Wednesday, August 09, 2006

Metal salt in ether? I should have known better!!

Today I was preparing for a reaction that requires the use of Rieke's Zinc, so since this morning I have been preping for it. First you flame dry your flask a few times and then you add your usual lithium and naphthalene then THF to make lithium naphthalite (this is a cool reaction). After you let the reaction stir at room temp. for 2 hours or until lithium completely dissolved (this is hard to see since the mixture is in dark dark green colour) you then add your zinc salt. In the paper where I got the procedure from they said to add zinc bromide in 1M ether solution to the lithium naphthlite solution. At first I thought, hmmm metal salt in ether interesting... so I blindly went along with it. Zinc bromide turned out to be as soluble in ether as my freaking toilet paper in water, I sonicated it, heat it, but it would not go completely into solution. I then realize I have committed one of the cardinal sin of being an organic grad student- I trusted the paper too much. I somehow had forgotten all those times when I do not even remotely get the result "suggested" in the papers. My own knowledge told me metal salts don't dissolve in ether that well, THF is a better solvent. I was right, zinc bromide dissolved up in THF faster than I can say Horshit, problem solved. Lesson of the day, ALWAYS trust your own knowledge.

5 Comments:

At 7:39 AM, Blogger Razor_goto said...

I spoke to a guy in my class who is also an orgo chemist, and he said this:

I can sympathize with your friend, Sammy. In this particular case, perhaps the author of the original paper was too vague about what he meant by "ether". In organic chemistry, "ether" can mean many things. Usually it means diethyl ether, which is what I imagine your friend used. But THF is technically an ether as well.

 
At 1:20 PM, Blogger jmizz said...

Yeah, but it's more reactive in the ether...

 
At 1:14 AM, Blogger koch said...

well actually ZnBr2 perfectly dissolves in Et2O, but the dissolution is kinetically much much slower than in THF. When I need its solution in ether I just leave it with stirring in ether overnight. try it.
also, in your case the dissolution can slow down by formation of elemental zinc on the ZnBr2 crystalls surface. one more argument to use its pre-prepared solution.
also i dont reccomend to make solutions more concentrated than 1M.

 
At 6:39 AM, Blogger Boya Okulu said...

hello,

i am also trying to prepare the rieke zinc by zncl2 and lithium-naphtalanide but unfortunately i could not obtained until now , i fell that i am stupid cause the rieke zinc is produced on industrial scale by sigma aldrich ,did you manage to prepare the rieke zinc i really wonder since i have tried lots of possibilities i really got bored and never trust anymore on the publications:( i am looking forward to hear your ideas

regards

 
At 6:44 AM, Blogger Boya Okulu said...

hello,

i am also trying to prepare the rieke zinc by zncl2 and lithium-naphtalanide but unfortunately i could not obtained until now , i fell that i am stupid cause the rieke zinc is produced on industrial scale by sigma aldrich ,did you manage to prepare the rieke zinc i really wonder since i have tried lots of possibilities i really got bored and never trust anymore on the publications:( i am looking forward to hear your ideas

regards

 

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