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Ugi NMR Analysis
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.
A saturated solution of
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.
saturated solution, and supernatants
The calculated concentration and density of saturated solutions are in the
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)
Density Std. Dev
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
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
14:50 Measured out 700uL chloroform (C
Cl3), in to a one dram vial (
), 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
15:00 Centrifuged the one dram vial
containing the saturated solution.
15:10 Transferred 300uL of the saturated solution from
(half dram vials), these vials are now renamed
15:12 Took pictures of sample vials
and the one dram vial
, containing the saturated supernatant with undissolved solid.
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
. These vials were weighed again,
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
(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
(2.80459g) were weighed.
19:00 Took pictures of sample vials
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