RECRYSTALLIZATION, MELTING POINT, and HPLC ANALYSIS of ANALGESICS Experiment 7: RECRYSTALLIZATION, MELTING POINT, and HPLC ANALYSIS of ANALGESICS

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.

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.

ANALGESICS IN GOODY’S POWDERS

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).

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.

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

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

WASTE MANAGEMENT Empty your filtrates from crystallization of aspirin and acetaminophen in the appropriately labeled bottle in the waste hood. Used melting point capillaries should be thrown in the broken glass box, NOT the trashcan!