1. Alcohols
IB Chemistry Topic 10.4

2. 10.4 Alcohols Asmt. Stmts
Describe, using equations, the complete combustion of alcohols.
Describe, using equations, the oxidation reactions of alcohols.
Determine the products formed by the oxidation of primary and secondary alcohols.

3. Properties of Alcohols
Alcohols have the general formula: CnH2n+1OH
The physical properties of alcohols are similar to those of both water and hydrocarbons
The shorter chain alcohols such as methanol and ethanol are similar to water, in general they
have higher boiling points than hydrocarbons but lower than water
dissolve in water to some degree
are more polar than hydrocarbons but less polar than water 7

4. Reactions of Alcohols
Alcohols undergo several types of reactions including:
Combustion
Oxidation
Esterification
Dehydration
Reactions with active metals
We will focus on the first 2 reactions… for now. 8

5. Describe, using equations, the complete combustion of alcohols.
10.4.1
Describe, using equations, the complete combustion of alcohols.

6. Reactions of Alkenes: The general mechanism
Alcohols burn in an excess supply of oxygen to form carbon dioxide and water in an exothermic reaction:
2CH3OH(l) + 3O2(g) → 2CO2(g) + 4H2O(l)
∆H = -726kJmol-1
2C5H11OH(l) + 15O2(g) → 10CO2(g) + 12H2O(l)
∆H = -3330kJmol-1

7. Describe, using equations, the oxidation reactions of alcohols.
10.4.2
Describe, using equations, the oxidation reactions of alcohols.

8. Oxidation
Alcohols are oxidized to alkanals (aldehydes) or alkanones (ketones) 9

9. Oxidizing Agents
The most common oxidizing agents are KMnO4 in basic solution, K2Cr2O7 in acidic solution, or oxygen from the air.
[O] over the yields arrow indicates an oxidizing agent
The most commonly used for organic reactions is acidified potassium dichromate (VI)
H+/Cr2O7 is bright orange
When heated, it oxidizes the alcohol and changes color, as Cr+7 is reduced to Cr+3
The reduced form of chromium is green
Figure 10.55

10. Primary Alcohols are Oxidized to Alkanals
Primary alcohols are oxidized to become carboxylic acids in a two-step process.
Step 1: alcohol → aldehyde
Ex. Ethanol is oxidized to become ethanal 10

11. Primary Alcohols are Oxidized to Alkanals
Primary alcohols are oxidized to become carboxylic acids in a two-step process.
Step 2: aldehyde → carboxylic acid
Ex. Ethanal is further reduced to become ethanoic acid 10

12. Mechanism of the Oxidation of Primary Alcohols

13. Oxidation of Primary Alcohols
Experimental conditions may be altered to yield the desired product…
Aldehydes can be removed by distilling it as it forms (due to its lower boiling point)
If the carboxylic acid is the desired product, then the aldehyde should be exposed to [O] for a long period of time and heated under reflux
See Fig

14. Secondary Alcohols are oxidized to Alkanones11

15. Secondary Alcohols are oxidized to Alkanones
Since secondary alcohols only have one hydrogen attached to the carbon atom, the only possible product is a ketone 11

16. Oxidation of Secondary Alcohols
Propan-2-ol will oxidize into propanone

17. Tertiary Alcohols are not easily oxidized12

18. 10.4.3
Determine the products formed by the oxidation of primary and secondary alcohols.

19. Testing Solutions
2,4-dinitrophenylhydrazine solution tests for the presence of aldehydes and ketones by forming orange crystals
To differentiate between the two classes:
Fehling’s solution starts blue and will turn orange-brown in the presence of aldehydes. It will remain blue for ketones.
Tollens’ reagent produces a silver mirror effect on the inside of the test tube in the presence of aldehydes, but will remain clear for ketones.
See Fig

20. Testing Solutions Fehling’s Solution Tollen’s Reagent
Aldehyde is produces the “silver mirror”
Ketone is clear (unreacted)
Fehling’s Solution
Aldehyde is orange
Ketone is blue (unreacted)