Why are tertiary alcohols not easily oxidised?

They have no hydrogen atom on the carbon bonded to the OH group.

Which oxidising agent is used, and what is its colour change?

Acidified potassium dichromate(VI): orange to green (Cr₂O₇²⁻ to Cr³⁺).

Write the equation for ethanol to ethanal using [O].

CH₃CH₂OH + [O] → CH₃CHO + H₂O

How do you obtain an aldehyde from a primary alcohol?

Heat with the oxidising agent and distil the aldehyde off as it forms.

Why does the aldehyde distil off first?

It has no hydrogen bonding, so its boiling point is lower than the alcohol's.

How do you obtain a carboxylic acid from a primary alcohol?

Heat under reflux with excess acidified dichromate(VI).

What is observed when Tollens' reagent is warmed with an aldehyde?

A silver mirror forms; a ketone gives no change.

What is observed when Fehling's solution is warmed with an aldehyde?

The blue solution gives a red precipitate; a ketone stays blue.

Oxidation of alcoholsAQA A-Level Chemistry: Flashcards

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How is an alcohol classified as primary, secondary or tertiary?

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How is an alcohol classified as primary, secondary or tertiary?: By the number of carbon atoms attached to the carbon that carries the OH group: one, two or three.
What is the product of limited oxidation of a primary alcohol?: An aldehyde.
What is the product of further oxidation of an aldehyde?: A carboxylic acid.
What is the product of oxidising a secondary alcohol?: A ketone.
Why are tertiary alcohols not easily oxidised?: They have no hydrogen atom on the carbon bonded to the OH group.
Which oxidising agent is used, and what is its colour change?: Acidified potassium dichromate(VI): orange to green (Cr₂O₇²⁻ to Cr³⁺).
Write the equation for ethanol to ethanal using [O].: CH₃CH₂OH + [O] → CH₃CHO + H₂O
How do you obtain an aldehyde from a primary alcohol?: Heat with the oxidising agent and distil the aldehyde off as it forms.
Why does the aldehyde distil off first?: It has no hydrogen bonding, so its boiling point is lower than the alcohol's.
How do you obtain a carboxylic acid from a primary alcohol?: Heat under reflux with excess acidified dichromate(VI).
What is observed when Tollens' reagent is warmed with an aldehyde?: A silver mirror forms; a ketone gives no change.
What is observed when Fehling's solution is warmed with an aldehyde?: The blue solution gives a red precipitate; a ketone stays blue.

Exam questions on Oxidation of alcohols

A school technician is given three unlabelled liquids, each with the molecular formula C₄H₁₀O: butan-1-ol, butan-2-ol and 2-methylpropan-2-ol. She warms a sample of each with acidified potassium dichromate(VI) solution.
State the colour of the mixture after warming for butan-2-ol and for 2-methylpropan-2-ol, and explain each result.2 marks
Propan-1-ol can be converted into either propanal or propanoic acid using acidified potassium dichromate(VI), depending on how the apparatus is set up. In one experiment the alcohol is heated in a flask fitted with a distillation head and the product is collected as it forms. In a second experiment the mixture is heated under reflux with excess oxidising agent for a long time.
Write two equations, using [O] to represent the oxidising agent, for the oxidation of propan-1-ol to propanal and then propanal to propanoic acid.2 marks
A forensic chemist has two colourless liquids, pentanal and pentan-2-one, which both have the molecular formula C₅H₁₀O. She tests a sample of each with warm Fehling's solution and with warm Tollens' reagent.
Describe the observations the chemist would make when each liquid is tested with Fehling's solution and with Tollens' reagent.3 marks

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Written by the Exaim team, led by Shaun Daswani (Head of Upper Secondary, Improve ME Institute; MSc Financial Mathematics, Imperial College London; BSc, UCL) and Jason Daswani (operational lead, Improve ME Institute; LSE).