Alcohols
Learning Objectives
Candidates should be able to:
•recall the chemistry of alcohols, as exemplified by
ethanol, including their oxidation to carbonyl
compounds and carboxylic acids.
•classify hydroxy compounds
secondary and tertiary alcohols.
into
primary,
•suggest characteristic distinguishing reactions,
e.g. mild oxidation.
Starter activity
Complete task 1 on your worksheet.
Production of alcohol
Method
Rate of
Reaction
Quality of
product
Raw
Type of
material process
Finite
resource?
hydration
fast
Almost
100%
ethene
continuous Yes
fermentation
slow
~15%
natural
sugars
batch
No
Classes of alcohols
Oxidation of alcohols
+ [O]
CH3CH2OH
CH3C
O
+
H2O
H
CH3 C
O
O
+
[O]
H
CH3 C
OH
OH
CH 3CHCH 3
Primary
alcohols
O
+
[O]
CH3 CCH 3
+
H2 O
Secondary
alcohols
Oxidation of alcohols
Primary alcohol  aldehyde  carboxylic acid
e.g. ethanol
ethanal
ethanoic acid
Secondary alcohol  ketone  no reaction
e.g. propan-2-ol
propanone
Tertiary alcohol  no reaction
Oxidising agent
Cr2O72-  Cr3+
Orange  Green
Heating under reflux
Prevents evaporation
of aldehyde
Physical properties
and general
chemistry
Learning Objectives
Candidates should be able to:
recall the chemistry of alcohols, exemplified
by ethanol:
•combustion
•substitution to give halogenoalkanes
•reaction with sodium
•dehydration to alkenes
Starter activity
Complete task 1 on your worksheet.
Physical properties – boiling point
Alcohol
Mr
ethanol
propan-1-ol
butan-1-ol
propane
butane
pentane
46
60
74
44
58
72
Boiling point
(K)
352
371
390
231
273
309
Physical properties – boiling point
•The boiling point of an alcohol is always much
higher than that of an alkane with similar Mr.
•This is due to hydrogen bonding between the
alcohol molecules.
• In alkanes the only
intermolecular forces
are vdW.
Physical properties – solubility
The small alcohols are
completely soluble in water.
Physical properties – solubility
In both pure water and pure ethanol the main
intermolecular forces are hydrogen bonds. In order to
mix them together you must supply energy to break
these bonds.
Physical properties – solubility
Fortunately, alcohols
can form hydrogen
bonds with water:
H – OH
R - OH
Physical properties – solubility
This bond-making process
releases energy which
more or less compensates
for the energy input.
N.B. an alcohol only has
one + H atom, unlike
water which has 2.
Physical properties – solubility
The hydrocarbon chains in an
alcohol cannot form hydrogen
bonds.
As the chains get longer they
force their way between
water molecules preventing
them from hydrogen bonding.
Too little energy is released
from
bond-making
to
compensate for that used in
bond-breaking.
Physical properties – boiling point
•The boiling point of an alcohol is always much
higher than that of an alkane with similar Mr.
•This is due to hydrogen bonding between the
alcohol molecules.
• In alkanes the only
intermolecular forces
are vdW.
General chemistry – combustion
Ethanol can be used as a fuel, mainly as a biofuel
alternative to gasoline. Because it is easy to
manufacture and process and can be made from
renewable resources such as sugar cane and corn, it is
an increasingly common alternative to gasoline in
some parts of the world, e.g. Brazil.
Anhydrous ethanol (ethanol with less than 1% water)
can be blended with gasoline in varying quantities and
most gasoline engines will operate well with mixtures
of 10% ethanol (E10).
General Chemistry - electron density map
Ethanol – CH3CH2OH
Chemistry can involve
breaking the C-O bond
and the O-H bond.
General chemistry – reaction with
Sodium
2Na + 2HO-H  2NaOH + H2
2Na + 2RO-H  2NaOR + H2
NaOR is more usually written as RONa or RO- Na+
2Na + 2CH3CH2OH  2CH3CH2O-Na+ + H2
sodium
ethanol
sodium ethoxide
hydrogen
General chemistry – substitution to
form halogenoalkanes
Consider the reaction below:
CH3CH2Br + OH-  CH3CH2OH + Br-
You should remember that this hydrolysis reaction
occurs quite readily in a warm, aqueous solution.
The reverse reaction is more difficult, -OH is not a
good leaving group. Presence of H+ required to form
water, a much better leaving group.
General equation
The general reaction looks like this:
ROH + HX  RX + H2O
Replacing –OH by bromine
Rather than using hydrobromic acid, you usually treat
the alcohol with a mixture of sodium or potassium
bromide and concentrated sulphuric acid.
This produces hydrogen bromide in situ which reacts
with the alcohol. The mixture is warmed to distil off
the bromoalkane (see page 338 of your textbook).
Replacing –OH by iodine
Iodoalkanes can be made by two different methods.
In the first method the alcohol is reacted with a
mixture of sodium or potassium iodide and concentrated
phosphoric(V) acid, H3PO4, and the iodoalkane is distilled
off.
Replacing –OH by iodine
In the second method the iodoalkane can be made by
warming the alcohol with a mixture of red phosphorus
and iodine:
This then reacts with the alcohol to give the corresponding
halogenoalkane which can be distilled off.
