Author Topic: the alcoholate formylations  (Read 1662 times)

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lutesium

  • Guest
the alcoholate formylations
« on: October 02, 2004, 12:20:00 AM »
Can Mg(meO)2 be substtuted for NaOMe (or another alcohol with Na) in a paraformaldehyde + mg(meo)2 formylation done in toluene? Or does magnesium have special withdrawing properties?

Have there been tries here at the hive to RT formylate HQ?

Thanx

Rhodium

  • Guest
The special role of Mg2+ is to stabilize the...
« Reply #1 on: October 02, 2004, 04:33:00 PM »
The special role of Mg2+ is to stabilize the reaction intermediates by "holding" the reagents together in a suitable conformation.

For details & diagrams, see

Post 481046

(Rhodium: "Magnesium ortho-Formylation Mechanism", Methods Discourse)



lutesium

  • Guest
RHodium Ýs the role of diethyl ether (and thf)
« Reply #2 on: October 06, 2004, 02:33:00 PM »
RHodium

Ýs the role of diethyl ether (and thf) the same (holding the ions)in a grignard rxn?

I read the mechanisn in vogel several times but I cant remember


EDIT: The pdf file in the post you linked above is a killer! I was mentioning and experimenting the reactiion with Mg turnings and had a great success with high yields (over %90)  I tried it with many types of phenols (which were derivated also by me - cleaned by three xtallyzations and looked like 2-3 cm long big white needles  ;D ) Reactions were on a max 2 g scale and I can say that its my favorite. But the phenol must be clean.
NOW
Hearing that we can use MgCl2 almost killed me! Poor chemist - me will benefit from this and keep on experimenting with the cheaper salt!

Thanx Rhode long live Science

Rhodium

  • Guest
The role of ethers in a grignard
« Reply #3 on: October 06, 2004, 07:55:00 PM »
Ýs the role of diethyl ether (and thf) the same (holding the ions)in a grignard rxn?

To some extent, yes - but that's a gross oversimplification. Here follows some explanation from

http://www.cm.utexas.edu/bauld/grignard.htm




Diethyl ether is an especially good solvent for the formation of Grignard reagents because ethers are non-acidic (aprotic). Water or alcohols would protonate and thus destroy the Grignard reagent, because the Grignard carbon is highly nucleophilic. This would form a hydrocarbon. But Grignard reagents are stable in ethers.



Another reason that ethers are good solvents for Grignard reagents is that the MgX bond is ionic and thus benefits greatly from being effectively solvated. The formation of ions in very nonpolar solvents, where they would not be effectively solvated is very difficult. Ethers are surprisingly good at solvating cations, because the C-O bond is relatively polar, thus allowing the oxygen end of the ether dipole to solvate and stabilize (electrostatically) the magnesium ion.




The Ether-RMgX complexes shown at work in a reaction can be seen here:

https://www.thevespiary.org/rhodium/Rhodium/chemistry/grignardnitrile.html