Trinitrophenol (TNP) Synthesis
Trinitrophenol (or picric acid) can be made with fairly easily obtainable materials. One word of warning – this stains yellow, and it stains everything. The staining is the main reason I don’t like making TNP, but besides that it’s a pretty nice explosive. When I had made it before I didn't have a camera so there are no pictures to go with this. The next time I make it I'll probably take pictures and redo this page. So for now here is just the procedure.
The chemicals needed here are pretty easy to get a hold of. You just need some sulfuric acid, KNO3, and ASA (acetylsalicylic acid). The ASA I use was in the form of generic brand "ASA tablets", aspirin being a brand name. Here is a quick way to purify the ASA from the tablets since they are held together with a binder.
Purification is done by dissolving crushed aspirin pills in warm acetone and then filtering to remove impurities (binders). The filtrate is then left to evaporate, leaving pure crystals of ASA. 80 generic brand ASA tablets (containing 325 mg of ASA) were dissolved in approximately 150 ml of acetone which was then warmed (in a hot water bath) and stirred. The hot solution was filtered leaving the undissolved impurities in the filter. The solution was then left in the sun for a few hours. The newly formed crystals were dried and weighed. Out of a possible 26 grams of ASA, 23 were recovered. There was loss of ASA due to is recrystallizing on any surface upon which it contacted (including the filter and the filter flask) and some remaining stuck to the filter paper. Once the ASA has been purified, it is ready for the next step.
There are various syntheses available on the production of TNP. The process described here is the one I have used. ASA, sulfuric acid, and KNO3 were used in this step. 135 ml of sulfuric acid were measured out in a graduated cylinder and were then added to a 250 ml beaker. This was heated in a hot water bath until approximately 70 degrees Celsius. At this point 25 grams of (purified) ASA were dissolved with stirring. The acid (previously red) turns black as the reaction (conversion to phenol-4-sulfonic acid) proceeds. Fifteen to 20 minutes are given for this reaction to complete. The solution was allowed to cool slightly. Fifty (50) grams of KNO3 were then added SLOWLY. Quick addition of the nitrate will cause the evolution of NO2. The solution foams during the addition and turns to a red/orange colour. The solution was then cooled down in an ice bath and became thick. It was stirred, and gas bubbles were seen to evolve. This thick solution was added to a 300 ml ice/water mixture, which sat in an ice bath. When the ice had all melted the solution was filtered leaving a crop of crude TNP in the filter. The crystals were beige in appearance. The filtrate was cooled down and again filtered, leaving a second crop of crystals in a filter. The crude TNP was dissolved in approximately 150-200 ml of boiling water and then cooled down. The recrystallized TNP, now a bright yellow, was then filtered and dried.
