Ethylene (EtO) is a colorless, flammable gas. It is used primarily in the manufacture of glycol ethers, ethanolamines, and other chemicals, and as a sterilant. It is irritating to eyes, skin, and respiratory tract. Solutions in contact with water cause blisters and dermatitis. Ethylene oxide, epoxyethane, vapor may cause frostbite.
Exposure to ethylene oxide increases the risk of certain cancers in mice and rats. NIOSH Method 1614 is a trapping method using a solid sorbent tube.
Ethylene is a colorless, flammable gas. It is used in the production of fabricated plastics, antifreeze; for making fibers and to manufacture ethylene oxide, polyethylene and other plastics; as a plant growth regulator; and to cause ripening of fruits and vegetables. It is also an industrial solvent, a food preservative and an aerosol degreaser. Exposure to ethylene gas may produce nose and throat irritation, headaches, dizziness and fatigue. Larger exposures can result in nausea, vomiting, respiratory distress and cardiovascular collapse. Death may occur due to asphyxia.
The absorption, distribution and excretion kinetics of inhaled ethylene have been studied in male Sprague-Dawley rats exposed to atmospheric concentrations in closed chambers. Uptake of ethylene is low and clearance due to uptake was about 20 ml/min for a rat of 250 g; the remainder of the inhaled ethylene is excreted into the lungs, where it is exhaled again without becoming systemically available. Most of the exhaled ethylene is metabolized to ethylene oxide, which binds to cellular proteins. Other metabolic products of ethylene are acetaldehyde and ethylene glycol.
Chronic exposure to ethylene produces a variety of symptoms including fatigue, weakness, loss of appetite and abdominal pains (gastric ulcers). Exposure to elevated levels for extended periods may result in heart damage, stroke and leukemia. Ethylene has been shown to be carcinogenic in experimental animals.
Environmental Releases and Exposure
About 74% of ethylene is released to the environment from natural sources; most of the remainder is anthropogenic and releases from petroleum refineries, chemical plants, natural gas processing and coal burning are major sources. In addition, ethylene is produced as a byproduct of the production of ethylene oxide and acetaldehyde from ethylene-containing raw materials.
Ethylene is a volatile organic compound that evaporates rapidly from soil and water and enters the atmosphere. It has been found in ambient air at concentrations of 1-5 ug/m3 in rural and remote sites worldwide. It is also emitted to the air during the destruction of spoiled fruit and vegetables.
In the USA, Japan and western Europe, about 80% of the ethylene is used to make polyethylene (high, low and linear low density), ethylene oxide/ethylene glycols, ethylene dichloride/vinyl chloride, ethylbenzene/styrene, oligomer products and acetaldehyde/acetic acid. An estimated 26% of the ethylene is consumed for producing olefins and cyclic olefins. The rest is used for manufacturing and other purposes. Total world ethylene production is about 18-45 million tonnes/year.
Preparation Of Epoxyethane
Epoxyethane can be produced by the treatment of 2-chloroethanol with potassium hydroxide.
Cl-CH2CH2-OH + KOH = (CH2CH2)O + KCl + H2O
Industrially, it is produced by oxidizing ethylene in the presence of a silver catalyst.
H2C= CH2 + O = C2H4O
Ethylene Oxide can be prepared by decomposing ethylene carbonate in the presence of hexachloroethane at a temperature of 392 – 401°F ( 200 – 210°C).
Epoxyethane can be prepared by the treatment of calcium oxide with ethyl hypochlorite.
2 CH3CH2 – OCl + CaO = 2 (CH2CH2)O + CaCl2 + H2O
It can also be produced by reacting diiodo ethane with silver oxide.
I-CH2CH2-I + Ag2O = (CH2CH2)O
Chemical Properties Of Epoxyethane
Epoxyethane reacts with ethanol to form polyethylene glycol ethers.
(CH2CH2)O + C2H5OH = HO-CH2CH2-OC2H5
Epoxyethane reacts with triethylamine in the presence of water to form choline.
(CH2CH2)O + (CH3)3N + H2O = [HOCH2CH2N(CH3)3]+OH-
It reacts with carboxylic acid like acetic acid and its anhydride in the presence of catalysts to form glycol di and monoesters.
(CH2CH2)O + CH3CO2H = HOCH2CH2-O2CCH3
(CH2CH2)O + (CH3CO)2O = CH3CO2CH2CH2O2CCH3
Ethylene oxide reacts with dialkylamino ethanols to form amino polyethylene glycols.
n (CH2CH2)O+ R2NCH2CH2OH = R2NCH2CH2O – (-CH2CH2O-)n-H
Ethylene oxide passes through an aqueous solution of metal halides to form halohydrins.
2 (CH2CH2)O + C2Cl2 + 2 H2O = 2 HO – CH2CH2 – Cl + Cu(OH)2
The addition of water in epoxyethane leads to the production of ethylene glycol.
(CH2CH2)O + H2O = HOCH2CH2OH
Epoxyethane reacts with hydrogen cyanide to form ethylene cyanohydrin.
(CH2CH2)O + HCN = HO-CH2CH2-CN
Physical Properties Of Epoxyethane
Epoxyethane is a flammable, odorless, and colourless gas which has an ether-like sweet odor. It is miscible in water and has a vapor pressure of 20°C.
It has a molar mass of 44.052 g-mol-1, and a density of -0.88 gcm-3. It melts at -112.46°C and -170.43°F and boils at 10.4°C and 50.7°F.
Uses Of Epoxyethane
• It is used in the production of thickeners.
• It is used as a major component in the production of polyethylene glycol(PEG).
• It is used to process storage facilities.
• It is used in the large-scale production of industrial chemicals.
• It is used as a sterilization agent in the medical industry.
• It is used to accelerate the maturity process of tobacco leaves.
• It is used as a raw material in the production of polysorbate 20.
• It is used as a major constituent in the production of fuel-air explosives.
• It is used as a pesticide.
• It is used in the clothing industry for packaging.
• It is used as a fungicide.
• It is used in the production of ethanolamines, polyglycol ethers, mono-ethylene, diethylene, tri ethylene, and polyethylene glycols which are in turn used in the production of antifreeze, thinners, lubricants, polyester, and lots more.
Despite its enormous uses and benefits in different industries, ethylene oxide is a very lethal substance.
Epoxyethane has a very high carcinogenic, mutagenic and neurotoxic potential and affects respiration hence long-term exposure to it can lead to leukemia, reproductive effects, breast cancer, dizziness, cataracts, pancreatic cancer, neurotoxicity, lymphoma, coma, stomach cancer, seizure.
Short-term exposure to ethylene oxide can lead to cyanosis, weakness, lung injury, skin burns, difficulty in breathing, diarrhea, vomiting, headache, frostbite, reproductive effects, eye burns, and nausea.
Exposure to epoxyethane can be by:
• Working in pharmaceutical companies which use it to sterilize its supplies and equipment, by working in industries that produce it, by working in agricultural firms which use it to regulate insects, by working in industries that produce adhesives, detergents, solvents etc.
• Living near these industries, heating cooking oils etc.
• Consuming products like tobacco which contains it or pharmaceutical products which are sterilized by it.
However, to avert this, the Occupational Safety and Health Administration (OSHA) has set limits to the level of exposure for workers in this industries and has also ordered for the provision of adequate safety clothing for each worker.
In addition, countries have placed laws on the emission of epoxyethane from industries producing and using it.