9.5.A - Replacement Products

Industrial chemistry not only produces materials that do not occur naturally, such as plastics and paints, pesticides and pharmaceuticals and chemicals for photography, printing and batteries, but it also produces materials to replace natural substances that have been largely used up or which because of short supply have become very expensive.

The synthesis of ammonia through the Haber Process was developed in response to growing demand for fertiliser and nitric acid and the inadequacy of supplies of Chilean saltpetre (sodium nitrate) to meet these demands. Some other examples of the development of synthetic chemicals to replace or supplement the supply of natural products will be studied in this section.

In this topic students:

  • Identify and outlion the chemistry of some synthetic products that have replaced natural products
  • Analyse reasons why the demand for natural products increased


The molecular structure of styrene-butadiene rubber.

Until the 1940s rubber had been obtained from plantations of rubber trees in tropical areas such as Malaya and Burma. Demand for rubber increased greatly during World War II (needed for tyres of military vehicles) while supplies were interrupted by the conflict. Consequently scientists in Germany and the US developed synthetic polymers that could replace rubber. Even after the war ended the traditional sources of natural rubber could not meet the greatly increased demand, so synthetic rubbers virtually 'took over' the market. Today about 80% of the world's rubber production is synthetic polymers. The most common synthetic rubber is called SBR (styrene-butadiene rubber) which is a copolymer of stryrene and butadiene.



Before the 1950s soap, made from left-over animal fats, was virtually the only available cleaning agent. However, with increasing world population increasing the demand for these fats for food, the manufacture of natural soap could not keep up with its growing demand. Consequently synthetic detergents were developed and eventually became the dominant cleaning agents: soap is now mainly used just for personal hygiene. Another factor in the rise in importance of synthetic detergents was the ready availability (as by-products from petrol refining) of starting materials.



Synthetic fabrics dominate the
market over wool and cotton.

Until the 1950s wool was one of the two major fibres used for clothing and textiles (cotton was the other). When demand increased after World War II as a result of increased population, growing affluence and increasing defence forces worldwide, supply was unable to keep up. Wool prices escalated dramatically and so synthetic substitutes became more competitive, especially as increasing oil refining was producing increasing amounts of starting materials for synthetics at decreasing prices. Eventually the synthetic fibres, polyester, acrylics and nylon, came to dominate the market. Today wool has become a 'specialty' rather than a common fibre.


Why Use Replacement Products

The key issues that lead to a natural product being replaced by a synthetic one are:

  • Increasing demand for the product, even if only temporarily.

  • Inability of the natural sources to keep up with demand, even if only temporarily.

  • Depletion of the natural resources (such as Chile saltpetre).

  • Competition for the natural resource from another use (fats for food, not soap).

  • Escalating prices for the natural product, often a result of resource depletion.

  • Increasing availability and/or decreasing cost of starting materials for the synthetic product.

  • Decreasing price for the synthetic product as quantities produced increase.

  • Greater reliability of supply and stability of price for the synthetic product (without the vagaries of weather).

The need to replace products or materials originally obtained from natural resources with ones made synthetically (from more readily available resources) will continue, because the human population is increasing, its level of consumption per person is increasing and natural resources currently in use are being depleted at significant rates.