Hello!
We synthesized t-Boc-aminoethyl 2-bromoisobutyrate (white solid). Following the removal of t-Boc protection group, we are still trying desperately to crystallize the final product (i.e. 'TFA salt of 2-aminoethyl 2-bromoisobutyrate'). The only two protocols published so far don't seem to work and we can't get any correspondence from their authors. We tried a number of different combinations of hexane, diethyl ether and ethyl acetate.
We would appreciate all kinds of help.
Thanks :)
I know nothing about your product but i work on crystallization and i am trying to help you. First identify your solvent Where you have your product. Is it possible to evaporate in a vaccum rotary evaporator? If yes you may concentrate you solution till avove saturation, crystallizing the product. Another possibility is to find a liquid chemical that do not dissolve your product but mix with the solvent.
Solvent quality is impotant for this and excluding water will probably be critical for success. Ether must be dry and try to avoid ethanol-stablized solvent. Other possible co-evaporation solvents include toluene (azeotropes excess TFA) and MTBE (tBu-OCH3 - ethyl ether substitute which is higher boiling and less hygroscopic - avoid heating until you are confident that excess TFA is gone.) Rotary evaporation of 2-3 small volume toluene "chasers" added to the cleavage reaction residue (TFA in CH2Cl2?) should give a dry (water-free) residual oil without excess TFA. Try redissolving this in dry CH2Cl2 and slowly add MTBE until it barely starts to cloud, then store in refrigerator. Also, avoid boiling the recrystalllization mixtures if you can.
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