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Chemistry Forums for Students => Organic Chemistry Forum => Topic started by: madisonwi on December 22, 2004, 01:43:20 PM

Title: 1-bromopropane to 1,1-dibromopropane or 1,2-dibromopropane
Post by: madisonwi on December 22, 2004, 01:43:20 PM

Hello,

In a reaction series, I've deduced every step except for the first.  I'm starting with 1-bromopropane and the intermediate product that I want (before I run another series) is propyne.  What I decided to do was do a double dehydrohaligonation using exess LDA on 1,1-dibromopropane.  It later occurred to me that I could also start with 1,2-dibromopropane.  The problem I keep running into is how to produce either of the dihaloalkanes while avoiding as much as possible a 1,3-dibromopropane product.  I'm guessing that if I used either Br2/hv or HBr, both would select dominately for the unsubstituted/unsaturated terminal 3-carbon.  

Am I going at this wrong, or is there clear way to produce my desired product?

Thanks!

Title: Re:1-bromopropane to 1,1-dibromopropane or 1,2-dibromopropane
Post by: dexangeles on December 22, 2004, 11:54:29 PM

I'm not sure what you're trying to make, can you specify it better?
why do you want propyne?  whats wrong with propene?

if you do an addition of Br2/chloroform on an alkene, you won't get a 1,3-dibromo, just a 1,2-dibromo

can you just explain first what your starting reactant is and what your desired final product is?

Title: Re:1-bromopropane to 1,1-dibromopropane or 1,2-dibromopropane
Post by: AWK on December 23, 2004, 01:18:52 AM

1. Bromination of propane  produces 2-bromopropane (and traces of 1-bromopropane)
2. Dehydrobromination of this mixture produces 1-propene (from both)
3, Bromination of propene produces 1,2 dibromopropane
4. Dehydrobromination  of 1,2-dibromopropane produces propyne

Title: Re:1-bromopropane to 1,1-dibromopropane or 1,2-dibromopropane
Post by: maxyoung on December 29, 2004, 06:27:14 AM

bromination is very selective, so 2-bromopropane should be the major product