Researcher

Rida Atif

Objective

To determine the recrystallization yield of cinnamic acid in cyclohexane

Procedure

1.0659g of cinnamic acid and 22.19mL of cyclohexane were added into a 25mL Erlenmeyer flask and set on a hot plate to boil. Once all of the cinnamic acid had dissolved into the cyclohexane, the flask was removed from the hot plate and set to cool down for about 48 hours. The crystals that formed in the flask were filtered through a suction filter and massed.

Results

Calculation Sheet
EXP309-HNMR
EXP309-HNMR2
The solubility of the cinnamic acid in cyclohexane was 0.31M at boiling point
The predicted recrystallization yield for this solubility was approximately 90.7%
The actual yield was 92.8%

Discussion

Since there was no literature yet found about the solubility of cinnamic acid in cyclohexane, the experiment was based off the values the solubility curve provided.
According to the curve, the solubility at boiling point should have been 0.86M which means about 96.6% of the crystals would be yielded back.
The experiment actually had a solubility of 0.31M at boiling point which predicted about 90.7% recrystallization yield.
The predicted solubility and actual solubility are about 0.5M different, and this is because far more cyclohexane was needed to dissolve the cinnamic acid than was predicted using the value from the solubility curve.
Since the actual yield slightly higher (92.8%) the crystals could still have not been completely dry; the EXP309-HNMR spectra proves this because there is small peak at 1.5 for cyclohexane.
This peak at 1.5 could also be water.
The NMR spectra for EXP309-HNMR2 has more clear peaks, and the peaks around 4ppm are no longer there. The peak around 1.5ppm is still existent, but that is just the water peak from the CDCl3

Conclusion

Although cyclohexane was a good solvent to recrystallize cinnamic acid, the solvent selector did not predict the solubility at boiling point as precisely as it did for experiments such as EXP305 in which the same solvent was used, but to dissolve benzoic acid.
This could mean that cinnamic acid should be looked at more carefully to figure out what the reason is the solubility curve is predicting higher solubilities.

Log

2012-07-03

10:32 - Turned on hot plate to 170C
10:38 - Added 1.0659g of cinnamic acid into a 25mL erlenmeyer flask
10:45 - Added 6mL of cyclohexane into the same flask and set on hot plate
10:47 - Added cyclohexane into a small flask and set that on hot plate too
10:56 - Added approximately 1mL of boiling cyclohexane into flask.
10:59 - Added approximately 1mL of boiling cyclohexane into flask.
11:03 - Added approximately 0.5mL of boiling cyclohexane into flask.
11:05 - Cinnamic acid was sticking to the walls of the flask, so a spatula-like tool was used to scratch the inside walls to get it off.
11:10 - Approximately another 1mL was added to the flask, and the walls were scratched.
11:15 - Approximately another 1mL was added to the flask, and the walls were scratched.
11:20 - Approximately another 1mL was added to the flask, and the walls were scratched.
11:29 - Approximately another 1mL was added to the flask, and the walls were scratched.
11:35 - Crystals are forming on the walls of the flask
11:46 - Approximately another 1mL was added to the flask, and the walls were scratched.
12:13 - Turned heat up to 210C
12:19 - All of the solid has dissolved into the cyclohexane and the flask was removed from the hot plate and set down to cool.

2012-07-05

11:13 - Filtered the contents of the flask through a suction filter
11:20 - The crystals look like flakes
11:41 - Mass of empty vial with cap: 13.6039g
11:42 - Stopped the vacuum of the filter
11:45 - Mass of vial, cap, and cinnamic acid crystals (exp309a): 14.5933g