green chemistry science

GreenChemistry

By :Faik

Outline:

• This chapter comprises manly of this topics:1. Introduction to Green Chemistry.2. 12 principles of Green Chemistry.3. Synthesis of Adipic acid.4. Synthesis of Indigo.5. Green solvents.

Introduction to Green Chemistry:

1. The knowledge of chemistry and development of it in last few decades,eg.drugs,fabrics,etc.

2. The more dependence of humans on this chemicals lead to increase in production.

3. The chemical reactions involved are associated with by-products harmful for environmental pollution.

4. Modify&review chemical process are toxic in varying extent & causes environmental Pollution.

5. Thus design of harmless process to produce various products is termed as Green Chemistry .

6. It came in existence decades back but it’s becoming popular now.

7. It involves any chemical process that improves the environment.

8. It is effective to prevent pollution.

9. There are 12 principles of Green Chemistry accepted all over the world.

12 Principles of Green Chemistry

Productively stands for:

Prevention of waste:

• There is a saying that prevention is better than cure.

• It’s better to prevent waste than treating and cleaning it.

• Our common practice is to dump waste in water, land or release in air.

• Thus Green Chemistry involves chemical process with less by-products/waste to be cleaned.

• The government has made compulsion to the industries for water treatment & disposal units attached to manufacturing plants.

Maximize Atom Economy:-

Atom economy is defined as the ratio of the formula weight of the target molecule to the formula weight of all the starting materials and the reagents.

It indicates the intrinsic efficiency of the desired transformation.

The design for synthesis of products should be such that all chemicals/materials used should be converted into product to maximum extent.

It is seen that most organic reactions release undesired products.

The unutilized material is considered as waste which causes trouble & the process becomes uneconomical.

Green chemistry requires new processes so that most of starting material gets converted into product & it’s called Maximising atom economy.

Non-hazardous Chemical Synthesis

• Synthetic method should be such that it produce little or no toxicity to human health and the environment.

• Starting material selected should be least toxic. For e.g. Pyridine,or β-naphthyl amine known as carcinogenic should be avoided as starting materials.

• In reactions alternative pathways be followed for synthesis where interdmediates or reagents are toxic.

• For example:In 1984,due to leakage of MIC at Bhopal (Bhopal gas tragedy).It was an intermediate of agricultural pesticides&it was highly poisonous.

• Green chemistry suggests design of synthesis to be little or not toxic to human and environment.

Safer chemicals & products

• While reducing toxicity,the efficiency of the desired function should be preserved.

• For medicinal formulation, should be put on trial before marketing to check toxic effect on human.

• If it is toxic then alternates are to be made keeping function of medicine & toxicity reduction in mind.

• For example. DDT,ALDRIN etc.which are toxic to humans so alternate biological pesticides are used.

• Green Chemistry emphasize to design chemicals to be fully effective , yet lower toxicity.

• The solvents, separating agents should not be used unnecessary.

• Acetone, benzene, ether , highly inflammable should be avoided.

• CCl4,CHCl3 ,because of health risk they are avoided.

• Water is universal solvent, certain eco-friendly solvents can be made.

Auxiliary substance

For Dry cleaning perchloroethylene was used, it is replaced by liquid CO2

Energy Efficiency

• Minimizing energy required for chemical process.The synthetic method to be at ambient temperature & pressure.

• Aim is to increase energy efficiency.

• It can be achieved by use of catalysts, and reducing fossil fuels, which release pollutants.

• Recent found, microwave & ultra sound is used where very less energy is required.

• Energy efficiency can be increased by:a) Minimum waste of energyb) Proper heat transfer

• Fermentation is used as energy requirement is low and product is also less harmful.

Renewable Feedstock• Raw materials should be renewable &

economically feasible.

• Renewable feedstock are made from agri-products,while depleting feedstock are from fossil fuels or are mined.

• For example:in adipic acid preparation benzene is repleased by corn starch/cellulose.

Avoid chemical Derivatives

• Unnecessary derivatisation blocking or temporary modification should be avoided.

• Derivatives increases in steps.

• Additional reagent are required.

• More waste products.

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• Alternate reagent are required to avoid this.

• For example: Synthesis of Ibuprofen, with Atom economy of 70% & recoverable catalyst.

Catalysts

• Catalytic reagent are preferred over stoichiometric reagent.

• Minimize waste by catalytic reaction.

• Small amount of catalysts can carry single reaction many times

• Stoichiometric reagent are used in excess and work only once.

• Reactions are faster so less energy is required.

• In recent years non-toxic recoverable & biocatalysts is used.

Degradable products• Chemical products be designed that break

down simple substance as they do not accumulate.

• DDT used as pesticides, it's causes pollution. Alternate is biological residues insecticides.

• Plastic is non-biodegradable which causes solid waste. So biodegradable

plastic containing cellulose is used.

New Analytical methods

• Analytical processes are developed to do on-line monitoring & control.

• Preparation of ethylene glycol, toxic substance are produced at higher temperature.

Prevent Accidents

• Substances and chemical process used should have less accident potential.

• Safer chemicals, minimizing temperature, pressure & catalysts used minimizes the accident potential.

Synthesis of Adipic acid.• In traditional pathway:• Benzene was starting material.

• But in Greener pathway:• D-Glucose is used as raw material which

is absolutely safe.

Synthesis of Indigo• It is basically a dye.

• Aniline used is highly toxic so waste products are more.

• Greener way is to produce indigo enzymatically.

Green solvents

• The concept of conventional solvent extraction as to eliminate need of organic solvents.

• Supercritical fluid possess properties of both gases & liquid in intriguing manner.

• It could offer wide application in synthetic & analytical chemistry.

• SFE CO2 is energy conserving, waste reducing alternate to organic solvents.

• It can lead reactions that are difficult to achieve in conventional solvents.

• It is a new technology with large potential for industries.

Principle:

• SFE technology is feed material is contacted with a supercritical fluid the volatile substance will partition in supercritical phase.

• After dissolution of soluble material SCF containing dissolve substance is removed for feed.

• The extracted component is completely separated from the supercritical fluids by temperature/pressure change.

• The SCF can then be recompressed to extraction conditions and recycled.

Choice of SFE solvent:

• The choice of SCF solvent is same as regular solvents.

• Good solvent property.

• Inert in the product.

• Easy separation from product

• Low cost.

• Carbon dioxide is the most commonly used SCF,due to it’s critical parameters(31.1o,73.8bar),low cost and non-toxicity.

• Several other SCF’s are also used in industries.

Plant as source of New Drugs :

• Plants play important role in pharmacy also.

• Different efficient pharmacophores are made from plants.

• Example are Mepridine(Demerol),Pentazocine(Darvon) which are totally synthetic drugs.