Download 02. Structure and chemical properties of carboxylic acids

CARBOXYLIC ACIDS
Functional group of carboxylic acid is called
carboxyl group
Carboxylic acid can be aliphatic or aromatic
Nomenclature of carboxylic acid
1. Select the longest carbon chain containing carboxyl group.
2. Drop the final –e from the hydrocarbon name.
3. Add the suffix –oic acid.
4. Number the carbon of parent chain starting with the
carboxylic group. Carboxylic group is always at the beginning
of the carbon chain.
5. Name other groups attached to parent chain as usual.
Examples:
CH4 – methane;
CH3CH3 – ethane;
CH3CH2CH3 – propane;
CH3CH2CH2CH3 – butane;
HCOOH – methanoic acid
CH3COOH – ethanoic acid
CH3CH2COOH – propanoic acid
CH3CH2CH2COOH – butanoic acid
Name the following compounds:
CH3CH2CHCH2COOH
CH2ClCH2CH2CHCH2COOH
CH3
3-methypentanoic acid
CH3CH2CH CH2COOH
CH3
3-methyl-2-pentenoic acid
CH3CHCH2COOH
OH
3-hydroxybutanoic acid
CH2CH3
6-chloro-3-ethylhexanoic acid
CH2 CBrCH2CHCH2COOH
CH3
5-bromo-3-methyl-5-hexenoic acid
CH3C
CClCOOH
OH
2-chloro-3-hydroxy-2-butenoic acid
Common names
of carboxylic
acids
IUPAC method is
not the most used
method for naming
carboxylic acids
Common names are
used more often
Carboxylic acids
with even number
of carbon atom
(from 4 to 36
carbon atoms) –
fatty acids
Nomenclature of carboxylic acids using Greek alphabet
Greek letter , , , , …. are used to name certain derivatives of
carboxylic acid.
The carbon atom adjacent to the carboxyl group is labeled , the next - …
Attention: when numbers are used
(IUPAC system), the numbers begin with
the carbon in the COOH group.
C
-hydroxybutiric acid
2-hydroxybutanoic acid
-aminopropionic acid
2-aminopropanoic acid
-chloropropionic acid
3-chloropropanoic acid
Write formula for the following:
3-chloropentanoic acid
CH3CH2CHClCH2COOH
2-methylpropanoic acid
CH3CHCOOH
CH3
-hydroxybutyric acid
-chlorocaproic acid
HO CH2CH2CH2COOH
CH3CH2CH2CHClCH2COOH
phenylacetic acid
CH2COOH
cyclohexanecarboxylic acid
COOH
Physical properties of carboxylic acids
 Carboxylic acid – polar molecule (-COOH group and hydrocarbon chain)
 formic, acetic, propionic and butyric acids are completely soluble
 5-8 carbons carboxylic acids are partially soluble
 containing more than 8 carbons are insoluble
 Carboxylic acids form hydrogen bonds (have high boiling point)
 Saturated carboxylic acids having less than 10 carbon atoms
are liquids, more than 10 – waxlike solids
 In water carboxylic acids can dissociate (can cause acidosis)
Classification of carboxylic acids
1.Saturated (contain only single bonds)
2.Unsaturated (contain one or more carbon-carbon
double bonds)
-Monounsaturated
-Polyunsaturated
Unsaturated carboxylic acids can undergo the reactions
of unsaturated hydrocarbons (for example, addition
reactions)
 The more double bonds in carboxylic acids the more
liquid this acid
 Plant oils contain unsaturated carboxylic acids
Oleinic, linolic,
linolenic and
arachidonic
unsaturated
carboxylic
acids are
essential for
living organisms
These acids are
building blocks
for biological
membranes
Unsaturated
fatty acids
can be in –cis
and –trans
forms
Monounsaturated
carboxylic acid
Polyunsaturated
carboxylic acid
Classification of carboxylic acids
1. Aliphatic carboxylic acids (straight chain)
2. Aromatic carboxylic acids (contain benzene ring)
The parent compound is benzoic acid
Carboxyl group –COOH is bonded directly to a carbon in
aromatic ring
Classification of carboxylic acids
1.Monocarboxylic acids (one carboxylic group)
2.Dicarboxylic acids (two carboxylic groups)
3.Polycarboxylic acids (more than two carboxylic groups)
Selected dicarboxylic acids
IUPAC naming of dicarboxylic acids
The IUPAC names for dicarboxylic acids are formed by
adding the suffix –dioic acid to the name of
corresponding hydrocarbon.
