Ethanol

Ethanol, also called ethyl alcohol, is an aliphatic organic chemical compound with a hydroxyl functional group, forming part of the alcohol family, with the empirical formula C ₂H₆O. Its semi-developed chemical formula is CH3-CH2-OH, and molecular weight of 46.0684. It is an alcohol that under normal conditions of pressure and temperature appears as a colorless liquid, with a very penetrating ethereal odor, similar to acetic acid (although it is not unpleasant) and is highly flammable. It has a boiling point of 78.4 °C. Miscible with water in any proportion, the 96% by weight concentration forms an azeotropic mixture.

It is a compound that has been obtained since ancient times through fermentative processes of simple sugars, and it can be ingested and behaves physiologically as a psychoactive substance. It is the characteristic compound of the so-called alcoholic beverages, such as wine (with around 13% V/V), beer (between 5% V/V and 8% V/V), liquors (up to 50 % V/V) or spirits (up to 70% V/V).

Etymology

ethanol is the systematic name defined by the International Union of Pure and Applied Chemistry (IUPAC) for a molecule with two carbon atoms (prefix "et-") that have a single bond between them (the suffix "-ane") and an attached hydroxyl group -OH (suffix "-ol").

The prefix ethyl was coined in 1834 by the German chemist Justus von Liebig. ethyl is a contraction of the French word ether (any substance that readily evaporates or sublimes at room temperature) and the Greek word ύλη (hylé, substance). The name ethanol was coined as a result of a resolution that was adopted at the International Conference on Chemical Nomenclature that was held in April 1892 in Geneva, Switzerland.

History

The ethanol used as fuel for a burner

Ethanol has been used by man since prehistoric times as the alkaloid of alcoholic beverages. Dried residues on 9,000-year-old ceramics found in China imply that alcoholic beverages were already in use even among Neolithic peoples. Its isolation as a relatively pure compound was achieved by the Persian alchemist Al-Razi (865-925). Alchemists called it aqua vitae.

Two other chemists who contributed to the development of distillation techniques were Geber (Gabir ibn Hayyān al-Sūfī) and Al-Kindi (Alkindus). In writings attributed to Geber (721-815) he mentions the flammable vapors of boiled wine. Al-Kindi (801-873) clearly describes the distillation of wine.

In 1796, Johann Tobias Lowitz obtained pure ethanol by distilling ethanol through activated carbon filtration.

Antoine Lavoisier described ethanol as a compound of carbon, hydrogen, and oxygen, and in 1808 Nicolas Théodore Saussure determined the chemical formula of ethanol. Fifty years later, A. Scott Coupe published the structural formula of ethanol, and it ranked among the first compounds to have their chemical structures determined.

Ethanol could be synthetically prepared in 1826 thanks to independent work by Henry Hennel in Great Britain and S.G. Serullas in France. In 1828, Michael Faraday prepared ethanol by catalyzing it with an acid hydration of ethylene, a process similar to that currently used by industry for ethanol synthesis.

In the United States, ethanol was used as lamp fuel as early as 1840, but a tax on industrial alcohol during the American Civil War made this type of use uneconomical. This tax was repealed in 1906, and from 1908 on Ford Model T automobiles could be adapted to run on ethanol. With the advent of Prohibition in 1920, sellers of ethanol fuel were accused of being allies of moonshiners, moonshiners, and ethanol fuel again fell out of favor until the late XX.

Magnitudes and units of measurement in beverages

The magnitude that measures the concentration of alcohol in beverages is alcohol content or, more technically, alcoholic degree by volume, often, but it is customary to abbreviate as volume or graduation.

The unit was formerly the alcohol content which was expressed on the bottles as a superscript o (°), currently expressed simply as a percentage preceded by the word Volume or Vol.. Both units are equivalent.

Physical properties

The ethanol cream with its represented spectrum

Ethanol is a volatile and colorless liquid that has a very characteristic intense odor. When burned it produces a smokeless blue flame that is not always visible in normal light.

The physical properties of ethanol derive primarily from the presence of its hydroxyl group and the shortness of its carbon chain. The hydroxyl group ethanol is able to participate in hydrogen bonding, which makes it more viscous and less volatile than other polar organic compounds of similar molecular weight.

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. It is also miscible with light aliphatic hydrocarbons, such as pentane and hexane, and with aliphatic chlorides, such as trichloroethane and tetrachlorethylene.

