Green Chemistry

Table of Contents

Introduction to Green Chemistry

We know that increasing population, has increased the use of fossil fuels and increasing number of industries and vehicles are polluting our environment to an alarming extent. The increase in pollution adversely affects the health of humans and other living organisms. It is believed that the advancement and modernization of our society is inducing certain types of cancers for our future. These pollutants are being added in air, in water, in our food supply and in soil. As we know self-sufficiency in food has been achieved in India since late 20th century by using fertilizers and pesticides and developing improved methods of farming, good quality of seeds, irrigation etc. But over exploitation of soil and excessive use of fertilizers and pesticides have resulted into deterioration of soil, water and air.

Symbol Promoting Green Chemistry Fig – Symbol Promoting Green Chemistry

With the growing awareness of the environmental pollution, the international community is under increasing pressure to find methods to save our lives from the increasing pollution. This does not mean that we should stop the process of advancement that has been set in but to search methods which would help in reduction of pollution of our environment. The scientists are searching new alternatives which do not cause environmental pollution. This new approach is called Green Chemistry which was introduced in early 1990s. It means zero discharge of toxic, persistent substances, into the environment guaranteed by the fact that they are never produced. Green chemistry may be defined as a strategy to design chemical processes and products that reduces or eliminates the use and generation of hazardous substances.
This hazards include toxicity, physical hazards (Example: Explosions, Fires), global climate changes, resource depletion. In other words, green chemistry aims to virtually eliminate toxic, persistent substances from the environment by ensuring their no further releases and destroying existing deposits of these chemicals. So, green chemistry means environmental friendly or no pollution. For Example, we have been using organic solvents as a media for many reactions. Now, scientists are planning greener alternative to use water or nonpolluting solvents as a medium in place of organic solvents. Similarly, instead of using synthetic materials for packing, green chemistry plans to use environmental friendly recyclable or safely disposable materials.

Aims of Green ChemistryFig – Aims of Green Chemistry 

Green chemistry also requires change in our habits and life-style. These days many green products are available in the market in developed countries. The Royal Society of Chemistry informs the scientists working in different fields about the latest developments in green chemistry revolution.

Basic Aims of Green Chemistry

The basic aims of green chemistry are:

(i) Reformulation of synthetic routes so that hazardous substances do not enter into the atmosphere.

(ii) During synthesis, care must be taken to select starting materials that can be converted into end products with all most 100% yield. This can be achieved by arriving at optimum conditions of synthesis.

(iii) The methods used to obtain starting materials e.g. Mining, refining, etc. should have minimum impact on the natural environment.

(iv) New routes for the production of green chemicals and materials.

(v) The development of environmentally improved methods for the existing industrial processes. The material inputs should be of low or no toxicity or at least reduced toxicity compared with the traditional method.

(vi) The use of starting materials-reagents and solvents that pose less hazard to man and his environment.

(vii) The synthetic reactions may preferably be carried out in aqueous medium because water has high specific heat and low volatility. Water is cost effective, non-inflammable and does not have any carcinogenic effects.

(viii) The raw materials and methods should produce less waste to avoid their treatment and problem of disposal.

(ix) The use of renewable rather than depleting resources wherever possible.

(x) The use of biotechnological alternatives.

(xi) New methods and tools for evaluating environmental impact.

(xii) The awareness among common man to use green products.

Achievements of Green Chemistry

Since the inception of green chemistry, scientists from all over the world are using the creative and innovative skills to develop new synthetic methods, new processes, analytical tools, reaction conditions, catalysts, etc. So, green chemistry prevents problems before they occur by designing new approaches. Green chemistry considers the full life cycle impacts of a product at the initial design stage. A lot of success has been achieved in developing new techniques. Some of these are:

(i) Consider the production of hexanedioic acid which is used for the manufacture of nylon 66. The most common process is petroleum derived benzene as the starting material. The last step for the synthesis of hexanedioic acid requires oxidation by nitric acid resulting nitrous oxide as a byproduct. Nitrous oxide released in the atmosphere causes air pollution. Recent green chemistry research has developed a new method known as Draths-Frost synthesis of hexanedioic acid. In this method hexanedioic acid is obtained by genetically engineered microbe from glucose. This method prevents air pollution by nitrous oxide. Glucose has the further advantage of being a renewable feed stock and the process materials are of no toxicity.

Process of formation hexanedioic acid using GlucoseFig – Process of formation hexanedioic acid using Glucose

(ii) Ibuprofen is a non-steroidal anti-inflammatory drug and for synthesizing this drug a new method has been developed using Green Chemistry which has a yield about 99%. This method avoids the use of large quantities of solvents and wastes associated with traditional stoichiometric use of auxiliary chemicals during chemical conversions.
Structure of Ibuprofen

Fig – Structure of Ibuprofen

(iii) For manufacture of polystyrene foam sheet packaging materials, the process of carbon dioxide as the blowing agent was developed. This method does not use conventional process chlorofluorocarbon blowing agents which contribute to ground level smog, global warming and ozone depletion.

(iv) A new technique for catalytic hydrogenation of diethanolamine was developed. This method allows the production of environmentally friendly herbicide in a less dangerous way. This technology does not use cyanide and formaldehyde and represents a major breakthrough in green chemistry. This technique is safer to operate, produces high overall yield and has less steps for the process.

(v) A safer marine antifouling compound ‘sea-nine’ was designed. It degrades far more rapidly than organotin which persist in the marine environment and cause pollution problems.

Green Chemistry in Day-to-Day Life

Some common examples of green chemistry in our day-today life are:

Dry cleaning of clothes

Earlier compound called Tetrachloroethene (Cl2C = CCl2) also known as was used as solvent for dry cleaning, which use to act as a carcinogen to environment and as contaminant to ground water. The current technology uses liquefied carbon dioxide along with suitable detergent. Replacement of hydrogenated solvent by liquid CO2 will result in less harm to ground water.
Conventional Process of Dry Cleaning

Fig – Conventional Process of Dry Cleaning

Similarly, hydrogen peroxide (H2O2) is used for the purpose of bleaching clothes in the process of laundry. This gives better results and makes use of less water, therefore, saving a lot of water. It is also not harmful.

Bleaching of paper

Toxic chemicals like Chlorine gas were used earlier for bleaching paper. But the latest technology now uses hydrogen peroxide with a suitable catalyst which promotes the bleaching action of hydrogen peroxide.

Synthesis of Chemicals

Ethanal (CH3CHO) is commercially prepared nowadays by one step oxidation of ethene in the presence of ionic catalyst in aqueous medium:
Synthesis of chemicals

The yield is about 90.0%.

Thus, we can say that green chemistry is a cost effective approach which involves reduction in material, energy consumption and waste generation.

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