Researchers

Khalid Mirza, Jean-Claude Bradley.

Objective

To construct a solubility curve for pyrene in acetonitrile by gradual cooling crystallization method.

Procedure

Weighed amounts of pyrene and acetonitrile are sealed in half dram screw capped vials with parafilm. The vials are immersed in a water bath with sonication at 40C until all samples dissolve completely then the temperature of the bath is decreased gradually by adding tap water then ice water. The bath is sonicated for a few seconds every few minutes to attempt to induce crystallization. When a precipitate forms the temperature is noted.

Results

Spreadsheet[only the first 3 temperatures are added, assuming that the solute precipitated in order of decreasing concentration JCB]

Discussion

The 22C measurement is about twice that found in EXP108. This could be due to under-integration due to longer relaxation times of aromatic protons.

Conclusion

Precipitates at 3 temperatures were obtained and the 22C solubility measurement is about twice that obtained by the SAMS NMR technique (EXP108).

Log

11:00 Labeled five half dram vials 1, 2, 3, 4 and 5.
11:20 Added a weighed amount of acetonitrile to vials 1, 2 and 3; vial 1 - 1.0091g, vial 2 1.0738g, vial 3- 1.0058g. After weighing out acetonitrile in the vials, they were immediately screw capped and parafilmed.
11:40 To vial 1 (tared to zero) added pyene (32mg). To vial 2 added pyrene (24mg) and to vial 3 added pyrene (40.4mg)
12:00 Weighed out pyrene 50.9mg in vial 4 and 45.6mg in vial... 5.
12:10 Vial 4 containing pyrene was tared on a top loading balance, acetonitrile (1.0021g) was added to it.
12:20 Vial 5 containing pyrene was trared on the balance and acetonitrile (1.0618g) was added to it.
Vial number
acetonitrile (wt g)
pyrene (wt mg)
1
1.0091
32
2
1.0738
24
3
1.0058
40.4
4
1.0021
50.9
5
1.0618
45.6
12:35 All vials were tightly screw capped and parafilmed. They were placed in a sonicator with water temperature at 29C. Started sonicating.
12:45 Solid in vial 1 had completely dissolved. Temp of the sonicator 29C
12:55 Solid in vial 2 dissolved completely.
13:00 Added a small amount (unknown volume)of hot water to get the temperature of the sonicator to 40C...continued sonicating...
13:05 Added more hot water until the temperature got up to 50C..continued sonicating..solid in vial 3 dissolved completely.
13:25 Solid in vials 4 and 5 dissolved....obtained a clear solution in all vials - (Cedric, Dr. Bradley).
13:35 Turned off the sonicator...
14:50 Started adding tap water..kept stirring the water bath...checked the vials no solid in yet, sonicated for a ~5s..kept adding water..temp started going down.
14:10 Temperature recorded 34C..first solution precipitated ---[vial 4] (Cedric, Dr. Bradley).
14:15 Started adding ice cold water to the sonicator bath..each time sonicating for few seconds....a continuously recording the temperature.
14:29 Temperature recorded 22C..second solution precipitated out..[vial 5] (Cedric, Dr. Bradley).
14:30 Continued added ice cold water to the sonicator bath..each time sonicating for few seconds....a continuously recording the temperature.
14:38 Temperature recorded 13C...third solution precipitated out.. [vial 3] (Cedric, Dr. Bradley).
17:00 Two vials still remained (vials 1 and 2) that had not yet formed ppts. Therefore the water bath in the sonicator was set again to 30C by adding in warm water...[why heat up if those are still in solution? JCB]- I am not sure why, but I did get the temp to 30C by adding warm water...
17:20 Starting sonicating the vials (vials 1 and 2), added a few mls of ice cold water...continuously recorded the temperature...kept mixing the water in the water bath...temp started to roll down..conitinued sonicating for a few secs after each addition.
17:45 Water temperature recorded to be 13C...vial 1 started getting ppt...[that has to be an error - why would the vial with 32 mg precipitate during this round of cooling at 13C, the same temperature where the 40.4 mg sample came out? JCB]- I agree with your assesment, wonder if I unwittingly recrystallized the sample whose solubility had already been measured vial-3.
17:50 Continued added ice cold water to the sonicator bath..each time sonicating for few seconds....a continuously recording the temperature.
18:20 Temperature recorded 6C..vial 2 started forming ppt.[Are we sure this is vial 2 and not 1? JCB]- As far as I could read the labels on the vials, I believe it was vial 2
18:22 Removed the vial from the sonicator.

References

[1] Chirality in Industry II ; By Andrew N. Collins, G. N. Sheldrake, J. Crosby; Pages 131-133; Chapter 7 by W.M.L Wood- Crystal Science Techniques in the Manufacture of Chiral Compounds- Solubility curves and their measurement : - Limited preview on google books
[2] Solubility of pyrene in non-aqueous solvents

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