O
C
HO
C
O
O
HO
OH
HO
C CH2 CH2 C
butanedioic acid
OH
propanedioic acid
ethanedioic acid
O
C CH2 C
O
O
OH
O
C CH CH
C
HO
O
OH
butenedioic acid
Significance of polycarboxylic acids
Oxalic acid:
-is included into different vegetables and plants;
-it is used in chemical industry (in the manufacturing of
leather)
Malonic acid:
-is used for the drug (barbiturates) production;
-precursor for the synthesis of fatty acids
Succinic, fumaric and citric acids:
-are metabolites of the citric acid cycle (Kreb’s cycle)
Citric acid:
is widely distributed in
plants (citrus fruits) and
animal tissue
Hydroxy acids
Contain functional groups of both a carboxylic acid and
alcohol
Lactic acid –
the end
product of
glycolysis in
cells
Salicylic acid –
precursor for
many drugs
(pain and
inflammation
relievers)
Amino acids
Amino acids – carboxylic acids containing amino group

Usually amino group is
located on carbon atom
Amino acid is amphoteric compound because it has
carboxyl group which can act as acid and amino group
which can act as a base
Amino acids are building blocks of proteins
There are 20 main amino acids including into the protein
structure
Chemical properties of carboxylic acids
1. Substitution reactions
 Carboxyl group is involved in substitution reactions
 Group –OH can be replaced by another group or atom
(halogens (-Cl, -Br); acyloxy group (-OOCR); an alkoxy group
(-OR))
a) Acid chloride formation
Thionyl chloride (SOCl2) reacts with carboxylic acids to
form acid chlorides. Chlorine atom replaces –OH group
b) Acid anhydride formation
Anhydride is formed by the elimination of a molecule
of water from two molecules of carboxylic acids
Acetic anhydride is the most commonly used anhydride
(can be prepared by the reaction of acetyl chloride with
sodium acetate)
Acetic anhydride is very reactive and can be used for
synthesis of esters and amides
c) Ester formation
Esters are formed by the reaction of an acid and an
alcohol or a phenol. The molecule of water is eliminated.
Such type of
reaction is
called
esterification
2. Acid-base reactions
Carboxyl group is acidic group (group –OH can donate
protons)
As acids carboxyl acids can react with basis
Carboxylic acids:
1. Have sour taste
2. Change colors of different indicators
3. Form water solution with pH less than 7
4. Undergo neutralization reaction with bases to form
water and a salt
ESTERS
General formula: RCOOR’
R – alkyl group or aryl (aromatic) group or hydrogen
R’ - alkyl group or aryl (aromatic) group
R’ can not be hydrogen
Esters are alcohol derivatives of carboxylic acids
Nomenclature of esters
1. In ester recognize the portion that
comes from the acid and the portion
that comes from the alcohol
2. Replace the –ic ending of carboxylic acid by –ate
(ethanoic acid - ethanoate or acetic acid - acetate)
3. Name the alcohol part R’ in R’O (for example: methyl,
ethyl, propyl etc)
4. The alcohol part is named first
followed by the name of carboxylic
acid (for example: methyl
athanoate or methyl acetate)
The ester formed from propanoic acid and
methanol:
methyl propanoate
(methyl propionate)
Esters of aromatic
acids are named in the
same way as those of
aliphatic acid
isopropyl benzoate
Many esters have a specific fruity odor
isopentyl ethanoate
(isopentyl acetate)
ethyl butanoate
(ethyl butyrate)
isobutyl methanoate
(isobutyl formate)
octyl ethanoate
(octyl acetate)
2-hydroxymethylbenzoate (methyl
salicylate)
Name the following esters:
propyl methanoate
ethyl benzoate
O
C O
phenyl benzoate
diethyl malonate
O
CH2 CHC OCH3
methyl propenoate
Name the following esters:
methyl propanoate
dimethyl succinate
methyl
benzoate
phenyl ethanoate
(phenyl acetate)
methyl
salicylate
Physical properties of esters
 colorless nonpolar liquids or solids
 don’t form hydrogen bonds to themselves
(low boiling point)
 up to 10 carbons - volatile liquids with specific
odors (fruity)
