Good afternoon Holly,
I was wanting to ask a chemist a couple of questions to help me prepare a lecture ...on the Stas method for extracting alkaloids.
After much consultation with the internet and some consultation with another chemist, I understand the first half of the process where an ether solution containing the alkaloid (in this case nicotine) has been separated from an aqueous solution. From here it was described as I understand it to involve the ether solution to be continuously distilled where the condensation would be slowly added to a container of sulfuric acid.
Here, the ether would run off back into the original container of the ether solution. But, the nicotine (which is basic as a result of earlier treatments in this process) would react with the acid and further extracted and/or purified into a salt.
Assuming this description is correct (which I’m not sure it is), what would you call this type of distillation? Is it just continuous distillation or is there a more specific term?
Also, what term best describes the acid-base reaction?
I understand that it may fall under acid-base extraction, but I also came across acid-alkaline reaction, neutralization, acid-catalyzed hydrolysis of glycosides/glycoalkinoids, a condensation reaction, and (Fischer) esterification. I believe the last term is the most accurate but I’d like a professional’s opinion. I just want to make sure I’m using the best language possible to describe these processes. I don’t plan on describing too much farther out of my area of expertise.
Thank you for any assistance on this matter and I hope you are having a great summer,
CG
Hi CG,
It seems like you are looking to find the right terminology to describe this separation procedure.
This seems to be a variation of a very old (like over 100 years old) procedure of alkaloid extraction.
What's an alkaloid?
Alkaloids are naturally-occurring molecules that have a nitrogen-containing functional group (or pattern of atoms) called an amine and they are known for their wide range of pharmacological effects. Amines are one of many types of bases. Since bases taste bitter, plants containing alkaloids tend to be bitter. Some of the alkaloids you might be familiar with include nicotine, quinine, ephedrine, atropine, morphine, codeine, caffeine, capsaicin.
The isolation of an alkaloid makes use of the fact that a neutral (meaning uncharged) amine is likely to dissolve in an oily solvent like ether, but not in a watery aqueous solution. But when acidified, the amine becomes a positively charged ammonium ion. Anything with a charge is likely to become water soluble. This difference in solubilities allows you to isolate the alkaloid.
This is the basis of the separation of alkaloids in general.
Here's my depiction of any amine reacting with acid. The R groups can be either hydrogen or carbon, the Rest of the alkaloid. The nonbonding pair of electrons on the amine become a bond to a loose hydrogen ion (in red) and the product is some sort of ammonium cation, which will always have a positive charge. In the case of nicotine, it will become the positively charged nicotinium ion. Notice how charge is conserved on both sides of the equilibrium arrow, as it should be.
So, treating your nicotine with acid will put a charge on it. Otherwise, it is soluble in nonpolar, hydrophobic solvents like ether. Once the alkaloid has a charge on it, you can further purify it as a salt, for example, you’ll get a sulfate salt if you use the sulfuric acid you mention. Salts either dissolve in aqueous solution or are solids, once you take the aqueous solvent away by heating or some other dehydration process.
The use of continuous distillation that you mention ought to squeeze out any residual alkaloid left in the ether, should it remain, and what comes out of the distillation should be called the condensate.
I would call this type of distillation simply continuous distillation.
The reaction of the nicotine or any alkaloid with acid such as sulfuric acid is simply an acid base reaction. Since alkali is another term for base, you could also call this reaction an acid-alkali reaction, though that term is less often used.
I wouldn’t really call the reaction of your nicotine with acid a neutralization. Some acid base reactions cause a solution to become neutral but I think of neutralization more in terms of making a solution pH 7 and you aren’t doing that.
Another meaning for neutralization, though, means literally to make the charge zero. So technically, if your nicotine is moved from an acid solution to a base solution, it will lose its positive charge and become zero-charged, and neutral. So if you do that in this process then that (shifting the nicotine from an acidic to a basic solution) would be a form of neutralization. But I am not clear you are doing that.
I definitely would avoid the term esterification, because I can’t imagine how you are making esters unless I am missing some information here.
Esters are a type of organic compound and I don’t see how that would be part of the procedure of isolating nicotine. Fischer esterification involves the reaction of a carboxylic acid (a type of acid that you do not have as far as what you have told me) and an alcohol to make and ester from the two molecules. Nicotine does not have an ester functional group (pattern of atoms).
I would avoid the term acid-catalyzed hydrolysis of glycosides/glycoalkinoids in your talk unless you have alkaloids that are also glycosides (nicotine is not one) you are working with and separating them from their sugars prior to the distillation. A glycoside is a molecule, often found in plants, that has one or more sugars attached. As far as I know, nicotine and the related nicotinoids do not come in the form of glycosides in tobacco, although many alkaloids do have sugars attached, and would then be called glyco-alkalinoids.
Hydrolysis means breaking one molecule into two molecules using water: one of the the products gains a H and the other gains an OH. So hydrolysis means splitting in two using water. I don’t see that you are doing any hydrolysis reactions here. Perhaps for a different alkaloid that has sugar attached, you might start by liberating the sugar from the alkaloid using acid hydrolysis. Incidentally, the name for a plant molecule that is liberated from its sugar is an aglycone.
Condensation reactions are a huge class of reactions where two molecules join together in a bond with the loss of water. Maybe I’m missing something but I don’t see any condensation reactions happening here either. So I would avoid the term condensation reaction. A condensation reaction, by the way, is just the reverse of a hydrolysis reaction.
Maybe there are parts of your purification that I am missing, in which case I might be wrong about some of what I have written. You might want to run this by your chemist friend so they can assure you that as far as what you have told me below, there are no esterification reactions, no condensation reactions, and no hydrolysis reactions going on, and no glycosides present.
I hope that helps simplify the terminology you want to use for your talk, and best wishes.
I appreciate your desire for clarity and I hope that I have helped you!
Holly
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