Objective

To dehydrate a preformed imine solution (EXP047) and proceed with the Ugi reaction by adding the amino acid component, and noting the changes.

Procedure

The methanol d-4 solution prepared in EXP047 consisting of the imine between 5-methylfurfurylamine and 3,4-dihydroxybenzaldehyde, with a 15% excess of aldehyde, was treated with MgSO4 and the changes were monitored by H NMR.

Results

(All spectra obtained on a 300MHz Varian Inova instrument)
Initial reaction mixture
HMR
After addition of MgSO4, filtering, and centrifuge
HMR
Spectral Overlay

Discussion

  1. After several days, the concentration of the imine remained approximately the same, based on comparison of the aldehyde peak (9.64ppm) and the imine carbon proton peak (8.14ppm) integrations. The final HMR of the imine solution in EXP047 showed that the percentage of aldehyde and amine (methylene peak at 3.87ppm - what did you compare this to?) remaining were 15.02% and 4.31% respectively based on the peak integrations. Just prior to performing this experiment, the percentages were calculated at 17.67% and 4.88%, respectively.
  2. Addition of magnesium sulfate had an adverse effect on the NMR spectrum in that peaks were shifted and severely broadened, and many multiplets were broadened into singlets. did it change the integration?

Conclusion

Addition of MgSO4 as a drying agent into CD3OD solution has an adverse effect on HMR spectra, indicating that it is dissolved into the solution.

Log

2007-01-31

16:50 - Mixed the solution in the NMR tube from EXP047 back with the leftover solution from the mixing of the two components. Shook vial for 30 sec. Transferred 800 uL of that solution into a clean, dry NMR tube.
16:56 - Obtained HMR of the initial imine solution. 57A
17:40 - Recombined the NMR sample to the orginal solution. Added excess (102.8 mg, 12.25 mol) anhydrous magnesium sulfate. Shook sample vigorously for 30 sec.
18:10 - Shook sample vigorously for 30 sec.
18:40 - Filtered sample through a 5.75" Pasteur pipet wadded with glass wool into another vial. Some visible magnesium sulfate remained, so the sample was transferred into a 12 mL centrifuge tube.
19:00 - Sample was centrifuged for 1.5 minutes.
19:05 - 800 uL of the solution was transferred into a clean NMR tube.
19:39 - Obtained HMR of dehydrated solution. 57B