Ethyl Alcohol

For other uses, see Ethanol (disambiguation).
"Grain alcohol" redirects here. It is not to be confused with Neutral grain spirit.
Ethanol



Identifiers
CAS number 64-17-5 YesY
Jmol-3D images Image 1
Properties
Molecular formula C2H6O
Molar mass 46.07 g mol−1
Melting point

−114 °C, 159 K, -173 °F

Boiling point

78.37 °C, 352 K, 173 °F

Acidity (pKa) 15.9 (H2O), 29.8 (DMSO)[2][3]
Hazards[4]
MSDS External MSDS
R-phrases R11
S-phrases (S2), S7, S16
Flash point 9 °C
Autoignition
temperature
425 °C
Supplementary data page
Structure and
properties
n, εr, etc.
Thermodynamic
data
Phase behaviour
Solid, liquid, gas
Spectral data UV, IR, NMR, MS
 N (verify) (what is: YesY/N?)
Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa)
Infobox references

Ethanol /ˈɛθɑːnɒl/, also called ethyl alcohol /ˈɛθɪl/, pure alcohol, grain alcohol, or drinking alcohol, is a volatile, flammable, colorless liquid with the structural formula CH3CH2OH, often abbreviated as C2H5OH or C2H6O. A psychoactive drug and one of the oldest recreational drugs known, ethanol produces a state known as alcohol intoxication when consumed as a beverage. Best known as the type of alcohol found in alcoholic beverages, it is also used in thermometers, as a solvent, and as a fuel. In common usage, it is often referred to simply as alcohol or spirits.

Etymology

Ethanol is the systematic name defined by the IUPAC nomenclature of organic chemistry for a molecule with two carbon atoms (prefix "eth-"), having a single bond between them (suffix "-ane"), and an attached -OH group (suffix "-ol").[1]

The term 'ethyl' is the Anglicised version of the German word äthyl, which was coined in 1838 by Liebig. It was modeled after the related term 'methyl.' Both terms originate from Greek, and share the segment 'yl', which is equivalent to 'hyle' meaning stuff. However, the preceding segment differs – 'eth', is equivalent to 'aither', meaning ether. Thus the word 'ethyl' is a contraction of 'aither hyle'.[5] Liebig used the term 'ethyl alcohol' to distinguish between ethanol and other alcohols.

The term "alcohol" now refers to a wider class of substances in chemistry nomenclature, but in common parlance it remains the name of ethanol. Ultimately a medieval loan from Arabic al-kuḥl,[6] use of alcohol in this sense is modern, introduced in the mid 18th century. Before that time, Middle Latin alcohol referred to "powdered ore of antimony; powdered cosmetic", by the later 17th century "any sublimated substance; distilled spirit" use for "the spirit of wine" (shortened from a full expression alcohol of wine) recorded 1753. The systematic use in chemistry dates to 1850.

Chemical formula

Ethanol is a 2-carbon alcohol with the empirical formula C2H6O. Its molecular formula is CH3CH2OH. An alternative notation is CH3–CH2–OH, which indicates that the carbon of a methyl group (CH3–) is attached to the carbon of a methylene group (–CH2–), which is attached to the oxygen of a hydroxyl group (–OH). It is a constitutional isomer of dimethyl ether. Ethanol is sometimes abbreviated as EtOH, using the common organic chemistry notation of representing the ethyl group (C2H5) with Et.

History

The fermentation of sugar into ethanol is one of the earliest biotechnologies employed by humans. The intoxicating effects of ethanol consumption have been known since ancient times. Ethanol has been used by humans since prehistory as the intoxicating ingredient of alcoholic beverages. Dried residue on 9,000-year-old pottery found in China implies that Neolithic people consumed alcoholic beverages.[7]

The earliest known scientific identification of ethanol was from the Persian polymath, Rhazes, in the 9th century.[8] Although distillation was well known by the early Greeks and Arabs, the first recorded production of alcohol from distilled wine was by the School of Salerno alchemists in the 12th century.[9] The first to mention absolute alcohol, in contrast with alcohol-water mixtures, was Raymond Lull.[9]

In 1796, German-Russian chemist Johann Tobias Lowitz obtained pure ethanol by mixing partially purified ethanol (the alcohol-water azeotrope) with an excess of anhydrous alkali and then distilling the mixture over low heat.[10] French chemist Antoine Lavoisier described ethanol as a compound of carbon, hydrogen, and oxygen, and in 1807 Nicolas-Théodore de Saussure determined ethanol's chemical formula.[11][12] Fifty years later, Archibald Scott Couper published the structural formula of ethanol. It was one of the first structural formulas determined.[13]

Ethanol was first prepared synthetically in 1825 by Michael Faraday. He found that sulfuric acid could absorb large volumes of coal gas.[14] He gave the resulting solution to Henry Hennell, a British chemist, who found in 1826 that it contained "sulphovinic acid" (ethyl hydrogen sulfate).[15] In 1828, Hennell and the French chemist Georges-Simon Sérullas independently discovered that sulphovinic acid could be decomposed into ethanol.[16][17] Thus, in 1825 Faraday had unwittingly discovered that ethanol could be produced from ethylene (a component of coal gas) by acid-catalyzed hydration, a process similar to current industrial ethanol synthesis.[18]

Ethanol was used as lamp fuel in the United States as early as 1840, but a tax levied on industrial alcohol during the Civil War made this use uneconomical. The tax was repealed in 1906.[19] Use as an automotive fuel dates back to 1908, with the Ford Model T able to run on gasoline or ethanol.[20] It remains a common fuel for spirit lamps.

