Eddygp
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Extraction of gluconic acid from sodium gluconate
I have some spare sodium gluconate and I think it would be a good idea to make gluconic acid out of it. My first idea was to add conc. HCl to make
sodium chloride and gluconic acid. I would add cold ethanol to dissolve the gluconic acid and precipitate the sodium chloride.
However, I have found out that gluconic acid is very soluble in water and only slightly soluble in ethanol or other organic solvents.
Having used the FSE and Internet, I have not seen a good easy procedure I can make to extract this troublesome gluconic acid from sodium gluconate.
Could someone help me?
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Vargouille
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You could try converting the sodium gluconate to the calcium salt, and then using aqueous sulfuric acid to precipitate calcium sulfate and solubilize
gluconic acid. The solubility of sodium gluconate (590 g/ L) is much higher than that of calcium gluconate (~30 g/ L). Here is an article about certain gluconates, which might help you in finding a procedure. It is massive, mind you.
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Eddygp
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So should I try calcium chloride, for example?
I mean, that would make sodium chloride as well, which may interfere in the process. When the sulfuric acid is added, the NaCl would also dissolve in
it, not only gluconic acid.
[Edited on 22-12-2012 by Eddygp]
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Vargouille
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I don't mean a one-pot process. What I propose is to add saturated or near-saturated solutions of a soluble calcium salt and of sodium gluconate,
precipitating calcium gluconate and (with any luck) keeping the sodium salt in solution. It would take a bit of calculation to ensure that only the
calcium salt precipitates. Once it does, it can be filtered, washed, and dried. At that point, with minimal sodium ion contamination, it can be
subjected to aqueous sulfuric acid. Calcium sulfate will precipitate, and gluconic acid will remain in solution. There will be a little calcium
sulfate in the resulting gluconic acid, but a recrystallization might be possible if more detailed information regarding solubility can be acquired
(the only information I could find is a solubility of 615 g / L at 20C). Perhaps a mixed-solvent recrystallization would be useful.
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Eddygp
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Location: University of York, UK
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OK, thank you!
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