Experiment 7:

1
Experiment 7

• RECRYSTALLIZATION,
• MELTING POINT, and
• HPLC ANALYSIS of ANALGESICS

2
Objectives

• To learn the purification technique of
  recrystallization.
• To further purify aspirin and acetaminophen
  samples isolated by extraction.
• To learn the technique of melting point analysis.
• To analyze purity of samples by melting point and
  HPLC analysis.

3
EFFECT OF TEMPERATURE ON SOLUBILITY
At low temperature the substance is much less
soluble. (Note that even at low temp. some of the
substance will remain dissolved.
At elevated temperature the substance is very
soluble.
4
ANALGESICS IN GOODYS POWDERS
5
RECRYSTALLIZATION Recovery and Analysis
The percent recovery of compound B is calculated
by

• Purity is evaluated by
• HPLC A single peak is one indication of purity
• Melting point a sharp melting point which is
  identical to the literature melting point is an
  indication of purity (next lab).

6
EXPERIMENTAL PROCEDURE Melting Point

• Dip the open end of a mp capillary tube into the
  sample to be tested.
• Invert the capillary tube and tap it on the
  bench top to pack the sample into the closed end.
• Insert the capillary tube into one of the slots
  in the heating block of the Mel-Temp melting
  point apparatus.

7
EXPERIMENTAL PROCEDURE Melting Point

• Turn the Mel-Temp power on and adjust the temp
  control to the desired rate of heating.
• In order to obtain an accurate mp, it is
  necessary to heat
• S L O W L Y, at a rate of 2-3oC/min.
• Heating too fast may lead to inaccurate results
  because of insufficient time for heat transfer.

Thermometer
Sample slot
Eyepiece
Power
Temp control
8
SAFETY CONCERNS

• Ethanol and reagent acetone are both extremely
  flammable. Keep away from open flames, and use
  extreme caution when applying heat!

9
WASTE MANAGEMENT

• Empty your filtrates from crystallization of
  aspirin and acetaminophen in the appropriately
  labeled bottle in the waste hood.