Measuring the solubility of benzoic acid and undecanoic acid in ethanol, methanol and THF. Remeasuring the solubility of 4-hydroxybenzaldehyde in THF.

The initial plan was to also measure solubility of 3.4-dimethoxybenzaldehyde in ethanol, methanol and THF, but on going to use it, it was found to have solidified into one single lump. (This has also happened to the decanoic acid sample and so I will melt these down as they have low melting temperatures and then take some smaller amounts to solidify/recrystallise)

Method

Seven 2 mL screp cap vials were taken and labelled with their planned contents. Seven 1.6 mL microcentrifuge tubes ("Eppendorfs") were labelled with the planned contents and the masses recorded.
Saturated solutions of benzoic acid in ethanol, methanol and THF were prepared by adding solid to 750 µL of each solvent, according to the detailed information in the log. Saturated solutions of undecanoic acid in ethanol and methanol were prepared by adding solid to 750 µL of each solvent. Undecanoic acid was particularly soluble and the solutions had to be transferred to larger tubes. 15 mL centrifuge tubes ("Falcon tubes") were chosen, but was unsuitable for the THF solution as the THF damaged the plastic. The THF solution could not be made as during preparation, the glass vial in which it was being prepared exploded.
A saturated solution of 4-hydroxybenzaldehyde in THF was prepared by adding solid to 750 µL THF as detailed in the log.
The solutions in 2 mL screw cap vials were centrifuged in an Eppendorf 5415D centrifuge for 1 minute at 13 200 rpm/16 100 rcf. The Falcon tubes were not centrifuged but there was more than sufficient volume of supernatant to avoid picking up solid.
500 µL each supernatant was transferred ['scuse my harping on this, but: how are you measuring this volume? Since this measurement is crucial to the calculation I think it's important to have some measure of its trustworthiness... e.g. what is the mass of 10 x 500 µL water transferred in the same manner? 10 x 500 µL ethanol? BH] to it's respective Eppendorf tube. The tubes were transferred to speedvac and the samples dried initially for 3 hours. After 3 hours, the sample masses were measured and the samples returned to the speedvac. The two undecanoic acid samples were gels which solidified slightly on "resting". The speedvac is getting warm despite the heater being off, so the undecanoic acid samples may need to be dried by vacuum desiccation overnight in order that the solvent is taken off at room temperature.
The samples were returned to speedvac for half an hour. At this point the undecanoic acid samples had melted again. The samples all had their masses measured. The benzoic acid samples and the 4-hydroxybenzaldehyde samples were found to be dry. The undecanoic acid samples had lost some mass.
The undecanoic acid samples put put under vacuum in a desiccator where they turned solid in a matter of minutes. The desiccator was kept under vacuum overnight and the samples had their masses measured bafter overnight drying. There was a very slight increase (<1 mg) in mass overnight. The samples were deemed to be dry and the solubilities calculated.

Results

The spreadsheet of results can be found in JennyHale-13.
The solubility of the 4-hydroxybenzaldehyde has increased dramatically and now falls much more closely in line with it's derivatives and related compounds as shown on the solubility query search. The solubility of 4-hydroxybenzaldehyde is now measured as 3.58 M, whereas the previous reading was 0.909 M. I don't know what caused the error in the previous experiment (JennyHale-12) but it is good to know that my instincts were correct that the measurement was wrong. [That was a very good observation - I just blogged about this and now you've resolved it :) JCB]
The solubility of benzoic acid in ethanol measured as 2.5 M. The solubility in methanol measured as 2.86 M. The solubility in THF measured as 2.81 M.

The solubility of undecanoic acid in ethanol was measured as 3.94 M and in methanol as 4.00 M.

