ESTERS

1
REACTIONS OF ORGANIC COMPOUNDS
POLYMERS
DIBROMOALKANES
KETONES
ALKANES
ALKENES
ALCOHOLS
ALDEHYDES
ESTERS
HALOGENOALKANES
AMINES
CARBOXYLIC ACIDS
NITRILES
CONVERSIONS
2
REACTIONS OF ORGANIC COMPOUNDS
POLYMERS
DIBROMOALKANES
KETONES
P
F
C
S
D
ALKANES
ALKENES
ALCOHOLS
E
M
N
A
G
R
U
T
B
L
V
ALDEHYDES
ESTERS
HALOGENOALKANES
Q
O
U
H
I
T
K
AMINES
CARBOXYLIC ACIDS
NITRILES
J
3
CHLORINATION OF METHANE
A
Initiation Cl2 gt 2Cl radicals
created Propagation Cl CH4
gt CH3 HCl radicals used and
Cl2 CH3 gt CH3Cl Cl then
re-generated Termination Cl Cl
gt Cl2 radicals removed Cl
CH3 gt CH3Cl CH3 CH3 gt
C2H6
Summary Due to the lack of reactivity of alkanes
you need a very reactive species to persuade them
to react Free radicals need to be formed by
homolytic fission of covalent bonds This is done
by shining UV light on the mixture (heat could be
used) Chlorine radicals are produced because the
Cl-Cl bond is the weakest You only need one
chlorine radical to start things off With excess
chlorine you will get further substitution and a
mixture of chlorinated products
CONVERSIONS
4
ELECTROPHILIC ADDITION OF HBr
B
Reagent Hydrogen bromide... it is
electrophilic as the H is slightly
positive Condition Room temperature. Equation
C2H4(g) HBr(g) gt C2H5Br(l)
bromoethane Mechanism Step 1 As the HBr
nears the alkene, one of the carbon-carbon bonds
breaks The pair of electrons attaches to the
slightly positive H end of H-Br. The HBr bond
breaks to form a bromide ion. A carbocation
(positively charged carbon species) is
formed. Step 2 The bromide ion behaves as a
nucleophile and attacks the carbocation. Overall
there has been addition of HBr across the double
bond.
CONVERSIONS
5
ELECTROPHILIC ADDITION OF BROMINE
C
Reagent Bromine. (Neat liquid or
dissolved in tetrachloromethane, CCl4
) Conditions Room temperature. No catalyst
or UV light required! Equation C2H4(g)
Br2(l) gt CH2BrCH2Br(l) 1,2 -
dibromoethane Mechanism It is surprising
that bromine should act as an
electrophile as it is non-polar.
CONVERSIONS
6
DIRECT HYDRATION OF ALKENES
D
Reagent steam Conditions high
pressure Catalyst phosphoric acid Product
alcohol Equation C2H4(g)
H2O(g) C2H5OH(g) ethanol Use
ethanol manufacture Comments It may be
surprising that water needs such vigorous
conditions to react with ethene. It is a
highly polar molecule and you would expect
it to be a good electrophile. However,
the O-H bonds are very strong so require a great
deal of energy to be broken. This
necessitates the need for a catalyst.
