elementcollector1 - 3-2-2013 at 16:45
DISCLAIMER: This is not a cheap method of getting chromium.
I've been thinking of preparing some chromium(III) salts from chromium picolinate, a nutritional supplement.
First off, what to do about all the other compounds? Just on the label, this product contains approx. 500 mcg chromium (III) picolinate (duh), calcium
phosphate, and cellulose (lists 'plant origin'). Less than 2%: Croscarmellose, Glycerin, Silica, sodium citrate, "Vegetable" magnesium stearate.
500mcg x 100 tablets = 0.05g per every 100 tablets. I could crush up 2,000 tablets and get 1g, but... it depends on how many bottles of this stuff I
want to buy. Unless each of these are less than a dollar, probably going to stick with buying 1 and using that. In other words, this is going to be
VERY small-scale extraction.
Now, this is not a preparative synth: I certainly do not wish to make large quantities of whatever Cr(III) salt may result from these experiments. I
do, however, want to have small amounts of 'reference' chromium (as in, pure) to compare the scaled-up stuff to.
To get rid of the other compounds, my first guess would be to add hydrated sulfuric acid to the finely ground tablets, precipitating calcium as
sulfate, converting sodium and magnesium into soluble sulfates, and leaving picolinic acid, citric acid, and cellulose (which may react to produce
carbon). Any solid products are filtered off, and the solution should be green (at least mildly). Next, the chromium and magnesium are precipitated as
hydroxides by the addition of Na2CO3, and this product is filtered off.
Finally, the magnesium is separated by an unknown process that I can't seem to figure out.
Now, I know I'm ignoring the stearic and picolinic acids, as well as the phosphoric acid. Hopefully I can get rid of these by addition of base to make
the (hopefully soluble) sodium salts. Stearic acid is barely soluble in water (3 mg/L), sodium phosphates are slightly soluble (anywhere from 2-80g /
100mL, depending on hydrogen content), and picolinic acid is very soluble, at 89g / 100mL.
What do you think: Worthy just-for-fun endeavor? Or lost cause in the making?
DraconicAcid - 4-2-2013 at 09:21
Chromium(III) picolinate is not going to be very labile (Cr3+ complexes usually aren't), and it's a neutral complex. It will probably be more soluble
in organic solvents than in water (13th Merck Index says it's solubility in water is 0.6 mmol/L, and 2.0 mmol/L in chloroform, so it's not very
soluble in either). I'd try extracting with an organic solvent such as methanol or acetone. That won't dissolve calcium phosphate, silica, or
cellulose, but it should dissolve your stuff. The evaporate to near dryness, and treat with hot nitric acid (carefully!). If the picolinate ligands
don't want to come off, you rip them to shreds. This will also destroy glycerol, stearic acid, along with any citrates that happened to dissolve.
elementcollector1 - 4-2-2013 at 09:26
Sounds good to me. I've got some acetone that needs to be cleaned of FeCl3, and this is a perfect excuse.