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Author: Subject: Grignard catalyst
CycloRook
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[*] posted on 4-2-2022 at 10:54
Grignard catalyst


I have a procedure that calls for dibromoethane to start and catalyze a grignard reaction.

Does anyone know of an OTC reliable catalyst. I prefer not to buy semi exotic chemicals.

Thanks
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Texium
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[*] posted on 4-2-2022 at 11:16


The classic initiator is a small crystal of iodine



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njl
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[*] posted on 4-2-2022 at 11:18


Iodine can be added, I believe this activates the magnesium.

edit: Didn't see that, tex

[Edited on 2-4-2022 by njl]




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CycloRook
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[*] posted on 4-2-2022 at 16:03


Quote: Originally posted by Texium  
The classic initiator is a small crystal of iodine
I know about the Iodine. I consider this to be semi exotic. Anything else in mind ?
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karlos³
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[*] posted on 4-2-2022 at 19:21


Just pre-dry your solvents properly with molsieves in advance, and if you can't get iodine or another likewise small (di)haloalkane, it will probably do not matter much.
They tend to work like a charm this way, but I always use a tiniest piece of iodine as well.

I would guess that a tiny quantity of DCM would work similar well to dibromoethane, though.
I've also seen ethyl iodide being used for this.




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AvBaeyer
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[*] posted on 4-2-2022 at 19:33


Do you have access to an ultrasonic cleaner? Putting some warm water in the cleaner then sonicating the reaction flask with a small amount halide solution and magnesium will almost always start the reaction. I say this assuming that you are running your reaction on a modest scale. I have been told (but not tried) that just sonicating some magnesium alone will activate it nicely. I cannot vouch for this but it may be worth a try.

By the way, iodine is not so exotic. If you have potassium iodide and an oxidizing agent like oxone pool sanitizer, you can make sufficient iodine to start a Grignard reaction. I cannot understand how you plan to run a Grignard reaction without the basic reagents so commonly used.

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timescale
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[*] posted on 4-2-2022 at 20:33


Not sure if you'd consider chloroform exotic, but that might work as well.

You could always just drip in some of your alkyl halide and cross your fingers! Grinding the Mg in a mortar and pestle before use might also help (temporarily removes oxides etc)




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Texium
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[*] posted on 4-2-2022 at 20:39


Quote: Originally posted by cycloknight19  
Quote: Originally posted by Texium  
The classic initiator is a small crystal of iodine
I know about the Iodine. I consider this to be semi exotic. Anything else in mind ?
Well that’s sad



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Tsjerk
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[*] posted on 5-2-2022 at 05:14


Ethyl bromide from ethanol and a bromide or iodine from KI.

But Grignards, maybe except some really deactivated halides, often start when molar sieves are used to pre-dry.

What you can do to get activated magnesium which starts Grignards without catalyst is treating it with HCl, followed by methanol. I found out about this trick when I was drying methanol with magnesium.

Magnesium and methanol react spontaneously and exothermic as long as there is no oxide layer on the magnesium or too much water in the methanol.

What you do is stir the magnesium with 0.5% HCl for as long as you think is necessary to get rid of most the oxide, probably one or two minutes. This you filter over vacuum, and rinse with methanol. Now you put the magnesium in some dry methanol and let it stand until it is warm to the touch.

The magnesium reacts with methanol to form methoxide, assuring there is no residual HCl or water left. This you filter over vacuum again and after drying over the vacuum for a minute or so you rinse with a little ether to get rid of the last methanol. Drying in vacuum would be even better. This way there will be even less oxide layer formed

This magnesium will be so reactive it will instantly react with your halide of choice, without any catalyst.
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Amos
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[*] posted on 5-2-2022 at 15:02


Just grind your magnesium in a mortar and pestle for a little while. You can add some sand to act as an abrasive if you want, it's not going to hurt anything in the reaction other than the most sensitive of magnetic stirring. On paper, nothing is needed to initiate the formation of the grignard at all, and if your reagents aren't bad quality it should form just fine albeit slowly.
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Tsjerk
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[*] posted on 6-2-2022 at 23:12


Nice contribution of AvBaeyer:

https://www.sciencemadness.org/whisper/viewthread.php?tid=15...

I thought I would link the two topics together.

[Edited on 7-2-2022 by Tsjerk]
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[*] posted on 1-3-2022 at 23:36


Hello, my choice would be Zinc II
The Grignard Reaction is a reaction in which an organomagnesium halide (Grignard reagent) is added to a ketone or aldehyde to produce tertiary or secondary alcohol. A primary alcohol is formed when formaldehyde reacts with it.
Grignard Reagents are also employed in the crucial reactions listed below: When an excess of a Grignard reagent is added to an ester or lactone, it generates tertiary alcohol with two identical alkyl groups, and when a Grignard reagent is added to a nitrile, it forms an unsymmetrical ketone through a metallocene intermediate.
Catalysts are particularly essential in chemistry, especially in organic synthesis, since they may considerably speed up chemical processes and reactions, allowing products to be synthesized more efficiently and sustainably. Zinc is a very inexpensive and widely accessible metal (zinc is easily extracted from the minerals in high purity). Zinc's low toxicity, low cost, availability and accessibility make it a likely candidate for use in chemical catalysis. Zinc (II) bromide (ZnBr2) is a zinc compound that has been widely employed as a catalyst in chemical synthesis. In recent years, literature has reported on the use of ZnBr2 as a catalyst for the synthesis of organic chemicals and heterocyclic molecules.
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