This is my first post, and i apologize if it is against forum ethics. From what i've seen lurking around here, you guys are quite welcoming to
newbies.
Here's my question - I've been trying to find a (relatively) simple synthesis for oxalic acid for a few weeks, but have come up with
nothing. Yesterday, i had myself a good old brainfart...I was looking at the structures of etylene glycol and oxalic acid on chemfinder, and realized
that they are quite similar in structure. Is there any simple way to oxidize (forgive me if it's the wrong term...i'm still an amateur in
organic chem) the two carbon atoms in ethylene glycol insomuch as to replace the two existing hydrogens with one oxygen, without destroying the carbon
skeleton or replacing the existing hydroxyl groups? Semi complicated proceses are no problem, it's just that my exotic precursor collection is
borderline nonexistant as of yet.
Any and all help would be greatly appreciated.Mephisto - 23-9-2004 at 14:57
Straight from Ullmann's Encyclopedia of Industrial Chemistry, Sixth Edition, 2002:
[color=darkblue]The oxidation of ethylene glycol with nitric acid is a one-step process. ... . An oxidizing mixture of 30 - 40 % sulfuric acid
and 20 - 25 % nitric acid is used. The oxidation is carried out in the presence of vanadium pentoxide and iron (III) salts, at 50 - 70 °C and
atmospheric pressure. Only CO2 is formed as a byproduct. This original process has been improved by the Mitsubishi Gas Company and in Japan
most of the oxalic acid is produced this way (Mitsubishi Gas, US 3691232, 1972). The improved process operates at about 10 bar in a pressure reactor,
in which ca. 60 % nitric acid and possibly also sulfuric acid at 80 °C, is pressurized with oxygen at 3 - 10 bar. Ethylene glycol is then continually
pumped in and the temperature and pressure are maintained by addition of oxygen. The exothermic reaction must be held at a temperature of 50 - 70 °C
by effective cooling. The yield of oxalic acid, based on ethylene glycol, is 90 - 94 % of the theoretical value. The nitric acid used can be recovered
almost completely. This indicates that the nitrogen oxides and nitric acid only act as catalysts and the actual oxidation has been effected by
oxygen.[/color]
Don't worry about loosing your OH group. Only weak oxidizing agents would oxidize to the aldehyde but stop there. It's a pain to stop
there usually. Many oxidizing agents should facilitate this reaction. Then due to the low solubility of oxalate it should start to crystallize out
as it is formed.
The trick with most things is finding the correct conditions that have the highest yield and work at the best rate. For this it is best to find a
reference work. However you could just start from square one and just start experimenting with different mixtures.
Somewhat on topic, what oxidizing agents do you have at your disposal to possibly facilitate this oxidation?Intergalactic_Captain - 23-9-2004 at 18:38
As of now, the only oxidizer i have access to is KNO3. Within the next few weeks, however, i will have access to HNO3 (need to make it), NaClO3, and
KMnO4. The KMnO4 is a bit touchy, however. My method comes from Nemsen's "Inorganic Chemistry", 4th ed. It claims the synthesis by
"fusing" KOH and MnO2 in the presence of oxygen. If it works, i will be a very happy man...if not, i won't have access to KMnO4 for
quite some time.S.C. Wack - 23-9-2004 at 21:18
HNO3 oxidation: US3691232 looks interesting, however - the pressure mentioned in Ullmann is not mentioned here. wtf?
Rhodium links: ning may be mistaken about the 50%. The MSDS says 5-10%. The MSDS of the other product says 10%, as the dihydrate.
Homemade KMnO4: I'd think that there is a thread on this here, didn't look though. Maybe your book is leaving a bit out. The product is
manganate, on boiling in water or on dilution this gives permanganate + MnO2. I recommend boiling the manganate/unreacted crap in a small amount of
water, much easier to crystallize out. Chlorate would be helpful, I think.
KMnO4 here: Well, there must be a patent...which one? There are other oxidation possibilities - glycollic acid, glyoxalic acid, CO2...the yield? In
any case, this has to take place with alkali, or else the permanganate will react with the acid.
But you say that you're looking for simple oxalic acid syntheses, not just from the glycol. Well - sugar, starch, and sawdust have all been
explored. I have some good info on sawdust but not where I can find it. It has already been covered here anyways. From sugar:
"Required: Cane sugar, 20 g.; nitric acid, 100 ml.