Replacing –OH by chlorine
Chloroalkanes are more easily made by the second route:
you can react an alcohol with phosphorus(III) chloride,
PCl3, phosphorus(V) chloride, PCl5, or sulphur dichloride
oxide (thionyl chloride, SOCl2).
CH3CH2OH + PCl5  CH3CH2Cl + HCl + POCl3
CH3CH2OH + SOCl2  CH3CH2Cl + HCl + SO2
Elimination
(when a small molecule is removed from
a larger molecule – converts a single bond to a double
bond)
C2H5OH(g)  CH2=CH2(g)
+ H2O(g)
Aldehydes and
Ketones
Learning Objectives
Candidates should be able to:
•describe the reduction of aldehydes and ketones e.g. using
NaBH4.
•describe the mechanism of the nucleophilic addition
reactions of hydrogen cyanide with aldehydes and ketones.
•describe the use of 2,4-dinitrophenylhydrazine (2,4-DNPH)
to detect the presence of carbonyl compounds.
•deduce the nature (aldehyde or ketone) of an unknown
carbonyl compound from the result of simple tests (i.e.
Fehling’s or Tollens’ reagents; ease of oxidation).
•describe the formation of carboxylic acids from nitriles.
Starter activity
Can you write balanced equations for the synthesis of
chloro-, bromo- and iodoethane from ethanol?
Give the names of the reagents and the reaction
conditions.
Aldehyde or Ketone
Using Tollens' reagent (the silver mirror test)
Tollens' reagent contains the diamminesilver(I) ion, [Ag(NH3)2]+.
To carry out the test, you add a few drops of the aldehyde or ketone to the
freshly prepared reagent, and warm gently in a hot water bath for a few
minutes.
ketone
No change in the colourless
solution.
aldehyde
The
colourless
solution
produces a grey precipitate
of silver, or a silver mirror
on the test tube.
Tollen’s reagent
Aldehyde or Ketone
Using Fehling's solution
A few drops of the aldehyde or ketone are added to the reagent, and the
mixture is warmed gently in a hot water bath for a few minutes.
ketone
No change
solution.
in
the
blue
aldehyde
The blue solution produces
a dark red precipitate of
copper(I) oxide.
Fehling’s reagent
Reduction of aldehydes and ketones
– H2
O
OH
CH 3CH 2CCH 3 + H2
butanone
CH3 CH2 CHCH 3

butan-2-ol
O
CH2=CHC
CH3CH 2CH 2OH
+ 2H2
H
prop-2-enal

propan-1-ol
Reduction of aldehydes and ketones
– NaBH4
ethanal
ethanol
propanone
propan-2-ol
Reduction of aldehydes and ketones
– NaBH4
O
+
CH2=CHC
2
H
CH2=CHCH2OH
H
prop-2-enal
prop-2-en-1-ol
Formation of hydroxy nitriles (or
cyanohydrins)
Reactions of nitriles
Hydrolysis
CH3C
N
+ 2H2 O
CH3COOH
+ NH3
Reduction
CH3C
N
+
4 H
CH3CH2NH2
Aldehyde or ketone?
2,4-DNPH
Test: Add a solution of 2,4-dinitrophenylhydrazine (2,4-DNPH).
Result: a deep yellow or orange precipitate
Carboxylic acids
Learning Objectives
Candidates should be able to:
•describe the reactions of carboxylic acids in the
formation of salts.
Starter activity – can you complete
task 1?
methanoic acid
2-methylbutanoic acid
hexanedioic acid
Acidity of the carboxylic acids
CH3COOH (aq)
+
H2 O (l)
-
CH3COO (aq)
+
+ H3O
(aq)
Reaction with metals
2 CH3 COOH (aq)
+ Mg(s)
CH3 COO
-
Mg
2
2+
(aq)
+
H2 (g)
Neutralisation reactions
Reaction with alkalis
CH3COOH(aq) + NaOH(aq)  CH3COO-Na+(aq) + H2O(l)
Reaction with carbonates
2H+(aq) + CO32-(aq)/(s)
 H2O(l) + CO2(g)
Reaction with hydrogencarbonates
H+(aq) + HCO3-(aq)/(s)
 H2O(l) + CO2(g)
Esters
Learning Objectives
Candidates should be able to:
•describe the formation of esters from carboxylic
acids using ethyl ethanoate as an example.
•Describe the acid and base hydrolysis of esters.
•State the commercial use of esters, e.g. solvents,
perfumes, flavourings.
Naming esters
Notice that the ester is named the opposite way around
from the way the formula is written. The "ethanoate" bit
comes from ethanoic acid. The "ethyl" bit comes from the
ethyl group on the end.
Naming esters
propyl ethanoate
propyl ethanoate
ethyl propanoate
butyl methanoate
Esterification and hydrolysis
c. H2SO4
warm
dil. H2SO4
reflux
Base hydrolysis
dilute
reflux
This reaction is irreversible !!
Note: These reaction is exactly the reverse of those used to make
an ester from a carboxylic acid and an alcohol. The only difference
in that case is that you use a concentrated acid as the catalyst. To
get as much ester as possible, you wouldn't add any water
otherwise you would favour the hydrolysis reaction
Alkaline hydrolysis of fats or oils
Because of its relationship with soap making, the alkaline
hydrolysis of fats and oils is sometimes known as
saponification.
Uses of esters
Adhesives
Solvents
Fragrances
Flavourings