Opylation - 12-5-2020 at 12:31
Hello once again everybody.
I’ve been looking at the synthesis of furfural from corn cobs and it seems like this works because of the conversion of pentose sugars into
furfural. Now, to bypass using corn cobs you could just use pentose sugars. I know different pentose sugars are easily purchased online; ribose,
xylose, etc. I was looking through a couple research papers and it looks like xylose is the best sugar to use in the production of furfural followed
by ribose.
Now, this got me thinking how easily could it be to make furfural using this process without having to buy these pentose sugars online?
Well, table sugar is of course sucrose, and sucrose is a disaccharide containing glucose and fructose. Sucrose can be easily hydrolyzed in acidic
solutions under reflux.
This leads to the second part of what I have found. Xylose can be made from glucuronic acid by simple decarboxylation. I found a research paper that
stated glucose can be converted to glucuronic acid using KMnO4 in an 2N solution of NaOH with a yield of 88%. It also stated that a low temperature
should be used to avoid decarboxylation. Well, this is essentially what is desired right?
Well, the paper of the synthesis of furfural says that solution of H2SO4 and NaCl is used to form furfural. Well, starting from table sugar and using
a solution of HCl acid to hydrolyze sucrose into fructose and glucose, then swinging the solution to alkaline using NaOH forming the salt we need and
providing the conditions for the production of xylose. Lastly, neutralize the solution after the formation of xylose with HCl acid again and then use
H2SO4 to form furfural.
To save time and money, avoid isolating the glucose and just run the whole thing in a single pot, except after the oxidizing step. You’ll most
likely want to filter the MnO2 out of the solution before moving onto the furfural production.
Idk, table sugar is super cheap, like a couple dollars a pound. And I’m just spitballing here. Let me know what you guys think. I’m gonna attach
the glucose to glucuronic acid paper
[Edited on 12-5-2020 by Opylation]
Attachment: Glucose to glucuronic acid.pdf (728kB)
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Opylation - 12-5-2020 at 12:58
Thinking a little more about this, the double decarboxylation of the oxidation product of fructose would make a tetrose sugar. Not sure what those
could be used for. Maybe dehydrates to THF? Probably wishful thinking
[Edited on 12-5-2020 by Opylation]
clearly_not_atara - 12-5-2020 at 13:26
The conversion of glucose to glucuronic acid sounds messy. Using sucrose will complicate the process severely because of the presence of fructose
which is difficult to separate. Instead pure glucose should be used such as corn syrup.
KMnO4 is not a particularly desirable oxidant due to its toxicity and difficulties with its production. Furthermore in every case mentioned in Table I
a protected derivative of glucose is used and a protected derivative of glucuronic acid is obtained. This is not promising. Using KMnO4 as oxidant the
cost of the resulting glucuronic acid would be dominated by the cost of KMnO4, not sugar.
See instead the remarkable ultrasound radical oxidation.
https://www.nature.com/articles/srep40650
Opylation - 12-5-2020 at 13:32
I was thinking removing the sucrose would not be necessary. Just leave it in. The second part of that paper also mentions using Pd/C or Pt/C and
atmospheric oxygen. I’ll take a look at that paper you posted. How easy would it be to produce ultra-sonic waves? Are ultrasound devices cheap?
Opylation - 12-5-2020 at 13:39
It also says that regular glycosides can be used. So maybe leaving sucrose unhydrolyzed and performing the oxidation with sucrose and then hydrolyzing
the product?
Boffis - 13-5-2020 at 09:38
Why umpteen separate posts?
I have done a few experiments in this line and I have to say thet even starting from a high grade refined pentose yields of >50% are hard to
obtain. Starting from other sources like glucosamine, gluconic acid, cherry gum etc gave variable but always lower yields. The first is oxidized by
H2O2 into arabinose, this was then treated with sulphuric acid in the presence of isobutyl methyl ketone as a collector but I could isolate no
furfural from the organic phase. I have papers on this procedure.
Another procedure is the fairly vigorous oxidation of sodium gluconate to xylose if I recall correctly which was then subject without isolation to the
same procedure as above. Cherry gum was hydroloysed with dilute acid first, the acid removed with barium hydroxide, filtered and then concentrated to
a syrup. This was diluted with twice its volume of methanol, chilled, filtered to remove a weird deliquescent sugar like compound and the residue
concntrated to a dark brown syrup that was then subject to strong acid hydrolysis and steam distillation. I don't have my notes on this work to hand
but I recall being pleased with the results.
However, pure pentoses give the best results on a small scale with either toluene collection or steam distillation. Good look and be prepared to clean
a lot of black crap out of your flasks afterwards 
!
clearly_not_atara - 13-5-2020 at 10:09
Just based on the geometry of furfural I would expect that you get better yields starting from a 2-ketopentose than from an aldopentose. That way the
aldehyde can be formed by direct elimination of the C2-OH in the cyclic state.
It seems like if you could hydrolyze ascorbic acid's lactone the decarboxylation product would preferentially be a 2-ketopentose.
[Edited on 13-5-2020 by clearly_not_atara]