green chemistry, its applications and benefits

Green ChemistryNOT just a definite solution…BUT an ultimate necessity…

Some light upon the term-Green Chemistry:

Definition- “The design of chemical products and processes that are more environmentally friendly and reduce negative impacts to human health and the environment.”

Green chemistry looks at pollution prevention on the molecular scale and is an extremely important area of Chemistry due to the importance of Chemistry in our world today and the implications it can show on our environment.

The Green Chemistry program supports the invention of more environmentally friendly chemical processes which reduce or even eliminate the generation of hazardous substances.

Property of Amit Amola. To be used only as a reference and by consent.

Father of Green ChemistryThe concept of green chemistry was formally established at the ENVIRONMENTAL PROTECTION AGENCY 15 years ago in response to the Pollution Prevention Act of 1990.

Paul T. Anastas for the first time in 1991 coined the term Green Chemistry. Though it is said that the concept was originated by Trevor Kletz in his 1978paper where he proposed that chemists should seekalternative processes to those involving more dangerous substances and conditions.


Principles of Green ChemistryPaul T. Anastas and John C. Warner developed 12 principles of green chemistry, which help to explain what the definition means in practice.

a. Prevention

b. Atom Economy

c. Less Hazardous Chemical Synthesis

d. Designing Safer Chemicals

e. Safer Solvents and Auxiliaries

f. Design for Energy Efficiency

g. Use of Renewable Feedstocks

h. Reduce Derivatives

i. Catalysis

j. Design for Degradation

k. Real-time Analysis for Pollution Prevention.

l. Inherently Safer Chemistry for Accident Prevention.


1.Prevention:“It is better to prevent waste than to treat or clean up waste after it is formed.”

It is advantageous to carry out a synthesis in such a way that the formation of waste products is minimum or absent. The waste if discharged in the atmosphere, sea and land causes not only pollution but also requires expenditure for cleaning up.

Chemical Process


Some dreadful examples of ill effects from untreated waste disposal:

1.Love Canal:

In Niagara Falls, NY a chemical and plastics company had used an old canal bed as a chemical dump from 1930s to 1950s. The land was then used for a new school and housing track. The chemicals leaked through a clay cap that sealed the dump. It was contaminated with at least 82 chemicals (benzene, chlorinated hydrocarbons, dioxin). Health effects of the people living there included: high birth defect incidence and seizure-inducing nervous disease among the children.


continued…

2.Cuyahoga River – Cleveland, Ohio• There were many things being dumped in the river such

as: gasoline, oil, paint, and metals. The river was called "a rainbow of many different colors".

• Fires erupted on the river several times before June 22, 1969, when a river fire captured national attention when Time Magazine reported it.

Some river! Chocolate-brown, oily, bubbling with subsurface gases, it oozes rather than flows. "Anyone who falls into the Cuyahoga does not drown," Cleveland's citizens joke grimly, “he decays.“


http://photos1.blogger.com/img/5/2980/1024/acc01.jpg

http://photos1.blogger.com/img/5/2980/1024/acc01.jpg

2.Atom Economy:“Synthetic methods should be designed to maximize the incorporation of all materials used in the process into the final product.”

A synthesis is Perfectly Efficient or Atom Economical if it generates significant amount of waste which is not visible in percentage yield calculation.

Percent yield:

%Yield=actual yield)

theoretical yield× 𝟏𝟎𝟎

Atom Economy:

%AE=𝑭𝑾 𝒐𝒇 𝒂𝒕𝒐𝒎𝒔 𝒖𝒕𝒊𝒍𝒊𝒔𝒆𝒅)

(𝑭𝑾 𝒐𝒇 𝒂𝒍𝒍 𝒓𝒆𝒂𝒄𝒕𝒂𝒏𝒕𝒔× 𝟏𝟎𝟎


Rearrangement and Addition reactions are 100% atom economical reactions since all the reactants are incorporated into products.

While Substitution and Elimination reactions are less atom economical.

1. H3C-CH=CH2 + H2 H3C-CH2-CH3propene propane

the reaction takes place in presence of Nickel. Here 64.8% reactants are incorporated into product. Hence this is an atom economical reaction.

2. CH3(CH2)4CH2OH +SOCl2 SO2 + CH3(CH2)4CH2Cl

this reaction is less atom economical as the % atom economy is 36.5%.Property of Amit Amola. To be used only as a reference and by consent.

3.Less Hazardous Chemical Synthesis“Wherever practicable, synthetic methodologies should be designed to use and generate substances that possess little or no toxicity to human health and the environment.”

Example of an unsafe drug is THALIDOMIDEfor lessening the effect of nausea and vomiting during pregnancy. The child born to women taking the drug suffers from birth defects like deformed-limbs.


