Oxygen Functional Groups: Alcohols

James Richard Fromm

Alcohols are the most simple organic oxygen compounds which contain one or more hydroxyl groups (-OH groups).  They are named systematically from the corresponding alkanes by changing the ending -ane to -ol.  Thus methane gives rise to methanol, CH3OH, and ethane to ethanol, CH3CH2OH.  The alcohol hydrogen is ionizable but only very weakly so. Alcohols can be oxidized but cannot generally be reduced.   A common reaction of alcohols is their reaction with carboxylic acids to form esters, which are discussed in later sections. Alcohols are used industrially as solvents, cleaning agents, and disinfectants.  Ethanol, often given the trivial name grain alcohol, is the alcohol found in alcoholic beverages; most other alcohols are highly toxic if ingested.

Alkanes Alcohols
Methane (CH4) Methanol (CH3OH)
Ethane (C2H6) Ethanol (C2H5OH)
Propane (C3H8) Propanol (C3H7OH)
Butane (C4H10) Butanol (C4H9OH)
Pentane (C5H12) Pentanol (C5H11OH)

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Ethanol (Ethyl Alcohol)

Methanol (Methyl alcohol):  Also known as wood alchohol it can be produced by the fermentation of wood products.  Methanol (CH3OH) has a strong flavour. Partially due to its small molecular weight and size it is easily absorbed by the body and is a dangerous poison.  Five to ten milliliters can cause damage to the optic nerves resulting in blindness.  It is known to damage other organs such as the liver, kidneys and heart.  The symptoms of a methanol poisoning are stomach cramps, headache, nausea, weakness, visual disturbances, breathing problems and unconsciousness.   Methanol is highly flammable.

Ethanol (Ethyl alcohol):  Ethanol is also referred to as grain alchohol and can be produced by the fermentation of sugar.  Because of its somewhat large molecular weight and size it is not absorbed by the body to the extent as is methanol.   However, it still effects the nervous system and other bodily function.  By means of fermentation ethanol (C2H5OH) and carbon dioxide (CO2) is produced.  The product has a relatively low alcohol content approximating 18%.   With distillation the concentration can approach 95%.  If a second distillation is conducted with the inclusion of a water extraction substance it is possible to achieve near 100% ethanol.  The boiling point of ethanol is 78.5o celsius.  Besides its use in alcoholic beverages it is also used as a solvent for oils, resins and many other industrial processes.

Molecules having two or more alcohol groups are called polyfunctional alcohols or polyols.  Polyols with two and only two alcohol groups are called diols although the older term glycols is still used.  Industrially, HOCH2CH2OH is called ethylene glycol rather than ethanediol. One of the most biologically important alcohols is 1,2,3-propanetriol, which is usually called glycerol or glycerin. Glycerol, HOCH2CH(OH)CH2OH, forms the storage fats for plant and animal cells. The chemistry of polyols is significant both industrially and biochemically.

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1, 2, 3-Propanitriol (Glycerol or Glycerin)

The ending -triol identifies a triple alcohol while the numbers indicate on which carbon atoms the OH groups are located. The formula for 1,2,3-propanitriol is C3H5(OH)3. This alcohol is producecd from the alkene known as propene.  Propene is an unsaturated hydrocarbon with the formula C3H6.  Due to the presence of the hydroxyl groups glycerin dissolves in water very well. Glycerin tastes sweet, has high viscosity and is water soluable.  High doses may lead to an intoxicated condition resulting in headache and kidney pain.  It is used in plastics, antifreeze, ointments, ink, brake fluid and coloring substances. Nitroglycerin is produced by the nitration glycerin. The correct name of nitroglycerin is glycerin trinitrate. It has the formula C3H5(NO3)3.

Phenol:  With the replacement of a hydrogen atom on a benzene molecule with a hydroxyl group (OH group) phenol is produced.  It has the chemical formula C6H5OH with a melting point of 43 degrees and a boiling point of 182 degrees.

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Phenol (Methyl-1,3,5-cyclohexatriene)

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Copyright 1997 James R. Fromm