In the glorious days of 1950\'s and 1960\'s chemists envisioned chemistry as the solution to a host of society\'s needs. Indeed, they created many things which improve the quality of life on earth like dyes, plastic, cosmetics and other materials. At  the same time chemistry brought about medical revolution i.e. through antibiotics which conquered infectious disease. All these things prove DuPont Slogan. \"Better things for better living through chemistry\". But there are some adverse outcome due to discovery of drugs, insecticides, herbicides, fertilizers etc. which causes a cancerous grip of the air, water, soil  and noise pollution on earth that grabbed this world  like an octopus, e.g. DDT which accumulated in birds, and causes egg shell thining and nesting failures results in decline of that species. Refrigerent like CFCs deplets the ozone layer remarkably which protects our earth from harmful UV rays of sun. So there are several advantages and disadvantages of chemistry, but there is main advantages of chemistry the beginning of green chemistry by the middle of 20th century.  

The term \" GREEN CHEMISTRY\" was coined by Professor Paul Anastas, who is known as the father of green chemistry, at US Environmental Protection Agency Green Chemistry is the effort of reducing or eliminating the use of or generation of hazardous substances in the design, manufacture and application of chemical products.Green Chemistry is defined as environmentally benign chemical synthesis. It is science based, non regulatory and economically driven approach to achieving the goals of environmental protection.

 The ultimate value of green chemistry lies in its applicability for the new millennium. So the challenge to reduce the waste, the toxicity of chemical and the amount of energy used, while still providing the goods that society needs, is overcome through green chemistry.  

Green Chemistry has been referred by a number of alternate name like \"Clean Chemistry\', \'Atom Economy\', Bengh by Design Chemistry, \'sustainable chemistry\', \'Eco-friendly chemistry\' and \'Environmentally Benign Chemistry\'. While Green Chemistry encompasses human health and the environment. The discovery and development of fundamental chemical transformations that are harmful to the environment will be the driving force that moves this area forward.  

Green Chemistry is the utilization of a set of principles that reduce or eliminate the uses or generation of hazardous chemicals in the design, manufacture and application of chemical products. It describes an area of research arising from scientific discoveries about pollution and covers the following areas :  

(i) Development of environmentally improved routes to products.  

(ii) Use of sustainable resources. 

(iii) Design of new green chemicals. 

(iv) Use of biotechnology, alternative  and innovative technology for industrial processes.

Green chemistry involves the design and redesign of chemical synthesis  and chemical products to prevent pollution and thereby solve environmental  problems. It is the use of chemical principles and methodologies for source-reduction which is the most desirable form of the pollution prevention. It incorporates pollution prevention practices in the manufacture of chemicals and promotes industrial ecology. It is a new way of looking at chemicals and minimizes any negative environmental effects. 

The  twelve principles of Green Chemistry can be applied  to almost every part of chemistry, that includes synthesis of molecules with a desired  structure and property, catalysis of a process, less polluting reaction conditions etc. 

1. Prevention    

It is better to prevent waste than to treat or clean up waste after it has been created. 

2. Less hazardous chemical synthesis   

Wherever practicable, synthetic methods should be designed to use and generate substances that possess little or no toxicity to human health and the environment.  

3. Designing Bafer Chemicals  Chemicals products should be designed to affect their desired function while minimizing their toxicity. 

4. Atom economy    

Synthetic methods should be designed to minimize the incorporation of all materials used in the process into the final product. A very good example is the BHC company synthesis of Ibuprofen, which creates less waste and fewer by products (Fig. 1). The % economy for the three step catalytic green  synthesis (BHC) Vs the six step brown synthesis (BOOTS) in 77% and 40% respectively. Considering the fact that acetic acid generated in steps 1 of green synthesis is recovered the % atom economy climbs to 99% from 77%.  

5. Safer solvents and auxillaries The use of auxillary substances (solvents, separation, agents, etc.) should be minimized whenever possible and should be made innocuous when used.  

6. Design for energy efficiency  Energy requirements of chemical processes should be recognized for their environmental and economic impacts and should beminimized. If possible, synthetic methods should be conducted at ambient temperature and pressure. 

7. Use renewable feedstocks   

Raw material or feedstock should be renewable  rather than depleting whenever technically and economically practicable.  

8. Reduce derivatives    

Unnecessary derivatization (use of blocking groups, protection / deprotection and temporary modification of physical / chemical processes)  should be minimized or avoided if possible, because such steps require additional reagents and can generate waste.  

9. Catalysis   

Catalytic reagents (as selective as possible) are superior to stoichiometric reagents. Using catalytic reagents creates opportunities for increased selectivity, better yield, and feasibility of non feasible reaction.  

10. Design for degradation

Chemical products should be designed so that at the end of then function they break down into innocuous degradation products and do not persists in the environment.  

11. Real-time analysis for pollution prevention    

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

12. Inherently safer chemistry for accident prevention   

Substances and the form of a substance used in chemical process should be chosen to minimize the potential for chemical accidents including releases, explosions and fires. Green Chemistry has changed our life style in many ways. Like now a days dry clearing of clothes is done with the use of liquid CO2 and a surfactant, thereby eliminating a need of halogenated solvents like PERC (per chloroethylene Cl2C=CCl2)

 This technology is known as micell Technology. In the same way, hydrogen peroxide (H2O2)  is  used  with  some activators like TAML activators as a bleaching agents rater than the use of halogenated compounds.