Has anyone tried a Stas-Otto extraction ?

I don't have journal access so my investigations are somewhat incomplete but the process seems to have some advantages over other extraction methods.

So the general concept is

1 - soak the powdered, sieved crude material in 90-95% ethanol that has been acidified with tartaric acid using the ratio of 1 litre ethanol to 1 kg crude material. I couldn't find any references to boiling at this stage only heating in some descriptions. Some sources say to filter off the ETOH and repeat this step once.
2 - distill or evaporate the alcohol off, leaving an aqueous suspension/residue of alkaloids, fats, waxes, oils etc
3 - Defat with toluene (could be a solvent saver due to the reduced volume after removing the ETOH) Xylene could probably be used here too.
4 - Evaporate the aqueous solution containing the alkaloids
5 - Extract the alkaloids with a suitable solvent.

So as I said my investigations are incomplete but this method seems to have some merit. For a plant material like cactus when soaking/cooking in ETOH the powdered cactus doesn't adsorb the ethanol like it does in water. It expands a bit but nothing like it does in water, so filtration after soaking is much,much easier and pressing/squeezing is not as much of a problem.

Greatly reduced volumes of ETOH are used compared to methods using water in the primary phase and a lot less energy is used during cooking. I even suspect that cooking to boiling point may not even be necessary. One caveat though the 1 kg to 1 litre of ETOH is described as the ratio for crude drug material - so that could be inadequate for some starting materials.

Defats would be done on a greatly reduced volume of aqueous solution which may or may not reduce solvent usage.

I'm still not clear on the entire process as I haven't tried it yet and there are several different solvents used for the final extraction that need to be selected for the alkaloid of choice. Some articles state the final extraction is done with acetone to extract the total alkaloids.

In many cases it seems to done in an acidic solution to extract the total alkaloid profile of the plant in question and acetone or chloroform seem to be the solvents used. I think the solvent would have to be selected to suit the alkaloids you want to extract here.

Maybe it could be taken one step further and basified and extracted with more selective solvent on a greatly reduced volume of soup to extract specific alkaloids that could be salted of just freeze precipitated at the end of the of the process.

scihub.cc


Interesting post. If I give it a try sometime, I'll report back.

Thanks for that link downwarfromzero, I can see myself browsing there quite a bit.

Alcohol extractions used to be quite common about 10 years ago. People would extract cactus with ETOH (sans the tartaric acid) and then mix the residue with flour to make goo balls that they would eat. The Stas-otto method seems to be similar in some ways but a lot more efficient.

My initial investigations have gone quite well & were mid way between a STB and water boil extract in time and effort and it certainly saves a lot of energy and greatly simplifies filtering, so it's well worth checking out.

I've none done a side by side with an A/B on the same quantity of starting material though, so I can't give any details about efficiency as far as yield is concerned. For me it's a much easier method than A/B.