Redox Reactions

1
Redox Reactions
33.1 Organic Synthesis 33.2 Redox
Reactions 33.3 Oxidation of Alkylbenzenes 33.4 Oxi
dation of Alcohols 33.5 Redox Reactions of
Aldehydes and Ketones 33.6 Redox Reactions of
Carboxylic Acids 33.7 Redox Reactions of
Alkenes 33.8 Autooxidation of Fats and Oils
2
Organic Synthesis
3
33.1 Organic Synthesis (SB p.51)
Organic Synthesis

• In planning syntheses,
• ? we need to think backwards
• ? think backwards from the desired product to
  simpler molecules (precursors)

Target molecule
4
33.1 Organic Synthesis (SB p.51)
Organic Synthesis

• A synthesis usually involves more than one step

Target molecule
5
33.1 Organic Synthesis (SB p.51)
Organic Synthesis

• Usually more than one way to carry out a synthesis

Target molecule
6
33.1 Organic Synthesis (SB p.52)
Number of Steps Involved in the Synthesis

• Most organic reactions are
• ? reversible reactions
• ? seldom proceed to completion
• ? impossible to have a 100 yield of the
  product from each step of the synthetic route

7
33.1 Organic Synthesis (SB p.52)
Number of Steps Involved in the Synthesis

• Consider the following synthetic route
• ? each step has a yield of 60

What is the yield of the desired product?
8
33.1 Organic Synthesis (SB p.52)
Number of Steps Involved in the Synthesis
Yield of the desired product 60 ? 60 ? 60
? 60 12.96
9
33.1 Organic Synthesis (SB p.52)
Number of Steps Involved in the Synthesis

• An efficient route of synthesis should consist of
  a minimal number of steps
• Limit the total number of reaction steps in a
  synthesis to not more than four

10
33.1 Organic Synthesis (SB p.52)
Availability of Starting Materials and Reagents

• Only a restricted number of simple, relatively
  cheap starting materials is available
• Include
• ? simple haloalkanes and alcohols of not more
  than four carbon atoms
• ? simple aromatic compounds (e.g. benzene and
  methylbenzene)

11
33.1 Organic Synthesis (SB p.52)
Duration of the Synthetic Process

• Many organic reactions proceed at a relatively
  low rate
• e.g. the acid-catalyzed esterification requires
  refluxing the reaction mixture of alcohols and
  carboxylic acids for a whole day
• Inclusion of these slow reactions in a synthetic
  route is impractical

12
Redox Reactions
13
33.2 Redox Reactions (SB p.53)
Redox Reactions

• Redox reactions are reactions that involve a
  change of oxygen or hydrogen content in organic
  compounds

14
33.2 Redox Reactions (SB p.53)
Oxidation

• Oxidation of an organic compound usually
  corresponds to
• ? an increase in oxygen content
• ? a decrease in hydrogen content

15
33.2 Redox Reactions (SB p.53)
Oxidation

• e.g.
• The change of ethanol to ethanoic acid is an
  oxidation
• ? the oxygen content of ethanoic acid is higher
  than that of ethanol

16
33.2 Redox Reactions (SB p.53)
Oxidation

• e.g.
• Converting ethanol to ethanal is also an
  oxidation process
• ? the hydrogen content of ethanal is lower than
  that of ethanol

17
33.2 Redox Reactions (SB p.53)
Oxidation

• Common oxidizing agents used in organic reactions
  include
• Acidified potassium manganate(VII) (KMnO4/H)
• Alkaline potassium manganate(VII) (KMnO4/OH)
• Acidified potassium dichromate(VI) (K2Cr2O7/H)
• Ozone (O3/CH3CCl3, Zn/H2O)

18
33.2 Redox Reactions (SB p.54)
Reduction

• Reduction of an organic compound usually
  corresponds to
• ? an increase in hydrogen content
• ? a decrease in oxygen content

19
33.2 Redox Reactions (SB p.54)
Reduction

• e.g.
• Converting ethanoic acid to ethanal is a
  reduction
• ? the oxygen content of ethanal is lower than
  that of ethanoic acid

20
33.2 Redox Reactions (SB p.54)
Reduction

• e.g.
• Converting ethanal to ethanol is also a
  reduction process
• ? the hydrogen content of ethanol is higher
  than that of ethanal

