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

Printable Version  
Author: Subject: Can DCM act as a Lewis Acid?
vanausen
Harmless
*




Posts: 1
Registered: 15-12-2022
Member Is Offline


[*] posted on 19-12-2022 at 22:18
Can DCM act as a Lewis Acid?


Hello everyone,
first post here, hope this is the right place.

I am performing a reaction with AlCl3 in DCM as my solvent.
My reaction and quenching setup works totally fine. I have a >95% purity after the step of water washing.
The problem I see is, that once I start to boil off my DCM at ambient pressure, I see a slow second order reaction occurring, which starts to degrade my product.

Before I reach the boiling point of my crude oil, I already lost most of my product. This second order reaction needs a lewis acid to be present.
I never worked with DCM in the past and I therefore asked myself if DCM can act as a lewis acid itself?

In this case boiling off the solvent under reduced pressure and the addition of another solvent (hexane, toluene,…) with a higher boiling point could help to get rid of any residual DCM in my crude oil?

Can anybody confirm this theory? Otherwise I need to reevaluate my whole process.



Thank you very much!

View user's profile View All Posts By User
Boffis
International Hazard
*****




Posts: 1840
Registered: 1-5-2011
Member Is Offline

Mood: No Mood

[*] posted on 20-12-2022 at 01:15


If you have washed the reaction mixture with water then the AlCl3 will have hydrolysed and perform no further function. Its difficult to give a more precise answer unless you are going to give us a more detailed description of the procedure as you performed it and a reference to the original procedure that you are following.
View user's profile View All Posts By User
blogfast25
International Hazard
*****




Posts: 10562
Registered: 3-2-2008
Location: Neverland
Member Is Offline

Mood: No Mood

[*] posted on 20-12-2022 at 13:26


MeCl2 is not an electron pair acceptor, so I can't see it functioning as a Lewis acid.

[Edited on 20-12-2022 by blogfast25]




View user's profile View All Posts By User
CharlieA
National Hazard
****




Posts: 646
Registered: 11-8-2015
Location: Missouri, USA
Member Is Offline

Mood: No Mood

[*] posted on 20-12-2022 at 14:46


Quote: Originally posted by blogfast25  
MeCl2 is not an electron pair acceptor, so I can't see it functioning as a Lewis acid.

[Edited on 20-12-2022 by blogfast25]


I second the motion.:)
View user's profile View All Posts By User
clearly_not_atara
International Hazard
*****




Posts: 2714
Registered: 3-11-2013
Member Is Offline

Mood: Big

[*] posted on 20-12-2022 at 17:33


You have AlCl3 in your system. So there's obviously a Lewis acid present! But maybe you meant to say "electrophile"? CH2Cl2 can act as an electrophile, but it's activity is low due to symmetry.



Quote: Originally posted by bnull  
you can always buy new equipment but can't buy new fingers.
View user's profile View All Posts By User
blogfast25
International Hazard
*****




Posts: 10562
Registered: 3-2-2008
Location: Neverland
Member Is Offline

Mood: No Mood

[*] posted on 21-12-2022 at 08:22


Quote: Originally posted by clearly_not_atara  
You have AlCl3 in your system.


Quote:
I am performing a reaction with AlCl3 in DCM as my solvent.
My reaction and quenching setup works totally fine. I have a >95% purity after the step of water washing.


There can't be much AlCl3 left after the wash with water. That's why he's looking for another Lewis acid...




View user's profile View All Posts By User
Dr.Bob
International Hazard
*****




Posts: 2667
Registered: 26-1-2011
Location: USA - NC
Member Is Offline

Mood: No Mood

[*] posted on 21-12-2022 at 10:46


Maybe you are generating HCl or some other byproduct from the workup. Hard to know without details. DCM is not going to be unstable to most things, but can hold HCl well, so if you make the reaction acidic and then concentrate, the HCl can become quite strong.
View user's profile View All Posts By User
Triflic Acid
Hazard to Others
***




Posts: 486
Registered: 27-9-2020
Member Is Offline

Mood: Slowly Oxidizing into Oblivion

[*] posted on 21-12-2022 at 18:35


Try a bicarb wash of the DCM layer after the water quench, it would get rid of any of the HCl that Dr. Bob mentioned. I'd stir strongly with bicarb for like 15 minutes to be super sure, then it should be fine to rotovap down. Otherwise, it might be from oxygen oxidizing your product, so doing an inert atmosphere distillation might be better than rotovaping.



There wasn't a fire, we just had an uncontrolled rapid oxidation event at the power plant.
View user's profile View All Posts By User

  Go To Top