Objective

Some solutes can be very volatile under low pressures within a vacuum. Knowing the time it takes to evaporate the solvent from the solution can greatly reduce the amount of error in the solubility data of the compounds. The following experiment was completed to reduce the amount of time chloroform containing solutions were kept in the speedvac.
To measure the solubility of 4-Chlorobenzaldehyde in Chloroform, by evaporating the solvent from a homogeneous, saturated solution under reduced pressure at ambient temperature.

Procedure

A saturated solution of p-Chlorobenzaldehyde was prepared in Chloroform. After centrifuging, 300uL of the supernatant was transferred to two pre-weighed half dram vials. The vials were weighed again and placed in a speed-vac for 10min. The temperature and the vacuum inside the speed-vac was noted. After evaporation for an initial 10min, the vials were weighed and placed back in the speed-vac. After another run for 10min, they were weighed. This process was performed for a third time.

Results

4-Chlorbenzaldehyde
saturated solution, and supernatants
After evaporation
The calculated concentration and density of saturated solutions are in the Spreadsheet


Discussion

The difference in the weights of the vials after the first evaporation run, when a dry solid was obtained indicated the amount of solid dissolved in chloroform. The difference in the weights of the vials after the second evaporation run indicated the amount of solid evaporated (sublimed) at 24.3C and a vacuum of 0.1Torr.
The concentration and density of a saturated solution of 4-chlorobenzaldehyde in chloroform obtained experimentally is provided below
Conc Avg (M)
Conc. Std.Dev.
Density Avg.
Density Std. Dev
3.61
0.02
1.23
0.01

Based on the results from the data, it is obvious that 4-chlorobenzaldehyde undergoes sublimation at a rate of 0.75-1.6mg every 10min at 0.1Torr and 24.3C
The results obtained in this experiment confirm that the solubility of the aldehyde cannot be obtained by evaporating the solvent for 6h under 0.1Torr at 24C, as was done in Exp208.

Conclusion

Since the chloroform is evaporated very quickly in the speedvac it is very useful to know the optimal time to keep the solutions in the speedvac without subliming the solid. This will reduce the amount of error in determining the solubility of organic compounds. However this method is very error-prone and will take much time to optimize with different compounds. Thus other methods in determing the solubility of volatile organic compunds will be looked into. Be specific about times

Log

2008-10-16

14:50 Measured out 700uL chloroform (CHCl3), in to a one dram vial (45), added 4-chlorobenzaldehyde to it, vortexed it for 30s, solid dissolved completely, added more solid, vortexed for 30s, the solution appeared saturated...
14:55 Weighed out two half dram vials labeled 45a (2.55945g) and 45b (2.59094g).
15:00 Centrifuged the one dram vial 45 containing the saturated solution.
15:10 Transferred 300uL of the saturated solution from 45 to vial 45a and 45b (half dram vials), these vials are now renamed 45b-1 and 46b-1
15:12 Took pictures of sample vials 45a, 45b and the one dram vial 45, containing the saturated supernatant with undissolved solid.
15:15 Weighed 45b-1 (2.93242g) and 46b-1 (2.95862g).
15:20 Inserted solutions into speedvac.
15:21 Read pressure on speedvac.(2.5Torr)
15:30 Read pressure on speedvac (1.8Torr) . Speedvac was shut off, the vials are now renamed 45b-2 and 46b-2. These vials were weighed again, 45b-2 (2.77983g) and 46b-2 (2.80693g).
15:31 Solutions were re-entered into speedvac, speedvac turned on.
15:40 Read pressure on speedvac. (1.5Torr) Speedvac was shut off and solutions 45b-3 (2.77918g) and 46b-3 (2.80618g) were weighed.
15:41 Solutions were re-entered into speedvac, speedvac turned on.
15:50 Read pressure on speedvac (1.0Torr) Speedvac was shut off and solutions 45b-4 (2.77762g) and 46b-4 (2.80459g) were weighed.
19:00 Took pictures of sample vials 45b-4 and 46b-4.

Tags


Compound
Inchikey
Inchi
4-chlorobenzaldehyde
AVPYQKSLYISFPO-UHFFFAOYAQ
InChI=1/C7H5ClO/c8-7-3-1-6(5-9)2-4-7/h1-5H
Chloroform
HEDRZPFGACZZDS-UHFFFAOYAG
InChI=1/CHCl3/c2-1(3)4/h1H