Researcher

Marshall Moritz

Objective

To determine the solubility of p-fluorobenzoic acid in 6 different solvents: ethanol, methanol, acetonitrile, THF, DMSO, and toluene by NMR spectropscopy.

Procedure

Saturated solutions of p-fluorobenzoic acid in 6 different solvents were prepared by adding excess solute to 200uL of solvent in a half-dram vial. The vials were vortexed for approximately 10 seconds and if necessary, more solute was added until after vortexing, precipitate remained on the bottom of the vial. The vials were sonicated until solid remained for 30 minutes of consecutive sonication. The supernatant was then removed from the vials by Pasteur pipette. NMR tubes were labelled appropriately; E for ethanol, M for methanol, A for acetonitrile, T for THF, D for DMSO, and O for toluene. 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 300MHz Varian instrument.

Results



Spreadsheet Exp106

Spectra

ONSCExp106A1 Raw data for JCAMP dx file ONSCExp106A1
ONSCExp106A2 Raw data for JCAMP dx file ONSCExp106A2
ONSCExp106A3 Raw data for JCAMP dx file ONSCExp106A3
ONSCExp106E1 Raw data for JCAMP dx file ONSCExp106E1
ONSCExp106E2 Raw data for JCAMP dx file ONSCExp106E2
ONSCExp106E3 Raw data for JCAMP dx file ONSCExp106E3
ONSCExp106M1 Raw data for JCAMP dx file ONSCExp106M1
ONSCExp106M2 Raw data for JCAMP dx file ONSCExp106M2
ONSCExp106O1 Raw data for JCAMP dx file ONSCExp106O1
ONSCExp106O3 Raw data for JCAMP dx file ONSCExp106O3
ONSCExp106T3 Raw data for JCAMP dx file ONSCExp106T3
ONSCExp106D1 Raw data for JCAMP dx file ONSCExp106D1
ONSCExp106D2 Raw data for JCAMP dx file ONSCExp106D2
ONSCExp106D3 Raw data for JCAMP dx file ONSCExp106D3

Discussion

The concentration of p-fluorobenzoic acid in any non-aqueous solvent had not been previously reported at the time of this experiment. Thus the values generated by this experiment could not be compared to any other values but themselves. There were several peculiarities in the solubilities yielded from this experiment [1]. While the solubilities for acetonitrile, DMSO, and methanol were nearly uniform, the solubility of p-fluorobenzoic acid in ethanol, toluene, and THF give rise to discussion. The solubility of p-fluorobenzoic acid in toluene was zero, however the integration of some peaks in the NMR spectra yielded non-zero concentration values even when the upper and lower limits of integration were set to zero. These values were manually changed to zero (noted as red numbers in the spreadsheet), as the concentration was assumed to be zero. It could also be the case that the toluene peaks covered up the aromatic peaks of the solute in the NMR, thus making it seem as though there were no solute peaks and that the solubility was zero. The solubility of p-fluorobenzoic acid in THF only yielded one data point, making the standard deviation misleading. Repeating this experiment to generate new values would be useful to verify the solubility measured in this experiment. Finally, the solubility of p-fluorobenzoic acid in ethanol yielded interesting results. Two of the solubilities, 0.55M and 0.45M are fairly close to each other, but the third, 1.39M, is much greater. All of their NMR spectra looked the same, so there was no contamination of the sample. It is most likely that vial E2 was not properly seeded and thus the supernatant was supersaturated [we could rule that out knowing the temperature after sonication JCB] and generating a larger concentration than the other two vials. Otherwise, the experiment generated good results barring any other potential uniform systematic errors, and the experiment was successful.

Conclusion

The solubility of p-fluorobenzoic acid in acetonitrile was found to be 0.37M, 0.33M, and 0.47M. The mean value was 0.39M and the standard deviation was 0.072.
The solubility of p-fluorobenzoic acid in ethanol was found to be 0.80M, 1.95M [based on EXP121 this value can't be right - marked DONOTUSE JCB], and 0.66M. The mean value was 1.137M and the standard deviation was 0.707.
The solubility of p-fluorobenzoic acid in DMSO was found to be 4.08M, 4.16M, and 4.33M. The mean value was 4.19M and the standard deviation was 0.127.
The solubility of p-fluorobenzoic acid in methanol was found to be 0.7M and 0.82M. The mean value was 0.76M and the standard deviation was 0.084.
The solubility of p-fluorobenzoic acid in toluene was found to be 0.00M and 0.00M. The mean value was 0.00M and the standard deviation was 0.00.
The solubility of p-fluorobenzoic acid in THF was found to be 2.49M. The mean value was 2.49M and the standard deviation was 0.00.

Log

2009-06-08
9:37--Added 200uL of acetonitrile to 3 vials labeled A1, A2, and A3.
9:39--Added 200uL of toluene to 3 vials labeled O1, O2, and O3.
9:40--Added 200uL of THF to 3 vials labeled T1, T2, and T3.
9:42--Added 200uL of DMSO to 3 vials labeled D1, D2, and D3.
9:44--Added 200uL of methanol to 3 vials labeled M1, M2, and M3.
9:46--Added 200uL of ethanol to 3 vials labeled E1, E2, and E3.
9:48--After adding 1 small scoop of p-fluorobenzoic acid to vials E1, E2, and E3, the vials were capped and vortexed for approximately 10 seconds. This was repeated two times and the solution was found to be saturated.
9:50--After adding 2 small scoops of p-fluorobenzoic acid to vials M1, M2, and M3, the vials were capped and vortexed for approximately 10 seconds. This was repeated one time and the solution was found to be saturated.
9:52--After adding 1 small scoop of p-fluorobenzoic acid to vials O1, O2, and O3, the vials were capped and vortexed for approximately 10 seconds. This was repeated one time and the solution was found to be saturated.
9:54--After adding 3 small scoops of p-fluorobenzoic acid to vials D1, D2, and D3, the vials were capped and vortexed for approximately 10 seconds. This was repeated three times and the solution was found to be saturated.
9:58--After adding 1 small scoop of p-fluorobenzoic acid to vials T1, T2, and T3, the vials were capped and vortexed for approximately 10 seconds. This was repeated three times and the solution was found to be saturated.
10:00--After adding 1 small scoop of p-fluorobenzoic acid to vials A1, A2, and A3, the vials were capped and vortexed for approximately 10 seconds. This was repeated one times and the solution was found to be saturated.
10:06--All vials E1, E2, E3, A1, A2, A3, O1, O2, O3, T1, T2, T3, D1, D2, D3, M1, M2, and M3 were set in a large beaker filled one-quarter with water and placed in the sonicator. The temperature was read at 19.0C and the timer was set to 30 minutes.
10:52--All vials were removed from the sonicator and set out to cool to room temperature.[did you get the temperature of the sonication bath at this point and the cooling "room temperature" bath? JCB]
10:59--All vials were seeded with crystals of p-fluorobenzoic acid to ensure solutions were not supersaturated.[You should sonicate at this point - seeding might take too long JCB]
11:12--All vials were filtered, passing the contents of the vials through a pasteur pipette packed with cotton, thus allowing only the supernatant to pass through.
11:31--NMR tubes were prepared for each vial by taking the respective supernatants and added 500uL of CDCl3 to appropriately labeled NMR tubes.
11:45--Vial M3 appeared to have two layers, perhaps contaminated by water during sonication. Vials O2, T1, and T2 yielded no supernatant.

2009-06-10
9:15--The NMR spectra of all vials except M3, O2, T1, and T2 were taken on the 300MHz Varian instrument.

References

[1] Solubility of p-fluorobenzoic acid in non-aqueous solvents

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