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Author: Subject: Hydroquinone from p-DCB
Meltonium
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[*] posted on 3-1-2017 at 15:03
Hydroquinone from p-DCB


I wanted to make hydroquinone from p-DCB. At first glance, it seems simple; add two moles of NaOH and one mole of p-DCB and heat to get products of 2NaCl and hydroquinone. After doing a bit of research, I discovered that this was not the case. The chlorine atoms on the p-DCB are not reactive enough to undergo this substitution. Something is needed to get the reaction going. I continued reading and found that DMSO (dimethylsulfoxide) increases the reactivity of bases and could allow the substitution to take place.

Objective: Synthesize Hydroquinone from p-DCB

Materials:

  • 147g p-DCB
  • 80g NaOH
  • DMSO
  • Distilled Water


Procedure:

  • Make a solution of 75mL of DMSO in 350mL of water
  • Add the solution, p-DCB, and NaOH to the flask
  • Begin heating and mixing
  • Continue to heat and stir for 3 hours
  • Let the solution cool and filter/decant off the crystals
  • Wash the crystals with distilled water and add the liquid to the filtered liquid
  • Evaporate off the water until crystals start to appear, then let chill
  • Filter/Decant off the crystals
  • Recrystalize then dry the product


Theoretical Yield: 110g

Notes:

  • The solution was attempted to be kept at 100C for the duration of the reaction. If the temperature increased beyond 168C, the DMSO may start to decompose and lead to an explosion.
  • The solution was originally in a 1L RBF, but had to be transferred to a tall-form 1L beaker because of inadequate mixing.
  • Before the solution was transferred, 3 distinct layers had formed. The top layer was assumed to be the aqueous NaOH layer, and the bottom layer melted p-DCB. The middle layer is unknown. It could not have been the DMSO because there was not enough DMSO added to create that big of a layer.
  • After the duration of time had passed in the beaker, two layers formed. Upon cooling, the bottom layer froze into off-white crystals. The top layer remained aqueous.
  • To speed up the evaporation, the liquid was transferred to a 1L Erlenmeyer flask and set up for vacuum distillation. (This has not been completed)


Results:
It may be premature, but I do not think that much hydroquinone formed. This was indicated to me by the abundance of p-DCB crystals that formed when the mixture cooled. I think the pressence of so much water hindered the reaction and a greater concentration of DMSO was needed to get a good yield. I had planned to use pure DMSO not as a solution, but I read that, in the presence of basic or acidic conditions, DMSO may decompose at low temperatures and could lead to an explosion. I didn't want to risk that.

--

What concentration do you think would be enough to warrant a good yield but keep the risk of an explosion at a minimum?
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halogen
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[*] posted on 3-1-2017 at 16:02


Quote:
The chlorine atoms on the p-DCB are not reactive enough to undergo this substitution. Something is needed to get the reaction going.


That's simply not true, it's a matter of preference. The hydrogen ion will come off before the HO- sticks to the ring, whch would be necessary for ipso (same place) substitution. The ring isn't sticky enough. It might be if you nitrate it, sulfonate, or further halogenate; hexachlorobenzene probably can be sustituted in this way to hexachlorophenol although both are well known environmental pollutants. In these cases, the sulfonate and nitro groups can themselves be targets of ipso substitution.

And of course the phenol that forms if one chlorine has been replaced would itself deprotonate and deactivate the ring towards a second reaction. So of course there was no hope of your aim being reached. You must be mad to have thought there was. Read a book!

There are other simple routes to hydroquinone, in particular by oxidation of phenol and simple reduction by any one of a variety of reducing agents. Electrical potential is, though I am not aware of these conditions, probably more suitable and convenient for both transformations than chemical reagents.

[Edited on 4-1-2017 by halogen]




F. de Lalande and M. Prud'homme showed that a mixture of boric oxide and sodium chloride is decomposed in a stream of dry air or oxygen at a red heat with the evolution of chlorine.
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AvBaeyer
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[*] posted on 3-1-2017 at 16:23


The DMSO effect you are musing about only occurs in anhydrous DMSO. The aqueous solution you used completely negates the effect of DMSO on hydroxide basicity/nucleophilicity. But no matter, halogen is correct - there is no way what you want to do will work in any practical manner.

AvB
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Meltonium
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[*] posted on 3-1-2017 at 16:41


Thanks for this information! I am an amateur chemist with no formal background in organic chemistry. I thought I might give this experiment a try and share it. At least I got rid of most of my stinky p-DCB and learned some new things.
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[*] posted on 3-1-2017 at 17:06


It would have been a great reaction if it worked. And it turns out, you aren't the first one to want to do this either. None other than Steve Buchwald has studied the same transformation: http://pubs.acs.org/doi/abs/10.1021/ja0639719 , http://www.organic-chemistry.org/abstracts/lit1/389.shtm . The catch is that it requires a Pd catalyst with a special ligand.

EDIT:

Also this reaction: http://www.organic-chemistry.org/abstracts/lit3/728.shtm
http://pubs.acs.org/doi/abs/10.1021/ol301523q

[Edited on 1-4-17 by DDTea]




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[*] posted on 3-1-2017 at 17:40


Now I also read that p-DCB will react with something such as sodium methoxide to produce the di ether Or is that wrong as well?

If that works could that be hydrolyzed to make methanol and the hydroquinone?
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[*] posted on 4-1-2017 at 08:43


Before you design an experiment, the least you can do is to check the literature and search the forum:

https://www.sciencemadness.org/whisper/viewthread.php?tid=14...
https://www.sciencemadness.org/whisper/viewthread.php?tid=17...
https://www.sciencemadness.org/whisper/viewthread.php?tid=12...
https://www.sciencemadness.org/whisper/viewthread.php?tid=12...

Admittedly, most posts in these treads are pretty much demented, but even non-sense has some use in the learning process.
Besides, the product of the reaction between NaOH and p-dichlorobenzene, if performed at the required conditions (>300 °C) and if it works at all, would not be hydroquinone, but a mixture of para- and meta-chlorophenol (and at least some chlorinated diphenylethers as impurities along with who knows what else - it would likely not be a clean reaction).




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[*] posted on 18-1-2017 at 19:09


Just a note on these proposals:

I think they tend to come up again and again because of people drawing an analogy with similar reactions on aliphatic molecules.

The problem is that these reactions on aliphatic molecules are bimolecular substitution reactions involving a backside attack on the carbon atom. This requires a sort of 'flip' of the other groups attached to that carbon like an umbrella being turned inside out.

This just can't happen with an aromatic for structural reasons having to do with the rigidity of the benzene ring.
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