Ethanol

"Grain alcohol" redirects here. For the distilled high-proof liquor of similar name, see neutral grain spirits.

Template:Chembox new Ethanol, also known as ethyl alcohol, drinking alcohol or grain alcohol, is a flammable, colorless, slightly toxic chemical compound, and is best known as the alcohol found in alcoholic beverages. In common usage, it is often referred to simply as alcohol. Its molecular formula is variously represented as EtOH, CH₃CH₂OH, C₂H₅OH or as its empirical formula C₂H₆O. Based on its abilities to change the human consciousness, alcohol is considered a drug.

History

Ethanol has been used by humans since prehistory as the intoxicating ingredient in alcoholic beverages. Dried residues on 9000-year-old pottery found in northern mainland China imply the use of alcoholic beverages even among Neolithic peoples. Its isolation as a relatively pure compound was first achieved by Persian alchemists who developed the art of distillation during the Abbasid caliphate, the most notable of whom was Al-Razi. The writings attributed to Jabir Ibn Hayyan (Geber) (721-815) mention the flammable vapors of boiled wine. Al-Kindī (801-873) unambiguously described the distillation of wine. Distillation of ethanol from water yields a product that is at most 95.6% ethanol, because ethanol forms an azeotrope with water. Absolute ethanol was first obtained in 1796 by Johann Tobias Lowitz, by filtering distilled ethanol through charcoal.

Antoine Lavoisier described ethanol as a compound of carbon, hydrogen, and oxygen, and in 1808, Nicolas-Théodore de Saussure determined ethanol's chemical formula, Template:Inote and fifty years later, in 1858, Archibald Scott Couper published a structural formula for ethanol: this places ethanol among the first chemical compounds to have their chemical structures determined.

Ethanol was first prepared synthetically in 1826, through the independent efforts of Henry Hennel in Great Britain and S.G. Sérullas in France. Michael Faraday prepared ethanol by the acid-catalysed hydration of ethylene in 1828, in a process similar to that used for industrial ethanol synthesis today.

Ethanol served as lamp fuel in pre-Civil War United States and helped power early Model T automobiles. But the fuel couldn't compete with the low cost and availability of petroleum, and ethanol faded from the public eye. The recent rise in oil prices has spurred renewed interest.

Physical properties

Chemical formula of ethanol, (C is carbon, the dash is a single bond, H is hydrogen, O is oxygen)

Ethanol's hydroxyl group is able to participate in hydrogen bonding. At the molecular level, liquid ethanol consists of hydrogen-bonded pairs of ethanol molecules (dimers); this phenomenon renders ethanol more viscous and less volatile than less polar organic compounds of similar molecular weight. Ethanol, like most short-chain alcohols, is flammable, colorless, has a strong odor, and is volatile.

Ethanol has a refractive index of 1.3614, and is a versatile solvent. It is miscible with water and with most organic liquids, including nonpolar liquids such as aliphatic hydrocarbons. Due to the hydrogen bonding properties of ethanol, it can absorb water from the air. Among ionic compounds, many monovalent salts are at least somewhat soluble in ethanol, with salts of large, polarizable ions being more soluble than salts of smaller ions. Most salts of polyvalent ions are practically insoluble in ethanol. Ethanol is used as a solvent in dissolving medicines, food flavorings and colorings that do not dissolve easily in water. The ethanol molecule has a hydrophilic OH group that helps it dissolve polar molecules and ionic substances. Additionally, ethanol's short, hydrophobic hydrocarbon chain can attract non-polar molecules. Thus ethanol can dissolve both polar and non-polar substances.

Several unusual phenomena are associated with mixtures of ethanol and water. Ethanol-water mixtures have less volume than their individual components: a mixture of equal volumes ethanol and water has only 95.6% of the volume of equal parts ethanol and water, unmixed. The addition of even a few percent of ethanol to water sharply reduces the surface tension of water. This property partially explains the tears of wine phenomenon: when wine is swirled inside a glass, ethanol evaporates quickly from the thin film of wine on the wall of the glass. As its ethanol content decreases, its surface tension increases, and the thin film beads up and runs down the glass in channels rather than as a smooth sheet.

