deadrush
Harmless
Posts: 16
Registered: 3-3-2014
Location: Worcester MA
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Thermal decomp of Salicylic acid -> phenol - odd results
As the title says, that is what I did. I used a bunsen burning w/ propane and heated a rbf attached in a vacuum distillation setup. Admittedly, there
were a few hiccups, the biggest being the condenser filling with sublimated salicylic crystals and eventually clogging. However, there was a
significant quantity of light pink throughout the clog. I scrapped all the precipitate out and dissolved in excess distilled water. Now, there was a
small amount i could not manage to get into a solution. I decided to try heating and stirring. I threw the beaker in a microwave for 1.5min.
Afterward, I moved the hot beaker to a stir plate.
Now, here is where it gets strange. After 3 or so heat & stir cycles, I noticed crystals forming on the bottom, white/ clear ones, at the peak
temperature. This happend everytime I removed the beaker from the microwave. After cooling and stirring 98% of solids were in solution.
From all the possible outcomes from thermal degradation of salicylic acid, i could not think of one with reverse solubility.
So I do plan on attempting to isolate what phenol I can from this if any. Any suggestions?
I also plan to redo the experiment in its entirety. If i change to a lieberg condenser and a oil bath for heating, that would solve the sublimation
problem right?
  
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Pumukli
National Hazard
Posts: 694
Registered: 2-3-2014
Location: EU
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I'd try adding NaHCO3 or Na2CO3 to the solution in excess then extraction with some water-immiscible solvent. Ethyl-acetate would be nice but there
are others too. Water phase: unreacted salicylic acid as sodium salt, organic phase: phenol (and possible other things).
At least this behaviour is what I would expect.
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