Neutralize HCl to stop self-polymeration

[Caffeinated Chemist]

I am trying to make a compound. The problem is that I can't keep it from self-polymerizing because a byproduct of the synthesis is concentrated HCl (see below).

 

 

I ran this rxn yesterday by adding SiCl₄ dropwise to the diol under N₂at 0^oC and it still polymerized. Does anyone have a good suggestion for a solvent or a neutralizing agent to put in the RB to preserve my desired product? Note: It cannot be aqueous because the SiCl₄ reacts VERY violently with water. Thanks for your help!

[Iota]

I don't think I can give an answer of any real value with my level of chemistry knowledge, but this is more for my own interest: how about adding sodium bicarbonate? Use up the strong acid and replace it with a weak acid, carbonic acid. It's in powdered form, so there's no problem concerning water. Assuming the carbonic acid created is too weak to react with your desired product, and creates no by-products which will become a hindrance with what your doing.

Nope my mistake, I missed a huge problem with that, it makes water. I was thinking of it as a buffer reaction for some reason.

[John Cuthber]

Tertiary amines are traditional, but I'm not sure they will help here.

 

High dilution techniques might.

[Caffeinated Chemist]

Tertiary amines are traditional, but I'm not sure they will help here.

 

High dilution techniques might.

 

 

I've been looking around online and I found some very similar advice here:

http://www.thieme-chemistry.com/fileadmin/Thieme/HW-100/pdf/november/v04-0371-dao.pdf

In section 4.4.17.1.1 they say that imidazole or triethylamine may be able to neutralize HCl formed during the reaction of an alcohol and chlorosilane, though in their example only one mole equivalent is formed as opposed to my reactions four moles.

 

Maybe I will do a hybrid of this and try adding the SiCl₄ to a much larger volume of imidazole then add that dropwise to the diol and see if the imidazole can't sop up the HCl before it ruins my compound. Thanks for the advice! I'll let you know how it goes!

Edited May 21, 2013 by Caffeinated Chemist

[Knumbnuts]

Try using a basic ion-exchange resin or better perhaps proton sponge.

http://en.wikipedia.org/wiki/1,8-Bis(dimethylamino)naphthalene

[Enthalpy]

Please forgive my ignorance...

 

I had expected most poly-chloro-something and poly-ol to make a polycondensate easily, just like a diacid makes a polycondensate easily with a diamine or a diol. Why is the produced HCl important to sustain the reaction?

 

Even if SiCl₄ is added dropwise, it is concentrated in or near the drops. To get it consumed by fresh diol rather than by the oligocondensate, I'd have thought to dilute SiCl₄ before dropping it in the concentrated diol, so the diol overwhelms the tetrachloro right from the beginning and eats it up before the concentration of product can increase.

 

Could you react them in gas phase? Butane-diol has some vapour pressure while the product has intuitively a very low one so the product will rain away from the reaction phase, avoiding the polycondensation. In fact, it should rain away at the di- or tri-thing step, but if this step rains into liquid diol you've won. N2, Ar... can dilute SiCl₄ and are easily separated from the excess diol for being much more volatile.

 

The diol can even stay liquid, as a mist. Or contact or bubble the diluted tetrachloro at the upper part of liquid diol, as your denser product will sink below the diol, thus escaping the tetrachloro. The density ratio between the liquid and the gas is to provide the overwhelming abundance of diol.

 

Did I miss something, like the diol being much more reactive than the resulting mono-ol?

And: why does the diol react only at its primary alcohol, instead of giving many isomers?