From Wikipedia, the free encyclopedia.
The chemical compound ethanol, also known as ethyl alcohol or grain alcohol, is the bio-alcohol found in alcoholic beverages. When non-chemists refer to "alcohol", they almost always mean ethanol. Its chemical formula is C2H5OH and its molecular structure is
H H
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H-C-C-O-H
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H H
Properties
Pure ethanol is a flammable, colorless liquid with a boiling point of 78.5° C. Its low melting point of -114.5° C allows it to be used in antifreeze products. It has a pleasant odor reminiscent of whiskey.
Its density is 789 g/L, about 20% less than that of water. It is easily soluble in water and is itself a good solvent, used in perfumes, paints and tinctures. Alcoholic drinks have a large variety of tastes, since various flavor compounds are dissolved during brewing.
A solution of 70-85% of ethanol is commonly used as a disinfectant; it kills organisms by denaturing their proteins and dissolving their lipids: it is effective against most bacteria and fungi, and many viruses, but is ineffective against bacterial spores. This disinfectant property of ethanol is the reason that alcoholic beverages can be stored for a long time.
Ethanol can lose a proton from the hydroxyl group and is a very weak acid, weaker than water.
The CAS number of ethanol is 64-17-5 and its UN number is UN 1170.
Ethanol for use in alcoholic beverages is produced by fermentation: it is a product of sugar metabolism in certain species of yeast in the absence of oxygen. The process of culturing yeast under conditions to produce alcohol is referred to as brewing. Yeasts can grow in the presence of up to only about 14% alcohol, but the concentration of alcohol in the final product can be increased by distillation.
Ethanol is also used as a fuel and in a wide variety of industrial processes. Ethanol for industrial use is often made from petroleum feedstocks, typically from ethylene; this is cheaper than the production by fermentation.
Ethanol for industrial use is normally denatured, meaning small amounts of unpleasant or toxic substances (such as methanol) are added so that it cannot be consumed by humans, thus avoiding the relevant taxes.
Denatured ethanol has the UN number UN 1987 and toxic denatured ethanol has UN 1986.
Beverages containing ethanol are among the most widely used recreational drugs. Their use is legal in the western world, but illegal in Muslim countries. During the period known as Prohibition, from 1919 to 1933, it was also illegal in the United States.
Most countries have laws against drunk driving, driving with a certain concentration of ethanol in the blood. The legal threshold of blood alcohol content ranges from 0.1% to 0.08%, 0.05% and even 0% in different countries.
Most countries also specify a legal drinking age, below which the consumption of alcohol is prohibited.
In many countries, production of alcoholic beverages requires a license, and alcohol production is taxed. In the U.S., the Bureau of Alcohol, Tobacco, Firearms, and Explosives and the Alcohol and Tobacco Tax and Trade Bureau (formerly one organization known as the Bureau of Alcohol, Tobacco and Firearms) enforce regulations related to alcohol. In the UK the Customs and Excise department issues distilling licences.
Some religious groups such as Muslims and Mormons prohibit the consumption of ethanol.
Some religious groups such as Roman Catholicism and Judaism use alcoholic beverages in their sacred rituals.
Several studies have confirmed that regular consumption of small amounts of alcohol has a beneficial effect, as it lowers the incidence of coronary heart disease.
In small amounts, ethanol causes a mild euphoria and removes inhibitions. In larger doses, ethanol acts as a central nervous system (CNS) depressant and causes drunkenness (at a blood ethanol content of about 0.1%), coma and death. A blood ethanol content above 0.4% is generally fatal, although regular heavy drinkers can tolerate higher levels.
Alcoholism, the dependency on alcohol, is a major public health problem. Alcoholics develop a number of health problems, with cirrhosis of the liver being the most important one.
If a mother drinks too much alcohol during pregnancy, the unborn child can develop mental and physical defects. This is known as fetal alcohol syndrome.
Ethanol is quickly absorbed into the bloodstream and reaches the brain. As a small molecule, it is able to cross the blood-brain barrier. The euphorizing effects of ethanol are probably due to its causing the release of endorphins, natural "feel-good" molecules.
