How can we easily obtain 2-bromoacetophenone from bromobenzene?

[Raghav Gupta]

By which reagent we would get 2-bromoacetophenone in one step from bromobenzene?

 

[AdityaDev]

You can do this:
1)iodine in NaOH (iodoform reaction) to get ph-COOH
2)Schmidt reaction using N3H to get ph-NH2
3)Diazotization
4)H3PO2

 

[Suraj M]

Will this work?#Aditya
By Dow's process.. get phenol, then reduce to benzene using Zn.
then by acylation.. you'll get acetophenone, then by bromination, α hydrogen of the substituent group gets replaced by Br?
#Raghav.. i still kept my word.. it was already out of the unanswered section.

 

[AdityaDev]

I'm sorry, I gave the answer for bromobenzene from 2-bromoacetophenone.
For the conversion, the answer is CH3Cl in anhydrous AlCl3 (acylation)

 

[Raghav Gupta]

I'm sorry, I gave the answer for bromobenzene from 2-bromoacetophenone.
For the conversion, the answer is CH3Cl in anhydrous AlCl3 (acylation)

But that will give 2-bromo toluene or 4-bromotoluene.
I'm asking 2-bromoacetophenone from bromobenzene.
See structure of 2-bromoacetophenone.

 

[TeethWhitener]

You can get 2'-bromoacetophenone (with the acetyl unit in the ortho position on the benzene ring) by a Friedel-Crafts acylation of bromobenzene with acetyl chloride. To get the compound you linked to (benzene with a 2-bromoacetyl group) directly from bromobenzene, I think you're going to need more than one step. Maybe a Pd-catalyzed coupling of some kind, but you'll get competition with the Br on the acetyl group.

 

[AdityaDev]

But that will give 2-bromo toluene or 4-bromotoluene.
I'm asking 2-bromoacetophenone from bromobenzene.
See structure of 2-bromoacetophenone.

No. I am talking about acylation. It will give the required product. Check NCERT book.

 

[Raghav Gupta]

No. I am talking about acylation. It will give the required product. Check NCERT book.

As TeethWhitener said it will give acetyl group in the para position of bromobenzene.
And I'm not wanting that. See again the structure in the link given above in post.
For reference: It was a recent cbse board exam question.

 

[Suraj M]

See again the structure in the link given above in post.

Raghav, my teacher said, that the link thing is wrong, 2-bromoacetophenone is bromine attached at ortho position on the benzene ring. the compound in the link is
1-phenyl-2-bromoethanone because acetophenone is nothing but 1-phenylethanone.

 

[Raghav Gupta]

Raghav, my teacher said, that the link thing is wrong, 2-bromoacetophenone is bromine attached at ortho position on the benzene ring. the compound in the link is
1-phenyl-2-bromoethanone because acetophenone is nothing but 1-phenylethanone.

Ya, I think you are right. Don't know why the wikipedia a famous site was showing that.
Now acylation will give para thing. How ortho?

 

[TeethWhitener]

Bromine is ortho-para directing, so Friedel-Crafts will give you a mixture of ortho and para isomers. Bonus question: how would you get meta-bromoacetophenone (starting from benzene)?

 

[AdityaDev]

Bromine is ortho-para directing, so Friedel-Crafts will give you a mixture of ortho and para isomers. Bonus question: how would you get meta-bromoacetophenone (starting from benzene)?

Easy.
First friedel crafts acylation to get acetophenone.
Then bromination in presence of FeBr3 to get meta brominated product.
this conversion is even better: benzene to benzene-(1,3)-dicarboxylic acid. Try it.

 

[TeethWhitener]

this conversion is even better: benzene to benzene-(1,3)-dicarboxylic acid. Try it.

We'll probably get the thread locked for being off-topic, but it's fun regardless. Friedel-Crafts alkylation of benzene with a methyl halide to get toluene, then oxidize with permanganate to benzoic acid (now it's meta-directing), then repeat the process to get the 1,3-dicarboxyl compound.

 

[Raghav Gupta]

Bromine is ortho-para directing, so Friedel-Crafts will give you a mixture of ortho and para isomers.

But para one would be in majority because of steric hindrance by ortho group.
So now what?

 

[TeethWhitener]

I don't know if there's really a good way to get ortho-bromoacetophenone in one step from bromobenzene with high regioselectivity. Typically, regioselective ortho-directed reactions require some sort of directing group. Look up "ortho-directed metalation" for more info. The general idea is that you have a benzene ring with a directing group (usually an acyl or amide group) which allows substitution of the ortho hydrogen with lithium. That ortho-lithiated product can be subsequently functionalized.

 

[AdityaDev]

We'll probably get the thread locked for being off-topic, but it's fun regardless. Friedel-Crafts alkylation of benzene with a methyl halide to get toluene, then oxidize with permanganate to benzoic acid (now it's meta-directing), then repeat the process to get the 1,3-dicarboxyl compound.

Correct. It is interesting indeed.

 

[Raghav Gupta]

Anyways, I think acylation would be fine enough for 1 step, no matter what the amount of ortho product would be.
Thanks to you all.