Ethanol
Background Information
Ethanol (also called ethyl alcohol, grain alcohol, drinking alcohol, or simply alcohol) is an organic compound with the chemical formula CH3CH2OH. It is an alcohol, with its formula also written as C2H5OH, C2H6O or EtOH, where Et stands for ethyl. Ethanol is a volatile, flammable, colorless liquid with a characteristic wine-like odor and pungent taste. It is a psychoactive recreational drug, and the active ingredient in alcoholic drinks.
Ethanol is naturally produced by the fermentation process of sugars by yeasts or via petrochemical processes such as ethylene hydration. Historically it was used as a general anesthetic, and has modern medical applications as an antiseptic, disinfectant, solvent for some medications, and antidote for methanol poisoning and ethylene glycol poisoning. It is used as a chemical solvent and in the synthesis of organic compounds, and as a fuel source. Ethanol also can be dehydrated to make ethylene, an important chemical feedstock. As of 2006, world production of ethanol was 51 gigalitres (1.3×1010 US gallons), coming mostly from Brazil and the U.S.
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's adiabatic flame temperature for combustion in air is 2082 °C.
Ethanol is slightly more refractive than water, having a refractive index of 1.36242 (at λ=589.3 nm and 18.35 °C or 65.03 °F). The triple point for ethanol is 150 K at a pressure of 4.3 × 10−4 Pa.
Properties | |
---|---|
Chemical formula | C2H6O |
Molar mass | 46.069 g·mol−1 |
Appearance | Colourless liquid |
Odor | wine-like, pungent |
Density | 0.78945 g/cm3 (at 20 °C) |
Melting point | −114.14 ± 0.03°C (159.01 ± 0.03 K) |
Boiling point | 78.23 ± 0.09°C (351.38 ± 0.09 K) |
Solubility in water | Miscible |
log P | −0.18 |
Vapor pressure | 5.95 kPa (at 20 °C) |
Acidity (pKa) | 15.9 (H2O), 29.8 (DMSO) |
Magnetic susceptibility (χ) | −33.60·10−6 cm3/mol |
Refractive index (nD) | 1.3611 |
Viscosity | 1.2 mPa·s (at 20 °C), 1.074 mPa·s (at 25 °C) |
Dipole moment | 1.69 D |
Uses
Medical
Anesthetic
Ethanol is the oldest known sedative, used as an oral general anesthetic during surgery in ancient Mesopotamia and in medieval times. Mild intoxication starts at a blood alcohol concentration of 0.03-0.05% and induces anesthetic coma at 0.4%. However, this use carried the high risk of deadly alcohol intoxication and pulmonary aspiration on vomit, which led to use of alternatives in antiquity, such as opium and cannabis, and later diethyl ether starting in the 1840s.
Antiseptic
Ethanol is used in medical wipes and most commonly in antibacterial hand sanitizer gels as an antiseptic for its bactericidal and anti-fungal effects.[24] Ethanol kills microorganisms by dissolving their membrane lipid bilayer and denaturing their proteins, and is effective against most bacteria, fungi and viruses. However, it is ineffective against bacterial spores, but that can be alleviated by using hydrogen peroxide.
A solution of 70% ethanol is more effective than pure ethanol because ethanol relies on water molecules for optimal antimicrobial activity. Absolute ethanol may inactivate microbes without destroying them because the alcohol is unable to fully permeate the microbe's membrane. Ethanol can also be used as a disinfectant and antiseptic because it causes cell dehydration by disrupting the osmotic balance across the cell membrane, so water leaves the cell leading to cell death.
Antidote
Ethanol may be administered as an antidote to ethylene glycol poisoning and methanol poisoning. Ethanol serves this process by acting as a competitive inhibitor against methanol and ethylene glycol for alcohol dehydrogenase. Though it has more side effects, ethanol is less expensive and more readily available than fomepizole, which is also used as an antidote for methanol and ethylene glycol poisoning.
Medicinal solvent
Ethanol, often in high concentrations, is used to dissolve many water-insoluble medications and related compounds. Liquid preparations of pain medications, cough and cold medicines, and mouth washes, for example, may contain up to 25% ethanol and may need to be avoided in individuals with adverse reactions to ethanol such as alcohol-induced respiratory reactions. Ethanol is present mainly as an antimicrobial preservative in over 700 liquid preparations of medicine including acetaminophen, iron supplements, ranitidine, furosemide, mannitol, phenobarbital, trimethoprim/sulfamethoxazole and over-the-counter cough medicine.
Pharmacology
In mammals, ethanol is primarily metabolized in the liver and stomach by alcohol dehydrogenase (ADH) enzymes. These enzymes catalyze the oxidation of ethanol into acetaldehyde (ethanal):
CH3CH2OH + NAD+ → CH3CHO + NADH + H+
When present in significant concentrations, this metabolism of ethanol is additionally aided by the cytochrome P450 enzyme CYP2E1 in humans, while trace amounts are also metabolized by catalase.
