Qualitative Analysis of Organic Compounds
and identification of unknown organic compounds constitutes a very
aspect of experimental organic chemistry. There is no definite set procedure
that can be applied overall to organic qualitative analysis. Sundry
have different approaches, but a systematic approach based on the scheme
given below will give satisfactory results. Qualitative tests that
substantial quantities of a number of (often hazardous) chemicals to
be stocked in the lab for experimental use are frequently being
of organic chemistry in favor of modern spectroscopic techniques. In
order to deduce the identity of your two unknowns, you will combine
test, that for the classification of halides, with modern analytical
techniques of infrared spectroscopy (IR) and mass spectrometry (MS).
on qualitative tests can be found in this Appendix and Hornback on
A. Preliminary Test
Note physical characteristics: solid, liquid, color, and odor. Compounds
that are yellow to red in color are often highly conjugated. Amines often
fish-like odor, while esters usually have a pleasant fruity or floral smell.
Acids have a sharp, biting odor. Odors can illicit information about your
unknown; it is wise to sniff them with caution. Some compounds can have
or make you feel nauseous.
B. Physical Constants
Determine the boiling point or melting point. Distillation is recommended
in case of liquids. It serves the dual purpose of determining the boiling
point as well as purifying the liquid for subsequent tests.
C. Solubility Tests
The solubility of the unknown in the following reagents provides very useful
information. In general, about 1 mL of the solvent is used with approximately
0.1 g or 0.2 mL (2-3 drops) of the unknown compound. Assistance in analyzing
the results from your solubility tests can be found in the solubility flowchart
given in Fieser and Williamson on page 606. (Careful, this flowchart is
much more complex than our lab requires and often can make it more difficult
to form conclusions from your solubility data..)
D. Group Classification Tests
After analysis of the previous tests and the compound's IR spectrum,
if needed, further information can be deduced by performing carefully
selected functional group classification tests.