Sciencemadness Discussion Board
Not logged in [Login ]
Go To Bottom

Printable Version  
Author: Subject: Grignard questions
organicchemist25
Hazard to Others
***




Posts: 136
Registered: 12-2-2014
Member Is Offline

Mood: No Mood

[*] posted on 16-8-2016 at 13:29
Grignard questions


I think I am posting in the right area since Grignards are reagents.

I am about to attempt my own Grignard reagent (organomagnesium). I have heard and read they are very sensitive to moisture.

What exact size of magnesium turnings should be used? does it matter as long as they are fine? I have magnesium, but mot sure if they are fine enough. I believe they are firework grade. I bought them a few years ago.

Is an inert gas necessary? I have nitrogen, will that work if needed? Or can it be pulled off with no inert gas?

I know it must be in dry conditions inside the reaction flasks.

Last, how will I know the experiment was a success? Is there a method for testing? Is there a way to tell if it was partially good or if it went really well or if it failed?

Thank you for your expertise :)
View user's profile View All Posts By User
Pasrules
Hazard to Self
**




Posts: 77
Registered: 4-1-2015
Location: Yellow Cake Deposit
Member Is Offline

Mood: Lacking an S orbital

[*] posted on 16-8-2016 at 14:57


Without more detail you would find more help in beginnings but not to worry.

They are incredibly sensitive to moisture, I have had the reaction fail even under textbook conditions.
The magnesium shouldn't be a problem as long as they are thin turnings otherwise you may need to reflux the reagent a little longer. As usual add a crystal of iodine in case your magnesium has oxidised (pyrotechnic grade should be fine).
The inert gas isn't so much the problem, you'll need a volatile gas usually diethylether or THF which creates a positive pressure inside the flask to stop moisture entering during reflux. Dry everything in an oven until use.

A TLC of your reaction mixture should be different to your starting material, if you post your starting materials I can be of more help.




Atropine, Bicarb, Calcium.
View user's profile View All Posts By User
Magpie
lab constructor
*****




Posts: 5939
Registered: 1-11-2003
Location: USA
Member Is Offline

Mood: Chemistry: the subtle science.

[*] posted on 16-8-2016 at 15:26


Dry everything including your glassware (oven dry or flame dry). You don't need to have an inert atmosphere as the ether will provide this as previously stated. You will see a fizzing reaction that will indicated the adduct is forming. Your yield will show you how successful you were. Don't expect a really high yield for most reactions. Something around 60-70% would be normal IIRC.

I use Mg turnings. If the Mg is too fine the rx might be too fast, but I don't know this from experience.

[Edited on 16-8-2016 by Magpie]

[Edited on 16-8-2016 by Magpie]




The single most important condition for a successful synthesis is good mixing - Nicodem
View user's profile View All Posts By User
Texium
Administrator
Thread Moved
16-8-2016 at 16:18
Nicodem
Super Moderator
Thread Moved
16-8-2016 at 21:52
organicchemist25
Hazard to Others
***




Posts: 136
Registered: 12-2-2014
Member Is Offline

Mood: No Mood

[*] posted on 16-8-2016 at 23:43
Grignard questions


Thank you for your responses! Always nice to receive some input from you, Magpie.

I have heard that ether is better from some and THF is better from others. I have both. I am going to run both at some point.

I will be using 250mL three-neck flask RBF, ether (freshly distilled over sodium), iodine crystals, cyclopentylbromide and the magnesium.

I will be using 600mm Liebig condenser for refluxing with a drying tube attached to the top with calcium chloride. The one drying tube I'll be using is the bent/upside down one to prevent any accumulated moisture from entering flask.

I will be using pressure equalizing addition funnel to dispense the cyclopentylbromide. Hotplate and stir bar. I will also flame dry all glassware after assembly.

Am I missing anything?
View user's profile View All Posts By User
Cryolite.
National Hazard
****




Posts: 269
Registered: 28-6-2016
Location: CA
Member Is Offline

Mood: No Mood

[*] posted on 17-8-2016 at 00:46


Making some ketamine derivatives, I see....

