2,4-dinitrophenylhydrazine, test for

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 ... 

Chemical Tests. The 2,4-dinitrophenylhydrazine test for aldehydes and ketones (see Chapter 9) may be done to confirm the presence of the carbonyl group. The isolation of this derivative and the determination of its melting point (Lit. value = 283 °C) would aid in establishing the identity of the product. 

Chemical Tests. Benzoin contains an aromatic ring. Confirm this fact by performing the ignition test (Chapter 9). To confirm the presence of the alcohol and ketone functions in benzoin carry out the chromic anhydride test for the —OH group and the 2,4-dinitrophenylhydrazine test for the C=0 group. Isolate the solid 2,4-dinitrophenylhydrazone derivative and compare its melting point to the literature value. 

The 2,4-dinitrophenylhydrazine test easily detects 1 part of acetone in 500 to 1000 parts of isopropyl alcohol. Since the reagent solution, even though kept in a stoppered bottle, may deteriorate in the course of several months, old solutions should be checked before use. For the use of the test with toluene instead of isopropyl alcohol see the note on p. 204. 

Dinitrophenylhydrazine test. Place 5 drops of each substance into separately labeled clean, dry test tubes (100 x 13 mm) and add 20 drops of the 2,4-dinitrophenylhydrazine reagent to each. If no precipitate forms immediately, heat for 5 min. in a warm water bath (60°C) cool. Record your observations on the Report Sheet. 

Although esters, like aldehydes and ketones, are neutral compounds that have a carbonyl group, they do not usually give a positive 2,4-dinitrophenylhydrazine test result. The two most common tests for identifying esters are the basic hydrolysis and ferric hydroxamate tests. 

Chemical Tests, Chemical classification data may also be useful. The ignition test, theToUens test, and the 2,4-dinitrophenylhydrazine test should aU give a positive result for the piperonal compound. 

Compound A (C7H14O) burned with a yellow, nonsooty flame and did not decolorize a bromine-methylene chloride solution. It did give a positive 2,4-dinitrophenylhydrazine test, but a negative Tollens test. Treatment of the compound with lithium aluminum hydride followed by neutralization with acid, produced compound B, which gave a positive Lucas test in about 5 min. Compound B also gave a positive ceric nitrate test. The NMR spectrum for compoimd A... 

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). 

Both aldehydes and ketones contain the carbonyl group, hence a general test for carbonyl compounds will Immediately characterise both classes of compoimds. The preferred reagent is 2 4-dinitrophenylhydrazine, which gives sparingly soluble phenylhydrazones with carbonyl compounds ... 

A mixture of 20 g (0.1 mol) of aluminum isopropoxide, 0.1 mol of an aldehyde or a ketone and 100 ml of dry isopropyl alcohol is placed in a 250 ml flask surmounted by an efficient column fitted with a column head providing for variable reflux. The mixture is heated in an oil bath or by a heating mantle until the by-product of the reaction - acetone - starts distilling. The reflux ratio is adjusted so that the temperature in the column head is kept at about 55° (b.p. of acetone) and acetone only is collected while the rest of the condensate, mainly isopropyl cohol (b.p. 82°), flows down to the reaction flask. When no more acetone is noticeable in the condensate based on the test for acetone by 2,4-dinitrophenylhydrazine the reflux regulating stopcock is opened and most of the isopropyl alcohol is distilled off through the column. The residue in the distilling flask is cooled, treated with 200 ml of 7% hydrochloric acid and extracted with benzene the benzene extract is washed with water, dried and either distilled if the product of the reduction is volatile or evaporated in vacuo in the case of non-volatile or solid products. Yields of the alcohols are 80-90%. 

Note. (I) With water-insoluble materials distillation will usually be continued until the distillate is quite clear. For water-soluble materials a suitable chemical procedure for detection must be used, e.g. for aldehydic or ketonic compounds, portions of the distillate would be tested with an aqueous acidic solution of 2,4-dinitrophenylhydrazine. 

To an ice-cold mixture of 1.0 ml of concentrated sulphuric acid and 5 ml of saturated aqueous potassium dichromate solution, add 2 ml of the alcohol or its concentrated aqueous solution. If the alcohol is not miscible with the reagent, shake the reaction mixture vigorously. After 5 minutes, dilute with an equal volume of water, distil and collect the first few ml of the aqueous distillate in a test tube cooled in ice. (Aldehydes and ketones are volatile in steam.) Test a portion of the distillate for a carbonyl compound with 2,4-dinitrophenylhydrazine reagent (p. 1218). If a solid derivative is obtained, indicating that the compound was a primary or secondary alcohol, test a further portion with SchifFs reagent (p. 1291) to distinguish between the two possibilities. The derivative may be recrystallised the m.p. may give a preliminary indication of the identity of the alcohol. 

Miscellaneous class reactions. (Section 9.5.) Determine the eifect of the following class reagents upon small portions of the original mixture (for some of the tests an aqueous solution or suspension may be used) (i) bromine in dichloro-methane solution (ii) potassium permanganate solution (iii) alcoholic silver nitrate solution (iv) 2,4-dinitrophenylhydrazine reagent (v) Schiffs reagent (vi) acetyl chloride (vii) benzoyl chloride (in the presence of aqueous sodium hydroxide) (viii) iron(m) chloride solution and (ix) bromine water. 

The distillate may contain volatile neutral compounds as well as volatile acids and phenols. Add a slight excess of 10-20 per cent sodium hydroxide solution to this distillate and distil until it is judged that all volatile organic compounds have passed over into the distillate. If necessary, the determination of the refractive index of the distillate or the application of specific chemical tests (e.g. for carbonyl compounds use the 2,4-dinitrophenylhydrazine reagent) should be used to confirm completion of distillation. Keep this distillate (S,) for Step 4. 

Aldehydes Alkanes Benedict s test Dichromate test 2,4-Dinitrophenylhydrazine (2,4-DNP) Fehling test Iodoform test Oxime Permanganate test Semicarbazone Tollen s test No test Positive for all aldehydes Positive for all aldehydes Positive for all aldehydes (and ketones) Positive for all aldehydes Positive only for acetaldehyde Positive for all aldehydes (and ketones) Positive for all aldehydes Positive for all aldehydes (and ketones) Positive for all aldehydes... 

The reaction of an aldehyde or a ketone with 2,4-dinitrophenylhydrazine produces a 2,4-dinitrophenylhydrazone derivative. This reaction is also used as a test for the presence of an aldehyde or ketone. A drop or two of a suspected aldehyde or ketone is added to a solution of 2,4-dinitrophenylhydrazine in ethanol and water. The formation of a precipitate, usually orange or red, of the derivative indicates that the unknown is an aldehyde or ketone ... 

Add to each graduate 1.0 mL of 2,4-dinitrophenylhydrazine solution (dissolve 100 mg of 2,4-dinitrophenylhydrazine in 50 mL of carbonyl-free methanol, add 4 mL of hydrochloric acid, and dilute to 100 mL with water), stopper, and heat at 70° in a water bath for 1 h. Cool to room temperature, then add to each graduate 13 mL of water and 5.0 mL of benzene, stopper, and shake vigorously. Allow the phases to separate, and pipet 2.0 mL of the benzene layer from each graduate into corresponding test tubes containing 10 mL of a 1 100 solution of diethanolamine in pyridine. Shake each tube, and allow the color to develop for 10 min. 

To 10 mL of the stock solution of 2,4-dinitrophenylhydrazine in phosphoric acid add about 0.1 g of the compound to be tested. Ten milliliters of the 0.1 M solution contains 1 millimole (0.001 mole) of the reagent. If the compound to be tested has a molecular weight of 100 then 0.1 g is 1 millimole. Warm the reaction mixture for a few minutes in a water bath and then let crystallization proceed. Collect the product by suction filtration (Fig. 1), wash the crystals with a large amount of water to remove all phosphoric acid, press a piece of moist litmus paper on to the crystals, and if they are acidic wash them with more water. Press the product as dry as possible between sheets of filter paper and recrystallize from ethanol. Occasionally a high-molecular-weight derivative won t dissolve in a reasonable quantity (20 mL) of ethanol. In that case cool the hot suspension and isolate the crystals by suction filtration. The boiling ethanol treatment removes impurities so that an accurate melting point can be obtained on the isolated material. 

A 0.1% solution of the reagent is prepared Iqr dissolving 0.12 g. of 2,4-dinitrophenylhydrazine in 26 cc. of distilled water and 21 cc. of concentrated hydrochloric acid Iqr warming on the steam bath. The clear yellow solution is then cooled and diluted to 126 cc. with distilled water. For use, several drops of the reagent and a few drops of the acetone-isopropyl alcohol distillate are mixed in a small test tube. The presence of acetone is shown by the formation of a yellow cloudy suspension or precipitate of acetone 2,4 dinitrophenylhydrazone. The test is considered negative if no cloudiness forms within one-half minute when 3 cc. of the reagent is added to 6 drops of distillate. After a negative test is obtained, it is advisable to reflux the mixture for flve to flfteen minutes with complete condensation and then to force over a few drops of distillate for another test. If no acetone is observed, reduction is complete. Otherwise the process is continued until no more acetone can be detected. This procedure indicates complete reduction even with ketones which are reduced very slowly. 

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