Part 6.
The Chemistry of Carboxylic Acids and their Derivatives
6.14 Examples of the uses of carboxylic acids and derivatives and their
occurrence in nature
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Brown's Chemistry Advanced Level Pre-University Chemistry Revision Study
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K12 grade 11 grade 12 organic chemistry uses of domestic and industrial uses
of carboxylic acids
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chemistry of carboxylic acids and derivatives
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6.14 Examples of the uses of carboxylic acids and derivatives and their
occurrence in nature
See also
Part 6.8
Esters
- preparation, reactions including hydrolysis and
transesterification, uses
The uses of carboxylic acids and their
derivatives
A few reminders
The aliphatic homologous series of
carboxylic acids are colourless liquids with very strong odours (pungent
smell) and tastes.
The obnoxious smell of rancid butter and sweaty
socks is due to the formation of carboxylic acids.
It should be mentioned here that carboxylic
acids with long carbon chains are called fatty acids, because they are
combined with an alcohol called glycerol to form large ester molecules
(glycerides/triesters) that
make up most natural oils from plants and fat in animals.
Long chain fatty acids may be saturated (no C=C
double bonds) or unsaturated (with at least one C=C double bond) in the
carbon chain and are associated with triglyceride esters found in animal
fats and vegetable oils.
This page includes links to previously written
material on the uses of carboxylic acids and their derivatives - some of
it is repeated here, but other new material has been added.
Domestic uses of carboxylic acids,
connection with pharmaceuticals, nutrition and the natural world
Vinegar contains ethanoic acid (old name 'acetic acid')
In the chemical industry ethanoic acid can be manufactured on a large
scale by oxidising the alcohol ethanol.
See
in section 9
Oxidation
of the alcohol ethanol
It is used as a
food preservative and in food flavourings.
It is the oxidation of ethanol to ethanoic
acid that results in alcoholic drinks
turning sour (e.g. cider, wine) when exposed to air.
The fruit material
already contains the enzymes that catalyse the oxidation of ethanol
('alcohol') in the presence of air.
ethanol + oxygen ====> ethanoic acid +
water
CH3CH2OH + O2
====> CH3COOH + H2O
+ O2
====>
+ H2O
This reaction occurs if wine, beer or cider
is left out open to the air, it eventually becomes vinegar and not very nice
to drink!, but vinegar is very nice in salad dressings and on your fish and
chips.
Methanoic acid (formic acid), HCOOH, is
found in the sting of ants, its not quite as 'weak' as carboxylic acids are
supposed to be.
Butanoic acid, CH3CH2CH2COOH,
a very smelly acid formed when butter goes rancid.
Carboxylic acids found in nature include citric acid and
ascorbic acid (Vitamin C) both found in citrus fruits.
The
ascorbic acid (vitamin C) present in fresh fruit and vegetables
and is vital for good health AND the body cannot synthesise it, so you
must eat fruit and vegetables regularly!
A lack of vitamin C can cause the
disease scurvy. The symptoms of scurvy are skin sores, spongy gums
and bleeding from mucous membranes. This is one example of malnutrition
diseases caused by a vitamin deficiency in a diet.
Citrus
fruits like oranges and lemons and many soft drinks contain the
tri–carboxylic acid citric acid. and
contribute to the 'tarter' or 'sour' taste of fruit. The molecule contains
three acidic carboxylic acid groups –COOH (molecular structure on the right).
Citric acid is a natural
preservative (E330 on food labels) and is found in the largest
quantities in oranges, lemons, limes and grapefruit.
It is an anti–oxidant.
Metal salts from citric acid, i.e. citrates, are used in dietary
supplements to deliver trace metal minerals in a biologically
available/absorbable chemical form.
(It's a nice little exercise in working out a
skeletal formula!)
Citric acid can be
used in baking powder to react with sodium bicarbonate giving the raising
action from carbon dioxide gas formation.
The same combination can be used
to give the fizzy drink effect in medicines like ant–acid stomach
powders.
Citric acid is made in large
quantities for the food industry, including fizzy drinks – which can
be quite acid – dental concerns about the health of teeth here!
Citric acid is strong enough to be
used in some limescale removers – so think about your teeth when
consuming all those fizzy drinks we might like!
Citric acid is an intermediate compound in the
Krebs cycle in the metabolic chemistry of carbohydrates, fats and
proteins.
2-hydroxybutanedioic acid (Malic acid) is found in apples
and gives the fruit its sharp taste. This molecule will exhibit R/S
stereoisomerism (optical isomers, two non-superimposable mirror
image forms), the 2nd carbon is chiral (asymmetric) with four
different groups attached to it.
Ethanedioic acid ('oxalic acid') is found in the leaves and stems of
rhubarb. It is a harmful acid and a high concentration in the leaves,
which should not be eaten.
However, there is much less in
the stem which is safe and delicious to eat after cooking (with
sugar!).
Aspirin is a carboxylic acid. Aspirin is a
drug used for pain relief and is taken regularly by those at risk from
heart attacks (see also
Drugs).
The molecule is based on an aromatic carboxylic
acid, often used as the sodium salt to make it more soluble..
from
+ NaOH
===>
+ H2O
Note that the benzene rings
shows up in other medications
used for pain and inflammation relief are:
Paracetamol is a secondary amide made from
ethanoylating 4-aminophenol with ethanoic anhydride.
Ibuprofen is an aliphatic carboxylic acid
with an alkyl substituted benzene ring tacked onto the middle carbon
of propanoic acid.
An 'aspirin' related carboxylic acid derived molecule is
C8H8O3,
or , methyl
2-hydroxybenzoate.
Commonly known as methyl salicylate or 'oil of
wintergreen', a molecule that has mild pain killing properties. This
methyl ester of salicylic acid is a colourless, viscous liquid
with a sweet, fruity minty odour and used in mint candies. It is
produced by many species of plants, particularly wintergreens, from
which it can be obtained by distillation. These days it is mostly
manufactured synthetically, by esterifying 2-hydroxybenzoic acid with
methanol, and used as a fragrance and flavouring agent.
Many plants produce methyl salicylate in small quantities, often in
response to biotic stress e.g. infection by pathogens, where it plays a
role in the induction of resistance. Methyl 2-hydroxybenzoate is also
released in some plants when they are damaged by herbivorous insects,
where they may function as a cue aiding in the recruitment of predators.
Some plants produce methyl salicylate in larger quantities to aid direct
defence against predators or pathogens
Incidentally, methyl 2-hydroxybenzoate can exhibit both
intermolecular and intramolecular hydrogen bonding.
Many traditional soaps are made from natural
oils and fats.
Long chain carboxylic acids, known as 'fatty
acids', are used to make soaps and detergents,
originally derived from
plant oils.
Below are some diagrams of the organic molecules or ions involved,
typically with 16 to 20 carbon atoms in the chain.
Diagram S1: The stearic acid molecule
C17H35COOH
or CH3(CH2)16COOH is a typical
long chain fatty acid obtained from naturally occurring plant oils and used
to make traditional soaps.
Diagram S2: The salt sodium stearate C17H35COO–Na+,
formed when stearic acid is neutralised with sodium hydroxide is a
typical soap molecule.
Vegetable oils and animal fats, both saturated and
unsaturated, are made of esters synthesised from long chain fatty acids
and propane-1,2,3-triol (glycerol), so found in most living organisms -
plants and animals.
Vegetable and fish oils contain esters from
unsaturated long chain fatty acids which are supposed to be more healthy
to eat that saturated fatty acids (actually we need both, but not too
much fat !!!).
For more details on glycerides and soaps see
Oils, fats,
margarine and soaps
and
Natural esters - triglyceride fats and oils,
manufacture of margarine and biodiesel
Esters occur in the milk
of animals e.g.
Esters of
2-hydroxypropanoic acid (lactic acid) and butanoic
acid are found in the milk of cows.
Ethyl 2-hydroxypropanoate
and ethyl butanoate
or skeletal formula
An ester of octanoic acid
are found in the milk of goats.
Ethyl butanoate is also found in fruit and is used as a
flavour enhancer in the
food and drinks industry.
I've already described many uses of
esters
on
Esters, chemistry and uses including perfumes, solvents
basic notes for IGCSE/GCSE chemistry students.
For more advanced notes on esters see
Esters
- preparation, reactions including hydrolysis and
transesterification, uses
Amino acids are the main
molecular constituent of protein - the amino acids are
polymerised by forming peptide bonds (a secondary amide
connection) the natural condensation polymer. For more advanced
level notes see
Part 6.13
Amino acids - molecular
structure, preparation and reactions - two functional group chemistries
and Part 8.8
LINKS to all my notes on amino acids, peptides, polypeptides and types
of proteins
Industrial uses of carboxylic acids
Ethanoic
acid is used in the manufacture of the fibre, acetate rayon.
Esters and amides are used in the manufacture of other
fibres and plastics e.g.
The manufacture, molecular structure, properties and uses of
polyesters
Amides
- a brief mention of
polyamides like Kevlar and Nylon
Esters are used in the perfume and food industries for
pleasant aromas and enhancing taste.
For basic notes on this see
Esters, chemistry and uses including perfumes, solvents
For more advanced notes on esters see
Esters
- preparation, reactions including hydrolysis and
transesterification, uses
See also
manufacture of plasticisers in section 6.8.5
See also
Part 6.8
Esters
- preparation, reactions including hydrolysis and
transesterification, uses
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