# Phenol preparation from Grignard reagent

Reaction: Phenyl magnesium bromide in presence of excess oxygen, on acidification yields phenol, as below.

My instructor told me that the above reaction occurs, and if the reagent is in excess then phenol is the end product. However, I'm not able to figure out the mechanism.

I've tried and got stuck at this point:

I wish to know the complete mechanism of this reaction.

• Feb 26, 2018 at 5:43
• In practice this is not how lab chemists make phenols from aryl halides as the yield not reliable. The route is to make the aryl boronate from the Grignard and oxidise that. Feb 26, 2018 at 9:30
• @Waylander, could you please post that as an answer with the reaction/mechanism? Feb 26, 2018 at 9:33
• I doubt that the peroxide compound is the real intermediate. In reality the Grignard probably reacts directly with water to give the phenol. Mar 2, 2018 at 14:30

As requested by the OP - the route that lab chemists use to form phenols from aryl halides (not aryl fluorides) is via formation of the aryl boronic acid or boronate. These may be formed by either metallation of the aryl halides to form the aryl lithium or Grignard and reaction with a trialkyl borate $\ce{B(OR)3}$, or by Pd catalysed reaction with pinacol borane (Suzuki-Miyaura reaction). These boronates or boronic acids may be isolated, but in practice an oxidative workup, most often with basic peroxide, yields the phenol in good to excellent yield.

image from US7678158B2.

Thanks to @Avatar Shiny, I found the mechanism: (a link has been posted in the comments section)

For the sake of completeness, I add the mechanism here as an answer -

• Why have an anion attack a negatively charged oxygen? The other oxygen of the hydroperoxy anion is the electrophile. Apr 28, 2020 at 14:50
• Does the oxygen lone pair or the electrons of the O−O bond attacks BrMg? Also what w/u means? Thanks in advance. May 9, 2020 at 11:49