 high-molar-mass esters are solid (waxes)
 nonpolar - good solvents for organic compounds
Using of esters
 have odors - flavoring agents
 good solvents for organic
compounds - in paints, varnishes,
and lacquers
 high-molar-mass esters (16 or
more carbons) are waxes - in
furniture wax and automobile wax
preparation
 polyesters - in the textile
industries
Polyesters
are formed by ester linkages between carboxylic acids that have
more than one carboxyl group and alcohols that have more than one
hydroxyl groups
Linear polyesters usually are obtained from dicarboxylic acid
p-phthalic acid and 1,2-ethanediol (ethylene glycol)
Using: production of fibers or transparent films of great strength
(synthetic textile, plastic bottles)
tricarboxylic acids + alcohols that have three
hydroxyl groups = cross-linked polyesters
Such polyesters are thermostable
Example: glycerol can react with o-phthalic
acid
The polymer formed - alkyd resin
Using: coating industry
Chemical properties of esters
Hydrolysis
Hydrolysis – splitting of molecule through the
addition of water
Types of hydrolysis:
- acid
- alkaline
- enzymatic (in living systems)
Acid hydrolysis
Is catalyzed by strong acid (H2SO4, HCl)
Alkaline hydrolysis (saponification)
Saponification – hydrolysis of ester by a strong base
(NaOH or KOH) to produce alcohol and salt
C
The carboxylic acid may be obtained by reacting the salt
with a strong acid
C
Glycerol Esters
Esters of glycerol and long chain tricarboxylic acids (fatty
acids) are called fats or oils or triacylglycerols or
triglycerides
Each molecule of triacylglycerols consist of one molecule of
glycerol and three molecules of fatty acids
There can be different triacylglycerols:
 different length of fatty acid chain (4 to 20 carbons). The number of
carbons in chain is usually even
 fatty acid may be saturated, monounsaturated and polyunsaturated
 may be the same fatty acids or different fatty acids
The most abundant saturated fatty acids are palmitic and stearic
fatty acids
The most abundant unsaturated fatty acids are 18 carbon chain acids oleic, linolic and linolenic
Triacylglycerols are the main form of energy storage in the body
 Oils contain greater amount of unsaturated fatty acids
 fats contain larger proportion of saturated fatty acids
 Fats are obtained from animal sources;
 oils are obtained from plant sources
Fatty acid composition of fats and oils
Hydrogenation of triacylglycerols
Hydrogenation – addition of hydrogen (addition reaction)
Unsaturated fatty acids contain double bonds therefore
hydrogen can be added to such fatty acids
 Using: production of solid fats from vegetable oils
- hydrogen gas is bubbled through hot oil
- catalyst - nickel
- the double bonds are saturated and solid fats are formed
The products can be used for cooking and baking, for making
margarine
Hydrogenation improves the keeping qualities of oils
Hydrogenolysis of triacylglycerols
Hydrogenolysis – splitting by hydrogen
 triacylglycerol react with hydrogen
 a molecule of glycerol and three molecules of
primary alcohols are yielded
 catalyst - copper chromite
 high temperature and high pressure are required
Hydrolysis of triacylglycerols
Splitting of triacylglycerols with participation of water
Hydrolysis of triacylglycerols
requires:
- acids
- alkalines and high temperature
- enzymes in room temperature
Enzymatic hydrolysis:
- in digestive tract and
adipose tissue
- enzyme – lipase
Acid or enzymatic hydrolysis
Fatty acids and glycerol are yielded
Saponification of triacylglycerols
 Saponification – alkaline hydrolysis of triacylglycerols
 Glycerol and sodium or potassium salts of fatty acids
are formed
 Such salts are called soaps
Soaps and synthetic detergents
Difference between soap and synthetic detergent - chemical
composition (functions or usage are the same)
Soaps - salts of long-chain fatty acids
How a soap works?
