Since several months I'm having troubles with some impurities in my NMRs. My final compounds have to be pure (>95%) for biological analysis.
Here an example of my reaction (see attached file)
I mix the reagents in EtOH with K2CO3, I put in under microwave irradiation and after 2 hours it's down.
- removal of solvent
- addition of Et2O + H2O
- Et2O extraction
- Drying and evaporation
Column chromatography: with EtOAc/Cyclohexane from 0 to 50% EtOAc with 40CV (around 30min)
After that, I get pure fraction in CCM, LCMS. I dry the oil under vaccun and then I do my nmr.
Product is okay, but few residual peaks are here around 1ppm and I don't know what it is.
1.42 ppm (probably some cyclohexane left)
but at 1.24ppm, 1.25ppm, 1.28 ppm and 1.33, no idea. It is not UV active since I do not see anything in the CCM or LCMS. But it's annoying me. I thought about grease but I don't use grease...
And these residuals peaks are here on every similar compounds with the same step. However, if I do a different reaction they are not present (it means it is not my deuterated solvent). I also tried new NMR tubes.
NMR is performed in CDCl3
Thank you for your help