This post will be about historic methods used for the extraction of organic chemicals, especially organic acids and plant-derived alkaloids, with a special focus on the extractions done by Carl Wilhelm Scheele (1742 - 1786) and Henri Braconnot (1780 - 1855).
Regardless of who first extracted them, I also hope to touch upon these organic acids: (abietic, acetic, ascorbic, aspartic, benzoic, butyric, caffeic, citramalic, citric, ellagic, folic, formic, fumaric, galacturonic, gallic, glucuronic, glutamic, glutaric, glycolic, isocitric, lactic, maleic, malic, mycophenolic, nicotinic, oxalacetic, oxalic, p-coumaric, pantothenic, pectic, propionic, pyrogallic, pyruvic, quinic, salicylic, shikimic, sorbic, succinic, tartaric, uric)...
And these alkaloids: (aconitine, anisodamine, anisodine, berberine, boldine, coniine, ephedrine, caffeine, cephaeline, chaconine, chelidonine, cinchonidine, cinchonine, cocaine, colchicine, cytisine, ecgonine, emetine, ergine, ergotamine, erythravine, galantamine, harmaline, harmine, huperzine A, hyoscyamine/atropine, ibogaine, ibogaline, ibogamine, lobeline, lupinine, mescaline, morphine, nicotine, pentoxifylline, physostigmine, pilocarpine, piperine, protopine, psilocin, psilocybin, quinidine, quinine, reserpine, scopolamine/hyoscine, solanine, strychnine, theobromine, theophylline, tomatine, vinblastine, vincamine, vincristine, yohimbine).
This all started when I was reading about Henri Braconnot. He discovered pectin, glycine, chitin, ellagic acid, legumin, and nitrocellulose, among other things. The more I read about his discoveries, the more I felt that modern scientists have lost the knowledge of how we used to get our organic chemicals, where once this knowledge was common across the scientists of Europe.
Scheele was an ever greater giant of chemistry than Braconnot. In addition to many elements and mineral acids, he discovered (lactic, gallic, pyrogallic, oxalic, tartaric, malic, and uric) organic acids. He also isolated glycerin and lactose.
I have a feeling that the historic methods of Scheele and Braconnot will be readily adapted to the laboratory of the modern amateur home chemist, and that's one reason I'm investigating these things. Another reason is that we seem to have... misplaced our recipes? YouTube is full of historic cooking shows based on cookbooks going back to Roman times and before. It seems to me that the original recipe for isolating malic acid should have similar cultural standing as a colonial recipe for apple pancakes, at least among chemists. These recipes are our heritage and I'm eager to inherit them.
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Another cool earl chemist was Louis Nicolas Vauquelin, who supposedly discovered malic acid, camphoric acid, and quinic acid, along with some notable inorganic discoveries. Also with his assistant he co-discovered the first known amino acid, asparagine. He's often credited with discovering pectin, but he didn't isolate it, and people already knew about jam making, so I'm not sure what possible accomplishment of discovery remains for him to have made originally.
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Looking these things up is surprisingly time consuming, and it seems like I might end up making separate posts for most of the chemicals. Maybe this post will organize them!
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Citric acid: In 1784, Scheele published a method to isolated citric acid from lemon juice in an article titled "Anmärkningar om citronsaft och ett sätt att kristallisera den" (Remarks on lemon juice and a method of crystallizing it). In "The Chemical Works of Carl Wilhelm Scheele", Anders Lennartson shares the method, which I'll summarize here:
Boil lemon juice. Add calcium carbonate, which will cause effervescence, and keeping adding it until the effervescence ceases. Allow the mixture to cool and calcium citrate will precipitate. Pour off the liquid and wash the solid until the washing water runs clear. Add very dilute sulfuric acid to the powder and boil for 15 minutes, producing a precipitate of calcium sulfate, which can be discarded by filtering. Add dilute sulfuric acid drop-wise to precipitate any remaining calcium. Crystallize the citric acid by concentrating the liquid through evaporation over gentle heat or by reducing the solubility of the solvent through cooling or through a combination of concentrating and cooling.
Scheele tried a different method before that which failed, and it's kind of interesting to compare the methods to see what differs: "Scheele evaporated lemon juice to the consistency of honey and extracted it with ethanol, which left a sticky substance. Scheele distilled off the ethanol and expected to get a pure acid, but still failed to crystallise it. ... Scheele found that after precipitating the acid with lime, there was a residue which had a bitter taste and was soluble in both water and ethanol."