-Sodium or potassium salts of fatty
acids dissociates in water (Na+, K+
and anions RCOO- are formed)
-RCOO- is amphiphilic molecule
-The hydrophobic end, R-, is soluble
in oils; hydrophilic, -COO-, is soluble
in water
-The hydrophobic end is dissolved in
grease
-Carboxylic groups are exposed on
the grease surface
-Carboxylic groups are attracted by
water, small droplets are formed, and
grease is lifted from soiled object
Hard water contains ions of calcium and magnesium
Ca2+ and Mg2+ form insoluble salts with carboxylic acids
Soaps are ineffective in hard water
In acidic solution anions of fatty acids react with protons
and water insoluble fatty acids are formed
Soaps are ineffective in acidic solutions
Synthetic detergents
Anionic detergents
Representatives of anionic
detergents:
-Sodium lauryl sulfate
-Sodium p-dodecylbenzene
sulfonate
Has a long hydrocarbon chain that is soluble in grease and a
sulfate group that is attracted to water
Advantage over soaps: their calcium and magnesium salts
are soluble in water (effective in hard water)
Cationic detergents
Nonionic detergents
LIPIDS
Lipids do not have the common chemical
structure
Distinctive characteristic - solubility behavior
Lipids - biomolecules that are insoluble in water
and highly soluble in organic solvents such as
chloroform, methanol, diethyl ether
The main elements – carbon and
hydrogen
Can contain oxygen, phosphorous
and nitrogen
Lipids - essential components of
living organisms
Functions of lipids
 Energetic role (fuel molecules)
 Structural role (components of membranes)
 Protective role (surround important organs)
 Regulatory role (prostaglandins, precursors
for steroids hormones)
 Vitamins (vitamin A, D, E, K - derivatives of
lipids)
 Insulation against temperature extremes
The most of lipids are esters of fatty acids and
different alcohols (glycerol, cholesterol etc)
Fatty acids
Fatty acids – biomolecules containing a
carboxyl functional group (-COOH) connected
to an unbranched aliphatic chain
Fatty acids - carboxylic acids with long carbon
chain
CH3-(CH2)14-COOH (palmitic acid)
General formula - R-COOH (R - hydrocarbon
chain)
Carboxyl groups are ionized at
neutral pH - hydrophilic
Hydrocarbon chain – hydrophobic
The molecule of fatty acid amphiphilic
Number of carbon atoms -from 4
to 36
Usually fatty acids contain an
even number of carbon atoms
(between 14 and 24)
Most common 16 and 18 carbon
atoms (palmitic and stearic)
Hydrocarbon
chain is
unbranched
Fatty acids can
contain one or
more double
bonds
If more then one
double bond is
present they are
not conjugated,
but are separated
by methylene unit
• Fatty acids (FA) differ from one another in:
(1) Length of the hydrocarbon tails
(2) Degree of unsaturation (double bond)
(3) Position of the double bonds in the chain
Classification of fatty acids
according to degree of unsaturation
• Saturated FA - no C-C double bonds
• Unsaturated FA - at least one C-C double bond
-Monounsaturated FA - only one C-C double bond
-Polyunsaturated FA - two or more C-C double bonds
Nomenclature of fatty acids
IUPAC nomenclature: carboxyl carbon is C-1
Common nomenclature: C-2 - ,C-3- ,,,...
Carbon farthest from carboxyl group - w
Double bonds in
fatty acids
• Unsaturated fatty acids
may be either cis- or
trans- isomers
• Trans- isomer is almost a
linear
• Cis- configuration
introduces the kink into
the fatty acid structure
• In nature double bonds
are usually cis• Kinked fatty acids can
not stack together and
hence do not solidify
easily
Nomenclature of fatty acids
•Shorthand notation example:
18:3D9,12,15 - linoleate
(total # carbons : # double
bonds, Ddouble bond positions)
Another method:
omega plus a number indicate
the location of the first
double bond, counting from
the w carbon
(linoleate – w-3)
• Unsaturated fatty acids have lower melting points than saturated
of same length
• Shorter chains have lower melting points than longer chains
• Short chain length and unsaturation enhance the fluidity of
fatty acids
Significance of unsaturated
fatty acids
Unsaturated fatty
acids – linolic,
linolenic and
arachidonic – are
essential for animal
nutrition
Lack of these fatty
acid in diet –
dermatitis,
retardation of
growth, disorders of
reproduction
Eczema may be result from
diet lacking essential
unsaturated fatty acids
• Arachidonic acid is a precursor of eicosanoids
• Eicosanoids have hormone-like activities
Subclasses:
- prostaglandins
- thromboxanes
- prostacyclins
- leukotrienes
Arachidonic acid
Prostaglandins (were first isolated from prostate
gland)
 distributed in all organs and tissues
 take part in the generation of inflammation, fever and
pain associated with injury and diseases
 aspirin, ibuprofen, naproxon decrease pain, fever, and
inflammation by inhibiting the synthesis of prostaglandins
Thromboxanes (were first isolated from blood platelets)
 stimulate platelet aggregation, blood clot formation
Leukotrienes (were first extracted from white blood
cells leucocytes)
 cause smooth-muscle contraction especially in bronchi
 cause allergic reactions, asthmatic attacks
Classification of lipids
LIPIDS
Simple lipids
Triacylglycerols
(neutral fats)
Waxes
Compound (conjugated) lipids
Phospholipids
Glycolipids
Sphingolipids
Steroids
Miscellaneous
lipids (fat
soluble vitamins,
lipoproteins)
Triacylglycerols
(fats and oils)
• Triacylglycerols are esters
of glycerol and fatty acids
The “R” can be either long-chain
saturated or unsaturated
hydrocarbon groups
All fatty acids are
saturated
One fatty
acid is unsaturated
(kink is formed)
 Fats may be considered to be triesters formed from
the glycerol and three molecules of fatty acids
 The three R groups are usually different
 TGs are the storage of energy in organism
 Oxidative metabolism of fats gives twice as much energy
per gram as for carbohydrates or proteins
 TGs are very hydrophobic, and are stored in cells in an
anhydrous form (e.g. in fat droplets)
 TGs isolated from animals
are called neutral fats
 are solid in room
temperature
 contain predominantly
saturated fatty acids
 TGs from plant seeds are
called oils
 are liquids in room
temperature
 contain mainly unsaturated
fatty acids
Waxes
• Waxes - nonpolar esters of longchain fatty acids and long chain
monohydroxylic alcohols
• Waxes are very water insoluble and
high melting
• They are widely distributed in
nature as protective waterproof
coatings on leaves, fruits, animal
skin, fur, feathers and
exoskeletons
The “shine” on these
leaves is due to a thick,
protective wax coating
Myricyl palmitate, a wax
Compound Lipids: Phospholipids
Class of lipids containing the residue of phosphoric acids
Phospholipids also contain one or more fatty acids,
alcohol and usually nitrogenous base.
