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dipotasssium glycyrrizinate
Experiment #1:
Mol weight gl acid: 822.94 g/mol
Mol weight KOH: 56.1 g/mol1. Added 8.23g of the acid (white powder) to a small beaker.
2. Added 0.66g solid KOH. (using 0.1g excess to ensure complete reaction)
3. Added 50mL distilled water.
4. Mix … an immediate reaction occurs, a yellow coloured liquid forms. The mixture is not clear however.
5. Microwave heat to 70C. The solution becomes a clear yellow liquid.
6. Test pH - around 11. Add small amounts of citric acid to get pH=7. The solution colour changes and lightens to a straw colour.
7. Cool down to room temp to see if any precipitation occurs. (Gl acid is only 0.2% soluble at room temp)
8. No precipitation occurs. I now have an intensely sweet straw-coloured liquid.Next step: to evaporate the solution and see if I can precipitate crystals of dpg. Hmm .. it is hygroscopic apparently. Damn, I will need to make a dessicating chamber!
So all you organic chemists out there, is it really this simple?
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12 Replies
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if it’s hygroscopic you’ll have a hell of a job drying it out, even with a desiccator
you could try precipitating it with acetone or isopropyl alcohol then recrystallising it from hot alcohol; it’s a more fiddly method but it’s reliable and it doesn’t need expensive equipment
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I don’t really need the solid form, but I do need to know if my procedure is correct. I can’t find anything on the Web. Only about using KOH to produce DPG from ammonium gl. A replacement reaction by the sound of it.
I guess if I allow for the fact that my acid is 95% pure, adjusting the mol mass by dividing by 0.95 … and I accurately weigh the predicted masses … and accurately determine how much acid/base is needed to produce pH=7, then if it comes close to neutral straight away, I should have DPG. I think. -
Potassium glycyrrhizate (glycyrrhizinate) is commerially available and I am somewhat surprised that your supplier of the free acid form does not supply the salts.
Regarding your method of synthesis, glycyrrhizic acid is a glycoside and susceptible to hydrolysis to form the aglycone - which has somewhat different properties. You may be better adding KOH solution slowly to a suspension of the acid to avoid exposure to high concentrations of alkali.
Be careful assuming the purity and concentration of KOH. Only very rarely does it even approach 90%.
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In organic chemistry recrystallising is an effective purification step. Of course it is possible to analyse a liquid but getting pure crystals with a defined melting point is a first “proof” of that your synthesis has succeeded
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I put the beaker on low heat and evaporated the solution leaving a mass of pale-straw coloured crystals. The mass corresponds to that expected.
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OK. Here is my proposed method. Any criticism welcomed.
GLA: glycyrrhizic acid 95% purity. KOH: High purity potassium hydroxide.
Intent: Synthesise a 25% vw/w solution of dipotassium glycyrrhinate.GLA: 41.2g
KOH: 2.8g
water: 132gDissolve 2.8g KOH in 132g water.
Warm to 50C
Add 41.2g GLA with stirring
When a clear solution is obtained, allow to cool to room temp and check for precipitate (GLA is only 0.2% soluble at room temp)
If not OK, raise temp to 70C and repeat.
Adjust pH as necessary to 7.0
Add 1% preservative (KEM NAT) -
Far easier just to buy the material - one less thing to worry about in getting your formulation standardised.
http://www.magnasweet.com/en/about-us.html
There are other manufacturers.
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I happen to have $500 of the pure acid, do you expect me to throw it away?
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This is the first time you have revealed that you have a stock of the material. I may have been more sympathetic to your circumstances if I had known that and a tortuous thread may have been much shorter.
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http://www.technology-x.net/CN54/201510005226.html has interesting details.
I used a somewhat different method to the one I described above. There are some interesting features to it. For instance, it buffers between pH 3.5 and 6, trying to exceed 6 results in precipitation of - what, exactly? (DPG in solution has a pH of 6 max.) Not the acid, at least I don’t think so. It’s really impossible finding much information about this. I suspect the precipitate is the monopotassium form, but can’t find information as to the solubility of that form. Anyway I produced 400mL of 12% solution. -
After cooling to 3C, no precipitation. Any remaining acid form would have come out of solution at that temperature.
The reaction is to my surprise as fast and complete as an inorganic acid-base reaction such as calcium carbonate and HCl. Titration is the go-to method. The main processing difficulty is dealing with dissolving the acid in hot water, it tends to clump. So then I used a high shear blender to break it all up. This created a Mr Whippy. I found a way of dealing with it but this is getting like writing a book. -
I still have 2Kg of 12% which is a brown powder. I suspect it is the initial extract of powdered root. I’d like to use this in a hair conditioner but I think I’d like to refine it further. Maybe I should dissolve it in alcohol, filter it, and let the alcohol evaporate out so as to precipitate the insoluble acid.
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