Chemistry

The chemistry of ethanol is largely that of its hydroxyl group. Ethanol is classified as a primary alcohol, meaning that the carbon to which its hydroxyl group is attached has at least two hydrogen atoms attached to it as well.

Acid-base chemistry

Ethanol's hydroxyl proton is very weakly acidic; it is an even weaker acid than water. Ethanol can be quantitatively converted to its conjugate base, the ethoxide ion (CH₃CH₂O⁻), by reaction with an alkali metal such as sodium. This reaction evolves hydrogen gas:

2CH₃CH₂OH + 2Na → 2CH₃CH₂ONa + H₂

Nucleophilic substitution

In aprotic solvents, ethanol reacts with hydrogen halides to produce ethyl halides such as ethyl chloride and ethyl bromide via nucleophilic substitution:

CH₃CH₂OH + HCl → CH₃CH₂Cl + H₂O

(Note that the above requires catalyst such as zinc chloride)

CH₃CH₂OH + HBr → CH₃CH₂Br + H₂O

Ethyl halides can also be produced by reacting ethanol by more specialized halogenating agents, such as thionyl chloride for preparing ethyl chloride, or phosphorus tribromide for preparing ethyl bromide.

Esterification

Under acid-catalysed conditions, ethanol reacts with carboxylic acids to produce ethyl esters and water:

RCOOH + HOCH₂CH₃ → RCOOCH₂CH₃ + H₂O

The reverse reaction, hydrolysis of the resulting ester back to ethanol and the carboxylic acid, limits the extent of reaction, and high yields are unusual unless water can be removed from the reaction mixture as it is formed. Esterification can also be carried out using more a reactive derivative of the carboxylic acid, such as an acyl chloride or acid anhydride.

Ethanol can also form esters with inorganic acids. Diethyl sulfate and triethyl phosphate, prepared by reacting ethanol with sulfuric and phosphoric acid, respectively, are both useful ethylating agents in organic synthesis. Ethyl nitrite, prepared from the reaction of ethanol with sodium nitrite and sulfuric acid, was formerly a widely-used diuretic.

Dehydration

Strong acids, such as sulfuric acid, can catalyse ethanol's dehydration to form either diethyl ether or ethylene:

2 CH₃CH₂OH → CH₃CH₂OCH₂CH₃ + H₂O

CH₃CH₂OH → H₂C=CH₂ + H₂O

Which product, diethyl ether or ethylene, predominates depends on the precise reaction conditions.

Oxidation

Ethanol combusting in the confines of an evaporating dish

Ethanol can be oxidized to acetaldehyde, and further oxidized to acetic acid. In the human body, these oxidation reactions are catalysed by enzymes. In the laboratory, aqueous solutions of strong oxidizing agents, such as chromic acid or potassium permanganate, oxidize ethanol to acetic acid, and it is difficult to stop the reaction at acetaldehyde at high yield. Ethanol can be oxidized to acetaldehyde, without overoxidation to acetic acid, by reacting it with pyridinium chromic chloride.

Combustion

Combustion of ethanol forms carbon dioxide and water:

C₂H₅OH + 3 O₂ → 2 CO₂ +3 H₂O

Production

94% denatured ethanol sold in a bottle for household use.

Ethanol is produced both as a petrochemical, through the hydration of ethylene, and biologically, by fermenting sugars with yeast. Which process is more economical is dependent upon the prevailing prices of petroleum and of grain feedstocks.

