4.4 Aldehydes and Ketones
1
Aldehydes and Ketones
O
H
R
R
C
H
O
H
C
C
C
H
H
H
C
H
R
•Carbonyl functional group
•Aldehyde: terminal carbon
•Ketone: non terminal carbon
2
Aldehydes and Ketones
 Aldehydes are prepared by a controlled oxidation of
the corresponding primary alcohol. The aldehyde is
distilled off as it forms to prevent further oxidation.
R
R
2--
H
C
O
H
H
Cr2O7
+
H
C
O
H
3
Aldehydes and Ketones
 Aldehydes are oxidised by acidified dichromate
ions to the corresponding carboxylic acid.
O
O
2--
Cr2O7
R
R
C
+
C
H
H
O
H
4
Aldehydes and Ketones
 Ketones are prepared by the oxidation of secondary
alcohols. No further oxidation occurs.
R
H
H
H
C
C
C
O
H
R
Cr2O7
2--
R
C
C
+
H
O
H
H
H
H
C
H
H
R
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Aldehydes and Ketones
 When heated with Tollen’s reagent (ammoniacal silver
nitrate), aldehydes are oxidised to carboxylate ions.
 RCHO  RCOO–
 The silver diamine ion is reduced to metallic silver which
can be deposited on the test tube giving a silver mirror.
 Ag(NH3)2+  Ag
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Aldehydes and Ketones
 Ketones (and alcohols) do not oxidise with Tollen’s
reagent.
 The silver mirror test is commonly used to identify
between aldehydes and ketones.
 It can also be used to identify between an aldehyde
and alcohol where dichromate ions would react
with both.
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Tetracycline (antibiotic)
Vanillin
8
4.5 Carboxylic Acids
9
Carboxylic Acids
O
H
R
C
H
Carboxyl group
C
O
H
 Carboxylic acids can be prepared by oxidation of
primary alcohols or aldehydes with excess
acidified dichromate solution.
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Carboxylic Acids
 Carboxylic acids are weak acids
 If they are soluble in water then they will partially
ionise to form hydronium and carboxylate ions.
 RCOOH + H2O  H3O+ + RCOO–
 Equilibrium position favours reactants.
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Carboxylic Acids
 Carboxylic acids react readily with bases such as:
 Hydroxides and Oxides (Products: Salt & Water)
RCOOH + OH–  RCOO– + H2O
 Carbonates (Products: Salt ,Water and CO2)
2RCOOH+CO32– 2RCOO– +H2O+CO2
 Hydrogen carbonates (Products: Salt ,Water and CO2)
RCOOH + HCO3– RCOO– + H2O+CO2
12
Carboxylic Acids
 Carboxylate salts of sodium and potassium are
water soluble due to strong ion-dipole interactions
which form between the negative carboxylate ion
and the water molecules
H
O
H
R
C
H
H
O
C
O–
H
H
O
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Ion dipole interactions
 Strongest type of secondary interaction
 Occurs between a full positive or negative charge (ion)
and a polar molecule
 Common between carboxylate ions and water or
protonated amines and water
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Carboxylic Acids
 Many drugs including (aspirin and other painkillers)
contain a carboxyl group. These drugs are often mixed
with solid sodium hydrogen carbonate which converts
the acid to the water soluble carboxylate on mixing
with water.
 This makes the drug easier to take and quicker acting
that it would be in its insoluble form.
15
Citric Acid
Salicylic Acid
16
4.6 Amines
17
Amines
 Based on ammonia
H
R
C
H
H
 1o (primary) amine
N
H
H
R
 2o (secondary) amine
C
H
N
H
H
C
H
R
18
Amines
R
H
C
H
R
C
H
 3o (tertiary) amine
N
H
H
C
H
R
 Amines tend to have unpleasant
odours, often fishy.
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Amines
 Like ammonia, amines can act as a base accepting a
proton from an acid
 NH3 + H+ → NH4+
 RNH2 + H+  RNH3+
 The product of this reaction is referred to as the
protonated form of the amine
 The protonated form is soluble in water due to ion
dipole interactions between the protonated amine
ion and water
20
Amines
 Many drugs (eg. Anaesthetics) contain amine
functional groups
 These drugs are insoluble in water and so would
not be effective if administered as the amine
 By protonating these drugs they are able to dissolve
in water within the body and so can act
H
O
H
H
H
H
N+
C
H
H
R
21
Nicotine
Chlorphenamine
(Antihistamine)
Methyl Orange
22
4.7 Esters
23
Esters
O
H
R
C
H
 Ester functional group
C
O
H
Acid
C
H
R
Alcohol
 Similar structure to carboxylic acids
 Hydrogen on carboxyl group replaced by alkyl
group
 Fruity odour
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Naming Esters
 Identify the alcohol carbon chain and the carbon
chain from the acid.
 Name the alcohol part first followed by the acid
H
H
H
H
O
H
C
C
C
C
H
H
H
H
H
H
C
C
C
O
H
H
H
 Ethyl pentanoate
25
Methyl Cinnamate (Strawberry)
Aspirin (Acetyl Salicylic Acid)
Oil of Wintergreen (Methyl
Salicylic Acid)
26
Production of Esters
 Esters are formed by the reaction of a carboxylic
acid and alcohol
 This reaction is called ESTERIFICATION but can
also be referred to as a CONDENSATION reaction
because water is one of the products.
 The reaction is slow at room temp and so the
reaction mixture must be refluxed for an extended
period and concentrated sulfuric acid is used as the
catalyst
 This is an equilibrium reaction
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Reflux
28
Production of Esters
 The yield of the ester can be increased by using
excess of one of the reagents. (Usually the alcohol
because it is cheaper)
 Large carbon chains (R groups) on the acid and
alcohol decrease the yield of ester
O
H
H C
H
H
+
C
H
O
reflux
H C
H
O
O
H
H
H2SO4
H C
H
C
H
C
H
O
H
+
H O
H
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Production of Esters
 The ester can be separated
from the mixture using a
separating funnel
 The mixture is washed with
sodium bicarbonate which
ensures the acid dissolves
in the water layer
30
Production of Esters
 The aqueous layer which contains any unreacted
alcohol and the sodium carboxylate salt can be tapped
off leaving the organic layer
 This layer is then distilled and the ester is collected at
the appropriate tb
31
Distillation
32
Reactions of Esters
 If an ester is refluxed with aqueous acid or base, it
undergoes hydrolysis
 In acidic conditions the products formed are a
carboxylic acid and an alcohol. The reaction
mixture is refluxed with sulfuric acid as the catalyst
 This is the reverse of esterification
Acidic conditions
R
H
C
O
O
R
+
H O
R
H+
reflux
R
C
O
O
+
O H
H
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Reactions of Esters
 In alkaline conditions the products formed are the
carboxylate ions and the alcohol
 The ester is refluxed with sodium hydroxide
solution and the alcohol product can be separated
from the sodium carboxylate salt by distillation
 The carboxylic acid will reform if a solution of
strong acid is added to the sodium carboxylate salt.
R
Alkaline conditions
R
–
O
C
O
O
R
+
R
+
C
H
O–
O
O H
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