Solubility of vanillin in methanol and ethanol at 30 and 40°C (vortexing method for longer periods)

This is a continuation of JennyHale-6 to get more accurate figures for solubility at higher temperatures and to answer, hopefully, whether there is any correlation.

Method

Four 1.5 mL microcentrifuge tubes ("eppendorfs") were weighed and labelled with planned contents. Four 2 mL microcentrifuge tubes were labelled with their planned contents. To two 2 mL tubes was added 750 µL ethanol and to the remaining two, 750 µL methanol. One ethanol and one methanol tube were placed to warm in a heat block at 30 °C and the remaining tubes in a hot block at 40°C.
Once warmed, four [narrow] spatula scoopfuls of vanillin was added to each tube and the contents dissolved by vortexing in 10 second intervals as per JennyHale-6. This process was repeated until the solutions were deemed saturated (each tube having been vortexed for at least 3 minutes in total) and been kept at their respective temperatures between addition of solute and vortexing. For in depth order and times see time log.
The saturated solutions were centrifuged for one minute in an Eppendorf 5415D centrifuge at 13,200 rpm/16,100 g. 500 µL of the supernatant from each solution was added to it's respectively labelled eppendorf and dried in the speedvac vacuum centrifuge for ~3 hours at room temperature (speedvac does not list rotor speed and is just on/off). Samples were removed and weighed before being returned to the speedvac for further drying until [almost] constant weight.
Full details can be found in the spreadsheet here http://spreadsheets.google.com/ccc?key=pUtF1N4vVD6fQMcEwUCFFGw&hl=en.

Time log

Friday 21.11.08 GMT

09.56 - Turned on heat blocks to warm to 30 and 40°C.
09.57 - Labelled 2 mL microcentrifuge tubes and eppendorfs.
10.00 - Weighed eppendorfs.
10.03 - Added solvent to tubes.
10.05 - Added one methanol and one ethanol tube to 30°C heat block.
10.10 - Added one methanol and one ethanol tube to 40°C heat block.
10.11 - Added four spatula scoopfuls of vanillin to the 30°C ethanol ("VE30"). Vortexed for 2 x 10 seconds. Vanillin had all dissolved so added 4 more scoops. Vortexed for 1 minute in 10 second intervals. Returned to heat block.
10.14 - Added four spatula scoopfuls of vanillin to the 30°C methanol ("VM30"). Vortexed for 2 x 10 seconds. Vanillin had all dissolved so added 4 more scoops. Vortexed for 1 minute in 10 second intervals. Added four more scoopfuls Returned to heat block.
10.16 - Vortexed VE30 for 1 minute in 10 second intervals. Added four scoops. Returned to heat block.
10.19 - Vortexed VM30 for 10 seconds. Added four scoops. Vortexed for 1 minute in 10 second intervals. Added 4 scoops and returned to heat block.
10.23 - Vortexed VE30 solution for 1 minute in 10 second intervals. Returned to heat block.
10.25 - Added four spatula scoopfuls of vanillin to the 40°C ethanol ("VE40"). Vortexed for 10 seconds. Vanillin had all dissolved so added 4 more scoops. Vortexed for 1 minute in 10 second intervals. Returned to heat block.
10.28 - Added four spatula scoopfuls of vanillin to the 40°C methanol ("VM40"). Vortexed for 10 seconds. Vanillin had all dissolved so added 4 more scoops. Vortexed for 1 minute in 10 second intervals. Returned to heat block.
10.30 - Vortexed VE30 for 1 minute in 10 second intervals. Solid remained. Returned to heat block.
10.32 - Vortexed VM30 for 1 minute in 10 second intervals. Added four scoops. Vortexed for 1 minute. Returned to heat block.
10.36 - Added 4 scoops to VE40, vortexed for 1 minute in intervals as previously. Returned to heat block.
10.39 - Added 4 scoops to VM40, vortexed for 10 seconds. All dissolved so 4 more scoops added. Vortexed for 1 minute as previously. Returned to heat block.
10.43 - Vortexed VE30 for 2 minutes in 10 second intervals. Solid remained. Returned to heat block.
10.46 - Vortexed VM30 for 2 minutes as previously. Added four scoops.
10.49 - Added four scoops to VE40, vortexed for 1 minute as previously. Returned to heat block.
10.51 - Vortexed VM40 for 10 seconds, added 4 scoops then vortexed for 1 minute as previously and returned to heat block.
10.54 - Vortexed VE30 for 1 minute as previously. Solid still remained. Deemed saturated.
10.56 - Vortexed VM30 for 2 minutes as previously. Solid still remained. Deemed saturated.
10.59 - Vortexed VE40 for 2 minutes as previously. Solid still remained. Deemed saturated.
11.02 - Vortexed VM40 for 10 seconds. Added 2 scoops. Vortexed for 2 minutes as previously. Small amount of solid remained, 2 scoops added but nothing else could be done as tube was now full. Decided it was saturated due to small amount of solid remaining.
11.11 - Centrifuged for 1 minute
11.13 - 500 µL of each solution added to it's respective Eppendorf.
11.15 - Samples added to speedvac and speedvac started.
14.35 - Samples removed from speedvac and mass measured.
14.39 - Samples returned to speedvac.
14.40 - Speedvac returns to vacuum.
15.50 - Samples removed from Speedvac and masses measured.
15.54 - Samples returned to speedvac and put back under vacuum.
16.25 - Samples removed from speedvac and masses measured.
16.50 - Spreadsheet completed.

Discussion

The results of this experiment show a very clear correlation between temperature and solubility. The trend is very clear when joined with the results of JennyHale-6. The trend can be seen on the graph in the spreadsheet accompanying this experiment. The trend looks like it may level off and stop at higher temperatures. This I think would be because at 40°C, the solvents are nearing their boiling point and would start to evaporate thus preventing the solubility from increasing limitlessly. It would be interesting to try and do the experiment with the solvents cooled down to see if the solubility decreases and follows the trend. I am however happy to stop the tests with vanillin and return to measuring compounds that are more relevant to the UGI reactions. (well vanillin is one of the aldehydes we use in the Ugi reaction JCB)
I believe that the experimental method is finally optimised to get very accurate solubilities. This method will be used for all future solubility recordings.
It looks like you can reproduce the room temperature result now - very nice. And it does looks like there is a definite temperature trend - this could be useful later on if we incorporate temperature as a variable in the Ugi reactions. JCB

effect_of_temperature_on_vanillin_solubility_in_ethanol_and_methanol.png