March 28, 2024, 02:02:03 PM
Forum Rules: Read This Before Posting


Topic: Does this work?  (Read 80541 times)

0 Members and 1 Guest are viewing this topic.

Offline discodermolide

  • Chemist
  • Sr. Member
  • *
  • Posts: 5038
  • Mole Snacks: +405/-70
  • Gender: Male
    • My research history
Re: Does this work?
« Reply #105 on: March 21, 2013, 02:26:14 AM »
Do not worry about it. Remove all the isopropanol on the rotavap. Weigh your compound and get a fresh NMR.
Then let's think about the PBr3 step.
Development Chemists do it on Scale, Research Chemists just do it!
My Research History

Offline discodermolide

  • Chemist
  • Sr. Member
  • *
  • Posts: 5038
  • Mole Snacks: +405/-70
  • Gender: Male
    • My research history
Re: Does this work?
« Reply #106 on: March 21, 2013, 02:37:23 AM »
Here is a link to the H-NMR spectrum of prolinol
http://sdbs.riodb.aist.go.jp/sdbs/cgi-bin/direct_frame_top.cgi
search under pyrrolidinemethanol
This is not the HBr salt.
Development Chemists do it on Scale, Research Chemists just do it!
My Research History

Offline Messi

  • Full Member
  • ****
  • Posts: 252
  • Mole Snacks: +1/-6
Re: Does this work?
« Reply #107 on: March 21, 2013, 07:44:38 PM »
I said heck with it, I continued my reaction and added this proposed "salt amine"  to my reaction mixture of heptyne and sulphur. Just saw my reaction and I have a real big juicy gooey gum-like mixture in the bottom of the RBF.

I have my usual liquid above it swirling patiently.


Offline Corribus

  • Chemist
  • Sr. Member
  • *
  • Posts: 3471
  • Mole Snacks: +526/-23
  • Gender: Male
  • A lover of spectroscopy and chocolate.
Re: Does this work?
« Reply #108 on: March 21, 2013, 08:50:15 PM »
In my experience, brown tarry goo at the bottom of your flask is rarely a good sign.  But you never know... :)
What men are poets who can speak of Jupiter if he were like a man, but if he is an immense spinning sphere of methane and ammonia must be silent?  - Richard P. Feynman

Offline discodermolide

  • Chemist
  • Sr. Member
  • *
  • Posts: 5038
  • Mole Snacks: +405/-70
  • Gender: Male
    • My research history
Re: Does this work?
« Reply #109 on: March 21, 2013, 10:02:43 PM »
Did you add a base to make the free amine?
Development Chemists do it on Scale, Research Chemists just do it!
My Research History

Offline Messi

  • Full Member
  • ****
  • Posts: 252
  • Mole Snacks: +1/-6
Re: Does this work?
« Reply #110 on: March 21, 2013, 10:15:42 PM »
Did you add a base to make the free amine?

Yes, added TEA.

Offline discodermolide

  • Chemist
  • Sr. Member
  • *
  • Posts: 5038
  • Mole Snacks: +405/-70
  • Gender: Male
    • My research history
Re: Does this work?
« Reply #111 on: March 21, 2013, 10:35:22 PM »
Did the TLC of your thioketene RM show a new product?
Development Chemists do it on Scale, Research Chemists just do it!
My Research History

Offline Messi

  • Full Member
  • ****
  • Posts: 252
  • Mole Snacks: +1/-6
Re: Does this work?
« Reply #112 on: March 21, 2013, 10:37:07 PM »
Did the TLC of your thioketene RM show a new product?

I took a 5:1 Hex:EtOAc TLC and didn't see anything. I think I need a more polar eluent perhaps. Theoretically speaking, the compound I should have made was a thioamide with a branched bromine.

Offline discodermolide

  • Chemist
  • Sr. Member
  • *
  • Posts: 5038
  • Mole Snacks: +405/-70
  • Gender: Male
    • My research history
Re: Does this work?
« Reply #113 on: March 21, 2013, 10:51:20 PM »
Yes, more polar, 5% MeOH/DCM perhaps?
Development Chemists do it on Scale, Research Chemists just do it!
My Research History

Offline Messi

  • Full Member
  • ****
  • Posts: 252
  • Mole Snacks: +1/-6
Re: Does this work?
« Reply #114 on: March 22, 2013, 08:00:36 PM »
Took the TLC in 10:1 DCM:MeOH. It looked OK.

