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Chemistry Forums for Students => Organic Chemistry Forum => Organic Chemistry Forum for Graduate Students and Professionals => Topic started by: CrazyGoat on April 04, 2020, 02:28:21 AM

Title: Drying a solution of zncl2
Post by: CrazyGoat on April 04, 2020, 02:28:21 AM
I have anhydrous zncl2 and I wanna use it dry (completely, not water :)
I can not dry it with a flame in a flask with vacuum, why? Becouse in case of have some water molecule attached to it, it reacts when heated:
Heating the hydrated form, ZnCl2•n(H2O), yields Zn(OH)Cl, not ZnCl2.(that is what I want, dried)
I can not have O on my system, that's why I do it in under argon.
By other side, I will use it, (for the reaction) solved ln chloroform
 (the chloroform, obviously, must be dried as well:)
My question here:
If I add, to the zncl2 solved in the chloroform, previous addition to the final reaction flask, a good quantity of anhydrous salt, like some type of magnesium...
Will I get, both, zncl2 and chloroform dried and ready for my non O reaction?
Thank you.
Title: Re: Drying a solution of zncl2
Post by: chenbeier on April 04, 2020, 06:29:00 AM
I would add thionylchloride to zinc chloride, all water will be converted to HCl and SO2.
After some reaction time, get it under vacuum and remove all gas.
Title: Re: Drying a solution of zncl2
Post by: CrazyGoat on April 04, 2020, 07:59:12 PM
Hey buddy, thank you for your answer.
You know...
I think this compound its not absolutely weet....
IT IS anhydrous zncl2!!
So I think that instead this I will just let it well keeped in a vaccum desiccator. 
And then flame dry it.
What do you think? is it going to be a big deal?
For a O2 and h20 sensitive reaction?
Do you know what i mean 😅?
Thank friends.
Title: Re: Drying a solution of zncl2
Post by: phth on April 05, 2020, 10:32:08 PM
recrystallize under argon. Check color and crystalline properties
Title: Re: Drying a solution of zncl2
Post by: wildfyr on April 06, 2020, 12:09:49 AM
I'm going back to the well, dry with P2O5.
Title: Re: Drying a solution of zncl2
Post by: CrazyGoat on April 08, 2020, 04:44:21 PM
I will rewrite my question:
I have to do a reaction free of water and O2.
For that I will use a reflux system in which all glass has been previously dried under vacuum and where a constant flux of argon is going on.
This reaction must be done with zncl2 which is highly hygroscopic,
I have bough it anhydrous and it is sealed but I will have to open it, and add it to the flask.
Will it in this moment get a lot of atmospheric water?
I pretend (once the flask is closed again)
flame dry it again, but this time with the zncl2 inside. (for remove added moisture in the flask + the one in the zncl2)
But according to the zncl2 literature
Heating the "hydrated" form, ZnCl2•n(H2O), yields Zn(OH)Cl, not ZnCl2.
My question here:
If (in this particular case) I flame dry it under vacuum and have got some water particle in the process of letting it inside of the flask...
The hydroxide gas will just go away by the pump suction and only will remains pure anhydrous zncl2 that I can use for my dried reaction, with out lossing, by the little watter adquiered in the short time of hadeling it, too much of the active zncl2 while been oxigen free.
So no a big deal.
Or it's a big deal?
Thank you.
Title: Re: Drying a solution of zncl2
Post by: kriggy on April 10, 2020, 04:02:06 PM
You can open the containter under argon shower and weight it into a sealed flask: make argon shower, take a small vial with top on, weight empty, add some ZnCl2, weight again to see how much you get, adjust the amount depending on your needs.

Furthermore, you can buy anhydrous ZnCl2 in various solvents which might be easier to work with than the solid
Title: Re: Drying a solution of zncl2
Post by: Reddart on April 19, 2020, 09:34:26 PM
Yes, try the organic solvent versions if the solvents are compatible with your reaction.

