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Chemistry Notes
Organic Chemistry: Alcohols
The homologous series alcohols have the general formula CnH2n+1OH.
Alcohols can be represented as R-OH, since the OH group is the functional group that takes part in reactions.
R, represents the rest of the molecule which is unaffected. The work alcohol is used to refer to ethanol (beers,
liquor, etc).
 Manufacture of Ethanol
There are 2 processes for commercially manufacturing ethanol:
Hydration of ethaneWater is added to ethane by passing a mixture of steam and ethane over a phosphoric acid in silica gel catalyst
at 300°C, 60 atm.
Fermentation of carbohydratesFermentation is the partial breakdown of glucose by anaerobic respiration. It is done in controlled conditions
using a carbohydrate (starch or sugar) and the unicellular fungi, yeast. The yeast provides enzymes (amylase
and maltase) that hydrolyse complex carbohydrates into simple fermentable sugars (glucose and fructose).
Ethanol is toxic to yeast, so about 12% ethanol the yeast dies and the reaction stops. To produce a greater
concentration of ethanol, the mixture is fractionally distilled.

Physical Properties of Alcohols
Alcohol molecules are covalent by nature. However, they contain the strongly polar O-H bond.
Alcohol structure consists of alcohol molecules held together by a combination of weak Van-der-Waals forces
and stronger hydrogen bonds. This has significant effects on the physical properties of alcohols. Boiling points,
viscosity and density of these substances are higher than expected. State is also affected, as C1 – C12 are all
liquids and the rest are solids.
As molecules get larger, the effect of the OH group becomes less significant. It is important to know that the
solubility of alcohols is also affected by the presence of the OH group.

Reaction of Alcohols
Reactions are based on the presence of the functional group –OH.
Combustion
Alcohols burn with a clean, blue flame in air or oxygen to produce carbon dioxide and water.
Reaction with reactive metals
Alcohols react with highly reactive metals (Na, K, Li, Mg and Ca) to give a salt and hydrogen gas.
Dehydration
Alcohols can be dehydrated in two ways:
1) Heating to about 170°C with concentrated sulphuric acid.
2) Passing ethanol vapour over aluminium oxide heated to 450°C.
Oxidation
Powerful oxidizing agents such as acidified potassium manganate (VII) and acidified potassium chromate (VI)
can oxidize alcohols to organic acids. The reaction is accompanied by the characteristic colour change of the
oxidizing agent.
Esterification
Alcohols react with organic acids to produce sweet-smelling liquids called esters. We will discuss more on a
later date.