2‐Amino‐N‐[4‐cyano‐3‐(trifluoromethyl)phenyl]‐2‐methylpropanamide A recent part of my PhD project required purification of the compound 2‐Amino‐N‐[4‐cyano‐3‐(trifluoromethyl)phenyl]‐2‐methylpropanamide. This primary amine was sticky and kept a low Rf with most common solvents. I experimented with silica deactivation to increase its Rf from 0.08 in 50% hexanes/50% EtOAc.
I was advised to first run the blank TLC plate in 1-3% triethylamine (TEA) in EtOAc. I was also advised to carry out the blank run this way two or three times. I tried 1% and 3% and did the blank run one, two and three times to obtain six results. I found that with 1% TEA the Rf increased to 0.09 and 3% TEA increased it to 0.10. There was no change in Rf when the blank run was carried out one, two or three times.
I had some diazobicyclooctane (DABCO) and I tried to deactivate with this and also to carry out the run itself with a small amount of DABCO in the solvent. I found that this worked poorly and that the DABCO was viewable itself under UV light which interfered with viewing the compound.
I was advised to first run the blank TLC plate in 1-3% triethylamine (TEA) in EtOAc. I was also advised to carry out the blank run this way two or three times. I tried 1% and 3% and did the blank run one, two and three times to obtain six results. I found that with 1% TEA the Rf increased to 0.09 and 3% TEA increased it to 0.10. There was no change in Rf when the blank run was carried out one, two or three times.
I had some diazobicyclooctane (DABCO) and I tried to deactivate with this and also to carry out the run itself with a small amount of DABCO in the solvent. I found that this worked poorly and that the DABCO was viewable itself under UV light which interfered with viewing the compound.
After reading this website I decided to try an ammonia strategy. I found a bottle of 28% ammonia in water and added 4 mL of this to 96 mL of MeOH to create a 1% ammonia in MeOH solution (it should be remembered that this is 3% water). I then ran TLCs in DCM with 5% (A) and 10% (B) '1% ammonia in MeOH'. As another option I ran a TLC with 10% '1% ammonia in MeOH' in tert-butylmethyl ether (TBME) (C). Solvent system C (10% '1% ammonia in MeOH' / 90% TBME) gave a discrete non-tailing spot with an Rf of 0.62. I therefore used this for a flash column to purify the amine.