Another example but with a remedial substitute:

Polycarbonate Synthesis:

1.Phosgene Process

Disadvantages:-

1.phosgene is highly toxic, corrosive

2.requires large amount of CH2Cl23.polycarbonate contaminated with Cl impurities

OH OHCl Cl

O

+NaOH

O O *

O

* n


2. Solid-State Process

Advantages:

1.diphenylcarbonate synthesized without phosgene2.eliminates use of CH2Cl23.higher-quality polycarbonates

OH OH

+ O O *

O

* n

O O

O


4.Designing Safer Chemicals“Chemical products should be designed to preserve efficacy of function while reducing toxicity.”

• Synthetic methodologies should be designed to generate substances that generate substances that possess less harmful or toxic products.

• This principle focuses on choosing reagents that pose the least risk and generate only safe by-products.

• For example: in the manufacture of Polystyrene, CFC’s which contribute to ozone depletion and global warming are replaced by CO2.


5.Safer Solvents and Auxiliaries“The use of auxiliary substances (e.g. solvents, separation agents, etc.) should be made unnecessary wherever possible and innocuous when used.”

• The solvent selected for a particular reaction shouldn't cause any environmental pollution or hazard (e.g. benzene, alcohol).

• One major problem with many solvents is their volatility that may damage environment and human health.

• To avoid this many reactions are carried out in safer green solvents like ionic liquids, supercritical CO2 fluid etc. which maintain the solvency of the material and are also non-volatile.


Solvent selection


Solvent replacement table


6.Design for Energy Efficiency“Energy requirements should be recognized for their environmental and economic impacts and should be minimized. Synthetic methods should be conducted at ambient temperature and pressure.”

In any chemical synthesis the energy requirement should be kept low ,for example:

1) If the starting material is soluble in the particular solvent, the reaction mixture has to be heated till the reaction is complete.

2) If the final product is impure it has to be purified by distillation or recrystallization .

All these steps involve the use of high amount of energy which is uneconomical.


7.Use of Renewable Feedstocks“A raw material or feedstock should be renewable rather than depleting wherever technically and economically practicable.”

Renewable feedstock are often made from agricultural products or are the wastes of other processes; depleting feedstock are made from fossil fuels (petroleum, natural gas or coal) or are mined.

For example :-Substances like CO2(generated from natural sources) and methane gas (marsh gas) are considered as renewable starting materials.


Polymers from Renewable Resources:Poly(lactic acid)


Raw Materials from Renewable Resources:The BioFine Process

Paper mill sludge

Agricultural residues,Waste wood

Municipal solid wasteand waste paper

O

HO

O

Levulinic acid

Green Chemistry Challenge Award1999 Small Business Award


Levulinic acid as a platform chemical


8.Reduce Derivatives“Reduce derivatives - Unnecessary derivatization (blocking group, protection/deprotection, temporary modification) should be avoided whenever possible.”

Avoid using blocking or protecting groups or any temporary modifications if possible. Derivatives use additional reagents and generate more waste.Two synthetic steps are added each time when one is used. Overall yield and atom economy decrease.

Instead, more selective and better alternative synthetic sequences that eliminate the need for functional group protection should be adopted.


9. Catalysis“Catalytic reagents (as selective as possible) are superior to stoichiometric reagents.”

Use of a catalyst facilitates transformation without the catalyst being consumed in the reaction and without being incorporated in the final product.

Some advantages of catalyst are:

1)Better yields

H3C-CH=CH2 + H2 H3C-CH2-CH3

Propene Propane

the hydrogenation of olefins is carried out in presence of nickel.

2)The reaction becomes feasible in those cases where no reaction is normally possible.

3)Better utilization of starting material and minimum waste product formation. Property of Amit Amola. To be used only as a reference and by consent.

10. Design for Degradation“Chemical products should be designed so that at the end of their function they do not persist in the environment and break down into innocuous degradation products.”

For example-

• Sulfonated detergents

Alkylbenzene sulfonates – 1950’s & 60’s

Foam in sewage plants, rivers and streams

Persistence was due to long alkyl chain

Introduction of alkene group into the chain increased degradation

• Chlorofluorocarbons (CFCs)

Do not break down, persist in atmosphere and contribute to destruction of ozone layer

• DDT

Insecticides like DDT tend to bio-accumulate in many plant and animal species and incorporate into the food chain resulting in population decline of beneficial insects and animals.Property of Amit Amola. To be used only as a reference and by consent.

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.”

Real time analysis for a chemist is the process of “checking the progress of chemical reactions as it happens.”

Knowing when your product is “done” can save a lot of waste,time and energy!


12. Inherently Safer Chemistry for Accident Prevention“Substances and the form of a substance used in a chemical process should be chosen to minimize potential for chemical accidents, including releases, explosions, and fires.”

Design chemicals and their forms (solid, liquid, or gas) to minimize the potential for chemical accidents including explosions, fires and releases to the environment.

