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This is the procedure I carried out in class:

  1. Reduction of nitrobenzene by using tin and $\ce{HCl}$ acid
  2. After the completion of the reaction, $\ce{NaOH}$ added to neutralize excess acid and dissolve any $\ce{Sn(OH)2}$
  3. Steam distillation is carried out to obtain suspension of phenylamine
  4. Salting carried out where $\ce{NaCl}$ salt is added. Aqueous layer discarded
  5. Solvent extraction: dry ether added and mixture shaken vigorously. Aqueous layer discarded
  6. Distillation under reduced pressure carried out and solid phenylamine left in flask

My questions:

  1. Instead of carrying out distillation under reduced pressure at the end of the procedure to remove the ether, could I have just carried out simple distillation?

  2. Why is steam distillation suitable in part 3? Could I have used vacuum distillation here?

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  • $\begingroup$ I'm not familiar with the procedure, so I have some questions. It doesn't sound like a distillation in step 6, it sounds like you just evaporated the solvent. Did you actually collect phenylamine in a receiving flask? Also, in step 3, what was collected in the receiving flask and what remained in the boiling flask? $\endgroup$ – LDC3 May 8 '14 at 5:15
  • $\begingroup$ @LDC3: In step 3, I collected a cloudy suspension of phenylamine and in the boiling flask the leftover tin and aqueous layer containing some NaOH etc. In step 6, obtained solid phenylamine (This was the procedure our teacher told us to follow but I want to know the reason behind each step... the last step seems a bit unnecessary to me... Shouldn't simple distillation be enough? ) $\endgroup$ – Eliza May 8 '14 at 5:56
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Instead of carrying out distillation under reduced pressure at the end of the procedure to remove the ether, could I have just carried out simple distillation?

You could have performed any procedure to remove the solvent:

  • Simple distillation - This would be slower than what you did and could overheat the undistilled aniline causing decomposition.
  • Vacuum distillation - This is what you did, perhaps even on a special apparatus called a rotary evaporator. This method is still a distillation, even if your product was not distilled. Something was distilled.
  • Evaporation on a hot plate (or steam bath)-

Why is steam distillation suitable in part 3? Could I have used vacuum distillation here?

Steam distillation is suitable because the aniline is already in an aqueous suspension. If do vacuum distillation, you would need to

  1. Separate the aniline from the aqueous mixture (extract with ether)
  2. Remove the ether (simple distillation or reduced pressure distillation)
  3. Vacuum distil the aniline

If you look at what you did, it is the same steps in a different order:

  1. Distil the aniline
  2. Separate the aniline from the aqueous mixture (extract with ether)
  3. Remove the ether (simple distillation or reduced pressure distillation)

Either is probably suitable. In the end, the steam distillation is easier and less hazardous than the full-blown vacuum distillation you would need.

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  • $\begingroup$ This was extremely helpful. Just one thing: Is steam distillation used in scenarios where the two liquids are immiscible and reduced pressure distillation when there are miscible liquids but one of them will decompose if too much heat is supplied (like phenylamine)? $\endgroup$ – Eliza May 8 '14 at 13:29
  • $\begingroup$ Steam distillation requires immiscible liquids to work well. $\endgroup$ – Ben Norris May 8 '14 at 15:24
  • $\begingroup$ and distillation under reduced pressure works with miscible liquids (as in this example, ether and phenylamine)? $\endgroup$ – Eliza May 8 '14 at 15:33

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