Ethylene hydration

Ethanol for use as industrial feedstock is most often made from petrochemical feedstocks, typically by the acid-catalyzed hydration of ethene, represented by the chemical equation

C₂H_4(g) + H₂O_(g) → CH₃CH₂OH_(l)

The catalyst is most commonly phosphoric acid, adsorbed onto a porous support such as diatomaceous earth or charcoal; this catalyst was first used for large-scale ethanol production by the Shell Oil Company in 1947. Solid catalysts, mostly various metal oxides, have also been mentioned in the chemical literature. The product formed from the reaction is usually in a liquid state, due to the high pressure system it is created in. It forms a vapour when it leaves the reaction vessel, due to the high temperature (300 degrees Celsius) that is used for the reaction.

In an older process, first practiced on the industrial scale in 1930 by Union Carbide, but now almost entirely obsolete, ethene was hydrated indirectly by reacting it with concentrated sulfuric acid to produce ethyl sulfate, which was then hydrolysed to yield ethanol and regenerate the sulfuric acid:

C₂H₄ + H₂SO₄ → CH₃CH₂SO₄H

CH₃CH₂SO₄H + H₂O → CH₃CH₂OH + H₂SO₄

Fermentation

Further information: Ethanol fermentation

Ethanol for use in alcoholic beverages, and the vast majority of ethanol for use as fuel, is produced by fermentation: when certain species of yeast (most importantly, Saccharomyces cerevisiae) metabolize sugar in the absence of oxygen, they produce ethanol and carbon dioxide. The overall chemical reaction conducted by the yeast may be represented by the chemical equation:

C₆H₁₂O₆ → 2 CH₃CH₂OH + 2 CO₂

The process of culturing yeast under conditions to produce alcohol is referred to as brewing. Brewing can only produce relatively dilute concentrations of ethanol in water; concentrated ethanol solutions are toxic to yeast. The most ethanol-tolerant strains of yeast can survive in up to approximately 15% ethanol by volume.

During the fermentation process, it is important to prevent contact with oxygen. In the presence of oxygen, yeast undergo aerobic respiration which produces carbon dioxide and water, and does not produce ethanol.

In order to produce ethanol from starchy materials such as cereal grains, the starch must first be broken down into sugars. In brewing beer, this has traditionally been accomplished by allowing the grain to germinate, or malt. In the process of germination, the seed produces enzymes that can break its starches into sugars. For fuel ethanol, this hydrolysis of starch into glucose is accomplished more rapidly by treatment with dilute sulfuric acid, fungal amylase enzymes, or some combination of the two.

Cellulosic ethanol

Main article: Cellulosic ethanol

Glucose for fermentation into ethanol can also be obtained from cellulose. Until recently, however, the cost of the cellulase enzymes that could hydrolyse cellulose has been prohibitive. The Canadian firm Iogen brought the first cellulose-based ethanol plant on-stream in 2004. The primary consumer thus far has been the Canadian government, which, along with the United States government (particularly the Department of Energy's National Renewable Energy Laboratory), has invested millions of dollars into assisting the commercialization of cellulosic ethanol. Realization of this technology would turn a number of cellulose-containing agricultural byproducts, such as corncobs, straw, and sawdust, into renewable energy resources.

Other enzyme companies are developing genetically engineered fungi which would produce large volumes of cellulase, xylanase and hemicellulase enzymes which can be utilized to convert agricultural residues such as corn stover, wheat straw and sugar cane bagasse and energy crops such as Switchgrass into fermentable sugars which may be used to produce cellulosic ethanol.

Cellulosic materials typically contain, in addition to cellulose, other polysaccharides, including hemicellulose. When hydrolysed, hemicellulose breaks down into mostly five-carbon sugars such as xylose. S. cerevisiae, the yeast most commonly used for ethanol production, cannot metabolize xylose. Other yeasts and bacteria are under investigation to metabolize xylose and so improve the ethanol yield from cellulosic material.

Prospective technologies

The anaerobic bacterium Clostridium ljungdahlii, recently discovered in commercial chicken wastes, can produce ethanol from single-carbon sources including synthesis gas, a mixture of carbon monoxide and hydrogen that can be generated from the partial combustion of either fossil fuels or biomass. Use of these bacteria to produce ethanol from synthesis gas has progressed to the pilot plant stage at the BRI Energy facility in Fayetteville, Arkansas.

