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Author: Subject: Separation of alkane/bromoalkane
dapper
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[*] posted on 4-2-2009 at 08:31
Separation of alkane/bromoalkane


I wasn't sure what forum was most appropriate but I was wondering what everyone thought would be the best logical starting point for finding/using a method to separate a long-chain (c18-c20) 1-bromoalkane from a mixture of similar non-brominated long chain alkanes. I try never to underestimate the power of the 'message in a bottle'

Thanks a lot
Dapper
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Klute
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[*] posted on 4-2-2009 at 09:48


Could you furnish boiling points? And do you want to keep the bromoalkane as is, or can it be chemically modified?



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chemrox
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[*] posted on 4-2-2009 at 17:34


Could you centrifuge the stuff? What kind of quantities are we talking about? Maybe fractional freezing is a possibility. Without more specific information it's kind of hard to suggest solutions. Why not tell us what the mixture is, how much of it there is and answer Klute's question?
Cheers,
CRX

[Edited on 4-2-2009 by chemrox]




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dapper
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[*] posted on 6-2-2009 at 12:25


I really appreciate everything so far. Basically the problem is I'm making a synthetic surfactant - It's two-armed, C20 as two arms with a 10C linker. The smaller than c20 armed varieties were easier to purify but now there isnt much solvent access? or something. It's a nasty waxy amorphous funky solid.

Gram or a couple gram scale

But really I want to do this on the 100 gram scale, and I'd be totally open to slightly over the top, excellent methods.
Thanks
Dapper

[Edited on 6-2-2009 by dapper]

[Edited on 6-2-2009 by dapper]
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smuv
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[*] posted on 6-2-2009 at 14:55


Use the crude alkane/bromoalkane as is for the next step of the reaction, then separate the amine/quat salt from the alkanes. This seperation is of course much easier.



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dapper
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[*] posted on 6-2-2009 at 15:00


There is no next step, I want to purify this product.
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smuv
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[*] posted on 6-2-2009 at 16:07


Quote:
Basically the problem is I'm making a synthetic surfactant - It's two-armed, C20 as two arms with a 10C linker. The smaller than c20 armed varieties were easier to purify but now there isnt much solvent access?


Quote:
There is no next step, I want to purify this product.


In a case like this where the impurity (an alkane) is unreactive there is no shame in passing the synthesis onto the next step and removing the impurities at that point.




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dapper
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[*] posted on 6-2-2009 at 18:16


I appreciate this advice, however I fear due to the particular use of the purified surfactant - templated self-layering material synthesis impurities might affect aggregation, morphology, etc.
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[*] posted on 6-2-2009 at 19:15


Could you possibly post a molecular picture of your target surfactant buy and chance dapper?
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chemrox
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[*] posted on 6-2-2009 at 19:26


I have to say I'm lost. Did this stuff come from a landfill, bottle, package, is it a product or an accident?



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dapper
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[*] posted on 6-2-2009 at 20:20


This is what I'm digging at:

[Edited on 6-2-2009 by dapper]

Attachment: gemini.pdf (252kB)
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dapper
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[*] posted on 6-2-2009 at 20:21


another PDF

Attachment: Gemini%20Surfactants.pdf (53kB)
This file has been downloaded 954 times

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not_important
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[*] posted on 6-2-2009 at 21:04


Looking at everything you've said, I would say that reduced pressure fractional distillation is your best bet. There's just not enough other differences that don't relate to reacting the halogen.
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[*] posted on 10-2-2009 at 15:22


I dont mind reacting with that halogen. Perhaps there's some way to 'derivitize' it into a filterable solid or something. I'm going to have to start mucking around with it some more the only thing is it's a surfactant so it's a foamy mess.
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[*] posted on 10-2-2009 at 20:29


There seems to be a discrepancy in your statements. First there is this one
Quote:
There is no next step, I want to purify this product.

and now this
Quote:
I dont mind reacting with that halogen. Perhaps there's some way to 'derivitize' it into a filterable solid or something. I'm going to have to start mucking around with it some more the only thing is it's a surfactant so it's a foamy mess.


If you react something with the halogen it is gone. Some substitutions would give products that could be converted back to the halogen, but they may not be very practical.

The size of the molecule and that it is a surfactant is going to make clean separations difficult, even after taking it towards the final product.

Taking the halocarbon a step further on to a ionic compound might allow the separation of the 2 products. Use dilute solutions, an alkane solvent (petroleum ether, ligroin) and water, perhaps run hot. The ionic product goes with the water, the hydrocarbon with the alkane solvent. However the surface active nature can interfere with such a separation.

If the next stage in the synthesis is ionic you might be able to melt-extract the hydrocarbon out, especially with the addition of a small portion of a nonpolar solvent to help get the hydrocarbon into the liquid phase.

But vacuum distillation (low to moderate temperature) of the hydrocarbon from an ionic product still seems like the best way, without further physical data. The ionic nature of the surface active agent will keep its volatility down, milder temperatures are needed to avoid bond breaking around or within the ionic portion.

The amount you want to process is pushing chromatographic methods, otherwise another possibility.

Tuning the process to minimise alkane production would seem to be helpful,.
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