explodes over 300 °C
|Picric Acid||molecular mass
Picric acid, or 2,4,6-trinitrophenol, has also been called picronitric acid; carbazotic acid; nitroxanthic acid; melinite; lyddite; pertite; shimose; melinit; granatfullung; sprengkorper 88; pertit; picrinit; ekrasit; TNF; and shimoza. Picric acid is both a useful explosive compound and a precursor to other explosives. It does not see much use now a days as a laboratory reagent or explosive. It is too dangerous for the lab and too costly for the battlefield. I found a very old bottle in the lab once, the bottle had not been used for 5 years and should not have been there. It is stable unless old, it will form a very unstable crystalline structure after many years. I have three different methods of synthesizing picric acid. The first is a laboratory procedure using fairly common chemical reagents, it will provide a better and cheaper product. The second is a lesser used, but economical, catalytic process for possible large scale manufacture, its chemicals are more difficult to get. The third is one of those improvisational procedures using aspirin tablets, it sounds feasible. Picric acid was first mentioned in the alchemical writings of Glauber in 1742. The old timers made it from nitrating animal horn, silk, indigo, natural resin, and the like. Its synthesis from phenol, and the correct determination of its formula, was in 1841. It was not until 1830 did anybody think to use picric acid as an explosive. Before then it was assumed that only the salts of picric acid were explosive, not the acid itself. In 1873 H. Sprengel proved it could be detonated and by 1894 the Russians had worked out a method of manufacture for artillery shells. Soon after, every military power used picric acid as their primary high explosive material. The 20th century saw the decline of picric acid, the replacement being TNT. The downfall was partially due to the acidic nature and the sensitivity of picric acid. Today picric acid is more suited to detonators or booster charges.
|benzene||500-mL Erlenmeyer flask|
|ethyl alcohol||100-mL Florence flask|
|mercuric nitrate||2-L Florence flask|
|nitric acid||glass filter paper|
|sodium nitrate||stirrer/stirring rod|
Add 24 mL of phenol and 14 mL of 98-100% sulfuric acid to a round-bottomed 100-mL Florence flask and reflux for 6 hours at 120°C on an oil bath. After the material has cooled, it is diluted with 46 mL of 72% sulfuric acid. Pour the solution from the round bottomed flask into a 500-mL Erlenmeyer flask. 175 mL of 70% nitric acid is added dropwise, with a pipet or buret, add the acid very slowly, a drop at a time. The addition of nitric acid will cause a vigorous reaction and release toxic gas, use a fume hood or go outside. When all of the acid has been added and the reaction has subsided, the mixture is heated for 2 hours on a steam bath to complete the nitration. After 8 to 12 hours the picric acid crystals should have separated. These crystals will need to be filtered with glass filter paper because of the solutions high acidity. Otherwise, pour off most of the acid, dilute with water, and filter with regular filter paper. Wash the crystals with several small portions of water and allow to dry in the open air. To purify, dissolve the picric acid in 1 L of boiling water per 15 g of crystals, filter while hot and allow to cool slowly. Any heavy droplets of brown oil which dissolve slowly during this boiling should be discarded. You will need a graduated cylinder for measuring liquids, and a thermometer to monitor the temperature.
This catalytic process skips the roundabout way above and converts benzene directly into picric acid in one step. The reagents of this reaction may be a bit hard to come by, however. Prepare a solution of 10 g of mercuric nitrate in 600 mL of 70% nitric acid. Add this solution to a round-bottomed 2-L Florence flask with 228 mL of benzene. Reflux the mixture for 7 hours on a sand bath. Transfer the contents of the flask to another flask and distill it with a steam bath (not steam distillation, simple or fractional will suffice). Benzene will distill over first, then nitrobenzene, and finally a mixture of dinitrobenzene and dinitrophenol will come over slowly. The distillation is continued until these volatile organics are removed. The remaining residue is filtered while hot to remove any impurities and allowed to crystallize. the picric acid that should have crystallized can be purified by recrystallizing from hot water.
This procedure uses aspirin tablets instead of phenol. Crush 100 aspirin tablets to a fine powder. Put 500 mL of 95% ethyl alcohol in a 1000-mL beaker then add the aspirin powder. Gently heat the alcohol while stirring to dissolve the acetylsalicylic acid within the tablets for 15 minutes. Acetylsalicylic acid is the active ingredient in aspirin and a phenol derivative. Filter the still hot alcohol to remove any excess tablet filler. Now heat the solution to evaporate off all of the alcohol, leaving behind crystals of acetylsalicylic acid. When the crystals have dried, add them to a 1000-mL beaker with 700 mL of 95-100% sulfuric acid. Heat the acid and stir to dissolve the acetylsalicylic crystals. When all of the crystals have been dissolved, add 90 g of sodium nitrate or potassium nitrate. Add a few grams at a time then wait for the reaction to subside before adding more. The nitrate addition must be done in a well ventilated area as it produces deadly nitrogen dioxide gas. When all of the nitrate has been added, allow the mix to cool to room temperature, stirring it every few minutes. Pour it into 1500 mL of ice water to precipitate the picric acid. Decant about 1000 mL of the acid water mix then add another 1000 mL of water. Filter the solution to collect the picric acid crystals. You may purify the crystals as per method one. You will need a stirring rod or magnetic stirrer for mixing.
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