Another prospective technology is the closed-loop ethanol plant. Ethanol produced from corn has a number of critics who suggest that it is primarily just recycled fossil fuels because of the energy required to grow the grain and convert it into ethanol. However, the closed-loop ethanol plant attempts to address this criticism. In a closed-loop plant, the energy for the distillation comes from fermented manure, produced from cattle that have been fed the by-products from the distillation. The leftover manure is then used to fertilize the soil used to grow the grain. Such a process is expected to have a much lower fossil fuel requirement. However, general thermodynamic considerations indicate that the total efficiency of such plants, in combination with the production of cellulose/sugar, will remain relatively low.

Though in an early stage of research, there is some development of alternative production methods that use feedstocks such as municipal waste or recycled products, rice hulls, sugarcane bagasse, small diameter trees, wood chips, and switchgrass.

Testing

In breweries and biofuel plants, the quantity of ethanol present is measured using one of two methods. Infrared ethanol sensors measure the vibrational frequency of dissolved ethanol using the CH band at 2900 cm^-1. This method uses a relatively inexpensive solid state sensor that compares the CH band with a reference band to calculate the ethanol content. This calculation makes use of the Beer-Lambert law.

Alternatively, by measuring the density of the starting material, and the density of the product, using a hydrometer, the change in specific gravity during fermentation is used to derive the alcohol content. This is an inexpensive and indirect method but has a long history in the beer brewing industry.

Purification

Main article: Ethanol purification

Near infrared spectrum of liquid ethanol.

The product of either ethylene hydration or brewing is an ethanol-water mixture. For most industrial and fuel uses, the ethanol must be purified. Fractional distillation can concentrate ethanol to 95.6% by weight (89.5 mole%). The mixture of 95.6% ethanol and 4.4% water (percentage by weight) is an azeotrope with a boiling point of 78.2 °C, and cannot be further purified by distillation.

In one common industrial method to obtain absolute alcohol, a small quantity of benzene is added to rectified spirit and the mixture is then distilled. Absolute alcohol is obtained in the third fraction that distills over at 78.2 °C (351.3 K).

Because a small amount of the benzene used remains in the solution, absolute alcohol produced by this method is not suitable for consumption, as benzene is carcinogenic.

There is also an absolute alcohol production process by desiccation using glycerol. Alcohol produced by this method is known as spectroscopic alcohol - so called because the absence of benzene makes it suitable as a solvent in spectroscopy.

Currently, the most popular method of purification past 95.6% purity is desiccation using adsorbents such as starch or zeolites, which adsorb water preferentially. Azeotropic distillation and extractive distillation techniques also exist.

Types of ethanol

Alcoholic beverages

Distilled alcoholic beverages are usually distilled to a high purity and then diluted. However, in some countries, rectified spirit (95-96%) is sold directly to the consumer, for human consumption. Also, vodka is rectified spirit diluted to 37.5-60% ABV.

Denatured alcohol

Main article: Denatured alcohol

In most jurisdictions, the sale of ethanol, as a pure substance, or in the form of alcoholic beverages, is heavily taxed. In order to relieve non-beverage industries of this tax burden, governments specify formulations for denatured alcohol, which consists of ethanol blended with various additives to render it unfit for human consumption. These additives, called denaturants, are generally either toxic (such as methanol) or have unpleasant tastes or odors (such as denatonium benzoate).

Specialty denatured alcohols are denatured alcohol formulations intended for a particular industrial use, containing denaturants chosen so as not to interfere with that use. While they are not taxed, purchasers of specialty denatured alcohols must have a government-issued permit for the particular formulation they use and must comply with other regulations.

