Carboxylic AcidsCarboxylic acids with up to 4 carbon chains are soluble in water. Highly polar C=O and O-H bonds allow the carboxylic acid molecules to form hydrogen bonds with polar water molecules. Solubility decreases as the number of carbon atoms increases. This is because longer hydrocarbon chains of the molecules do not form hydrogen bonds with water – they are hydrophobic. They prevent the formation of hydrogen bonds between water and hydrophilic carboxylic acid functional group.

:

δ+

δ-

δ+

δ-

Reactions of Carboxylic Acids

Acid + Base Carboxylate Salt + Water

Acid + Metal Carboxylate Salt + Hydrogen

Acid + Carbonate Carboxylate Salt +Water +Carbon Dioxide

EstersEsters contain the functional group ‘COOC’. They are formed in esterification reactions. Esterification reactions are condensation reactions because water is released. There are 2 ways in which an ester can be formed: 1. Carboxylic Acid + Alcohol Ester + Water

2. Acid Anhydride+ Alcohol Ester + Carboxylic Acid

+ +

Example: Propanoic Acid + Ethanol Ethyl Propanoate + Water

Example: Butanoic Anhydride + Ethanol Ethyl Butanoate + Butanoic Acid

Conc. H2SO4 Reflux

Warm

+ +

Hydrolysis of Esters Hydrolysis uses water to split an ester. It is the reverse reaction of

esterification.

Ester + Water Carboxylic Acid + Alcohol

1. Acid Catalysed Hydrolysis - Reflux, Sulphuric Acid (Hot Aqueous Acid)

2. Alkaline Catalysed Hydrolysis[Reflux, Sodium Hydroxide(Hot Aqueous Alkali]

Ester + Hydroxide Carboxylate Salt+ Alcohol

+ +

Ethyl Propanoate + Water Propanoic Acid + Ethanol

This reaction occurs in 2 steps: the ester is hydrolysed with water from NaOH (aq) and then the acid is neutralised by the alkali to produce the salt.

Triglycerides Animal and vegetable fats and oils are esters of long chain carboxylic acids. The simplest is a triester known as a triglyceride. Triglycerides are triesters of glycerol and fatty acids.

Glycerol is an alcohol– its

systematic name is propane-1,2,3-

triol

Fatty acids are long change carboxylic acid. Fatty acids can be saturated (containing C-C single bonds only) or unsaturated (containing at least one C=C double bond)

+

Triglyceride

+ 3 H2OTriglycerides are

formed in condensation

reactions – when each fatty acid joins

to the glycerol molecule, 1 water

molecule is release – so 3 are produced in

total.

Triglycerides can be saturated or unsaturated:

Saturated fats are triglycerides containing only carbon-carbon single bonds.

Saturated fats are derived from fatty acids that are saturated -containing single C-C bonds only

Saturated fats tend to be solid at room temperature because they have stronger intermolecular forces between molecules which require more energy to break and so they have a higher melting point.

Animal fats are rich in saturated fatty acids

Unsaturated fats are triglycerides containing at least 1 carbon=carbon double bond.

Unsaturated fats are derived from fatty acids that are unsaturated - containing at least one C=C double bond.

Unsaturated fats tend to be oils at room temperature because they have weaker intermolecular forces between molecules which require less energy to break and so they have a lower melting point.

Vegetable fats are rich in saturated fatty acids

Foods high in saturated fats are known to increase the risk of heart disease by raising blood cholesterol levels.

Unsaturated fats are often believed to be better for us than saturated fats. Unsaturated fats however can exist in 2 isometric forms: cis and trans.

Trans fats are thought to behave like saturated fats in the body: they raise Low

Density Lipoprotein levels and so increase the risk of coronary heart

disease and strokes.

Lipoproteins are particles that carry lipids, such as cholesterol and fats, through the blood. High Density Lipoproteins (HDLs) are ‘good’ lipoproteins – they transport cholesterol out of the bloodLow Density Lipoproteins (LDLs) deposit lipids onto the artery wall, building up fatty acids and restricting blood flow.

Making Biodiesel

Biodiesel is made in a process called transesterification: Triglycerides in fats and oils are reacted with methanol or ethanol in the presence of a sodium or potassium hydroxide catalyst. Biodiesel and glycerol are formed:

Biodiesel is easily produced suing waste cooking oil, but naturally sources of suitable oils also occur in crops like palm or soya bean and rapeseed. Soaring oil prices, the non-renewable nature of fossil fuels and the desire to protect the environment have lead to an increase in biodiesel, because it is a renewable source of fuel.

Isomerism

Unsaturated fats can display stereoisomerism. Stereoisomers are molecules with the same structural formula but a different arrangement of atoms in space.

This is dec-4-enoic acid. It can display cis-trans isomerism because: There is restricted rotation

about a C=C double bond There are 2 different atoms or

groups attached to each carbon in the C=C double bond

Two of the substituent groups are the same

There is a difference in melting points of the cis and trans isomers: Trans isomer of the unsaturated fatty acid is more linear Molecules can pack closer together Stronger Van der Waals’ intermolecular forces More energy required to break forces between molecules Trans form has a higher melting point In the cis form, unsaturated fatty acid molecules are more likely to exist

as a liquid at room temperature as they have a lower melting point.