1492 is one of the most significant dates in world history because that is the date on which Christopher Columbus sailed across the Atlantic and discovered the Americas, whether or not he ever realized he discovered the Americas is a topic for another discussion. In the Americas, there were numerous species which did not occur in the Old World and, likewise, in the Old World, there were numerous species that did not occur in the new. But Columbus' crossing of the Atlantic allowed those species to intermingle, and this is called the Colombian Exchange. And the Old World did very well out of it and gained many valuable and useful species from the New World. For instance, pineapples, papaya, potatoes, tomatoes, chilies, chocolate, corn, turkeys, the anti-malarial medicine quinine. All of these came to the Old World from the New World after 1492 and made the Old World a much better place. In exchange, the Old World sent to the new world wheat, horses, and hard liquor. But not all the things that came from the New World were quite so beneficial. For instance, tobacco, syphilis, and the subject of this part of the lecture, cocaine. Well, cocaine is a chemical that produced by this plant, Erythroxylum coca, which has been cultivated in the Andes since ancient times, particularly in countries such as Bolivia, Peru, Ecuador, and Colombia. Most of this area was part of the Inca empire. Under the Incas, cocaine production and use was very strictly regulated. Of course, when the Inca empire collapsed under the pressure from the Spanish conquistadors, the strict control of cocaine also disappeared. Now, why did the people up in the Andes grow the coca plant? And the reason is that living up in the Andes at such high altitude, you need a lot of stamina. And small doses of cocaine which you could obtain, for instance, by chewing some coca leaves or drinking some coca tea, boost your physical stamina. And visitors to high altitude areas of these countries today may well still be offered a cup of coca tea to help them cope with the altitude. In fact, it is still widely cultivated in South America and many of the poor farmers in these parts of South America, still depend on this plant for their livelihood. Indeed, the current president of Bolivia, Evo Morales, was a former leader of the Coca Farmer's Union in that country. Well, how did cocaine get out of South America? Well, after Columbus' discovery, for as long as possible, the Spanish tried to close their empire in South America from the rest of the world. They didn't want other countries benefiting from the trade with their empire. So, it's only with the collapse of Spanish power in South America, in the early part of the 19th century, that materials, such as coca, could come to North America and to Europe. And when people first experience the effects of coca, they thought it was wonderful. And so, it initially became very fashionable. But, when the side effects became apparent, it was very quickly banned. Early users who thought it was good stuff include Sherlock Holmes and Sigmund Freud. Freud thought that cocaine use would allow him to see inside the minds of his patients. In the Sherlock Holmes stories particularly the early stories, Sherlock Holmes quite often injects himself with cocaine. Another use for cocaine was as an ophthalmic anaesthetic. Ophthalmologist would use it on the eye of their patients. Though now, again, that use has been superseded by the use of synthetic chemicals which don't have all the other biological effects of cocaine. So, here's an example, cocaine tooth drops. If you got a toothache, put some cocaine on your teeth and the pain will go away. You can't get cocaine tooth drops anymore. Well, there are different forms of cocaine and this is because cocaine is what we call an alkaloid. It is a natural compound that contains a nitrogen atom which is basic. So, the free cocaine molecule, which exists as a chunky material and is known as crack cocaine, is the neutral nitrogen-containing molecule. And this can be smoked, it can be snorted, or it can be injected. Powder, that you often see, is actually cocaine hydrochloride and that is a compound of the free base cocaine with hydrochloric acid. And this forms the white powder. Now, cocaine that is sold on the streets may also be cut. That means it has been diluted with other white-colored materials simply to make the smuggled material go further. And it may be cut with materials that have no effect on the user, such as mannitol or sugar, or it may be mixed for instance with anaesthetics. And the reason that the drug dealers can do this and get away with it is because of course their customers can't go complaining to the Better Business Bureau about it. Now, I said earlier that cocaine comes from the coca leaf, that's the leaf of the coca plant. And you're probably aware of a well-known soft drink that has the word coca in its name. And it's believed that the original recipe for that soft drink actually did contain extracts of coca leaf, and therefore, would have contained small amounts of cocaine. It's well-known. It's famous that the recipe for that soft drink is a secret but we can be quite confident that nowadays that has been removed from the recipe. The other part of the name of course is cola. And cola is this tree here, and cola is a flavoring ingredient extracted from the nuts of this tree. A refreshing beverage after a long day's MOOC. But have you ever considered that the process of making a cup of tea is analogous to the process used to extract chemicals such as cocaine? In both cases, we're extracting a psychoactive substance from processed plant material. In the case of tea, we're extracting caffeine from the dried leaves of Camellia sinensis using a solvent. That solvent, of course, is hot water. In the case of cocaine, you're extracting the chemical from the dried leaves of Erythroxylum coca, and you can do that using hot water but it's probably more efficient with an organic solvent. In each case, there's no actual chemical change. We are merely moving the chemical in question from one place to another, from the plant material into the solution. And there's no chemical change, the caffeine or the cocaine, remains caffeine or cocaine. It's just we're getting it into solution. We're back in the NTU Chemistry Teaching Lab and we're going to be extracting a psychoactive substance. But it's not cocaine, it's caffeine. And here's our raw plant material, tea. This is our solvent, which is water. So, we can simply put the plant material in the solvent. Now, plants contain more than one chemical. And tea contains a lot of other chemicals which are actually the ones that give it the flavor. But, we want to extract the caffeine and we don't want those other chemicals. Now, most of those other chemicals, the tannins, are acidic. So, I'm also adding some base, this is calcium carbonate which chemically is chalk. And that will absorb those tannins and help us get pure caffeine at the end of the experiment. So, that's in cold water. Now, we've got to heat it up to extract the caffeine from the tea leaves into the solvent. After boiling the mixture, we can filter it to remove the solids. So, this is our filtrate and it has cooled down to room temperature. So, caffeine is quite soluble in hot water, but not very soluble in cold water. So, now we're going to take a cold solution and extract the caffeine into an organic solvent. So, I put the tea that we have made into this separating funnel. This is the water solution, the aqueous solution, and I'm going to add the organic solvent. Because the organic solvent does not dissolve in water, you can see that two layers form. So, when I swirl the separating funnel, the two layers mix, and the caffeine goes into the organic solvent in which it is much more soluble. So, we have separated the organic layer and now, we can evaporate the solvent. The best way to do that is with a rotary evaporator. So, after evaporation, here is our caffeine and it looks reasonably pure. So, what we're going to do, finally, is to demonstrate that it is caffeine and a quick check on the purity using one of the techniques that we learned about earlier, which is thin layer chromatography. So, I've taken some of our caffeine and dissolved it in solvent ready for chromatography. And we're going to compare it with some commercial caffeine and I've made a solution of that in the same way. So, from the TLC, you can see that we really do have caffeine and the purity looks pretty good.