Identification of an unknown carbonyl Practicum
You will be given an unknown aldehyde or ketone. You will be given IR and nmr
spectra, and you must prepare two solid derivatives. In the report, identify the unknown
and compare the experimental values with the ones given in the table of possible
compounds. Be sure to include balanced equations for 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 5 drops (0.25 mL) of your unknown in 10 mL of 95% ethanol. To
this solution, add 5 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 the
following page and obtain the mp.
Do a simple distillation to measure the boiling point of your unknown carbonyl
compound.
Label all definable IR and NMR peaks on your spectra.
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.
Oxime Derivative Preparation
Disolve 0.5 gm. hydroxylamine hydrochloride in 5 mL. of water and 3 mL. of 3M NaOH.
Add 0.5 gm./mL of your unknown to the above solution.
Warm the mixture in a boiling water bath for 10 minutes.
Cool in an ice bath and collect the crystals using vacuum filtration.
Dry overnight and determine the compound’s melting range.
Semicarbazone Derivative Preparation
Disolve 0.5 gm. semicarbazide hydrochloride and 0.8 gm. of Na(OAc) in 5 mL. of water.
Add 0.5 gm. of your compound, stopper and shake the solution vigorously.
Warm the mixture in a boiling water bath for 10 minutes.
Remove the beaker from the heat source and allow the solution to cool to cool to room
temperature in the beaker.
Collect the crystals using vacuum filtration.