Ethanol intended for industrial use is often produced from ethylene.[21] Ethanol has widespread use as a solvent of substances intended for human contact or consumption, including scents, flavorings, colorings, and medicines. In chemistry, it is both a solvent and a feedstock for the synthesis of other products. It has a long history as a fuel for heat and light, and more recently as a fuel for internal combustion engines.

Properties

Physical properties

Ethanol is a volatile, colorless liquid that has a slight odor. It burns with a smokeless blue flame that is not always visible in normal light.

The physical properties of ethanol stem primarily from the presence of its hydroxyl group and the shortness of its carbon chain. Ethanol's hydroxyl group is able to participate in hydrogen bonding, rendering it more viscous and less volatile than less polar organic compounds of similar molecular weight, such as propane.

Ethanol is slightly more refractive than water, having a refractive index of 1.36242 (at λ=589.3 nm and 18.35 °C).[22]

The triple point for ethanol is 150 K at a pressure of 4.3 × 10−4 Pa.[23]

Solvent properties

Ethanol is a versatile solvent, miscible with water and with many organic solvents, including acetic acid, acetone, benzene, carbon tetrachloride, chloroform, diethyl ether, ethylene glycol, glycerol, nitromethane, pyridine, and toluene.[22][24] It is also miscible with light aliphatic hydrocarbons, such as pentane and hexane, and with aliphatic chlorides such as trichloroethane and tetrachloroethylene.[24]

Ethanol's miscibility with water contrasts with the immiscibility of longer-chain alcohols (five or more carbon atoms), whose water miscibility decreases sharply as the number of carbons increases.[25] The miscibility of ethanol with alkanes is limited to alkanes up to undecane, mixtures with dodecane and higher alkanes show a miscibility gap below a certain temperature (about 13 °C for dodecane[26]). The miscibility gap tends to get wider with higher alkanes and the temperature for complete miscibility increases.

Ethanol-water mixtures have less volume than the sum of their individual components at the given fractions. Mixing equal volumes of ethanol and water results in only 1.92 volumes of mixture.[22][27] Mixing ethanol and water is exothermic, with up to 777 J/mol[28] being released at 298 K.

Mixtures of ethanol and water form an azeotrope at about 89 mole-% ethanol and 11 mole-% water[29] or a mixture of about 96 volume percent ethanol and 4% water at normal pressure and T = 351 K. This azeotropic composition is strongly temperature- and pressure-dependent and vanishes at temperatures below 303 K.[30]


Hydrogen bonding causes pure ethanol to be hygroscopic to the extent that it readily absorbs water from the air. The polar nature of the hydroxyl group causes ethanol to dissolve many ionic compounds, notably sodium and potassium hydroxides, magnesium chloride, calcium chloride, ammonium chloride, ammonium bromide, and sodium bromide.[24] Sodium and potassium chlorides are slightly soluble in ethanol.[24] Because the ethanol molecule also has a nonpolar end, it will also dissolve nonpolar substances, including most essential oils[31] and numerous flavoring, coloring, and medicinal agents.

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 in a glass, ethanol evaporates quickly from the thin film of wine on the wall of the glass. As the wine's 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.

Flammability

An ethanol-water solution that contains 40% ABV (alcohol by volume) will catch fire if heated to about 26 °C (79 °F) and if an ignition source is applied to it. This is called its flash point.[32] The flash point of pure ethanol is 16.60 °C (61.88 °F), less than average room temperature.[33]

The flash points of ethanol concentrations from 10% ABV to 96% ABV are shown below:[34]

  • 10% — 49 °C (120 °F)
  • 12.5% — about 52 °C (126 °F)
  • 20% — 36 °C (97 °F)
  • 30% — 29 °C (84 °F)
  • 40% — 26 °C (79 °F)
  • 50% — 24 °C (75 °F)
  • 60% — 22 °C (72 °F)
  • 70% — 21 °C (70 °F)
  • 80% — 20 °C (68 °F)
  • 90% — 17 °C (63 °F)
  • 96% — 17 °C (63 °F)

Alcoholic beverages that have a low concentration of ethanol will burn if sufficiently heated and an ignition source (such as an electric spark or a match) is applied to them. For example, the flash point of ordinary wine containing 12.5% ethanol is about 52 °C (126 °F).[35]

Production

Ethanol is produced both as a petrochemical, through the hydration of ethylene and, via biological processes, by fermenting sugars with yeast.[36] Which process is more economical depends on prevailing prices of petroleum and grain feed stocks.

Ethylene hydration

Ethanol for use as an industrial feedstock or solvent (sometimes referred to as synthetic ethanol) is made from petrochemical feed stocks, primarily by the acid-catalyzed hydration of ethylene, represented by the chemical equation

C2H4 + H2O → CH3CH2OH

The catalyst is most commonly phosphoric acid,[37][38] adsorbed onto a porous support such as silica gel or diatomaceous earth. This catalyst was first used for large-scale ethanol production by the Shell Oil Company in 1947.[39] The reaction is carried out with an excess of high pressure steam at 300 °C. In the U.S., this process was used on an industrial scale by Union Carbide Corporation and others; but now only LyondellBasell uses it commercially.

