Nitric acid

Nitric acid, or hydrogen nitrate, is a very common laboratory acid with a wide array of uses. One of the main uses is for nitrating various compounds. There are many explosives based around nitro groups, which makes nitric acid incredibly useful as an explosives precursor. I plan to use nitric acid to make 4-nitrotoluene which in turn I will eventually use to synthesize a local anesthetic called benzocaine.

Nitric acid is usually supplied at an azeotropic concentration of 68%. However the nitric acid produced in this procedure is almost pure.

To a 1000ml round-bottom flask, I added 101g of powdered potassium nitrate and 54ml of 98% sulphuric acid. I then quickly set the flask up for simple distillation with the receiving flask in an ice bath. I then began distilling the mixture at a medium heat, gradually increasing the temperature whenever the yellow nitric acid stopped coming over. At the start of distillation, the flask was full of red nitrogen dioxide gas. This quickly faded to a yellow once the nitric acid started coming over. Gradually increasing the temperature throughout distillation is needed to free the nitric acid from all the sulphate salts formed. Pure nitric acid initially comes over at about 70-80 C then later on, azeotropic nitric comes over at over 100 C. However the vapour temperature was never allowed to rise above 100 C, so when nothing came over below this, the distillation was ended.

I collected the yellow nitric acid in the receiver and transferred it to a glass bottle for storage. I got 38ml of practically pure nitric acid which corresponds to a 91% yield.

Such concentrated acid is very dangerous, and despite what one might expect, its best to wear no gloves at all when handling it since anything above 87% nitric acid can ignite latex and nitrile.
The yellow colour of the nitric acid is due to a small amount of decomposition to nitrogen dioxide. This really isn't a problem though, as the contamination is very minimal.

KNO3 + H2SO4 ==> KHSO4 + HNO3