Hexabromobenzene
Hazard to Others
Posts: 128
Registered: 27-4-2021
Member Is Offline
|
|
Propanoic acid from plexiglass
PMMA plastic(About 1 kg) was pyrolized and about 1 liter distillate was obtained(About 80% methyl methacrylate).
100ml plastic distillate(without repeated distillation) mixed with 55 gr KOH in 400ml water on a magnetic stirrer. Plastic distillate quickly
dissolved(About 5-10min).
The mixture was placed in a distillation setup and collected fraction to temperature 100C(methanol can be obtained from distillate). Also methanol can
be evaporated off in well ventilated area
After distillation water solution was placed in stainless pot and continued to evaporate until crystals are formed. 100 gr KOH was added and mixture
heated until melting and was fused about 40 minutes(very much)
DO NOT OVERHEAT. CAN IGNITE DUE STRONG GAS EVAPORATION(ETHANE and other) FORMED BY DECOMPOSITION PROPANATE
After cooling in molten salt was added water and battery sulfuric acid(37%) 500 ml and mixture was distilled. Collected fraction 99-100C
Do the distillate slaked lime was added. 40 gr salt was obtained. Yield about 40% theoretical сonsidering crude acrylate
This salt do not bleaches acid permanganate solution unlike potassium methacrylate.
NOTES
Sodium hydroxide also works
40 minute it much. 5-10 minute fusion enough.
Crude methyl methacrylate need to distill.
Propanoic acid may be use to propiophenone preparation
|
|
|
Boffis
International Hazard
Posts: 1879
Registered: 1-5-2011
Member Is Offline
Mood: No Mood
|
|
Hello Hexabromobenzene! well done! That's an impressive amount of PMMA to distil. What sort of equipment did you use? Is borosilicate glass suitable?
Does the hydroxide inhibit re-polymerisation of the free acid/salt? If potassium methacrylate is formed and stable this would be an interesting
intermediate
|
|
|
Hexabromobenzene
Hazard to Others
Posts: 128
Registered: 27-4-2021
Member Is Offline
|
|
I distilled up to 5kg PMMA in stell retort in wood burning furnace. Stell paint container works great. This is interesting procedure. But i do not
know what to do with so much MMA monomer 
Methymethacrylate with few drops hydroquinone is stored no problem for about 4 years in the garage. It slowly diffuses through HDPE
Potassium methacrylate must be stable in dry form
[Edited on 13-11-2021 by Hexabromobenzene]
[Edited on 13-11-2021 by Hexabromobenzene]
|
|
|
unionised
International Hazard
Posts: 5128
Registered: 1-11-2003
Location: UK
Member Is Offline
Mood: No Mood
|
|
I can't see how this produces propanoic acid.
I accept the sequence
Perpex to
methyl methacrylate to
potassium methacrylate.
But I can't see how heating that gives propanoate.
I'd expect decarboxylation to isobutylene or some such.
(EDIT I lost count of the carbons; the product should be propene)
Am I missing something?
[Edited on 13-11-21 by unionised]
|
|
|
macckone
Dispenser of practical lab wisdom
Posts: 2168
Registered: 1-3-2013
Location: Over a mile high
Member Is Offline
Mood: Electrical
|
|
Decarboxylation will yield propene which will hydrolyze at the double bond.
that gives 1 and 2 propanol with 1-propanol being the minor product but it would oxidize to propionic acid.
Decarboxylations are usually around 50% yield.
The propene hydrolysis would probably give around 20 or 30% yield of the desired 1-propanol.
If the hydrolysis takes place before the decarboxylation then the yield of 1-propanol is going to be much higher.
ie. close to 100%. Which given the claimed yield it would seem that it is undergoing alkaline hydrolysis as part of the ester cleavage step.
So it isn't potassium methacrylate but rather a funky isobutyrate with an alcohol group.
I am still not clear on how the oxidation is happening but at high temperatures with oxygen it should be spontaneous.
The haloform reaction on MEK would be much higher yield and not have to deal with tar and crap.
[Edited on 13-11-2021 by macckone]
|
|
|
unionised
International Hazard
Posts: 5128
Registered: 1-11-2003
Location: UK
Member Is Offline
Mood: No Mood
|
|
This looks very fishy to me.
A series of three reactions, only one of which is plausible- the decarboxylation .
Propylene isn't going to hang around- it will boil off immediately.
And the next step- the conversation to the acid seems to be driven by wishful thinking.
|
|
|
Hexabromobenzene
Hazard to Others
Posts: 128
Registered: 27-4-2021
Member Is Offline
|
|
It's a Varrentrapp reaction. Methacrylate with molten alkali gives propanal which oxidizes to propanate and release H2
Also it gives formate which immediately decomposes to carbonate
https://en.wikipedia.org/wiki/Varrentrapp_reaction
the reaction takes place at a temperature of up to 300 degrees. Decarboxylation occurs at 400-500. Sodium hydroxide give lower yield may be due to
high melting temperature temperature(300-320). Potassium hydroxide solution has no phase transition when heated . Water needs to this reaction
Some potassium hydroxide need to added to lower the melting point
[Edited on 13-11-2021 by Hexabromobenzene]
|
|
|
macckone
Dispenser of practical lab wisdom
Posts: 2168
Registered: 1-3-2013
Location: Over a mile high
Member Is Offline
Mood: Electrical
|
|
That mechanism is interesting and confirms my speculation although not exactly.
The alcohol is formed as an intermediate.
So when the decarboxylation happens you are going to an aldehyde radical which forms the acid with water.
So it isn't really potassium methacrylate as the intermediate.
It is hydrolyzed.
|
|
|
unionised
International Hazard
Posts: 5128
Registered: 1-11-2003
Location: UK
Member Is Offline
Mood: No Mood
|
|
Apologies for my cynicism.
A rather odd reaction.
|
|
|
macckone
Dispenser of practical lab wisdom
Posts: 2168
Registered: 1-3-2013
Location: Over a mile high
Member Is Offline
Mood: Electrical
|
|
Unionised,
Yes, I haven't seen that mechanism before.
But it makes sense when you look at it.
|
|
|
draculic acid69
International Hazard
Posts: 1371
Registered: 2-8-2018
Member Is Offline
|
|
Quote: Originally posted by Hexabromobenzene  | It's a Varrentrapp reaction. Methacrylate with molten alkali gives propanal which oxidizes to propanate and release H2
Also it gives formate which immediately decomposes to carbonate
https://en.wikipedia.org/wiki/Varrentrapp_reaction
the reaction takes place at a temperature of up to 300 degrees. Decarboxylation occurs at 400-500. Sodium hydroxide give lower yield may be due to
high melting temperature temperature(300-320). Potassium hydroxide solution has no phase transition when heated . Water needs to this reaction
Some potassium hydroxide need to added to lower the melting point
[Edited on 13-11-2021 by Hexabromobenzene] |
I seen acetyldehyde reacts with NaOH to give Na acetate and benzene so it's probable any propanal would turn to propionate
|
|
|
![[*]](images/xpblue/default_icon.gif){kind=icon}
