deadrush
Harmless
Posts: 20
Registered: 3-3-2014
Location: Worcester MA
Member Is Offline
Mood: Fungible
|
|
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?
  
|
|
|
Pumukli
National Hazard
Posts: 697
Registered: 2-3-2014
Location: EU
Member Is Offline
Mood: No Mood
|
|
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.
|
|
|
chemister2015
Harmless
Posts: 30
Registered: 25-2-2015
Location: Russia, Khabarovsk
Member Is Offline
Mood: No Mood
|
|
Salicylic acid decomposes above 280 C in stream of nitrogen to phenol and xanton. The vacuum interferes with this process.
|
|
|
![[*]](images/xpblue/default_icon.gif){kind=icon}
