I was taught that Sn/HCl should be used for reduction of nitrobenzene to aniline. Can I ask if there are any alternative reducing agents (for example, LiAlH4?) to do the same task?


Hydrogenation of aromatic nitro groups (over, for example, $\ce{Pd/C}$) usually results in reduction to the corresponding aniline and is probably easier to carry out and work up as compared to $\ce{Sn/HCl}$.

Wikipedia has a list of several conditions for reduction of $\ce{ArNO2}$ to $\ce{ArNH2}$. It also states that $\ce{LiAlH4}$ reduces it to the azo compound $\ce{ArN=NAr}$, which is corroborated by March's Advanced Organic Chemistry (7th ed.).

In any case, from a practical perspective, you would probably want to avoid using $\ce{LiAlH4}$ if there's a simpler alternative. It's dangerous and the workup is not fun.

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    $\begingroup$ Hydrogenation would always be my preferred conditions because of the ease of running and working up. My second choice was tin (II) chloride in EtOAc at reflux. $\endgroup$ – Waylander Aug 2 '18 at 11:01
  • $\begingroup$ Can I ask if you have any idea why do my school's notes state that H2(g) with Pt(s) is not able to reduce nitrobenzene? Has there been a shift in the consensus brought by, for example, the publication of certain papers)? $\endgroup$ – timing Aug 4 '18 at 7:10
  • $\begingroup$ @TimingLiu they're probably simply wrong, as hydrogenation over Pd or Pt is very common. doi.org/10.1016/B978-0-12-395532-6.50014-3 "Aromatic nitro groups are easily hydrogenated to the corresponding aromatic amine. Palladium or platinum catalysts are by far the most used in these reductions; rhodium and ruthenium catalysts have as yet found only limited and specialized use. The reductions occur readily under mild conditions and usually without complication." This was written in 1967. $\endgroup$ – orthocresol Aug 4 '18 at 7:48
  • $\begingroup$ I agree with @orthocresol, the notes are just wrong. I've used Pt on C many times to reduce a range of aromatic nitro groups. AFAIK this is done on an industrial scale. $\endgroup$ – Waylander Aug 4 '18 at 8:36

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