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.
BEFORE COMING TO LAB…

Watch the following videos:

Recrystallization
http://www.wonderhowto.com/how-to/video/how-to-illustraterecrystallization-in-organic-chemistry-271753/

Melting Point Analysis
http://www.wonderhowto.com/how-to/video/how-to-measure-meltingpoints-in-the-chemistry-lab-259806/view/
EFFECT OF TEMPERATURE ON
SOLUBILITY
Solubility vs Temperature
Solubility (g/L)
30
25
20
15
10
5
0
0
At low temperature the
substance is much less soluble.
(Note that even at low temp.
some of the substance will
remain dissolved.
20
40
Temperature (ºC)
60
80
At elevated
temperature the
substance is very
soluble.
ANALGESICS IN GOODY’S
POWDERS
O
O
H3C
O
O H
H
N
CH 3
O
Aspirin
Acetylsalicylic acid
MF: C9H8O4
MW: 180.2 g/mol
mp: 138-140 oC
Hazards: Toxic, Irritant
Solubility in H20:
1g in100mL at 37oC
1g in 300mL 21oC
o
1g in 400mL 15 C
o
~1g in 550 mL at 0 C
OH
Acetaminophen
4-acetamidophenol
MF: C8H9NO2
MW: 151.2 g/mol
mp 169-172oC
Hazards: Toxic, Irritant
Solubility in H20
1g in 70mL at 31oC
1g in 150 mL at 21oC
PERCENT RECOVERY
• Percent recovery: an indication of how much of the
active ingredient you were able to recover after the
purification method.
•HPLC Area %: the percent of the active ingredient
present in the sample submitted for analysis.
•The percent recovery of compound B is calculated
by:
Mass of B recovered
x 100
% Recovery of B =
Mass of B used initially
OVERVIEW

ASPIRIN

Reweigh aspirin + filter papers from last lab.

Subtract out filter paper weights to get ACTUAL RECOVERY OF
ASPIRIN.

Prepare 2 melting point capillaries of the EXTRACTION
ASPIRIN.

Dissolve aspirin in hot ethanol, then hot water, then few
drops of hot ethanol.

Cool to room temp, then in ice for 15 minutes.

Suction filter.

Prepare HPLC sample.

Secure small filter paper + aspirin in larger filter paper and
submit.

No final weight or melting point sample until next lab!
OVERVIEW

ACETAMINOPHEN

Transfer acetone/acetaminophen solution from vial
to beaker and evaporate acetone completely.

Dissolve acetaminophen in hot water (dropwise).

Cool to room temp, then in ice for 15 minutes.

Suction filter.

Prepare HPLC sample.


Secure small filter paper + aspirin in larger filter
paper and submit.
No final weight or melting point sample until next
lab!
Table 7.1
Aspirin
Acetaminophen
* Theoretical recovery after extraction (g)
• Same # as
Table 6.1
• Same # as
Table 6.1
*Actual recovery after extraction (g)
• Same # as
Table 6.1
• Same # as
Table 6.1
*% Recovery after extraction
• Same # as
Table 6.1
• Same # as
Table 6.1
Theoretical recovery after recrystallization (g)
Actual recovery after recrystallization (g)
% Recovery after recrystallization
• % Recovery is
≠
HPLC Area %

Same as…
• Obtain weight
during next lab
Actual
X 100
Theoretical

Same as…
• Obtain weight
during next lab
Actual
Theoretical
X 100
OVERVIEW

MELTING POINT ANALYSIS




Prepare a melting point capillary containing the
provided impure aspirin.
Perform a melting point analysis on this along with
the EXTRACTION ASPIRIN prepared above.
Begin MelTemp on setting of 4. Back down temp
slightly as thermometer approaches 20o C from the
expected melting point (lit value).
Record melting range (Ti-Tf).
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
Table 7.2
Impure Aspirin preparation
Aspirin
Acetaminophen
(Week 1)
---
Ti-Tf
Extraction sample melting range (oC)
(Week 1)
---
Ti-Tf
Recrystallized sample melting range
(oC)
Literature melting point value (oC)
(Week 2)
(Week 2)
Ti-Tf
Ti-Tf
139-140
169-172
Table 7.3
HPLC retention times (min) and area %
Sample
Compound
Standards
Rt
(min)
Aspirin
Sample
Chromatogram
Rt
(min)
area %
Acetaminophen
Sample
Chromatogram
Rt
(min)
area %
Aspirin
Acetaminophen
•Samples containing a single compound are considered PURE samples,
while those containing both compounds are considered MIXED (IMPURE)
samples.
• Be sure to attach both sample chromatograms to final lab report!
• ANY SAMPLE CONTAINING VISIBLE SOLID WILL BE DISCARDED.
Student will receive a penalty for not providing a sample.
SAFETY CONCERNS
• Ethanol
and reagent acetone are both
extremely flammable. Keep away from open
flames, and use extreme caution when
applying heat!
WASTE MANAGEMENT


Place all liquid waste from recrystallization
in container labeled “LIQUID ORGANIC
WASTE”.
Used melting point capillaries should be
thrown in the broken glass box, NOT the
trashcan!

Any student leaving the melting point capillary
tubes in the MelTemp apparatus will receive a
technique grade penalty!
LABORATORY NOTEBOOK
(Pre-lab)
• OBJECTIVE
(Must clearly state…)
•What is the goal of the experiment?
• How will you accomplish this goal?
• How will you determine if it worked?
• TABLE OF PHYSICAL DATA
(Complete the following table using
MSDS sheets from a site on WWW Links ONLY. Wikipedia is unacceptable)
Compound
MW
(g/mol)
bp (Co)
mp
(Co)
Acetone
XXX
Ethanol
XXX
d
(g/mL)
aspirin
XXX
XXX
acetaminophen
XXX
XXX
• REFERENCE TO PROCEDURE
HAZARDS
(Must include…)
•full title
•Edition
•authors
•page numbers where actual procedure can be found
LABORATORY NOTEBOOK
(In-lab)
DATA/CALCULATIONS
•
•
•
ASPIRIN
•
•
•
•
•
•
•
Weight of large filter paper + small filter paper + aspirin (from extraction)
Actual weight of aspirin (from extraction)
Weight of small filter paper
Weight of large filter paper (for storage)
Experimental melting point of extracted aspirin
Experimental melting point of IMPURE aspirin
HPLC vial slot #
•
•
•
Initial weight of acetaminophen (from extraction)
Weight of large filter paper (for storage)
HPLC vial slot #
ACETAMINOPHEN
• EXPERIMENTAL PROCEDURE
•
•
In paragraph form, describe the procedure that you actually followed during
the lab.
Paragraph must be written in PAST TENSE, PASSIVE VOICE.
•
•
Include any volumes or weights of chemicals used during the experiment.
Include any mistakes, accidents, or observations if necessary.