Experiment 9
Identification of an Alcohol or Carbonyl Compound
I. Summary
In this experiment you will be given an unknown from one of the three sets listed below. Using the classification
tests, you will be able to determine the functional group present in your unknown. You will then prepare a solid
derivative. After obtaining the melting point of this derivative, you should be able to determine the identity of your
unknown.
Unknowns:
Unknown Set A~
2-Butanone
Benzaldehyde
2-Butanol
2-Pentanone
I -Pentanol
Unknown Set B:
2-methyl- 1 -propanal
2-propanone
1-pentanol
2-methyl-l-propanol
2-propanol
Unknown Set C:
trans-cinnamaldehyde
acetophenone
1-octanol
cyclohexanone
4-methyl-2-pentanol
11. Prelab
Before you come to class, prepare flow charts describing identification of unknowns in a// three sets. Each flow
chart should be specific to that set and should show which compounds give
positive/negative results for each test. Your flow charts will be checked by your TA before you
begin the experiment.
III. Procedure
Bring a clean, dry 13 x 100 nun test tube to the storeroom manager, and trade it in for a
sample of your unknown. Your unknown will be labeled as being from set "A", " B ", or "C".
Perform the identification of your unknown using the procedures described on pages 642-650 and
661-665 in the text. The three reagents you will require have been prepared for you. These are the
chromic acid (Cr03) reagent, the 2,4-DNP (2,4dinitrophenylhydrazine) reagent, and the iodoform
(12/KI/NaOH) reagent. It is very important that you run control experiments with these reagents.
You should treat known compounds with these reagents to learn what the positive and negative
tests look like.
After you have identified the functional group present in your compound, prepare the
appropriate derivative for that functional group. For alcohols, prepare the 3,5dinitrobenzoate
derivative following the directions given below. For aldehydes or ketones, prepare a 2,4-DNP
derivative according to the instructions given in the text (643). It is very important to prepare and
purify this derivative carefully and to determine its melting point accurately. Compare the melting
point of your derivative with the tabulated values for those of the possible unknowns to obtain
support for your structural assignment.
3,5-dinitrobenzoate derivatives:
Follow Method A (pages 664-665) in your text. However, you should use the following amounts
of reagents:
0.5 g 3,5-dinitrobenzoylcWoride (this will be preweighed and available in the storeroom)
1.5 m1L of your alcohol
20 drops of pyridine*
Recrystallize the product from 95% ethanol
*Pyridine should be used in the fume hood since it has a very unpleasant odor. Do not pour
pyridine nor any filtrates containing pyridine in the sink.
IV. Report Requirements
Your lab report should contain the following information:
1.
References to procedure with any changes noted - each test and derivative procedure
should be referenced specifically.
2.
Flow chart for your set -
3.
Results of each test and interpretation of these results
4.
Melting point of derivative
5. Identification of unknown. You should include a 1-paragraph discussion of how you
determined the identity of your unknown