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Author Topic: Friedel Craft Alkylation of Polystyrene  (Read 1191 times)

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darkdevil

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Friedel Craft Alkylation of Polystyrene
« on: December 19, 2012, 04:08:36 AM »

Hi,
I have a question on the alkylation of polystyrene. I carried out a reaction using the the friedel crafts condition to alkylate polystyrene. But unluckily the reaction do not proceed. (same NMR spectrum as the starting material). Here are the reactants and conditions I tried:

Polystyrene
Bromodecane
Catalyst: FeCl3
Solvent: THF (anhydrous)

I tried polystyrene to bromodecane ratio = 1:1 and 1:2, while using 10% catalyst at 85 degrees and 120degrees celsius. But still no luck to see any alkylation in NMR. I am not sure if I should add more catalyst. If so, How do I remove them during the work-up procedure??
Any help or suggestions will be greatly appreciated! Thank you! :)
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discodermolide

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Re: Friedel Craft Alkylation of Polystyrene
« Reply #1 on: December 19, 2012, 06:09:56 AM »

Are you talking about an internal temperature or an external temperature?
I'm wondering how you can get THF to heat above it's BPt.
Also THF is rather reactive, would it not be better to use a chlorobenzene as a solvent? I could imagine THF opening up under these conditions and polymerising.
Have you tried with no solvent?
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opsomath

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Re: Friedel Craft Alkylation of Polystyrene
« Reply #2 on: December 20, 2012, 05:21:03 AM »

Yeah, THF is a very poor choice. I would try chloroform or carbon tet with AlCl3 or FeCl3. And do you mean to say that you are trying to use 1-bromodecane as the alkylating agent? That won't work. If you want to put on the long chain like that, you'll have to start with decanoyl chloride and then reduce the product afterward.

You can also halogenate polystyrene and then perform a Kumada coupling.
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darkdevil

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Re: Friedel Craft Alkylation of Polystyrene
« Reply #3 on: December 20, 2012, 10:13:10 PM »

Thank you so much!!

I havnt tried to perform reaction without solvent. I think polystyrene would not dissovle completely in my alkylating agent. The temperature is external..

mmm.. it seems the Kumada coupling method is also a good way to do so.. I also realized the 1-bromalkane would rearrange to give a secondary more stable carbocation. and the final product would be a sec-alkylated Polystyene.

BTW.. Why is THF a bad choice?
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discodermolide

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Re: Friedel Craft Alkylation of Polystyrene
« Reply #4 on: December 21, 2012, 01:41:51 AM »

I said why in my post. THF is quite a reactive solvent, and under Friedel-Craft conditions I would expect it to ring open and polymerise. This can be dangerous depending upon the amount of solvent you are using.
For example THF and tri-isobutylaluminium will give a very exothermic reaction and can lead to a runaway reaction.
Why is it called a runaway? Because you run away from the decomposing mess before it gets you.
Mind you I am talking about reactions with >50kgs THF. But it can also happen on a small scale as well.
« Last Edit: December 21, 2012, 02:16:48 AM by discodermolide »
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darkdevil

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Re: Friedel Craft Alkylation of Polystyrene
« Reply #5 on: December 21, 2012, 05:26:09 AM »

Yeah, THF is a very poor choice. I would try chloroform or carbon tet with AlCl3 or FeCl3. And do you mean to say that you are trying to use 1-bromodecane as the alkylating agent? That won't work. If you want to put on the long chain like that, you'll have to start with decanoyl chloride and then reduce the product afterward.

You can also halogenate polystyrene and then perform a Kumada coupling.

Why it wont work for the bromodecane??  is it because of the bulkyness??
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discodermolide

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Re: Friedel Craft Alkylation of Polystyrene
« Reply #6 on: December 21, 2012, 06:00:48 AM »

Bromodecane is probably not reactive enough. As opspmath said going via the acid chloride is better and you can use milder conditions as it is much more reactive.
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darkdevil

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Re: Friedel Craft Alkylation of Polystyrene
« Reply #7 on: December 21, 2012, 06:43:12 AM »

Bromodecane is probably not reactive enough. As opspmath said going via the acid chloride is better and you can use milder conditions as it is much more reactive.

Thsbk you so much.. since we dont have the decyl acid chloride,  I think we will try the polystyrene halogenation method,  followed by the Kumada coupling.. I"ll let you know if it works by next week after the chrismas holiday :P Thanks again!
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Wastrel

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Re: Friedel Craft Alkylation of Polystyrene
« Reply #8 on: December 21, 2012, 11:17:46 PM »

Also you would expect a mixture of products as the cation rearranges (with the 2 position being more stable than the 1).  You may also find that the polystyrene disproportionates slightly under successful FC conditions into crosslinked products and some benzene.
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darkdevil

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Re: Friedel Craft Alkylation of Polystyrene
« Reply #9 on: December 22, 2012, 02:48:57 AM »

Yeah, THF is a very poor choice. I would try chloroform or carbon tet with AlCl3 or FeCl3. And do you mean to say that you are trying to use 1-bromodecane as the alkylating agent? That won't work. If you want to put on the long chain like that, you'll have to start with decanoyl chloride and then reduce the product afterward.

You can also halogenate polystyrene and then perform a Kumada coupling.

I wonder if it is necessary to use the metal catalyst (Pd / Ni) in Kumada coupling.. Is the Kumada coupling just the ordinary Grignard Reaction without the catalyst if stereochemistry is not a concern in my reaction?? Is it possible to perform a Grignard coupling between my halogenated polystyrene and a bromoalkyl grignard reagent?
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opsomath

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Re: Friedel Craft Alkylation of Polystyrene
« Reply #10 on: February 07, 2013, 10:17:51 AM »

Quote
I wonder if it is necessary to use the metal catalyst (Pd / Ni) in Kumada coupling

The short version is, yes. There are many modifications of metal-mediated Grignard coupling, though, mostly with different metal catalysts. It's easy and cheap to get Ni(dppp) or something of that sort, though, so I'd go with that. Also, iodination of the polystyrene is probably the way to go, the iodinated stuff reacts well in the coupling. I have a paper around here someplace with conditions for that, if you want to see it.
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darkdevil

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Re: Friedel Craft Alkylation of Polystyrene
« Reply #11 on: February 12, 2013, 02:49:13 AM »

Quote
I wonder if it is necessary to use the metal catalyst (Pd / Ni) in Kumada coupling

The short version is, yes. There are many modifications of metal-mediated Grignard coupling, though, mostly with different metal catalysts. It's easy and cheap to get Ni(dppp) or something of that sort, though, so I'd go with that. Also, iodination of the polystyrene is probably the way to go, the iodinated stuff reacts well in the coupling. I have a paper around here someplace with conditions for that, if you want to see it.

Thank you so much
Sure I want to know more about that!
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