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.
Carboxylic acids found in nature include citric acid and
ascorbic acid (Vitamin C) are both citrus in 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 rhubarb leaves - which you
shouldn't eat, this acid is poisonous!
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.
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
I've already described many uses of
esters
on
Esters, chemistry and uses including perfumes, solvents
or
