p-Nitrobenzoic acid is light yellow in crystaline form. It is made by the oxidation of p-Nitrotoluene. Oxidisers to use include, but are not limited to: potassium permanganate, sodium dichromate and nitric acid. This synthesis will revolve mainly around the use of potassium permanganate.
C6H4(NO2)CH3 + 2KMnO4 ----> C6H4(NO2)COOH + 2KOH + 2MnO2
|p-Nitrotoluene||500ml Rould bottomed flask|
|Potassium Permanganate||Oil bath equipment|
|Ethanol||400mm reflux column|
|Hydrochloric acid (Prep/OTC)||Filtration equipment (vacuum optional)|
|Sodium Hydroxide||1000ml Flask|
|Decolorizing charcoal||500ml Flask|
Into the 500ml round bottomed flask, add 5.0g of p-Nitrotoluene. To this, add 11.5g of potassium permanganate, followed by 150ml of distilled water. Insert the reflux column into this flask and place in the oil bath. Start a constant flow of cold water through the reflux column and reflux this solution for 16 hours. After this point, remove the flask and reflux column from the oil bath. Once it stops visibly boiling inside the flask, shut off the cooling water. Remove the reflux column and add 1ml of ethanol to this black-ish solution. The ethanol addition is not neccesary, but will make your life easier by removing the unreacted potassium permangante (if there is any). Pour this solution into a 500ml beaker, then add some distilled water to the flask. Swirl the flask around a bit, then add this to the 500ml beaker as well. Wait for the manganese dioxide to settle to the bottom of the beaker. Filter this solution out using two coffee filters folded together as the size of the particle of manganese dioxide will slip through a single coffee filter. Make sure all of the manganese dioxide makes it into the filter too, as there is still a bit of product in there. Once the 500ml beaker is empty, fill it up with 400ml of distilled water and begin boiling it. Once it is boiling, pour it through the manganese dioxide in the filter. This part will take a lot of patience. Even with a vacuum filtration set up this will take a while. Just bear with it. Once all of the water is through, discard the filter and contents. If you wish to keep the manganese dioxide; leave the filter paper out to dry to purify it later.
You should now have a dark solution. Almost the color of coca-cola. It should be basic due to the potassium hydroxide. The p-Nitrobenzoic acid will form a potassium salt with the potassium hydroxide which is why it is soluble in the water right now. To isolate it, acidify the solution with hydrochloric acid. Soon a precipitate will be formed and will gradually float to the top. This is crude p-Nitrobenzoic acid. Place this solution containing the precipitate in the fridge to make sure all of the p-nitrobenzoic acid has been precipitated. Filter the solution to obtain this p-nitrobenzoic acid. Into a 250ml beaker, place 3g of sodium hydroxide. To this, add 100ml of water and begin heating it on high. While it is warming up, add the crude p-nitrobenzoic acid. Once the majority of it is off the filter paper, dip the filter paper into the solution to get the remains off, then pour a small ammount of water over the filter. Discard the filter paper. This will form a solution of sodium nitrobenzoate. Bring this solution up to a boil and leave it there for 5 minutes. After this point, turn the heat off and let it cool down slowly. When it reaches room temperature, acidify the solution with hydrochloric acid. This will precipitate the p-nitrobenzoic acid. Place this beaker in a fridge overnight to ensure that all of the p-nitrobenzoic acid has precipitated. Pour the contents of this beaker through filter paper. Add some cold water to get the remaining crystals of p-nitrobenzoic acid out of the beaker and pour it into filter as well. Lastly, pour a small ammount of cold water through the filter to wash any remaining hydrochloric acid away. Open this filter up and set it some place to dry. Theoretical Yeild is 6.09g
-For some reason, when I attempted this synthesis, my p-nitrobenzoic acid came out brown. I can not explain this unless somehow the manganese dioxide was trapped in the crystal lattice during the oxidation. Though I don't know why it stayed in there when this stuff was neutralized and dissolved in water.