[reggiehg]

Hi,

I'm researching the synthesis of picric acid (2,4,6-trinitrophenol), and while I found several recipes and some explanations, some questions still bug me.

The best procedure I found (subjectively speaking) is the disulfonation of phenol followed by nitration. My questions are:

1. What exactly are the possible reactions when trinitrating phenol directly?
2. Why trinitrate the disulfonated phenol? Why not trisulfonated phenol or monosulfonated phenol?

Regards,

Reggie

[ARGOS++]

Dear reggiehg,

I don’t believe, somebody was able to build trisulfonated products on ONLY
ONE benzene ring with a countable yield.
“Sulfo(n)-“ is NOT equal “Nitro-“ in ALL it sense.  This is possible
if you use at least “two” benzene rings, “starting” with Naphtalin.

Otherwise to prepare conditions for TRI-nitration builds automatically "some" 
Di-Sulfo-product in a quite high yield.
On the otherside, if you study the Nitration of "Aromats", you will find out,
that almost all start at least with a partial Sulfonation-step.
For the mono substituted product you need weaker reaction conditions, as
maybe with quite weaker Sulphuric acid,  —  but don’t talk about the yield, if
you not prepare otherwise special condition too (mixture!).

But the reaction is very easy to do, because it is
a “Two-step” reaction done in a “One-step” process:
      Dissolve the Phenol in high conc. Sulphuric acid for 1 till 2 hours on a
      Steam-bath (The Di-Sulfo-product is build in a more higher yield!); cool
      down to 0° Celsius, and start SLOWLY the Nitration.
      I had in mind, that the final yield must be close/above 90%. To be
      sure I consulted the OLD “ORGANIKUM”, which told me, the yield has
      to be at least 90%! (122° Celsius).
      With more then 90% yield you will have some problems with
      “by-products” anyway.
      “ORGANIKUM” means, that the preparation is good for
      “Half-micro-scale” too, with other word: A standard procedure! I thought.

I hope to have drawn you a picture to think about.
Good Luck!
                    ARGOS⁺⁺