3.9.3

Oxidation of Alcohols - 2

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Primary Alcohol Oxidation Products

Looking further into the oxidation of primary alcohols, we shall determine how to produce an aldehyde or a carboxylic acid.

Oxidation of primary alcohols

Oxidation of primary alcohols

  • As we have seen before, there are two possible oxidations of primary alcohols:
    • One produces an aldehyde.
    • The other produces a carboxylic acid.
Producing an aldehyde

Producing an aldehyde

  • To make an aldehyde, you carry out the reaction under distillation.
    • This condenses any reacted aldehyde, which forms as a gas, into a new flask.
Producing a carboxylic acid

Producing a carboxylic acid

  • To make a carboxylic acid, you carry out the reaction under reflux.
    • This involves use of a reflux condenser.
    • The reflux condenser condenses any gases and forces them back into the reaction vessel.
    • This puts the aldehyde back in the flask to be oxidised again.

Testing Oxidation Products

We can determine whether a chemical is either an aldehyde or a ketone through two possible tests.

Aldehydes and ketones

Aldehydes and ketones

  • Aldehydes and ketones have very similar functional groups and so are hard to tell apart.
    • The one feature they have that is different is their oxidising ability.
    • So we can use oxidising agents to identify which is present.
Oxidising ability

Oxidising ability

  • Aldehydes can be oxidised further to carboxylic acids.
    • This is because it still has a C-H bond that can be broken for oxidation.
  • Ketones cannot be further oxidised.
    • You would have to break a C-C bond.
Fehling's solution

Fehling's solution

  • Our first test is Fehling’s solution.
    • It contains Cu2+ and is deep blue.
  • When you add an aldehyde, the Cu2+ oxidises the aldehyde and is reduced to Cu+.
    • This causes a colour change from deep blue to brick red.
    • With a ketone, you get no colour change because it can’t be oxidised.
Tollen's reagent

Tollen's reagent

  • Tollen’s reagent contains the diammine silver 1+ ion: [Ag(NH3)2]+.
    • This is a clear solution.
  • This reagent also oxidises an aldehyde but will do nothing to a ketone.
    • When it oxidises an aldehyde, it is reduced to solid silver and is said to form a ‘silver mirror’ on the surface of the test tube.
Overall test results

Overall test results

  • Fehling's solution:
    • Aldehyde: Deep blue → brick red.
    • Ketone: Remains deep blue.
  • Tollen's reagent:
    • Aldehyde: Clear → silver mirror.
    • Ketone: Remains clear.
Jump to other topics
1

Structure - Models of the Particulate of Matter

2

Structure - Models of Bonding & Structure

3

Structure - Classification of Matter

3.1

The Periodic Table: Classification of Elements

3.2

Periodic Trends

3.3

Group 1 Alkali Metals

3.4

Halogens

3.5

Noble gases, group 18

3.6

Functional Groups: Classification of Organic

3.7

Functional Group Chemistry

3.8

Alkanes

3.9

Alcohols

3.10

Halogenoalkanes

4

Reactivity - What Drives Chemical Reaction?

5

Reactivity - How Much, How Fast & How Far?

6

Reactivity - The Mechanisms of Chemical Change

7

Measurement, Data Processing & Analysis

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