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I am a high school student and while reading about reactions on amines, I was trying to figure out a way to convert aniline $(\ce{C6H5NH2})$ to phenol $(\ce{C6H5OH})$ without diazotizing it with sodium nitrite $(\ce{NaNO2})$ and dilute hydrochloric acid $(\ce{HCl})$ in temperature conditions of $\pu{273 K}$ to $\pu{278 K}$ and then reacting it with $\ce{H2O},$ i.e. anything that does not involve the following reaction:

$$\ce{RNH_2 + NaNO_2 + HCl ->[$273–\pu{278 K}$] [RN2^+Cl^-] ->[H2O] ROH}\tag{R1}$$

I tried converting it to an isocyanide via the carbylamine reaction, but that seemed to make things more complicated. The closest I found to solving this was Tilden's reagent $(\ce{NOCl}),$ which reacts with primary amines in the following way:

$$\ce{RNH2 + NOCl -> RCl + N2 + H2O}\tag{R2}$$

However, this is limited to primary amines by definition.

Is there any way to convert aromatic amines to aromatic alcohols without diazotizing the compound? More specifically, is there a way to convert aniline to phenol without converting it to a benzene diazonium ion?

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    $\begingroup$ Names of compounds aren't supposed to be capitalised. $\endgroup$
    – Mithoron
    Apr 11, 2021 at 15:16
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    $\begingroup$ There's plenty of ways, but reaction itself is pretty much exercise in futility - pointless in practice. $\endgroup$
    – Mithoron
    Apr 11, 2021 at 16:05

1 Answer 1

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Benzenediazonium salt is so versatile that it can be used to make many compounds. That's why, diazotization reaction is so popular and useful. The reaction conditions is not that harsh and is easily achievable. Coming to the reaction, diazotization is a straight one-way procedure to achieve aniline to phenol conversion. If you talk about other ways of converting aniline to phenol, the reaction conditions for such ways are generally harsh and hence not done practically to obtain phenol. In addition, there are so many steps, that the conversion is practically not feasible.

One of the ways of converting aniline to phenol without diazotizing is to convert aniline to acetanilide and then hydrogenolyze it to make benzene which can be then used to make phenol.

  1. Step 1

Aniline to acetamide

  1. Step 2

Acetamide to benzene

The reaction is taken from a paper1. The paper discussed the use of $\ce{NiMo}$ based catalyst along with novel neo-microporous composite material HSM/ZSM-5 as support. The reaction result is compared with other supports like $\ce{\gamma-Al2O3}$ and lone ZSM-5 and HSM system.

  1. Step 3

Benzene to phenol

Reference

  1. Sajedeh Jafarian, Ahmad Tavasoli, Hasan Nikkhah, "Catalytic hydrotreating of pyro-oil derived from green microalgae spirulina the (Arthrospira) plantensis over $\ce{NiMo}$ catalysts impregnated over a novel hybrid support," International Journal of Hydrogen Energy 2019, 44(36), 19855-19867 (https://doi.org/10.1016/j.ijhydene.2019.05.182) 44. 10.1016/j.ijhydene.2019.05.182(PDF).
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    $\begingroup$ Step 2 does not guarantee hydrogenation would stop at benzene, it may continue to give cyclohexane under the conditions. It is also possibility that N-ethylaniline may converted to cyclohexylethylamine first, which then hydrogenalize to cyclohexane. I attached the PDF in the reference for your information. $\endgroup$ Apr 11, 2021 at 17:31

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