I know that aliphatic alcohols react with reagents like $\ce{PBr3},$ $\ce{PBr5},$ $\ce{SOCl2}$ etc. to give alkyl halides as a product. But what will happen if we put aromatic alcohols like phenols with these types of reagents? Will haloarenes formation take place?


1 Answer 1


TL;DR: It is a possible but complicated reaction and you get a mixture of products but formation of haloarene is not significant in any reaction

Long answer:

  1. phosphorus trichloride: form triphenyl phosphite

$$\ce{3 PhOH + PCl3 → P(OPh)3 + 3 HCl}$$

(The phenol is essentially acting as a nucleophile through oxygen, attacking the phosphorus.)

  1. phosphorus tribromide give a similar reactions. See this researchgate post for more information (Note: phosphorus pentabromide is already a reactive compound and it decomposes/dissociates to phosphorus tribromide and bromide. So, if you use it to react with phenol, the reactive species would ultimately be $\ce{PBr3}$)
  2. phosphorus pentachloride: See this posts (here and here). In short, it is difficult and you get multiple products.
  3. Thionyl chloride: Possible but very complicated. As noted from a paper:

Studies on the reaction with phenol and thionyl chloride are greatly complicated by the existence of readily-occurring nuclear [sic] substitution reaction. This probably account for the fact that the preparation of diphenyl sulfite by the direct reaction of phenol and thionyl chloride in the absence of hydrogen chloride acceptors had not been reported prior this time and that the preparation of phenyl chlorosulfinate have been accomplished only recently.

A Study of the Reaction of Phenol with Thionyl Chloride, William E. Bissinger and Frederick E. Kung, Journal of the American Chemical Society 1948 70 (8), 2664-2666, DOI: 10.1021/ja01188a015

  • 1
    $\begingroup$ "readily-occurring nuclear substitution reaction." Nuclear? Huh? Autocorrect maybe? Recheck the original source. $\endgroup$ Jul 29, 2021 at 13:33
  • $\begingroup$ @OscarLanzi First page, left column, third line (still first phrase) of the source cited indeed uses «nuclear». $\endgroup$
    – Buttonwood
    Jul 29, 2021 at 13:47
  • $\begingroup$ [sic]: an expression used to indicate that a seemingly incorrect or paradoxical quotation is in fact rendered correctly. $\endgroup$ Jul 29, 2021 at 14:11

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