Chemical Forums
Chemistry Forums for Students => Organic Chemistry Forum => Organic Chemistry Forum for Graduate Students and Professionals => Topic started by: Ingeniosuccinimide on July 08, 2014, 07:57:15 AM
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Hello,
could anyone suggest a simple procedure for preparation of 1,6-dibromohexane from either:
1,6-hexanediol (would prefer this one because we have really a lot of it) or
1-bromohexane?
I'm trying to avoid using anything with HBr or Br2. What about NBS or CBr4/PPh3? Or some other procedure with relatively easy purification and high yields?
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Use PBr3 , but HBr would be the easiest choice.
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What about NBS or CBr4/PPh3? Or some other procedure with relatively easy purification and high yields?
Appel reaction should work, but it's a complete waste of money - 1,6-dibromohexane is cheaper than PPh3 (and much cheaper than PBr3).
Unless you use HBr you'll end up spending more on reagents than the commercial value of the product. Even using HBr you are probably wasting resources once you factor in the cost of solvents, purification and time).
Why not buy it?
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I see, but due to some circumstances (e.g. I'm a master student hence I have no permission to buy chemicals, and neighboring lab does not have dibromohexane). We weren't eager to buy bulk quantity of dibromohexane, regardless of the fact it's inexpensive, but rather prepare 2-3 mL, we don't need more. And we need it today or tomorrow.
The funny thing is that we have quite a lot of PPh3 and CBr4 in our lab.
Does typical Appel involve complicated purification? As far as I understood conditions are quite mild, only question is about typical purifying procedure.
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1,6-dichlorohexane could be converted by means of the Finkelstein reaction.
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Does typical Appel involve complicated purification? As far as I understood conditions are quite mild, only question is about typical purifying procedure.
Depends on your definition of complicated - it'll be an aq/org extraction followed by column I expect.
There are some refs at the bottom of this page:
http://www.organic-chemistry.org/namedreactions/appel-reaction.shtm
Have a look at some papers and see if it looks attractive to you. You can do a more extensive search on the usual databases for more examples.
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1) Note that Appel reaction requires water-free system
2) It is very unlikely to make 1,6-dibromohexane from 1-bromohexane
3) For 1,6-hexanediol, in addition to HBr, you may also try H2SO4/NaBr. This is indeed high school chemistry..
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OK, the Appel was quite successful, thanks for advices.
I have one more question: the purpose of 1,6-dibromohexane is to make thiepane from it, according to the work from:
Mandolini, Vontor, Synthetic Communications, 9 (9), 857-861 (1979). (I didn't find any better procedure to prepare thiepane.)
In that work, the autors state that there were "three tested solvents, namely dimethylformamide, dimethylsulfoxide, and hexamethylphosphoramide, of which the last was by far the most effective". Since we don't have the latter in the lab, I'm considering switching it With something else but I really don't know which other polar aprotic solvent to use, especially after they wrote that DMF and DMSO were not effective.
Can you suggest some better way to get thiepane on 1-5 gram scale? Preferably from acyclic precursors, since we don't have any thiepane derivatives in the lab. (buying is excluded unfortunately)
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The arsenal of highly polar aprotic organics is usually centered around DMF and DMSO. Maybe carbon disulfide (stinks like hell) acetonitrile (easy to work with, not as polar). N-Methyl-2-pyrrolidone (NMP) is an option, as is Dimethylacetamide. After that, things quickly stop being considered "solvents" and start becoming "reagent." If dibromohexane was out of your budget, and you don't already have one of those, then you might be stuck using DMF/DMSO.
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Oh you think CS2 stinks like "hell"???
Indeed, CS2 is a few organic compounds with sulphur atom that has a sweet smelling.