Easy Pyridine Synthesis Pt.2 - Qualitative Analysis
Hi,
I have posted a thread about an easy way to massproduction of pyridine a month ago or so but is was mostly about the theoretical aspect and got to
long and off track. Thats why I decided to start a new one on actual results. The old one: (http://www.sciencemadness.org/talk/viewthread.php?tid=75016#...)
First of all: The reaction composition. I initially went with diammoniumphosphate fertilizer but that stuff was not pure enough and very difficult to
purify. I switched to ammonium sulfate which was too expensive and didn't work and finally I use urea.
(The second reactant is always glycerol).
Urea and glycerol are both cheap and available in pure form. As catalyst I use a small amount of 90% commercial phosphoric acid.
The ratio for this reaction was 130g glycerol, 80g urea and 10g phosphoric. Everything was added to a flat bottom flask and heated. At lower temps
nothing but urea decompusition will happen so you need to heat fast and high. (around 270 - 300°C) The mixture will quickly colour black and first
some ammonium carbamate, then clear liquid will enter the condensor. The flask will be flooded with a white cloud. This destillation is kept alive
until the destillate starts to get yellow. (I continued for testing purposes and finally it was black non water soluble crap, higly condensated) All
of the destillate is collected in a flask filled with a dillute naoh solution to neutralize any acrolein and keep the bases free. If the first "dry"
destillation is done the recieving flask is swapped for the second destillation. The goal is to separate the lighter pyridine derivates using
azeotropic destillation with water (in this case naoh solution).
Therefore destillation is kept up until 100°C (I stopped earlier, because I was impatient). The temp range something came over was 80 to 100°C. I
have collected some data on binary azeotropes (If you want a ref, ask):
Pyridine: 93.6°C
2-Picoline: 93.5°C
2,6-Lutidine: 96°C
Pyrazine(Diazine): 93°C
I didn't find something for collidine or ethyl-pyridine or tertiary or quarternary azeotropes. However these are all pretty close together so one just
collects the lighter fraction. After this second destillation there are two layers in the recieving flask. One large aquous and a tiny organic that is
floating on top. I guess that is lutidine or collidine or other higher alkylated pyridine derivates. This is transferred to a separatory funnel to
recieve the lower water layer.
Now there are two ways I came up with:
- Dry the water layer and fractional destill the bases
- Oxidize the methyl groups with kmno4 and destill off the unaffected pyridine azeotrope + drying
The "yield" of water layer is around 70ml. However this was an incomplete run, so expect around 80.
Some side notes:
- working outside with a sealed aperatus limits the disgusting smell.
- cleaning the glassware needs water and acetone, gloves recommended
- dumping hydrochloric in the cold still seald aperatus (well not the recieving flask) can make the cleaning much more comfortable
- if you get diarrhea you came in contact with too much stuff or vapor.
- use gas wash bottles at the vacuum adapter to trap any leaked bases and excess ammonia
The end of the first "dry" destillation, the first recieving (obvivously I didn't stop early enough but I needed to find that point first), the second
destillation and the two layers.
   
[Edited on 23-8-2017 by subskune]
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