In an older process, first practiced on the industrial scale in 1930 by Union Carbide,[40] but now almost entirely obsolete, ethylene was hydrated indirectly by reacting it with concentrated sulfuric acid to produce ethyl sulfate, which was hydrolysed to yield ethanol and regenerate the sulfuric acid:[41]

C2H4 + H2SO4CH3CH2SO4H
CH3CH2SO4H + H2O → CH3CH2OH + H2SO4

Fermentation

Main article: Ethanol fermentation

Ethanol for use in alcoholic beverages, and the vast majority of ethanol for use as fuel,[42] is produced by fermentation. When certain species of yeast (e.g., Saccharomyces cerevisiae) metabolize sugar in reduced-oxygen conditions they produce ethanol and carbon dioxide. The chemical equations below summarize the conversion:

C6H12O6 → 2 CH3CH2OH + 2 CO2
C12H22O11 + H2O → 4 CH3CH2OH + 4 CO2

Fermentation is the process of culturing yeast under favorable thermal conditions to produce alcohol. This process is carried out at around 35–40 °C. Toxicity of ethanol to yeast limits the ethanol concentration obtainable by brewing; higher concentrations, therefore, are usually obtained by fortification or distillation. The most ethanol-tolerant strains of yeast can survive up to approximately 18% ethanol by volume (Red Star Pasteur Champagne wine yeast, Lalvin EC-1118 wine yeast) and 20% or greater using "Turbo Yeast" as sold for spirit and fuel distillation.

To produce ethanol from starchy materials such as cereal grains, the starch must first be converted into sugars. In brewing beer, this has traditionally been accomplished by allowing the grain to germinate, or malt, which produces the enzyme amylase. When the malted grain is mashed, the amylase converts the remaining starches into sugars. For fuel ethanol, the hydrolysis of starch into glucose can be accomplished more rapidly by treatment with dilute sulfuric acid, fungally produced amylase, or some combination of the two.[43]

Cellulosic ethanol

Main article: Cellulosic ethanol

Sugars for ethanol fermentation can be obtained from cellulose.[44][45] Until recently, however, the cost of the cellulase enzymes capable of hydrolyzing cellulose has been prohibitive. The Canadian firm Iogen brought the first cellulose-based ethanol plant on-stream in 2004.[46] Its primary consumer so far has been the Canadian government, which, along with the United States Department of Energy, has invested heavily in the commercialization of cellulosic ethanol. Deployment of this technology could turn a number of cellulose-containing agricultural by-products, such as corncobs, straw, and sawdust, into renewable energy resources. Other enzyme companies are developing genetically engineered fungi that produce large volumes of cellulase, xylanase, and hemicellulase enzymes. These would convert agricultural residues such as corn stover, wheat straw, and sugar cane bagasse and energy crops such as switchgrass into fermentable sugars.[47]

Cellulose-bearing materials typically contain other polysaccharides, including hemicellulose. Hydrolysis of hemicellulose gives 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 ferment xylose and other pentoses into ethanol.

Hydrocarbon-based ethanol production

A process developed and marketed by Celanese Corporation under the name TCX Technology uses hydrocarbons such as natural gas or coal for ethanol production rather than using fermented crops such as corn or sugarcane.[48]

Testing


Breweries and biofuel plants employ two methods for measuring ethanol concentration. 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. The 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 indicates the alcohol content. This inexpensive and indirect method has a long history in the beer brewing industry.

Purification

Distillation

Ethylene hydration or brewing produces an ethanol–water mixture. For most industrial and fuel uses, the ethanol must be purified. Fractional distillation can concentrate ethanol to 95.6% by volume (89.5 mole%). This mixture is an azeotrope with a boiling point of 78.1 °C, and cannot be further purified by distillation. Addition of an entraining agent, such as benzene, cyclohexane, or heptane, allows a new ternary azeotrope comprising the ethanol, water, and the entraining agent to be formed. This lower-boiling ternary azeotrope is removed preferentially, leading to water-free ethanol.[38]

At pressures less than atmospheric pressure, the composition of the ethanol-water azeotrope shifts to more ethanol-rich mixtures, and at pressures less than 70 torr (9.333 kPa), there is no azeotrope, and it is possible to distill absolute ethanol from an ethanol-water mixture. While vacuum distillation of ethanol is not presently economical, pressure-swing distillation is a topic of current research. In this technique, a reduced-pressure distillation first yields an ethanol-water mixture of more than 95.6% ethanol. Then, fractional distillation of this mixture at atmospheric pressure distills off the 95.6% azeotrope, leaving anhydrous ethanol at the bottoms.

Molecular sieves and desiccants

Molecular sieves can be used to selectively absorb the water from the 95.6% ethanol solution. Synthetic zeolite in pellet form can be used, as well as a variety of plant-derived absorbents, including cornmeal, straw, and sawdust. The zeolite bed can be regenerated essentially an unlimited number of times by drying it with a blast of hot carbon dioxide. Cornmeal and other plant-derived absorbents cannot readily be regenerated, but where ethanol is made from grain, they are often available at low cost. Absolute ethanol produced this way has no residual benzene, and can be used to fortify port and sherry in traditional winery operations.