CONVERSIONS
7
HYDROGENATION
E
Reagent hydrogen Conditions nickel
catalyst - finely divided Product
alkanes Equation C2H4(g) H2(g)
gt C2H6(g) ethane Use margarine
manufacture
CONVERSIONS
8
POLYMERISATION OF ALKENES
F
EXAMPLES OF ADDITION POLYMERISATION
ETHENE
POLY(ETHENE)
PROPENE
POLY(PROPENE)
CHLOROETHENE
POLY(CHLOROETHENE) POLYVINYLCHLORIDE PVC
TETRAFLUOROETHENE
POLY(TETRAFLUOROETHENE) PTFE Teflon
CONVERSIONS
9
NUCLEOPHILIC SUBSTITUTION
G
AQUEOUS SODIUM HYDROXIDE Reagent Aqueous
sodium (or potassium) hydroxide Conditions Reflux
in aqueous solution (SOLVENT IS
IMPORTANT) Product Alcohol Nucleophile hydroxide
ion (OH) Equation e.g. C2H5Br(l)
NaOH(aq) gt C2H5OH(l)
NaBr(aq) Mechanism WARNING It is
important to quote the solvent when answering
questions. Elimination takes place when
ethanol is the solvent The reaction (and
the one with water) is known as HYDROLYSIS
CONVERSIONS
10
NUCLEOPHILIC SUBSTITUTION
H
AMMONIA Reagent Aqueous, alcoholic ammonia (in
EXCESS) Conditions Reflux in aqueous, alcoholic
solution under pressure Product Amine Nucleophile
Ammonia (NH3) Equation e.g. C2H5Br
2NH3 (aq / alc) gt C2H5NH2 NH4Br
(i) C2H5Br NH3 (aq / alc) gt
C2H5NH2 HBr (ii) HBr NH3 (aq /
alc) gt NH4Br Mechanism Notes The
equation shows two ammonia molecules. The second
one ensures that a salt is not formed. Excess
ammonia is used to prevent further substitution
(SEE NEXT SLIDE)
CONVERSIONS
11
NUCLEOPHILIC SUBSTITUTION
H
AMMONIA Why excess ammonia? The second ammonia
molecule ensures the removal of HBr which would
lead to the formation of a salt. A large excess
ammonia ensures that further substitution doesnt
take place - see below Problem The amine
produced is also a nucleophile (lone pair on N)
and can attack another molecule of halogenoalkane
to produce a 2 amine. This in turn is a
nucleophile and reacts further producing a 3
amine and, eventually a quarternary ammonium
salt. C2H5NH2 C2H5Br gt HBr
(C2H5)2NH diethylamine, a 2
amine (C2H5)2NH C2H5Br gt HBr
(C2H5)3N triethylamine, a 3
amine (C2H5)3N C2H5Br gt
(C2H5)4N Br tetraethylammonium bromide, a 4
salt
CONVERSIONS
12
NUCLEOPHILIC SUBSTITUTION
I
POTASSIUM CYANIDE Reagent Aqueous, alcoholic
potassium (or sodium) cyanide Conditions Reflux
in aqueous , alcoholic solution Product Nitrile
(cyanide) Nucleophile cyanide ion
(CN) Equation e.g. C2H5Br KCN
(aq/alc) gt C2H5CN KBr(aq)
Mechanism Importance it extends the carbon
chain by one carbon atom the CN group can then
be converted to carboxylic acids or
amines. Hydrolysis C2H5CN 2H2O gt
C2H5COOH NH3 Reduction C2H5CN
4H gt C2H5CH2NH2
J
K
CONVERSIONS
13
ELIMINATION
L
Reagent Alcoholic sodium (or potassium)
hydroxide Conditions Reflux in alcoholic
solution Product Alkene Mechanism Elimination Equ
ation C3H7Br NaOH(alc) gt C3H6
H2O NaBr Mechanism the OH
ion acts as a base and picks up a proton the
proton comes from a C atom next to the one bonded
to the halogen the electron pair moves to form a
second bond between the carbon atoms the halogen
is displaced overall there is ELIMINATION
of HBr. With unsymmetrical
halogenoalkanes, a mixture of products may be
formed.
CONVERSIONS
14
ELIMINATION OF WATER (DEHYDRATION)
L
Reagent/catalyst conc. sulphuric acid (H2SO4) or
conc. phosphoric acid (H3PO4) Conditions reflux
at 180C Product alkene Equation e.g.
C2H5OH(l) gt CH2 CH2(g)
H2O(l) Mechanism Step 1 protonation of the
alcohol using a lone pair on oxygen Step 2 loss
of a water molecule to generate a
carbocation Step 3 loss of a proton (H) to give
the alkene Note Alcohols with the OH in the
middle of a chain can have two ways of losing
water. In Step 3 of the mechanism, a proton
can be lost from either side of the carbocation.
This gives a mixture of alkenes from
unsymmetrical alcohols...