Completely denatured alcohols are formulations that can be purchased for any legal purpose, without permit, bond, or other regulatory compliance. It is intended that it be difficult to isolate a product fit for human consumption from completely denatured alcohol. For example, the completely denatured alcohol formulation used in the United Kingdom contains (by volume) 89.66% ethanol, 9.46% methanol, 0.50% pyridine, 0.38% naphtha, and is dyed purple with methyl violet.

Absolute ethanol

Absolute or anhydrous alcohol generally refers to purified ethanol, containing no more than one percent water. Many forms of absolute alcohol are not intended for human consumption and contain trace amounts of toxic benzene. For human consumption, currently, the most popular method of purification past 95.6% purity is desiccation using adsorbents such as starch or zeolites, which adsorb water preferentially.

Pure ethanol is classed as 200 proof in the USA, equivalent to 175 degrees proof in the (now rarely used) UK system.

Neutralized ethanol

Neutralized ethanol is used for some analytical purposes. The pH indicators are acid/base molecules that change color in solution depending on the solution's acidity. Neutralized ethanol is used in order to compensate for this error. Indicator (for example, phenolphthalein) is added to the ethanol solvent first and KOH is added until the color of the solution turns pale pink. The so obtained "neutralized ethanol" is then added to the target of the titration, which may be sample of neat organic acid. The titration stops when the same pale pink color is achieved. This way, the indicator neutralization error is eliminated.

Use

As a fuel

A Ford Taurus "fueled by clean burning ethanol" owned by New York City.

Main article: Ethanol fuel

The largest single use of ethanol is as a motor fuel and fuel additive. The largest national fuel ethanol industries exist in Brazil (gasoline sold in Brazil contains at least 20% ethanol and hydrous ethanol is also used as fuel). For ethanol to be suitable for use as a replacement to petrol in its pure form, it must be distilled to at least 70-80% purity by volume. For use as an additive to petrol, almost all water must be removed, otherwise it will separate from the mixture and settle to the bottom of the fuel tank, causing the fuel pump to draw water into the engine, which will cause the engine to stall.

Today, almost 50% of Brazilian cars are able to use 100% ethanol as fuel, which includes ethanol-only engines and flex-fuel engines. Flex-fuel engines are able to work with all ethanol, all gasoline, or any mixture of both, giving the buyer a choice for a perfect balance between price and performance. That was possible only due to the capability of efficient sugar cane production. Sugar cane not only has a greater concentration of sucrose (about 30% more than corn), but is also much easier to extract. The bagasse generated by the process is not wasted; it is utilized in power plants as a surprisingly efficient fuel to produce electricity. World production of ethanol in 2006 was 51 billion liters, (13.5 billion gallons), with 69% of the world supply coming from Brazil and the United States.

According to the Renewable Fuels Association, as of November 2006, 107 grain ethanol biorefineries in the United States have the capacity to produce 5.1 billion gallons of ethanol per year. An additional 56 construction projects underway (in the U.S.) can add 3.8 billion gallons of new capacity in the next 18 months. Over time, it is believed that a material portion of the ~150 billion gallon per year market for gasoline will begin to be replaced with fuel ethanol. The United States RFS (renewable fuel standard) requires that 4 billion gallons of "renewable fuel" be used in 2006 and this requirement will grow to a yearly production of 7.5 billion gallons by 2012.

Controversy

As reported in "The Energy Balance of Corn Ethanol: an Update," the energy returned on energy invested EROEI for ethanol made from corn in the U.S. is 1.34 (it yields 34% more energy than it takes to produce it). Input energy includes natural gas based fertilizers, farm equipment, transformation from corn or other materials, and transportation. However, other researchers report that the production of ethanol consumes more energy than it yields.

Lately criticism and controversy has been growing over the massive subsidies that some companies have been receiving for ethanol production, including "the bulk of the more than $10 billion in subsidies to [Archer-Daniels-Midland] since 1980," according to the CATO institute. Recent articles have also blamed subsidized ethanol production for the nearly 200% increase in milk prices since 2004, although that is disputed by some.

