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Author: Subject: prepration of 1,6-dibromohexane
aroma princess
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[*] posted on 25-8-2014 at 20:23
prepration of 1,6-dibromohexane


Dear all...:) I am a newbie here...I am trying to synthesize 1,6-dibromohexane using 1,6-hexanediol and hydrobormic acid (48%). The procedure I am following is,
1) Charge 1 mol 1,6-hexanediol to reactor followed by 8 equivalents of aq. HBr (48%) and heating the mass to reflux for 4 Hr.
2)Cool the mass to RT ,extract with benzene wash benzene layer with aq.NaOH followed by aq.HCl and distill off benzene on Rotavap. The product obtained shows 95% purity on GC (area%) is it 1,6-dibromohexane?
I have plenty of aq HBr lying at my end so im not planning to use any other reagents for that. Can somebody guide me....
please

Thanks for reading
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Nicodem
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25-8-2014 at 21:26
blogfast25
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[*] posted on 26-8-2014 at 04:06


Compare peak position on GC with a certified sample of 1,6-dibromo hexane.

Determine BP, MP and density of your product, compare to lit values.

Take IR spectrum and compare to database spectrum of 1,6-dibromo hexane.




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Paddywhacker
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[*] posted on 26-8-2014 at 04:37


Quote: Originally posted by aroma princess  
Dear all...:) I am a newbie here...I am trying to synthesize 1,6-dibromohexane using 1,6-hexanediol and hydrobormic acid (48%). The procedure I am following is,
1) Charge 1 mol 1,6-hexanediol to reactor followed by 8 equivalents of aq. HBr (48%) and heating the mass to reflux for 4 Hr.
2)Cool the mass to RT ,extract with benzene wash benzene layer with aq.NaOH followed by aq.HCl and distill off benzene on Rotavap. The product obtained shows 95% purity on GC (area%) is it 1,6-dibromohexane?
I have plenty of aq HBr lying at my end so im not planning to use any other reagents for that. Can somebody guide me....
please

Thanks for reading


If that is all of the information that you have then the answer is "not necessarily", as it might be unchanged starting material.
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aroma princess
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[*] posted on 27-8-2014 at 01:20


Dear Blogfast,

I have taken IR and mass spectrum but its kinda confusing...the spectrum matches with 1,5 dibormohexane instead of 1,6 dibromohexane and it seems unlikely that i will end up with 1,5-dibromohexane when i am using 1,6-hexanediol as starting material.
thanks for reading guys..
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kavu
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[*] posted on 27-8-2014 at 01:36


Well the IR and MS are doomed to be very similar. You really need to have a 1H and 13C NMRs done on the sample. 1H NMR is always the first thing you check once you have a crude product. Also it would be highly advisable to run a fractional distillation or a column on the crude product as it's most likely contaminated with at least some monobromination product and/or diol. What literature procedure did you follow?

[Edited on 27-8-2014 by kavu]
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smaerd
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[*] posted on 27-8-2014 at 04:12


1,5-dibromo is definitely possible. All it would take is a sigmatropic rearrangement if one of the substitution reactions went via SN1 rather then SN2. Granted this seems highly unlikely to me, but I've heard of weirder things happening.

I'm sure you know this, but just in case. Make sure the FT-IR spectra you are comparing were run in the same conditions IE: neat, vs nujol mull, whatever solvent. The relevant bands are probably all in the fingerprint region though which can be a scary place to be.

Please post a literature precedence, but yes an 1H-NMR would really make things easy. Or the FT-IR spectra, I might have time to take a look at it tonight.

[Edited on 27-8-2014 by smaerd]




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[*] posted on 27-8-2014 at 10:22


Does the product dissolve in water? (The diol does, so you can rule out the starting material)


Also, since you have GC, are you familiar with this trick?
http://en.wikipedia.org/wiki/Kovats_retention_index
where you can get retention time estimates by comparison with alkanes.
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[*] posted on 27-8-2014 at 12:36


If the products and byproducts and reagents are similar, i suppose all the IR and MS are going to be similar.

I suppose that's why so many routes to a product are worked out, just to be able tell if the product was what was expected.




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