Alcohols - Organic Chemistry
The Alcohols have the general formula CnH2n +1 OH
The Properties of Ethanol
It is a good solvent. Many substances that do not dissolve in water dissolve in ethanol.
The boiling temperature is 78 degrees Celsius
Uses of Ethanol
Ethanol is used to make many substances a few of these being: polish, inks, dyes, a wide range of pharmaceuticals and alcohols.
Ethanol is used in alcoholic drinks and
this ethanol is obtained by anaerobic fermentation of carbohydrates e.g. fruits
CARBOHYDRATES → ETHANOL + CARBON DIOXIDE
(Enzymes supplied by yeast)
Reactions of Alcohols
The functional group of Alcohols is the –OH group.
The reactions of Alcohols are based on this group.
Some alcohols react with the very reactive metals
Metals high in the electrochemical series e.g. Na. Li, Mg, Ca react with the alcohols lower in the alcohol series (methanol, ethanol, and propanol).
2Na(S) + 2CH3CH2OH (g) → 2 CH3CH2ONa(s) + H2 (g)
Alcohols undergo oxidation with powerful oxidizing agents such as acidified potassium dichromate and acidified potassium manganate (vii).
They convert alcohols to organic acids.
In these reactions an intermediate aldehyde is formed.
Rxn: CH3CH2OH + KMnO4/H+ → H2O + CH3CHO (ethanal )
CH3CHO + KMnO4/H+ → CH3COOH ethanoic acid
The reaction mixture changes colour from purple to colourless.
With potassium dichromate (VI) the colour change is from orange to green.
The Breathalyser Test
This test is based on the fact that high levels of ethanol vapour in the breath reduce acidified K2Cr2O7 (potassium dichromate) crystals from orange to green
Dehydration to Alkenes
CH3CH2OH → CH2 = CH2
Conditions for dehydration
Ethanol is heated with excess H2SO4 (conc.) at 170 degrees Celsius or passing ethanol vapour over activated alumina (Al2O3) heated to 450 degrees Celsius
Conversion of Alcohols to esters
Organic acid + Alcohol → Ester + Water
Combustion of Alcohol
The combustion is highly exothermic and they are combusted with O2
e.g. CH3CH2OH + 3O2 → 2CO2 + 3H2O + heat
Citation: Lambert and Mohammed (1993), Chemistry for CXC Halley court, Jordon Hill Oxford.