Dinitrophenylhydrazine test

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. All aldehydes and ketones give an immediate... 

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. 

Primary and secondary alcohols are also oxidized by this reagent (see Experiment 52H). Therefore, this test is not useful in identifying aldehydes unless a positive identification of the carbonyl group has already been made. Aldehydes give a 2,4-dinitrophenylhydrazine test result, whereas alcohols do not. 

Alcohols are neutral compounds. The only other classes of neutral compounds used in this experiment are the aldehydes, ketones, and esters. Alcohols and esters usually do not give a positive 2,4-dinitrophenylhydrazine test aldehydes and ketones do. Esters do not react with Ce(lV) or acetyl chloride or with Lucas reagent, as alcohols do, and they... 

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. Several chemical tests (see Chapter 9) may also be used to establish that an alcohol has been formed by the reduction of a ketone. Perform the ceric nitrate and 2,4-dinitrophenylhydrazine test on both the starting ketone and the alcohol product. Do your results demonstrate that an alcohol was obtained You may also wish to prepare a phenyl- or a-naphthylurethane derivative of the cyclohexanol. Before the development of chemical instrumentation, the formation of solid derivatives was used extensively to identify reaction products. 

Chemical Tests. Chemical tests can assist in establishing the nature of the functional groups in usnic acid. Perform the 2,4-dinitrophenylhydrazine test and the ferric chloride test (see Chapter 9). Are the results significant ... 

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. Chemical classification tests may also be run to assist in the characterization of this material. The 2,4-dinitrophenylhydrazine test (Chapter 9) should give a positive result. Isolation of this derivative and the determination of its melting point would further establish the identity of the product as cyclohexanone. 

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. 

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... 

An unknown organic liquid, compound A, was found to bum with a yellow, sooty flame and give a positive Lucas test ( 5 min). Upon treatment with sodium dichromate-sulfuric acid solution it produced compound B, which also burned with a yellow, sooty flame. Compound B gave a positive 2,4-dinitrophenylhydrazine test, but a negative result when treated with the Tollens reagent. However, compound B did give a positive iodoform test. 

The 2,4 dinitrophenylhydrazine test does not distinguish between aldehydes and ketones. However, there are two simple tests which can do so, based on the feet that aldehydes can be oxidized whereas ketones cannot. Fehling s solution and Tollens reagent are both mild oxidizing reagents that react with aldehydes to produce carboxylic acids (Figure 10.80). 

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