Green chemistry

The following examples illustrate the ideas of Green Chemistry embodied in the above principles.

Ibuprofen

Ibuprofen is a widely used anti-inflammatory drug. Its synthesis has stimulated the development of many new synthetic routes which tend to conform to the principles of Green Chemistry. The original and the new routes given below clearly demonstrate how resources can be saved by careful planning.

The original Boots method

The new Boots-Hoechst-Celanese Synthesis

The new synthesis avoids MeCOCl, AlCl₃, alkali, acid, ethyl chloroacetate, hydroxylamine, etc., most of which do not form part of the final product. This demonstrates how the original process causes huge amounts of waste generation, resulting in not only cost enhancement, but environmental pollution through wrong use of resources.

In the new method, there is hardly any product that can be considered as waste. The only by-product is acetic acid which can be converted to acetic anhydride. All other chemicals are either catalysts (Raney nickel, PdCl₂-Ph₃P, HF) which are recoverable or reactants that form part of the product (Ac₂O), H₂, CO), and solvents (MEK and others not shown in the equation).

Clay as an acid-catalyst

Clay modified by suitably treating with protic acids or salts of metal ions that act as Lewis acids behaves like an acid. This enables it to be used as an acid catalyst in place of Bronsted acid or Lewis acid in reactions that are catalyzed by such acids, e.g., esterification, ether synthesis, rearrangements, elimination reactions, etc.

The use of clays confers the following advantages, as they are
1. Abundant and easily available
2. Economical
3. Easily modified to bestow them with desired properties
4. Environment-friendly
5. Reusable

To understand the catalytic function of clay, let us very briefly consider the structure. Though there are several classes of clay, a simplified gross structure can be described as given below.

Structure of Clay

The interstitial space contains protons, alkali and alkaline earth metal ions as seen in the structure.. The last two ionic species can be replaced by protons, aluminium, magnesium, nickel, iron, copper, cobalt and many other metal ions. This modification of clay makes it behave like a Bronsted acid or Lewis acid and enables it to be used as an acid catalyst. Because such catalysts can be used repeatedly or regenerated, the chemical waste produced in such reactions will be considerably reduced.