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Solubility book (3rd Edn)
To determine the temperature at which different concentrations of BOC-Glycine in THF solution will come out.
Five samples of solution were prepared with THF and BOC-Glycine. Five one-inch tall vials were filled with one half-gram of THF each, then a known amount of BOC-Glycine powder was added to each vial to produce the desired concentration. First, each empty glass vial was weighed and the scale zeroed. THF was then added to the vial until it weighed 1/2 gram. The exact weights are recorded in the results. After all five vials contained the solvent, the solute was added. We used wax paper to weigh specific amounts of BOC-glycine powder and then scoop/pour into the appropriate marked vial. Now we have 5 marked vials containing different concentrations of BOC-Glycine and solvent. We covered the vials in parafilm and vortexed them for 30 seconds. We labeled vials with copper wire and paper tag. We sonicated the vials in a bath for 10 minutes. At this point, A5 was the only sample that contained precipitate at room temperature. We raised the temperature of the bath to 60 degrees and dropped in sample A5. After alternating the vortex and water bath a few times we got the precipitate to dissolve. Note: 60 degrees is the maximum temperature allowed for these ingredients. The temperature was lowered down to 43 degrees without reappearance of precipitate. Samples A1-A4 were dropped into a water bath temperature 25 degrees and was lowered to -25 degrees without appearance of precipitate. An NMR was taken of the supernatant of A5, after being left at room temperature overnight.
[are you sure? The log says A5 was heated to 60C on the same day the NMR was taken JCB]
Yes. We tried heating it again but it did not go in completely, so an NMR was taken of the centrifuged sample.
[If you heated it to 60C on the second day why does the previous sentence say the NMR was taken after A5 was left at room temperature overnight? JCB]
It was left at room temperature overnight, then heated to 60 degrees the next day. It was taken out of bath and then the NMR was taken.
No results were found to indicate that BOC-glycine would come out of the solution at any temperature. This may be good, if right. More testing will be carried out to basically repeat this experiment at higher concentrations to provide further data. [Is this surprising based on the reported solubility data so far? JCB] Not really, two similar experiments were done using NMR to determine solubility and the mean of the two experiments was 4.11M concentration
[Taking the average is misleading link to the two results separately - do you see why your experiment could be more or less reliable than either of those two? JCB]
Yes. I was comparing my experiment to two seperate experiments,
. Sample 13- from
was 3.45M and Sample 9- from
was 4.77M. This is less confusing than using just the average of the two. So, more testing between a range of 3.0-5.0 may be a good starting point for some firmer results. SAMS method reveals a concentration of 3.76M.
We obtained a concentraion of 3.76M by NMR and the SAMS method. This quantity lies in between two results taken from the previous two experiments conducted using this solute and solvent. Although we were unable to contstruct a temperature-concentration curve, we did obtain good results which were entered into
Weigh out 1g of solvent
Place beaker in scale
Add THF until about half-gram in each vial
Covered in parafilm
Label vials with copper wire and paper tag
Sonicate for 10 minutes
All samples dissolved with exception of A5
Dropped in sample A5 and raised temperature to max 60 degrees
Vortexed sample A5 then dropped back in
A5 dissolved at 60 degrees but did not recrystalize with temperature dropped to 43 degrees
A5 sample was removed from bath and is at room temperature. precipitate has formed in sample A5
A5 is put in bath and temperature raised to maximum 60 degrees, but it will not go in
A5 and dropped bath temperature to 25 degrees
Temperature is set to 25 degrees and samples A1-A4 are dropped into bath; A5 is not dissolved, but A1-A4 are fully dissolved at room temperature
[you didn't say A5 was removed at this point so that implies it was taken to -25C JCB]
Lowered temperature in increments of two degrees going from 25 all the way to -25 degrees
No visible precipitates
Sample A5 was centrifuged and the supernatant extracted
[did you get the temp of the lab at this point and how long was the sample out of the bath? JCB]
No, I did not. At least 10 minutes passed after it was taken out of the bath.
[I'm still not clear on what happened - and it makes a huge difference in the validity of your data - according to this log the sample A5 was left at -25C overnight? JCB]
NO, that was a mistake. I checked my paper log to see if I missed anything and so I added some things to try to make clearer what happened. I did record this in the log, but I am pretty certain that sample A5 was removed what A1-A4 were dropped in the bath and after that is when the NMR was taken. Samples A1-A4 were fully dissolved at room temperature, then they never came out of solution when they were lowered down to -25 degrees.
Supernatant is combined with deuterated chloroform in NMR tube and NMR is taken of sample
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