1,3,5-trinitrobenzene, also known as sym-trinitrobenzene; s-trinitrobenzene; trinitrobenzeen; trinitrobenzene; trinitrobenzol; benzite; Rcra waste number U234; or just TNB, is a stable high explosive compound with slightly greater explosive force than TNT. There are two other isomers of trinitrobenzene, namely 1,2,4- and 1,2,3- , but they are less stable and harder to form. Trinitrobenzene is very poisonous, causing severe skin irritation, so it is best to use every precaution when handling it. The good qualities of trinitrobenzene are its high stability, great explosive power, and low sensitivity to friction and impact. On the down side, this procedure is not exactly an economical choice since it uses perfectly good TNT as the main ingredient. This procedure is a variant of the original that dates back to 1893 when the German scientists Tiemann, Claus, and Becker observed that trinitrotoluene can be oxidized with nitric acid to trinitrobenzoic acid, and the latter being readily decarboxylated to form sym-trinitrobenzene:
This lab substitutes sulfuric acid and a chromium compound for nitric acid, the reaction is the same either way. There are other methods of forming TNB but this procedure is the easiest and has the highest yield.
|sodium dichromate||500-mL beaker|
|sulfuric acid||small beaker|
Prepare a mixture of 30 g of purified trinitrotoluene and 300 mL of 95-100% sulfuric acid in a tall 500-mL beaker. Slowly add, with stirring, powdered sodium dichromate in small portions, do not allow any lumps to form or powder to rise to the surface. When the temperature of the mixture reaches 40 °C, place the baker into a cold water bath. Continue adding dichromate, while stirring, until a total of 45 g has been added, maintain the temperature between 40-50 °C at all times. After the addition, continue stirring and maintaining the temperature between 40-50 °C for 2 hours. After this time, allow the mixture to cool undisturbed to room temperature over a 12 hour period. Crystals of trinitrobenzoic acid should have formed. Decant off as much of the acidic liquid as possible, then drown the crystals in water. Filter the crystals to collect them, wash with cold water, then transfer them to a small beaker. Add just enough 50 °C water to dissolve the crystals. Filter this solution hot to remove any undissolved impurities, then boil it until no more crystals precipitate. Allow the solution to cool, filter to collect the crystals, then wash them with water. These should be colorless to greenish yellow crystals of trinitrobenzene. You will need a graduated cylinder for measuring liquids, a stirring rod or magnetic stirrer for mixing, and a thermometer to monitor the temperature.
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