I think one lesson here is that plants have lots of chemicals and the success of extracting one chemical from the multitude can be very sensitive to small changes in your procedure. I don't know what the bitter residue was in the failed ethanol extraction (maybe some mix of flavonoids, carotenoids, limonoids, tannins, and terpenoids?), but probably the sulfuric acid is removing the bitter thing in the successful extraction method. My guess is that there's some way to use sulfuric acid in combination with the ethanol extraction method to get citric acid crystals, but it's great that Scheele found an isolation procedure that works and doesn't require a distillation.
: Pectin
Henri Braconnot discovered pectin and lectured on its isolation to the Royal Academic Society of Nancy in 1824 and published about it in Annales De Chimie Et De Physique volume 28 in 1825 in "Recherches sur un nouvel Acide universellement répandu dans tous les végétaux" ("Research on a new acid universally diffused in all plants"). I'm still translating, but here's a paragraph about a jelly-like acid he found in dozens of plants, and probably every plant he investigated:
[I]t is very easy to obtain it from the various parts of plants. If we operate on roots which contain starch, such as those of celery or carrot, we reduce them to a pulp with the aid of a grater to squeeze out the juice; the marc is exhausted by boiling in water sharpened with muriatic acid, then washed and heated with an extremely diluted solution of potash or soda: a thick, mucilaginous, slightly alkaline liquor results, from which the muriatic acid separates the new acid in the form of an abundant jelly, which only asks to be well washed off: in this state it is scarcely colored, especially when it comes from the parts of the vegetables who are not. This jelly has a noticeably sour flavor. Applied to a paper dyed blue by litmus, it reddens it very distinctly, although it does not retain any foreign acid.
Maybe that's pectic acid and the actual pectin is later in the paper. I'll let you know. But it's probably pectin. That's my take. To summarize his procedure here: boil grated plant matter with hydrochloric acid, then heath with dilute potassium carbonate. A jelly separates out which can be washed clean of the source liquid.
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I was curious how pectin is extracted in the modern setting. I found some weird procedures with freeze driers and chromatography and stuff, but these excerpts of pages provided by google seem pretty normal:
"The pectin is extracted with mineral acids such as nitric, hydrochloric or sulfuric acid, phosphoric acid and citric acid in an acidic aqueous medium."
That's from "Current Advancements in Pectin: Extraction, Properties and Multifunctional Applications", which I haven't read. All of those are mineral acids except citric, which is organic. I wouldn't be surprised if you can just use any acid, provided you get a low enough pH.
"Extraction process of pectin is carried out under reflux using acidified water at 97°C for 30 min. The hot acid extract was then filtered using a cheese cloth to remove the pulp. The filtrate was then cooled to 4°C and precipitated using double the volume of ethanol."
That's from "Extraction and Purification of Pectin from Agro-Industrial Wastes", which I haven't read. If you're refluxing a liquid but not removing a component by condensing, that's better known as boiling. So you boil pectin-containing plant matter with acid and then filter out the pulp. Next, cool the liquid and add ethanol to precipitate. The ethanol acts as an anti-solvent since pectin is a polar polysaccharide (the carboxyl groups can be protonated or deprotonated) that's well-dissolved by polar solvents, while ethanol is less polar than water.
A few studies have found that pH around 3.5 is good for precipitating the most pectin across different circumstances. A pH between 2 and 3.5 is also needed in order for pectin to gel sugar, which is why SureJell brand pectin comes preloaded with sugar and citric acid.
I hear that reducing the water content before adding ethanol means you have to add less ethanol, so maybe boiling the plant material for longer has economic merit.
The precipitated pectin is a lump of jelly. Washing a few times over a filter with neutral or acidified ethanol will improve the purity. The pectin can then be dried and ground to a powder if you like, although drying might reduce the pectin "jelly-grade" a little, which is the number of grams of sugar that a gram of pectin and gel. It's a big deal in manufacturing to find slight modifications of production steps to retain a high jelly grade, but I don't have specific tips for you on how to do that.
Anyway: we've been talking about boiling with acid and precipitating with ethanol. But Henri Braconnot boiled with acid and then precipitated with potash, an alkali. Does that work too? Did he precipitate something different?
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