3.2.9 oxidation of functional groups in organic compounds

chem whatarethemechanismsofchemicalchange

Reactivity 3.2.9 - functional groups in organic compounds may undergo oxidation

oxidation of alcohols

• combustion (breaks carbon chain)

• selective oxidation of the carbon atom attached to the group (keeps chain intact)

• commonly, acidified potassium dichromate(VI) is used.

• the oxidising agent is sometimes shown as

the degree of oxidation can be related to the number of atoms attached to the carbon with the hydroxyl group.

primary alcohols

• 2 atoms attached to carbon with hydroxyl group
• can be oxidised in a two-step reaction

CCO>>CC=O

CC=O>>CC(=O)O

it is possible to remove the aldehyde product by distillation. aldehydes do not have hydrogen bonding, unlike the alcohol or the acid.

the reaction mixture is heated under reflux, meaning the aldehyde condenses back into the reaction mixture when it evaporates.

• electric heating mantle
• vapour condenses back into the reaction vessel

secondary alcohols

• one atom attached to the carbon with the hydroxyl group
• oxidised to ketones

CC(O)C>>CC(=O)C.[H]O[H]

tertiary alcohols

• no atoms attached to carbon bonded to hydroxyl group
• not readily oxidised without breaking the carbon chain

challenge questions

9. use oxidation numbers to show the differences in the extent of oxidation in the complete combustion of propane, , and propene,

propane:

propene:

combustion of propane involves a bigger change of oxidation state and more oxygen is needed

10. deduce the half-equations of oxidation and reduction for oxidation of ethanol to produce ethanal with acidified potassium dichromate(VI) and state the overall reaction

oxidation:

reduction:

overall: