2,4-Dinitro-6 -phenylhydrazine

Brady s reagent A solution of 2,4-dinitro-phenylhydrazine sulphate in methanol. Gives characteristic crystalline yellow to deep red 2,4-dinitrophenylhydrazone products with aldehydes and ketones. 

Dissolve I g. of pinacol (preparation, p. 148) in 20 ml. of water, and add 20 ml. of the 5% aqueous sodium periodate solution. After 15 minutes, distil the clear solution, collecting the first 5 ml. of distillate. Treat this distillate with 2,4-dinitro-phenylhydrazine solution A (p. 263). Acetone 2,4-dinitrophenyl-hydrazone rapidly separates from the solution when filtered off, washed with a small quantity of ethanol, and dried, it has m.p. 126-127°, and after recrystallisation from ethanol it has m.p. 128°. 

To a few drops of formalin solution add a few drops of dinitro-phenylhydrazine reagent A (p. 263) a yellow precipitate is produced in the cold. Acetaldehyde and acetone give orange-coloured precipitates. Dissolve water-insoluble compounds e.g-y benzaldehyde, salicylalde-hyde, acetophenone and benzophenone) in a small volume of methanol before adding reagent B. With benzophenone the precipitate forms slowly. 

To the clear solution obtained by warming 0-5 g. of 2 4-dinitro-phenylhydrazine, 1 ml. of concentrated hydrochloric acid and 8- 10 ml. of ethanol, add 0-25 g. of the aldehyde and heat just to boiling. Allow to cool to room temperature, filter off the 2 4-dinitrophenylhydiuzone and recrystallise it from ethanol or glacial acetic acid. 

The acetone test reagent consists of a 0 1 per cent, solution of 2 4-dinitro-phenylhydrazine and is prepared as follows Dissolve 0-25 g. of 2 4-dinitrophenyl-hydrazine in 60 ml. of water and 42 ml. of concentrated hydrochloric acid by warming on a water bath cool the clear yellow solution and dilute to 250 ml. with water. The acetone test is considered negative when 5 ml. of the reagent and 4-5 drops of the distillate give no cloudiness or precipitate of acetone 2 4-dinitro-phenylhydrazone within 30 seconds. After a negative test is obtained, it is stron y recommended that the mixture in the flask be refluxed for 5-10 minutes with complete condensation and then to collect a few drops of distillate for another test. If no acetone is now detected, the reduction is complete. 

Compounds related to phenylhydrazine react in an analogous way p Nitrophenylhydrazine yields p nitrophenylhydrazones 2 4 dinitro phenylhydrazine yields 2 4 dinitrophenylhydrazones... 

In order to characterize them and more readily separate them from interfering accompanying substances carbonyl compounds (aldehydes, ketones) can be converted to hydrazones at the start. The reagent mainly employed is 2,4-dinitro-phenylhydrazine in acidic solution [70], This yields osazones with aldoses and ketoses. Some examples are listed in Table 15. 

Phenolic aldehydes Apply sample solution and then acidic 2,4-dinitro-phenylhydrazine solution, allow to react, dry and develop [15]... 

Imine formation from such reagents as hydroxylamine and 2,4-dinitro-phenylhydrazine is sometimes useful because the products of these reactions— oximes and 2,4-dinitrophenylhydrazones (2,4-DNPs), respectively—are often crystalline and easy to handle. Such crystalline derivatives are occasionally prepared as a means of purifying and characterizing liquid ketones or aldehydes. 

Isolation of Citronellal and Citral. At the close of each experiment (7 to 10 days), the nests were frozen intact. Groups of 200 workers were placed in a micro-Soxhlet apparatus and extracted for 8 hours with methylene chloride. A few milligrams of carrier citronellal and citral were added and the mixture was applied to a thin-layer chromatoplate (silica gel G) which was developed with hexane-ethyl acetate (92 to 8) to separate citronellal and citral (3). The aldehydes were detected by spraying with a solution of 2, 4-dini-trophenylhydrazine in tetrahydrofuran (20) and the citronellal and citral peaks were scraped off and allowed to react with excess dinitro-phenylhydrazine reagent for a further 12 hours. 