21
33.2 Redox Reactions (SB p.54)
Reduction

• Common reducing agents used in organic reactions
  include
• Lithium tetrahydridoaluminate in dry ether
  (LiAlH4/ether, H3O)
• Sodium tetrahydridoborate (NaBH4/H2O)
• Hydrogen with palladium (H2/Pd)

22
Oxidation of Alkylbenzenes
23
33.3 Oxidation of Alkylbenzenes (SB p.55)
Alkylbenzenes

• A group of aromatic hydrocarbons in which an
  alkyl group is bonded directly to a benzene ring
• Sometimes called arenes

24
33.3 Oxidation of Alkylbenzenes (SB p.55)
Alkylbenzenes

• Examples of alkylbenzenes

25
33.3 Oxidation of Alkylbenzenes (SB p.55)
Oxidation of Alkylbenzenes

• Oxidation of alkylbenzenes
• ? carried out by the action of hot alkaline
  potassium manganate(VII) solution
• In the oxidation process, a benzoate is formed

26
33.3 Oxidation of Alkylbenzenes (SB p.55)
Oxidation of Alkylbenzenes

• Benzoic acid can be recovered
• ? by adding a mineral acid such as dilute H2SO4
  to the benzoate
• This method gives benzoic acid in almost
  quantitative yield

27
33.3 Oxidation of Alkylbenzenes (SB p.55)
Oxidation of Alkylbenzenes
28
33.3 Oxidation of Alkylbenzenes (SB p.55)
Oxidation of Alkylbenzenes
29
33.3 Oxidation of Alkylbenzenes (SB p.56)
Oxidation of Alkylbenzenes

• All alkylbenzenes are oxidized to benzoic acid
• ? except the alkylbenzenes with a tertiary
  alkyl group
• ? they do not have a benzylic hydrogen atom

30
33.3 Oxidation of Alkylbenzenes (SB p.56)
Oxidation of Alkylbenzenes

• In the above oxidation processes,
• ? the alkyl groups of alkylbenzenes are
  oxidized, rather than the benzene ring
• In the first step, the oxidizing agent abstracts
  a benzylic hydrogen atom
• The oxidizing agent oxidizes the side chain to a
  carboxyl group

31
33.3 Oxidation of Alkylbenzenes (SB p.56)
Oxidation of Alkylbenzenes

• Side-chain oxidation by KMnO4 is not restricted
  to alkyl groups
• C C bonds and C O groups in the side chain
  are also oxidized by hot alkaline KMnO4

32
33.3 Oxidation of Alkylbenzenes (SB p.56)
Oxidation of Alkylbenzenes

• e.g.

33
33.3 Oxidation of Alkylbenzenes (SB p.56)
34
Oxidation of Alcohols
35
33.4 Oxidation of Alcohols (SB p.56)
Alcohols

• A group of compounds with one or more hydroxyl
  groups (?OH) attached to an alkyl group
• For alcohols having only one hydroxyl group,
• ? their general formula is CnH2n1OH

36
33.4 Oxidation of Alcohols (SB p.56)
Alcohols

• Examples of alcohols

37
33.4 Oxidation of Alcohols (SB p.57)
Alcohols

• Depending on the number of alkyl groups attached
  to the carbon to which the hydroxyl group is
  linked,
• ? alcohols can be classified as primary,
  secondary and tertiary alcohols

38
33.4 Oxidation of Alcohols (SB p.57)
Alcohols

• Differentiating an alcohol as a 1o alcohol, a 2o
  alcohol or a 3o alcohol is extremely important
• ? when oxidized, these alcohols give different
  products

39
33.4 Oxidation of Alcohols (SB p.57)
Alcohols
40
33.4 Oxidation of Alcohols (SB p.57)
Oxidation of Primary Alcohols

• Primary alcohols are firstly oxidized to
  aldehydes and subsequently to carboxylic acids
• Using oxidizing agents like acidified KMnO4 and
  acidified K2Cr2O7

41
33.4 Oxidation of Alcohols (SB p.57)
1. Oxidation of Primary Alcohols to Aldehydes

• The oxidation of alcohols is difficult to stop at
  the aldehyde stage
• ? aldehydes are a reducing agent
• One way of solving this problem
• ? remove the aldehyde as soon as it is formed
• ? by distilling off the aldehydes from the
  reaction mixture

42
33.4 Oxidation of Alcohols (SB p.57)
1. Oxidation of Primary Alcohols to Aldehydes

