N
N
N
N
H
N
N
N
N
CH3
CH3
O
H3C
O
purine
caffeine
Coffee 80-125 mg per cup
Coffee, decaf 2-4 mg per cup
Tea 30-75 mg per cup
Cocoa 5-40 mg per cup
Milk chocolate 6 mg per ounce
Baking chocolate 35 mg per ounce
Coca-Cola 46 mg per 12 ounces
Excedrin, extra strength 65 mg per tablet
No-Doz 100 mg per tablet
Experiment #6 – Isolation of Caffeine
from Tea Leaves
Introduction
Caffeine is a member of the class of compounds
organic chemists call alkaloids. Alkaloids are nitrogen-
containing basic compounds that are found in plants. They
usually taste bitter and often are physiologically active in
humans. The names of some of these compounds are
familiar to you even if the structures aren’t: nicotine,
morphine, strychnine, and cocaine. The role or roles these
compounds play in the life of the plants in which they are
found is not well understood. In some cases they may act as
pesticides; nicotine is found in tobacco and has been sprayed
onto other plants, in which it is not found, to function as an
insecticide. The structure of caffeine is shown to the right. It
can be considered to be constructed from the purine ring
system, which is important biologically, being found in
nucleic acids and elsewhere.
Caffeine is found in a
number of things ingested by
people. The table to the right lists
some of them. Caffeine acts as a
stimulant. It stimulates the heart,
respiration, the central nervous
system, and is a diuretic. Its use
can cause nervousness, insomnia
and headaches. It is physically
addictive. A person who drinks as
few as 4 cups of coffee a day and
who attempts to stop “cold turkey”
may experience headache,
insomnia, and possibly nausea as
the result of withdrawal.
Tea has been consumed as a
beverage for almost 2,000 years,
starting in China. It is a beverage produced by steeping in freshly boiled water the
young leaves and leaf buds of the tea plant, Camellia sinensis. Today, two principal
varieties are used, the small-leaved China plant (C. sinensis sinensis) and the large-leaved
Assam plant (C. sinensis assamica). Hybrids of these two varieties are also grown. The
leaves may be fermented or left unfermented. Fermented teas are referred to as black
tea, unfermented teas as green tea, and partially fermented teas as oolong. As trade
routes opened to Asia in the 17th century, tea was imported to Europe.
Today, you are going to make a small but strong cup of tea and extract the
caffeine from it.
