Chemistry - How can we synthesize para-nitrophenol

Solution 1:

This can be done by first reating the phenol with $\ce{HNO2}$ Which gives us this

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Then reacting with dil $\ce{HNO3}$ we get 90% yield of para nitro phenol

This happens because $\ce{N=O}$ has a very strong $- I$ effect thus it concentrates the electrons more towards the para position so on reacting with dil $\ce{HNO3}$ we get max yield of para

P.S - Another way of getting only para is using a protecting agent but i cant recall the reaction now. I will post it later

Solution 2:

You can always fractionally distillate the two. In this case, since the boiling points have a large difference, simple distillation works as well.

(I'm not too good with "collateral damage" of reactions, so if a reaction affects an extra group that it shouldn't, please let me know)

Otherwise, you can use the Claisen rearrangement to protect the ortho position.

(I'll see if I can get a chemdrawing software later)

Take phenol, add $\ce{Na+ CH2=CH-CH2-}$ (you may use lithium instead of sodium--easily prepared from $\ce{CH2=CH-CH2-X}$). You will get $\ce{Ph-O-CH2-CH=CH2}$

Heat it, the group migrates to ortho.

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Repeat, and now you have a phenol with two $\ce{CH2=CH-CH2\bond{-}}$ groups at each ortho position.

Now nitrate. The nitro group will go to para, since $\ce{R\bond{-}}$ groups are weakly activating/orthopara directing, whereas $\ce{-OH}$ is strongly activating.

Now, vigorously oxidize with acidic $\ce{KMnO4}$. The $\ce{CH2=CH-CH2\bond{-}}$ groups become $\ce{-COOH}$ groups, and the other stuff stays intact.

Now, decarboxylate it. I'm not exactly sure of it, but we can do this via:

  • Treating with $\ce{NaOH}$ or soda lime.

  • (or) Treating with Vit. C

(few more from Wikipedia):

  • Barton decarboxylation
  • (check the stuff here)

The acidic and basic media may have some adverse effects on the compound, but I doubt it.

Solution 3:

The current set of solutions are rather too complicated, I think. Here's what I'd do:

  • Make phenyl acetate with acetic anhydride and phenol.
  • Nitrate your ester with the usual conditions; the bulky acetyl group makes o-nitration less likely.
  • Separate out your p-nitrophenyl acetate
  • Hydrolyze your nice ester.

There are a number of bulky protecting groups one could use for the phenolic -OH, but acetic anhydride is rather cheap in my neck of the woods, and it's what I'm accustomed to.

Tags:

Synthesis

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