Repeat of JennyHale-2: Measuring the solubilities of 2-hydroxypropane-1,2,3-tricarboxylic acid (citric acid); 2-oxopentanedioic acid (2-oxoglutaric acid); 3-(4-hydroxy-3,5-dimethoxyphenyl)prop-2-enoic acid (sinapic acid) and 4-methylbenzoic acid (p-toluic acid) in methanol, ethanol and THF.

This is being done to check the results now that it has come to light that there was originally a mistake with one of these compounds and the samples were inadequately mixed. The n-octanoic acid (caprylic acid), which was in fact the sodium salt of the acid has been omitted as there is none in pure carboxylic acid form. The citric acid this time is anhydrous rather than the monohydrate as a pot of anhydrous was located.

Method

12 2mL screw cap vials were labelled with their planned contents. 12 'Eppendorfs' 1.5 mL microcentrifuge tubes were labelled with their planned contents and the masses of each vial measured. Saturated solutions of each compound were prepared in ethanol, methanol and THF by adding 750 µL of each solvent to the correct vials and adding the solids as necessary and vortexing. The full details of the preparation of each solution is outlined in the experiment log. The saturated solutions were centrifuged at 13 200 rpm/16 100 rcf in an Eppendorf 5415D centrifuge. 500 µL of each supernatant was added to it's respectively labelled Eppendorf and the samples dried by speedvac, initially for around 3 hours. After 3 hours, the mass of the samples was recorded and the samples returned to the speedvac for a further hour. After this time half of the samples had dried to constant mass. the remaining samples were returned to the speedvac for around 45 minutes.
The remaining samples had their masses recorded and but two had dried to constant mass. The two that had not dried appear to have done something unexpected, so the non-drying maybe due to some chemical reaction having taken place.
The calculations can be found in the JennyHale-10a spreadsheet.

Results and Discussion

The results show a marked difference between this experiment and JennyHale-2. It seems likely that the results in JennyHale-2 can be written off as unreliable, resulting from inadequate mixing. It is likely that the solutions were not saturated in the previous experiment.
The results for citric acid cannot be directly compared to the previous experiment as in JennyHale-2 the monohydrate was used and in this experiment, anhydrous citric acid was used. This experiment measures the solubilities as 1.862 M in ethanol, 3.079 M in methanol and 1.798 M in THF.
The results for 2-oxoglutaric acid show a definite increase in the measured solubility. The solubilities were calculated as 2.994 M in ethanol, 5.018 M in methanol and 3.123 M in THF. The results for ethanol and methanol may be a bit high as the samples don't seem to be drying. The samples started off as white solids after 3 hours, but were looking waxy and damp in appearance at the point of final mass measurement. In JennyHale-2, the solubilities were measured as 0.89 M, 2.48 M and 1.54 M respectively.
The results for sinapic acid show a definite increase in solubility in ethanol and methanol, but only a very modest increase in THF. The solubilities were measured as 0.785 M in ethanol compared to 0.08 M in JennyHale-2; 1.044 M in methanol compared to 0.11 M in JennyHale-2; and 0.453 M in THF compared to 0.44 M in JennyHale-2.
The results for p-Toluic acid show modest rises in solubility compared to JennyHale-2. The solubilities were measured as 0.786 M in ethanol, 0.837 M in methanol and 1.748 M in THF. By comparison the solubilities in JennyHale-2 were 0.76 M, 0.72 M and 1.46 M respectively.

Overall, the solubilities have all increased and the results should now fit in better with the results of solubility modelling, which was what was queried in the original results.
[Now that we know that some compounds take longer to get into solution even these higher values might be a bit under with only a few minutes vortexing - it would be worth trying to sonicate for at least 30 min or heat them and observe solid coming out when cooling to room temperature - that would confirm saturation JCB]

