Researcher

Marshall Moritz

Objective

To ascertain the solubility of phenylacetic acid in DMF, DMSO, THF, and benzene by NMR and by recrystallization, generating a solubility-temperature curve.


Procedure

Saturated solutions of phenylacetic acid in 4 different solvents were prepared by adding excess solute to 300uL of solvent in a half-dram vial. The vials were vortexed for approximately 10 seconds and sonicated until solid remained in the vial after 30 minutes of consecutive sonication. The supernatant was then removed from the vials by Pasteur pipette. NMR tubes were labelled appropriately; B for benzene, D for DMSO, T for THF, and F for DMF. 2-3 drops of the supernatant were added to 500uL of CDCl3 in the appropriate NMR tubes. An NMR of each sample was taken on the 500MHz Variac instrument.
Solutions of known concentration of phenylacetic acid in DMF, DMSO, THF, and benzene were made by weighing out a known amount of solvent, approximately 0.5 grams, in a tared half-dram vial. Weighed amounts of phenylacetic acid were added to each vial, which wastightly capped, parafilmed, and labelled with a sticker. Vials were set in a thermostated 3:2 water:ethylene glycol bath until the bath reached 55.0C. The bath was cooled, and the temperature at which each vial showed precipitate was recorded to create a solubility-temperature curve.


Results


EXP123NMR Spreadsheet


Exp123 Spreadsheet

Spectra

ONSCExp123DMF Raw data for JCAMP dx file ONSCExp123DMF
ONSCExp123DMSO Raw data for JCAMP dx file ONSCExp123DMSO
ONSCExp123THF Raw data for JCAMP dx file ONSCExp123THF
ONSCExp123Benz Raw data for JCAMP dx file ONSCExp123Benz

Discussion

The data yields a relatively good trendline for each plot, consistent with the solute having higher solubility at higher temperatures. The data for THF seems to suggest that phenylacetic acid is not very soluble at high temperatures, as four vials showed precipitate between 54 and 37 degrees Celsius, followed by a large gap and then precipitation near 15 and -6 degrees Celsius. However, the boiling point for THF is 66.0C, and putting the vials of THF too close to the boiling point (within 15-20 degrees) may have caused some boiling and evaporation, even with the vials capped and parafilmed. With THF evaporating, the concentration of phenylacetic acid would have been higher than recorded (same amount of solute but in less solvent), so the vials of higher concentrations would have showed precipitate at higher temperatures and thus the gap in the data. The other solvents used in this experiment all have significantly higher boiling points and this did not appear to be an issue with their respective data.
The temperature data also was very consistent with the NMR data for all solvents. The solubility of phenylacetic acid in each solvent recorded by NMR matched the solubility generated by intrapolating the solubility-temperature curve generated by the data.

Conclusion

From the data and the temperature-solubility curves, DMF would be the best solvent in which to conduct a Ugi reaction with phenylacetic acid at any temperature.

Log

2009-07-13
9:35--Added 300uL of DMF, DMSO, THF, and benzene to vials labelled F, D, T, and B.
9:49--2 scoops of phenylacetic acid were added to each vial. The vials were capped and vortexed for approximately 10 seconds. This was repeated enough times for each vial such that solid remained on the bottom of each vial after vortexing.
9:59--All vials F, D, T, and B were set in a small beaker filled one-third with water and placed in the sonicator. The temperature was read at 21.0C and the timer was set to 30 minutes.
10:12--Sonication was stopped after it was found that the cap of vial F had fallen off and vials T and D were no longer saturated.
10:14--Vial F was again made up of 300uL of DMF and enough phenylacetic such that solid remained in the vial. Phenylacetic acid was also added to vials T and D so that they again appeared to be saturated.
10:25--All vials F, D, T, and B were set in a small beaker filled one-third with water and placed in the sonicator. The temperature was read at 24.0C and the timer was set to 30 minutes.
10:59--All vials were removed from the sonicator and set out to cool to room temperature.
11:10--All vials were found to be saturated. All vials were seeded to induce precipitation in case of super-saturation.

2009-07-14
9:17--NMR tubes were prepared for all vials with appropriate labels and 500uL of CDCl3.
9:24--The saturated solutions from vials D and T were carefully collected by pasteur pipette; the supernatant was cleanly separated from the precipitate and thus easily removed.
9:36--The supernatant from vials B and F was removed by filtration. The solution was passed through a Pasteur pipette packed with cotton, thus filttering off the solids and preserving the supernatant.
9:42--All supernatants were added to their respective NMR tubes.
9:45--NMR of al vials was taken on the 500MHz machine.
10:36--Six vials with 0.5 grams of solvent were made up for each solvent: DMF, DMSO, THF, and benzene, labelled F1-F6, D1-D6, T1-T6, and B1-B6 respectively.


2009-07-14
10:34--Varying, predetermined amounts of phenylacetic acid were weighed out and added to each vial so that each vial had a known concentration.
12:07--Vials D4, D5, D6, and T6 were remade with 0.25 grams of solvent; after adding solute to 0.5 grams of solvent in these vials, the vials overflowed.
12:38--All vials were tightly capped and parafilmed.

2009-07-20
9:20--Vials with benzene as the solvent appeared to show evaporation or leaking with solute clearly on the outside of the vials, so these vials were remade, capped, and parafilmed.
9:54--All vials not in solution at room temperature were placed in the sonicator at 55.0C to equilibrate.
10:00--Vials with THF were placed in the sonicator, though very close to he boiling point of THF--evaporation of solvent possible.The following procedure describes the duration of the experiment: the bath was set to a temperature and the lid was removed from the bath so that all vials could be observed as the temperature fell. When the bath reached the desired temperature, it was left to equilibrate for approximately 5 minutes. After again looking for saturated solutions, the temperature of the bath could be lowered again.
10:13--All vials had clear, unsaturated solutions. The temperature was turned to 51.0C.
10:21--Vial T6 showed precipitate at 54C and was removed from the thermostated bath.
10:28--Vial T5 showed precipitate at 51.8C and was removed from the thermostated bath
10:29--All remaining vials were unsaturated. The temperature was turned to 47.0C
11:32--When the bath reached room temperature, 19.0C, the remaining vials were added to the bath and set to equilibrate.
11:37--Procedure continued until the last vial, F1, was removed at -24.4C.

References


Tags

loadtochemspider