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$$\ce{C6H5Cl + NaOCH3 -> C6H5OCH3 + NaCl}$$

So this reaction undergoes $\ce{S_N2}$ mechanism, but $\ce{C6H5Cl}$ is not likely to undergo such mechanism, so I doubt if anisole would be formed or not?

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  • $\begingroup$ Aryl halides are much less reactive towards nucleophilic substitution reactions than alkyl halides . So no reaction will occur $\endgroup$
    – Manroop
    Jun 25, 2023 at 18:44

4 Answers 4

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Chlorobenzene is inert towards most forms of nucleophilic substitution. In particular:

  • A $\mathrm{S_N1}$ mechanism is not likely here because the carbon is $\mathrm{sp^2}$ hybridised, the $\ce{C-Cl}$ bond is strong, and the dissociation of $\ce{Cl-}$ is therefore not very likely.
  • $\mathrm{S_N2}$ substitution doesn't occur because 1) the $\ce{C-Cl}$ bond is strong 2) the $\sigma^*$ orbital is in the middle of the ring and is inaccessible to a nucleophile.
  • The $\mathrm{S_NAr}$ mechanism could be followed if there is an electron-withdrawing group ortho or para to the chlorine atom, but in chlorobenzene, there is no such EWG.

I would like to suggest the possibility of a benzyne mechanism, i.e. an elimination-addition mechanism. The elimination step follows an $\mathrm{E1_{cb}}$ mechanism:

Benzyne mechanism, part 1

The benzyne intermediate is very electrophilic and nucleophilic attack by methoxide ion proceeds rapidly to give anisole.

Benzyne mechanism, part 2

Although this reaction is well-documented with both $\ce{NaOH}$ and $\ce{NaNH2}$, I can't find any real-life examples with $\ce{NaOMe}$. Most examples of chlorobenzene → anisole reactions involve some kind of catalyst. However, if it were to happen, it would probably occur via this parthway.

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Aryl Halides are less reactive than alkyl halides and Nucleophilic aromatic substitution on aryl halides only possible if strong electron drawing group is present at ortho and para position to chloride.

Due to their low reactivity toward nucliophile, the reaction usually occur at higher temperature. For example 1-chloro-4-nitrobenzene the reaction occur at high temperature.,

enter image description here

Nucleophilic substitution reaction probably occur through the slow addition of nucleophile to the ring, and second step fast removal of Cl group.

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    $\begingroup$ Does the diagram of 4-nitrochlorobenzene contain a typo? $\endgroup$
    – DHMO
    Sep 4, 2016 at 11:02
  • $\begingroup$ Without an EWG ortho or para it's probably not going to proceed via SNAr. More likely benzyne in this case. $\endgroup$ Oct 4, 2016 at 13:35
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    $\begingroup$ There is still a typo in the diagram. The middle structure should have a $\ce{C=N}$ double bond and two $\ce{-O^-}$ on the nitrogen. $\endgroup$
    – Jan
    Oct 5, 2016 at 15:26
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The C---Cl bond of chlorobenze acquires partial double bond character due to the +M effect of Cl-atom. As a result bond energy of C---Cl bond becomes high which leads to low reactivity of chlorobenze towards nucleophilic substitution. So chlorobenze doesn't react with sodium methoxide to form anisole at ordinary reaction conditions. To prepare anisole by Williamson's synthesis the appropriate choice of reagents is Sodium phenoxide and chloromethane. This reaction follows SN2 mechanism because of least steric hindrance around the partial postive charged Cl-atom of chloromethane.! Reaction of Sodium phenoxide and alkyl halide

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The C---Cl bond of chlorobenze acquires partial double bond character due to the +M effect of Cl-atom. As a result bond energy of C---Cl bond becomes high which leads to low reactivity of chlorobenze towards nucleophilic substitution. So chlorobenze doesn't react with sodium methoxide to form anisole at ordinary reaction conditions. To prepare anisole by Williamson's synthesis the appropriate choice of reagents is Sodium phenoxide and chloromethane. This reaction follows SN2 mechanism because of least steric hindrance around the partial postive charged Cl-atom of chloromethane.

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