Experiment Log

Friday 16.01.09 GMT
Measured lab temperature as 22°C by holding a thermometer in the air until temperature settled.
10.32 - Measured masses of empty Eppendorfs.
10.49 - Added 2 normal spatula scoops of citric acid to ethanol. Vortexed for 1 minute in 10 second intervals.
10.51 - Added 2 normal spatula scoops of citric acid to ethanol. Vortexed for 1 minute in 10 second intervals. Cloudy solution produced.
10.53 - Added 2 normal spatula scoops of citric acid to methanol. Vortexed for 20 seconds in 10 second intervals.
10.54 - Added 2 normal spatula scoops of citric acid to methanol. Vortexed for 10 seconds.
10.55 - Added 2 normal spatula scoops of citric acid to methanol. Vortexed for 20 seconds in 10 second intervals.
10.56 - Added 2 normal spatula scoops of citric acid to methanol. Vortexed for 1 minute in 10 second intervals.
10.58 - Added 2 normal spatula scoops of citric acid to methanol. Vortexed for 1 minute in 10 second intervals. Cloudy solution produced.
11.00 - Added 2 normal spatula scoops of citric acid to THF. Vortexed for 1 minute in 10 second intervals. Cloudy solution produced.
11.02 - Vortexed the solution of citric acid in ethanol for 1 minute in 10 second intervals.
11.04 - Added 2 normal spatula scoops of citric acid to ethanol. Vortexed for 1 minute in 10 second intervals. Solution apparently saturated.
11.06 - Vortexed the solution of citric acid in methanol for 1 minute in 10 second intervals. Solution apparently saturated.
11.08 - Added 2 normal spatula scoops of citric acid to THF. Vortexed for 1 minute in 10 second intervals. Solution apparently saturated.
11.11 - Added 4 narrow spatula scoops of 2-oxoglutaric acid to ethanol. Vortexed for 1 minute in 10 second intervals.
11.13 - Added 4 narrow spatula scoops of 2-oxoglutaric acid to ethanol. Vortexed for 1 minute in 10 second intervals.
11.16 - Added 4 narrow spatula scoops of 2-oxoglutaric acid to methanol. Vortexed for 30 seconds in 10 second intervals.
11.18 - Added 4 narrow spatula scoops of 2-oxoglutaric acid to methanol. Vortexed for 1 minute in 10 second intervals.
11.22 - Added 4 narrow spatula scoops of 2-oxoglutaric acid to methanol. Vortexed for 1.5 minutes in 10 second intervals.
11.25 - Added 4 narrow spatula scoops of 2-oxoglutaric acid to methanol. Vortexed for 2 minutes in 10 second intervals. Solution apparently saturated.
11.30 - Added 4 narrow spatula scoops of 2-oxoglutaric acid to THF. Vortexed for 20 seconds in 10 second intervals.
11.31 - Added 4 narrow spatula scoops of 2-oxoglutaric acid to THF. Vortexed for 1.5 minutes in 10 second intervals.
11.34 - Added 4 narrow spatula scoops of 2-oxoglutaric acid to THF. Vortexed for 2 minutes in 10 second intervals. Solution apparently saturated.
11.39 - Added 4 large narrow spatula scoops of sinapic acid to ethanol. Vortexed for 1 minute in 10 second intervals. Produced cream opaque saturated solution.
11.42 - Added 4 large narrow spatula scoops of sinapic acid to methanol. Vortexed for 1 minute in 10 second intervals. Produced cream opaque saturated solution.
11.45 - Added 4 large narrow spatula scoops of sinapic acid to THF. Vortexed for 2 minutes in 10 second intervals. Produced cream opaque saturated solution.
11.48 - Added 4 large narrow spatula scoops of p-toluic acid acid to ethanol. Vortexed for 1 minute in 10 second intervals. Produced off-white opaque saturated solution.
11.50 - Added 4 large narrow spatula scoops of p-toluic acid acid to methanol. Vortexed for 1 minute in 10 second intervals. Produced off-white opaque saturated solution.
11.52 - Added 4 large narrow spatula scoops of p-toluic acid acid to THF. Vortexed for 1 minute in 10 second intervals. Produced off-white opaque saturated solution.
11.55 -Checked saturation of all solutions. Vortexed all oxo-glutaric acid solutions for 30 seconds each. All solutions saturated.
12.01 - Centrifuged samples for 1 minute.
12.11 - Started speedvac having transferred 500 µL supernatant from each sample to respectively labelled Eppendorf and set up samples in Speedvac.
15.19 - Samples removed from Speedvac, masses measured and samples returned to speedvac.
15.28 - Speedvac re-started.
Remaining method not timed. My fault, I forgot to check the time accurately.