Most cola drinks and other carbonated beverages such as Mountain Dew have a large caffeine content. My understanding is that these drinks have the caffeine added to them at the time of manufacture. Where does caffeine extract come from? How is it extracted? Is it possible to buy a gallon/liter of pure caffeine from a distributor of some sort? Is the sale of pure caffeine regulated?
I don’t know how it’s done on an industrial scale, but I can tell you that I once extracted caffeine from tea leaves in my organic chemistry lab in college. I forget the exact process, but there was fractional distillation and solvents and condensation and whatnot involved. We ended up with a small amount of grayish powder that probably wasn’t safe for consumption because of the chemicals we used.
This page says
Caffeine exists naturally in tea leaves and coffee beans, as well as in cocoa. It is also found in the leaves of a plant called Camellia sinensis and in the leaves of the kola plant. [sup]1[/sup] (This is half of the origin of the name “Coca-Cola”; kola leaf extract and coca leaf extract were used in the original formula [sup]2[/sup].)
Like Smeghead, I also extracted caffeine from tea leaves in Organic Chemistry pracs. However, that was … quickmaths … 7 years ago, so I don’t remember how we did it. The yield wasn’t that great, I remember that! Unfortunately I don’t know how it’s done on an industrial scale - I suppose it could even be synthesised, if that would be easy enough or give high enough yield.
[1: Moffat, CM, Osselton, MD, Widdop, B, and Galichet, LY. Eds. 2004. Clarke’s Analysis of Drugs and Poisons. Pharmaceutical Press. UK.]
[2: Perrine, DM. 1996. The Chemistry of Mind-Altering Drugs: History, Pharmacology, and Cultural Context. American Chemical Society. Washington, DC. USA.]
On preview: I see chukhung has answered the other half of your question. While it’s true that the caffeine in Coke now comes from other sources, it was originally there due to the kola extract. But, that was a long time ago 
According to a chemist I used to work with, caffiene is highly soluble in carbon dioxide held at its triple point. Caffeine-containing items like coffee beans placed in this will have the caffeine rapidly diffuse from the bean into the CO[sub]2[/sub]. I am not aware if this is how it is done on an industrial scale.
Now that the question’s answered, a hijack:
My ex worked for a beverage company, and one day “requisitioned” a sandwich baggie full of caffeine. It was a white powder (looked to my uneducated eyes a lot like cocaine!) and tasted bitter as all get out.
The two of us worked at a nightclub (he was a bouncer, I was the concession stand floozie) and he’d make killer pots of coffee by putting a few pinches of the caffeine powder on top of the coffee grounds before brewing. Made awful tasting coffee, but kept all the bouncers really alert! 
[/hijack]
The above might be a bit misleading for those not familiar with tea production. Camellia sinensis is the plant species whose leaves and leaf buds are used to produce tea. Cite. The Assam variety (used for many black teas) is sometimes referred to as Camellia sinensis assamica or just Camellia assamica.
I am not sure from your OP if you are aware that you can buy nearly pure caffeine over the counter at pretty much any pharmacy…it is the primary ingredient in products like No Doz and Vivarin.
It’s the primary active ingredient in those products, of course.
There is a relevant page here: http://antoine.frostburg.edu/chem/senese/101/consumer/faq/print-decaffeinating-coffee.shtml
It seems to indicate that the CO2 process erislover described is being used on a large scale in some places.
I am intrigued by the mention of genetic engineering of coffee plants so that they no longer produce caffeine. Being a molecular biologist as well as coffee fiend I had contemplated this years ago as probably the best way to remove caffeine from coffee while affecting the flavor as little as possible (I was thinking of a genetic “knockout” of the caffeine gene).
The kind of people who worry about the chemicals from traditional decaffeination processes are also in general the kind who are not too keen on genetically engineered food products though so maybe it wouldn’t fly comercially.
Thanks for the correction, chukhung. My cites both had them listed as separate entities - as I’m not an avid tea drinker, and in fact have very little interest in tea, I never would have known.
This refers to the “supercritical fluid extraction” process.
As other have alluded to, the original method of extraction was with the use of liquid/liquid extraction. Take two liquids which are immiscible, such as water and benzene, and add some ground coffee. Water is polar, as is caffeine. Benzene is non-polar. If you shake this mixture , the caffeine dissolves into the water, while the benzene will dissolve the more non-polar components. If you then let the whole thing stand without shaking, it will separate into two layers; benzene (and dissolved non-polar coffee components) on top, water (and caffeine and other polar components) on the bottom.
You then physically strain out the coffee solids , separate the two liquids and evaporate the water portion to recover the caffeine. Similarly, evaporating the benzene portion will result in recovery of any non-polar constituents which have dissolved.
The problem with this method is that benzene is carcinogenic, and traces can remain if not dried completely.
SCE (supercritical fluid extraction) uses carbon dioxide gas. Under the correct combination of temperature and pressure, CO2 becomes a “supercritical fluid.” not quite a liquid, and not quite a gas, it can be thought of as a very viscous gas, or a very thin liquid. Supercritical CO2 is a great solvent for caffeine. Once dissolved, if you remove the pressure, it flashes back into a non-toxic gas (CO2), while any dissolved components are left behind. This avoids all of the hassles of the older extraction methods.