Ethanol

Ethanol, also known as ethyl alcohol or grain alcohol, is a type of alcohol with chemical formula (CH₃CH₂OH). It is the specific alcohol in alcoholic beverages. In fact, when non-chemists refer to "alcohol", they almost always mean ethanol.

Properties

Ethanol is a flammable, colorless liquid with a boiling point of 78.5° C. Its low melting point of -114.5° C allows it to be used in anti-freeze products. It has a pleasant odor reminiscent of whiskey.

Its density is 789 g/L, about 20% less than that of water. It is easily soluble in water and is itself a good solvent, which is a reason alcoholic drinks have a large variety of tastes, since various flavor compounds are solubilized during brewing.

It acts as a disinfectant, which is why alcoholic beverages can be stored for a long time.

The CAS number of ethanol is 64-17-5 and its UN number is UN 1170.

Production

Ethanol for use in alcoholic beverages is produced by fermentation: it is a product of sugar metabolism in certain species of yeast in the absence of oxygen. The process of culturing yeast under conditions to produce alcohol is referred to as brewing. Yeasts can grow in the presence of up to only about 10% alcohol, but the concentration of alcohol in the final product can be increased by distillation.

Ethanol is also used in a wide variety of industrial processes and, for this use, it is generally made from petroleum feedstocks, often from ethylene. It can also be produced from acetaldehyde.

Legalities

Ethanol is the most widely used recreational drug. Its use is legal in the western world, but illegal in muslim countries. During the prohibition from 1919 to 1933, it was also illegal in the United States.

Most countries have laws against drunk driving, driving with a certain concentration of ethanol in the blood. The legal threshold of blood alcohol content ranges from 0.1% to 0.08%, 0.05% and even 0% in different countries.

Most countries also specify a legal drinking age, below which the consumption of alcohol is prohibited.

In many countries, production of alcoholic beverages requires a license. In the U.S., the Bureau of Alcohol, Tobacco and Firearms enforces regulations related to alcohol.

Effects on the human body

In small amounts, ethanol causes a mild euphoria and removes inhibitions; in larger doses, ethanol acts as a depressant and causes drunkenness, coma and death. A major public health problem is alcoholism, the dependency on alcohol.

Several studies have confirmed that regular consumption of small amounts of alcohol has a benefitial effect, as it lowers the incidence of coronary heart disease.

In its pure form (anhydrous - without water) ethanol can be toxic. It is also toxic if ingested in excess in diluted form (whether with water or in alcoholic drinks). Even in moderate concentrations the body (specifically the liver) has to work hard to break ethanol down into aldehydes and ketones. These impurities, combined with general dehydration (due to ethanol's diuretic effects), are for the hangover experienced by people who over-indulge. In addition, certain people lack adequate amounts of these enzymes and thus become drunk after drinking less alcohol than other people.

In high dosages and/or over sustained periods, ethanol consumption can cause serious injury or disease. Even moderate consumption can cause non-permanent cirrhosis of the liver. A blood ethanol content above 0.25% is generally fatal, although regular heavy drinkers can tolerate higher blood alcohol levels.

Ethanol is quickly absorbed into the bloodstream and reaches the brain where it interferes with synaptic firing and causes the death of brain cells. This cell death is caused by an increased concentration of intracellular calcium which weakens the electrochemical gradient across the cell membranes. It is this gradient which is the motive force of membrane pumps and channels (cells, esp. neurons, quickly die without proper membrane pump and channel function). There is also direct damage to cell membranes from free-radicals that are produced from alcohol metabolism.

The liver produces a special enzyme (alcohol dehydrogenase) that breaks down alcohols into acetaldehyde which is turned into acetic acid by another enzyme, and then yet another enzyme converts the acid into fatty acids, carbon dioxide and water. The fatty acids are mostly deposited locally which leads to the characteristic "beer belly". Chronic drinkers, however, so tax this metabolic pathway that things go awry; fatty acids build up as plaques in the capilaries around liver cells and those cells begin to die which leads to cirrhosis of the liver. The liver is part of the body's filtration system and if it is damaged then certain toxins build up thus leading to symptoms of jaundice.

If the mother drinks too much alcohol during pregnancy, the unborn child can develop mental and physical defects. This is known as fetal alcohol syndrome.

Ethanol as fuel

Ethanol is flammable and burns more cleanly then many other fuels. When fully combusted its combustion products are only carbon dioxide and water. For this reason, it is favoured for environmentally conscious transport schemes and has been used to fuel public busses. Pure ethanol attacks certain rubber and plastic materials and cannot be used in unmodified car engines.

A mixture of gasoline and ethanol (typically 10%) is known as gasohol; it can be used to fuel regular cars.

In Brazil and the United States, the use of ethanol from grain in gasohol car fuel has been promoted by government programs. One argument in favor is the increased independence from oil producing countries. Some critics argue that it is mainly a government subsidy for farmers. The environmental effect is not altogether clear, as some studies have claimed that the total energy needed to produce one gallon of ethanol (fertilizing, harvesting, transporting the grain, building and operating an ethanol plant) exceeds the energy content of one gallon of ethanol.