[curiouscat]

I have a rough outline of an aldehyde-oxidation process where the small density difference between an aqueous KMnO4 solution (~10% w/w SG~1.0) & my organic (SG~1.05) makes phase separation a hard task.  Employing centrifuges is a possibility, but I'd like to avoid it if at all possible.

I am hopeful if the density difference were larger the phase separation problems might ease. With this aim I tried adding salt (NaCl) but somehow this impaired the aldehyde-oxidizing ability of KMnO4 (I'm not sure why! Would one expect a KMnO4 / NaCl reaction?)

What might be other, fairly inert soluble additives to boost up the density of the aq. phase without interfering with the activity of KMnO4? Process temperature is ~70°C. One constraint is that the pH needs to stay above 6 since my organic degrades under acidic conditions.

[discodermolide]

How about adding some carbowax (polyethylene glycol)

http://www.dow.com/polyglycols/polyethylene/products/carbowaxp.htm

[Borek]

Why don't you add brine after the oxidation took place?

[curiouscat]

Why don't you add brine after the oxidation took place?

No reason! Just never thought of it. Will try that and see if it works. 

PS. By add brine "after", you mean add the solid NaCl at end, correct? The water's already in with the KMnO4 addition.

[curiouscat]

How about adding some carbowax (polyethylene glycol)

http://www.dow.com/polyglycols/polyethylene/products/carbowaxp.htm

Thanks! Will try.

[Borek]

PS. By add brine "after", you mean add the solid NaCl at end, correct? The water's already in with the KMnO4 addition.

Either solid NaCl or the saturated NaCl solution (if that's enough to change the density). It is easier and faster to mix solutions than to dissolve a solid. But... whichever works and suits you best.

[curiouscat]

PS. By add brine "after", you mean add the solid NaCl at end, correct? The water's already in with the KMnO4 addition.

Either solid NaCl or the saturated NaCl solution (if that's enough to change the density). It is easier and faster to mix solutions than to dissolve a solid. But... whichever works and suits you best.

On deeper thought, there's a problem. In the "add brine / solid NaCl post oxidation" approach there's no good way to recycle the wash water. It'd be a hassle getting rid of all that spent water each time.

In the original approach, all I need is some makeup and KMnO4 and the whole aqueous part can be recycled for the next round of treatment.

Unless I'm not seeing the obvious.

[DrCMS]

Can you add another solvent to make the organic layer density less than 1 rather than adding salt to make the water layer more than 1.05?

[curiouscat]

Can you add another solvent to make the organic layer density less than 1 rather than adding salt to make the water layer more than 1.05?

Don't think that's viable. Will add a downstream separation step, most likely distillation to remove solvent from organic. Too expensive. 

Adding stuff to water is easier coz' no separation is needed. It could just stay in the water and be recycled (with makeup KMnO4 added)