organicchemist25
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Grignard question (magnesium)
Question on the type of Mg I have.
I'm doing a grignard tomorrow and I have a question on the magnesium I will be using. I have fine magnesium almost like sand, maybe just a little more
course. Its not powdered like graphite or flour etc. The one time i used it in ochem II it was more chunky turnings. Also, a couple videos show the
turnings too.
Its about 250$ in reagents, so before I start I wanted to get some input.
Is there enough surface area for Mg that is as fine as course sand to react? Or only the bigger turnings?
Everything else is good to go. I am just questioning the Mg
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Dr.Bob
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It should work fine. It you want to speed up the reaction, you can grind the Mg in a mortar and pestle right before the reaction, or even wash it
with dilute acid and then rinse well with water, MeOH, and then ether to dry it well.
Powdered Mg will not last long before it oxidizes, so that is worse than big turnings. Just grinding them manually (don;t put it in a blender and
start a fire, please) for a minute or two before the reaction is the simplest way to get fresh surfaces to react. You can also put a small (piece of
sand small) bit of iodine in the flask and heat it well with the Mg, until the purple color is filling the flask. This will both dry the Mg, as well
as help clean it of oxides. A hot air gun works well, or even a burner, if you keep the ether and flammables away during that time.
If you add the solvent and then a small bit of the halide and let those sit a while, then heat it slowly, once the reaction starts going, then you can
add the halide SM slowly to keep the reaction going.
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Magpie
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I've had good luck with Mg turnings.
The single most important condition for a successful synthesis is good mixing - Nicodem
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zed
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I've used granulated Mg for Grignards. Works fine.
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organicchemist25
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Quote: Originally posted by Dr.Bob  | It should work fine. It you want to speed up the reaction, you can grind the Mg in a mortar and pestle right before the reaction, or even wash it
with dilute acid and then rinse well with water, MeOH, and then ether to dry it well.
Powdered Mg will not last long before it oxidizes, so that is worse than big turnings. Just grinding them manually (don;t put it in a blender and
start a fire, please) for a minute or two before the reaction is the simplest way to get fresh surfaces to react. You can also put a small (piece of
sand small) bit of iodine in the flask and heat it well with the Mg, until the purple color is filling the flask. This will both dry the Mg, as well
as help clean it of oxides. A hot air gun works well, or even a burner, if you keep the ether and flammables away during that time.
If you add the solvent and then a small bit of the halide and let those sit a while, then heat it slowly, once the reaction starts going, then you can
add the halide SM slowly to keep the reaction going. |
Thanks for all the information. I attempted it. It did not go as expected, I don’t think. I just posted details and questions with pic on organic
section. I do appreciate your help.
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organicchemist25
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Thanks Magpie! Although it didn’t go quite right. Just posted details and questions and attached pics in organic.
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