Tiêu đề 10.HALOALKANES AND HALOARENES.pdf ✅

Polyhalogen Compounds Polyhalogen compounds are useful in various industries and in agriculture.Some important polyhalogen compounds: Polyhalogen compounds: Carbon compounds containing more than one halogen atom per molecule. Dichloromethane (Methylene chloride) p,p'-Dichlorodiphenyl- trichloroethane (DDT) Trichloromethane (Chloroform) Polyhalogen Compounds Freons Triiodomethane (Iodoform) Tetrachloromethane (Carbon tetrachloride)
ChemContent | Haloalkanes and Haloarenes ChemContent 3 Dichloromethane (Methylene chloride) Uses: Dichloromethane (methylene chloride) is used as a: 1. Solvent for paint removers 2. Propellant in aerosols 3. Process solvent in the manufacture of drugs 4. Metal cleaning and finishing solvent Harmful effects: 1. It endangers the human central nervous system. 2. Exposure to lower levels of methylene chloride in air can lead to slightly impaired hearing andvision. 3. High levels of methylene chloride in air cause dizziness, nausea, tingling and numbness in thefingers and toes. 4. In humans, direct skin contact with methylene chloride causes intense burning and mild rednessof the skin. 5. Direct contact with the eyes can burn the cornea. Trichloromethane (Chloroform) Uses: 1. Chemically, chloroform is used as a solvent for fats, alkaloids, iodine and other substances. 2. The major use of chloroform today is in the production of the freon refrigerant R-22. 3. It was once used as a general anaesthetic in surgery but has been replaced by less toxic, saferanaesthetics such as ether.
ChemContent | Haloalkanes and Haloarenes ChemContent 4 Harmful effects: 1. As might be expected from its use as an anaesthetic, inhaling chloroform vapour depresses the central nervous system. 2. Breathing about 900 parts of chloroform per million parts of air (900 ppm) for a short time can cause dizziness, fatigue and headache. 3. Chronic chloroform exposure may cause damage to the liver (where chloroform is metabolised to phosgene) and to the kidneys. Some people develop sores when the skin is immersed inchloroform. 4. Chloroform is slowly oxidised by air (oxygen) in the presence of light to an extremely poisonous gas, carbonyl chloride, also known as phosgene. It is therefore stored in closed dark-coloured bottles which are completely filled so that air is keptout. Triiodomethane (Iodoform) Uses: • It was used earlier as an antiseptic, but the antiseptic properties are due to the liberation of freeiodine and not due to iodoform itself. Drawback: • Because of its objectionable smell, it has been replaced by other formulations containing iodine. Tetrachloromethane (Carbon tetrachloride) Uses: 1. It is produced in large quantities for use in the manufacture of refrigerants and propellants foraerosol cans. 2. It is also used as feedstock in the synthesis of chlorofluorocarbons and other chemicals, inpharmaceutical manufacturing and general solvent use. 3. Until the mid-1960s, it was also widely used as a cleaning fluid, both in industry, as a degreasingagent, and in the home, as a spot remover and fire extinguisher.
ChemContent | Haloalkanes and Haloarenes ChemContent 5 Harmful effects: 1. There is evidence that exposure to carbon tetrachloride causes liver cancer in humans. 2. The most common effects are dizziness, light headedness, nausea and vomiting, which cancause permanent damage to nerve cells. 3. In severe cases, these effects can lead rapidly to stupor, coma, unconsciousness or death. Exposure to CCl4 can make the heart beat irregularly or stop. 4. The chemical may irritate the eyes on contact. When carbon tetrachloride is released into the air,it rises to the atmosphere and depletes the ozone layer. 5. Depletion of the ozone layer is believed to increase human exposure to ultraviolet rays, leading toincreased skin cancer, eye diseases and disorders, and possible disruption of the immunesystem. Freons • The chlorofluorocarbon compounds of methane and ethane are collectively known as freons. • They are extremely stable, unreactive, non-toxic, non-corrosive and easily liquefiable gases. • They are manufactured from tetrachloromethane by Swarts reaction. • By 1974, the total freon production in the world was about 2 billion pounds annually. Uses: 1. These are usually produced for aerosol propellants, refrigeration and air conditioning purposes. 2. Freon 12 (CCl2F2) is one of the most common freons in industrial use. 3. Most freons, even those used in refrigeration, eventually make their way into the atmospherewhere it diffuses unchanged into the stratosphere. Harmful Effect: • In stratosphere, freons can initiate radical chain reactions which can upset the natural ozonebalance.