RareEarth
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Alkylation of PVC by Iodide salt catalysis?
Could it be plausible to dissolve PVC (the polymer), and then use an iodide salt to cause an in-situ finkelstein reaction that would allow the alkyl
groups to become reactive?
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Dr.Bob
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I don't think that will work well, dichlorides are much harder to react that mono-chlorides, plus reactions on most polymers are tough due to limited
solubility and access to the entire chain.
You can buy peptide synthesis resins with a benzyl halide type group already installed in a Polystyrene resin or other various polymers, for very
cheap prices, they can be made, but most techniques are not easy at home. The best ones are macroporous polymers with benzyl halides, acids, or
amines.
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RareEarth
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I could easily get the PVC to dissolve, and I could throw in an iodide-based quaternary salt to overcome salt solubility issues.
Wouldn't the dichlorides being harder to react be somewhat irrelevent since the alkyl iodide would form (even if momentarily) due to the finkelstein
reaction? The goal would not be to isolate the formed PVI, but to have whatever it is I am alkylating it with in the reaction with it.
I have used the polystyrene chloromethyl resins before. There's a number of downsides to them, not to mention low catalyst loading per gram. While I
can buy them, I am really looking for a way to make something from cheaply availible materials.
[Edited on 28-10-2015 by RareEarth]
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Dr.Bob
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Dichloromethyl groups are much more sterically hindered than a monochloromethyl group is. Thus an SN2 type reaction will be very difficult, as the
carbon atom will be very hindered to approach. And if you have a whole chain of -C(Cl)2- groups, every carbon is very hindered.
Thus DCM is not a good methylating agent while methyl chloride is a decent one. The bromide and iodide are even better, as while they are larger,
they also are better leaving groups.
The problem is that the higher loading the resin, the more sterically hindered it is, thus if you make a highly substituted polymer like PVC, the
reactivity goes down with each extra substitution, until it approaches zero reactivity. I learned very quickly that in peptide synthesis the higher
the resin loading, the lower the yield of larger peptides. Once you try to put too many atoms in one space, it fills up and you can't fit any more in
it.
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Nicodem
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Thread Moved
29-10-2015 at 01:19 |
Nicodem
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Even if you could somehow force the Cl/I substitution (which obviously cannot be done using quat iodide salts as the chloride ion is a stronger
nucleophile in the solvents that dissolve PVC), there are only few types of reactive enough and not too basic nucleophiles that would be able to
substitute such a nonreactive polymeric secondary alkyl iodide. One of these might be the mercaptides, but it is probably not trivial to cause a
complete substitution, as polymers fold and some regions become hardly accessible. You need a much more reactive group, like the benzyl chloride in
poly(chloromethylstyrene) for such things to work.
Please open threads using vague questions without proper references only in the Beginnings forum section. See forum guidelines for more information.
PVC is poly(vinylchloride), therefore [-CH2-CHCl-]n, so there are no geminal dichloro substitutions.
…there is a human touch of the cultist “believer” in every theorist that he must struggle against as being
unworthy of the scientist. Some of the greatest men of science have publicly repudiated a theory which earlier they hotly defended. In this lies their
scientific temper, not in the scientific defense of the theory. - Weston La Barre (Ghost Dance, 1972)
Read the The ScienceMadness Guidelines!
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AJKOER
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Don't forget the power of sunlight and air (now I am starting to sound like a mad scientist)!
Recently read on how the action of uv light (or, irradiation) on iodide can form solvated electrons (see, for example,
" Photoinduced Electron Transfer and Solvation in Iodide-doped Acetonitrile Clusters" , by Oli T. Ehrler, et.al., at https://www.google.com/url?sa=t&source=web&rct=j&... . The latter can directly effect reactions (see, for example, https://www.google.com/url?sa=t&source=web&rct=j&... ) or react via CO2 (found in air) to form the carbon dioxide radical anion, to
quote a source:
".CO2− radical is produced by the reaction of e(aq)− with CO2 or by the reaction of .OH and .H with formate ion or formic acid.
e(aq)− + CO2 → .CO2− "
Source link: https://www.google.com/url?url=http://scholar.google.com/sch...
The CO2 radical anion has, apparently, been used on a long list of organic compounds (see, for example, "Rate Constants for Reactions of Inorganic
Radicals in Aqueous ...", and the associated list of rate constants for this anion starting on page 1065 at https://www.google.com/url?sa=t&source=web&rct=j&... ) to break them down, so my answer is a possible yes.
I would, however, not characterize the role of the iodide as a catalyst here, as it is not likely completely regenerated in my irradiation approach,
and no guarantee of the actual products created coinciding with your goals.
[Edited on 29-10-2015 by AJKOER]
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RareEarth
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Here are some links of relevence. The fineklstein reaction to form the polyvinyl iodide does indeed work:
http://link.springer.com/article/10.1007%2Fs10965-005-9034-6...
Here's an interesting link showing that direct substitution of the chloride ions in PVC is indeed possible with EDA (strongly basic) (page 5 top)
http://www.scientificbulletin.upb.ro/rev_docs_arhiva/full134...
Dr.Bob, as you say, the reactivity of the chloro groups is close to null, nobody is contesting that. The goal of what I was proposing
was to form an in-situ alkyl iodide by using an iodide salt, by virture of the equilibrium finkelstein reaction. There is no question on whether or
not the alkyl iodide will form.
Nicodem, you may be right about the reactivity of the secondary alkyl iodide.
However, it happens that the specific amine that I planned to use for the reaction was EDA(Ethylenediamine), which also happens to be the one they
used in the (2nd) link above. It appears that I may not even need the iodide to begin with. They show that EDA can react directly with the chloro
groups. EDA is a very strong base in general, so much so that it reacts with moisture in the air.
As you both stated, benzylic chloride resins are readily availible. I actually have a bunch of it, I was just interested to see what all I can do with
PVC.
[Edited on 29-10-2015 by RareEarth]
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