Owing to the copious evolution of nitrous fumes, this prepara-
tion must be carried out in a fume-cupboard having an efficient
draught. Place 20 g. of coarsely powdered cane sugar (sucrose)
in a 750 ml. flat-bottomed flask, add 100 ml. of concentrated
nitric acid and heat the flask on a boiling water-bath. As the
mixture becomes warm, the greater part of the sugar dissolves
and a vigorous but harmless reaction, accompanied by a tremen-
dous evolution of nitrous fumes, takes place. Immediately the
evolution of gas starts, remove the flask from the water-bath and
place it on a wooden block or some similar non-conducting
surface. When the reaction subsides (after about 15 minutes)
pour the hot solution into an evaporating-basin, wash out the flask
with about 20 ml of concentrated nitric acid, and then evaporate
the acid solution on the water-bath until it has a volume of about
20 ml. Some oxidation continues in the solution during the
evaporation, which is comparatively rapid. Now add about 40 ml.
of water to the solution, and again evaporate to about 20 ml.
Cool the solution thoroughly in ice-water; oxalic acid rapidly
crystallises. When crystallisation is complete, filter at the pump,
and then recrystallise from a small quantity of hot water. Dry
by pressing between pads of drying-paper, or in an atmospheric
desiccator, but not in an oven where partial loss of water of
crystallisation may occur. Yield, 7 g. The hydrated acid
has m.p. 101°; the anhydrous acid decomposes on heating.
Oxalic acid is poisonous." - Mann and Saunders.Geomancer - 24-9-2004 at 19:55
Not usefull preparatively, but you could drink it. Oxidation to oxalic acid, followed by precipitation of needlelike crystals of calcium oxalate in
the blood, is the primary mechanism for EG toxicity.Theoretic - 24-10-2004 at 10:37
So its actual toxic mechanism is, on end, MECHANIC (CaC2O4 crystals)? The crystals actually damage something so hard it can kill you? That's...
really freaky.
The sugar oxidation is quite inefficient. If you calculate what percentage of the C atoms from the sugar are converted into oxalic acid, you'll
find it has actually a very low yield.
An alternative method is to catalytically dehydrogenate EG and then air-oxidize the resulting aldehyde.neutrino - 25-10-2004 at 08:23
This sounds like HF's toxicology: the F- binds to the calcium to the blood as an insoluble salt. This causes a decrease in the blood calcium
level, leading to a cardiac arrest.BromicAcid - 25-10-2004 at 09:47
Quote:
So its actual toxic mechanism is, on end, MECHANIC (CaC2O4 crystals)? The crystals actually damage something so hard it can kill you?
Partially, calcium is an essential ion in your muscles, if it precipitates your muscles cease to function, for example, your heat is a muscle. (Just
like neutrino said) That is the main knockdown power of oxalates and fluorides. The actual abradtion (from abrade, to grind) power of oxalates and
fluorides is weak, except in areas where they precipitate in mass, such as the liver, they will tear up a liver quite readily, especially if they are
formed there, as is the case from metabolic oxidation of ethylene glycol.
Substances that cause their destructive damage strictly though abrading are somewhat uncommon (among substances taken orally, inhalation is a somewhat
common mode of taking on substances that cause this kind of damage), however one good example is diamond dust.
[Edited on 10/25/2004 by BromicAcid]Theoretic - 26-10-2004 at 13:32
Sorry about that, I myself thought it was improbable the crystals would do mechanical harm, just that I saw the word "needlelike" and
thought oh, so it COULD actually be doing mechanical
damage .
[Edited on 26-10-2004 by Theoretic]macckone - 13-9-2018 at 19:13
In ethylene glycol poisoning the oxalic acid does form crystals and cause mechanical damage. The fatal poisoning is usually from damage to the
kidneys where it mechanically blocks the flow of urine and urea builds up in your body and you die. Having one kidney blocked was excruciating and
the nausea was overwhelming, literally. Mine is from an incorrect break down of protein and sugar in the body, not ethylene glycol but it hurts
anyway. You could also find someone that naturally produces oxalic acid stones and collect them.
