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Trinitrophenol (Picric Acid)

Picric acid is a cool, but carcinogenic little explosive. It has more power than TNT, but is also more sensitive. In its normal state, it is a yellow solid and can usually show different crystaline forms. The first time I performed this synthesis, the picric acid was grainy. The second time, the picric acid was really flakey and didn't have as great of a density. It can be prepared one of two ways; Nitration of phenol, or using acetylsalicylic acid which will turn into phenol in situ. The latter of the two will be discussed here.

I can not figure out the equation for turning acetylsalicylic acid into phenol, but for phenol into trinitrophenol, it goes like this:

C6H5OH + 3HNO3 ----> C6H2(NO2)3OH + 3H2O

Materials
Equipment
Acetylsalicylic acid 600ml beaker
>94% Sulfuric Acid Thermometer
Potassium nitrate or ammonium nitrate 1000ml beaker
Water Funnel
  500ml flask
   

Wear gloves at all times during this synthesis because it is a carcinogen and it stains like no other. The first step is to sulfonate the acetylsalicylic acid. To a 600ml beaker, add 225ml of sulfuric acid. Place this on a hotplate and heat it to about 90C. While its warming up, add 40grams of acetylsalicylic acid and stir. Keep stirring until all of it is dissolved. If you choose not to extract the acetylsalicylic acid from your asprin (which will still work), use about 42 grams of powdered asprin. Once it gets to 90C, hold it there for about 20-30minutes. After this, bring the temp down to about 70-75C and hold it there. The solution should be a dark black at this point. Measure out 80grams of potassium nitrate (or 65 grams of ammonium nitrate) and begin adding it with constant stirring. You can stop once in a while to let your hands rest, but don't dump any in without stirring it. Add it slowly, because if you add it too fast, it will foam up a lot. The addition should take between 1 hour to 1 hour and 30 minutes. A color change will usually happen during this period. At first, it will be a dark black, then it will become a deep red color. After the last of the addition of potassium nitrate, it usually takes on a reddish color. At least thats what I got. After the addition, keep holding it at 70-75 for another 20-30 minutes. It will change back to a black color during this period.

You now have to get the picric acid out of this black mess. Into a 1000ml beaker, place about 600ml of very cold water and place it in a freezer. Take the 600ml beaker off the heat source and let it cool down to room temp. By the time it cools down, the 600ml of water should have a thin later of ice over the top. Break this ice up with a stirring rod, then quickly but carefully add the contents of the 600ml beaker to the ice water in the 1000ml beaker. This is by far my favorite part of this whole synthesis. The black mess will disappear and a yellow cloud will come out of the solution. Below is a picture of the magnificent precipitation:

Place the 1000ml beaker in a freezer for about 6 hours or so, or until the temperature of the beaker contents reach about 0C. While it is cold, filter the TNP out. By the way, TNP is an acronym used for "Trinitrophenol" which is picric acid. It will take multiple filters. This is your crude TNP. It is pretty much neccesary to purify this, otherwise it will never dry because of the extra acids in it. Save the filtrate since there is more TNP dissolved in it if you feel like extracting it. To extract it, just boil the solution down to between 100-200mls, then cool it to room temp (don't freeze it though). You can filter the crystals that precipitate and purify them also.

Purification:

To a 1000ml beaker, add 300ml of water. Bring this water to a boil. While you are waiting for it to boil, set up some glassware for hot filtration. You can do this by placing a 500ml flask in a pot of boiling water. Put a funnel in the flask and put your filter paper in this funnel. The boiling water will keep the flask warm, and the steam will keep the funnel and filter paper warm. Once the water in the 1000ml flask is boiling, add your crude TNP to it. Leave it boiling until all of the TNP dissolves in it (there will be some impurities left over of course). While its boiling, run it through the glassware that you set up for warm filtration earlier. Discard the filter paper now and pour the contents of the flask into a 600ml beaker. Place this 600ml beaker in a freezer until its down to about 0C. Your TNP will crystalize out. Filter this out and dry it. You can also attempt to get any TNP out of the solution by boiling it down and filtering it out. This is already pure enough to dry with the other batch. From this process, I got 33.7grams of TNP. I did not extract any of this from the solutions, its just the stuff that precipitated.