The miscibility of ethanol with water contrasts with that of alcohols with longer chains, with five or more carbon atoms; mixing with water decreases dramatically as carbon number increases. Mixing of ethanol with alkanes is limited to alkanes above undecanene, mixtures to dodecanene, and alkanes show a greater range of mixing below a certain temperature (approx. 13 °C for dodecanene). In miscibility the range tends to be wider with higher alkanes and the temperature required to achieve full miscibility increases.

Mixtures of ethanol and water have less volume than the sum of their individual components in the given fractions. Mixing equal volumes of ethanol and water results in only 1.92 mixing volumes. The mixture of ethanol and water is exothermic. At 298 K up to approx. 777 J/mol are released.

Ethanol and water form an azeotropic mixture at approx. 89% mol-mol ethanol and 11% water, or a mixture by volume of 96% ethanol and 4% water, at normal pressure, and at T = 351 K. This mixture Azeotrope is very closely dependent on the existing temperature and pressure, and vanishes at temperatures below 303 K.

• Thermophysical properties of ethanol mixtures with water and dodecanene
• 

  Excess volume of ethanol and water mixture (volume contraction)

• 

  Ethanol and water blend heat

• 

  Liquid-vapor balance of ethanol and water mixture (including azeotropics)

• 

  Miscibility difference in ethanol and dodecanene mixture

In the shadow of the cup the "lagrims of wine" phenomenon in which the content of ethanol of wine is involved are clearly observed.

Hydrogen bonding causes pure ethanol to be hygroscopic in that it readily absorbs water from the air.

Hydrogen links in solid ethanol to −186 °C

The polar nature of the hydroxyl group makes it possible for ethanol to dissolve many ionic compounds, especially sodium and potassium hydroxides, magnesium chloride, calcium chloride, ammonium chloride, ammonium bromide, and sodium bromide. Sodium and potassium chlorides are slightly soluble in ethanol. Since ethanol also has a nonpolar final molecule, it can also dissolve nonpolar substances, including most essential oils, and numerous flavorings, dyes, drugs, and agents.

Adding a few percent ethanol to water drastically reduces the surface tension of water. This property partly explains the phenomenon of "tears of wine". When wine is stirred in a glass, the ethanol quickly evaporates from the thin layer of wine and ends up on the glass wall. As the ethanol content of the wine decreases, its surface tension increases and the film of droplets slides down the glass in a characteristic manner.

Mixtures of ethanol and water that contain approximately more than 50% ethanol are flammable and can be easily ignited. An alcohol stove has been developed in India, which works with a 50% mixture of ethanol and water. The degree of alcohol is a widely used test to measure the amount of ethanol (i.e. alcohol) contained in it. the mixture, often an alcoholic drink. In the 18th century, proof was determined by adding a liquor, such as rum, to gunpowder. If gunpowder can explode, it is considered the "100 degree test" and that it is a good liquor.

Ethanol and water solutions that contain less than 50% ethanol can also be flammable if the solution is heated. Some cooking methods in which wine is added to a hot pan causes a steam that can then be ignited to burn off excess alcohol.

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

Chemical properties

Alcohols can be primary, secondary or tertiary, depending on the number of hydrogen atoms substituted on the carbon atom to which the hydroxyl group is attached. Ethanol is classified as a primary alcohol, which means that the carbon to which its hydroxyl group is attached has at least two hydrogen atoms. The chemistry of ethanol is closely related to that of its hydroxyl group.

• Acid-base chemistry. The ethanol of the hydroxyl group makes the molecule a little basic, even though it is almost neutral like water. The 100% ethanol pH is 7.33, compared to 7.00 pure water. Quantitatively ethanol can be converted into its conjugated base, ion etoxide (CH)₃CH₂O^?), by a reaction with alkaline metals like sodium:

Primary alcohol

2 CH₃CH₂OH + 2 Na → 2 CH₃CH₂ONa + H₂,

Or a very solid base, like sodium hydrouro:

CH₃CH₂OH + NaH → CH₃CH₂ONa + H₂.

This reaction is not possible in an aqueous solution, since water is more acidic, so that hydroxide is preferred to a formation of an alcoxide.

• Halogenation. Ethanol reacts with hydrogen halogenides to produce haloalcans like ethyl chloride and ethyl bromide:

CH₃CH₂OH + HCl → CH₃CH₂Cl + H₂O

The reaction of chloric acid (HCl) requires a catalyst how zinc chloride. The reaction of hydrogen chloride in the presence of the respective zinc chloride is known as the reactive or test of Lucas.

CH₃CH₂OH + HBr → CH₃CH₂Br + H₂O

Bromhydric acid (HBr) requires a reflux with sulfuric acid as a catalyst.

Ethyl haloalcans can also be produced by ethanol reaction with more specialized halogenative agents, such as tionyl chloride for the preparation of ethyl chloride, or tribromide phosphorus (PBr₃) for the preparation of ethyl bromide.

CH₃CH₂OH + SOCl₂ → CH₃CH₂Cl + SO₂ + HCl

• Haloformo. Haloform reaction is a chemical reaction where a haloform (CHX3, where X is a halogen) is produced by the exhaustive halogenation of a cetonous methyl (a molecule containing an R-CO-CH3) in the presence of a base.

Molecula in 3D and in red rotation: oxygen; gray: carbon; white: hydrogen

• Training of esters. Under the conditions with acid catalysts, ethanol reacts with carboxylic acids (RCOOH) to produce ethyl and water esters:

RCOOH + HOCH₂CH₃ → RCOOCH2CH3 + H₂Or.

In this reaction, to produce useful yields, you have to remove the water that appears as a product. Ethanol can also form esters with inorganic acids. The sulfate diethyl and triethyl phosphate, prepared respectively by the reaction of ethanol with phosphoric acid and sulfuric acid, are useful as agents in organic synthesis. Ethyl nitrite, prepared from ethanol reaction with sodium nitrite and sulfuric acid, had been widely used as diuretic.

• Dehydration. Strong acids that are desiccating, such as sulfuric acid, causes dehydration of ethanol, whether to form dietary or ethylene ether:

2 CH₃CH₂OH → CH₃CH₂OCH₂CH₃ + H₂O (120'C)

CH₃CH₂OH → H₂C=CH₂ + H₂Or (at 180'C)

The predominant product, the dietary or ethylene ether, depends on the accuracy of the reaction conditions.

• Oxidation. Ethanol can be oxidized in acetaldehid, and is also oxidized to acetic acid. In the human body, these are oxidation reactions catalyzed by enzymes. In the lab, ethanol oxidation to acetic acid is performed by aqueous solutions of strong oxidant agents, such as chromatic acid or potassium permanganate, and it is difficult to stop acetaldehid reaction when it is at full yield. Ethanol can be oxidized to acetaldehid, without going through oxidation to acetic acid, making it react with pyridinium chlorocyroma. Direct oxidation of ethanol to acetic acid using chromic acid is indicated below:

C₂H₅OH + 2 [O] → CH₃COOH + H₂O

The oxidation product of ethanol, acetic acid, the human body is consumed as nutrients in the form of acetyl CoA, where the acetyl group can be used as an energy source or used for biosynthesis.

• Closure. When exposed to chlorine, ethanol is oxidized and its alpha carbon is chlorinated to form a compound, chloral.

4 Cl₂ + C₂H₅OH → CCl₃CHO + 5HCl

• Combustion. Ethanol combustion forms carbon dioxide and water:

C₂H₅OH(g) + 3 O₂(g) → 2 CO₂(g) + 3 H₂O(l);

Other constants

• Refrection Index: n_D²⁰ = 1.361
• Maximum concentration allowed in workplaces: 1000 ppm
• Lethal dose: LD50: 15.05 g/kg (oral)

Summary

For more information, see ethanol (fuel)

Ethanol, at room temperature and pressure, is a colorless and volatile liquid that is present in various fermented beverages. Since ancient times, ethanol was obtained by anaerobic fermentation of a solution containing sugars with yeast and subsequent distillation.

Depending on the type of alcoholic beverage that contains it, ethanol appears accompanied by different chemical substances that give it color, flavor, and smell, among other characteristics.

Distillation: absolute alcohol (100% alcohol)

To obtain water-free ethanol (absolute alcohol) azeotropic distillation is applied in a mixture with benzene or cyclohexane. The azeotrope, formed by the auxiliary solvent with water, is distilled from these mixtures at lower temperatures, while the ethanol remains retained. Another currently widely used purification method is physical absorption through molecular sieves.^{[citation needed]}

On a laboratory scale, desiccants such as magnesium can also be used, which reacts with water to form hydrogen and magnesium oxide.^{[citation needed]}

Applications and uses

General uses

In addition to being used for culinary purposes (alcoholic beverage), ethanol is widely used in many industrial sectors and in the pharmaceutical sector, as an excipient for some medicines and cosmetics (this is the case of antiseptic alcohol 70º GL and in the preparation of air fresheners and perfumes).

