Objective

To ascertain the solubility of 2-phenylbutyric acid in methanol, ethanol, and acetonitrile by NMR spectroscopy.

Procedure

Saturated solutions of 2-phenylbutyric acid were prepared in methanol, ethanol, and acetonitrile. The solutions were prepared by mixing together the solute and 300μL of the solvent into a vial. With each subsequent addition of solute, there were bouts of vortexing. Once the solutions showed an excess of solute, the vials were sonicated, using a Branson 1510 instrument, for 30 minutes. Solutions were then left to equilibriate. 100μL of the supernatants were micropipetted out and then dissolved into NMR tubes containing 900μL of deuterated chloroform (CDCl3). Proton NMR readings of the solutions are obtained with the use of a 500MHz instrument.

Results

Sample
Solvent
Solute
HNMR
HNMR Raw Data
Solubility (M)
1
Ethanol
2-phenylbutyric acid
HNMR
2-phbutyricacid-ethanol
6.2
2
Acetonitrile
2-phenylbutyric acid
HNMR
2-phbutyricacid-acetonitrile
6.18

Image of the supernatants
Spreadsheet




Discussion


Based upon the image of supernatants, an observation and prediction for the solubility of 2-phenylbutyric acid was made. Because each solution began with 300μL of solvent and the resulting solutions showed a dramatic increase in volume, it can be assumed that 2-phenylbutyric acid is very soluble in the choosen solvents.

Saturated solutions in each solvent was obtained. This was verified by observation of solid solute contained within the sample vials after the sonication process. Therefore, the NMR spectra obtained could be held in confidence that the spectra was from a saturated solution, and that solubilites obtained from the spectra were validated.


For the ethanol and acetonitrile results, there is a closeness in the solute-solvent ranges used for the SAMS spreadsheet. To work around and correct for the closeness of the peaks, other possible protons for integration should be checked for (preferentially in the solvent, so that the proton(s) signature used for the solute remains uniform for all samples). In the case of ethanol, the CH2-group can be used. It's signature shows up at around 3.687ppm, well away from the proton signature used for 2-phenylbutyric acid. Changing the solvent range to incorporate this new proton integration yielded a solubility result of 6.2M, it was 6.23M when using the close peak-ranges. For the case of the acetonitrile result, there was not another choice of a proton signature to use. However, a better estimation of the upper range for the solute was made. Therefore, greater care should be taken when assessing the ranges, values should be taken for the points at which peaks flatten out. The upper range for the solute was reassessd to be 1.04 from 1.1, which changed the solubilty result to 6.18M from 6.19M.

It was observed that there existed an overlap issue for the methanol result. The get the correct value of the methanol aspect of the peak, the peak integration of the overlapping peak was subtracted by the peak integration corresponding to the the CH2 peak of the solute (Actually both protons on the CH2 group are not the same). That value was then divided by 3 (# of protons used to correctly integrate the solvent). The obtained value of 0.9 was then plugged into the spreadsheet for the "solvent integral per H". The new value for the concentration of methanol is 5.38M. However, even with this correction by peak subtraction, the solubility result was not good. Therefore, the solubility result data for methanol is to be excluded.

Conclusion

The solubility of 2-phenylbutyric acid has been determined in ethanol and acetonitrile. The obtained data shows that 2-phenylbutyric acid is indeed capable of making 2M solutions for the Ugi product.




Log

(includes Observations)

2009-04-14

15:40 Ambient temperature in the lab was measured to be 26-27°C.
15:44 A saturated solution of 2-phenylbutyric acid in methanol was made by adding the solute to 300μL of methanol solvent in a vial labeled "methanol". Vortexed the vial briefly inbetween additions of solute till saturation was reached (visible solute collecting at the bottom of the vial). The volume of the solution was observed to increase greatly as solute was added.
15:55 Sonicated the solution for 30 minutes.
16:30 Left the solution to equilibriate.
16:53 More solute was added to the solution, because solute was no longer visible at the bottom of the vial.
16:56 A saturated solution of 2-phenylbutyric acid in ethanol was made by adding the solute to 300μL of ethanol in a vial labeled "ethanol". The vial was vortexed briefly inbetween additions of solute till saturation was reached. The volume of this solution also greatly increased.


17:10 A saturated solution of 2-phenylbutyric acid in acetonitrile was made by adding the solute to 300μL of acetonitrile in a vial labeled "acetonitrile". Vortexed the vial briefly inbetween additions of solute till saturation was reached.
17:26 Sonicated all 3 solutions for 30 minutes. Visible sold was let after sonication process.
18:01 Left the 3 solutions to equilibriate.
18:xx Obtained images of supernatants.
19:12 Added 100μL of supernatant from the "methanol" solution to a NMR tube containing 900μL of deuterated chloroform. Briefly swirled.
19:14 Added 100μL of the "ethanol" supernatant to a NMR t
ube containing 900μL of deuterated chloroform. Swirled briefly.
19:15 Added 100μL of the "acetonitrile" supernatant to a NMR tube containing 900μL of deuterated chloroform. Briefly swirled.
19:19 Obtained NMR spectra using a 500MHz instrument.



References

Solubility of 2-phenylbutyric acid in ethanol (Solubility data viewer)
Solubility of 2-phenylbutyric acid in acetonitrile (Solubility data viewer)

|| Compound || Inchi Key || Inchi || || 2-phenylbutyric acid || OFJWFSNDPCAWDK-UHFFFAOYAE || InChI=1/C10H12O2/c1-2-9(10(11)12)8-6-4-3-5-7-8/h3-7,9H,2H2,1H3,(H,11,12) || || Methanol || OKKJLVBELUTLKV-UHFFFAOYAX || InChI=1/CH4O/c1-2/h2H,1H3 || || Ethanol || LFQSCWFLJHTTHZ-UHFFFAOYAB || InChI=1/C2H6O/c1-2-3/h3H,2H2,1H3 || || Acetonitrile || WEVYAHXRMPXWCK-UHFFFAOYAJ || InChI=1/C2H3N/c1-2-3/h1H3 ||