Revision:Alcohols

TSR Wiki > Study Help > Subjects and Revision > Revision Notes > Chemistry > Alcohols

Alcohols are organic compounds with the -OH group on it. The general formula is C_nH_2n+1OH. Alcohols have the ending -ol, such as methanol, ethanol. There are 3 types of alcohols:

• Primary alcohols have 1 group attached to the carbon with the -OH group (Except for methanol) i.e. they have 2 hydrogens on the carbon next to the -OH group.
• Secondary alcohols have 2 groups attached to the carbon with the -OH group i.e. they have 1 hydrogen on the carbon next to the -OH group.
• Tertiary alcohols have 3 groups attached to the carbon with the -OH group i.e. they have no hydrogens on the carbon next to the -OH group.

Reactions

• Combustion:

The combustion of alcohols go as expected

• Reaction with sodium:

Alcohols react in a similar way to water with sodium

• Forming haloalkanes:

The -OH group can be replaced by a halide group with phosphorus trihalides - e.g. . The phosphorus bromide and iodide can be prepared by adding bromine/iodine to phosphorus. More commonly, however, phosphorus pentachloride is used to for the substitution of chloride into alcohols, as this produces white fumes of hydrogen chloride gas - a test for the -OH group:

• Oxidation:

Primary and secondary alcohols can be oxidised using acidified (Usually H₂SO₄) potassium dichromate (K₂Cr₂O₇). In each case, the dichromate ions are reduced to chromate(III) ions. [O] indicates an oxygen atom from an oxidising agent:

Primary alcohols are oxidised to aldehydes: . The aldehyde produced can then be oxidised further, or distilled off: .

Secondary alcohols are oxidised to ketones: