Saturday, July 2, 2011

Alcohols

Origin of the word alcohol:
Of those, ethanol (C2H5OH) is the type of alcohol found in alcoholic beverages, and in common speech the word alcohol refers specifically to ethanol.The word alcohol appears in English in the 16th century,  loaned via French from medical Latin, ultimately from the Arabic الكحل (al-kuḥl, "the kohl, a powder used as an eyeliner").The current Arabic name for alcohol is الكحول al-kuḥūl,  re-introduced from western usage.

The general formula of alcohol  is CnH2n+1OH. An alcohol is any organic compound in which a hydroxyl functional group  (-OH) is bound to a carbon atom, usually connected to other carbon or hydrogen atoms.
The suffix -ol appears in the IUPAC chemical name of all substances where the hydroxyl group is the functional group with the highest priority.




Common Alcohols :
The most commonly used alcohol is ethanol, C2H5OH. Ethanol has been produced and consumed by humans for millennia, in the form of fermented and distilled alcoholic beverages. It is a clear flammable liquid that boils at 78.4 °C, which is used as an industrial solvent, car fuel, and raw material in the chemical industry. Ethanol in this form is known generally as denatured alcohol; when methanol is used, it may be referred to as methylated spirits or "surgical spirits".
The simplest alcohol is methanol, CH3OH, which was formerly obtained by the distillation of wood and, therefore, is called "wood alcohol". It is a clear liquid resembling ethanol in smell and properties, with a slightly lower boiling point (64.7 °C), and is used mainly as a solvent, fuel, and raw material. Unlike ethanol, methanol is extremely toxic: One sip (as little as 10 ml) can cause permanent blindness by destruction of the optic nerve and 30 ml (one fluid ounce) is potentially fatal.Two other alcohols whose uses are relatively widespread (though not so much as those of methanol and ethanol) are propanol and butanol. Like ethanol, they can be produced by fermentation processes.



Etymology:

Because of hydrogen bonding, alcohols tend to have higher boiling points than comparable hydrocarbons and ethers. The boiling point of the alcohol ethanol is 78.29 °C, compared to 69 °C for the hydrocarbon Hexane (a common constituent of gasoline), and 34.6 °C for Diethyl ether.
Alcohols, like water, can show either acidic or basic properties at the O-H group. With a
pKa of around 16-19, they are, in general, slightly weaker acids than water, but they are still able to react with strong bases such as sodium hydride or reactive metals such as sodium. The salts that result are called alkoxides, with the general formula RO- M+.
Meanwhile, the oxygen atom has
lone pairs of nonbonded electrons that render it weakly basic in the presence of strong acids such as sulfuric acid. Mild oxidation in the presence of oxygen gives the products below : 

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