Also beware, I was recently burned by "anhydrous" ZnCl2 (2 different lots from the same very large, but for now un-named manufacturer). My reaction isn't even that sensitive, but gave very lousy yields until I switched to material from another vendor. I suspect it has a lot of hydrate form in it.
Title: Re: Drying a solution of zncl2
Post by: rolnor on April 20, 2020, 03:21:18 AM
I have done hundreds of reactions with BuLi without flame-drying anything, also in small scale. I have seen people flame-drying Hammilton-syringes to the point where the glass is deformed and the syringe starts to leak. If you have a fresh bottle of ZnCl2 just use it.
Title: Re: Drying a solution of zncl2
Post by: kamiyu2550 on April 20, 2020, 01:19:26 PM
I have done hundreds of reactions with BuLi without flame-drying anything, also in small scale. I have seen people flame-drying Hammilton-syringes to the point where the glass is deformed and the syringe starts to leak. If you have a fresh bottle of ZnCl2 just use it.

n-BuLi is of course sensitive to water. But because it is usually used in stoichiometric quantity, not flame-dry your flask can be OK. However, oven dry glassware at about 100 oC does not completely dry the glass. If you flame dry this glassware under vacuum, you will immediately see a mist coming off. In case where the reaction is very very sensitive to water, for example organometallic complexes used in catalytic amount, flame dry is required.

Glassware should not be deformed upon flame dry, unless something wrong with the glass itself.
Title: Re: Drying a solution of zncl2
Post by: rolnor on April 20, 2020, 01:53:37 PM
The moisture you see "comming of the glass" is water vapor formed from the flame, not comming from the glass. How often do you use these very sensitive organometallic complexes? I would say not very often.
Title: Re: Drying a solution of zncl2
Post by: kamiyu2550 on April 20, 2020, 03:06:29 PM
The moisture you see "comming of the glass" is water vapor formed from the flame, not comming from the glass. How often do you use these very sensitive organometallic complexes? I would say not very often.

Well, may I suggest you Google yourself about flame dry glassware? If not, maybe this demonstration helps illustrate my point.

https://www.youtube.com/watch?v=AsWohoQNJb8

I was an undergraduate when I learnt how to do this flame drying for high level water-free reactions.
Title: Re: Drying a solution of zncl2
Post by: rolnor on April 20, 2020, 04:01:36 PM
I know that glass can have moisture bonded to it but the moisture you can see comming of the flask is just moisture from combustion from the flame, this is a common missconception.
Title: Re: Drying a solution of zncl2
Post by: kamiyu2550 on April 20, 2020, 04:09:15 PM
I know that glass can have moisture bonded to it but the moisture you can see comming of the flask is just moisture from combustion from the flame, this is a common missconception.

Did you do Google search about flame dry glassware that I told you to do?

Any proof that is "combustion due to the flame"? I really have difficulty understanding what you say..

If combustion, then what in the glass combust to form water? And why there is only initial mist coming off then no more....

By the way, are you a synthetic chemist?
Title: Re: Drying a solution of zncl2
Post by: rolnor on April 20, 2020, 06:15:06 PM
The vapor from the flame condenses on the cold part of the flask, if you try this with a mirror you will se the same effect. If you use a heating gun, wich does not give any water from combustion, you will not have this effect.
Title: Re: Drying a solution of zncl2
Post by: CrazyGoat on April 21, 2020, 07:52:26 AM
I was searching for a vid where they are doing a glass drying under vacuum and you can see how the condensation goes away when vacuum is activated, and they day sl, they say: "do you see how it sucks the condensation" while that happens, but I don't find it.
Anyway I like the idea of whom says you don't see the condensation from the inside the glass.
Thank you for your replies to this.
May you take a look to another question I posted and may be answer some of the questions I did?
https://www.chemicalforums.com/index.php?topic=103908.msg366062#msg366062
Thank you very much.

Title: Re: Drying a solution of zncl2
Post by: kriggy on April 28, 2020, 01:38:07 AM
The vapor from the flame condenses on the cold part of the flask, if you try this with a mirror you will se the same effect. If you use a heating gun, wich does not give any water from combustion, you will not have this effect.

That indeed might be true but how do you explain my observation: When flame drying a flast while it is connected to vacuum, the vapor is seen only one the first or second flame drying runs which include cooling down the flask to room temperature before heating again?
Title: Re: Drying a solution of zncl2
Post by: rolnor on April 28, 2020, 03:19:00 AM
Try this with a heatinggun, do you see any moisture?