Chemical Forums
Chemistry Forums for Students => Organic Chemistry Forum => Topic started by: Tootella on June 04, 2008, 06:33:24 PM
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I understand what "oiling out" is but I don't understand how to fix this problem when doing re-crystallization. I'm working on my lab report for the re-crystallization of acetanilide. Does anyone know how to fix this problem? Thanks.
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There are a number of reasons why oiling out occurs when attempting a recrystallization. If you are using an antisolvent it could be that you added too much of this too quickly, forming a solution that was too supersaturated to crystallize. Sometimes the presence of residual solvents can result in oiling out. I would recommend assaying your acetanilide to determine the level of residual solvent (including water), and then screening different solvent systems than to one which resulted in oiling out. A general rule in crystallizations is to generate supersaturation slowly for best results; this can be accomplished by slow addition of antisolvent, slow cooling, or slow distillation/evaporation.