CONVERSIONS
15
OXIDATION OF PRIMARY ALCOHOLS
N
Primary alcohols are easily oxidised to
aldehydes e.g. CH3CH2OH(l)
O gt CH3CHO(l) H2O(l)
it is essential to distil off the aldehyde before
it gets oxidised to the acid
CH3CHO(l) O gt CH3COOH(l)
OXIDATION TO ALDEHYDES DISTILLATION
OXIDATION TO CARBOXYLIC ACIDS REFLUX
Aldehyde has a lower boiling point so distils off
before being oxidised further
Aldehyde condenses back into the mixture and gets
oxidised to the acid
CONVERSIONS
16
OXIDATION OF ALDEHYDES
O

• Aldehydes are easily oxidised to carboxylic acids
• e.g. CH3CHO(l) O
  gt CH3COOH(l)
• one way to tell an aldehyde from a ketone is to
  see how it reacts to mild oxidation
• ALDEHYES are EASILY OXIDISED
• KETONES are RESISTANT TO MILD OXIDATION
• reagents include TOLLENS REAGENT and
  FEHLINGS SOLUTION
• TOLLENS REAGENT
• Reagent ammoniacal silver nitrate solution
• Observation a silver mirror is formed on the
  inside of the test tube
• Products silver carboxylic acid
• Equation Ag e- gt Ag
• FEHLINGS SOLUTION
• Reagent a solution of a copper(II) complex
• Observation a red precipitate forms in the blue
  solution
• Products copper(I) oxide carboxylic acid

CONVERSIONS
17
OXIDATION OF SECONDARY ALCOHOLS
P
Secondary alcohols are easily oxidised to
ketones e.g. CH3CHOHCH3(l)
O gt CH3COCH3(l) H2O(l) The
alcohol is refluxed with acidified K2Cr2O7.
However, on prolonged treatment with a powerful
oxidising agent they can be further oxidised to a
mixture of acids with fewer carbon atoms than the
original alcohol.
CONVERSIONS
18
REDUCTION OF CARBOXYLIC ACIDS
Q
Reagent/catalyst lithium tetrahydridoaluminate(III
) LiAlH4 Conditions reflux in
ethoxyethane Product aldehyde Equation
e.g. CH3COOH(l) 2H gt
CH3CHO(l) H2O(l)
CONVERSIONS
19
REDUCTION OF ALDEHYDES
R
Reagent sodium tetrahydridoborate(III)
NaBH4 Conditions warm in water or ethanol
Product primary alcohol Equation
e.g. C2H5CHO(l) 2H gt
C3H7OH(l)
CONVERSIONS
20
REDUCTION OF KETONES
S
Reagent sodium tetrahydridoborate(III)
NaBH4 Conditions warm in water or
ethanol Product secondary alcohol Equation
e.g. CH3COCH3(l) 2H gt
CH3CH(OH)CH3(l)
CONVERSIONS
21
ESTERIFICATION
T
Reagent(s) carboxylic acid strong acid catalyst
(e.g conc. H2SO4 ) Conditions reflux Product es
ter Equation e.g. CH3CH2OH(l)
CH3COOH(l) CH3COOC2H5(l)
H2O(l) Notes Concentrated H2SO4 is also a
dehydrating agent, it removes water as it is
formed causing the equilibrium to move to the
right and thus increasing the yield of
ester. Uses of esters Esters are fairly
unreactive but that doesnt make them
useless Used as flavourings Naming
esters Named from the alcohol and carboxylic acid
which made them... CH3OH CH3COOH
CH3COOCH3 H2O from ethanoic acid
CH3COOCH3 from methanol
METHYL ETHANOATE
CONVERSIONS
22
HYDROLYSIS OF ESTERS
U
Reagent(s) dilute acid or dilute
alkali Conditions reflux Product carboxylic acid
and an alcohol Equation
e.g. CH3COOC2H5(l) H2O(l)
CH3CH2OH(l) CH3COOH(l) Notes If alkali
is used for the hydrolysis the salt of the acid
is formed CH3COOC2H5(l) NaOH(aq) gt
CH3CH2OH(l) CH3COO-Na(aq)
CONVERSIONS
23
BROMINATION OF ALCOHOLS
V
Reagent(s) conc. hydrobromic acid HBr(aq) or
sodium (or potassium) bromide and
concentrated sulphuric acid Conditions reflux Prod
uct haloalkane Equation C2H5OH(l) conc.
HBr(aq) gt C2H5Br(l)
H2O(l) Mechanism The mechanism starts off in a
similar way to dehydration (protonation of the
alcohol and loss of water) but the
carbocation (carbonium ion) is attacked by a
nucleophilic bromide ion in step 3.
Step 1 protonation of the alcohol using a lone
pair on oxygen Step 2 loss of a water molecule to
generate a carbocation (carbonium ion) Step 3 a
bromide ion behaves as a nucleophile and attacks
the carbocation
CONVERSIONS