Oil has historically had a much higher EROEI, especially on land in areas with pressure support, but also under the sea, which only offshore drilling rigs can reach. Apart from this, the amount of ethanol needed to run the United States, for example, is greater than its own farmland could produce, even if fields now used for food were converted for production of non-food-grade corn. It has been estimated that "if every bushel of U.S. corn, wheat, rice and soybean were used to produce ethanol, it would only cover about 4% of U.S. energy needs on a net basis." It is for these reasons that ethanol alone is generally not seen as a solution to replacing conventional oil.

In the United States, preferential regulatory and tax treatment of ethanol (and methanol) automotive fuels introduces complexities beyond the energy balance inherent in the engineering merits of the fuels themselves. North American automakers have in 2006 and 2007 promoted a blend of 85% ethanol and 15% gasoline, marketed as E85, and their flex-fuel vehicles, e.g. GM's "Live Green, Go Yellow" campaign. The apparent motivation is the nature of U.S. Corporate Average Fuel Economy (CAFE) standards, which give an effective 54% fuel efficiency bonus to vehicles capable of running on 85% alcohol blends over vehicles not adapted to run on 85% alcohol blends. In addition to this auto manufacturer-driven impetus for 85% alcohol blends, the United States Environmental Protection Agency had authority to mandate that minimum proportions of oxygenates be added to automotive gasoline on regional and seasonal bases from 1992 until 2006 in an attempt to reduce air pollution, in particular ground-level ozone and smog. As a consequence, much gasoline sold in the United States is blended with up to 10% of an unspecified oxygenating agent. Groundwater contamination scares and the State of California's ban of the substance as a gasoline additive has allowed ethanol to displace methyl tert(iary)-butyl ether (MTBE) as the most popular fuel oxygenate in the United States.

Rocket fuel

Ethanol was commonly used as fuel in early bipropellant rocket vehicles, in conjunction with an oxidizer such as liquid oxygen. The German V-2 rocket of World War II, credited with beginning the space age, used ethanol, mixed with water to reduce the combustion chamber temperature. The V-2's design team helped develop U.S. rockets following World War II, including the ethanol-fueled Redstone rocket, which launched the first U.S. satellite. Alcohols fell into general disuse as more efficient rocket fuels were developed.

Alcoholic beverages

Main article: Alcoholic beverage

Ethanol is the principal psychoactive constituent in alcoholic beverages, with depressant effects to the central nervous system. Similar psychoactives include those which also interact with GABA receptors, such as gamma-hydroxybutyric acid.

Alcoholic beverages vary considerably in their ethanol content and in the foodstuffs from which they are produced. Most alcoholic beverages can be broadly classified as fermented beverages, beverages made by the action of yeast on sugary foodstuffs, or as distilled beverages, beverages whose preparation involves concentrating the ethanol in fermented beverages by distillation. The ethanol content of a beverage is usually measured in terms of the volume fraction of ethanol in the beverage, expressed either as a percentage or in alcoholic proof units.

Fermented beverages can be broadly classified by the foodstuff from which they are fermented. Beers are made from cereal grains or other starchy materials, wines and ciders from fruit juices, and meads from honey. Cultures around the world have made fermented beverages from numerous other foodstuffs, and local and national names for various fermented beverages abound. Fermented beverages may contain up to 15–25% ethanol by volume, the upper limit being set by the yeast's tolerance for ethanol, or by the amount of sugar in the starting material.

Distilled beverages are made by distilling fermented beverages. Broad categories of distilled beverages include whiskeys, distilled from fermented cereal grains; brandies, distilled from fermented fruit juices, and rum, distilled from fermented molasses or sugarcane juice. Vodka and similar neutral grain spirits can be distilled from any fermented material (grain or potatoes are most common); these spirits are so thoroughly distilled that no tastes from the particular starting material remain. Numerous other spirits and liqueurs are prepared by infusing flavors from fruits, herbs, and spices into distilled spirits. A traditional example is gin, which is created by infusing juniper berries into a neutral grain alcohol.

