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Offline jayashae

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benzene synthesis problem
« on: June 21, 2012, 11:50:15 AM »
Given 3 molescules: 1-chloropropane, 1-butyne, and a benzene ring, how do I synthesize 1-butyl-3-propylbenzene?

I'm not sure how to change the 1-chloropropane or 1-butyne to something that will not result in branched products.  These 2 must be used to start.

Offline Dan

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Re: benzene synthesis problem
« Reply #1 on: June 21, 2012, 01:11:06 PM »
These 2 must be used to start.

Can you clarify this statement? Do you mean you must propose a synthesis like this:

ClPr + HC≡CEt  :rarrow: A
A + PhH  :rarrow:  1-butyl-3-propylbenzene

If so, it is either a ridiculous question or you don't mean 1-butyl-3-propylbenzene.

Start by drawing the product and look at the structure. For each carbon atom, or group of carbon atoms, think about which starting material each atom/group came from.

Your product has 13 carbons, and your starting materials have 3, 4 and 6.
Forget about reagents for the moment, think about how you need to clip your starting materials together to make the product. What bonds need to be formed?
Now think about how those bonds could be formed.
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Offline jayashae

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Re: benzene synthesis problem
« Reply #2 on: June 21, 2012, 04:45:23 PM »

Offline Dan

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Re: benzene synthesis problem
« Reply #3 on: June 21, 2012, 07:30:03 PM »
Ok, so "these two must be used to start" was not actually in the question. Good, so:

Start by drawing the product and look at the structure. For each carbon atom, or group of carbon atoms, think about which starting material each atom/group came from.

Your product has 13 carbons, and your starting materials have 3, 4 and 6.
Forget about reagents for the moment, think about how you need to clip your starting materials together to make the product. What bonds need to be formed?
Now think about how those bonds could be formed.
My research: Google Scholar and Researchgate

Offline jayashae

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Re: benzene synthesis problem
« Reply #4 on: June 22, 2012, 11:38:19 AM »
the only way I can think of placing the chloropropane on there is by acylating o.o, but not sure how to do that given the chloropropane already.

Offline Dan

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Re: benzene synthesis problem
« Reply #5 on: June 22, 2012, 12:20:34 PM »
For the third time:

Forget about reagents for the moment, think about how you need to clip your starting materials together to make the product. What bonds need to be formed?
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Offline jayashae

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Re: benzene synthesis problem
« Reply #6 on: June 22, 2012, 01:06:19 PM »
not sure what you mean by what bonds need to be formed.  As for how I should structure it, there needs to be meta-directors.  I don't think I'm understanding your question, can you rephrase?

Offline jayashae

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Re: benzene synthesis problem
« Reply #7 on: June 24, 2012, 01:23:10 AM »
sorry, I really need help on this :/

Offline Dan

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Re: benzene synthesis problem
« Reply #8 on: June 24, 2012, 07:11:10 AM »
Identify the new C-C bonds that need to be formed. Then think about which C-C bond forming reactions you could use.
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Offline orgopete

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Re: benzene synthesis problem
« Reply #9 on: June 24, 2012, 10:15:04 AM »
To the poster, this is what I think. Since the pieces required are given and they match the number of carbons in the product, you must do one or more functional group transformations in order to find chemical reactions that are compatible with the chemistry and regiochemistry of the product.

For example, 1-chloropropane can do a Friedel-Crafts alkylation of benzene, but it would give a lot of rearranged product. If the chloride were converted to an alcohol to a carboxylic acid to a acid chloride, it could be used in a F.-C. acylation. This would avoid rearrangement. Then further transformations would be required to convert a C=O to a CH2.

The question is, what functional group transformations are required to convert, either a CH of the benzene ring to couple with an acetylene or what functional group transformations would be required to allow coupling with the benzene ring? 
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Offline jayashae

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Re: benzene synthesis problem
« Reply #10 on: June 24, 2012, 01:17:15 PM »
hmm, if I convert the acetylene to an alkane using metal-catalyzed hydrogenation and then applying the same concept to the deduced alkane with chlorination and follow same steps?

Offline discodermolide

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Re: benzene synthesis problem
« Reply #11 on: June 24, 2012, 01:28:34 PM »
hmm, if I convert the acetylene to an alkane using metal-catalyzed hydrogenation and then applying the same concept to the deduced alkane with chlorination and follow same steps?

It may be better to use the acetylene in a more useful way. Once it is reduced to an alkane it is effectively useless for further manipulation.
You may like to look up the Sonogashira coupling, although this may be a bit above your Org chem level at the moment.
http://en.wikipedia.org/wiki/Sonogashira_coupling.
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Offline jayashae

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Re: benzene synthesis problem
« Reply #12 on: June 24, 2012, 03:00:28 PM »
hmm, this is a sample problem I'm studying for an exam for tomorrow.  I didn't learn that coupling and so I don't think it wouldn't be expected of us to know for solving this problem.  So I guess it wouldn't be feasible to chloronate the alkane because the alkane would yield more secondary substituted.  hmm, not sure where to go

Offline orgopete

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Re: benzene synthesis problem
« Reply #13 on: June 24, 2012, 09:55:18 PM »
How would you synthesize propylbenzene from benzene and propanoic acid or butylbenzene from butanoic acid?
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Offline jayashae

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Re: benzene synthesis problem
« Reply #14 on: June 24, 2012, 10:36:31 PM »
from benzene to propylbenzene, I would have to somehow acylate the propane to be added to the benzene.

Ok my exam is tomorrow and I honestly don't know how to do this and won't know it in time if we're only doing Q&A.  I need someone to teach me how to get a carbonyl group on that carbon with a chlorine, but I don't know the steps.

also, I'm pretty lost in term of the butyne as well, I can reduce it to an butane, but apparently thats of no help.

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