride. If the current at —1-3 V is plotted as a function of the eluated volume, three separate elution peaks are obtained. 

Periodate ion has been determined by the formation of a chromophore with 2,2 -azinobis(3-ethylbenzothiazoline-6-sulphonic acid) and by means of an iodide-selective electrode. " The 2,4-dinitrophenylhydrazones derived from aldehydic fragments produced on periodate oxidation of carbohydrates have been separated by t.l.c., after which the individual hydrazones could be determined spectrophotometrically. ... 

Hydrolysis of the labeled compound with 2 N sulfuric acid furnished 3-amino-4-methyl-2-hexanone which, on treatment with iodine in the presence of sodium hydroxide, furnished isoleucine and iodoform. The iodoform was oxidized to carbon dioxide, while treatment of isoleucine with ninhydrin furnished 2-methylbutanal, isolated as its 2,4-dinitrophenylhydrazone. Kuhn-Roth oxidation of the aldehyde gave acetic acid which was degraded by the Schmidt procedure to carbon dioxide and methylamine. The 2-methylbutanal was also degraded stepwise by the method of Strassman. Determination of the radioactivity of the various degradation products showed that 94% of the activity was equally shared between the lactam C(2) and side-chain C(10) carbonyl atoms. The remaining activity was shared between C(4) of the lactam ring and the a> carbon atom of the ec-butyl side chain. The results are consistent with derivation of tenuazonic acid from isoleucine and two molecules of acetic acid. However, the direct incorporation of isoleucine into tenuazonic acid was not investigated. 

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