Organic halides are organic compounds containing a halogen atom bonded to a carbon (C) atom. Fluorine (F), chlorine (Cl), bromine (Br), and iodine (I) are all types of halogen atoms. A compound that contains an carbon atom bonded to a fluorine atom (C–F) is called an organofluoride. If the carbon atom is part of a chain of carbon atoms, the organofluoride compound is referred to as an alkyl fluoride. If the carbon atom is contained in a benzene or phenyl ring, the organofluoride is called an aryl fluoride. Other halide compounds are named in a similar fashion.
The reactivity of organic halides depends on the halogen atom that is bonded to the carbon atom in the particular compound. Organoiodides are the most reactive and can be converted into many other compounds. Organobromides are less reactive than organoiodides but more reactive than organochlorides. Organofluorides are the least reactive of the organic halides.
Organofluorides are very stable compounds that are nonflammable, have very limited toxicity, and do not react with other chemicals. Perfluorocarbons (PFCs) are alkyl fluorides that consist of chains of carbon atoms bonded only to fluorine atoms. In 1966, scientists demonstrated that large amounts of oxygen could be dissolved in PFCs. Two years later, scientists replaced the blood in a laboratory rat with a solution of oxygen dissolved in PFCs. The animal lived and scientists began researching the use of PFCs as artificial blood. In 1990, the Food and Drug Administration (FDA) approved the use of Fluosol-DA, a PFC solution licensed to Green Cross Corporation, as an oxygen carrier during the medical process of cleaning heart-arteries with a balloon. PFCs are also used as a temporary replacement for eye fluid during surgery. PFC chains are the foundation of many products used to repel water, oil, and dirt from carpets and upholstery.
Many aryl fluorides are important pharmaceutical and agricultural products. The anti-inflammatory agent dislunisal, the tranquilizer haloperidol, and the sedative flurazepam hydrochloride are examples of drugs that are also aryl fluorides. Fluometuron, an aryl fluoride herbicide, is used to kill weeds in grain and cotton fields. Flutriafol, another aryl fluoride, is a fungicide used to stop diseases on the grains used in the manufacture of various cereals.
Because of their low chemical reactivity, alkyl chlorides are useful in dissolving other chemicals, greases, and oils. They are used as solvents for dry cleaning, removing oil from metal parts, and running chemical reactions. Methylene chloride (CH2Cl2) is an alkyl chloride with a low molecular weight that is used in many paint and varnish removers. It is also used as a solvent for removing caffeine from coffee. The well-known pesticide DDT is an aryl chloride that was first used in 1939 to kill the mosquitoes that transmitted malaria. This chemical was beneficial in eliminating the spread of malaria throughout the world. However, DDT is also poisonous to fish and birds; as a result, the Environmental Protection Agency (EPA) stopped its use in 1972. Aryl chlorides, such as chlozolinate and quintozene, are used to stop the growth of fungus on fruits and vegetables.
Chlorofluorocarbons (CFCs) are compounds that contain both chlorine atoms and fluorine atoms bonded to carbon atoms. These compounds are very stable and are usually gases at room temperature. Several types of CFCs are freons, a name trademarked by E.I. du Pont de Nemours & Co.); prior to being banned they were used in refrigerators and air conditioners. CFCs were also employed in the manufacture of various hard foams used under the siding in buildings and around dish washers and refrigerators for insulation and sound proofing. Since CFCs are excellent at dissolving oil and grease, they were a primary component of dry cleaning solutions. They are also used to remove oil and grease from electronic parts. The chlorofluorocarbon, dichlorodifluoromethane (CCl2F2), is not poisonous and is employed as the carrier gas in asthma and allergy inhalers. This compound is mixed with ethylene oxide, and the resulting gas is used to sterilize medical equipment and materials that are sent into outer space. In 1971, scientists determined that CFCs were accumulating in the atmosphere; they later showed that this “build up”
Chlorofluorocarbons (CFCs)— Compounds that contain both chlorine atoms and fluorine atoms bonded to carbon atoms.
Halide, organic— An organic functional group that consists of a halogen atom bonded to a carbon atom.
Montreal Protocol— An agreement initially between 24 nations to limit and eventually stop the production of ozonedepleting chlorofluorocarbons.
Organobromide— A compound that contains a carbon atom bonded to a bromine atom (C-Br).
Organochloride— A compound that contains a carbon atom bonded to a chlorine atom (C-Cl).
Organofluoride— A compound that contains a carbon atom bonded to a fluorine atom (C-F).
Organoiodide— A compoundthat containsan carbon atom bonded to a iodine atom (C-I).
Perfluorocarbons (PFCs)— Compounds that consist of chains of carbon atoms bonded exclusively to fluorine atoms.
was destroying the ozone layer, a level of the stratosphere that absorbs much of the harmful ultraviolet rays from the Sun. The Antarctic ozone hole was discovered in 1985, prompting the international community to sign the Montreal Protocol to limit and then ban the use of CFCs in the manufacture and operation of prodcuts. The original agreement between 25 nations limited the production of CFCs with the intention of ceasing production by the year 2000. The protocol went into effect on January 1, 1989. As of 2006 more than 165 countries were signatories to the treaty to save the ozone layer.
Organobromides form highly reactive compounds when mixed with metals such as magnesium (Mg) or aluminum (Al); for this reason, they are used extensively in the manufacture of dyes, drugs, and other chemicals. The alkyl bromide, bromotrifluorome-thane (CBrF3) is not poisonous and will not burn. It is used in portable fire extinguishers and in airplanes to stop engine fires while in flight. Halothane (CF3CHClBr), another organobromide, is used as a general medical anesthetic. Aryl bromides are colored and are used extensively as dyes and colorants. Alizarine Pure Blue B is an aryl bromide used to dye wool. The orange color in lipsticks is often D & C Orange number 5, another member of the organobromide family.
The most chemically reactive of the organic halides are those that contain carbon atoms bonded to iodine atoms. Organoiodides are not used as extensively as organobromides or chlorides because they are expensive. Alkyl iodides react with metals such as lithium (Li) or mercury (Hg) to make useful chemicals in the manufacture of pharmaceutical and organic intermediates. The aryl iodide, thyroxin, is a thyroid hormone used to stimulate human metabolism. Erythrosin, or FD&C; Red No. 3, was used to add red color to maraschino cherries. This dye was removed from the market when researchers found that it caused cancer in laboratory animals.
See also Dyes and pigments; Halogens; Halogenated hydrocarbons; Ozone layer depletion.
CFC.com. “Chemical Compounds—Halides” <http://www.c-f-c.com/supportdocs/halides.htm> (accessed November 26, 2006).