Think ethylene to form ethyl benzene. Then ethyl benzene

Think
it Over!!!

          After studying air, water and
soil pollution, as responsible individuals we must take responsibility to
protect our environment. Think of steps which you would like to undertake for
controlling environmental pollution not only in your locality but also in  national and international level. We must realise about our
environmental threat, focus strongly on this issues and be an eye opener to save our
environment  Efforts
to control environmental pollution resulted in development of science for
synthesis of chemical favorable to environment which is called green chemistry.

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15.10 Green Chemistry

An ideal
chemical process would fully incorporate the reactants into products. There
is no hazardous waste. This
is a ‘clean’ or ‘green’ reaction.
For this scientist are trying to develop methods to produce eco friendly
compounds. The chemistry that developed by such efforts is known as Green chemistry.
It was introduced in 1900’s. In short green chemistry means science of
environmentally favourable chemical synthesis and it was
coined by Paul Anatas of America.

Green Chemistry is the design of chemical products and processes that
reduce or eliminate the use and generation of hazardous substances.

Example:
Production of styrene

Traditional
route

This method involves two steps. Ccarcinogenic benzene
reacts with ethylene to form ethyl benzene. Then ethyl benzene on dehydrogenation using
Fe2O3 / Al2O3
gives styrene.

 Ggreener route

To avoid carcinogenic benzene, greener route is
to start with cheaper and environmentally safer xylenes.

15.10.1
Principles of Green Chemistry

The objective of green chemistry is to promote
research, development, and implementation of innovative chemical technologies
that accomplish pollution prevention in a scientifically sound and cost
effective manner. PaulAnastas of America postulated following principles of
Green Chemistry in 1994.

1.             
Prevention of waste

          It is better not to create waste
rather than treating it after it has been created.

2.             
 Maximize atom
economy

          Synthetic methods should be designed
to convert completely starting reactants into final products and only small
amount of unwanted by products is formed.

3.     
 Less Hazardous Chemical
Syntheses

           Where ever possible synthetic methods should
be designed to use and generate substances that possess no toxicity to human
health and the environment.

 

4       
   Safer
Solvents and Auxiliaries

          The use of auxiliary substances like solvents,
emulsifiers etc. should be made unnecessary wherever possible and if used
should be nontoxic.

 

                  5.        Designing Safer
Chemicals

          Chemical products should be designed
to effect their desired function while minimising their toxicity.

 

6.       Increase
Energy Efficiency

          Energy requirements of chemical
processes should be minimised. If possible, synthetic methods should be
conducted at room temperature and pressure.

 

                  7.       Use of Renewable Feed stocks

          A raw material feedstock should be
renewable rather than depleting whenever technically and economically practical

      8.       Reduce Derivatives

          Unnecessary derivatization like
intermediate compound formation, modification of physical or chemical processes
should avoided or minimised  because such
steps require additional reagents and can produce waste.

 

      9.
      Catalysis

          Catalytic reagents are superior to
stoichiometric reagents.

 

                 10.    Design chemicals and products to degrade
after use

          Chemical products should be designed in
such a way that after their utility is over these should be biodegradable into harmless materials and do not persist in
environment.

 

      11.     Real-time
analysis for Pollution Prevention

          Analytical methods need to be
developed further to allow for real-time, in process monitoring and control
prior to the formation of toxic substances.

 

      12.      Minimize potential for accidents

Reagents used in a chemical process should be chosen to minimize
the potential for chemical accidents like explosions and fires.

 

 

 

 

 

 

15.10.2. Contributions of Green Chemistry

                 A
few contribution of green chemistry in our day to day life is  given below

(1) Dry
cleaning of clothes

                 Solvents like tetra chloro ethylene used in dry
cleaning of clothes, pollutes the ground water and is carcinogenic. In the place of tetra
chloro ethylene, liquefied CO2
with suitable detergent is an alternate solvent used. Liquified CO2 is not harmful to the ground water. Now
a days H2O2 is used for bleaching
clothes in laundry gives better results and utilize less water.

(2)  Bleaching of paper

Conventional
method of bleaching was done with chlorine. Now a days H2O2 can be used  for bleaching paper in presence of catalyst.

(3) Synthesis
of chemicals

                 Acetaldehyde
is now
commercially prepared by one step oxidation of ethene in the presence of
ionic catalyst in aqueous medium with 90% 
yield.

(4) The new process using CO2 as
the blowing agent for the manufacture of packing material polystyrene foam
eliminates the use of CFC compounds which result on ozone depletion, global
warming

(5) Instead of petrol, methanol is used as a
fuel in automobiles.

(6) Neem based pesticides have been synthesised, which are more
safer than the chlorinated hydrocarbons.

                 Every individual has an
important role for preventing pollution and improving our environment. We are
responsible for environmental protection. Let us begin to save our environment
and provide a clean earth for our future generations.

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