Picric acid trouble
On this particularly pleasant day, I decided to try my hand at making Picric Acid. Being unable to currently purchase Phenol, and finding aspirin to
be a tad pricey, I decided I would substitute with Salicylic acid since it is on hand in a suitable quantity. I will admit organic chemistry is not my
strong suite, but I concluded I could figure this one out plenty. Many people use acetylsalicylic acid as a precursor to synthesizing Picric acid,
with the first step being the hydrolysis of the acetylsalicylic acid to salicylic acid via sulfuric acid. I figured there would be no problem in
starting from salicylic acid directly and proceeding as usual.
I began by dissolving 1/8 of a mole of salicylic acid, with mild heating (~75 C) and stirring, into 65 grams 98% sulfuric acid. The salicylic
dissolved nicely and rather quickly. As this was happening, I started doing other things, and when I was about to start adding my nitrate salt, 45
minutes after the addition of the salicylic acid, the solution almost spontaneously turned into a thick paste with a light pink colouration with a
strong exotherm (jump to 105 C).
This seemed quite odd, but I figured it was sulfosalicylic acid percipitating due to my sparring use of sulfuric acid. I figured it would be best to
cool the emulsion to a more reasonable temperature, keeping in mind the impending addition of saltpetre, so I did, all the way down to 45 C. I then
added an additional 100 grams of sulfuric acid to try and redissolve the sulfosalicylic acid. This did not seem to do much other than thinning the
now slightly less viscous emulsion. I then cranked the temperature back up to 60 C. At this point I figured what the hell, so I added about a gram of
potassium nitrate to the mix. This resulted in some yellow foaming and slight off gassing of some white fumes, which I figure are nitric acid. I
repeated this a second time but not a third, not wanting to damage my already heavily taxed hood fan.
So my question is: is this a viable route to picric acid (Salicylic acid as precursor) and should I continue adding the remainder of the nitrate
(outside).
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