Sciencemadness Discussion Board

BnCl synthesis - Using anhy. CaCl2 as catalyst?

SuperOxide - 9-4-2022 at 09:34

I've made benzyl chloride a few different ways, with just a vast excess of HCl as well as only a slight excess of HCl with some anhydrous zinc chloride as a catalyst. I was telling a friend about the synthesis, and he mentioned that maybe even anhydrous calcium chloride could be used either in place or in addition to the zinc chloride.

I didn't think about it at first, but then I remembered that I actually have concentrated some 20% HCl to >30% by bubbling dry HCl through it, and the HCl was generated by heating up some other 20% HCl with a lot of anhydrous calcium chloride in it. And from what I understand about using the zinc chloride as a catalyst, it basically helps push the reaction forward by releasing additional HCl while reacting with the water that's released from that reaction of BnOH + HCl. Calcium chloride may not release HCl, but it would definitely grab onto the water biproduct.

Has anyone tried using anhydrous calcium chloride in this manner? Is there any reason it wouldn't work?

Thanks.

SplendidAcylation - 10-4-2022 at 02:04

I have been wondering about this myself lately!

I think it would work, as it works for similar reactions:

Vogel has a synthesis for cyclohexyl chloride using calcium chloride (see attached image)



And here is an excellent video on the preparation of isopropyl chloride this way; I have tried this, and it worked very well.

So I'm sure it'd work for BnCl too, I'm not exactly sure how it works in these reactions though; Does it act as a dehydrating agent, pushing the equilibrium forward by removing water by forming hydrates, or does it increase the conc. of chloride ions in solution?

Perhaps it is both of these factors.

Screenshot_2022-04-10_10-57-07.png - 158kB

[Edited on 10-4-2022 by SplendidAcylation]

SuperOxide - 10-4-2022 at 07:05

Quote: Originally posted by SplendidAcylation  
I have been wondering about this myself lately!

I think it would work, as it works for similar reactions:

Vogel has a synthesis for cyclohexyl chloride using calcium chloride (see attached image)



And here is an excellent video on the preparation of isopropyl chloride this way; I have tried this, and it worked very well.

So I'm sure it'd work for BnCl too, I'm not exactly sure how it works in these reactions though; Does it act as a dehydrating agent, pushing the equilibrium forward by removing water by forming hydrates, or does it increase the conc. of chloride ions in solution?

Perhaps it is both of these factors.

I think its both of these factors. I think by forming the hydrates, it increases the concentration of chloride ions in solution, thus pushing it forward.

The reason ZnCl2 probably is usually used more often is because not only does it form hydrates, but it also releases HCl when it does. So it doesn't just free up HCl, but actually adds to it. (Pretty sure about that anyways).

njl - 10-4-2022 at 08:47

ZnCl2 is also a Lewis acid which helps with the reaction, while CaCl2 is not.

clearly_not_atara - 10-4-2022 at 09:03

I think ZnCl2 is used as an example because it's undergraduate pedagogy, not practical engineering, and ZnCl2 is a bit stronger and so works with primary aliphatic alcohols, while CaCl2 may not, and the goal is to keep it simple, stupid. CaCl2 is definitely easier to work with if you can use it, and it can be dried and used over and over.

kmno4 - 10-4-2022 at 11:46

BnCl comes back like a boomerang.....
Read this, for example:
https://www.sciencemadness.org/whisper/viewthread.php?tid=71...

.. and the paper by Clark ( ZnCl2 in chlorides preparations)



Attachment: Clark.pdf (299kB)
This file has been downloaded 340 times

[Edited on 10-4-2022 by kmno4]

unionised - 10-4-2022 at 12:04

Quote: Originally posted by njl  
ZnCl2 is also a Lewis acid which helps with the reaction, while CaCl2 is not.

I'm pretty sure it is.

DraconicAcid - 10-4-2022 at 12:34

Quote: Originally posted by unionised  
Quote: Originally posted by njl  
ZnCl2 is also a Lewis acid which helps with the reaction, while CaCl2 is not.

I'm pretty sure it is.

Zinc chloride is a much stronger Lewis acid than calcium chloride.

At least, I zinc so.

SuperOxide - 10-4-2022 at 12:54

Quote: Originally posted by kmno4  
BnCl comes back like a boomerang.....

Not sure what you mean here.