1. 13.4 Reactions of Alcohols and Thiols
CH3—CH2—OH(g) + 3O2(g)  2CO2(g) + 3H2O(g) + energy
A flaming dessert is prepared using heat from the combustion of an alcohol. Δ
Learning Goal Write equations for the combustion, dehydration, and oxidation of alcohols and thiols.

2. Dehydration of Alcohols
Alcohols undergo
the loss of — H and — OH from adjacent carbon atoms from the same alcohol, producing an alkene and a water molecule.
dehydration when heated with an acid catalyst:
H+, heat H2O
alcohol alkene
Core Chemistry Skill Writing Equations for the Dehydration
of Alcohols

3. Dehydration of Alcohols
The dehydration of a secondary alcohol can result in the formation of a minor product and a major product.
Saytzeff’s rule states that
the major product is the one that forms by removing the hydrogen from the carbon atom that has the smaller number of hydrogen atoms.
hydrogen atoms are easier to remove from the carbon atom adjacent to the carbon atom attached to the — OH group that has fewer hydrogen atoms.

4. Study Check
Draw the condensed structural formula for the major alkene produced by the dehydration of the following alcohol: OH
CH3—CH—CH2—CH2—CH3
H+, heat

5. Solution
Draw the condensed structural formula for the major alkene produced by the dehydration of the following alcohol: OH
CH3—CH—CH2—CH2—CH3
major product CH3—CH CH—CH2—CH3
H+, heat

6. Oxidation and Reduction
In organic chemistry,
oxidation reactions increase the number of carbon–oxygen bonds by the addition of oxygen or a loss of hydrogen atoms.
reduction reactions reduce the number of bonds between carbon and oxygen atoms.
Core Chemistry Skill Writing Equations for the Oxidation of Alcohols

7. Oxidation of 1° Alcohols
Alcohols undergo oxidation, increasing the number of carbon and oxygen bonds. To indicate the process of oxidation, [O] is placed over the reaction arrow.
Primary alcohols are oxidized to produce an aldehyde.
1 bond to O bonds to O
[O]
1° alcohol aldehyde

8. Oxidation of 1° Alcohols
Aldehydes can further oxidize to produce a carboxylic acid.
2 bond to O bonds to O
[O]
aldehyde carboxylic acid

9. Oxidation of 2° Alcohols
Secondary alcohols are oxidized to produce a ketone.
1 bond to O bonds to O
[O]
2° alcohol ketone

10. Oxidation of 3° Alcohols
Tertiary alcohols do not readily oxidize because there is no hydrogen atom on the carbon bonded to the — OH group.
[O] no product formed
no H to oxidize
3° alcohol

11. Chemistry Link to Health: Methanol Poisoning
Methanol is
also known as methyl alcohol.
highly toxic and found in windshield washer fluid, Sterno, and paint strippers.
rapidly absorbed and oxidized to formaldehyde and then formic acid.
[O] [O]
methyl alcohol formaldehyde formic acid

12. Oxidation of Thiols When thiols undergo oxidation,
an H atom is lost from each of two — SH groups.
the product is a disulfide.
Protein in hair is cross-linked by disulfide bonds found in the amino acid cysteine.
CH3—S—H + H—S—CH CH3—S—S—CH H2O
[O]

13. Chemistry Link to Health: Oxidation of Alcohol in the Body
Ethanol
acts as a depressant and kills or disables more people than does any other drug.
consumption can be analyzed by using a breathalyzer.
is metabolized by a social drinker at a rate of 12–15 mg/dL per hour.
is metabolized by an alcoholic at a rate of 30 mg/dL per hour.

14. Chemistry Link to Health: Oxidation of Alcohol in the Body
The acetaldehyde produced from ethanol in the liver is further oxidized to acetic acid, which is converted to carbon dioxide and water in the citric acid cycle.
Liver enzymes can eventually break down ethanol, but the aldehyde and carboxylic acid intermediates can cause considerable damage to liver cells.

15. Chemistry Link to Health: Oxidation of Alcohol in the Body

16. Study Check Select the product for the oxidation of [O] A. B.
C. CO2 + H2O D.

17. Solution Select the product for the oxidation of [O]
The correct answer is B.

18. Study Check
Select the product when CH3–CH2–CH2–OH undergoes each of the following reactions:
[O] [O] A.
B. CO2 + H2O D.

19. Solution
Select the product when CH3–CH2–CH2–OH undergoes each of the following reactions:
[O] [O]
1. C.
2. D.

20. Concept Map