Sunday, October 5, 2014


Recently I've been playing around with growing crystals. It was always a fun and easy thing to do when I was a kid, so I thought I'd try some that are more interesting than the usual salt, sugar, alum, epsom, etc.

This is recrystalized acetylsalicylic acid, asprin, from OTC tablets. 10g pulverized, washed with cold water, vacuum filtered, then dissolved in 250mL of 75C water and allowed to cool slowly. Crystals approximately 3-5 mm in length. I will chill this and allow crystal formation to finish, then wash the crystals and recrystallize at a slower rate.

This is benzocaine, extracted from Oragel tooth gel. 0.5g of gel stirred in 15mL cold water until dissolved. Benzoncaine will form white flakes. Centrifuge and draw off supernatant. Add 20mL water and heat in hot water bath. A bead of molten benzocaine will form. Add sufficient water to dissolve the bead. Allow to cool and crystallize. Vacuum filter and collect for recrystallization.

This is what I think is probably salicyclic acid. 1g of OTC tablets, pulverized, heated in 20mL water until dissolved. When cooled the entire 20mL formed one huge crystal block, which was amusing. Melted again, added 10mL water and heated until acetic acid formed. Cooling produced fine, hair-like crystals, which I suspect are salicyclic acid (more research to do). Washed and vacuum filtered, will recrystallize to see if more pure crystals look different.


After filtering and cleaning a bit more (there were still some components of the asprin tablets in the solution which affected crystalization), I got some recognizable salicylic acid crystals:

I was hoping to get some more acetylsalicylic acid crystals, but I accidentally hydrolyzed them. I'll have to give that try again later. For now I'm bored with salicylic acid, needle crystals are hard to photograph. I think I'll move on to something else.


I had a couple of 50mL beakers with more ASA and SA crystallizing by evaporation. One had mostly SA dissolved in a small amount of isopropanol, and the other was water. They've been sitting for about 5 days doing nothing, and apparently just reached the point where crystals could form. They went from nothing to quite a lot of crystals very quickly.

This one started out with what I think is SA making little needles at the bottom. I left it to evaporate and a few days later this big block formed overnight. I'm not sure if it's ASA or SA. The size suggests ASA, but I'm not sure how completely I hydrolyzed this solution, so I don't know how much of each compound is left. I'm going to let it keep evaporating and see what happens.

This one is the alcohol. It's evaporating faster than the water, and it wants to crawl up the sides a lot more, so it's probably not as likely to make crystals that are as nice. I will probably let this one go for a while until the alcohol is mostly gone and then rinse the crystals and redissolve them in alcohol and try again but with slower evaporation.

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