Haloalkanes (Alkyl Halides) in Industry and AgricultureIn industry, halogen-containing hydrocarbons represent important raw materials and solvents.

Dichloromethane (CH2Cl2, methylene dichloride), trichloromethane (CHCl3, chloroform) and

trichloroethylene (Cl2CCHCl), for example, are used as solvents and degreasing agents.

However, their environmental compatibility is questionable because they also dissolve fats in the skin and can accumulate in fatty tissue. Therefore, they are suspected of causing dermatitis.

In agriculture, haloalkanes are applied as herbicides (e.g. 2,4-D) and fungicides (e.g. captan). The insecticide DDT (1,1,1-trichloro-2,2-bis(p-chlorophenyl)ethane) is effectively used to control infectious insects in countries which are plaqued by malaria, typhus, and cholera. In Germany and many other industrial countries, the use of DDT has been outlawed since the early 1960s. Since DDT accumulates in fatty tissue of warm-blooded animals (and humans), it was suspected to be carcinogenic. This assumption has been proven not to be correct.

Fig.1

Haloalkanes in agriculture

At present, more than 15,000 halogenated organic compounds are produced for industrial purposes. They are used as feedstock for the production of PVC, industrial lubricants, pesticides, insecticides, herbicides, solvents and many others. Many of these compounds are either not at all or only barely biodegradable. Gammexane (lindane) and chlordane, as well as PCBs (polychlorinated biphenyls), even cause hereditary injuries.

Fig.2

Decachlorobiphenyl, a PCB

Until the mid-1980s, chlorofluorocarbons (CFCs) were produced in large quantities. Freons such as trichlorofluoromethane (freon-11), tetrafluoromethane (freon-14) and trichlorotrifluoroethane (freon-113), for example, are relatively simple CFCs in which all hydrogen atoms have been substituted by chlorine or fluor. CFCs are produced at a reasonable price and are stable, non-toxic, non-inflammable, and non-corrosive. Therefore, CFCs were considered perfect materials for usage in many practical applications, including propellants, coolants in refrigerators and fire-extinguishing agents. Unfortunately, due to their high chemical stability, CFCs have been identified as a severe environmental liability. They are a main cause of ozonolysis in the stratosphere and are largely responsible for the ozone hole. As a result, the production of CFCs is prohibited worldwide. However, due to their high stability, the CFC concentration in the stratosphere will not considerably decrease to a safe level until the year 2050.

A halogenated hydrocarbon, commonly known as haloalkanes or alkyl halides is a compound that is derived from alkanes with one or more halogens attached to it. Halogen is a group of five elements found on the periodic table that includes fluorine, bromine, iodine, chlorine, and astatine. Halogens are the only group of elements on the periodic table that contain elements in all three states of matter under normal conditions of standard temperature and pressure. Haloalkanes have many trade names, and they are widely implemented for many chemical reactions. Prolonged exposure to this compound has some adverse effects. This article will discuss the uses of halogenated hydrocarbon compounds.

Haloalkanes as Fire ExtinguishersFor more than 50 years and still counting, halogenated hydrocarbons have been the only fire extinguishing agents used in aircraft. Although, halogenated alkanes react with the ozone layer, the aviation industry has been given a special exemption to use this compound since it is practically the best fire extinguishing agent for use in aircraft. Halogenated hydrocarbons are best suited for fire extinguishers in aircrafts because they are electrically nonconductive and they are very efficient in per weight basis over a wide range of distance under aircraft conditions. Moreover, they leave no residue after usage.

For AnesthesiaHalothane is a derivative of halogenated hydrocarbons, which is commonly used as an anesthetic. This drug is an inhalation anesthesia that is used for the induction and maintenance of general anesthesias. Moreover, this drug effectively decreases abnormal excitement in the brain. Halothane is contraindicated for pregnant women, but it can be used if relaxation of the uterus is required. Caution should be taken when administering halothane to patients with a history of heart, kidney, or liver disease. Side effects of using this drug include: abnormal increase in temperature, liver damage, and cardiac arrest. Your physician will do a thorough medical check up on you before recommending halothane for you. Don't use this drug without a doctor's prescription.

Used as Refrigerants

Chlorofluorocarbons (CFC) are derived from halogenated hydrocarbons. They are widely used as refrigerants and propellants due to their low toxicity level and high heat of vaporization. When it became evident that they posed a threat to the ozone layer, their use became restricted. Most chlorofluorocarbons have been replaced with hydroflurocarbons. Chlorofluorocarbons are commonly known by their brand names. Apart from being used as refrigerants and propellants, they are also used as blowing agents and de-greasing solvents. Chlorofluorocarbons are gradually being phased out due to their harmful effect from reacting with the ozone layer.

Specialized UseDichloromethane is a derivative of halogenated hydrocarbons, and is used as a universal solvent for organic compounds because it is volatile and reacts with carbon. It is often used as a degreaser and a paint stripper. It can also be used to decaffeinate coffee and tea, prepare flavorings, and extracts of hops. Due to its volatile nature, it has been used to produce aerosol spray propellants and blowing agents for polyurethane foams. Dichloromethane is sometimes used to weld certain plastics, such as sealing the case of electric meter boxes.Halogenated hydrocarbons are popularly called haloalkanes. These compounds and their derivatives are used for the production of many useful substances. Haloalkanes are useful for the production of fire extinguishers in airplanes. Certain compounds derived from haloalkanes can be used to produce anesthesias, propellants, refrigerants, blowing agents, and de-greasing agents and solvents for organic compounds. Suffice it to say that halogenated hydrocarbons are very useful in the chemical industry. However, these compounds have adverse side effects associated with their use; therefore, you must take adequate precaution when handling these chemicals.