Identification of an unknown carbonyl
In this experiment you will be given an unknown aldehyde or ketone. You will obtain the IR and nmr spectra, do the Tollen's test, and prepare two solid derivatives. In the report, identify the unknown and compare the experimental values with the ones given in the text; make a TABLE for comparison. Be sure to include balanced equations for the Tollen's test, the preparations of the derivatives, as well as appropriate mechanisms. Do not weigh derivatives or calculate % yield.
Prepare the 2,4-dinitrophenylhydrazone derivative of your unknown. The reagent is already prepared. Mix 10 drops (0.5 mL) of your unknown in 20 mL of 95% ethanol. To this solution, add 15 mL of the 2,4-DNPH reagent. Shake the mixture vigorously. If a precipitate does not form immediately, let it stand for 15 minutes. Suction filter the solid derivative and recrystallize from 95% ethanol. After air drying, obtain the mp.
Make an additional derivative, the semicarbazone, according to the directions on page 1014 and obtain the mp.
Test the unknown with Tollen's Reagent (p 494) to see if it is a ketone or an aldehyde. Page 1000-1001 lists possible aldehydes in increasing order of boiling point and the melting points of easily prepared derivatives. Ketones are listed in the table on pages 1001-1003.
Do a simple distillation to measure the boiling point of your unknown carbonyl compound.
Obtain the IR and nmr spectra of your unknown carbonyl compound.
Answer the following questions:
1) An unknown organic compound (b. 212-216 oC) gives a positive 2,4-DNPH test and is positive with Tollen's reagent. A semicarbazone derivative is made that melts at 228-232 oC. What is the identity of the unknown? What would you do next?
2) Predict the products of the reaction of the following with silver nitrate in ammonium hydroxide:
cylcohexanone
formaldehyde
acetone
acetophenone
butyraldehyde
3) In the reaction of an aldehyde or ketone with derivatives of ammonia, the reaction can be catalyzed by sulfuric acid. However, it is important that the pH not be too low since the reaction will slow down at very high acid concentrations. Explain.
4) Ketones do not oxidize readily. However, cyclohexanone will react with powerful oxidizing agents at high heat to adipic acid (HO2C-(CH2)4-CO2H). The reaction is not really one of the ketone, but the enol. Write equations to show how this is possible.