It's a good solvent, and can be used as antifreeze. It is also a disinfectant. Its greatest bactericidal potential is obtained at a concentration of approximately 70%, since the surface tension of the bacterial cell is reduced, facilitating the process of protein denaturation.

For its use as a topical antiseptic, it is usually mixed with additives such as camphor or benzalkonium chloride in order to prevent its ingestion and for this reason it is sold as denatured ethyl alcohol. It should be noted that isopropyl alcohol is also used for this same purpose, which is not drinkable.

Chemical industry

The chemical industry uses it as a starting compound in the synthesis of various products, such as ethyl acetate (a solvent for glues, paints, etc.), diethyl ether, etc.

Its disinfectant properties are also used.

Fuel

It is used as industrial and domestic fuel. This also contains compounds such as pyrobites exclusively to alcohol. This last application is also spreading more and more in other countries to comply with the Kyoto protocol. Studies by the United States Department of Energy say that use in automobiles reduces the production of greenhouse gases by 85%.^{[citation needed]}

Mixed with 5% methyl alcohol, it is used as fuel for some distillation burners and is therefore called burning alcohol.

Toxicology

The most significant effects of alcohol on the body, both positive and negative and depending on consumption. In addition, pregnant women can cause fetal alcoholic syndrome.

Ethanol acts on γ-aminobutyric acid receptors type A (GABA_a) as a positive allosteric modulator, increasing the flow of transmembrane ions, which induces a state of neurochemical inhibition (slowing effect). It produces effects similar to benzodiazepines and barbiturates, which act on the same receptor but at different sites. This similarity includes the addictive potential, which is also similar.

Ethanol can affect the central nervous system, causing states of euphoria, disinhibition, dizziness, drowsiness, confusion, illusions (such as seeing double or everything moving spontaneously). At the same time, lower the reflections. With higher concentrations it slows down movements, prevents correct coordination of the limbs, temporary loss of vision, emetic discharges, etc. In certain cases there is an increase in the irritability of the intoxicated subject as well as in aggressiveness; in another certain number of individuals the area that controls impulses is affected, becoming impulsively uncontrolled and frantic. The consumption of large doses of ethanol causes drunkenness (alcohol intoxication), which can cause a hangover once the effects have worn off. Depending on the dose and the frequency with which it is consumed, ethanol can cause ethyl coma, loss of consciousness, acute respiratory paralysis or even death. Because ethanol impairs cognitive abilities, it can encourage reckless or irresponsible behavior. The toxicity of ethanol is largely caused by its major metabolite, acetaldehyde, and its secondary metabolite, acetic acid.

The median lethal dose (LD₅₀) of ethanol in rats is 10.3 g/kg. Other alcohols are significantly more toxic than ethanol, in part because they take much longer to metabolize and in part because its metabolization produces substances (metabolites) that are even more toxic. Methanol (wood alcohol), for example, is oxidized in the liver, forming the poisonous substance formaldehyde by the enzyme alcohol dehydrogenase; this can cause blindness or death. An effective treatment to prevent formaldehyde poisoning after ingesting methanol is to administer ethanol. The alcohol dehydrogenase enzyme has a higher affinity for ethanol, thus preventing methanol from binding to and serving as a substrate. In this way, the rest of the methanol will have time to be excreted by the kidneys. The remaining formaldehyde will be converted to formic acid and then excreted.

Resistance to alcohol does not appear to increase in older, heavier, and shorter individuals, while children are especially vulnerable. Cases have been reported of infants dying from poisoning due to inhalation of ethanol vapors after alcohol-impregnated rags were applied to them. Intake in children can lead to aggravated mental retardation or physical and mental underdevelopment (it is for this reason that the sale of alcohol to minors is prohibited). There have also been studies showing that if mothers drank alcohol during pregnancy, their children could be more prone to fetal alcohol syndrome.

Analytics

A method of determining the approximate concentration of ethanol in the blood takes advantage of the fact that an equilibrium is formed in the lungs that relates this concentration to the concentration of ethanol vapor in exhaled air. This air is passed through a tube containing silicon gel impregnated with a mixture of dichromate and sulfuric acid. The red-orange dichromate oxidizes the ethanol to acetaldehyde and is in turn reduced to green chromium(III). The length of the area that has changed color indicates the amount of ethanol present in the air if a certain volume is passed through the tube.