boc-alanine
boc-glycine
boc-phenylalanine

Researcher

Khalid Mirza

Objective

To measure the solubility of boc-alanine and boc-phenyl alanine in hexane, acetonitrile, methanol, t-butanol and benzene by the NMR based SAMS method
Solubility of boc-alanine, boc-phenylalanine and boc glycine is also measured in water.

Procedure

A solution of boc-alanine and boc-phenylalanine ws made-up in alanine in hexane, acetonitrile, methanol, t-butanol and benzene by dissolving the acids in ~0.4mL of the solvents in half dram vials. It was ensured that some of the solute remained undissolved in the solution after vortexing the vials for 30s each. The vials were then tightly capped, sealed with parafilm and placed in a temperature control bath set at 40C for 1h. The temperature of the bath was then reduced to 25C with the vials in it. The supernatants from the solutions were then carefully transferred in to new half dram vials and placed in to the water/glycol bath at 25C.
The solutions were then left to equilibrate for two hours. The supernatant (mother liquor) from each solution was carefully separated and mixed with CDCl3 (or DMSO-d6) . Proton NMR of each sample was obtained to assess the solubility of the acid in the solvent. For water containing samples DMSO-d6 was used to obtained HNMR.

Results

HNMR
[Remember to add these spectra to ChemSpider JCB]
boc-L-alanine
boc-L-phenylalanine
boc-L-leucine
boc-L-serine
(Note: Right click, 'Reverse Plot' under 'view')
Google Spreadsheet
ONSCExp194[Because of rotamer splitting your integration is not correct in many cases - I fixed the first one for you JCB]

Solubility summary results (complete rest and add to solsum sheet JCB)

in water:
boc-gly 0.83 M
boc-ala 0.18 M
boc-phe 0.007 M

Pictures after removing from the bath at 40C, all samples had undissolved solute remaining
10vialsfrom40C.JPG
1-5from40C.JPG
6-10from40C.JPG
w1-w3from40C.JPG

Discussion

Conclusion

Log

2010-12-16
12:20 Turned on the heater of the water bath and set it to 45C
13:50 Made-up a solution of boc-alanine and boc-phenyl alanine in hexane, acetonitrile, methanol, t-butanol and benzene by dissolving a small quantity of the acid in approximately 400uL of the solvent in labeled half dram vials (1-10). The solutions were vortexed and extra solute was added in the vials until no more of the solute dissolved. A lot of solute was required to saturate methanol and acetonitrile solutions in both cases. Vials 1-5 contained boc-alanine and 6-10 contained boc-phenyl alanine.
Solvents: hexane 1,6; acetonitrile 2,7; methanol 3,8; t-butanol 4,9 and benzene 5,10
14:01 Parafilmed the vials and placed them in the water bath now at 45C.
14:10 Made-up a solution of boc-alanine, boc-phenylalanine and boc-glycine in water in three half dram vials labeled w1-w3
14:10 Placed the vials in water bath at 45C.
15:35 Reduced the temperature setting of the water bath to 25C
2010-12-17
12:20 Temperature of the water bath at 26C, changed it to 25C (will wait for 30min before removing the vials)
12:50 Removed the vials from the water/glycol-bath. Except for the hexane samples (1 and 6) and the water-boc-glycine sample (W3) there was no visible solute remaining in the vials.
13:45 Set the temperature on the water/glycol bath at 40C
16:00 Added more solute to the vials which had clear solutions. The vials were tightly capped and parafilmed.
17:00 The vials were placed back in the water/glycol bath now at 40C
18:00 Removed the sample vials from the water/glycol bath, changed the temperature setting on the bath to 25C. Obtained pictures of the vials
18:30 Carefully transferred the supernatants from the vials in to identically labeled new half dram vials. Capped them tightly and placed them in the water/glycol bath now at 25C. [Too late to pour the supernatant - you have to pour it out when at 40C JCB]
20:45 Checked the vials in the temperature control bath at 25C, just two sample vials contained some recrystallized solute..therefore left the vials in the bath.
2010-12-18
13:10 Some vials have started forming crystals, however there are a few that are still completely clear.
16:25 Still no crystals in most of the sample vials..
2010-12-20
13:10 All solutions appeared to contain some solid accumulation at the bottom of the vials, except a few.[which ones? JCB]
13:25 Removed the vials from the bath.
13:30 Pipetted out ~700uL DMSO-d6 in to three one dram vials, carefully removed the supernatants from the vials labeled W1, W2 and W3 and mixed then well with DMSO-d6 in to separate vials. These solutions are labeled ONSCExp194-W1, ONSCExp194-W2 and ONSCExp194-W3. The solutions were then transferred in to clean NMR tubes.
17:00 Similarly proton NMR spectra of the remaining solutions (ONSCExp194-1 to ONSCExp194-10) was obtained in CDCl3.