I attempted to synthesize Martius yellow (2,4-dinitro-1-naphthol) today using the procedure from Fieser’s Experiments in Organic Chemistry, which may be found in the Sciencemadness library. Unfortunately, I did not get the expected results.
10 mL of 95% ACS grade sulfuric acid was added swiftly to a 50 mL Erlenmeyer flask containing 5 grams of finely powdered, freshly distilled 1-naphthol. Most of the naphthol quickly dissolved, and the mixture instantly turned bright red.
The flask was heated and swirled for 15 minutes, and the color of the contents changed during this time from red, to amber, to dark green. Sulfur dioxide was evolved.
The dark green mixture was cooled in an ice bath, causing it to become very viscous. 25 mL of cool distilled water was added to dilute it, and it was added to an addition funnel, as shown above.
The green solution was then added dropwise to a beaker containing 6 mL of azeotropic nitric acid over the course of 10 minutes. The color of the solution changed from green to red as it reacted with the nitric acid.
Once all of the solution was added, the beaker was placed on a hot plate and heated gently for 15 minutes. A vigorous reaction appeared to take place, but the appearance of the reaction mixture did not change. A yellow precipitate should have formed.
I would like to attempt this synthesis again as soon as I can figure out what went wrong with it. It could be that the acid I used was too concentrated, that I heated the reaction mixture too much, that my nitric acid was not concentrated enough, or a combination of these factors.