Researcher

Rani Saba

Objective

To recrystallize trans-cinnamic acid from a high boiling point 1:1 ethanol-water solvent and washing with the low boiling point solvent pentane at a concentration of 1M.

Procedure

Created a 1:1 ethanol-water solvent in excess. Added 1.5284 of the ethanol-water to a 10 ml test tube containing 0.2500 g of trans-cinnamic acid. Once the solution was created, the test tube was carefully placed in a 400 ml hot water bath. The sample was then heated until the crystals went completely into the solution - which occurred at around 75C. The solution was then removed from the bath and began to crystallize instantaneously at room temperature. Once crystallization completed, the recovered crystals were then filtered through a sintered glass funnel and washed twice with 1.2500 g of ethanol-water. Next, the crude product was washed 5 times with pentane. After 5 minutes, the sample was removed from suction and the sintered glass funnel containing the crude product was weighed for yield calculation. Finally, the recovered crystals were analyzed by HNMR to determine purity.

Results

Recrystallization Sheet
Trans-cinnamic acid recovered: 0.0913 g
Percent Yield: 37%
Appearance: White crystals
HNMR Spectrum of Sample 1
Purity: Fairly pure but with traces of ethanol and pentane

Discussion

Overall, the performed experiment resulted in a very low yield, but did show evidence that the performed method could be very useful in recrystallizing cinnamic acid from a high boiling point 1:1 ethanol-water solvent. One key note while observing the experiment was that much of our desired product passed through the sintered funnel and was lost. This stems from the reality that cinnamic acid is slightly soluble in water, but extremely soluble in ethanol. After our solution was formed, proper time may not have been given for our crude product to recrystallize. However, this was a function of necessity, as the 10 mL test tube made it very difficult to remove our gel-like formation. As time went on, the product became more and more dense and thus difficult to remove. Using a slightly larger test tube, although adding to the risk of transfer loss or lack of thorough mixture, may greatly increase the ability to remove our product and transfer it to the sintered glass funnel at an appropriate time. In addition, cinnamic acid is known to be slightly soluble in pentane, thus multiple washes (five in this case) can also lead to a loss of product. Therefore, while our low yield of 37% leaves room for improvements, the fairly high purity of our final product is promising. Improving lab techniques, and using a slightly larger test tube would be suggestions for improving our yield, while trying to minimize the amount of required pentane washes would be ideal.

Conclusion

After completion of the experiment, we saw that the above method does have several opportunities for improvement, but was still successful in recrystallizing pure cinnamic acid. While the opportunities are noted above, the experiment serves as a great guideline for future experiments that can test cinnamic acid recrystallization in a water-ethanol solvent. While the experiment was performed a 1 M solution, it would be worth expanding on a solution of lower concentration. While the yield in this particular experiment wasn't particularly high, the solution did recrystallize fairly easily, which would be a great advantage in situations of lower concentration. The solubility in pentane is of particular importance however, as using an excess can further diminish our yield or contaminate our product. While suction was used as a drying method in this case, noticeable traces of the pentane remain. Attempts to dry the product by applying suction were necessary, but also ran the risk of product loss due to the solubility of cinnamic acid in the pentane. Balancing these constants should be the guidelines for advancing this technique, while performing this experiment was successful in substance and in theory.

Log

2013-03-13

11:21 Added 3 g ethanol to a 25 mL beaker
11:22 Added 3.8423 g water to the beaker
11:24 Mixed the solution well in order to create our 1:1 ethanol-water solvent
11:27 Added 0.2500 g of trans-cinnamic acid into a 10 mL test tube
11:31 Added 1.5284 g of the ethanol-water to the 10 mL tube
11:34 Created a 400 mL hot water bath in a 500 mL beaker, set on 300 C
11:36 Carefully placed the 10 mL test tube into the hot water bath along with a thermometer
11:45 Observed the crystals go into the solution at 75C
11:46 Removed the test tube from the hot bath and allowed for crystallization to occur at room temperature
11:55 Crystallization is observed as complete
12:00 Sintered glass funnel is weighed
12:09 Once crystallization completed, the recovered crystals were filtered through the sintered glass funnel
12:13 Crystals are washed with 1.2532 g of ethanol-water solution
12:18 Crystals are washed with 1.3011 g of ethanol-water solution
12:20 Crystals are washed five times at three minute intervals with pentane
12:45 Suction removed from sample and sintered glass funnel removed
12:52 Glass funnel containing crude product is weighed and mass of product is determined to be 0.0913 g
12:53 Sample is removed from funnel and placed in 10 mL test tube for storage
13:05 HNMR analysis is performed using 0.0252 g of our sample