• e.g.
• Ethanal can be synthesized from ethanol using
  acidified K2Cr2O7
• ? ethanal is removed by distillation

43
33.4 Oxidation of Alcohols (SB p.58)
1. Oxidation of Primary Alcohols to Aldehydes
A typical laboratory set-up for the oxidation of
ethanol to ethanal
44
33.4 Oxidation of Alcohols (SB p.58)
2. Oxidation of Primary Alcohols to Carboxylic
Acids

• Primary alcohols can be oxidized to carboxylic
  acids by acidified KMnO4
• Acidified KMnO4 is a powerful oxidizing agent
• ? the oxidation of the alcohols does not stop
  at the aldehydes
• ? but directly to the carboxylic acids

45
33.4 Oxidation of Alcohols (SB p.58)
2. Oxidation of Primary Alcohols to Carboxylic
Acids

• e.g.
• Ethanol can be oxidized to ethanoic acid by
  acidified KMnO4

46
33.4 Oxidation of Alcohols (SB p.59)
2. Oxidation of Primary Alcohols to Carboxylic
Acids
A reflux apparatus used for the oxidation of
ethanol to ethanoic acid
47
33.4 Oxidation of Alcohols (SB p.59)
2. Oxidation of Primary Alcohols to Carboxylic
Acids
A distillation apparatus used for the separation
of ethanoic acid from the reaction mixture
48
33.4 Oxidation of Alcohols (SB p.59)
2. Oxidation of Primary Alcohols to Carboxylic
Acids

• The oxidation of ethanol by acidified K2Cr2O7
• ? the basis of the breathalyser used by the
  police
• ? to rapidly estimate the ethanol content of
  the breath of suspected drunken drivers

49
33.4 Oxidation of Alcohols (SB p.59)
2. Oxidation of Primary Alcohols to Carboxylic
Acids

• When the drunken driver blows into the bag
• ? the ethanol molecules reduce the orange
  Cr2O72- ions to green Cr3 ions
• If more than a certain amount of the orange
  crystal changes colour,
• ? the driver is likely to be over the limit

50
33.4 Oxidation of Alcohols (SB p.59)
2. Oxidation of Primary Alcohols to Carboxylic
Acids
Demonstration of the use of the breathalyser
51
33.4 Oxidation of Alcohols (SB p.59)
Oxidation of Secondary Alcohols

• Secondary alcohols can be oxidized to ketones by
  either acidified K2Cr2O7 or acidified KMnO4

52
33.4 Oxidation of Alcohols (SB p.59)
Oxidation of Secondary Alcohols

• The reaction usually stops at the ketone stage
• ? further oxidation requires the breaking of a
  carbon-carbon bond
• ? difficult to proceed

53
33.4 Oxidation of Alcohols (SB p.60)
Oxidation of Secondary Alcohols

• e.g.
• Propan-2-ol can be oxidized to form propanone

54
33.4 Oxidation of Alcohols (SB p.60)
Oxidation of Tertiary Alcohols

• Tertiary alcohols are generally resistant to
  oxidation unless they are subjected to severe
  oxidation conditions
• ? any oxidation would immediately involve the
  cleavage of the strong C ? C bonds in the
  alcohol molecule

55
33.4 Oxidation of Alcohols (SB p.60)
Oxidation of Tertiary Alcohols

• Tertiary alcohols can be oxidized by acidified
  KMnO4
• ? give a mixture of ketones and carboxylic
  acids
• ? both with fewer carbon atoms than the
  original alcohol

56
33.4 Oxidation of Alcohols (SB p.60)
Oxidation of Tertiary Alcohols

• e.g.

57
Redox Reactions of Aldehydes and Ketones
58
33.5 Redox Reactions of Aldehydes and Ketones
(SB p.62)
Aldehydes and Ketones

• Carbonyl compounds that contain the carbonyl group

59
33.5 Redox Reactions of Aldehydes and Ketones
(SB p.62)
Oxidation of Carbonyl Compounds

• Aldehydes are readily oxidized by acidified KMnO4
  or K2Cr2O7 to form carboxylic acids

60
33.5 Redox Reactions of Aldehydes and Ketones
(SB p.62)
Oxidation of Carbonyl Compounds

• Ketones do not undergo oxidations readily
• ? their oxidation involves the cleavage of the
  strong C?C bond
• ? more severe conditions are required to bring
  about the oxidation