In a few beverages, ethanol is concentrated by means other than distillation. Applejack is traditionally made by freeze distillation: water is frozen out of fermented apple cider, leaving a more ethanol-rich liquid behind. Eisbier (most commonly, eisbock) is also freeze-distilled, with beer as the base beverage. Fortified wines are prepared by adding brandy or some other distilled spirit to partially-fermented wine. This kills the yeast and conserves some of the sugar in grape juice; such beverages are not only more ethanol-rich, but are often sweeter than other wines.

Alcoholic beverages are sometimes used in cooking, not only for their inherent flavors, but also because the alcohol dissolves hydrophobic flavor compounds which water cannot.

Chemicals derived from ethanol

Main article: Chemical derivatives of ethanol

Ethanol is an important industrial ingredient and has widespread use as a base chemical for more complicated compounds.

Other uses

Ethanol is easily soluble in water and is a good solvent. Ethanol is less polar than water and used in perfumes, paints and tinctures.

Ethanol is used in medical wipes and in most common antibacterial hand sanitizer gels at a concentration of about 62% (percentage by weight, not volume) as an antiseptic. Ethanol kills organisms by denaturing their proteins and dissolving their lipids and is effective against most bacteria and fungi, and many viruses, but is ineffective against bacterial spores. Alcohol does not act like an antibiotic and is not effective against infections by ingestion, nor can bacteria develop resistance.

Ethanol is sometimes used as an antidote in cases of methanol poisoning.

Ethanol is also used in design and sketch art markers, such as Copic, and Tria.

Metabolism and toxicology

Main article: Ethanol metabolism

Pure ethanol is a tasteless liquid with a strong and distinctive odor that produces a characteristic heat-like sensation when brought into contact with the tongue or mucous membranes. Ethanol adds a distinctive taste to drinks. When applied to open wounds (as for disinfection) it produces a strong stinging sensation. Pure or highly concentrated ethanol may permanently damage living tissue on contact. Ethanol applied to unbroken skin cools the skin rapidly through evaporation.

Ethanol is a central nervous system depressant and has significant psychoactive effects in sublethal doses; for specifics, see effects of alcohol on the body by dose.

Metabolism

In the human body, ethanol is first oxidized to acetaldehyde, and then to acetic acid. The first step is catalysed by the enzyme alcohol dehydrogenase, and the second by acetaldehyde dehydrogenase.

Magnitude of effect

Some individuals have less effective forms of one or both of these enzymes, and can experience more severe symptoms from ethanol consumption than others. Conversely, those who have acquired ethanol tolerance have a greater quantity of these enzymes, and metabolize ethanol more rapidly.

BAC (mg/dL)	Symptoms
50	Euphoria, talkativeness, relaxation
100	Central nervous system depression, impaired motor and sensory function, impaired cognition
>140	Decreased blood flow to brain
300	Stupefaction, possible unconsciousness
400	Possible death
>550	Expiration

The amount of ethanol in the body is typically quantified by blood alcohol content (BAC), the milligrams of ethanol per 100 milliliters of blood. The table at right summarizes the symptoms of ethanol consumption. Small doses of ethanol generally produce euphoria and relaxation; people experiencing these symptoms tend to become talkative and less inhibited, and may exhibit poor judgment. At higher dosages (BAC > 100 mg/dl), ethanol acts as a central nervous system depressant, producing at progressively higher dosages, impaired sensory and motor function, slowed cognition, stupefaction, unconsciousness, and possible death.

