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The common name of ethanol is ethyl alcohol, grain alcohol or drinking alcohol is a volatile, flammable and colourless liquid, powerful psychoactive drug and is one of the oldest known recreational drugs. It is the commonly known alcohol used in thermometers and alcoholic beverages. Also used in the preparation of spirits. It is a straight chain alcohol sharing the molecular formula C2H5OH and empirical formula C2H6O. It can also be written alternatively as CH3-CH2-OH where the carbon of a methyl group is attached to another carbon of methyl group which in turn is attached to a hydroxyl group. Ethanol is also written as Et-OH.

Fermentation of sugars into ethanol is one of the oldest known organic reactions known to humans so far. Consumption of ethanol as a beverage has been known since ancient times and in the modern scenario it is produced from the by-products of petroleum refining. Ethanol has a widespread use for humans like it is a component of solvents, medicines, scents, falvourings and fuel. Ethanol has been a part of alcoholic beverage since 9000 years ago and was consumed by the natives of China. Distillation of ethanol was known to early Greeks and Arabs who produced the distilled wine with the trade name School of Salerno in the 12th century. First absolute alcohol was produced by Raymond Lull. First synthetic ethanol was produced by Henry Hennel of Great Britain and S.G. Sérullas of France in 1826. Michael Faraday produced ethanol in 1828 by acid catalyzed hydration of ethylene in the similar manner as it is produced today for commercial production.

Ethanol is a volatile, colourless liquid with a strong characteristic odour and burns with a smokeless flame not visible in the normal light. Its physical properties are generally based on its hydroxyl group and its short carbon chain. The hydroxyl group participates in hydrogen bonding making it more viscous and volatile in comparison to other polar organic compounds of similar molecular weight. It is a versatile solvent, miscible with water and other organic solvents like acetic acid, acetone, benzene, carbon tetrachloride etc. It is also miscible with light aliphatic hydrocarbons like pentane and hexane. The miscibility of ethanol is limited with alkanes up to undecane. The ethanol-water mixture has a very less volume in comparison to the volume of individual components. Mixing of ethanol with water is a exothermic change resulting in the liberation of 777 J/mol of energy at 298K.

Pure ethanol is hygroscopic and readily absorbs water from air and this is due to hydrogen bonding. The polar nature of the hydroxyl group in ethanol is responsible for dissolving many ionic compounds like sodium and potassium hydroxides, magnesium chloride, sodium bromide, sodium and potassium chlorides are slightly soluble in ethanol. One end ethanol carries non-polar end so it also dissolves non-polar substances like the essential oils, flavouring agents and medicinal agents. The addition of some percent of ethanol to water reduces the surface tension of water considerably explaining the tears of wine property. When wine is poured in a glass the ethanol evaporates forming a layer of foam over the glass. As the ethanol content of wine decrease the surface tension of wine increases. The ethanol water mixture with ethanol content of 50% is flammable. The refractive index of ethanol is more than that of water and is 1.36242.

Ethanol is produced both by the hydration of ethylene as a petrochemical as well as by the fermentation of sugars by yeast and this process of production is a biological process. The production of ethanol by these two processes is equally depending upon the need of market. The production of ethanol as an industrial solvent by hydration of ethylene is a chemical reaction occurring in the presence of catalyst. Phosphoric acid is used as a catalyst in this reaction which is first adsorbed on the silica gel. The Shell Oil Company used phosphoric acid for commercial production of ethanol in 1947. The reaction is carried out at extremely high pressure steam of at about 300°C. In US the Union Carbide Corporation also utilized this process for commercial production of ethanol but at present only Lyondell Basell uses this process for commercial production.

At present indirect hydration of ethylene is carried out by reacting it with concentrated sulphuric acid in order to generate ethyl sulphate which is later on hydrolyzed to obtain ethanol and sulphuric acid again. Production of ethanol to be used in alcoholic beverages and industrial fuel is carried out by fermentation only. There are certain strains of yeast which convert sugars into ethanol and carbon dioxide. The process of yeast culture under controlled environment to produce alcohol is called as fermentation. Ethanol can be produced by the cereal grains but first these are converted into sugars. In brewing of the beer, the grains are first allowed to germinate or malt is used which produces the enzyme amylase. This amylase is responsible for conversion of all the starch present in the malted grain into sugars. For production of ethanol as a fuel, starch is first hydrolyzed into glucose by treating it with sulphuric acid.

