Thin-Layer and Column Chromatography: Identifying an Unknown Analgesic, Determining an
combination of different solvents, allows
Ideal Mobile Phase and Monitoring
for the possibility of an infinite range of
the Progress of the Mitsunobu Reaction.
solvents will result in a wider variety of
polarities. The choice of mobile phase is
Nazareth College of Rochester, 4245 East Ave,
solvent front and likewise if the solvent
remain too close to the origin. In either
analgesics using thin-layer scenario, separation is poor. The ideal chromatography (TLC). The ideal
the stationary phase consists of silica or
In most chromatography chromatography is advantageous. The
chromatography experiment is also silica
polarity remains constant throughout the
experiment. The term absorbent is
suffice, some separations require ratios
cm to spare and the height of the column should be at least ten times its diameter.
1 Lehman J.W. Operational Organic Chemistry. A Problem-Solving Approach to the Laboratory Course, Third ed; Prentice Hall: Upper Saddle
the movement of the solvent front 2.
does not need to reach any specific point
before it is removed from the developing
chamber. Rf values ensure the ability to
different distances up the plate they must
different plate, assuming that the mobile
phase used remained constant for all the
acid. The spot for the unknown was view under a UV lamp to be between the spots of aspirin and acetaminophen 1. We knew that the analgesic could not be acetaminophen because acetaminophen is too weak to react with HCl of the aqueous layer in the extraction mee concluded,
TLC plates are given in Table 1. There is a difference of 0.066 between the Rf value for the unknown and the Rf value
for acetaminophen, and there is a -0.077 difference between the Rf values of the
4 Knoerzer, T. Fall Organic Chemistry Exp. #3.
http://www.pub.naz.edu:9000/~organic/fall/fallor
for identification, even though we know the unknown is not acetaminophen.
acetaminophen should be spotted on another TLC plate using a solvent that is not as polar as the mobile phase. A slightly less polar solvent would move the spots towards the middle of the plate, away from the solvent front and hopefully yield more distinct Rf values.
Azacycles, part of a reaction was found to contain 77% of the desired product by “chroma
5 Occiato, E.G.; Prandi, C.; Ferrali, A.; Guarna, A.; Deagostino, A.; Venturello, P. J. Org. Chem.2002, Vol. 67, No. 20, 7144-7145.
Monitoring the progress of a reaction is
collecting ten fractions, the first, fifth
fraction contained a faint spot while the
phases consisting of different quantities
along with a faint impurity spot. The ten
4. The ideal mobile phase is somewhere Experimental Section
halfway up the plate. The lower spots in
Identification of aspirin. To separate
reactant mixture is not pure 3. However,
unknown, salacyimide, aspirin, caffeine,
because there is no starting material or
Determination of the ideal mobile
polar and the spots moved too far up the
phase in order to monitor the progress of the Mitsunobu reactoin. The mobile
solvent was very non-polar and the spots
Column chromatography. To a buret
testing or reactions. The desired product
of the Mitsunobu reaction, was separated
using a 1:9 ethyl acetate: hexane mobile
flashed with nitrogen. Ten fractions were
collected and the first, fifth and tenth
fractions were tested using TLC with a 35% ethyl acetate, 65% hexane mobile phase. Supporting Information Available: Lehman, John. Operational Organic Chemistry: A Problem-Solving Approach to the Laboratory Course, Third edition. Prentice Hall: Upper Saddle River, NJ, 1999; pp 116, 617 – 630.
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the movement of the solvent front 2. 
for identification, even though we know the unknown is not acetaminophen.
acetaminophen should be spotted on another TLC plate using a solvent that is not as polar as the mobile phase. A slightly less polar solvent would move the spots towards the middle of the plate, away from the solvent front and hopefully yield more distinct Rf values.
Azacycles, part of a reaction was found to contain 77% of the desired product by “chroma
5 Occiato, E.G.; Prandi, C.; Ferrali, A.; Guarna,