Transcript Reactions of alcohols File

Alcohols – nomenclature and reactions
L.O. To be able to name alcohols and assign primary,
secondary and tertiary status.
To know some specific reactions of alcohols
OH
OH
C
C
H
H
C
C
H
C
OH
C
C
C
C
TYPES OF ALCOHOL
PRIMARY
ALCOHOLS
SECONDARY
ALCOHOLS
TERTIARY
ALCOHOLS


OH
OH

OH
C
C
H
H
OH at end of
a chain
C
C
C
H
C
C
C
C
OH at middle
of a chain
OH at junction
of 2 chains
CH3CH2CH2CH2OH
CH3CH2CH(OH)CH3
CH3C(CH3)(OH)CH3
Butan-1-ol
Butan-2-ol
Methyl propan-2-ol
ISOMERS OF PENTANOL
SELECT PRIMARY (P), SECONDARY (S)
OR TERTIARY (T)
Make sure you can draw full
displayed, structural and skeletal
representations of each.
CH3CH2CH2CH2CH2OH
Pentan-1-ol
P
S
T
CH3CH2CH2CH(OH)CH3
Pentan-2-ol
P
S
T
CH3CH2C(CH3)(OH)CH3
2-Methylbutan-2-ol
P
S
T
CH3CH2CH(OH)CH2CH3
Pentan-3-ol
P
S
T
CH3C(CH3)2CH2OH
2,2-Dimethylpropan-1-ol
P
S
T
CH3CH(OH)CH(CH3)CH3 3-Methylbutan-2-ol
P
S
T
CH3CH(CH3)CH2CH2OH
3-Methylbutan-1-ol
P
S
T
CH3CH2CH(CH3)CH2OH
2-Methylbutan-1-ol
P
S
T
Dehydration (removal of water) of alcohols
H
OH
C
C
ALKENES
Removal (elimination)
of water by :
1.Heating with concentrated
sulphuric acid at 170C
or 2. Passing vapour over
Al2O3 at 350C
C
C
+ HOH
NB
Used to make ETHENE in countries where
carbohydrate plentiful for fermentation but
petroleum oil not avialable for cracking
H may be removed from more than one C
adjacent to C-OH  mixture of alkenes
Deduce the dehydration products of : 1. Ethanol?
2. Methyl-propan-2-ol?
3. Butan-2-ol ?
1.
H
H
OH
C
C
H
H
H
2.
H H
H
C
H
OH
C
C
H
CH3
CH3 H
CH3
C
H
+ HOH
H
H
C
3.
OH H
H
C
C
C
C
H
H
H
H
H
C
H
CH2CH3
C
CH3
H
H
C
+ HOH
H
H
CH3
+ HOH
and
H E & Z!
C
H
C
CH3
Reaction of an alcohol (R-OH) with sodium metal
 an alkoxide (R-O- Na+) + hydrogen gas (H2)
C-OH + Na
C-O- Na+ + ½ H2
Notes :
1. The bonding is ionic between O and Na
2. The reaction is parallel (but slower) to the
reaction of sodium with the OH group in water
HOH + Na
Na+OH- + ½ H2
Note : These are all redox reactions
because the Na is oxidised (electron loss)
and the H of OH is reduced (electron gain)
PRIMARY
ALCOHOLS
SECONDARY
ALCOHOLS
OH
C
C
H
H
TERTIARY
ALCOHOLS
OH
C
C
C
H
OH
C
C
C
Rate decrease
For isomeric alcohols:
the rate of reaction with sodium decreases
from primary to secondary to tertiary
C
Products of sodium with :
2. Methyl-propan-2-ol?
3. Butan-2-ol ?
1.
H
H
OH
C
C
H
H
2.
H
H
H
O- Na+
C
C
H
H
H
Sodium ethoxide
+ ½H2
H
OH
C
C
H
CH3
3.
CH3
H
H
OH H
H
C
C
C
C
H
H
H
H
+ Na
+ Na
H
1. Ethanol?
H
+ Na
H
O- Na+
C
C
H
CH3
CH3
Sodium (methylprop-2oxide)
+ ½H2
H
H
H
O-Na+ H
H
C
C
C
C
H
H
H
H
Sodium but-2-oxide
+ ½H2
H
Try some more examples for yourself!
Write an equation, giving the full structure and name of the
main organic product, for the reactions between :
1. Methanol + Na
2. Propan-1-ol + Na
3. Propan-2-ol + Na
4. Butan-1-ol + Na
5. Methyl-propan-1-ol + Na
Substitution of an alcohol by HBr  a bromoalkane
δ+
δ-
C-OH + HBr
C-Br + H2O
HBr produced by reacting KBr with conc. H2SO4.
KBr + H2SO4  KHSO4 + HBr
In practice, the alcohol is mixed with KBr in a reflux