Cellulose can also be used as a source of sugar for ethanol fermentation. At present many enzyme producing companies are trying to develop genetically modified fungi for the production of cellulase, xylanase, and hemicellulase enzymes. These enzymes will convert the starch present in the agricultural residue into sugars which will be fermented later on for commercial production of ethanol. Ethanol can also be produced from anaerobic bacterium Clostridium ljungdahlii which is present in the chicken wastes and used as a fuel. Production of ethanol from corn is under strong criticism. Ethanol can also be produced from the closed loop ethanol plant where ethanol is produced from manure and the manure left after ethanol production is used for fertilizing the crops. 75% of ethanol is produced by this process a good success. Alternative methods for ethanol production are also in use where ethanol is produced from waste materials like wood chips, sugarcane bagasse and switch grass.

The ethanol concentration is measured by two methods by the breweries and ethanol producing plants. Infrared ethanol sensors are used for measuring the vibrational frequency of the dissolved ethanol using CH band at 2900 cm-1. Calculation is done by the Beer Lambert Law. Another method uses hydrometer which measures the alcohol content during fermentation by detecting change in the specific gravity. Hydration of ethylene and brewing produces mixture of ethanol and water which requires purification. Fractional distillation produces 95.6% concentrated ethanol by volume which is an azeotrope mixture having boiling point of 78.1°C and cannot be further purified by distillation. Absolute ethanol can be obtained by desiccation using adsorbents like starch, corn grits or zeoloites which adsorb water and other methods include azeotropic distillation and extractive distillation. Most ethanol fuel refineries used an adsorbent for obtaining pure and concentrated ethanol. Absolute ethanol can also be obtained by distillation carried out with benzene and rectified spirit and in the third fraction ethanol is obtained at 78.3°C. Some benzene is left in the alcohol so obtained and is not fit for consumption as benzene is carcinogenic. Desiccation of glycerol also produces absolute alcohol and the alcohol so obtained is called as spectroscopic alcohol because of the absence of benzene in it so used as a solvent in spectroscopy.

The pure ethanol and alcoholic beverages are highly taxed by the government of the country but apart from consumption ethanol shares a number of uses in human life. To remain free from the taxes bittering agents like denatonium benzoate and toxins such as methanol, naphtha, and pyridine are added to absolute ethanol in order to make it unfit for consumption. The products so obtained are tagged with the term denatured alcohol. Absolute alcohol contains very low water content not fir for human consumption. It may contain toxic benzene if ethanol is obtained by azeotropic distillation. It is used as a solvent in the laboratory and industries. Spectroscopic ethanol has a low absorbance in ultraviolet and visible region so ideal foe ultraviolet and visible spectroscopy.

Rectified spirit is an azeotropic mixture with 4% water content is used instead of anhydrous ethanol for various purposes. Ethanol shares the category of primary alcohol as the carbon atom which is attached to the hydroxyl group is also attached to two hydrogen atoms in order to complete the valency. This hydroxyl group is mainly responsible for its chemical as well as physical properties. In presence of acid catalysts ethanol reacts with carboxylic acids to produce esters. This reaction is carried out industrially and water removal is very necessary from the ester thus, obtained. Esters again react with acid or base and produce ethanol and carboxylic acid. This reaction is known as saponification as it is used in preparation of soaps. Ethanol can also form esters with inorganic acids. Strong acid desiccants cause dehydration of alcohol resulting in the production of diethyl ether and byproducts. If the temperature of dehydration exceeds up to 160°C then ethylene is obtained as a main product. Complete combustion of ethanol produces carbon dioxide and water.

Ethanol is a neutral molecule with a pH of nearly 7.00. It can be completely converted into ethoxide ion by reacting it with a strong base like sodium. Ethanol also reacts with halogens to produce ethyl halides but this reaction requires zinc chloride as a catalyst. The reaction of halogens with ethanol in the presence of base results in the formation of haloforms and this reaction is called as haloform reaction. Ethanol can be oxidized to acetaldehyde and further oxidized to acetic acid depending upon the conditions and reagents. Oxidation of ethanol has no industrial significance but in human body the oxidation of ethanol is carried out by the enzyme liver alcohol dehyrogenase. The oxidation byproduct of ethanol is acetic acid which has a nutritive value for humans as it acts as a precursor to acetyl-CoA and the acetyl group is used for energy production during the biosynthesis of metabolites.

