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Advanced Level Organic Chemistry: The uses of carboxylic acids and their derivatives

Part 6. The Chemistry of  Carboxylic Acids and their Derivatives

Doc Brown's Chemistry Advanced Level Pre-University Chemistry Revision Study Notes for UK KS5 A/AS GCE IB advanced level organic chemistry students US K12 grade 11 grade 12 organic chemistry

6.14 The uses of carboxylic acids and derivatives and their occurrence in nature

INDEX of all My carboxylic acids and derivatives notes

All My Advanced A Level Organic Chemistry Notes

Index of My GCSE/IGCSE basic organic chemistry notes

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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.

The fatty acids may be saturated (no C=C double bonds) or unsaturated (with at least one C=C double bond) in the carbon chain.

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 + H2

+ 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.

molecular structure of vitamin C ascorbic acid displayed formulaThe 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.

CITRIC ACIDCitrus 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).

skeletal formula of citric acid molecular structure of a tribasic acid advanced organic chemistry notesCitric 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.

molecular structure of 2-hydroxybutanedioic acid structural formula of malic acid advanced organic chemistry notes 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.

skeletal formula for ethanedioc acid oxalic acid doc brown's advanced organic chemistry revision notes 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..

molecular structure of soluble aspirin sodium salt from  +  NaOH  ===>   +  H2O

molecular structure of Paracetamol Ibuprofen Aspirin structural formula doc brown's advanced A level organic chemistry notes 

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 C17H35COONa+, 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

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 structural formula of ethyl 2-hydroxypropanoate ethyl ester of lactic acid cows' milk doc brown's advanced A level organic chemistry revision notes

and ethyl butanoate  structural formula of ethyl butanoate ethyl ester of butanoic acid butyric acid cows' milk doc brown's advanced A level organic chemistry revision notes or  skeletal formula of ethyl butanoate ethyl ester of butanoic acid butyric acid cows' milk doc brown's advanced A level organic chemistry revision notes

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.

 

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.


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 more on this see Esters, chemistry and uses including perfumes, solvents


Doc Brown's Advanced Level Chemistry Revision Notes

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INDEX of all My carboxylic acids and derivatives notes

All My Advanced A Level Organic Chemistry Notes

Index of My GCSE/IGCSE Oil - useful products and basic organic chemistry notes

 

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