Log

Thursday 12.02.09 GMT
Pre 11.05 - experiment prepared.
11.05 - Added 4 narrow spatula scoopfuls of benzoic acid to ethanol. Vortexed for 1 minute in 10 second intervals.
11.07 - Added 4 narrow spatula scoopfuls of benzoic acid to ethanol. Vortexed for 2 minutes in 10 second intervals.
11.10 - Added 4 narrow spatula scoopfuls of benzoic acid to ethanol. Vortexed for 3 minutes in 10 second intervals. Solution saturated.
11.16 - Added 4 narrow spatula scoopfuls of benzoic acid to methanol. Vortexed for 20 seconds in 10 second intervals.
11.17 - Added 8 narrow spatula scoopfuls of benzoic acid to methanol. Vortexed for 1 minute in 10 second intervals.
11.19 - Added 8 narrow spatula scoopfuls of benzoic acid to methanol. Vortexed for 3 minutes in 10 second intervals. Solution saturated.
11.24 - Added 4 narrow spatula scoopfuls of benzoic acid to THF. Vortexed for 20 seconds in 10 second intervals.
11.25 - Added 8 narrow spatula scoopfuls of benzoic acid to THF. Vortexed for 20 seconds in 10 second intervals.
11.27 - Added 4 narrow spatula scoopfuls of benzoic acid to THF. Vortexed for 3 minutes in 10 second intervals. Solution saturated.
11.31 - Noticed long needle like crystals had formed throughout the solutions of benzoic acid in ethanol and methanol. Vortexed each for 10 seconds to try and remove.
11.34 - Discovered that another aldehyde planned to be used had formed a single solid lump in the pot.
11.38 - Added 4 narrow spatula scoopfuls of undecanoic acid to ethanol. Vortexed for 10 seconds.
11.40 - Added 8 narrow spatula scoopfuls of undecanoic acid to ethanol. Vortexed for 20 seconds in 10 second intervals.
11.42 - Added 8 narrow spatula scoopfuls of undecanoic acid to ethanol. Vortexed for 20 seconds in 10 second intervals.
11.44 - Added 4 normal spatula scoopfuls of undecanoic acid to ethanol. Vortexed for 20 seconds in 10 second intervals.
11.45 - Added 4 normal spatula scoopfuls of undecanoic acid to ethanol. Vortexed for 20 seconds in 10 second intervals.
11.47 - Added 4 normal spatula scoopfuls of undecanoic acid to ethanol. Vortexed for 20 seconds in 10 second intervals.
11.49 - Added 4 heaped normal spatula scoopfuls of undecanoic acid to ethanol. Vortexed for 1 minute in 10 second intervals. Transferred solution to 15 mL Falcon tube.
11.55 - Added 8 heaped normal spatula scoopfuls of undecanoic acid to ethanol. Vortexed for 30 seconds in 10 second intervals.
11.57 - Added 4 heaped normal spatula scoopfuls of undecanoic acid to ethanol. Vortexed for 1 minute in 10 second intervals.
11.59 - Added 4 heaped normal spatula scoopfuls of undecanoic acid to ethanol. Vortexed for 1 minute in 10 second intervals.
12.01 - Added 4 heaped normal spatula scoopfuls of undecanoic acid to ethanol. Vortexed for 1 minute in 10 second intervals.
12.05 - Added 12 heaped normal spatula scoopfuls of undecanoic acid to methanol. Vortexed for 2 minutes in 10 second intervals.
12.09 - Added 8 heaped normal spatula scoopfuls of undecanoic acid to ethanol. Vortexed for 3 minutes in 10 second intervals. Possibly saturated.
12.14 - Added 8 heaped normal spatula scoopfuls of undecanoic acid to methanol. Vortexed for 2 minutes in 10 second intervals.
12.18 - felt faint so stopped for brief break.
12.29 - Vortexed undecanoic acid in ethanol solution for 40 seconds in 10 second intervals.
12.41 - Added 8 heaped normal spatula scoopfuls of undecanoic acid to ethanol. Vortexed for 2 minutes in 10 second intervals. Saturated.
12.45 - Added 8 heaped normal spatula scoopfuls of undecanoic acid to methanol. Vortexed for 2 minutes in 10 second intervals.
12.49 - Added 8 heaped normal spatula scoopfuls of undecanoic acid to methanol. Vortexed for 2 minutes in 10 second intervals.
12.52 - Added 8 heaped normal spatula scoopfuls of undecanoic acid to methanol. Vortexed for 2 minutes in 10 second intervals. Saturated.
12.55 - Added 8 narrow spatula scoopfuls of undecanoic acid to THF. Vortexed for 20 seconds in 10 second intervals.
12.59 - Added 8 narrow spatula scoopfuls of undecanoic acid to THF. Vortexed for 1 minute in 10 second intervals.
13.08 - Having transferred undecanoic acid in THF solution to larger glass vessel. Added 8 narrow spatula scoopfuls of undecanoic acid to THF. Vortexed for 40 seconds in 10 second intervals.
13.11 - Added 8 narrow spatula scoopfuls of undecanoic acid to THF. Vortexed for 1 minute in 10 second intervals.
13.13 - Added 8 narrow spatula scoopfuls of undecanoic acid to THF. Vortexed for 40 seconds in 10 second intervals.
13.15 - Added 4 normal spatula scoopfuls of undecanoic acid to THF. Vortexed for 1 minute in 10 second intervals.
13.17 - Added 8 normal spatula scoopfuls of undecanoic acid to THF. Vortexed for 1 minute in 10 second intervals.
13.20 - Added 8 normal spatula scoopfuls of undecanoic acid to THF. Vortexed for 1 minute in 10 second intervals.
13.21 - Glass vessel containing undecanoic acid in THF solution exploded whilst vortexing. Gave up on this sample due to time.
13.28 - Added 4 heaped normal spatula scoopfuls of 4-hydroxybenzaldehyde to THF. Vortexed for 1 minute in 10 second intervals.
13.30 - Added 4 heaped normal spatula scoopfuls of 4-hydroxybenzaldehyde to THF. Vortexed for 1 minute in 10 second intervals.
13.32 - Added 4 heaped normal spatula scoopfuls of 4-hydroxybenzaldehyde to THF. Vortexed for 1 minute in 10 second intervals. Saturated.
13.34 - Centrifuged the three benzoic acid solutions and the 4-hydroxybenzaldehyde solution.
13.36 - Transferred supernatants to labelled Eppendorfs
13.40 - Started speedvac.