Acetaldehyde toxicology

The initial product of ethanol metabolism, acetaldehyde, is more toxic than ethanol itself. The body can quickly detoxify some acetaldehyde by reaction with glutathione and similar thiol-containing biomolecules. When acetaldehyde is produced beyond the capacity of the body's glutathione supply to detoxify it, it accumulates in the bloodstream until further oxidized to acetic acid. The headache, nausea, and malaise associated with an alcohol hangover stem from a combination of dehydration and acetaldehyde poisoning; many health conditions associated with chronic ethanol abuse, including liver cirrhosis, alcoholism, and some forms of cancer, have been linked to acetaldehyde. The judicial system in the United States, in a number of jurisdictions, controversially, promoted the use of disulfiram, known as Antabuse, for persons convicted of driving while (alcohol) intoxicated. Disulfiram interferes with hepatic acetaldehyde metabolism, severely exacerbating the discomforts noted above. Numerous deaths, said to be related to disulfuram use, led to the elimination of these court-based programs.. Some medications, including paracetamol (acetaminophen), as well as exposure to organochlorides, can deplete the body's glutathione supply, enhancing both the acute and long-term risks of even moderate ethanol consumption.. Frequent use of alcoholic beverages has also been shown to be a major contributing factor in cases of elevated blood levels of triglycerides.

Bacteria-favoring

Ethanol has been shown to increase the growth of Acinetobacter baumannii, a bacterium responsible for pneumonia, meningitis and urinary tract infections. This finding may contradict the common misconception that drinking alcohol could kill off a budding infection. (Smith and Snyder, 2005)

Hazards

Ethanol-water solutions greater than about 50% ethanol by volume are flammable and easily ignited (in some cases ethanol will burn at as low as a 45% solution). Ethanol-water solutions below 50% ethanol by volume may also be flammable if the solution is vaporized by heating (as in some cooking methods that call for wine to be added to a hot pan, causing it to flash boil into a vapor, which is then ignited to "burn off" excessive alcohol).

See also

• Biodiesel
• Breathalyzer
• Cellulosic ethanol
• Cellulosic ethanol commercialization
• Corn liquor
• Denatured alcohol
• Ethanol (data page)
• Ethanol fuel
• Ethanol fuel in Brazil
• Effects of alcohol on the body
• Isopropyl alcohol
• List of energy topics
• 2,2,2-Trichloroethanol
• 1-Propanol
• Rubbing alcohol
• Timeline of alcohol fuel
• Corn Ethanol

Further reading

• "Alcohol." (1911). In Hugh Chisholm (Ed.) Encyclopædia Britannica, 11th ed. Online reprint
• Lodgsdon, J.E. (1994). "Ethanol." In J.I. Kroschwitz (Ed.) Encyclopedia of Chemical Technology, 4th ed. vol. 9, pp. 812–860. New York: John Wiley & Sons.
• Smith, M.G., and M. Snyder. (2005). "Ethanol-induced virulence of Acinetobacter baumannii". American Society for Microbiology meeting. June 5-June 9. Atlanta.
• Sci-toys website explanation of US denatured alcohol designations
• Boyce, John M., and Pittet Didier. (2003). “Hand Hygiene in Healthcare Settings.” Centers for Disease Control, Atlanta, Georgia, United States.
• Rene Martinez VitalSensors Technologies LLC. "VS1000A Series In-Line Ethanol Sensors for the Beverage and BioFuel Industry" (PDF).— Martinez describes the theory and practice of measuring brix on-line in beverages.

External links

• International Labour Organization ethanol safety information
• Reducing the negative effects of alcohol by taking cysteine and vitamin C
• National Pollutant Inventory - Ethanol Fact Sheet
• Ethanol Information
• Ethanol Facts
• Coordinates of the ethanol molecule on Computational Chemistry Wiki. Accessed on 8 September 2005.
• Molview from bluerhinos.co.uk See Ethanol in 3D
• National Institute of Standards and Technology chemical data on ethanol
• Specifications
• Ethanol Worldwide and India
• FoodandFuelAmerica.com discusses the Food vs. Fuel debate with Ethanol
• United Bio Energy- (UBE) General information on ethanol plants and products. Also industry links
• ChEBI - biology related
• Energy Supply Logistics Ethanol Plant/Terminal Database
• Chicago Board of Trade news and market data on ethanol futures