Author Topic: The grignard thread  (Read 176 times)

shroomedalice

  • Guest
The grignard thread
« on: February 25, 2010, 10:26:24 AM »
Grignards are very usefull reagents. acids alcohols ketones alkenes and many more groups can be worked with or obtained via grignard synthesis.

I propose a thread that deals with these reagents and how to work with them via over the counter methods.

the first problem I can see with grignard reagents is the drying of our solvents to work with them.

mercury amalgums I belive both sodium and aluminium will dry ether well enough for a grignard reaction.

if we look at this abstract on interscience we can see that Al amalgums are water sensative and are recomended to be stored under dry ether.

http://www.mrw.interscience.wiley.com/eros/articles/ra076/abstract.html
{
   Handling, Storage, and Precautions:  moisture-sensitive. Precautions should be taken as it readily reacts with water with hydrogen evolution. Can be stored under dry ether. Toxic.
}

this is the easist way to dry ether for a grignard for us I belive. form an Al amalgum then place it in our salt dryed ether and leave over night.
in the morning distill the ether from the amalgum to furnish a very very dry ether.

powdered zeolite will also work though I belive that the granulised zeolite will not work for all grignards as it does not dry ether as well as its powdered counterpart.
I still belive that Al amalgum will dry ether better than both of these options though.

I have only preformed a grignard in class and as of yet have not preformed one at home. I wish to make my first home grignard over the next few months if
time will allow me.

So I would love to collect as much information and practicle experiance as possible in this thread.

of course I shall start this thread with two links both to wikipedia.

http://en.wikipedia.org/wiki/Victor_Grignard

http://en.wikipedia.org/wiki/Grignard_reaction

you will notice that like most chemists of the old days this guy has spent the time to aquire a true forrest under his nose.

dont hold that against him he made some of the greatest discoveries of organic chemistry.

one very usefull grignard for bee's of course is the grignard with nitriles http://designer-drugs.com/pte/12.162.180.114/dcd/chemistry/grignardnitrile.html
this link shows the grignard being preformed in benzene as a solvent but toluene or xylene will do the trick.

this grignard reaction will give a compound from the reaction of phenyl aceto nitrile (the product from TCCA oxidation of phenyl alanine) and methyl magnesium bromide
that is either a reduction away from amphetamine or a hydrolisis step from p2p.

the highest yeild that was obtained from the document posted above was 48% and this was belived to be due to higher temperatures rather than the solvent
being any better than ether for the reaction.

but if we were to look at this paper http://pubs.acs.org/doi/abs/10.1021/jo00226a033 we can see that by simply adding a Cu(I) salt we can acheve much higher
yeilds in the 80+% range.

I honestly belive that girgnards are not as difficult as a lot of people belive. the hardest part being drying your ether for the reaction.

I think that if drying your ether is preformied with an Al/Hg reduction this is not out of our reach.
« Last Edit: February 25, 2010, 11:22:02 AM by shroomedalice »