61
33.5 Redox Reactions of Aldehydes and Ketones
(SB p.62)
Oxidation of Carbonyl Compounds

• With the action of hot acidified KMnO4,
• ? the C?C bonds in ketones would be broken
• ? a mixture of carboxylic acids would be formed

62
33.5 Redox Reactions of Aldehydes and Ketones
(SB p.63)
Reduction of Carbonyl Compounds

• Both aldehydes and ketones undergo reduction
  reactions readily
• ? forming 1o and 2o alcohols respectively
• Reducing agents
• ? lithium tetrahydridoaluminate (LiAlH4)
• ? sodium tetrahydridoborate (NaBH4)

63
33.5 Redox Reactions of Aldehydes and Ketones
(SB p.63)
Reduction of Carbonyl Compounds

• LiAlH4 is a powerful reducing agent
• ? it reacts violently with water
• Those reduction reactions using LiAlH4 must be
  carried out in anhydrous solutions
• ? usually in dry ether

64
33.5 Redox Reactions of Aldehydes and Ketones
(SB p.63)
Reduction of Carbonyl Compounds
65
33.5 Redox Reactions of Aldehydes and Ketones
(SB p.63)
Reduction of Carbonyl Compounds

• The reduction of aldehydes and ketones to
  alcohols is most often carried out by NaBH4
• NaBH4 is a less powerful reducing agent
• ? it does not react with water
• ? the reduction reactions using NaBH4 can be
  carried out in water or alcohols

66
33.5 Redox Reactions of Aldehydes and Ketones
(SB p.63)
Reduction of Carbonyl Compounds
67
Redox Reactions of Carboxylic Acids
68
33.6 Redox Reactions of Carboxylic Acids (SB
p.64)
Carboxylic Acids

• A group of organic compounds containing the
  carboxyl group
• Examples

69
33.6 Redox Reactions of Carboxylic Acids (SB
p.64)
Reduction of Carboxylic Acids

• Reductions of carboxylic acids are difficult to
  carry out
• Can be achieved with the use of very powerful
  reducing agents (e.g. LiAlH4)
• LiAlH4 reduces carboxylic acids to 1o alcohols
  in excellent yields

70
Redox Reactions of Alkenes
71
33.7 Redox Reactions of Alkenes (SB p.65)
Alkenes

• Alkenes are unsaturated hydrocarbons containing C
  C bonds
• The C C bonds are readily oxidized
• ? alkenes are able to undergo oxidation
  reactions

72
33.7 Redox Reactions of Alkenes (SB p.65)
Alkenes

• Alkenes can accept hydrogen to form alkanes
• ? alkenes are also able to undergo reduction
  reactions

73
33.7 Redox Reactions of Alkenes (SB p.65)
Oxidation of Alkenes by Potassium Manganate(VII)

• Alkenes react with alkaline KMnO4
• ? form 1,2-diols called glycols

74
33.7 Redox Reactions of Alkenes (SB p.65)
Oxidation of Alkenes by Potassium Manganate(VII)

• Ethene is oxidized to ethane-1,2-diol
• The manganate(VII) ions are reduced to
  manganese(IV) oxide

75
33.7 Redox Reactions of Alkenes (SB p.65)
Oxidation of Alkenes by Potassium Manganate(VII)

• A change from the purple colour of manganate(VII)
  ions to the brown precipitate of manganese(IV)
  oxide
• ? a chemical test to distinguish between
  alkenes and alkanes

76
33.7 Redox Reactions of Alkenes (SB p.66)
Oxidation of Alkenes by Ozone

• Alkenes react rapidly and quantitatively with
  ozone
• ? form an unstable compound, known as ozonide
• Ozonides are very unstable
• ? they are not usually isolated
• ? treated directly with a reducing agent
  (Zn/H3O)

77
33.7 Redox Reactions of Alkenes (SB p.66)
Oxidation of Alkenes by Ozone

• The reduction produces carbonyl compounds
• ? can be safely isolated and identified

78
33.7 Redox Reactions of Alkenes (SB p.66)
Oxidation of Alkenes by Ozone

• The net result of this reaction is
• ? the breaking of the C C bond to form two
  carbonyl groups
• This process is called ozonolysis
• ? can be used to locate the position of the C
  C bond in an alkene