Example of such incident due to lack of such measures:-December 3, 1984 – poison gas leaked from a Union Carbide factory, killing thousands instantly and injuring many more (many of who died later of exposure). Up to 20,000 people have died as a result of exposure (3-8,000 instantly). More than 120,000 still suffer from ailments caused by exposure.


Synthesis Of Some Industrial Compounds Involving Basic Principles Of Green Chemistry

Ibuprofen


Synthesis Of AcetaldehydeCommercially

• Acetaldehyde was obtained by catalytic oxidation of ethyl alcohol or by hydration of acetylene.

• CH3CH2OH oxidation CH3CHO

• The above reaction occurs at a very high temperature (675K).

Green Synthesis Of Acetaldehyde

• It is most conveniently obtained by oxidation of ethylene in presence of catalyst solution.

• CH2=CH2 +O2oxidation CH3CHO

• The reaction takes place in the presence of Pd/Cu and in aqueous medium.Property of Amit Amola. To be used only as a reference and by consent.

Free Radical Bromination

• The usual Bromination of toluene with N-bbomosuccinimide (NBS)gives benzyl bromide. This process requires a solvent (CCl4).

• It has been found that free radical bromination of toluene with NBS in supercritical carbon dioxide gave 100% yield of benzyl bromide.

• Toluene (hv,NBS,CO2,139 bar) Benzyl bromide(100%)


Synthesis Of Adipic Acid• Adipic acid is required in large

quantities for synthesis of nylon and lubricants.

• But Adipic acid is obtained from benzene which causes environmental and health problems. Also, nitrous oxide is generated as by-product which causes greenhouse effect.

• Green synthesis of adipic acid usesD-glucose (renewable source) as starting material. Also the synthesis is conducted in water instead of organic solvents.


Disinfection of water

• Disinfection of water by chlorination. Chlorine oxidizes the pathogens there by

killing them, but at the same time forms harmful chlorinated compounds.

• A remedy is to use another oxidant, such as O3 or supercritical water oxidation.


Production of allyl alcohol CH2=CHCH2OH• Traditional route: Alkaline hydrolysis of allyl chloride, which generates the

product and hydrochloric acid as a by-product

• Greener route, to avoid chlorine: Two-step; using propylene (CH2=CHCH3),

acetic acid (CH3COOH) and oxygen (O2)

• Added benefit: The acetic acid produced in the 2nd reaction can be recovered

and used again for the 1st reaction, leaving no unwanted by-product.

CH2=CHCH2Cl + H2O CH2=CHCH2OH + HCl

problem product

CH2=CHCH3 + CH3COOH + 1/2 O2 CH2=CHCH2OCOCH3 + H2O

CH2=CHCH2OCOCH3 + H2O CH2=CHCH2OH + CH3COOH


Production of styrene (benzene ring with CH=CH2 tail)

• Traditional route: Two-step method starting with benzene, which is carcinogenic) and

ethylene to form ethylbenzene, followed by dehydrogenation to obtain styrene

• Greener route: To avoid benzene, start with xylene (cheapest source of aromatics and

environmentally safer than benzene).

• Another option, still under development, is to start with toluene (benzene ring with

CH3 tail).

+ H2C=CH2

catayst

CH2CH3

ethylbenzene

catayst

CH=CH2CH2-CH3

ethylbenzene

styrene


Synthesis Of Ibuprofen

• Ibuprofen is one of the products used in large quantities for making pharmaceutical drugs, in particular various kinds analgesics (pain killers).

• The traditional commercial synthesis of ibuprofen was developed by the Boots Company of England in 1960s. It is a 6 step process and results in large quantities of by-products. There is 40% atom economy in this synthesis.


conti…Classic Route to Ibuprofen…

Ac2O

AlCl3

COCH3

HCl, AcOH, Al Waste

ClCH2CO

2Et

NaOEt

OEtO

2C

HCl

H2O / H+

OHC

AcOH

NH2OH

OHNN

H2O / H+

HO2C

NH3Property of Amit Amola. To be used only as a reference and by consent.

conti…Green Synthesis Of Ibuprofen

The BHC Company developed a new greener synthesis of Ibuprofen that consists only of 3 steps. It results in small amount of unwanted products and has very good atom economy(77%).

O

HF

AcOH

Ac2O

H2 / Ni

OH

CO, Pd

HO2C


Conclusion

As Paul T. Anastas said that his dream is not that Green Chemistry is practiced by every person but rather whole Chemistry is Green.

Remember:-Green chemistry is NOT a solution to all environmental problems BUT the most fundamental approach to preventing pollution.


Acknowledgement

I am really thankful to my teacher Dr. Shuchi Dhingra who gave me this topic as my project and had faith in my work. Her sincere help and devotion has led me to fulfillment of this presentation.

I would also like to thank my family, my parents, my friends and above all my brother Summit Amola whose utmost help led me to finalize my presentation.


green chemistry, its applications and benefits

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