tsathoggua1
Hazard to Others
Posts: 335
Registered: 8-1-2017
Location: Beyond the pale
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Mood: Phosphorescent
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Salting out polar compounds into polar solvents from aq. phases, PH dependence?
For the salting out effect to occur, how dependent is it on the PH of the solution?
The substrate to be extracted is a primary amine, originally present as base, but it had to be dissolved in acid to the point of around neutrality
owing to the fact that it had become trapped in a solidified mass of caustic sludge which needed first alcohol to be applied (MeOH/EtOH mixture mostly
the latter) and rather than extract with dichloromethane, this was already too basic and may well have resulted in chlorocarbene formation had it been
treated with dichlor, so alcohol was used instead, and a steel bar bent and used to dig the solidified cake of post-reaction mixture out piecemeal,
this was liquefied once again with aqueous sodium hydroxide, poured into a HDP£ container thats disposable and can go to the local toxic waste
remediation section of the local dump (it contains some rather nasty heavy metal waste) or reused for the same purpose as a dedicated container.
So long story short, there being so much NaOH in there that had set to a little bit of goo and one giant cake of solid byproducts. The needed HCl
brought things from highly basic to neutral or just the basic side of neutrality. There was additional NaCl added after dissolution of the Al so what
I'd like to know, is how much the amine is likely soluble in EtOH/MeOH as an HCl salt (mostly) as a function of PH during salting out type extractions
(the solution was supersaturated with NaCl when still warm to hot then allowed to cool, causing the alcohol to salt out as a layer above the
remainder.
I don't need specific figures for a specific primary amine but rather the general behaviour of amine salts vs bases under such hypersaline
conditions, since the base can be extracted into Eg IPA/EtOH, and the salt is soluble in it under normal conditions, is is the general trend likely to
mean that it'll be in the aqueous, hypersaline layer or in the alcoholic one so I can decide whether it needs further basification or if making sure
the alcoholic layer is acidified before washing with dichlor several times, basification, back extraction into dichlor before washing with neutral
water, and potentially, steam distillation to rid the result of any nasty traces of heavy metal wastes. (and recovery of the metals from same for
recycling)
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JJay
International Hazard
Posts: 3440
Registered: 15-10-2015
Member Is Offline
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The pH most definitely matters when salting out amines and carboxylic acids. How much it matters depends on the particular compound, but as long as
your aqueous solution is strongly acidic or strongly basic, as required, it won't be an issue.
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