11-17-02 05:38
No 380412
      Buffering an Al/Hg?  Bookmark   

You know how carbinolamines are best dehydrated under a slighly acidic PH?
And the typical Al/Hg runs under basic conditions?
How about buffering this system by adding methylamine base and methylamine hydrochloride?
(Chief Bee)
11-17-02 08:33
No 380432
      * The Al/Hg reducing system is active at whatever ...  Bookmark   

* The Al/Hg reducing system is active at whatever pH you want, but the closer to neutral, the slower it will go.

* If the pH is too acidic, all of the methylamine will be in the form of methylammonium ion, which is not nucleophilic enough to add to the ketone and form the carbinolamine.

* If the pH is too basic, the dehydration of the carbinolamine to form the imine will be too slow.

What pH are we aiming for here? We have three reactions that needs to take place at the same time, and each of them wants a different pH environment - we cannot make the solution too acidic or too basic, but on the other hand we cannot make it too neutral either...
(Hive Bee)
11-17-02 09:07
No 380435
      Rhodium  Bookmark   

I am aware that if the system is too acidic the amine will become protanted and the lone pair on the nitrogen atom won't undergo a nuclephilic attack on the carbocation of the ketone function.
OTOH, at aroun PH 6.4 the alcohol function get's protonated making it a H2O function which is a good leaving group to form the carbinolamine.
This is for primary amines and methylamine may have different requirements because of it's electric feild inductive effects as it's in the form of a carinolamine so a slightly basic PH will probably favor this.
As you said it can't be too basic either.
(Chief Bee)
11-17-02 09:19
No 380440
      Yup, put at pH 6.5 the aluminum will not dissolve ...  Bookmark   

Yup, put at pH 6.5 the aluminum will not dissolve at a sufficient rate...
(Stoni's sexual toy)
11-18-02 10:16
No 380603
      The Al/Hg works well without buffering.  Bookmark   

The Al/Hg works well without buffering. The MeNH2 isn't that basic. And when I added solid NaOH and the reaction indeed turned pretty basic it worked just as well.
No need to fix it if it's not broken.

I'm not fat just horizontally disproportionate.
(Hive Bee)
11-18-02 16:37
No 380699
      I agree with both of you  Bookmark   

No need to reinvent the wheel, maybe improve the wheel.
I'm satisfied with conventions myself, just an idea.