[darkdevil]

Hi.. I wonder which method should I use to alkylate polystyrene... I tried using the friedel craft alkylation  to add a carbon tail to PS. but it all failed... I tried to use THF and Chloroform as solvents.. but none of them work. Im so frustrated about this

I even tried to perform a blanc chloroalkylation of PS using polystyrene, heptanal, HCL and Zinc chloride as catalyst , using THF as solvent at 60 deg celcius for 3-hrs.. but  proton NMR results showed NOTHING happened. PS is still PS

Anyone can help with this.. I have been struggling with this simple PS alkylation for almost ,three months already... any help will be greatly appreciated.. Thanks!!

[discodermolide]

You asked this on Dec the 19th, here is the link
http://www.chemicalforums.com/index.php?topic=64485.msg232093#msg232093

[darkdevil]

im sorry.. but im not sure  why friedel craft alkylation is not suitable for polystyrene, and am looking for other advices or ways to do the alkylation of PS

[discodermolide]

Chloroform and THF are bad solvents for FC reactions.
Use a chlorobenzene and aluminium trichloride and heat it to the BPt.
By the way what is the heptonal doing? This is an aldehyde.

[darkdevil]

heptanal is for the chloroalkylation of PS . Its not friedel Craft.

I wonder what other choices of solvent is appropriate?  Thank you.

[discodermolide]

heptanal is for the chloroalkylation of PS . Its not friedel Craft.

I wonder what other choices of solvent is appropriate?  Thank you.

I do not follow the logic of using heptanal for the chloroalkylation. And you say it's not an FC???
So what is this thread all about. Either it is about FC or not but it can't be both. Perhaps is you knew what you were doing and could communicate this to us it would be rather helpful in order to assist you.
As for solvents I already suggested one, others are for example decalin, carbon disulphide, sulfolane……...

[darkdevil]

Thank you so much

I just want to add a long carbon tail to PS, no matter its FC , chloroalkylation or  any method. I tried the Blanc Quellet Chloroalkylation  method using THF assolvent, but there was no positive outcome...

Now I think the problem is regarded to the solvent  I chose(i guess). Do you think if acetonitrile will work for FC reaction of PS???  because we have too many of them in our lab welalso need  to consume them haha..

[discodermolide]

No acetonitrile will not work. Try some of the solvents I suggested. Or look in the literature.

[darkdevil]

Thank you very much!! I will update  the post if  once the problem is solved! hope it wont get long to have it solved.

[darkdevil]

I tried to perform the following conditions today:

Reactants     Mole ratios

Polystyrene                       1
Bromodecane                    1.2
FeCl3                              0.1
Nitrobenzene as solvent

At first when the temperature reached 100 deg celcius, the mixture turned into orange red. After 3 hours of reaction at around 200 deg (refluxing), it gave me a very dark viscous material. I cannot separate any solid from this black liquid. I first tried to precipitate the modified-PS by dropping it into methanol. The black visvous material become more viscous when dropped into methanol. It is more like a gel or gummy substance.  I still cannot obtain NMR for this dark oily gel. I doesnt dissolve well in chloroform.. which I expect it should

I tried to do a separation with water, it formed two layers, water on top and the black gel at the bottom.but the water layer is just so clear, and seemed nothing had transferred to the aqueous layer. THe dark oily gel is still at the bottom layer.

Is this really my product ?? or am I doing wrong in some work-up procedures?
I am not sure if I used too less solvent? or too much catalyst??

Thank you!

[discodermolide]

Several things.
I think you may have heated it to hard. Start off at 100°C then monitor it by TLC. If nothing is happening raise the temp by 10-20°C.
Bromodecane will be quite un-reactive here, use decanoyl chloride or bromide which you get from decanoic acid, then reduce the carbonyl. Acylation is more facile than alkylation.
Polystyrene is very often used as a solid support for FC reactions, this indicates to me that it is very unreactive. Perhaps you should FC styrene then polymerise.
Use a more active catalyst, scandium triflate is often employed.
Why don't you do a) a literature search and or b) google FC alkylation of styrene.

[darkdevil]

oo... thank you so much

I will try again with a lower temperature. Do you think I added too much catalyst??

I also wonder how do I separate/work-up an Acyl Bromide if I start with an alkanoic acid and PBr3?

[discodermolide]

Better to use thionyl chloride, then distill the acid chloride.
The amount of catalyst is ok, you can always add more. But go for a more active one as I said.

[Captain Sci]

Greetings

You may have seen this already (my apologies if it is old news) but have you consulted the Functionalisation of Polystyrene article on J. Org. Chem., Vol. 43, 1978 (page 3151)? The direct link to this paper is http://pubs.acs.org/doi/abs/10.1021/jo00410a012

Please let me know whether this has been helpful in your research. 

Best wishes

[darkdevil]

Greetings

You may have seen this already (my apologies if it is old news) but have you consulted the Functionalisation of Polystyrene article on J. Org. Chem., Vol. 43, 1978 (page 3151)? The direct link to this paper is http://pubs.acs.org/doi/abs/10.1021/jo00410a012

Please let me know whether this has been helpful in your research. 

Best wishes

Dear,
Thank you ! I have read this before. The author used PS:catalyst ~ 1:1 or even higher. But the greater amout of catalyst I used, the darker is the sticky gel (mentioned in the last reply) I obtained.
 I used THF and chloroform as solvent for the last ~30 trials (with no alkylation seen in H-NMR)... And the previous conditions I mentioned is my first trial for FC rxn using nitrobenzene as solvent. Perhaps I will lower the temperature a bit.

If it fails again, I think I will use the FC acylation as discodermolide suggested...
THanks!