Synthetic pesticides

Pesticides are chemical agents used to kill ani­mal or vegetable life-forms that harm agricul­tural produce, such as wheat products, 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, which is termed a "hard" insecticide. A hard insecticide resists decay by the environ­ment and may persist for months or even years. Other chlorinated pesticides include Al-drin and Dieldrin.

Organo-phosphates are the most powerful insecticides. They are rapidly destroyed in the environment after use. The most lethal agents in this group are the parathions and maiathion. The carbamates are obtained from carbamic acid. The most important of them is Sevin, a highly toxic insecticide.

Because most insecticides are also lethal to man and other mammals, their use has aroused much concern among environmental­ists. But scientists are now developing new ways to combat insect pests. One of the most effective is the use of pheromones. These are manufactured naturally by insects. Insects dis­charge pheromones into the atmosphere to at­tract the opposite sex of the species for mat­ing. Some insects can be attracted in this way from many miles (kilometers) away. By making pheromones artificially, scientists can lure in­sects into traps. Pheromones can also be used simply to confuse insects and disrupt mating. This can severely reduce the insect popula­tion.

Other pesticides include herbicides (to kill weeds) and fungicides (to kill fungi). The most widely-used herbicide is acetic acid. A particu­lar type of acetic acid has attracted attention recently because it is claimed to pose a threat if used improperly. Fungicides are very di­verse. They range from simple inorganic sub­stances (such as lime) to complex organic compounds of mercury and tin.

Organic chemistry: Complex organic compounds 95

Locustsand many other species of insects produce pheromones. These are complex organic com­pounds that the insects (usually females of the spe­cies) discharge into the air to attract mates. These sub­stances are extremely po­tent. In many species, indi­viduals respond after detecting only a few mole­cules. Chemists are now able to synthesize some pheromones. This offers the possibility of controlling in­sect populations without the extensive ecological dis­ruption that can result from using conventional insecti­cides.

Synthetic and natural drugs

Drugs are chemical agents usually used to combat disease, to help repair the body after disease or injury, and to suppress pain. How­ever, some other uses do exist, such as the building up of muscle tissue by athletes.

Some medicinal products can be isolated from natural sources. Such substances usually have to be modified chemically before they can be used. Other drugs are entirely syn­thetic. An example is aspirin, which is now produced from phenol, a type of organic com­pound discussed in the article "Alcohols." Per­haps the best known of all drugs is the antibi­otic penicillin. It was first discovered in 1928 by Alexander Fleming. Several different forms exist. Nowadays, it is produced industrially from a type of mold called Penicillium chryso-genum. Penicillin combats two types of bacteria—cocci and spirochaetes—very well. It is less effective against rod-shaped bacteria. Different penicillins can be synthesized (made artificially) by altering the chemical composi­tion of the medium in which the mold grows.

Other important antibacterial drugs are the "sulfa" compounds. All contain the sulfanil­amide grouping (a type of nitrogen com­pound) in their structures. They act by compet­ing with p-aminobenzoic acid. This is a substance that some microbes require in order to survive. Removal of the nutrient by the sulfa drug starves and kills the bacteria and cures the patient who was infected.

A newly developing way to produce 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 by this novel tech­nique. More products are sure to follow as re­search into biotechnology intensifies.

Date: 2015-12-11; view: 1696