The CNS depressant effect likely is due to ethanol's acting on the BK channels. A BK channel is a calcium dependent potassium channel.
It has been known to act on GABA receptors, but this is probably just a secondary effect from activation of the BK channels. It's effect on GABA receptors is probably similar to the action of benzodiazepines such as diazepam. GABA is an inhibitory neurotransmitter, meaning it acts to slow down or inhibit nerve impulses. Ethanol increases the effectiveness of GABA acting through GABAA receptors. When used over a long time, ethanol changes the number and type of GABA receptors, and this is thought to be the cause of the violent withdrawal effects of alcoholics.
Ethanol also interferes with synaptic firing and causes the death of brain cells. This cell death is caused by an increased concentration of intracellular calcium which weakens the electrochemical gradient across the cell membranes. It is this gradient which is the motive force of membrane pumps and channels (cells, especially neurons, quickly die without proper membrane pump and channel function). There is also direct damage to cell membranes from free-radicals that are produced from alcohol metabolism.
The liver contains a special enzyme (alcohol dehydrogenase) that breaks down alcohols into acetaldehyde, which is turned into acetate by the enzyme acetaldehyde dehydrogenase, and then yet another enzyme converts the acetate into fats or carbon dioxide and water. The fats are mostly deposited locally which leads to the characteristic "beer belly". Chronic drinkers, however, so tax this metabolic pathway that things go awry: fatty acids build up as plaques in the capillaries around liver cells and those cells begin to die which leads to cirrhosis of the liver. The liver is part of the body's filtration system and if it is damaged then certain toxins build up thus leading to symptoms of jaundice.
The alcohol dehydrogenase of women is less effective than that of men. Combined with the lower amount of water in women's bodies, this means that women typically become drunk earlier than men. Some people, especially in East Asia, have a genetic mutation in their alcohol dehydrogenase gene, resulting in less potent alcohol dehydrogenase. These people are unable to drink much alcohol before becoming drunk, and are therefore less susceptible to alcoholism.
Drugs like disulfiram block the enzyme acetaldehyde dehydrogenase, thus leading to a buildup of acetaldehyde after alcohol consumption. This causes severe hangover symptoms, and the drugs are therefore used to support treatment of alcoholism.
Consumption of ethanol has a rapid diuretic effect, meaning that more urine than usual is produced. Ethanol inhibits the production of antidiuretic hormone, and this is the cause of the diuretic effect.
Overconsumption can therefore lead to dehydration (the loss of water).
It is difficult to replenish the body's fluids using only alcoholic beverages. As large amounts of alcohol are consumed, the diuretic effect causes the body to lose more water than is contained in the beverage.
After overconsumption of ethanol, a hangover develops with symptoms of dry mouth, headache, nausea and light sensitivity. These symptoms are partly due to the toxic acetaldehyde produced from alcohol by alcohol dehydrogenase, and partly due to general dehydration.
Ethanol is flammable and burns more cleanly than many other fuels.
When fully combusted its combustion products are only carbon dioxide and water. For this reason, it is favoured for environmentally conscious transport schemes and has been used to fuel public buses. However, pure ethanol attacks certain rubber and plastic materials and cannot be used in unmodified car engines. Additionally, ethanol has a much migher octane rating than ordinary gasoline, requiring changes to the spark timing in engines.
A mixture containing gasoline with at least 10% ethanol is known as gasohol. One common gasohol variant is "E15", containing 15% ethanol and 85% gasoline. These concentrations are generally safe for regular automobile engines, and some regions and municipalities mandate that the locally-sold fuels contain limited amounts of ethanol.
The term "E85 ethanol" is used for a mixture of 15% gasoline and 85% ethanol. Beginning with the model year 1999, a number of vehicles in the U.S. were manufactured so as to be able to run on E85 fuel without modification. Most of the vehicles have been officially classified as light trucks (a class containing minivans, SUVss, and pickup trucks). These vehicles are often labeled dual fuel or flexible fuel vehicles, since they can automatically detect the type of fuel and change the engine's behavior to compensate for the different ways that they burn in the engine cylinders.
