some of you may know that I am currently approaching pyridine synthesis. Unfortunately my reagents did not arrive yet so I tried myself today on
propylene carbonate.
I started adding 200ml propylene glycol, 1.2g zinc oxide and 110g urea to a flat bottom flask. On top I placed a 3-way Vigreux column. The top hole
was pluged with aluminium foil and plastic wrap, the side connection was attached to a hose. The hose led to a primitive aspirator pump in a bath of
sulfuric acid to trap the ammonia. The vacuum was not very strong but sufficient enough. This was allowed to reflux for 2h.
Afterwards I conducted a shortpath destillation with air cooling what worked really well (There is a hose at the vac adapter but no pump attached
to!). I collected a large fraction at 187°C which I suppose to be propylene glycol and a second equal sized fraction at 238°C which I believe to be
crude propylene carbonate. The stuff was yellow and did smell horrible. I repeated the same destillation on that and recieved a yellow small fraction
at 170 to 195°C. The temperature then rose quickly to 238°C and I collected a large slightly coloured fraction with a density of 1.2g/cm3 and a
fruity / stinky smell. First it smells fruity then like burned urea. The yield after the second destillation was 45% until I tossed the flask
Finally I put it under molecular sieves to dry it and activated charcoal to get rid of the urea polymer crap.
Here are some pics:
[Edited on 9-7-2017 by subskune]
[Edited on 9-7-2017 by subskune]clearly_not_atara - 9-7-2017 at 11:29
You tossed the flask? Like across the room? Or it slipped out of your hands?
Anyway, sounds like a job well done, although I can't tell if your product is now in a jar or all over the floor...subskune - 9-7-2017 at 11:37
I leaned the flask against the wall and touched it (ahhh what stupidity to lean a rfb against the wall). The majority blasted across the room like an
explosion - not really it just pooled on the table. The remainings can be seen in
pic4.Vosoryx - 18-7-2017 at 17:16
Didn't really know where else to post my findings on this topic, so i'm here.)
I am too trying this synthesis. (To win the hotplate from http://www.sciencemadness.org/talk/viewthread.php?tid=74020. My failure can be found there)
During it, I accumulated a large amount of some white crystalline powder in the condenser, much more than had been reported in any post I have found
on this experiment. (Including you) I believe that this is because of the absence of a vacuum pump on my end, and everyone else having a vacuum. Being
that I had much more of this material, I decided to try to use it to figure out what it is. One suggestion was ammonium carbonate, so I decided to
test the melting point of it. (Ammonium carbonate melts at 54 C.)
I put some of the powder I had in a beaker in a water bath with a thermometer, and turned on the heat. It passed 54, and the water started bumping
quite heavily around 80. I was worried about dislodging the beaker from my lab stand, so I turned down the temp and tried to keep it in the 75-85 C
range for about 10 minutes. (Just to make sure the inside of the beaker came up to temperature.) When poked, the material crumbled slightly easier
than when it is cold, but did not melt. I believe that is evidence against the ammonium carbonate theory. subskune - 19-7-2017 at 01:42
It might be ammonium carbonate or ammonium carbamate. However this white stuff smells like ammonia which means that it decomposes and it does only
sublime not melt. That means that it is one of those two candidates.
Now to your failure: Not the greatest failure you did. If your reflux mixture gets yellow you refluxed too long (second looks better). Your propylene
carbonate will be impure. The colour ramp is clear, yellow, red, brown (hazy).
I really reccomend a 1l flask and 340g propylene glycol to 220g urea.
That gives you 140ml ~ 170g of propylene carbonate each run. The time for this is approx. 2:30 to 2:45. The amount of white crap is somehow
proportional to the water content of your mixture and if you dry your reagents you can ignore it.
Add boiling stones best some silicia gel kitty litter. This will help ammonia removal. Build a proper trap for the ammonia (not necessary but there
will be up to 120l of that!). Calcinate your zinc oxide at 500°C for 4h.
The destillation: Don't go for fractional, it does loose too much heat. Use shortpath instead, you don't even need a water condensor. Wrap all in foil
and in kitchen towel (I did this in my last run and it works really well). Dont recive anything below 232°C. Thats the point where my thermometer has
an accuracy of +- 5°C and thats the correct fraction. Stop if it exceeds 242°C.
nice to eventually have a buying option. for me its too late, I spent the time, further optimized this synth. switched to ethylene carbonate for
higher yield, directly from fertilizer and antifreeze.Hunterman2244 - 27-6-2018 at 05:35
it just pooled on the table. The remainings can be seen in
pic4.