Glycerophospholipids (contain alcohol glycerol) – the
most common phospholipids
H2C
O
fatty acid
hydrophobic
HC
O
fatty acid
H2C
O
phosphate + nitrogen base
hydrophilic
The foundation molecule for glycerophospholipids is
phosphatidic acid
Fatty acids with 16 and 18 carbon atoms are most
prevalent
Saturated fatty acid
is usually attached to
C1, unsaturated – to
C2
Phosphatidic acid is a
key intermediate in the
biosynthesis of
triacylglycerols and
phospholipids
Free hydroxyl group of phosphoric acid is
esterified with hydroxyl group of nitrogenous
base
Nitrogenous bases:
amino alcohols ethanolamine, choline, or amino
acid serine
Phosphatidyl choline (lecithin)
glycerol ester of fatty acids, phosphoric acid and
choline
 the most important membrane component (amphipathic
molecule)
 digestible emulsifying agent (in food industry –
chocolate and margarine production)
Phosphatidyl ethanolamine (cephalin)
glycerol ester of fatty acids, phosphoric acid and
ethanolamine
 membrane component
Compound Lipids: Sphingolipids
compound lipids containing the alcohol sphingosine
Sphingosine - amino alcohol that contains a long unsaturated hydrocarbon chain
Sphingomyelin
 amino group of sphingosine backbone is linked to
a fatty acid by an amide bond
 the primary OH group of sphingosine is
esterified to phosphorylcholine
Sphingomyelin
is found in cell
membranes
especially in
myelin
membranes
Compound Lipids: Glycolipids
compound lipids containing carbohydrate group
The most important glycolipids are cerebrosides and
gangliosides
Cerebrosides contain
a single sugar residue
(glucose or galactose
attached)
Gangliosides contain
oligosaccharides
Function: abundant in
the membranes of the
brain and nervous
system
Steroids
Steroids – compounds containing the
characteristic four fused ring systems: 3-six
carbon rings and a 5-carbon ring (17 carbon atoms)
Cholesterol
 is the best known steroid
 has hydroxyl group and long hydrocarbon tail
and double bond
Functions:
 component of the cell
membranes
 precursor of the
steroid hormones (sex
hormones and adrenal
cortex hormones), bile
salts, vitamin D
Structures of several steroids
ATHEROSCLEROSIS
metabolic disease that leads to deposits
of cholesterol and other lipids on the
inner walls of the arteries
 plaque
accumulates,
 the arterial
passages become
progressively
narrower
 artery
thrombosis
(heart attack,
stroke)
The causes atherosclerosis: high level and improper transport
of cholesterol through the blood
Cholesterol and other lipids are insoluble in water and must be
packaged for transport in spherical particles called
lipoproteins
The surface of
lipoproteins contains
a layer of
phospholipids and
proteins, while the
core contains
hydrophobic
triacylglycerols and
cholesterol
There are different kinds of lipoproteins.
Low-density lipoproteins (LDL) deliver cholesterol to
peripheral tissues
People with high-plasma LDL concentrations are prone
to atherosclerosis
High-density
lipoprotein (HDL)
acts as a
cholesterol
scavenger by
collecting
cholesterol and
returning it to the
liver – prevents
the development
of atherosclerosis