4.10 Triglycerides
1
Triglycerides
 Fats and oils from plants and animals
 Tri-esters of propan-1,2,3-triol (glycerol)
 Three long straight chain carboxylic acids (fatty acids)
form ester linkages with each glycerol molecule
2
Triglycerides
O
R
H
H
O
C
H
C
C
H
C
O
H
O
H
H
O
H
H
Carboxylic
acid
Propan-1,2,3-triol
3
4
5
Triglycerides
 Fatty acids contain an even number of
carbon atoms (between 12 and 20). The
carbon chain can be saturated or
unsaturated.
 If there is more than 1 double bond the
molecule is referred to as
polyunsaturated
 Naturally occurring tri-esters of propan1,2,3-triol generally will contain three
different fatty acids
6
Examples of Fatty Acids
7
Oleic Acid
8
Olive Oil
9
Triglycerides
 Triglycerides can be hydrolysed to produce glycerol
and three fatty acid molecules.
 In biological organisms that can utilise triglycerides for
energy this reaction is catalysed by lipase enzymes
 In the laboratory concentrated acid or alkali combined
with heating can be used to break down the
triglyceride
10
Triglycerides
 The state of an edible fat or oil at room temperature
can be used to determine its source.
 Edible fats are solids at 25oC and generally are obtained
from land animals
 Edible oils are liquids at 25oC and are obtained from
plants or marine animals
11
Triglycerides
Melting points of fats and oils
 As the length of the carbon chain increases so does the
tm increase, due to increased dispersion forces.
 As the degree of unsaturation increases (i.e. number of
C=C bonds increases) the tm decreases. The molecules
can’t pack together as closely and so don’t solidify
 Fat contains a greater percentage of saturated fatty
acids than unsaturated fatty acids and as a result it is
solid at room temperature
 Oils contain a greater percentage of unsaturated fatty
acids and are liquids
12
13
Reactions of Triglycerides
 The degree of unsaturation of a triglyceride can be
determined by its reaction with bromine or iodine
H
H
C
H
C
+
H
Br
Br
Br
H
H
C
C
H
H
Br
 This is referred to as an Addition reaction
 The orange colour of the bromine disappears as the
reaction occurs. (The products are colourless)
 To enable the bromine to mix with the triglyceride
both the bromine and triglyceride are dissolved in a
non polar solvent (cyclohexane)
14
Reactions of Triglycerides
 By titrating a standard solution of bromine (burette)
with a known volume of a standard solution of fat or
oil the degree of unsaturation can be measured.
 The greater the amount of bromine required the
greater the degree of unsaturation.
 The end point is indicated by the first permanent
orange colour in the flask.
15
Reactions of Triglycerides
Iodine number
 The degree of unsaturation of a fat or oil is
often described in terms of the iodine
number
 The iodine number is the mass of iodine
that reacts with 100g of the fat or oil
 The greater the iodine number the greater
the degree of unsaturation
Olive oil Iodine Number =75–94 (virgin and
refined)
16
Reactions of Triglycerides
 Liquid oils can be converted to solid fats by catalytic
hydrogenation
 The vegetable oil is heated with hydrogen gas under
pressure in the presence of a nickel catalyst. These
conditions increase the rate of reaction.
 Sufficient hydrogen is added to produce a product that
is solid at room temperature
H
H
H
H
C
C
H
H
Ni
C
H
+
C
H
H
H
H ig h P
H
H
17
4.11 Carbohydrates
18
Carbohydrates
 General formula is usually CxH2yOy
 This can often be written as Cx(H2O)y
 Carbohydrates are polyhydroxyaldehydes or
polyhydroxyketones or compounds that produce these
when hydrolysed
 Can be monosaccharides, disaccharides or
polysaccharides depending on the number of simple
sugars in the molecule
19
Monosaccharides
 Monomers
 General formula CxH2xOx where x = 3 to 8
 Water soluble (Hydrogen bond with water)
 Simple sugars eg. Glucose, Fructose
 Solids at room temperature
 Sweet
20
Glucose
 C6H12O6
 Can exist as a chain or ring structure
 These structures are in equilibrium in aqueous
solution
D-Glucose
α-D-Glucose
21
22
Glucose
 In the chain form the aldehyde can be oxidised by
Tollen's reagent forming the silver mirror and the
carboxylate ion but there is no reaction with the ring
form
H
H
O
H
H
H
C
C
C
O
O
H
H
H
H
C
C
C
O
H
Tollens
H
O
H
C
C
C
H
H
H
O
H
C
C
H
O
O
O
O
O
O
H
H
H
H
H
H
C
O–
 This reaction causes the equilibrium to favour the
formation of the chain structure
23
Disaccharides
 Two monosaccharides per molecule
 Formed by a condensation reaction (eliminating
water)
 Can be hydrolysed to form monosaccharides
 Water soluble compounds (Hydrogen bond with
water)
24
Sucrose
Maltose
Lactose
25
Polysaccharides
 Large polymers of monosaccharides
 Formed by condensation reaction and broken down
to monosaccharides by hydrolysis
 (C6H10O5)n +½nH2O ½nC12H22O11
polysaccharide
disaccharide
 C12H22O11 + H2O  2C6H12O6
disaccharide
monosaccharide
 Overall
 (C6H10O5)n + nH2O  nC6H12O6
26
Polysaccharides
 Insoluble in water. Although hydrogen bonding can
occur the large molecular size prevents mixing with
water
 Will absorb water
27
Polysaccharides
Cellulose
 Structural material in plants
 Made up of approx. 3000 glucose units
 Straight chain polymer
28
Polysaccharides
Starch
 Made up of amylose 250-2000 glucose units in a
straight chain and amylopectin which contains
hundreds of thousands of glucose in a branched
chain structure.
29
Amylose
Amylopectin
30
Polysaccharides
Glycogen
 Storage molecule for glucose in liver and muscle
 Branched chain polymer
31