2,4"Dinitrophenylhydrazine preparation

Dinitrophenylhydrazine. Prepare a saturated solution in 20 mL of the purified methanol. This solution should be discarded after one week (solution A). 

The exothermicity and violence of the reaction of hydrazine hydrate with 1-chloro-2,4-dinitrophenol caused destruction of the reactor in which the reaction was carried out. This reaction is of the same kind as the previous one (2,4-dinitrophenylhydrazine preparation). 

Method. The keto acid residue is dissolved in 1.0 ml of 2,4-dinitrophenylhydrazine (prepared by dissolving 500 /rmoles in 100 ml of 2.0 Nhydrochloric acid at 40 °C stable for 2 weeks) and left to stand for 30 min at 30 °C. A minimum of a four-fold molar excess of 2,4-dinitrophenylhydrazine is required for stoichiometric conversion of the keto acid into the hydrazone. The reaction is complete in 5 min for keto monocarboxylic acids, and in ca. 20 min for keto dicarboxylic acids. The hydrazones may be extracted from the reaction mixture with ethyl acetate. An aliquot portion of this solution is subjected to TLC. 

Place 2 mL of a solution of 2,4-dinitrophenylhydrazine (prepared as described for the classification test in Experiment 52D) in a test tube and add 0.15 g of the unknown compound. If the unknown is a solid, it should be dissolved in the minimum amount of 95% ethanol or 1,2-dimethoxyethane before it is added. If crystallization is not immediate, gently warm the solution for a minute in a hot water bath (90°C) and then set it aside to crystallize. Collect the product by vacuum filtration. 

Dinitrophenylhydrazine is a very important reagent for the identification of aldehydes and ketones (pp. 342, 346). It is readily prepared from chloro-2,4-dinitrobenzene (I). In the latter compound the chlorine is very reactive in... 

This method cannot be applied to polynitro amines, since these are so weakly basic that they can be diazotised only under special conditions in strongly acidic solutions. In such cases use may, however, be made of the mobility oonfared upon halogen atoms by the presence of nitro groups in the orlko and para positions. Thus the valuable reagent 2 4-dinitrophenylhydrazine is readily prepared by the condensation of 2 4-dinitrochlorobenzene with hydrazine ... 

If an unknown compound gives a positive test with the 2 4-dinitrophenylhydrazine reagent, it then becomes necessary to decide whether it is an aldehyde or a ketone. Although the dimedone reagent (Section 111,70,2) reacts only with aldehydes, it is hardly satisfactory for routine use in class reactions. It is much simpler to make use of three other reagents given below, the preparation and properties of which have already been described (Section 111,70). 

Dinitrophenylhydrazine reagent may be prepared by either of the following methods. 

The following reagent, a 0.25 m solution of 2,4-dinitrophenylhydrazine, may be used for the preparation of derivatives of keto compounds. Dissolve 25 g of 2,4-... 

Assay Transfer 2.0 ml of camphor spirit to a suitable pressure bottle containing 50 ml of freshly prepared dinitrophenylhydrazine TS. Close the pressure bottle, immerse it in a water bath, and maintain at about 75° for l6 hours. Cool to room temperature, and transfer the contents to a beaker with the aid of 100 ml of dilute sulfuric acid (1 in 12). Allow to stand not less than 12 hours at room temperature, transfer the precipitate to a tared filter crucible, and wash with 100 ml of dilute sulfuric acid (1 in 12) followed by 75 ml of cold water in divided portions. Continue the suction until the excess water is removed,dry the crucible and precipitate at 80° for 2 hours, cool, and weigh. The weight of the precipitate so obtained, multiplied by O.U58I, represents the weight of 10 l6 n sample taken. 

These reagents have a number of drawbacks. First of all, they are toxic especially via contact with skin. The LD50 (dermal, rat) of DCC is 71 mg kg. This should always be considered if the reaction is used for the preparation of materials for biological applications. Moreover, the N.N -dialkylurea formed during the reaction is hard to remove from the polymer except for preparation in DMF and DMSO, where it can be filtered off. In case of esterification of polysaccharides in DMSO in the presence of these reagents, oxidation of hydroxyl functions may occur due to a Moffatt type reaction (Fig. 25, [188]). The oxidation products formed can be detected with the aid of 2,4-dinitrophenylhydrazine, e.g. in case of the conversion of dextran with DCC in DMSO [189],... 

Dinitrophenylhydrazones (DNPHs) were applied to the GC analysis of keto acids. As with carbonyl compounds, they are prepared by reaction with 2,4-dinitrophenylhydrazine and are also used mainly for the preliminary isolation of keto acids. They can be isolated from a dilute aqueous sample by adsorption on activated carbon and selective desorption [178] hydrazones of aldehydes with a methyl formate-dichloromethane mixture and hydrazones of keto acids with a pyridine-water azeotropic mixture. Hydrazones of acids are released from their pyridine salts with methanol containing hydrogen chloride. After... 

A series of azophenol acerands 4 was prepared by condensation of crowned benzoquinones 10 with 2,4-dinitrophenylhydrazine in ethanol [7b], The quinone was derived from p-methoxyphenol (6) as shown in Scheme 1 [8]. By bis(hy-droxymethylation) (67% yield of 6, followed by methylation (92%) of the phenol group and Williamson-type reaction with ditosylates of oligoethyleneglycol in the presence of sodium hydride, crowned 1,4-dimethoxybenzene 9 was obtained in reasonable yields. Oxidative demethylation of 9 with ceric ammonium nitrate (CAN) in aqueous acetonitrile at 50 °C gave the desired crowned benzoquinones 10 in good yields. 

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