Apart from distillation, ethanol may be dried by addition of a desiccant, such as molecular sieves, cellulose, and cornmeal. The desiccants can be dried and reused.[38]

Membranes and reverse osmosis

Membranes can also be used to separate ethanol and water. Membrane-based separations are not subject to the limitations water-ethanol azeotrope because separation is not based on vapor-liquid equilibria. Membranes are often used in the so-called hybrid membrane distillation process. This process uses a pre-concentration distillation column as first separating step. The further separation is then accomplished with a membrane operated either in vapor permeation or pervaporation mode. Vapor permeation uses a vapor membrane feed and pervaporation uses a liquid membrane feed.

Other techniques

A variety of other techniques have been discussed, including the following:[38]

Grades of ethanol

Ethanol is available in a range of purities that result from its production or, in the case of denatured alcohol, are introduced intentionally.

Denatured alcohol

Main article: Denatured alcohol

Pure ethanol and alcoholic beverages are heavily taxed as psychoactive drugs, but ethanol has many uses that do not involve consumption by humans. To relieve the tax burden on these uses, most jurisdictions waive the tax when an agent has been added to the ethanol to render it unfit to drink. These include bittering agents such as denatonium benzoate and toxins such as methanol, naphtha, and pyridine. Products of this kind are called denatured alcohol.[50][51]

Absolute alcohol

Absolute or anhydrous alcohol refers to ethanol with a low water content. There are various grades with maximum water contents ranging from 1% to a few parts per million (ppm) levels. Absolute alcohol is not intended for human consumption. If azeotropic distillation is used to remove water, it will contain trace amounts of the material separation agent (e.g. benzene).[52] Absolute ethanol is used as a solvent for laboratory and industrial applications, where water will react with other chemicals, and as fuel alcohol. Spectroscopic ethanol is an absolute ethanol with a low absorbance in ultraviolet and visible light, fit for use as a solvent in ultraviolet-visible spectroscopy.[53]

Pure ethanol is classed as 200 proof in the USA, equivalent to 175 degrees proof in the UK system.[54]

Rectified spirits

Rectified spirit, an azeotropic composition of 96% ethanol containing 4% water, is used instead of anhydrous ethanol for various purposes. Wine spirits are about 94% ethanol (188 proof). The impurities are different from those in 95% (190 proof) laboratory ethanol.[55]

Reactions

Ethanol is classified as a primary alcohol, meaning that the carbon its hydroxyl group attaches to has at least two hydrogen atoms attached to it as well. Many ethanol reactions occur at its hydroxyl group.

Ester formation

In the presence of acid catalysts, ethanol reacts with carboxylic acids to produce ethyl esters and water:

RCOOH + HOCH2CH3RCOOCH2CH3 + H2O

This reaction, which is conducted on large scale industrially, requires the removal of the water from the reaction mixture as it is formed. Esters react in the presence of an acid or base to give back the alcohol and a salt. This reaction is known as saponification because it is used in the preparation of soap. Ethanol can also form esters with inorganic acids. Diethyl sulfate and triethyl phosphate are prepared by treating ethanol with sulfur trioxide and phosphorus pentoxide respectively. Diethyl sulfate is a useful ethylating agent 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 acid desiccants cause the dehydration of ethanol to form diethyl ether and other byproducts. If the dehydration temperature exceeds around 160 °C, ethylene will be the main product. Millions of kilograms of diethyl ether are produced annually using sulfuric acid catalyst:

2 CH3CH2OH → CH3CH2OCH2CH3 + H2O (on 120 °C)

Combustion

Complete combustion of ethanol forms carbon dioxide and water:

C2H5OH (l) + 3 O2 (g) → 2 CO2 (g) + 3 H2O (liq); −ΔHc = 1371 kJ/mol[56] = 29.8 kJ/g = 327 kcal/mol = 7.1 kcal/g
C2H5OH (l) + 3 O2 (g) → 2 CO2 (g) + 3 H2O (g); −ΔHc = 1236 kJ/mol = 26.8 kJ/g = 295.4 kcal/mol = 6.41 kcal/g[57]

Specific heat = 2.44 kJ/(kg·K)

Acid-base chemistry

Ethanol is a neutral molecule and the pH of a solution of ethanol in water is nearly 7.00. Ethanol can be quantitatively converted to its conjugate base, the ethoxide ion (CH3CH2O), by reaction with an alkali metal such as sodium:[25]

2 CH3CH2OH + 2 Na → 2 CH3CH2ONa + H2

or a very strong base such as sodium hydride:

CH3CH2OH + NaH → CH3CH2ONa + H2

The acidity of water and ethanol are nearly the same, as indicated by their pKa of 15.7 and 16 respectively. Thus, sodium ethoxide and sodium hydroxide exist in an equilbrium that is closely balanced:

CH3CH2OH + NaOH is in equilibrium with CH3CH2ONa + H2O

Halogenation

Ethanol is not used industrially as a precursor to ethyl halides, but the reactions are illustrative. Ethanol reacts with hydrogen halides to produce ethyl halides such as ethyl chloride and ethyl bromide via an SN2 reaction:

CH3CH2OH + HCl → CH3CH2Cl + H2O

These reactions require a catalyst such as zinc chloride.[41] HBr requires refluxing with a sulfuric acid catalyst.[41] Ethyl halides can, in principle, also be produced by treating ethanol with more specialized halogenating agents, such as thionyl chloride or phosphorus tribromide.[25][41]

CH3CH2OH + SOCl2 → CH3CH2Cl + SO2 + HCl

Upon treatment with halogens in the presence of base, ethanol gives the corresponding haloform (CHX3, where X = Cl, Br, I). This conversion is called the haloform reaction.[58] " An intermediate in the reaction with chlorine is the aldehyde called chloral:

4 Cl2 + CH3CH2OH → CCl3CHO + 5 HCl

Oxidation

Ethanol can be oxidized to acetaldehyde and further oxidized to acetic acid, depending on the reagents and conditions.[41] This oxidation is of no importance industrially, but in the human body, these oxidation reactions are catalyzed by the enzyme liver alcohol dehydrogenase. The oxidation product of ethanol, acetic acid, is a nutrient for humans, being a precursor to acetyl CoA, where the acetyl group can be spent as energy or used for biosynthesis.