apparatus.
The acid is then added to the mixture, drop wise.
Note : This is a nucleophilic substitution because
the δ+C is attacked by the δ-Br
HBr substitution products of :1. Ethanol?
2. Methyl-propan-2-ol?
3. Butan-2-ol ?
1.
H
H
OH
C
C
H
H
2.
H
H
H
Br
C
C
H
H
Bromoethane
+ H2O
OH
C
C
H
CH3
CH3
H
H
OH H
H
C
C
C
C
H
H
H
H
+ HBr
+ HBr
H
H
3.
H
H
H
Br
C
C
H
CH3
+ HBr
CH3
Methyl-2-bromopropane
+ H2O
H
H
H
Br
H
H
C
C
C
C
H
H
H
H
2-Bromobutane
+ H2O
H
Reaction of alcohols with phosphorus pentachloride (PCl5)
R-OH (l) + PCl5 (s)
C-Cl (l) +HCl (g) + POCl3 (l)
Fumes of HCl being given off makes this a useful
reaction to identify the presence of an alcohol
functional group.
Try some more examples for yourself!
Give the full structure and name of the
main organic product produced by :
1. Methanol + HBr
2. Propan-1-ol + HBr
3. Propan-2-ol + HCl
4. Butan-1-ol + HBr
5. Methyl-propan-1-ol + HCl
AS Chemistry
OXIDATION OF ALCOHOLS
OXIDATION OF ALCOHOLS
Oxidised to aldehydes and acids
or ketones
NOT
for PRIMARY
SIGNIFICAN
for SECONDARY
alcohols
T for
alcohols
TERTIARY
-CH2OH
-C-CH(OH)-Calcohols!
NB Oxidant = hot acidified Cr2O72- [dichromate(VI)] ion]
Provided by mixture of potassium dichromate(VI), K2Cr2O7,
and excess dilute sulphuric acid, H2SO4.
Oxidant is represented by : [O]
OBSERVATION: Orange Cr2O72- reduced to green Cr3+
SECONDARY
PRIMARY
C
H
C
C
C
C
H
OH
 + [O]
H
C
+ H2O
Aldehyde
O
 + [O]
OH
C
Acid
C
H
C
OH
 + [O]
C
TERTIARY
C
O
C
C
C
C
C
OH
 + [O]
NO SIGNIFICANT
OXIDATION
+ H2O
Ketone O
 + [O]
NO FURTHER
OXIDATION
- no C – H bond
- no C–H bond
Any oxidation
that does
occur involves
breaking C-C
bonds  loss
of original
structure.
What are the oxidation products of :
1. Ethanol?
2. Methyl-propan-2-ol? 3.Butan-2-ol?
CH3CH2OH
CH3C(CH3)(OH)CH3
Primary
Tertiary
CH3CH2CH(OH)CH3
Secondary
Controlling Oxidation Products
To Maximise the
Production of an
ALDEHYDE
To Maximise the
Production of an ACID or
a KETONE
This is PARTIAL oxidation
This is FURTHER oxidation
Use only molar proportions of
dichromate and acid
Use excess of dichromate
and acid
Use minimum contact time
between alcohol and oxidant
by use of immediate distillation
Use maximum contact time
between alcohol and oxidant by
use of reflux
Add acidified dichromate to
the alcohol to avoid the
presence of excess oxidant
Pre-mix acidified dichromate
and alcohol to ensure excess
oxidant at all times
1. Reflux with conc.
NaOH in ethanol
Alkene(s)
C=C
2. + HBr
1 Eliminations
Halogenoalkane
C-Br
3. Reflux
with aq.
NaOH
3. Heat with excess
conc. NH3 in
ethanol
Primary
amine
C-NH2
3. Heat with
NaBr + conc.
H2SO4
Electrophilic
2 addition
Nucleophilic
3 substitutions
Alcohol
C-OH
5. Heat with carboxylic
acid (-COOH) + conc.
H2SO4 cat.
Ester
CO.OC
4 Oxidations
5 Condensations
Ketone
C-CO-C
(if alcohol
SECONDARY)
4. Heat with molar
propns. of K2Cr2O7
+ dil. H2SO4 ; distil
Aldehyde
CHO
(if alcohol
PRIMARY)
5. Heat with
alcohol (C-OH)
+ conc. H2SO4
catalyst
4. Reflux with
excess K2Cr2O7
+ dil. H2SO4
Acid
COOH