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Chemistry Forums for Students => Organic Chemistry Forum => Topic started by: g-bones on April 07, 2008, 12:44:16 AM

Title: replacing an alcohol with an iodine using triphenylphosphine (Ph3P) and imid
Post by: g-bones on April 07, 2008, 12:44:16 AM

anybody know how an alcohol can be replaced with an iodine when using Ph3P, imid, and I2?  anyhelp would be great.   

Title: Re: replacing an alcohol with an iodine using triphenylphosphine (Ph3P) and imid
Post by: Dan on April 07, 2008, 03:03:58 AM

It's basically the same as the Appel reaction:

http://www.organic-chemistry.org/namedreactions/appel-reaction.shtm

but you are using I₂ instead of CI₄, the reactive intermediate is the same: Ph₃P⁺I

Title: Re: replacing an alcohol with an iodine using triphenylphosphine (Ph3P) and imid
Post by: g-bones on April 07, 2008, 04:34:30 AM

yeah but in that situation there is no base strong enough, the only anion is I- when triphenylphospine splits the I₂.  not strong enough to deprotanate an alcohol like a carbon base.  right?

Title: Re: replacing an alcohol with an iodine using triphenylphosphine (Ph3P) and imid
Post by: Dan on April 08, 2008, 10:43:31 AM

Fair point, but Ph₃P⁺I is electrophilic enough to be attacked by alcohols. The HI generated is "mopped up" by the imidazole.