In Brazil and the United States, the use of ethanol from sugar cane and grain as car fuel has been promoted by government programs. Some individual U.S. states in the corn belt began subsidizing ethanol from corn (maize) after the Arab oil embargo of 1973. The Energy Tax Act of 1978 authorized an excise tax exemption for biofuels, chiefly gasohol. The excise tax exemption alone has been estimated as worth US$11.4 billion per year. Another U.S. federal program guaranteed loans for the construction of ethanol plants, and in 1986 the U.S. even gave ethanol producers free corn.
Arguments in favor of ethanol are the search for decreased dependency on oil producing countries and the decreased net ouptut of the greenhouse gas carbon dioxide. Some critics argue that it is mainly a government subsidy for corn-growing agribusiness. The Archer Daniels Midland Corporation of Decatur, Illinois, better known as ADM, the world's largest grain processor, produces 40% of the ethanol used to make gasohol in the U.S.. The company and its officers have been eloquent in their defense of ethanol and generous in contributing to both political parties.
Other critics contend that it is economically absurd to consider ethanol from grain as a replacement for petroleum, when industrial ethanol is made from petroleum feedstocks because it is far cheaper than fermented ethanol. Environmentalists do not like arguments like this, since they advocate continued usage of fossil fuels rather than a transition to renewable energy.
There is widespread belief that ethanol containing fuel is more environmentally friendly than gasoline without additives. However, there is a controversy over whether requiring ethanol in automotive fuel is wise since it has been argued that the beneficial effects of ethanol can be achieved with other cheaper additives made from petroleum. Also, both the Environmental Protection Agency and the National Academy of Sciences have issued "reports showing that adding ethanol to gasoline will at best have no effect on air quality and could even make it worse. Studies show ethanol could even increase emissions of nitrogen oxides and volatile organic compounds, which are major ingredients of smog."[1]
Some studies have found that the total energy needed to produce one gallon of ethanol by fermentation (fertilizing, fuel for farm tractors, harvesting and transporting the grain, building and operating an ethanol plant, the natural gas used to distill corn sugars into alcohol) exceeds the energy content of that gallon of ethanol. Since production energy comes mostly from fossil fuels, gasohol isn't just wasting money but hastening the depletion of nonrenewable resources, critics have argued.
Early corn ethanol production systems have largely been shown to have a negative net energy balance, meaning that the energy produced did not equal or exceed the amount of energy going in to make the ethanol. However, refinements to ethanol production procedures has turned the tide, and most studies of modern systems indicate that they now have a positive net energy balance. As late as 2001, analyses have continued to indicate that ethanol has a negative energy balance. A peer-reviewed study by Cornell University ecology professor David Pimentel pointed toward this conclusion, but the study was rebutted by others in the field, forcing Pimentel to revise his figures. In August 2003, he stated in a Cornell bulletin that production of a gallon of ethanol only takes 29% more energy than it produces.
Many other studies of corn ethanol production have been conducted, with greatly varied net energy estimates. Most indicate that production requires energy equvialent to 1/2, 2/3, or more of the fuel produced is required to run the process. A 2002 report by the United States Department of Agriculture concluded that corn ethanol productin in the U.S. has a net energy value of 1.34, meaning 34% more energy was produced than what went in. Doing the math, this means that 75% (1/1.34) of each gallon produced is required to replace the energy used in production.
The country of Brazil mostly uses sugar cane to make ethanol. Producing ethanol from that plant is much easier than it is with corn, though there have been other environmental concerns regarding the use of sugar cane. Many fields are burned once the harvesting is complete, and some researchers have indicated that this biomass left over after harvesting could also be a large fuel resource.
Sugar cane grows in the southern United States, but not in the cooler climates where corn is dominant. However, many regions that currently grow corn are also appropriate areas for growing sugar beets. Some studies indicate that using these sugar beets would be a much more efficient method for making ethanol in the U.S. than using corn.
Production
Legalities
Social and religious customs
Effects on the human body
Action on the brain
Metabolism of alcohol and action on the liver
Dehydration
Hangover
Ethanol as fuel
Environmental friendliness
Net energy value
Alternate sources
See also
External links
