Download REACTIONS OF ALCOHOLS

REACTIONS OF ALCOHOLS
& ETHERS
1.
Combustion (Extreme Oxidation)
alcohol + oxygen
carbon dioxide + water
2 CH3CH2OH + 6 O2
4 CO2 + 6 H2O
2.
3.
Elimination (Dehydration)
alcohol
H2SO4/100 °C
alkene + water
CH3CH2CH2OH
H2SO4/100 °C
CH3CH=CH2 + H2O
Condensation
excess alcohol
2 CH3CH2OH
H2 SO4/140 °C
H2 SO4/140 °C
ether + water
CH3CH2OCH2CH3 + H2O
4.
Substitution
alcohol + hydrogen halide
Lucas Reagent
ZnCl2
CH 3CH2OH + HCl
ZnCl2
alkyl halide + water
CH3CH 2Cl + H2O
• This reaction with the Lucas Reagent (ZnCl2) is a qualitative
test for the different types of alcohols because the rate of the
reaction differs greatly for a primary, secondary and tertiary
alcohol.
• The difference in rates is due to the solubility of the
resulting alkyl halides
• Tertiary Alcohol→ turns cloudy immediately (the alkyl
halide is not soluble in water and precipitates out)
• Secondary Alcohol → turns cloudy after 5 minutes
• Primary Alcohol → takes much longer than 5 minutes to
turn cloudy
5.
Oxidation
• Uses an oxidizing agent such as potassium
permanganate (KMnO4) or potassium dichromate
(K2Cr2O7).
• This reaction can also be used as a qualitative test
for the different types of alcohols because there is a
distinct colour change.
dichromate → chromium 3+
(orange) → (green)
permanganate → manganese (IV) oxide
(purple) → (brown)
Tertiary Alcohol
not oxidized under normal conditions
CH 3
KMnO4
H 3C
C
OH
NO REACTION
K2Cr2O7
CH 3
tertbutyl alcohol
Secondary Alcohol
ketone + hydrogen ions
H
O
KMnO4
H 3C
C
CH 3
H3C
OH
CH 3CH2CH 2OH
1-propanol
CH 3
propanone
2-propanol
Primary Alcohol
+ 2 H+
C
K2Cr2O7
aldehyde + water
KMnO4
K2Cr2O7
H
O
H
H
C
C
C
H
H
propanal
H
carboxylic acid + hydrogen ions
+ H 2O
KMnO4
K2 Cr2O 7
HO
O
H
H
C
C
C
H
H
propanoic acid
H
+ 2 H+
6.
Acid-Base Reactions
• Like water, alcohols can act as an acid or base,
depending on what it is reacting with.
• When they react as an acid, the alkyl oxide ion
(R-CH2O-) is formed.
ethanol + sodium
ethoxide ion + sodium ion + hydrogen
2 CH3CH2OH + 2 Na
2 CH3CH2O- + 2 Na+ + H2
• When they react as a base, the alkyl oxonium ion
(R-CH2OH2+) is formed
ethanol + sulfuric acid
CH3CH2OH + H2SO4
ethyloxonium ion + bisulfate ion
CH3CH2OH2+ + HSO4-
Preparation of Alcohols
1. Hydration of an Alkene
alkene + water
H2C CHCH3 + H2O
H2 SO 4 / 100°C
alcohol
H2 SO4 / 100°C
H
H
H
H
C
C
C
H
OH H
H
2. Oxidation of an Alkene
• This reaction uses an oxidizing agent like KMnO4 or
K2Cr2O7 to produce a “diol”.
alkene + water
H2C CHCH3 + H2O
KMnO4
K2Cr 2O7
"diol"
KMnO4
K2Cr 2O7
H
H
H
H
C
C
C
OH OH H
H
1.
2.
Reactions of Ethers
Ethers do not react with oxidizing or reducing
agents.
Combustion
ether + oxygen  carbon dioxide + water
CH3-O-CH3 + 3 O2  2 CO2 + 3 H2O
3.
Reaction with Concentrated
Binary Acids

ether + 2 binary acid
CH 3OCH 2CH3 + 2 HCl

2 alkyl halides + water
H3CCl + ClCH2CH3 + H2O
4. Reaction with Atmospheric Oxygen
•
This is a slow reaction in which highly unstable
peroxides are formed
ether + oxygen
CH 3OCH 2CH3 + O2
peroxide
H3COOCH2CH 3
HOMEWORK
• Pg 44 # 7-9
• Pg 48 # 12, 13 of Practice
• Pg 48 # 2-4, 6 of Section