Diphenyl Ether

A quick post to share my experience with this reagent, as it was really a joy to work with.

Firstly, diphenyl ether is a solid at room temperature, melting at 25-26 C. I was using it as a solvent for a high temperature reaction – it seems like a primary use for it is to enable quite high temperature reactions, as its reflux is 258 C. It also demonstrated that I need a thermometer that goes over 250 C. Let me also add that this is notably higher than I like to work at, but when the procedure calls for it, I stand ready.

Anyway, this was supposed to be the solvent but fortunately you can get essentially the same thing as Dowtherm A and that is actually a pourable liquid.

The procedure was one in which a solid was added to the heated Dowtherm A then heated at reflux to give a cyclization reaction. Adding solid to a reaction vessel at above 200 C is not among my favorite procedure methods.

Getting rid of such a high boiling solvent was, surprisingly, not so bad as my product was a solid and it was just a matter of washing the pad with a more friendly solvent. However, getting rid of it off the glassware was somehow more tricky and all the more annoying because of its peculiar smell, which seems to linger for quite some time on anything it is spilled on.

The best part was how I got to do it again as it worked so well. And how I am penciled it to run it when we ever need some more of that material.

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5 comments on “Diphenyl Ether

  1. milkshake says:

    they actually use diphenyl ether as a fragrance for really cheap soaps and detergents, hence the familiar and not-so-great flowery scent. Apparently Ph2O is practically nontoxic. However the biphenyl in Dowtherm is quite carcinogenic, supposedly more than benzene.

    For room-temp solid solvents, nothing beats melting stuff with pyridine hydrochloride to 150C, (to deprotect phenols masked as arylmethyl ethers)

    • Chemikanji says:

      Milkshake, how easy is that pyridine hydrochloride prep? I’ve seen it listed a few times, but it always seemed like one of those greybeard organic transformations from the dark ages. BBr3 is just too much of a headache to scale-up, even if it is a slam-dunk.

      • milkshake says:

        it is not difficult, I have seen it done on a pretty large scale. You load up flask with py.HCl solid (it is pretty hygroscopic), maybe 10 weight equivs, add your compound, put a simple Liebigs or Align reflux condenser on, flush with argon and heat to 150C for about 2-3 hours. Then cool and drown with water. You may want to use a condenser that has enough internal space or even use just a wide simple tube as air cooled condenser because there is going to be some sublimation of py.HCl so you watch out that you dont plug up the flask outlet.

        On large scale (kilos of Py.HCl) you may want to pre-melt py.HCl and add the material to it portion-wise because some demethylation could be slightly exothermic and you are evolving MeCl gas…

  2. yogesh says:

    how can we remove diphenyl ether from reaction mixture

    • David Perrey says:

      That is the key thing about diphenyl ether. In my reactions, the product was precipitated and then washed. You might be able to extract into aqueous, then change the pH and re-extract.

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