In addition to comparatively simple compounds, organic chemistry includes thousands of complex compounds. Many of these occur naturally. They are of importance in living organisms and as medicinal drugs. Others are synthetic—artificial organic chemicals for use in a wide range of products, including drugs such as aspirin, and pesticides such as DDT.
More than 2,000 compounds have been classified as alkaloids—compounds containing ring structures that bear at least one nitrogen atom. All show physiological activity and most act as bases in chemical reactions, reacting with acids to make salts. Most are colorless and crystalline. They are also used as drugs, although they have a bitter taste and may be poisonous.
Scientists have discovered that all alkaloids are made from amino acids, the building blocks of protein molecules, and all alkaloids are derived from plants. Among the best known are nicotine from tobacco, opium and its derivatives from poppies, caffeine from coffee, strychnine from the nux vomica tree, and quinine from the bark of the cinchona tree. Opium and derivatives such as heroin and morphine are addictive drugs that dull the nerves. Strychnine, a highly poisonous drug that stimulates the central nervous system, is now used mainly to kill rats. Quinine is an anti-malarial drug.
Pesticides are chemical agents used to kill animals or plant life harmful to agricultural produce, such as grains, fruits, and vegetables. Those used to kill insect pests are in three main categories: chlorinated pesticides, organo-phosphates, and carbamates. The most familiar chlorinated pesticide is DDT, termed a “hard” insecticide because it resists decay by the environment and may persist for months or years. Other chlorinated pesticides include Aldrin and Dieldrin.
Organo-phosphates, the most powerful insecticides, are rapidly destroyed in the environment after use. The most lethal agents in this group are the parathions and malathion. The carbamates include several highly toxic insecticides, the most important being Sevin.
Most insecticides can also be lethal to humans and other animal life, so their use arouses concern among environmentalists.
But scientists are now developing better ways to combat insect pests, such as the use of pheromones. Manufactured naturally by insects, pheromones are emitted to attract the opposite sex for mating. With artificial pheromones, scientists can lure insects into traps or disrupt mating, thereby severely reducing the insect population.
Other pesticides include herbicides (weedkillers) and fungicides (fungi killers). One of the most widely used herbicides is acetic acid. Fungicides range from simple inorganic substances (such as lime) to complex organic compounds of mercury and tin.
Synthetic and natural drugs
Drugs are chemical agents primarily used to combat disease, to help repair the body after disease or injury, or to suppress pain. Some medicinal products are obtained from plants but usually have to be modified chemically before they can be used. Other drugs are entirely synthetic, such as aspirin, produced from phenol, a type of organic compound discussed in the article on alcohols. Penicillin, the well-known antibiotic discovered in 1928 by Alexander Fleming, is now produced industrially from a type of mold called PeniciHium chrys-ogenum. Different penicillins can be synthesized by altering the chemical composition of the medium in which the mold grows.
Other important antibacterial drugs are the “sulfa” compounds, all of which contain the sulfanilamide grouping (a type of nitrogen compound). They work by competing with a substance that microbes need to survive, removing the substance and thus starving the bacteria.
A newly developing method of producing drugs is by manufacturing special bacteria or plant cells that act as tiny drug factories. They can be modified genetically to produce important drugs. Insulin and interferon are already being produced commercially in this way.
Artificial sweeteners and flavorings
The most widely used artificial sweetener is aspartame. It is derived from aspartic acid and phenylalanine, two chemicals that occur naturally in certain foods. Aspartame is about 200 times as sweet as table sugar. Other artificial sweeteners include saccharin and acesul-fame-K.
About 800 synthetic food flavorings are also in use today. A common flavor enhancer, monosodium glutamate (MSG), is isolated from natural sources—such as flour or soybean-fermented, and then purified.