Alcohols react with conc. H2SO4 to form different products under different conditions.
At 413 K, Ethers are formed : When alcohols are heated with conc. H2SO4 at 413 K, ethers (ROR') are formed.
At 433-443 K, Alkenes are formed : When alcohols are further heated at 433-443 K with conc. H2SO4, alkenes are formed.
The mechanism of formation of alkene by dehydration can be understood by using the example of ethanol (CH3CH2OH).
Different products are obtained when vapours of an alcohol are passed over heated alumina.
At 513-523 K : Ethers are formed
At 623 K : Alkenes are formed
In oxidation, the oxygen atom of an alcohol and the carbon atom attached to the oxygen lose a hydrogen atom each to form carbon-oxygen double bond.
Alcohols can be oxidised using the following reagents :
Primary alcohols are oxidised first to aldehydes and then to carboxylic acids
Note : The oxygen coming from oxidising agent can be represented as [O].
PCC (pyridinium chlorochromate) or Collin's reagents (CrO3.C5H5N, chromium trioxide pyridine) are used to obtain aldehydes.
Secondary alcohols are oxidised to carboxylic acid under drastic conditions containing fewer number of carbon atoms than the original alcohol.
Secondary alcohols can be converted to ketones easily using PCC or CrO3.
Acidified K2Cr2O7 or acidified KMnO4 react with tertiary alcohols to form a mixture of a ketone and a carboxylic acid each containing fewer number of carbon atoms than the original alcohols.
The vapours of alcohols react with heated copper at 573 K to form different products depending on whether the alcohol is primary, secondary or tertiary.
Reaction of primary alcohols with Cu : Primary alcohols undergo dehydrogenation to form aldehydes.
Reaction of secondary alcohols with Cu : Secondary alcohols undergo dehydrogenation to form ketones.
Reacton of tertiary alcohols with Cu : Tertiary alcohols undergo dehydrogenation to form alkenes.