Halogen Uses

 

Learning Objective

  • Discuss┬áthe uses of various halogens.

Key Points

    • Fluoride can be found in many everyday products, including toothpaste, vitamin supplements, baby formulas, and even public water. However, overconsumption of fluoride can be fatal.
    • Chlorine accounts for about 0.15 percent of human body weight and plays several important roles in the body’s functioning. Compounds of both chlorine and bromine are used as disinfectants for sterilization.
    • Iodine is essential for the functioning of the body’s thyroid gland. Without iodine, thyroid hormones cannot be produced, which leads to hypothyroidism.
    • Drug candidates that have incorporated halogen atoms are usually more lipophilic and less water-soluble than their analogues, and so have improved penetration through lipid membranes and tissues. Because of this, some halogenated drugs can accumulate in adipose tissue.
    • Polyhalogenated compounds (PHCs) are highly reactive and also bioaccumulate in humans; some of them have toxic and carcinogenic properties. PHCs are used in a vast array of manufactured products and in pest control.

Terms

  • disinfectantA substance that kills germs and/or viruses.
  • polyhalogenated compoundsCompounds with multiple halogen atoms.
  • hypothyroidismThe disease state caused by insufficient production of thyroid hormones by the thyroid gland.

Fluoride

Despite its toxicity, fluoride can be found in many everyday products, including toothpaste, vitamin supplements, baby formulas, and even public water. Many dental products contain fluoride in order to prevent tooth decay, but overconsumption of fluoride can be fatal.

Chlorine

Chlorine accounts for about 0.15 percent of human body weight. Chlorine is primarily used in the production of hydrochloric acid, which is secreted from the parietal cells in the stomach and is used in maintaining the acidic environment for pepsin. It plays a vital role in maintaining the proper acid-base balance of body fluids. It is neutralized in the intestine by sodium bicarbonate.

Chlorine also reacts with sodium to create sodium chloride, more commonly known as table salt.

Both chlorine and bromine are used as disinfectants for drinking water, swimming pools, fresh wounds, spas, dishes, and surfaces. They kill bacteria and other potentially harmful microorganisms through a process known as sterilization. Chlorine and bromine are also used in bleaching. Sodium hypochlorite, which is produced from chlorine, is the active ingredient of most fabric bleaches. Chlorine-derived bleaches are also used in the production of some paper products.

Iodine

Iodine is an essential mineral for the body. It is used in the thyroid gland but can also be found in breast tissue, salivary glands, and adrenal glands. Without iodine, thyroid hormones cannot be produced, which leads to a condition called hypothyroidism. Without treatment, the thyroid gland will swell and produce a visible goiter. Children with hypothyroidism may develop mental retardation. In women, hypothyroidism can lead to infertility, miscarriages, and breast and ovarian cancer. Thyroid problems have been a common issue for many years, particularly in middle aged women; studies correlate this with the fact that iodine levels in the general population have significantly decreased in recent years. Because of certain health problems, many people have been consuming less salt, which usually contains iodine.

In drug discovery, the incorporation of halogen atoms into a lead drug candidate results in analogues that are usually more lipophilic and less water-soluble. Therefore, halogen atoms are used to improve penetration through lipid membranes and tissues. It follows that there is a tendency for some halogenated drugs to accumulate in adipose tissue.

Polyhalogenated Compounds

Polyhalogenated compounds (PHCs) are of particular interest and importance because halogens are generally highly reactive and bioaccumulate in humans. Halogens are also part of a superset that includes many toxic and carcinogenic industrial chemicals — PBDEs, PCBs, dioxins (PCDDs), and PFCs are all polyhalogenated compounds.

DDT

DDT (dichlorodiphenyltrichloroethane) is a polyhalogenated pesticide that was banned in the United States in 1972 because of the potential harmful effects on human health. In the second half of World War II, it was used to control malaria and typhus among civilians and troops. The Swiss chemist Paul Hermann M├╝ller was awarded the Nobel Prize in Physiology or Medicine in 1948 “for his discovery of the high efficiency of DDT as a contact poison against several arthropods. ” After harmful environmental impacts of DDT were recognized, it was banned in agricultural use worldwide under the Stockholm Convention, but its limited use in disease vector control continues to this day, though it remains controversial. The US ban on DDT is cited by scientists as a major factor in the comeback of the bald eagle, the national bird of the United States, from near extinction.

The Chemical Structure of DDTDDT (dichlorodiphenyltrichloroethane) is an organochlorine used as an insecticide. It is now banned in the United States because of its potential harmful effects on human health. Key: chlorine atoms: green, carbon atoms: black, hydrogen atoms: white.

PHCs are generally immiscible in organic solvents or water but miscible in some hydrocarbons, from which they are often derived. PHCs are used in a vast array of products and industries, such as:

  • Wood treatments
  • Non-stick, waterproof, and fire-resistant coatings
  • Cosmetics
  • Medicine (e.g., cancer therapy, surgery, and medical imaging)
  • Electronic fluids
  • Plastics (e.g., food containers and wrappings)
  • Automobiles
  • Airplanes
  • Clothing and cloth
  • Insulation
  • Adhesives
  • Paints
  • Polyurethane foams
  • Pest control (DDT)