Rani+Saba+Research+Report+Winter+2013

**Winter 2013**
During my senior project, the research I conducted focused on improving methods of recrystallization of organic compounds. While recrystallization in itself is a fairly common and practical method for purifying a compound, special care must be made in selecting the proper solvent for each experiment. Using solubility curves in conjunction with the Abraham Model, we were able to design and conduct several experiments using caffeine and trans-cinnamic acid as test compounds. The methods that were tested were rather new, as they used a high boiling point solvent as the recrystallization solvent. Conducting the experiments, we were focused mainly on the level of purity – which was later tested using HNMR analysis, rather than yield – which could be improved with instrumental revisions and stricter calculations. In addition, multiple experiments were run with samples of varying concentrations, a true test to how useful a solvent or method could be in recrystallizing our pure compound.

While it was noted that high boiling points recrystallizations solvents have been often avoided due to their difficulty in being removed, their benefits were equally noted. Using high boiling point solvents like 1-octanol would easily allow solutes such as caffeine or trans-cinnamic acid with high boiling points to enter into solution. In our initial experiments, the high boiling point solvent 1-octanol was tested for its usefulness and found to be extremely successful. In a later experiment, a 1:1 ethanol-water solvent was used and found to be useful but not equally as successful. In both cases, pentane washes were used to remove the original solvents and assist in the recrystallization of the original compound. Since pentane evaporates rather quickly, multiple washes were proven to successfully remove the high boiling point solvents without contaminating the recrystallized pure compounds.

**Experiments:**
Scheme for EXP344:

The first experiment performed, EXP344, was a modification of EXP343 performed by fellow researcher Matthew McBride. In this experiment, three samples of trans-cinnamic acid were recrystallized using the centrifuge method. The three samples were prepared at varying concentrations - 0.25 M, 0.74 M, and 1.48 M and were prepared in 1-octanol. To reduce loss of product and to maximize our yield, the samples were prepared in 10 mL screw cap test tubes, and were not transferred from the tube during the procedure. After thick gels developed during the recrystallization process, centrifuging our samples was necessary to begin removing the 1-octanol. Once initiated, pentane washes completed the 1-octanol removal. While recrystallization only occurred within our first two samples, this was expected due to the lower concentration of our third sample. However, once everything was complete, we were able to recover 86% of our 1.48 M sample, and 77% of our 0.74 M sample. More importantly, we were able to attest to the purity of our samples by testing the melting point and to say that while lengthy, the new method did succeed in removing all of the 1-octanol used in our solution.

Scheme for EXP348:

The second experiment performed, EXP348, was a modification of EXP347 performed by fellow researcher Paris Dayon Favors II. In this experiment, we attempted to recrystallize caffeine using a sintered glass funnel in a 0.73 M solution using 1-octanol as the solvent. In addition, we experimented with a 50% trans-cinnamic acid contamination to our reactant. Using a heat gun to heat our solvent, we were able to have our crystals enter solution much faster than we had in previous experiments. Once our solution had gone to completion, we were able to begin the recrystallization process by placing our sample in an ice bath. Then, as done in Exp347, our sample was filtered through the sintered glass funnel and washed with 1-octanol. Finally, one last wash was done with pentane and the sample was left on the vacuum filter to dry. Once completed, our pure caffeine was tested using both melting point and HNMR analysis, and proved successful in both cases. Along with recovering a high 86.60% yield, the HNMR spectrum of our sample showed no evidence of the trans-cinnamic acid contamination and only trace amounts of 1-octanol. Our melting point was also very supportive of these findings. In comparison to our earlier experiments, the addition of the sintered glass funnel proved extremely useful, as it reduced the amount of pentane washes necessary, while ensuring the maximum yield. This is especially useful for future experiments where we are dealing with lower concentrations, as our sample size and yield are more greatly affected by loss of product due to transfer or solubility in pentane.

Scheme for EXP350:

The third and final experiment performed, EXP350, focused on recrystallizing trans-cinnamic acid using a different high boiling point solvent - a 1:1 ethanol-water solvent. Considering our earlier findings, and using information on trans-cinnamic acid's solubility in other high-boiling point solvents, we constructed a procedure investigating the ability to recrystallize trans-cinnamic acid starting with a 1M solution. In addition to seeing how useful a 1:1 ethanol-water solvent would be for compounds such as trans-cinnamic acid, using a higher concentration allows for a projection of the range at which it would perform. If we were able to obtain a higher pure yield, than a lower concentration could be used for future experiments. Whereas, a lower yield could suggest opportunities for its usefulness or help make alterations for future experiments. After our sample was prepared, it was heated over a 400 mL hot water bath, removed and cooled at room temperature, filtered through the sintered glass funnel, washed with our high boiling solvent, and finally washed five times with pentane. Along the way, there were several challenges that ultimately lead to a fairly low yield (37%) and that showed traces of both solvents. First and foremost, the gel that developed was very difficult to remove from our test tube, suggesting that a larger tube would be beneficial in future experiments. Furthermore, as our HNMR suggests, both solvents were present in our sample. This would lead to the belief that while mildly useful, removing the ethanol-water solvent in a different way should be discussed. In addition, it is known that trans-cinnamic acid is slightly soluble in pentane. With ethanol-water being more difficult to remove, more pentane washes are necessary. Unfortunately, while helping to remove the high boiling point solvent, multiple pentane washes result in loss of our original product, as evidenced by our low 37% yield. Therefore, while using a higher concentration could ultimately result in a more pure sample, using a lower concentration solution runs the risk of being heavily diminished or contaminated by the necessary solvent washings performed. Future experiments adjusting the mentioned variables could provide further insight of the usefulness of ethanol-water solution as a recrystallization solvent, but seemed unfavorable under the conditions of this experiment.

All of the experiments above, and collaboration with my fellow researchers proved an invaluable experience over my winter term. In addition to refining lab skills, I was provided a wealth of knowledge and direction under Dr. Bradley. While experimenting with both old and new methods, I was able to research and report on the usefulness and range of high boiling point solvents on the recrystallization method. Using multiple methods, including melting point and HNMR analysis, the reactions of caffeine and trans-cinnamic acid were investigated, altered, and refined to gather maximum yields and purity levels. The new method of using high boiling point solvents and then washing with pentane not only serves useful for the compounds tested, but leaves open the possibility to test its usefulness on other compounds. More importantly, using the results of these experiments, along with those found [|here] can be starting points for others looking to understand and expand the range of usefulness this new method by designing their own experiments.
 * Conclusion**