Took NMR of final product. It was certainly not the product I was looking for I don't think. NMR shown below. This sucks!


Offline discodermolide

  • Chemist
  • Sr. Member
  • *
  • Posts: 5038
  • Mole Snacks: +405/-70
  • Gender: Male
    • My research history
Re: Does this work?
« Reply #115 on: March 22, 2013, 11:28:59 PM »
Sorry, but another useless NMR. Too much chloroform in it, too much TMS. The phase needs correction, as do the integrals. Sort that out and expand the region between 5-0.5 ppm, in the vertical as well.
Is this a single spot on TLC?
Does it correspond to anything you have seen in the past in this series of thioketene experiments?
Can you get a MS done?
It may be worth thinking about using protection to do this chemistry instead of trying the "quick way"?
Development Chemists do it on Scale, Research Chemists just do it!
My Research History

Offline Messi

  • Full Member
  • ****
  • Posts: 252
  • Mole Snacks: +1/-6
Re: Does this work?
« Reply #116 on: March 23, 2013, 01:04:30 AM »
Sorry, but another useless NMR. Too much chloroform in it, too much TMS. The phase needs correction, as do the integrals. Sort that out and expand the region between 5-0.5 ppm, in the vertical as well.

Good idea, will do that.

Is this a single spot on TLC?
Does it correspond to anything you have seen in the past in this series of thioketene experiments?

I have a few spots on my TLC. It doesn't particularly correspond to anything I have seen in the past. When using pyrrollidine as an amine and getting the thioamide, the hydrogens of the carbons adjacent to nitrogen had a chemical shift of 3-4 which doesn't seem to be the case here...

It may be worth thinking about using protection to do this chemistry instead of trying the "quick way"?

Yes, good idea. Do you know of any reason why my reaction may not be working however?

Offline discodermolide

  • Chemist
  • Sr. Member
  • *
  • Posts: 5038
  • Mole Snacks: +405/-70
  • Gender: Male
    • My research history
Re: Does this work?
« Reply #117 on: March 23, 2013, 01:27:33 AM »
I have no idea only a few guesses. The compound you obtained after the HBr treatment followed by hot ethhanol. You need to purify and characterise that before going any further.
I suggested you add the thioketene to the amine hydrobromide and then add triethylamine, you didn't do that.
Most importantly you need to make sure that the amine hydrobromide salt is what you think it is.

p.s. the quick and dirty routes don't usually work very well. Take each step and make sure it is what it is supposed to be and pure before using it in the next step.
« Last Edit: March 23, 2013, 01:41:53 AM by discodermolide »
Development Chemists do it on Scale, Research Chemists just do it!
My Research History

Offline Messi

  • Full Member
  • ****
  • Posts: 252
  • Mole Snacks: +1/-6
Re: Does this work?
« Reply #118 on: March 23, 2013, 01:43:24 AM »
I suggested you add the thioketene to the amine hydrobromide and then add triethylamine, you didn't do that.

I did do that :)

p.s. the quick and dirty routes don't usually work very well. Take each step and make sure it is what it is supposed to be and pure before using it in the next step.

Columns are so painful!

Offline discodermolide

  • Chemist
  • Sr. Member
  • *
  • Posts: 5038
  • Mole Snacks: +405/-70
  • Gender: Male
    • My research history
Re: Does this work?
« Reply #119 on: March 23, 2013, 01:50:46 AM »
Above you said "I said heck with it, I continued my reaction and added this proposed "salt amine"  to my reaction mixture of heptyne and sulphur."

So you added the salt to the thioketene.

Columns are a part of organic chemistry. If you can crystallise something fine, if not you need to chromatograph it.
It is vital to have pure compounds especially at the beginning of a new synthetic sequence. Later on when you gain experience with the reaction(s) you get to know what needs to be pure and what doesn't.
Development Chemists do it on Scale, Research Chemists just do it!
My Research History

Sponsored Links