SEPARATION AND RECOVERY OF ORGANIC COMPOUNDS, THIN LAYER
CHROMATOGRAPHY, COLUMN CHROMATOGRAPHY,
CRYSTALLIZATION AND MELTING POINTS
In the first few weeks of this semester you will be learning a variety of techniques
that are routinely used by organic chemists.
In the first week, you will separate two
organic compounds from a mixture that also contains sand.
Once you have recovered the
organic compounds, you will need to separate them from each other, and to purify each
To accomplish this, you will use thin layer chromatography (TLC) to determine
solvents appropriate to separate the components, and then use this information the second
week to run a column separation.
The third week you will check the purity of the
separated compounds by taking melting points and then purify the compounds further by
crystallizing each from an appropriate solvent or solvent pair.
A brief discussion of most
of the techniques is provided, but you are responsible for reading more comprehensive
treatments in the laboratory textbooks available in the Science Library.
Background and Procedure
Obtain approximately 3.0 grams (weighed to the nearest 0.1g) of one of the
mixtures of sand, 9-fluorene and 9-fluorenone.
Place this into a 125 mL Erlenmeyer
flask and add about 10 mL of dichloromethane, CH
(an older name, still in use, is
Add a magnetic stir bar and heat on a stirrer-hot plate, set as low as
possible, under your fume hood
Swirl the flask and note that some of the organic
Add dichloromethane, a little at a time, and observe if more solid
Keep the solution stirring to avoid bumping.
Add enough solvent to
completely dissolve the organic compounds.
The amount of solvent used is not terribly
critical at this point because you will be evaporating it after you remove the sand.
the solution by gravity, using a fluted filter paper.
Fluting filter paper increases the
surface area of the paper and allows air to enter the flask to permit rapid pressure
equalization. Gravity filtration is used to remove insoluble impurities, in this case, the
Save a small amount of the filtrate for thin layer chromatography (just a few drops
in a spot plate are sufficient), transfer the rest to an appropriately sized round-bottomed
flask, i.e. one that will be no more than half full, and evaporate the filtrate on the rotary
Transfer the residue from the flask to a storage vial labeled with
your name, lab day, and identity of the contents.
The next step is to spot your filtrate and authentic samples of fluorene and
fluorenone side-by-side on a TLC plate and elute the plate with an available solvent you
think should separate them.
Thin layer chromatography is a very rapid technique, so if
your “educated guess” proves incorrect, you can easily run plates using several different
solvents in a short period of time.
The following discussion of thin layer chromatography
should help to familiarize you with the technique.
Chromatography is defined as the