Lionel Spanner
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Unexpected product in mucic acid dry distillation
Hello all,
I recently carried out a dry distillation of mucic acid, the idea being to produce furoic acid. Instead of the expected product (m.p. 130 °C, b.p.
230 °C), from 27 grams of mucic acid I got 11 grams of a thin water-miscible liquid that boiled at around 80 °C, and oxidised in air from colourless
to brown within the space of about 15 minutes.
Its s.g. is 1.01, and it smells of burnt sugar, though it does not have a strong smell. When conc. sulphuric acid was added to it, it rapidly turned
dark red, and when conc. hydrochloric acid was added, it slowly turned grey to black.
I suspect it's a mixture of water with something else, possibly furan or succinaldehyde.
Any ideas?
[Edited on 13-2-2023 by Lionel Spanner]
[Edited on 13-2-2023 by Lionel Spanner]
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clearly_not_atara
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The list of water-miscible organic liquids with atmospheric pressure bp <100 C is very short, and comprises short-chain monoalcohols, formic acid
and acetaldehyde (bp 20 C). But all of these compounds are quite strongly malodorous. Furfuryl alcohol would explain the odor, but it has a bp 170 C.
Furfuryl alcohol containing some furfural would explain the discoloration as well. I don't believe that unsubstituted furan is particularly reactive
in air, and it has a low water solubility.
But I am afraid I just don't know any volatile organic liquids that don't stink. The natural conclusion is that the distillate contains a high
fraction of water, suppressing any odors.
[Edited on 04-20-1969 by clearly_not_atara]
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Texium
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It’s also possible (and likely) that higher boiling organic compounds were carried over with the water, as in a steam distillation.
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Lionel Spanner
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It's a puzzler for sure. The furfural explanation seems most likely.
A little while back, I attempted to produce pyrrole by dry distillation of ammonium mucate, and got a very poor yield because I heated the distilland
too strongly and burned it.
At some point I will repeat both experiments, and take the heating step nice and easy this time round.
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Lionel Spanner
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An update: this is a full account of an attempt at dry distillation of mucic acid.
Mucic acid (31.7 g, 0.15 mol) was added to a two-necked 250 mL round bottomed flask, which was incorporated into a simple distillation apparatus; the
second neck contained a thermometer which was immersed in the distilland. The flask was heated gently with a gas burner.
Almost immediately, the powder at the base of the flask began to darken and turn to liquid. As the temperature increased beyond 150 °C, the
distilland started releasing a vapour that condensed as a yellow liquid that turned orange over several minutes' exposure to air, and also
periodically released white vapour that was heavier than air, whose vapour pressure reduced significantly in the condenser, and was reduced to
negligible levels when the receiving flask was cooled in a cold water bath. The total yield of orange liquid was 13 g, its s.g. was 0.96, and its
odour was similar to that of burnt sugar. Its pH was approximately 3.
When the mixture stopped releasing these products, and a clear liquid, not yet boiling, started to condense in the junction above the flask, heating
was ceased and the apparatus was cooled to ambient temperature; during cooling, it was observed that the liquid parts of the distilland solidified.
Industrial methylated spirit (100 g) was added to the flask, mixed thoroughly, and filtered by vacuum to yield a clear dark brown filtrate, which was
concentrated by boiling. Once the filtrate had reached approx. 20 mL in volume, deionised water (50 g) and activated charcoal (1 g) were added, and
the mixture was crudely refluxed for an hour before being gravity-filtered. Filtration yielded a dark red acidic filtrate (pH around 2), which was
concentrated to approx. 10 mL by boiling, before being cooled to ambient temperature and cooled overnight in the fridge.
On cooling, the filtrate became turbid and yielded a small amount of fine brown solids, which were not separated or quantified. If the precipitated
solids contained furoic acid, it would represent a very low yield of very impure product.
The distillate was stored for future use.
[Edited on 25-2-2023 by Lionel Spanner]
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Lionel Spanner
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The combined distillates from both reactions were basified to pH 14 with 25% caustic soda solution; the colour darkened to brown, some sediment was
observed, and the burnt-sugar smell became a weaker, glue-like odour. The distillate was filtered by gravity, yielding a dark orange filtrate. A
sample was weighed onto a watch glass, which was placed in the oven at 125 °C for 10 minutes, yielding a solids content of approximately 26% w/w.
It appears there is an acid of some kind in there, and I've produced the sodium salt of it; the acidic distillate boils without a trace. Will update
with further developments.
[Edited on 2-3-2023 by Lionel Spanner]
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Lionel Spanner
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The filtrate was distilled to dryness, yielding dark brown solids, and a clear distillate with a slight odour of glue, s.g. 0.97, pH approximately 7.
The distillate was acidified to pH 3 using 15% sulphuric acid and re-distilled to yield a few milligrams of dark brown solid and a clear fluid, pH
approximately 4, which became slightly turbid on standing, with some precipitated solids. This was placed in the fridge, yielding no further solid
material.
The distilland was washed with acetone (50 mL), redissolved in deionised water (50 mL) and acidified to pH 3 with 15% sulphuric acid, resulting in
effervescence and gas evolution. On standing, some sedimentation was observed, and the mixture was concentrated to approximately 15 mL by boiling,
then placed in the fridge. The concentrated solution turned to a paste (10.6 g recovered), which was mixed thoroughly with ethyl acetate (30 g). The
ethyl acetate extract was boiled dry, yielding 0.5 g of a dark brown solid substance that formed acidic aqueous solutions (pH approx. 3), was
sparingly soluble in water at room temperature and much more so at higher temperatures, and had a melting range similar to that of furoic acid.
Due to its low yield and purity, no attempt was made to refine this product further.
This does at least confirm that furoic acid can be made from mucic acid, but it's not a useful process for making significant quantities of pure
product.
[Edited on 11-3-2023 by Lionel Spanner]
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Alucard
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Quote: Originally posted by Lionel Spanner  |
This does at least confirm that furoic acid can be made from mucic acid, but it's not a useful process for making significant quantities of pure
product.
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It's well known that dry distillation of mucic acid leads to furoic acid, but this technology is too old and not very effective.
Pyromucic acid is an another name of furoic acid, by the way...
Anyway thanks for sharing your own experience, I enjoyed reading this topic.
[Edited on 11-3-2023 by Alucard]
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clearly_not_atara
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Recently my thoughts came back to this.
https://www.mdpi.com/2073-4344/13/7/1114
In the above paper a high selectivity for 2-furoic acid formation from mucic acid was achieved by autoclaving in dimethyl carbonate at 200 C with
catalytic hydrotalcite. However, this was not the desired product, so the authors didn't investigate further. My thoughts:
- The authors credit hydrotalcite for promoting the first decarboxylation. This is pretty convenient.
- The desired rxn is unimolecular; using a solution of mucic acid instead of the pure substance should suppress intermediate reactions in favor of the
production of furoates
- The autoclave was necessary because dimethyl carbonate boils at 90 C. If a high-boiling solvent is used, this should not be necessary.
- It's possible that methylation of the carboxylic acid moiety increased the selectivity over the undesired pyrone. Unfortunately this might be hard
to do pragmatically.
Ethylene glycol (bp 197 C) seems like a good choice of solvent. It's not clear if this will give an esterified product. Anyway, refluxing mucic acid
in EG with hydrotalcite for 2h is a relatively simple procedure.
EDIT: it seems like the much more common saccharic acid aka glucaric acid might undergo the same reactions
[Edited on 5-3-2024 by clearly_not_atara]
[Edited on 04-20-1969 by clearly_not_atara]
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