[Ingeniosuccinimide]

I have a somewhat peculiar product of one reaction, and I'm trying to guess how to purify it. I tried flashing on silica and also aqueous extraction (the reaction is done in DCM), but none of these worked.

I guess the reason is the ticklish aminal-hydrazone portion of the molecule. I guess it decomposes on silica, and might also be hydrolysed during the aqueous extraction. Maybe extraction at different pH could work? One of few "waste" components of the reaction mixture is potassium phthalimide, and I'm trying to get rid of that through aqueous extraction.

How do the aminals and hydrazones in general behave in aqueous solutions? And is it too risky to purify them by flashing? Maybe some stationary phase other than ordinary silica, e.g. alumina?

[pgk]

Aminals are unstable compounds and very difficult to isolate (and if isolated, that happens only at a narrow range of conditions). So, the best is to purify by recrystallization.
Anyway, Schiff bases are unstable at acidic medium but they are relatively stable under neutral and basic conditions. So you try to effectuate aqueous extractions at pH ≈ 10 and then wash your organic phase by repeated extractions with water until neutral to litmus. That way, you get rid of the phthalimide, too. The problem is that dichloromethane forms emulsion during extractions with alkaline medium. You can break the emulsion, by adding a few drops of silicon oil or ethanol (Not always but sometimes, it works).

[Ingeniosuccinimide]

Thanks, will try that. BTW is anyone familiar with some way I could visualise potassium phthalimide/phthalimide on TLC? Tried UV, KMnO₄, chromate, vanilin... does not work. It would help a lot when monitoring the reaction.

Regarding the nature of the double bond in the ring, is there a chance I could have a tautomerism here or that one would be induced by changing the pH? What is the stability of aminals themselves when it comes to increased pH, especially given that the upper nitrogen is tertiary?

[pgk]

1). Try to spray the TLC with Dragendorff’s reagent for alkaloids (If you can find it) or else with isatin or isatin-5-sulfonic salt and heat it.
2). You don’t even need a pH change for that tautomerism which may occur via a diazo derivative. Traces of a Lewis acid are enough.
3). Aminals are quickly hydrolyzed under pH. In presence of organometallic Lewis acids, they can also be hydrolyzed under neutral or even basic conditions by they atmospheric humidity. So, take care.

[Ingeniosuccinimide]

1). Try to spray the TLC with Dragendorff’s reagent for alkaloids (If you can find it) or else with isatin or isatin-5-sulfonic salt and heat it.

Do you have a recipe for isatin dip? I tried to find it but nothing.

[pgk]

Unfortunately not. You have to find a old book of Practical Analytical Chemistry in the closest library. The edition year must be around 50s-60s, when plate and paper chromatography were fashionable (before the generalization of spectroscopic identification methods).

[sjb]

1). Try to spray the TLC with Dragendorff’s reagent for alkaloids (If you can find it) or else with isatin or isatin-5-sulfonic salt and heat it.

Do you have a recipe for isatin dip? I tried to find it but nothing.

Various options at https://www.google.com/search?q=isatin+dip&ie=utf-8&oe=utf-8 ?

[pgk]

Very good.