Phenyl-hydrazino)- , 3,4-oxadiazole konnen aus 2-(2-Benzyliden-l-phenyl-hydr-azino)-l,3,4-oxadiazolen durch limhydrazonisierung mit 2,4-Dinitro-phenylhydrazin in miiBi-gen Ausbeuten synthetisiert werden547 (vgl. Synthesen anderer 2-Hydrazino-l,3,4-oxadiazole S. 607) ... 

Reaction with 2 4-dinitrophenylhydrazine. Add 2 drops (or 0 05-0-1 g.) of the substance to be tested to 3 ml. of the 2 4-dinitro-phenylhydrazine reagent, and shake. If no precipitate forms immediately... 

Xanthone is unreactive towards hydrazine and phenylhydrazine. The oxime is obtained by reaction of xanthione (xanthene-9-thione) with hydroxylamine, or from xanthone and hydroxylamine in pyridine. When the oxime is heated in water with phenylhydrazine, the phenylhydrazone is formed. In acid solution, xanthone reacts normally with 2,4-dinitro-phenylhydrazine but xanthone-1 -carboxylic acid (435) gives the pyridazinone (436), possibly via the hydrazone (57JCS1922). When the oxime is heated with phosphorus pentachloride it undergoes a Beckmann rearrangement to give the amide (437) (70MI22300). 

Removal of unchanged salicylaldehyde by steam distillation (followed conveniently by testing the distillate with 2,4-dinitro-phenylhydrazine reagent) provides a product sufficiently pure for use in the next step. Also, the recovered salicylaldehyde can be used again without further purification. 

An alternative procedure49 for effecting the conversion of acid chlorides into aldehydes is chemical reduction with bis(triphenylphosphine)copper(i) tetrahy-droborate (see also Section 5.7.4, p. 594). The procedure is illustrated by the synthesis of 3,4-dimethoxybenzaldehyde which is isolated as the 2,4-dinitro-phenylhydrazine derivative50 (cognate preparation in Expt 6.120). 

When unknown compounds are identified without the aid of spectroscopy classification tests are used. Reacting the carbonyl in a ketone or aldehyde with an amine (2,4 dinitro-phenylhydrazine) to form an inline is the easiest way to detect a ketone or aldehyde (Reaction l). The iinine that forms is a highly colored solid. The color of the solid also helps to indicate structural characteristics. Ketones and aldehydes with no conjugation tend to form itnines with yellow to orange colors, while highly conjugated ketones or aldehydes form imines with red color. 

Dissolved nitrite in natural waters was determined at subnanomolar levels by derivatization with 2,4-dinitro-phenylhydrazine followed by hplc (102). The method has a detection limit of 0.1 nM, with an average precision of 4% RSD at ambient natural water concentrations. Irgasan 300 ((2,4-dichlorophenoxy)-phenol) has been determined in the wastewater of a slaughterhouse, using gc/ecd after derivatization with diazomethane (103). The detection limit was found to be 0.2 ng/L. 

Among hazardous reactive chemicals, special attention should be paid to those which easily explode by mechanical impact or friction. The use of these chemicals without knowledge of their characteristics inevitably leads to an accident These chemicals include Dibenzoylperoxide (BPO), 5—chloro-1,2,3-thiadiazole (5—CT),mixtures of chlorate and red phosphorus, and 2,4—dinitro- phenylhydrazine (DNPH). Appropriate handling procedures for these highly sensitive chemicals during preliminary evaluations must be established. 

Procedure Add 0.4 mL of sample to 20 mL of 2,4-Dinitro-phenylhydrazine Reagent. Mix by swirling, and allow the mixture to stand for 5 min. Collect the precipitate on a filter, and rinse thoroughly with alcohol. Dissolve the precipitate in 20 mL of hot ethylene dichloride, filter, and cool the filtrate in an ice bath until crystallization occurs. Collect the precipitate on a filter. Redissolve the precipitate by refluxing with 30 mL of acetone, filter, and cool the filtrate in an ice bath until crystallization occurs. Collect the precipitate on a filter. The 2,4-di n i trophenyI hydrazone so obtained melts between 185° and 195° (see Melting Range or Temperature, Appendix KB). 

Carbonyl compounds Azobenzene-4-carboxylic acid hydrazide. l,2-Dimethyl-4,3-di(mercaptomethyl)benzene. N,N-Dimethylglycinehydrazide hydrochloride. 2,4-Dinitro-phenylhydrazine. 2-Diphenyiacetyl-l,3-indanedione-l-hydrazone. Ethoxycarbonylhydrazine. 

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