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Specialty Chemistry Forums => Citizen Chemist => Topic started by: ithronor on January 19, 2015, 02:09:58 PM

Title: Freeze precipitation of caffeine in basic solution?
Post by: ithronor on January 19, 2015, 02:09:58 PM: Quick question on caffeine extraction from coffee,

After having LLE'd caffeine from a concentrated coffee solution into a non-polar solvent, and migrated it back into an acidic aqueous phase using acetic acid or HCl, is it feasible to simply revert it to the base form using NaOH, and have it freeze precipitate out of the basic solution? Or would this simply not happen, and if so, then why? I'm looking to avoid the standard sublimation. Thanks.
Title: Re: Freeze precipitation of caffeine in basic solution?
Post by: discodermolide on January 19, 2015, 07:09:05 PM: What is freeze precipitation?
Title: Re: Freeze precipitation of caffeine in basic solution?
Post by: ithronor on January 20, 2015, 09:37:11 AM: Recrystallization is probably a better moniker.
Title: Re: Freeze precipitation of caffeine in basic solution?
Post by: ithronor on January 21, 2015, 11:00:04 AM: Perhaps I should rephrase my question. Supposing I cool the basic solution containing the caffeine to near freezing, will the substance crystallize out of the solution? Or is sublimation the only way to go? I guess this is fairly textbook for you trained chemists. Hoping to resolve this!
Title: Re: Freeze precipitation of caffeine in basic solution?
Post by: discodermolide on January 21, 2015, 12:48:04 PM: It will only crystallise out if the solution is saturated.
Title: Re: Freeze precipitation of caffeine in basic solution?
Post by: ithronor on January 21, 2015, 04:29:45 PM: Yes. Thank you. Could you alter the solution in some other way, so as to lower the solubility to the point at which a solid would precipitate out?
Title: Re: Freeze precipitation of caffeine in basic solution?
Post by: discodermolide on January 21, 2015, 08:03:38 PM: If you do that you stand a chance of precipitating out all the inorganic salts as well.
You need to have as much caffeine HCl salt as possible, dissolved in the smallest possible volume of water. Then add concentrated (30-40%) NaOH solution until the HCl salt is neutralised. That can be calculated.
Then cool it and see if it crystallises.
Title: Re: Freeze precipitation of caffeine in basic solution?
Post by: ithronor on January 22, 2015, 04:39:01 AM: Ok! I guess I'll need to reduce the volume by boiling off a sufficient amount of water. Thanks for the feedback!