Uses

As a fuel

Energy content of some fuels compared with ethanol:[59]
Fuel type MJ/L MJ/kg Research
octane
number
Dry wood (20% moisture) ~19.5
Methanol 17.9 19.9 108.7[60]
Ethanol 21.2[61] 26.8[61] 108.6[60]
E85
(85% ethanol, 15% gasoline)
25.2 33.2 105
Liquefied natural gas 25.3 ~55
Autogas (LPG)
(60% propane + 40% butane)
26.8 50.
Aviation gasoline
(high-octane gasoline, not jet fuel)
33.5 46.8 100/130 (lean/rich)
Gasohol
(90% gasoline + 10% ethanol)
33.7 47.1 93/94
Regular gasoline/petrol 34.8 44.4[62] min. 91
Premium gasoline/petrol max. 104
Diesel 38.6 45.4 25
Charcoal, extruded 50 23
Main article: Ethanol fuel

The largest single use of ethanol is as a motor fuel and fuel additive. More than any other major country, Brazil relies on ethanol as a motor fuel. Gasoline sold in Brazil contains at least 25% anhydrous ethanol. Hydrous ethanol (about 95% ethanol and 5% water) can be used as fuel in more than 90% of new cars sold in the country. Brazilian ethanol is produced from sugar cane and noted for high carbon sequestration.[63] The US uses Gasohol (max 10% ethanol) and E85 (85% ethanol) ethanol/gasoline mixtures.

Ethanol may also be utilized as a rocket fuel, and is currently in lightweight rocket-powered racing aircraft.[64]

Australian law limits of the use of pure ethanol sourced from sugarcane waste to up to 10% in automobiles. It has been recommended that older cars (and vintage cars designed to use a slower burning fuel) have their valves upgraded or replaced.[65]

According to an industry advocacy group for promoting ethanol called the American Coalition for Ethanol, ethanol as a fuel reduces harmful tailpipe emissions of carbon monoxide, particulate matter, oxides of nitrogen, and other ozone-forming pollutants.[66] Argonne National Laboratory analyzed the greenhouse gas emissions of many different engine and fuel combinations. Comparing ethanol blends with gasoline alone, they showed reductions of 8% with the biodiesel/petrodiesel blend known as B20, 17% with the conventional E85 ethanol blend, and that using cellulosic ethanol lowers emissions 64%.[67]

Ethanol combustion in an internal combustion engine yields many of the products of incomplete combustion produced by gasoline and significantly larger amounts of formaldehyde and related species such as acetaldehyde.[68] This leads to a significantly larger photochemical reactivity that generates much more ground level ozone.[69] These data have been assembled into The Clean Fuels Report comparison of fuel emissions[70] and show that ethanol exhaust generates 2.14 times as much ozone as does gasoline exhaust. When this is added into the custom Localised Pollution Index (LPI) of The Clean Fuels Report the local pollution (pollution that contributes to smog) is 1.7 on a scale where gasoline is 1.0 and higher numbers signify greater pollution. The California Air Resources Board formalized this issue in 2008 by recognizing control standards for formaldehydes as an emissions control group, much like the conventional NOx and Reactive Organic Gases (ROGs).[71]


World production of ethanol in 2006 was 51 gigalitres (1.3×1010 US gal), with 69% of the world supply coming from Brazil and the United States.[72] More than 20% of Brazilian cars are able to use 100% ethanol as fuel, which includes ethanol-only engines and flex-fuel engines.[73] Flex-fuel engines in Brazil are able to work with all ethanol, all gasoline or any mixture of both. In the US flex-fuel vehicles can run on 0% to 85% ethanol (15% gasoline) since higher ethanol blends are not yet allowed or efficient. Brazil supports this population of ethanol-burning automobiles with large national infrastructure that produces ethanol from domestically grown sugar cane. Sugar cane not only has a greater concentration of sucrose than corn (by about 30%), but is also much easier to extract. The bagasse generated by the process is not wasted, but is used in power plants to produce electricity.


The United States fuel ethanol industry is based largely on corn. According to the Renewable Fuels Association, as of October 30, 2007, 131 grain ethanol bio-refineries in the United States have the capacity to produce 7.0 billion US gallons (26,000,000 m3) of ethanol per year. An additional 72 construction projects underway (in the U.S.) can add 6.4 billion US gallons (24,000,000 m3) of new capacity in the next 18 months. Over time, it is believed that a material portion of the ≈150-billion-US-gallon (570,000,000 m3) per year market for gasoline will begin to be replaced with fuel ethanol.[74]


One problem with ethanol is its high miscibility with water, which means that it cannot be efficiently shipped through modern pipelines, like liquid hydrocarbons, over long distances.[75] Mechanics also have seen increased cases of damage to small engines, in particular, the carburetor, attributable to the increased water retention by ethanol in fuel.[76]

In 2011, the Open Fuel Standard Coalition introduced a bill into Congress that would mandate most cars sold in the United States to be warranted to run on ethanol, as well as methanol and gasoline. The bill aims to provide enough financial incentive to find better ways to make ethanol fuel so it could compete economically against gasoline.

