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I put the quotes because Wikipedia says it's an outdated theory.

What exactly happens when nitrobenzene is converted to aniline using $\ce{Sn/conc HCl}$?

According to a few books which haven't been updated, even $\ce{Na}$/ethanol, $\ce{Zn/dil H2SO4}$ produce this. I guess a metal may have an important role in the actual mechanism.

Is there any specific reason why $\ce{Na}$/ethanol is used to reduce cyanides to amines, and $\ce{Sn/conc HCl}$ to reduce nitrobenzene? (and not the other way around)

Even $\ce{KMnO4}$ produces "nascent oxygen"? What exactly is going on?

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  • $\begingroup$ Which question are you asking? Currently there's three ? marks in your post (excluding the one in your title) :( As for the middle one, I was taught that tin+conc HCl will reduce cyanide to amine, but then further reduce it to aldehydes because it is in an aqueous medium. A similar thing won't happen with sodium/ethanol (alcoholic medium). I am not sure of the exact mechanism though. $\endgroup$ – Gaurang Tandon Feb 15 '18 at 7:56