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Topic: Carboxylic acid + PBr3 gives what product?  (Read 3523 times)

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Offline webassignbuddy

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Carboxylic acid + PBr3 gives what product?
« on: November 19, 2013, 07:08:17 PM »
Take but-1-ene and treat it with HBr in the presence of peroxides followed by addition of sodium cyanide. To this product add aqueous acid and heat it up.

(a) Draw the major organic product that results from the 3-step synthesis above.

CCCCC(=O)O

(CORRECT)

Take the MOP you drew for part a and treat it with phosphorus tribromide. To that product add molecular bromine then follow that up with an aqueous workup.

(b) Draw the major organic product that results from the second 3-step synthesis.

CCCC(Br)C(=O)O

I understand the answer to part A, but HOW is the answer to part B that?
OH is essentially supposed to be replaced by Bromine to give you an acyl bromide, no? Instead, it adds to the alpha carbon.
I'm so confused.. Why is that???

Offline discodermolide

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Re: Carboxylic acid + PBr3 gives what product?
« Reply #1 on: November 19, 2013, 07:10:59 PM »
Hell-Volhard-Zelinsky Reaction - Organic Chemistry Portal
www.organic-chemistry.org › Reactions › Name Reactions
Hell-Volhard-Zelinsky Reaction. Treatment with bromine and a catalytic amount of phosphorus leads to the selective α-bromination of carboxylic acids.

Try reading there
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Offline antimatter101

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Re: Carboxylic acid + PBr3 gives what product?
« Reply #2 on: November 20, 2013, 11:46:43 PM »
The Hell-Volhard-Zelinskii reaction is a derivative of carbonyl-alpha substitution reactions. The only thing different is that an acid enol is formed in the process, rather than a regular enol. Also, the acid halide is formed in the process, but since the alpha-substituted alkyl halide is so electrophilic, it undergoes nucleophilic attack by water to form the original carboxyl group.

Offline webassignbuddy

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Re: Carboxylic acid + PBr3 gives what product?
« Reply #3 on: November 21, 2013, 03:02:49 PM »
Ohh ok.
Thanks  :D

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