79
33.7 Redox Reactions of Alkenes (SB p.66)
Oxidation of Alkenes by Ozone

• e.g.
• Ozonolysis of but-1-ene gives two different
  aldehydes

80
33.7 Redox Reactions of Alkenes (SB p.66)
Oxidation of Alkenes by Ozone

• e.g.
• Ozonolysis of but-2-ene gives one aldehyde

81
33.7 Redox Reactions of Alkenes (SB p.68)
Reduction of Alkenes (Hydrogenation of Alkenes)

• Alkenes react with hydrogen in the presence of
  metal catalysts (Ni, Pd and Pt)
• ? form alkanes

82
33.7 Redox Reactions of Alkenes (SB p.68)
Reduction of Alkenes (Hydrogenation of Alkenes)

• The atoms of the hydrogen molecule add to each
  carbon atom of the C C bond of the alkene
• ? the alkene is converted to an alkane

83
33.7 Redox Reactions of Alkenes (SB p.68)
Reduction of Alkenes (Hydrogenation of Alkenes)

• Useful in analyzing unsaturated hydrocarbons
  (alkenes or alkynes)
• By measuring the number of moles of hydrogen
  reacted with one mole of an unsaturated
  hydrocarbon
• ? the number of double or triple bonds present
  in an unsaturated hydrocarbon molecule can be
  deduced

84
Autooxidation of Fats and Oils
85
33.8 Autooxidation of Fats and Oils (SB p.69)
Oxidation of Fats and Oils

• Fats and oils are esters of propane-1,2,3-triol
  and carboxylic acids of fairly long carbon chains
• Some of these acids may contain one or more C C
  bonds in them
• ? known as unsaturated carboxylic acids

86
33.8 Autooxidation of Fats and Oils (SB p.69)
Oxidation of Fats and Oils

• When fats and oils are exposed to air,
• ? the C C bonds will be oxidized
• ? the fats and oils will develop an off
  odour and unpleasant flavour

87
33.8 Autooxidation of Fats and Oils (SB p.70)
Oxidation of Fats and Oils

• Fats and oils having a high degree of
  unsaturation are more susceptible to oxidation
• The oxidation follows a free radical mechanism
• ? accelerated by trace metals, light and free
  radical initiators

88
33.8 Autooxidation of Fats and Oils (SB p.70)
Oxidation of Fats and Oils

• The hydroperoxides produced are flavourless and
  odourless
• ? decompose readily to form highly reactive
  hydroperoxide free radicals

89
33.8 Autooxidation of Fats and Oils (SB p.70)
Oxidation of Fats and Oils

• These radicals set up a chain reaction
• ? produce volatile, flavoured compounds of
  aldehydes, ketones and carboxylic acids
• ? responsible for their rancid flavour
• This process is called autooxidation

90
33.8 Autooxidation of Fats and Oils (SB p.70)
Oxidation of Fats and Oils

• Autooxidation can be controlled but cannot be
  stopped
• The addition of antioxidants (e.g. BHA and BHT)
  can slow down the oxidative spoilage of fats and
  oils
• Many vegetable oils contain natural antioxidants
  (e.g. vitamin C)
• ? can withstand autooxidation for a longer time

91
33.8 Autooxidation of Fats and Oils (SB p.70)
Principle of BHA/BHT as Antioxidants

• BHA and BHT are common antioxidants used in food
• ? retard the development of oxidative rancidity
  in unsaturated fats and oils

92
33.8 Autooxidation of Fats and Oils (SB p.70)
Principle of BHA/BHT as Antioxidants

• BHA and BHT work by
• ? donating the hydrogen atom of the ?OH group
  to the free hydroperoxide radical (ROO )
  involved in the autooxidation of fats and oils
• ? stopping the chain reactions in oxidative
  spoilage
• AH ROO ?? ROOH A

