[organicstudent20]

Hi,

earlier I posted what solvent would be ideal for recrystallization of benzophenone. However, I can't even get to a point in lab where it seems I can carry out recrystallization. I am given a compound of ethyl aminobenzoate, benzophenone, and 1,4 dibromobenzene (in small amount-this is just an impurity). I basically have to separate and purify the aminobenzoate and benzophenone. I began by dissolving the mixture in DCM, and using 1.0M HCl to extract out the aminobenzoate since this is a base, which I then precipitated back out using 6M NaOH. This seemed to work fine. I was then left with benzophenone and my impurity dissolved in the organic layer (DCM) which I thought I could evaporate off the DCM and do recrystallization of the benzophenone using 95% ethanol or a nonpolar organic solvent. However, every time I try to evaporate off the DCM, I can't get a solid/residue that I can therefore redissolve in the crystallization solvent. Anyone have any insight as to what's going wrong? We're only supposed to use extraction and recrystallization techniques, so I'm just at a loss for how to remedy this.

[MOTOBALL]

When you evaporate the DCM, how viscous is the non-solid residue?
Have you tried chilling product in a  refrigerator overnight, preferably in the freezer ?
If it does not solidify then stir around while chilled, with a glass rod.
If no success, chill in an acetone/ dry ice bath , or even liquid N2, and repeat glass rod action.
If still no success, repeat whatever freezing procedure is convenient and cover with a layer of the liquid that you intend to recrystallize from, and use the glass rod.
The trick is to remove virtually all of the DCM at the beginning!!
These methods have worked well for me with carbohydrates, so please let us know what happens.

Regards,
Motoball
Regards,
Motoball