Sciencemadness Discussion Board - Enamine formation help

Enamine formation help

ovit.us - 18-3-2017 at 17:18

I think I'm having issues forming an Enamine. This is the procedure I've been following:

An apparatus was setup for the azeotropic removal of water using a Dean-Stark water-trap and Dimroth refux condensor. Into the 250ml round-bottom flask, 40ml of Pyrrolidine, 35ml of Cyclohexanone, 500mg of P-Toluenesulfonic acid, and 100ml of Toluene was added. This was heated with stirring for about 5 hours until ~6ml of water separated.

The reaction mixture was slightly yellow, but had what appeared to be a white precipitate floating in it. This has happened every time this reaction was performed. Is this what should occur? I have done a similar reaction involving Morpholine, and it has always appeared clear after reflux (although still yellowish).

Following this I would performed a distillation and the result would be a clear liquid, which would gradually change back to yellow. With the Morpholine reaction, this distillation liquid would remain stable, and would not change color.

Any ideas? I'd like to know if I've missed some vital step or am going about this incorrectly. I could take a picture of the reaction, it just appears yellow with a cloudy substance suspended in it.

Corrosive Joeseph - 18-3-2017 at 17:35

Attachment: Imines, enamines and oximes.pdf (337kB)
This file has been downloaded 628 times

/CJ

ovit.us - 18-3-2017 at 19:53

Quote: Originally posted by Corrosive Joeseph

/CJ

Thanks, I don't see my particular reaction in that document, but good info to have.

This is what my reaction looks like, and I've tried two sources of Pyrrolidine. Must be my technique, or is this normal?

clearly_not_atara - 18-3-2017 at 20:13

I believe morpholine is used because other enamines are more likely to polymerize. The polymerized enamine may be what you are seeing.

CuReUS - 19-3-2017 at 01:02

you could try this method:

Quote:

A 50 mL round-bottomed flask containing cyclohexanone (3.82 g, 39 mmol) in anhydrous toluene (20 mL) was fitted with a Dean-Stark trap containing 3 Å molecular sieves, reflux condenser and a heating mantle, pyrrolidine (6.00 mL) was added, and the solution heated to reflux for 18 h. The solvent was evaporated and the crude product 1-cyclohex-1-en-1-ylpyrrolidine was used directly for the next reaction. (6.0 g, 102% yield, 95% purity by HPLC). MS(ESI+): 152.3; MS(ESI−): 150.1

https://www.google.com/patents/US8288432?cl=en10

[Edited on 19-3-2017 by CuReUS]

ovit.us - 19-3-2017 at 04:04

What exactly is a Polymerized Enamine? Can I still use it?

My next step would be to wash with H2O to remove the catalyst acid, then separate, dry with Sodium Sulfate, and vacuum distill. This should produce a colorless Enamine, but as mentioned, it later has turned yellow on me and not produced the desired reactions later on.

Quote: Originally posted by CuReUS

you could try this method:

Quote:

https://www.google.com/patents/US8288432?cl=en10

[Edited on 19-3-2017 by CuReUS]

The differences I see in this procedure are the absence of p-Toluenesulfonic-acid, addition of Molecular Sieves, and longer reaction time. I suppose using the crude product is also something to consider.

zed - 27-3-2017 at 17:47

Well, the reaction certainly works when Piperidine is employed as the amine.

Which has led to Piperidine becoming list one, and cyclohexanone becoming a special surveillance item.

[Edited on 28-3-2017 by zed]

[Edited on 28-3-2017 by zed]

Racconized - 17-4-2017 at 08:26

Looks like the procedure posted by xicori(may be wrong, can't remember his name exactly). Either way, maybe try going for the nitrile procedure instead (if all else fails)