93
33.8 Autooxidation of Fats and Oils (SB p.70)
Principle of BHA/BHT as Antioxidants
AH ROO ?? ROOH A
where AH represents the antioxidant, and A is a
radical derived from the antioxidant
94
33.8 Autooxidation of Fats and Oils (SB p.71)
Principle of BHA/BHT as Antioxidants
Foods containing BHA and BHT
95
The END
96
33.1 Organic Synthesis (SB p.52)
Let's Think 1
Why are simple alcohols and simple aromatic
compounds relatively cheap starting materials for
organic syntheses?
Answer
They can be made from alkanes and benzene which
can be obtained directly from fractional
distillation of petroleum.
Back
97
33.1 Organic Synthesis (SB p.53)
Check Point 33-1
(a) What are the main reasons for carrying out an
organic synthesis?
Answer
(a) To make new substances such as medicines,
dyes, plastics or pesticides To make new organic
compounds for studying reaction mechanisms or
metabolic pathways
98
33.1 Organic Synthesis (SB p.53)
Check Point 33-1
(b) What are the factors that determine the
feasibility of an organic synthesis?
Answer
(b) Number of steps involved in the
synthesis Availability of starting materials and
reagents Duration of the synthetic process
Back
99
33.2 Redox Reactions (SB p.54)
Check Point 33-2
(a) State two common oxidizing agents used in
organic reactions.
Answer
(a) Acidified potassium manganate(VII)
(KMnO4/H) Alkaline potassium manganate(VII)
(KMnO4/OH) Acidified potassium dichromate(VI)
(K2Cr2O7/H) Ozone (O3/CH3Cl3, Zn/H2O) (Any two)
100
33.2 Redox Reactions (SB p.54)
Check Point 33-2
(b) State two common reducing agents used in
organic reactions.
Answer
(b) Lithium tetrahydridoaluminate in dry ether
(LiAlH4/ether, H3O) Sodium tetrahydridoborate
(NaBH4/H2O) Hydrogen with palladium
(H2/Pd) (Any two)
101
33.2 Redox Reactions (SB p.54)
Back
Check Point 33-2
(c) State whether each of the following reactions
is an oxidation or a reduction. (i) Conversion
of ethanol to ethanal (ii) Conversion of ethene
to ethanol (iii) Conversion of nitrobenzene to
phenylamine (iv) Conversion of propene to
propane (v) Conversion of propan-2-ol to
propanone
Answer
(c) (i) Oxidation (ii) Oxidation (iii) Reduction
(iv) Reduction (v) Oxidation
102
33.3 Oxidation of Alkylbenzenes (SB p.56)
Let's Think 2
Why is tert-butylbenzene resistant to
side-chain oxidation?
Answer
tert-Butylbenzene does not have a benzylic
hydrogen atom.
Back
103
33.3 Oxidation of Alkylbenzenes (SB p.56)
Check Point 33-3
State the conditions under which ethylbenzene can
be converted to benzoic acid in the laboratory.
Answer
Reagents 1. potassium manganate(VII), sodium
hydroxide 2. dilute sulphuric
acid Condition heating under reflux
Back
104
33.4 Oxidation of Alcohols (SB p.60)
Check Point 33-4
Back
Answer
105
33.5 Redox Reactions of Aldehydes and Ketones
(SB p.63)
Let's Think 3
What is the species responsible for the
reducing property of LiAlH4 and NaBH4?
Answer
Hydride ion, H
Back
106
33.5 Redox Reactions of Aldehydes and Ketones
(SB p.64)
Check Point 33-5
Answer
107
33.5 Redox Reactions of Aldehydes and Ketones
(SB p.64)
Check Point 33-5
Back
108
33.6 Redox Reactions of Carboxylic Acids (SB
p.65)
Check Point 33-6
Answer
109
33.6 Redox Reactions of Carboxylic Acids (SB
p.65)
Back
Check Point 33-6
Answer
110
33.7 Redox Reactions of Alkenes (SB p.67)
Example 33-7
Predict the structures of the following
hydrocarbons A, B and C using the information
given below
Answer
111
33.7 Redox Reactions of Alkenes (SB p.67)
Example 33-7
112
33.7 Redox Reactions of Alkenes (SB p.67)
Example 33-7
113
33.7 Redox Reactions of Alkenes (SB p.67)
Example 33-7
Back
114
33.7 Redox Reactions of Alkenes (SB p.68)
Check Point 33-7
Answer
115
33.7 Redox Reactions of Alkenes (SB p.68)
Check Point 33-7
Back
116
33.8 Autooxidation of Fats and Oils (SB p.71)
Check Point 33-8
(a) What causes fats and oils to go
rancid? (b) Explain how BHA and BHT can slow down
the oxidative spoilage of fats and oils.
Answer
(a) Carbon-carbon double bonds in fats and oils
as well as oxygen in air (b) BHA and BHT donate
the hydrogen atoms of their hydroxyl group to the
free hydroperoxide radical involved in the
autooxidation of fats and oils.
Back