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The question is asking for the reason of obtaining an acidic solution. The only reason can be when ethanol follows a substitution reaction approach to substitute the bromine atom and form HBr as a sidr product. This will indeed form an acidic solution.

However, if we had gone for Elimination pathway, we can see that it would require

  1. Lesser role of steric hindrance by adjacent methyl groups.

  2. Resonance stabilised carbocation (if we choose E1 mechanism).

  3. The aquous solvent will too stabilise the carbocation (although both 2,3 points also valid in SN1 reaction).

    1. The product form will be in conjugation with the benzene ring.

Aren't these enough for ethanol to act a bit more acidic and lead to elimination than substitution?

  • $\begingroup$ Couldn't it also be an elimination reaction? In this case the other end products will be $\ce{Br-}$ and $\ce{CH3CH2OH2+}$ (protonated ethanol). Protonated ethanol is also acidic. $\endgroup$ – rcAlex36 Jun 9 '17 at 8:25

Other organic chemists out there, please correct me if I'm wrong: I would say it's mostly water (rather than ethanol) that reacts with the organic molecule, probably by substitution, forming HBr as a side product. Even if there weren't an inherent difference in nucleophilic reactivity between water and ethanol, the big difference in molecular weight between them means that even a solution where there is more ethanol in mass % may actually have a higher molar fraction of water. But OK, my main point is that it's probably a substitution that we're looking at rather than an elimination.

As for elimination, I am not sure why the acidity of ethanol should favour it. I would say elimination is facilitated in acidic conditions when there is a group that must be protonated to become a good leaving group (e.g. OH). Here we have Br, which is an 'OK' leaving group most of the time, no protonation involved.

  • $\begingroup$ Would the person who downvoted my answer be so kind as to explain what they think is wrong with it? As far as I can tell, I answered the original post. If I am right, there is no reason to downvote what I wrote. If I am wrong, but I'm not told why, how am I supposed to improve my contributions in the future? $\endgroup$ – user6376297 Jun 8 '17 at 18:42

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