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

Printable Version  
Author: Subject: AlCl3 is an alternative to SOCl2
EverythingAl2O3
Harmless
*




Posts: 9
Registered: 3-9-2019
Member Is Offline


[*] posted on 3-12-2020 at 18:12
AlCl3 is an alternative to SOCl2


Hey everyone. I was thinking about reactions for Al2O3 (Not kidding really do this every second I have time to think) and my mind turned to halogenation of primary alcohols and how SOCl2 kinda sucks but is the only option.

So I thought about the mechanisms of how they work, and realized that AlCl3 works in a very similar way in Friedel-Crafts alkylation. So I came up with the mechanism attached and thought it looked good and set out to find a paper to confirm my hypothesis and low and behold here it is. I do not know its effects in aliphatic alcohols but benzylic alcohols work very well. (I'm aware anhydrous AlCl3 has its dangers but nothing near SOCl2 with the HCl and SO2)

So for anyone who is looking to do this type of reaction with any type of primary alcohol but doesn't want to use SOCl2, you might want to give this a try instead.

Edit By extension this might mean bromination and iodination by AlBr3 and AlI3 may be possible.

20201203_204531.jpg - 2MB

Attachment: A_New_Facile_Route_to_Chlorination_of_Alcohols_via.pdf (375kB)
This file has been downloaded 7 times

[Edited on 4-12-2020 by EverythingAl2O3]
View user's profile View All Posts By User
Opylation
Hazard to Self
**




Posts: 77
Registered: 30-8-2019
Member Is Offline


[*] posted on 3-12-2020 at 19:40


Alcl3 cannot be used to form alkyl halide (very well). The product formed will mostly me aluminum trialkoxides. There is a caveat though, I have seen some people used iodine and aluminum to form methyl iodide but it’s terrible yields

It's odd though because using the constituents enthalpies of formation technically alkyl chlorides are more thermodynamically favorable. At least when dealing with isopropanol and aluminum chloride. I couldn't find info on Al(OC2H5)3 thermodynamics. Must be other factors at play. I think it has something to do with reduction potentials

I'm gonna guess it has to do with Aluminum Trichloride being such a powerful lewis acid it binds hard to the alcohol oxygens electrons, creating a positive charge on the oxygen and booting off the proton. The protons get scavenged by the chloride anion and since hydrogen chloride is volatile it escapes via the heat of reaction.

It's interesting though because AlCl3 is used to deprotonate aryl ethers and the resulting product is deprotection, after reacting with water. Maybe since arene's are electron dense the aluminum and arene are in a stalemate due to electron deficiencies in the reaction medium. Add a little water and everyone's happy.

[Edited on 4-12-2020 by Opylation]
View user's profile View All Posts By User
EverythingAl2O3
Harmless
*




Posts: 9
Registered: 3-9-2019
Member Is Offline


[*] posted on 4-12-2020 at 04:42


Interesting that it doesn't tend to yield well. If that is normally the case then this paper found a niche use in benzylic alcohols because they had yields between 50-99%.

Are typical chlorination procedures done in pure alcohol and AlCl3, with the alcohol acting like a solvent and reagent? That might be a significant factor. In the paper it looks like they used dioxane as the major solvent and added the alcohol as a minor constituent. With that the dioxane might be a bad enough base that it doesn't want to pick up the hydrogen so it's stuck with it until the chlorine has time to attack and relieves the acidity.
View user's profile View All Posts By User

  Go To Top