deadrush - 14-9-2024 at 00:25
So I have a small stoppered flask sitting in a 6L pressure cooker. It contains trichloroethylene and 80% H2SO4. The reaction is supposed to be done at
120-140C. I should also mention the flask fits just barely and the lid is actually holding down the glass stopper. So if too much pressure builds up
in it, boom. But boom inside a steel pressure cooker.
Now I decided I want to try this because the pressure cooker acting as a water bath at high pressure should be just the right temperature. In
addition, the stoppered flask when heated will build up pressure and likely turn the trichloroethylene gaseous. I believe if the pressure outside the
flask is similar to inside there's less of a chance of boom. Is this thinking correct?
Also I was wondering if anyone has found a way to use a pressure cooker as an autoclave and hydrogenation aparatus.
unionised - 14-9-2024 at 03:59
" But boom inside a steel pressure cooker."
or "shrapnel" as it's sometimes called.
Tsjerk - 14-9-2024 at 04:46
What is the vapor pressure of trichloroethylene compared to the pressure inside the cooker is what you should be asking.
And pressure cooker == autoclave
[Edited on 14-9-2024 by Tsjerk]
bnull - 14-9-2024 at 05:18
If you want to heat the stuff at 120-140 °C, why not a bath? Cooking oil, silicon oil, paraffin wax. There are many options safer than a pressure
cooker.
deadrush - 14-9-2024 at 16:41
Because trichloroethylene boils at 86C. Hence adding pressure MIGHT enable a completely liquid liquid reaction.
bnull - 14-9-2024 at 18:27
Did you take into account the pressure due to HCl being produced?
I suppose you could try another, safer, way: ether. Not exactly ether, but the way it is produced. Trichloroethylene is slowly added to hot sulfuric
acid at ~140 °C under good stirring. The TCE that boils off is condensed and recovered, while chloroacetic acid stays dissolved in the distilling
flask. The only difficulty remaining is the rate of hydrolysis of TCE. Do you happen to have this information?
clearly_not_atara - 14-9-2024 at 20:29
Probably around 1-5 megapascal. I would be surprised if a pressure cooker could do this. The typical pressure cooker goes to two atmospheres, or about
0.2 MPa.
Alternatively, you can consider the temperature gap. Most pressure cookers heat water to 120 C. About 20 C over its boiling point. You are trying to
heat trichloroethylene to 34-54 C above the boiling point. The exact trend line is different for every substance, but in general the vapor pressure is
a roughly exponential function of temperature.
Verdict: Do not do this. It is not safe and probably not possible.
If you want to hydrolyze trichloroethylene, my suggestion would be that instead of trying to reach the industrial reaction temperature, you could use
a stronger acid. Instead of 75% sulfuric acid/water, which is roughly two moles of H2O for each mole of H2SO4, consider using 10-20% concentrated
sulfuric acid in anhydrous acetic acid, which is a much stronger acidic system because it contains the species H2O2CMe+, the protonated acetic acid,
instead of the hydronium ion. The expected reaction product is 1,1,2-trichloroethyl acetate, which can then be subjected to conventional acid
hydrolysis (or possibly base hydrolysis, but this could destroy the product) at lower temperatures.