The resulting intermediate, acetaldehyde, is a known carcinogen, and poses significantly greater toxicity in humans than ethanol itself. Many of the symptoms typically associated with alcohol intoxication—as well as many of the health hazards typically associated with the long-term consumption of ethanol—can be attributed to acetaldehyde toxicity in humans.
The subsequent oxidation of acetaldehyde into acetate is performed by aldehyde dehydrogenase (ALDH) enzymes. A mutation in the ALDH2 gene that encodes for an inactive or dysfunctional form of this enzyme affects roughly 50% of east Asian populations, contributing to the characteristic alcohol flush reaction that can cause temporary reddening of the skin as well as a number of related, and often unpleasant, symptoms of acetaldehyde toxicity. This mutation is typically accompanied by another mutation in the alcohol dehydrogenase enzyme ADH1B in roughly 80% of east Asians, which improves the catalytic efficiency of converting ethanol into acetaldehyde.
Recreational
As a central nervous system depressant, ethanol is one of the most commonly consumed psychoactive drugs.
Despite alcohol's psychoactive, addictive, and carcinogenic properties, it is readily available and legal for sale in most countries. There are laws regulating the sale, exportation/importation, taxation, manufacturing, consumption, and possession of alcoholic beverages. The most common regulation is prohibition for minors
Fuel
The largest single use of ethanol is as an engine fuel and fuel additive. Brazil in particular relies heavily upon the use of ethanol as an engine fuel, due in part to its role as one of the world's leading producers of ethanol. 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 gasoline-fueled cars sold in the country.
The US and many other countries primarily use E10 (10% ethanol, sometimes known as gasohol) and E85 (85% ethanol) ethanol/gasoline mixtures. 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.
According to an industry advocacy group, ethanol as a fuel reduces harmful tailpipe emissions of carbon monoxide, particulate matter, oxides of nitrogen, and other ozone-forming pollutants. Argonne National Laboratory analyzed greenhouse gas emissions of many different engine and fuel combinations, and found that biodiesel/petrodiesel blend (B20) showed a reduction of 8%, conventional E85 ethanol blend a reduction of 17% and cellulosic ethanol 64%, compared with pure gasoline.[50] Ethanol has a much greater research octane number (RON) than gasoline, meaning it is less prone to pre-ignition, allowing for better ignition advance which means more torque, and efficiency in addition to the lower carbon emissions.
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. This leads to a significantly larger photochemical reactivity and more ground level ozone. This data has been assembled into The Clean Fuels Report comparison of fuel emissions and show that ethanol exhaust generates 2.14 times as much ozone as gasoline exhaust. When this is added into the custom Localized Pollution Index of The Clean Fuels Report, the local pollution of ethanol (pollution that contributes to smog) is rated 1.7, 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).
More than 20% of Brazilian cars are able to use 100% ethanol as fuel, which includes ethanol-only engines and flex-fuel engines. Flex-fuel engines in Brazil are able to work with all ethanol, all gasoline or any mixture of both. In the United States, 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 fleet of ethanol-burning automobiles with large national infrastructure that produces ethanol from domestically grown sugarcane.
Ethanol's high miscibility with water makes it unsuitable for shipping through modern pipelines like liquid hydrocarbons. Mechanics have seen increased cases of damage to small engines (in particular, the carburetor) and attribute the damage to the increased water retention by ethanol in fuel.
See also
Procedures
Page | Description | Requires | Produces | Status |
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Dummy procedure which produces Ethanol | chemical:alcohol:ethanol | Placeholder only |
Related Resources
Page | Designation | Distinguishing factors | Is a |
---|---|---|---|
Ethanol | chemical:alcohol:ethanol | hygiene:disinfectant, material:fuel:liquid:light, material:solvent:alcohol:drinkable | |
Methanol | chemical:alcohol:methanol | material:fuel:liquid:light, material:solvent:alcohol | |
Alcohol | chemical:alcohol | material:fuel:liquid:light, material:solvent:alcohol | |
Biodiesel | chemical:fuel:liquid:biodiesel | material:fuel:liquid:light |
Resources (net.forthefall/ontology:resources) | |
---|---|
Designation | chemical:alcohol:ethanol |
Is a type of | hygiene:disinfectant, material:fuel:liquid:light, material:solvent:alcohol:drinkable |
Importance | 3 - Important |
Cost | ≤ 10 €/$ |
Shelf life (≥) | 2 600 weeks |
Hazard / Health rating | 1 - Irritation |
Hazard / Fire rating | 3 - Flammable |
Hazard / Reactivity rating | 1 - Mostly stable |