morsagh
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Pentaerythritol oxidation
I want to oxidize pentaerythritol to methanetetracarboxylate. I have read about oxidation catalyzed by Pd in NaOH solution with air. Can´t be used
something like permanganate or chromate? Thank for any help
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Boffis
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@morsagh, what an interesting idea! I don’t know for certain if it will work but in alkaline solution I suspect that methanetetracarboxylate ions
will be resistant to further oxidation so providing you keep the solution alkaline you should be OK. It appears from my limited research that the free
acid is unstable and decarboxylates spontaneosuly but I am not sure whether it will loose one or two carboxylate groups (two would give malonic acid
which is stable, I don’t know about methanetricarboxylic acid).
In theory you would need about 6.2g of potassium permanganate per gram of penterythritol and a look at the equation below indicates that KOH would be
formed in the reaction so keeping the reaction mixture alkaline but I think you would need to add a little KOH (I would try about 0.1g of KOH per gram
of penterythritol) at the beginning and monitor the pH throughout the reaction.
3C<sub>5</sub>H<sub>12</sub>O<sub>4</sub> + 16KMnO<sub>4</sub> →
3C<sub>5</sub>O<sub>8</sub>K<sub>4</sub> + 16MnO<sub>2</sub> + 4KOH + 16H<sub>2</sub>O
From my experience of producing carboxylic acids by potassium permanganate oxidation is that the acids are usually isolated by acidifying the reaction
mixture but this process may not be applicable in this case since the acid may decompose. Also the Mn oxide precipitated during the reaction tends to
occludes a good deal of the free potassium in solution and the pH sometimes falls rather then rises as you would expect; hence the need for a little
extra KOH at the beginning. Since most of the other reaction products are removed with the Mn oxide precipitate it may be possible to isolate the
potassium salt by simply evaporating the solution down until it crystallizes, the remaining KOH would remain in solution. Remember to wash the
precipitated Mn oxide well by dispersing it in water and filtering again since as much as 30% of the product can be occluded by the Mn oxide
precipitate. I have found that using more dilute solutions result in a Mn oxide precipitate that is more easily filtered.
If you try this let us know how you get on. I for one, would be very interested in your results. By the way why is this anion interesting apart from
being another of those, often weird and obscure, carboxide anions like carbonate, oxalate, croconate, rhodizonate, acetylenedicarboxylate, mellitate,
squarate etc.?
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morsagh
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I will try tomorrow so i let know you.
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morsagh
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News
So, here i am with results. I slowly mixed 0.2g of penterythritol in 15ml of water with 1.2g of KMnO4 and 0.5g NaOH in 30ml of water. I attach photo
of crystallized penterythritol and the second is photo of my product.
 
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Pumukli
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So it seems you successfully synthesized a SNOWFLAKE! :-)
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papaya
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And then you esterify pentaerythritol with your tetra acid and.. get the highest strength 3D polymeric material ever?
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morsagh
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Good idea, maybe i will add some CCl4 to esterify and see.
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Boffis
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@morsagh, that looks promising. I have been unable to get on the internet for a few days so I was not able to check out the properties of this acid
and its salts other than what I reported above. But many polycarboxylic acids form sparingly soluble but crystalline salts with alkaline earth metals
so I would try mixing a little of your product solution with either calcium or barium acetate if you have them and see if you get some crystals under
the microscope. By the way is the "product" the Na/K salt or have you acidified it?
One comment about the oxidation is that it is better in my experience to add the KMnO4 to the compound being oxidized so that it is always the one in
excess. This minimises over-oxidation.
When you say "add some CCl4 to esterify.." I presume you are thinking about azeotropic distillation as a means of esterification but this would still
require the free acid. I think the free acid will decarboxylate if you try to esterify it by conventional means but you might be able to do this by
precipitating the silver salt and treating the dried product with ethyl iodide or bromide in a suitable solvent. I am not sure what would constitute a
"suitable solvent" but someone on this forum may be able to help there.
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morsagh
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I can´t acidify it because it rapidly decarboxylate. I want to make C(CH2Br)4 from penterythritol and mix with sodium methanetetracarboxylate to
produce NaBr and my polymer.
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Boffis
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Mmmmh... still not sure where the CCl4 comes in but my comment about the use of the silver salt would still be my preferred route with your proposed
starting materials.
By the way how do you intend to get from penterythritol to C(CH2Br)4?
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morsagh
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C(CH2OH)4+H2SO4(conc)+KBr ---> C(CH2Br)4+K2SO4+H2O
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Pumukli
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Primary alcohols react sluggishly with halo-acids, even if they are generated in situ from salts. Concentrated H2SO4 may oxidize
bromide ions to Br2 and may or may not cause additional problems in the synthesis.
You have 4 OH groups in each molecule and you must make a successful OH - Br exchange on all these 4 points else you just waste your reagents.
I think PBr3 would be a more appropriate reagent to use.
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morsagh
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So i can use concentrated H3PO4 instead.
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