Ethanol is generally used as a motor fuel and fuel additive on large scale. Brazil has the largest industry for producing ethanol to be used as a fuel. Gasoline sold in Brazil contains 25% of anhydrous ethanol. Hydrous ethanol has got its use in greater proportion as a fuel in majority of cars being sold in the modern era. The combustion of ethanol in an internal engine yields many products of incomplete combustion as produced by gasoline including larger quantity of formaldehyde and other compounds of acetaldehyde. These byproducts show strong photochemical activity resulting in the production of ozone. The world production of ethanol was 51 gigaliters in 2006 and Brazil and US topped in ethanol production. More than 20% of the Brazilian cars utilize 100% ethanol as a fuel as their engine is specially designed for using ethanol as a fuel along with the flex engines. Flex fuel engines in Brazil are able to work with ethanol, gasoline or with the mixture of both. Brazil utilizes sugarcane crop for the production of ethanol and the bagasse left after ethanol production is utilized for the production of electricity.

The United States industries are largely dependent on corn for the commercial production of ethanol. One major problem with ethanol is that it cannot be efficiently shipped through the pipelines as it is easily miscible with water. Ethanol is the major psychoactive constituent of alcoholic beverages with strong depressing effect on the central nervous system. It has a complex mode of action on different parts of brain and is a strong agonist to the GABA receptors. Gamma-hydroxybutyric acid (GHB) is also another agonist to the GABA receptors. Ethanol is metabolized in human body as an energy providing nutrient as it acts as a precursor for acetyl-CoA which is a common intermediate in both glucose and fatty acid metabolism. Alcoholic beverages vary widely in their alcoholic content. Most of the alcoholic beverages are classified as fermented beverages as they are produced by the action of yeast on the sugary foodstuffs or distilled beverages which include ethanol addition by distillation. The ethanol content of an alcoholic beverage is measured in term of volume fraction of ethanol expressed as alcoholic proof units.

Fermented beverages can be easily classified on the basis of their key foodstuffs. Beers are made from cereal gains or starchy materials while wines and ciders are prepared from fruit juices and meads from honey. Different cultures and different nations use different sorts of foodstuffs for the preparation of alcoholic beverages. Distilled beverages are prepared by distilling the fermented beverages. The important categories of distilled beverages include whiskeys made from fermented cereal grains, brandies obtained from fermented fruit juices and rum obtained from fermented molasses or sugarcane juice. Vodka and similar neutral grain spirits can be obtained by distilling either potatoes or grains and the products thus obtained lack the taste of key ingredient. Many other alcoholic beverages are also prepared from fruits, herbs and spices in different parts of the globe. In many beverages ethanol is concentrated other than distillation like in Applejack which is obtained by freeze distillation and water is frozen out of the apple cider leaving an ethanol rich liquid. Ice beer is also freeze distilled with beer as a base liquid. Fortified wines are prepared by adding brandy to partially fermented wine. This step kills the yeast and retains some sugar in the grape juice as a result these wines are quite sweeter than other wines.

Alcoholic beverages are also used in cooking as they impart flavour and also dissolve some of the hydrophobic compounds which are insoluble in water. Ethanol is a very important industrial ingredient which finds its use as base in production of many chemicals like ethyl halides, ethyl esters, diethyl ether, acetic acid, ethyl amines and to a lesser extent butadiene. Ethanol is more commonly used in medical wipes and in hand sanitizers as well as an antiseptic. It kills microbes by neutralizing their proteins, dissolving lipids and is effective against most bacteria and fungi and many viruses but ineffective against bacterial spores.

Ethanol is also used as an antidote for poisoning many other toxic alcohols like methanol and ethylene glycol. It competes with other alcohols for the alcohol dehydrogenase enzyme and thus, prevents formation of toxic aldehyde and carboxylic acid derivatives and declines the tendency of glycol to form crystals in kidneys. Ethanol is miscible with water and so is an effective purpose solvent. It finds use in paints, tinctures, markers and personal care products like perfumes and deodorants. It is also used in vodka sauce a popular flavouring agent for foods. Before the development of modern medicines ethanol was used as a medicine against depression and as an anesthetic. Ethanol was also used as a fuel in the bipropellant rockets during the World War-II.

The removal of ethanol through the oxidation by alcohol dehydrogenase in the liver from human body is limited. Removal of large concentration of ethanol from blood follows zero order kinetics. The blood alcohol concentration can be used for modifying the biochemistry of methanol and ethylene glycol. Pure ethanol causes irritation on skin and the eyes. Nausea, vomiting and intoxication are the common symptoms of ingesting it. Long term effects can result in serious liver damage. Ethanol is not a carcinogen but its metabolites may act as carcinogens.

We can summarize that ethanol is good as well as bad as it adds a flavour to our life.