The Vespiary

The Hive => Novel Discourse => Topic started by: tropine on October 16, 2003, 02:14:00 AM

Title: Really wet reductive amination question
Post by: tropine on October 16, 2003, 02:14:00 AM

So far,

  200 mL allylbenzne, 3 g PdCl2, 15 g CuCl2, a few mL's of water and about 500 mL 85% ethanol/15% methanol, many pressurization with pure O2 and about 10 hours of time/periodic shaking, yeilded 170 grams of very yellow, very sweet smelling ketone.  This was then diluted to a transparent solution with about 500 mL IPA. 200mL of 40% MeNH2 was added into the IPA, immediately turning the solution crimson red.  THis was stirred for 2 hours.  At that point the solution still smelled strongly of the ketone smell so it was put in a bottle and stored for probably 72 hours.  Any comments on the stability of this stored solution or how it should smell when the imine formation is complete?  NaBH4 reduction is soon to follow BTW

Title: Imine formation should be done in a few ...
Post by: Lilienthal on October 16, 2003, 11:38:00 AM

Imine formation should be done in a few seconds, it's a dynamic equilibrium! (It's also proton-catalyzed...)

Title: thanks! It now smells like methylamine and P2P
Post by: tropine on October 16, 2003, 04:12:00 PM

no new smell is there, just the two smells of the reagents.  Proton catalyzed? It's pretty damn basic, where is it gonna get protons from? Well at least 24 hours had passed since the methylamine (aquoues 40%) was added, so about 50 grams of NaBH4 in 200 mL of water with ~1 gram of NaOH was added in small portions to the mixture, porducing alot of bubbles, heat and a black colour.  This was stirred for an hour and set aside.  A few hours later there is a 2 phased solution of opaque black on the bottom and light yellow/clear on the top.  The black bottom is making alot of bubbles with the top layer at the interface.  The mixture is put back on the stir plate and left for over night.  I am thinking the black bottom phase is the NaBH4 and meth free base, and the top is aqueous/IPA/imine, slowly being reduced by the NaBH4, comments?

Title: Imine formation speed
Post by: Rhodium on October 16, 2003, 10:57:00 PM

Imine formation should be done in a few seconds

Huh? Are you sure? Most references I've read where one step is the formation of an imine usually allows between several minutes and 1-2 hours, sometimes  even with azeotropic removal of water during that time. It cannot be that fast, can it?

Title: In line with this
Post by: SPISSHAK on October 19, 2003, 07:16:00 PM

your talking about a NaBH4 reduction of an unsubstituted (no subs on the ring) imine.
The problem here is imines aren't as stable using unsubstitued phenylacetones.
That's why the NaBH4 Reduction works really well with MDMA but you have to dry the imine on silica gel if you are using plain P2P or you  will get reversal reactions followed by reduction of the ketone to the alcohol.

Title: I don't believe you
Post by: Rhodium on October 19, 2003, 08:26:00 PM

your talking about a NaBH4 reduction of an unsubstituted (no subs on the ring) imine.
The problem here is imines aren't as stable using unsubstitued phenylacetones.

Huh? Do you have any references whatsoever for this difference? I could understand if there would be such a difference with an aromatic imine (i.e. from a phenyl-1-propanone), but not with a phenyl-2-propanone. 

And as you can see in

https://www.thevespiary.org/rhodium/Rhodium/chemistry/redamin.aqueous.nabh4.html (https://www.thevespiary.org/rhodium/Rhodium/chemistry/redamin.aqueous.nabh4.html)

aqueous NaBH₄ reductive amination can be performed in almost 80% yield with P2P's having both electron-withdrawing (fluorine) and electron-donating (methoxy) substituents.

Title: Anectdotal
Post by: SPISSHAK on October 20, 2003, 01:41:00 AM

The information I have is anectdotal so consider myself corrected.