Alcoholic beverages

Main article: Alcoholic beverage

Ethanol is the principal psychoactive constituent in alcoholic beverages, with depressant effects on the central nervous system, It has a complex mode of action and affects multiple systems in the brain, most notably increasing the activity of GABA receptors.[77] Through positive allosteric modulation, it enhances the activity of naturally produced GABA. Other psychoactives such as benzodiazepines, barbiturates exert their effects by binding to the same receptor complex, thus have similar CNS depressant effects.[78]

Alcoholic beverages vary considerably in ethanol content and in foodstuffs they are produced from. Most alcoholic beverages can be broadly classified as fermented beverages, beverages made by the action of yeast on sugary foodstuffs, or 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 they are fermented from. 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 classifications for various fermented beverages abound.

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 and 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.

The ethanol content in alcoholic beverages can be increased by means other than distillation. Applejack is traditionally made by freeze distillation, by which water is frozen out of fermented apple cider, leaving a more ethanol-rich liquid behind. Ice beer (also known by the German term Eisbier or 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 a portion of the sugar in grape juice; such beverages are not only more ethanol-rich but are often sweeter than other wines.

Alcoholic beverages are used in cooking for their flavors and because alcohol dissolves hydrophobic flavor compounds.

Just as industrial ethanol is used as feedstock for the production of industrial acetic acid, alcoholic beverages are made into vinegar. Wine and cider vinegar are both named for their respective source alcohols, whereas malt vinegar is derived from beer.

Feedstock

Main article: § Reactions

Ethanol is an important industrial ingredient and has widespread use as a base chemical for other organic compounds. These include ethyl halides, ethyl esters, diethyl ether, acetic acid, ethyl amines, and, to a lesser extent, butadiene.

Antiseptic

Ethanol is used in medical wipes and in most common antibacterial hand sanitizer gels at a concentration of about 62% v/v 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.[79]

Treatment for poisoning by other alcohols

Ethanol is sometimes used to treat poisoning by other, more toxic alcohols, in particular methanol[80] and ethylene glycol. Ethanol competes with other alcohols for the alcohol dehydrogenase enzyme, lessening metabolism into toxic aldehyde and carboxylic acid derivatives,[81] and reducing one of the more serious toxic effect of the glycols to crystallize in the kidneys.

Solvent

Ethanol is miscible with water and is a good general purpose solvent. It is found in paints, tinctures, markers, and personal care products such as perfumes and deodorants.

Historical uses

Before the development of modern medicines, ethanol was used for a variety of medical purposes. It has been known to be used as a truth drug (as hinted at by the maxim "in vino veritas"), as medicine for depression and as an anesthetic.

Ethanol was commonly used as fuel in early bipropellant rocket (liquid propelled) 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 25% of water to reduce the combustion chamber temperature.[82][83] 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.[84] Alcohols fell into general disuse as more efficient rocket fuels were developed.[83]

Pharmacology

Ethanol binds to α7-nAChRs as an agonist, GABA (especially the δ subunit) as a positive allosteric modulator, 5-HT3 receptor agonist, NMDA receptor antagonist, AMPA receptor antagonist, Kainate receptor antagonist, glycine receptor agonist and an inhibitor of potassium, sodium and calcium ion channels. It also appears to cause an increase in dopamine through a poorly understood process that may involve inhibiting the enzyme that breaks dopamine down.[85] Ethanol also appears to block the reuptake of adenosine, additionally.

The removal of ethanol through oxidation by alcohol dehydrogenase in the liver from the human body is limited. Hence, the removal of a large concentration of alcohol from blood may follow zero-order kinetics. This means that alcohol leaves the body at a constant rate, rather than having an elimination half-life.

Also, the rate-limiting steps for one substance may be in common with other substances. For instance, the blood alcohol concentration can be used to modify the biochemistry of methanol and ethylene glycol. Methanol itself is not highly toxic, but its metabolites formaldehyde and formic acid are; therefore, to reduce the concentration of these harmful metabolites, ethanol can be ingested to reduce the rate of methanol metabolism due to shared rate-limiting steps. Ethylene glycol poisoning can be treated in the same way.

Drug effects

Pure ethanol will irritate the skin and eyes.[86] Nausea, vomiting and intoxication are symptoms of ingestion. Long-term use by ingestion can result in serious liver damage.[87] Atmospheric concentrations above one in a thousand are above the European Union Occupational exposure limits.[87]

Short-term

BAC (g/L) BAC
(% v/v)
Symptoms[88]
0.5 0.05% Euphoria, talkativeness, relaxation
1 0.1 % Central nervous system depression, nausea, possible vomiting, impaired motor and sensory function, impaired cognition
>1.4 >0.14% Decreased blood flow to brain
3 0.3% Stupefaction, possible unconsciousness
4 0.4% Possible death
>5.5 >0.55% Death

Effects on the central nervous system

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". Based on its abilities to change the human consciousness, ethanol is considered a psychoactive drug.[89] Death from ethanol consumption is possible when blood alcohol level reaches 0.4%. A blood level of 0.5% or more is commonly fatal. Levels of even less than 0.1% can cause intoxication, with unconsciousness often occurring at 0.3–0.4%.[90]

The amount of ethanol in the body is typically quantified by blood alcohol content (BAC), which is here taken as weight of ethanol per unit volume of blood. The table at the right summarizes the symptoms of ethanol consumption. Small doses of ethanol, in general, produce euphoria and relaxation; people experiencing these symptoms tend to become talkative and less inhibited, and may exhibit poor judgment. At higher dosages (BAC > 1 g/L), 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.

