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Specialty Chemistry Forums => Citizen Chemist => Topic started by: limpet chicken on March 12, 2006, 10:16:15 PM

Title: 2,6 alkylation of phenols
Post by: limpet chicken 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 ???
Title: Re:2,6 alkylation of phenols
Post by: Donaldson Tan 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.
Title: Re:2,6 alkylation of phenols
Post by: Will 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 (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!)