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Ethylene oxide
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Ethylene oxide is the organic compound with the formula C2H4O. This colorless flammable gas with a faintly sweet odor is the simplest epoxide, a three-membered ring consisting of two carbon and one oxygen atom. It is commonly handled and shipped as a refrigerated liquid. It is the chief precursor to ethylene glycol and other high volume chemicals but is also used for medical sterilization.
lene oxide was first reported in 1859 by the French chemist Charles-Adolphe Wurtz, who prepared it by treating 2-chloroethanol with a base.
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Ethylene oxide is the organic compound with the formula C2H4O. This colorless flammable gas with a faintly sweet odor is the simplest epoxide, a three-membered ring consisting of two carbon and one oxygen atom. It is commonly handled and shipped as a refrigerated liquid. It is the chief precursor to ethylene glycol and other high volume chemicals but is also used for medical sterilization.
History
Ethylene oxide was first reported in 1859 by the French chemist Charles-Adolphe Wurtz, who prepared it by treating 2-chloroethanol with a base. It achieved industrial importance during World War I as a precursor to both the coolant ethylene glycol and the chemical weapon mustard gas. In 1931, Theodore Lefort, another French chemist, discovered a means to prepare ethylene oxide directly from ethylene and oxygen, using silver as a catalyst. Since 1940, almost all ethylene oxide produced industrially has been made using this method. Ethylene oxide sterilization for the preservation of spices was patented in 1938 by the American chemist Lloyd Hall, and it is still used in that role.
Production
Ethylene oxide is produced by oxidation of ethylene with oxygen using a modified silver catalyst at 200–300 °C. Typically, chemical modifiers such as chlorine are also included. Pressures used are in the region of 1-2MPa. The chemical equation are:
- H2C=CH2 + ½ O2 ? C2H4O
The typical yield for this reaction under industrial conditions is 70-80%. Approximately 15,000,000,000 kg are produced annually.
In terms of the mechanism of this reaction, an intermediate oxametallacycle is proposed to react by either of two pathways, to give the desired ethylene oxide or acetaldehyde. The latter pathway is the first step in complete combustion, leading to carbon dioxide and water:
- CH3CHO + 5/2 O2 ? 2 CO2 + 2 H2O
Ethylene oxide can be produced in the laboratory by the action of an alkali hydroxide on ethylene chlorohydrin.
- HOH2CCH2Cl + NaOH ? C2H4O + NaCl + H2O
Uses
Most ethylene oxide is consumed as the precursor to ethylene glycol as well as a variety of other chemicals. Ethylene glycol is more commonly known for its use as an automotive coolant and antifreeze. Other chemical applications include ethanolamine, diverse surfactants (see reactions section below), and glycol ethers such as ethoxyethanol.
Ethylene oxide is also used as sterilant, although the amount used for this purpose is minor compared to the applications in the chemical industry. The gas kills bacteria (and their endospores), mold, and fungi. It is used to sterilize substances that would be damaged by high temperature techniques such as pasteurization. Ethylene oxide is widely used to sterilize the majority of medical supplies such as bandages, sutures, and surgical implements. In traditional chamber sterilization method, where a chamber is flooded with a mixture of ethylene oxide and other gases that are later aerated. The more recent gas diffusion method developed in 1967 relies on a bag that wraps the elements to be sterilized and serves as a mini-chamber in order to minimize gas consumption and make the process economically feasible for small loads. Other names for this alternative method for small loads are the Anprolene method, bag sterilization method or micro-dose sterilization method.
Reactions
Most reactions are ring openings by nucleophiles. In industry, ethylene oxide is hydrolyzed (reacted with water) in the presence of a sulfuric acid catalyst. A tenfold molar excess of water is used to obtain ethylene glycol:
- C2H4O + H2O ? HOCH2CH2OH
Despite the large excess of water, various types of polyethylene glycol (PEG) or polyethylene oxide (PEO) are still formed as secondary products. The degree of polymerization increases as a smaller proportion of water is used:
- n(CH2CH2O) + H2O ? HO(CH2CH2O)nH
For example, under the right conditions it can give diethylene glycol (HOCH2CH2OCH2CH2OH), triethylene glycol, etc.
Similarly, reaction with ammonia yields ethanolamine as well as diethanolamine and triethanolamine.
Ethylene oxide is also important in the manufacture of surfactants and other detergents, in a process called ethoxylation.
One class of ethylene oxide derivatives that has attracted much scientific attention is the crown ethers, which are cyclic oligomers of ethylene oxide. These compounds have the ability to make ionic compounds such as salts soluble in nonpolar solvents which they otherwise could not dissolve in. However, the high cost of these compounds has largely confined their use to the laboratory rather than industrial practice.
Health effects
Ethylene oxide is toxic by inhalation with an LD50 of 330 mg/kg. Symptoms of overexposure include headache and dizziness, progressing with increasing exposure to convulsions, seizure and coma. It is also an irritant to skin and the respiratory tract, and inhaling the vapors may cause the lungs to fill with fluid several hours after exposure.
Ethylene oxide is usually stored as a pressurized or refrigerated liquid. At room temperature and pressure, it rapidly evaporates, potentially causing frostbite in cases of skin exposure.
Laboratory animals exposed to ethylene oxide for their entire lives have had a higher incidence of liver cancer. However, studies on human beings who have worked with ethylene oxide for extended periods and may have experienced low doses during that time have found no increase in cancer risk. Chronic ethylene oxide exposure may increase the risk of cataracts in humans.
In animals, ethylene-oxide can cause numerous reproductive effects, including mutations and a higher rate of miscarriages. Its reproductive effects on humans have not been well studied, but it is considered probable that ethylene oxide exposure has similar effects on human reproduction.
Ethylene oxide is classified as carcinogenic to humans by the International Agency for Research on Cancer (IARC).
See also
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