Ethanol acts in the central nervous system by binding to the GABA-A receptor, increasing the effects of the inhibitory neurotransmitter GABA (i.e., it is a positive allosteric modulator).[91]

Prolonged heavy consumption of alcohol can cause significant permanent damage to the brain and other organs. See Alcohol consumption and health.

According to the US National Highway Traffic Safety Administration, in 2002 about "41% of people fatally injured in traffic crashes were in alcohol related crashes".[92] The risk of a fatal car accident increases exponentially with the level of alcohol in the driver's blood.[93] Most drunk driving laws governing the acceptable levels in the blood while driving or operating heavy machinery set typical upper limits of blood alcohol content (BAC) between 0.02% and 0.08%.

Discontinuing consumption of alcohol after several years of heavy drinking can also be fatal. Alcohol withdrawal can cause anxiety, autonomic dysfunction, seizures, and hallucinations. Delirium tremens is a condition that requires people with a long history of heavy drinking to undertake an alcohol detoxification regimen.

The reinforcing effects of alcohol consumption are also mediated by acetaldehyde generated by catalase and other oxidizing enzymes such as cytochrome P-4502E1 in the brain.[94] Although acetaldehyde has been associated with some of the adverse and toxic effects of ethanol, it appears to play a central role in the activation of the mesolimbic dopamine system.[95]

Effects on metabolism

Ethanol within the human body is converted into acetaldehyde by alcohol dehydrogenase and then into the acetyl in acetyl CoA by acetaldehyde dehydrogenase. Acetyl CoA is the final product of both carbohydrate and fat metabolism, where the acetyl can be further used to produce energy or for biosynthesis. As such, ethanol is a nutrient. However, the product of the first step of this breakdown, acetaldehyde,[96] is more toxic than ethanol. Acetaldehyde is linked to most of the clinical effects of alcohol. It has been shown to increase the risk of developing cirrhosis of the liver[78] and multiple forms of cancer.

During the metabolism of alcohol via the respective dehydrogenases, NAD is converted into reduced NAD. Normally, NAD is used to metabolise fats in the liver, and as such alcohol competes with these fats for the use of NAD. Prolonged exposure to alcohol means that fats accumulate in the liver, leading to the term 'fatty liver'. Continued consumption (such as in alcoholism) then leads to cell death in the hepatocytes as the fat stores reduce the function of the cell to the point of death. These cells are then replaced with scar tissue, leading to the condition called cirrhosis.

Drug interactions

Ethanol can intensify the sedation caused by other central nervous system depressant drugs such as barbiturates, benzodiazepines, opioids, phenothiazines, and anti-depressants.[90] It interacts with cocaine in vivo to produce cocaethylene, another psychoactive substance.[97]

Alcohol and metronidazole

One of the most important drug/food interaction that should be noted is between alcohol and metronidazole.

Metronidazole is an antibacterial agent that kills bacteria by damaging cellular DNA and hence cellular function.[98] Metronidazole is usually given to people who have diarrhea caused by Clostridium difficile bacteria. C. difficile is one of the most common microorganisms that cause diarrhea and can lead to complications such as colon inflammation and even more severely, death.

Patients who are taking metronidazole are strongly advised to avoid alcohol, even after 1 hour after the last dose. The reason is that alcohol and metronidazole can lead to side effects such as flushing, headache, nausea, vomiting, abdominal cramps, and sweating.[99][100][100] These symptoms are often called the disulfiram-like reaction. The proposed mechanism of action for this interaction is that metronidazole can bind to an enzyme that normally metabolizes alcohol. Binding to this enzyme may impair the liver's ability to process alcohol for proper excretion.[101]

Alcohol and digestion

A part of ethyl alcohol is hydrophobic. This hydrophobic or lipophilic end can diffuse across cells that line the stomach wall. In fact, alcohol is one of the rare substances that can be absorbed in the stomach. Most food substances are absorbed in the small intestine. However, even though alcohol can be absorbed in the stomach, it is mostly absorbed in the small intestine because the small intestine has a large surface area that promotes absorption. Once alcohol is absorbed in the small intestine, it delays the release of stomach contents from emptying into the small intestine. Thus, alcohol can delay the rate of absorption of nutrients.[102]

After absorption, alcohol reaches the liver where it is metabolized. Interestingly, the amount of alcohol that can be metabolized is associated with ethnicity. Apparently, Asians, Native Americans, and Inuit secrete relatively less of alcohol's metabolizing enzyme (alcohol dehydrogenase ADH) than Caucasians.[103] This difference in metabolizing ability could be a reason why Caucasians are less likely to get drunk.[103]

