Caffeine (kaf-EEN) is an organic base that occurs naturally
in a number of plant products, including coffee beans,
tea leaves, and kola nuts. It occurs as a fleecy white crystalline
material, often in the form of long, silky needles. It
usually exists as the monohydrate, C8H10N4O2 H2O, although
it gives up its water of hydration readily when exposed
to air.
Scientists believe that humans have been drinking beverages
that contain caffeine for thousands of years. The first
recorded reference to a caffeine drink can be found in a
Chinese reference to the consumption of tea by the emperor
Shen Nung in about 2700 BCE. Coffee is apparently a much
more recent drink, with the earliest cultivation of the coffee
tree dated at about 575 CE in Africa.
Caffeine was first studied scientifically by two French
chemists, Joseph Bienaime´ Caventou (1795–1877) and Pierre
Joseph Pelletier (1788–1842), who were very interested in
the chemical properties of the alkaloids. Between 1817
and 1821, Caventou and Pelletier successfully extracted
caffeine, quinine, strychnine, brucine, chinchonine, and
chlorophyll (not an alkaloid) from a variety of plants. The
first synthesis of caffeine was accomplished in 1895 by the
German chemist Emil Hermann Fischer (1852–1919), who was
awarded the 1902 Nobel Prize in chemistry for his work on
the alkaloids.
Caffeine belongs to a class of alkaloids called the methylxanthines.
Chocolate, from the cocoa tree Theobroma cacao
contains another member of the class, theobromine. Both
caffeine and theobromine are stimulants, that is, compounds
that act on the nervous system to produce alertness, excitement,
and increased physical and mental activity.
Caffeine can be extracted from coffee, tea, and kola
plants by one of three methods. These methods are used
primarily to produce the decaffeinated counterparts of the
products: decaffeinated coffee, decaffeinated tea, or decaffeinated
soft drinks. A commercial variation of these procedures
is to treat the waste products of tea or coffee processing, such
as the dust and sweepings collected from factories, for the
extraction of caffeine.
In the first of the three extraction methods, the natural
product (coffee beans, tea leaves, or kola beans) are treated
with an organic solvent that dissolves the caffeine from the
plant material. The solvent is then evaporated leaving behind
the pure caffeine. A second method follows essentially the
same procedure, except that hot water is used as the solvent
for the caffeine. A more recent procedure involves the use of
supercritical carbon dioxide for the extraction process.
Supercritical carbon dioxide is a form of the familiar gas
that exists at high temperature and high pressure. It behaves
as both a liquid and a gas. Not only is the supercritical carbon
dioxide procedure an efficient method of extracting caffeine,
but it has virtually none of the harmful environmental and
health problems associated with each of the other two methods
of extraction.
Caffeine is also made synthetically by heating a combination
of the silver salt of theobromine (C7H8N4O2Ag) with
methyl iodide (CH2I), resulting in the addition of one carbon
and two hydrogens to the theobromine molecule and converting
it to caffeine.
Caffeine is used in foods and drinks and for medical
purposes. Its primary action is to stimulate the central nervous
system. People drink coffee, tea, or cola drinks to stay
awake and alert because caffeine creates a feeling of added
energy. It does this by increasing heart rate, improving blood
flow to the muscles, opening airways to aid breathing, and
releasing stored energy from the liver to provided added fuel
for the body. In large quantities, caffeine can also cause
nervousness, insomnia, and heart problems. The effects of
caffeine can linger in the body for more than six hours. In
medical applications, caffeine is sometimes used as a heart
stimulant for patients in shock, to treat apnea (loss of breathing)
in newborn babies, to counteract depressed breathing
levels as a result of drug overdoses, and as a diuretic.
Caffeine stimulates the brain in two ways. First, because
it has a chemical structure similar to that of adenosine, it
attaches to adenosine receptors in the brain. Adenosine is a
substance that normally attaches to those receptors, slowing
brain activity and causing drowsiness. By blocking those
receptors, caffeine increases electrical activity in the brain,
creating a feeling of alertness. Caffeine also works in the
brain like drugs such as heroin and cocaine, although in a
much milder way. Like those drugs, caffeine increases dopamine
levels. Dopamine is a chemical present in the brain that
increases the body’s feeling of pleasure.
Studies have shown that caffeine can become addictive.
People who use the compound eventually need to take more
and more of it to get the same effect. When some people try to
stop using caffeine, they may suffer from headache, fatigue,
and depression, though these symptoms can be controlled
by gradually reducing the amount of caffeine consumed.
Either way, withdrawal symptoms end after about a week.
