In this post I will describe an easy synthesis of o-DDNP from picric acid and common chemicals. Unlike some other methods of preparing it, it does not involve that much hydrogen sulfide or any hard to acquire reducing agents (like borohydride), with the reduction done with a sulfide slurry.
This method was shown in a video by ReactiveChem, and is originated from a 1969 US Army Improvised Munitions manual. I will not provide the exact quantities of chemicals, as I precisely followed the guide, and if this needs to be replicated, the source material should be followed.
First, a solution of Sodium Picrate (left) was prepared with a small amount of NaOH and 3 grams of Picric Acid and was kept warm to prevent precipitation of the salt.
In another beaker, powdered sulfur was added to lye pellets. The mixture was wetted with a couple drops of water and stirred until a dark red solution (right) was achieved.
The sulfide solution was added with stirring in three portions to the sodium picrate solution, yielding barbeque sauce a suspension of sodium picramate.
After cooling, the solution was vacuum filtered, and a brick-red solid was obtained, and the solution discarded.
The brick red sodium picramate was dissolved in boiling hot water, and vacuum filtered again, this time discarding the solid and keeping the filtrate.
The filtrate was cooled down to room temperature and acidified with of dilute sulfuric acid, until a brown precipitate of picramic acid was obtained, after which 3 more milliliters of H2SO4 were added to make the solution acidic.
In an erlenmeyer flask, 1.8 grams of Sodium Nitrite were dissolved in 80 milliliters of water.
The resulting solution was supposed to be added in one portion with stirring, but I made a little mistake, adding it in three portions, but im fairly sure it did not affect the yield in a significant way.
A very light brown solid was obtained, and vacuum filtered on a buchner funnel (which may be not safe, but wet DDNP isn’t supposed to be very sensitive).
The next post will contain the characterisation of dried o-DDNP, and at a later date I will perform a can test of the primary.