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Chemistry Forums for Students => Organic Chemistry Forum => Topic started by: Altered State on April 24, 2013, 07:21:04 AM

Title: Is there any way to obtain benzene from haloalkyl-benezenes?
Post by: Altered State on April 24, 2013, 07:21:04 AM

I have to do an exercise where I have (methylbromo)benzene  (Ar-CH2Br) and I need to get: Ar-C(O)CH2CH2CH3

I suppose that this is not the way of doing it, but I'm curious if I could do it this way:

Ar-CH2Br --- (UNKNOWN REACTANTS AND STEPS) ----> Benzene

And then just use friedl-craft acylation and I got it.


Is this possible? In that case, how should we do it?
Whether if its possible or not, how should be the best way?

Thanks in advance..

Title: Re: Is there any way to obtain benzene from haloalkyl-benezenes?
Post by: discodermolide on April 24, 2013, 07:54:35 AM

I can't think of a way to go from an alkylhalobenzene to benzene.
Why not convert it to the benzyl alcohol, do a Pinnick oxidation to the acid, make the acid chloride then react it with a 3 carbon nucleophile?

Title: Re: Is there any way to obtain benzene from haloalkyl-benezenes?
Post by: Archer on April 24, 2013, 08:57:07 AM

It's a bit of a convoluted route but you could reduce the halide to produce toluene, oxidise the toluene to benzoic acid then decarboxylate to benzene.

Title: Re: Is there any way to obtain benzene from haloalkyl-benezenes?
Post by: orgopete on April 24, 2013, 09:03:09 AM

As I look at this problem, it appears as though PhCHOHCH2CH2CH3 was the precursor to the ketone. This looks like a Grignard addition to an aldehyde.

Title: Re: Is there any way to obtain benzene from haloalkyl-benezenes?
Post by: Altered State on April 24, 2013, 05:01:04 PM

I can obtain the alcohol in a good yield just with Ar-CH2Br in water?
Any special condition required?
I got the rest of the problem, thanks you all, just that final question...

Title: Re: Is there any way to obtain benzene from haloalkyl-benezenes?
Post by: Altered State on April 24, 2013, 05:07:16 PM

Quote from: orgopete on April 24, 2013, 09:03:09 AM

As I look at this problem, it appears as though PhCHOHCH2CH2CH3 was the precursor to the ketone. This looks like a Grignard addition to an aldehyde.

If I get the aldehyde and then I add CH3CH2CH2MgBr, won't it give me the alcohol, but not the ketone?


Edit: oh, fml, then I oxidate it with any strong oxidant like Ag2O,H2O  or  KMnO4 and I get the product aswell.

Anyway, I think (don't really know why, lol) the acid chloride reacting with Gilman reactant, (CH3CH2CH2)2CuLi will give better results...

Title: Re: Is there any way to obtain benzene from haloalkyl-benezenes?
Post by: souro10 on April 28, 2013, 04:22:53 PM

You can use a very strong reducing agent to convert the aryl halide ( alkene level oxidation of side chain ) into toluene (alkane level oxidation  of side chain ). Then you can go to benzene in two different ways

(i) you could oxidize it all the way upto benzoic acid using Permanganate oxidation, and then decarboxylate.
(ii) you could use AlCl3 and heat it to a high temperature to make the reaction come under equilibrium with benzene and methane. Methane can be removed continuously to keep the yield of benzene high.