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Topic: 2,6 alkylation of phenols  (Read 5000 times)

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Offline limpet chicken

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2,6 alkylation of phenols
« on: March 12, 2006, 10:16:15 PM »
I have a synthesis I would like to attempt, but how to go about it, I wish to alkylate phenol, at a pinch would do, in both the 2- and 6- positions, I initially thought friedel-crafts, but that is ortho/meta/para directing, any pointers as to how to go about it? as I really haven't a clue on this one ???
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Offline Donaldson Tan

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Re:2,6 alkylation of phenols
« Reply #1 on: March 20, 2006, 02:34:04 PM »
positions 2 and 6 are essentially the same thing, beside the alpha carbon where the hydroxyl group is attached to. the 2 and 6 positions fall under the ortho-position.

unfortunataly,  the hydroxyl functional group is electron withdrawing, so it is is meta-directing.  meta refers to position 4 for your information.

an alternate method is to add an hydroxyl group to a benzene ring that has a ortho-para directing functional group attached to it, eg. methyl benzene. the methyl group is electron-donating, so it is ortho-para directing.

in the case of methyl benzene, convert it into a diazonium salt, then hydrate the diazonium salt. This will replace the diazonium group with with -OH.
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Offline Will

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Re:2,6 alkylation of phenols
« Reply #2 on: April 05, 2006, 06:57:20 PM »
I thought in most cases the hydroxyl group is ortho-/para- directing in practice because it makes addition-elimination reactions at these positions a lot easier. Also, it isn't electron withdrawing becasue the oxygen's lone pairs join in with the conjugated system, making e- density higher at the ortho-/para- positions. I found a website which explains it quite well here (although it is a bit basic): http://www.chemguide.co.uk/organicprops/phenol/ring.html

How would you avoid the para- substitution? (Sorry if this is too much organic chemistry for the citizen chemist forum!)

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