Keep an ice bath handy to prevent the exothermic reaction between the metal and the alkyl halide from going out of control if you screw up and accidentally add way more alkyl halide then you were anticipating. Other than that, make sure your cyclopentyl bromide is dry and you should be OK.
View user's profile View All Posts By User
stoichiometric_steve
International Hazard
*****




Posts: 818
Registered: 14-12-2005
Member Is Offline

Mood: satyric

[*] posted on 17-8-2016 at 01:36


Quote: Originally posted by Cryolite.  
Making some ketamine derivatives, I see....


So easy to spot, eh?
View user's profile View All Posts By User
Melgar
Anti-Spam Agent
*****




Posts: 2004
Registered: 23-2-2010
Location: Connecticut
Member Is Offline

Mood: Estrified

[*] posted on 17-8-2016 at 06:55


I've had the best luck with drying my ether for about a week over sodium hydroxide, then using turnings that I cut immediately by drilling holes in a block of magnesium. Distillation shouldn't be necessary, and seems like it'd be more likely to inadvertently add water. IIRC, it's done to ensure that explosive peroxides haven't formed, but the last step really should be drying over sodium.
View user's profile View All Posts By User
organicchemist25
Hazard to Others
***




Posts: 136
Registered: 12-2-2014
Member Is Offline

Mood: No Mood

[*] posted on 17-8-2016 at 09:39


Quote: Originally posted by Cryolite.  
Making some ketamine derivatives, I see....

Keep an ice bath handy to prevent the exothermic reaction between the metal and the alkyl halide from going out of control if you screw up and accidentally add way more alkyl halide then you were anticipating. Other than that, make sure your cyclopentyl bromide is dry and you should be OK.


I wasn't trying to keep a secret. I remember back in my days around 2000 I had quite a few good times on it. Been years. Wouldnt mind sampling a little again, plus gain experience. I also do not want to deal with anyone trying to get it. So, I figure I'd attempt it for my own personal and go back in time a little :)

Thanks
View user's profile View All Posts By User
organicchemist25
Hazard to Others
***




Posts: 136
Registered: 12-2-2014
Member Is Offline

Mood: No Mood

[*] posted on 17-8-2016 at 09:44
Grignard questions


Besides, I knew just about everyone would know when I put it out there. I've seen memebrs try to lie and make things up about what they are doing. Im not big at all on making illegal compounds myself, but this compound has always intrigued me. Pretty safe in moderation. Been 15+ years since my last encounter.
View user's profile View All Posts By User
myristicinaldehyde
Hazard to Others
***




Posts: 166
Registered: 23-4-2016
Location: .͐͌ ͛҉̻̫̰̻̖E̮ͮ̐́̚ ̢̗̅̉ͩ͂̒̌.̯̻̺̯̀̎͂̄ͩ̚
Member Is Offline

Mood: сорок пять

[*] posted on 22-8-2016 at 06:55


Quote: Originally posted by organicchemist25  
Besides, I knew just about everyone would know when I put it out there. I've seen memebrs try to lie and make things up about what they are doing. Im not big at all on making illegal compounds myself, but this compound has always intrigued me. Pretty safe in moderation. Been 15+ years since my last encounter.


Did you carry out the reaction, and how were the yields? Do you have any photos?

Chemplayer showed that methylmegnesium grignards are rather friendly, but I've heard that the larger alkyl groups are very sensitive. Once I get my hands on nice magnesium (accepting donations!:P ) I would like to try a Grignard out.
View user's profile View All Posts By User
organicchemist25
Hazard to Others
***




Posts: 136
Registered: 12-2-2014
Member Is Offline

Mood: No Mood

[*] posted on 28-3-2017 at 21:32


Quote: Originally posted by myristicinaldehyde  


Did you carry out the reaction, and how were the yields? Do you have any photos?

Chemplayer showed that methylmegnesium grignards are rather friendly, but I've heard that the larger alkyl groups are very sensitive. Once I get my hands on nice magnesium (accepting donations!:P ) I would like to try a Grignard out.


No, I never got around to do it. I will be soon now though and I will take pics. Ive seen quite a few of chemplayers vids. I really appreciate the effort put into them. I will also check receive email box on all future posts. I always forgot to do that.
View user's profile View All Posts By User

  Go To Top