I intend to prepare 2,2-dichlorobutane from MEK and an excess of HCl, with a zinc chloride catalyst. I'm not sure if the second stage of the reaction
is possible.
Here's the scheme:
First, HCl reacts with MEK to form 2-chlorobutan-2-ol.
Normally, with 2-butanol for example, the alcohol's O atom has enough electron density to do a nucleophilic attack on an HCl molecule, protonating
the alcohol, which then leaves as water. Next, the chloride is able to attack the resulting secondary carbocation, in this case forming
2-chlorobutane.
This is where I'm stuck: In 2-chlorobutan-2-ol, the chlorine and the alcohol group share that #2 carbon, where the chlorine pulls electron density
away from the alcohol. I'm not sure whether 2,2-dichlorobutane will be able to form, as I'm not sure that the alcohol will become protonated. I
suspect that the reaction doesn't proceed this way, as I was unable to find the 2,2-dichlorobutane in several organic chemistry PDFs.
Any help is appreciated. DraconicAcid - 29-12-2014 at 21:06
I doubt it. 2-chloro-2-butanol will spontaneously eliminate HCl to give butanone (MEK).UC235 - 29-12-2014 at 21:53
No, this won't work at all. You need far more powerful chlorinating agents than Lucas reagent to make a ketone into a geminal dihalide. You'll only
get acid catalyzed aldol condensations using these reaction conditions.
Instead you need to use a far more oxophilic chlorinating reagent. PCl5 will work, as will the product of chlorinating triphenylphosphine.
There's a chance that you might make treatment with benzotrichloride (or perchloropropylene) and a lewis acid work, but definetly don't quote me on
that. It might still make a mess with an enolizable ketone.
[Edited on 30-12-2014 by UC235]subsecret - 29-12-2014 at 23:21
Thanks for the input. I made the beginner mistake of getting excited about this before I figured out if it would work.
Yes, I am. I got locked out of my normal account due to a password issue and am waiting for Polverone to get back to me about sorting it out. subsecret - 30-12-2014 at 09:16
Sorry CuReUS - 4-1-2015 at 09:50
what would you get if you did free radicle substitution of malonic acid with excess chlorine ?
would you get 2,2-dichloromalonic acid ?
