20.4 – Condensation Reactions
20.4.1 – Describe, using equations, the reactions of alcohols with carboxylic acids to form esters, and state the uses of esters
Esters are formed in the reaction of carboxylic acids and alcohols, producing a small water molecule as a by-product. Hence, it is called a condensation reaction. The -OH group on the carboxylic acid is replaced with an -OR group from the alcohol.
This is a reversible reaction. It is catalysed by acid because it removes water, shifting the equilibrium to the right. Esters usually have a sweet smell.
20.4.2 – Describe, using equations, the reactions of amines with carboxylic acids
Amides are formed in the reaction of carboxylic acids and amines.
However, it is difficult to produce amides by this method because the basic amine tend to convert the acid into its RCOO– ion. Therefore, an acyl chloride – RCOCl – is often used instead.
20.4.3 – Deduce the structures of the polymers formed in the reactions of alcohols with carboxylic acids
Polyester is produced by the reaction of ethan-1,2-diol and benzene-1,4-dicarboxylic acid. Each of these monomers has two functional groups, allowing for the formation of long chains.
The carbonyl groups create strong dipole-dipole attractions between molecules, causing polyester to be very strong.
20.4.4 – Deduce the structures of the polymers formed in the reactions of amines with carboxylic acids
Amino acids, which make up proteins, have both a carboxylic acid group and an amino group, which allows them to react together in an acid-base reaction.
The presence of the two functional groups on the monomer allows them to form polymers called polypeptides. Water is produced as a by-product.
These condensation reactions continue so that long chains are formed.
A synthetically-produced polyamide is nylon.
These chains can then form cross-links through hydrogen bonding, increasing its strength.
20.4.5 – Outline the economic importance of condensation reaction
The polymers formed in condensation reaction have many commercial applications.
Polycarbonates are used in bulletproof windows due to their strength. Polyurethanes are used as foam rubber. Nylon is used in women’s stockings, carpet, parachutes, rope, tents, and countless other products. It is the most commonly used polymer in the world. Kevlar® is a polyamide that is used in bulletproof vests, fire-protective clothing, tennis racquets and boats. Polyester is used in cords, carpets, patches to repair human arteries, yacht sails and parachutes.
Other condensation polymers are used for their strength, electrical conductivity and light weight. They are used in replacement body parts and construction of vehicles.
However, many polymers are derived most petroleum or natural gas, which are non-renewable resources. This means that, in the future, alternative starting materials will need to be found