How Breathalyzers work:
Alcohol that is not processed by the liver goes to the heart. The liver can process only a certain amount of alcohol per unit time. Thus, when a person drinks too much alcohol, more alcohol can reach the heart. In the heart, alcohol reduces the force of heart contractions. Consequently, the heart will pump less blood, lowering overall body blood pressure.[103] Also, blood that reaches the heart goes to the lungs to replenish blood's oxygen concentration. It is at this stage that a person can breathe out traces of alcohol.[103] This is the underlying principle of the alcohol breath testing (or breathalyzers) to determine if a driver has been drinking and driving.[104]

From the lungs, blood returns to the heart and will be distributed throughout the body. Interestingly, alcohol increases levels of high-density lipoproteins(HDLs), which carry cholesterol.[103] Alcohol is known to make blood less likely to clot, reducing risk of heart attack and stroke. This could be the reason why alcohol could produce health benefits when consumed in moderate amounts.[105] Also, alcohol dilates blood vessels. Consequently, a person will feel warmer, and their face turns flush and pink.[103]

Why people lose their sense of balance after drinking alcohol:
When alcohol reaches the brain, it has the ability to delay signals that are sent between nerve cells that control balance, thinking and movement.[103]

Why people frequently urinate after drinking alcohol:
Moreover, alcohol can affect the brain's ability to produce antidiuretic hormones. These hormones are responsible for controlling the amount of urine that is produced. Alcohol prevents the body from reabsorbing water, and consequently a person who recently drank alcohol will urinate frequently.[103]

Alcohol and gastrointestinal diseases


Alcohol stimulates gastric juice production, even when food is not present. In other words, when a person drinks alcohol, the alcohol will stimulate stomach's acidic secretions that are intended to digest protein molecules. Consequently, the acidity has potential to harm the inner lining of the stomach. Normally, the stomach lining is protected by a mucus layer that prevents any acids from reaching the stomach cells.

However, in patients who have a peptic ulcer disease (PUD), this mucus layer is broken down. PUD is commonly associated with a bacteria H. pylori. H. pylori secretes a toxin that weakens the mucosal wall. As a result, acid and protein enzymes penetrate the weakened barrier. Because alcohol stimulates a person's stomach to secrete acid, a person with PUD should avoid drinking alcohol on an empty stomach. Drinking alcohol would cause more acid release to damage the weakened stomach wall.[106] Complications of this disease could include a burning pain in the abdomen, bloating and in severe cases, the presence of dark black stools that indicate an internal bleed.[107] A person who drinks alcohol regularly is strongly advised to reduce their intake to prevent PUD aggravation.[107]

Magnitude of effects

Some individuals have less effective forms of one or both of the metabolizing enzymes, and can experience more severe symptoms from ethanol consumption than others. However, those having acquired alcohol tolerance have a greater quantity of these enzymes, and metabolize ethanol more rapidly.[108]

Long-term

Birth defects

Ethanol is classified as a teratogen. See fetal alcohol syndrome.

Other effects

Frequent drinking of alcoholic beverages has been shown to be a major contributing factor in cases of elevated blood levels of triglycerides.[109]

Ethanol is not a carcinogen.[33][110] However, the first metabolic product of ethanol in the liver, acetaldehyde, is toxic, mutagenic, and carcinogenic.

Ethanol is also widely used, clinically and over the counter, as an antitussive agent.[111]

Natural occurrence

Ethanol is a byproduct of the metabolic process of yeast. As such, ethanol will be present in any yeast habitat. Ethanol can commonly be found in overripe fruit.[112] Ethanol produced by symbiotic yeast can be found in Bertam Palm blossoms. Although some species such as the Pentailed Treeshrew exhibit ethanol-seeking behaviors, most show no interest or avoidance of food sources containing ethanol.[113] Ethanol is also produced during the germination of many plants as a result of natural anerobiosis.[114] Ethanol has been detected in outer space, forming an icy coating around dust grains in interstellar clouds.[115]

Charts

Thermophysical properties of mixtures of ethanol with water and dodecane
Excess volume of the mixture of ethanol and water (volume contraction) Heat of mixing of the mixture of ethanol and water Vapor-liquid equilibrium of the mixture of ethanol and water (including azeotrope)
Solid-liquid equilibrium of the mixture of ethanol and water (including eutecticum) Miscibility gap in the mixture of dodecane and ethanol

See also

Pharmacy and Pharmacology portal

References

Further reading

  • The ETOH Archival Database (1972–2003) Alcohol and Alcohol Problems Science Database.
  • Boyce, John M., and Pittet Didier. (2003). Georgia, United States.
  • Sci-toys website explanation of US denatured alcohol designations
  • Smith, M.G., and M. Snyder. (2005). "Ethanol-induced virulence of Acinetobacter baumannii". American Society for Microbiology meeting. Volume 1 June 5 – June 9. Atlanta.

External links

  • The Periodic Table of Videos (University of Nottingham)
  • International Labour Organization ethanol safety information
  • National Pollutant Inventory – Ethanol Fact Sheet
  • CDC – NIOSH Pocket Guide to Chemical Hazards – Ethyl Alcohol
  • National Institute of Standards and Technology chemical data on ethanol
  • ChEBI – biology related
  • Chicago Board of Trade news and market data on ethanol futures
  • Calculation of surface tension of ethanol
  • Ethanol History A look into the history of ethanol
  • ChemSub Online: Ethyl alcohol
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