Green chemistry

Green chemistry is the design of chemical

products and processes that reduce or eliminate
the use or generation of hazardous substances.
Green chemistry applies across the life cycle of a
chemical product, including its design,
manufacture, use, and ultimate disposal. Green
chemistry is also known as sustainable chemistry.
• Prevents pollution at the molecular level
• Is a philosophy that applies to all areas of
chemistry, not a single discipline of chemistry
• Applies innovative scientific solutions to real-
world environmental problems
• Results in source reduction because it
prevents the generation of pollution
• Reduces the negative impacts of chemical
products and processes on human health and
the environment
• Lessens and sometimes eliminates hazard
from existing products and processes
• Designs chemical products and processes to
reduce their intrinsic hazards
Green chemistry and Pollution clean-up:
• Green chemistry reduces pollution at its
source by minimizing or eliminating the
hazards of chemical feedstocks, reagents,
solvents, and products.
• This is unlike cleaning up pollution (also called
remediation), which involves treating waste
streams (end-of-the-pipe treatment) or clean-
up of environmental spills and other releases.
• Remediation may include separating
hazardous chemicals from other materials,
then treating them so they are no longer
hazardous or concentrating them for safe
disposal.
• Most remediation activities do not involve
green chemistry. Remediation removes
hazardous materials from the environment; on
the other hand, green chemistry keeps the
hazardous materials out of the environment in
the first place.
Green chemistry's 12 principles:
• These principles demonstrate the breadth of
the concept of green chemistry:
• 1. Prevent waste: Design chemical syntheses
to prevent waste. Leave no waste to treat or
clean up.
• 2. Maximize atom economy: Design syntheses
so that the final product contains the
maximum proportion of the starting materials.
Waste few or no atoms.
• 3. Design less hazardous chemical syntheses:
Design syntheses to use and generate
substances with little or no toxicity to either
humans or the environment.
• 4. Design safer chemicals and products: Design
chemical products that are fully effective yet
have little or no toxicity.
• 5. Use safer solvents and reaction conditions:
Avoid using solvents, separation agents, or
other auxiliary chemicals. If you must use
these chemicals, use safer ones.
• 6. Increase energy efficiency: Run chemical
reactions at room temperature and pressure
whenever possible.
• 7. Use renewable feedstocks: Use starting
materials (also known as feedstocks) that are
renewable rather than depletable. The source
of renewable feedstocks is often agricultural
 products or the wastes of other processes; the
source of depletable feedstocks is often fossil
fuels (petroleum, natural gas, or coal) or
mining operations.
• 8. Avoid chemical derivatives: Avoid using
blocking or protecting groups or any
temporary modifications if possible.
Derivatives use additional reagents and
generate waste.
• 9. Use catalysts, not stoichiometric reagents:
Minimize waste by using catalytic reactions.
Catalysts are effective in small amounts and
can carry out a single reaction many times.
They are preferable to stoichiometric
reagents, which are used in excess and carry
out a reaction only once.
• 10. Design chemicals and products to degrade
after use: Design chemical products to break
down to innocuous substances after use so
that they do not accumulate in the
environment.
• 11. Analyse in real time to prevent pollution:
Include in-process, real-time monitoring and
control during syntheses to minimize or
eliminate the formation of by-products.
 • 12. Minimize the potential for accidents:
Design chemicals and their physical forms
(solid, liquid, or gas) to minimize the potential
for chemical accidents including explosions,
fires, and releases to the environment.

Application of green chemistry:

1.Green Dry Cleaning of Clothes:
• Perchloroethylene is the solvent most
commonly used in dry cleaning clothes. Perc
(Cl2C = CCl2) is suspected to be carcinogenic
and it contaminates ground water on its
disposal.
• A new technology known as micell technology
is developed by Joseph De Simons, Timothy
Remark and James Mc clain in which liquid
carbon dioxide can be used as a safer solvent
along with a surfactant to dry clean clothes.
• This method is now being used commercially
by some dry cleaners. Dry cleaning machines
have been modified for using this technology
so carcinogen PERC is replaced by green
solvent.
2.Green Bleaching Agents:
• Conventionally during manufacturing of good
quality white paper, lignin from wood used for
it, is removed by placing small pieces of wood
into a bath of sodium hydroxide and sodium
sulphide followed by its reaction with chlorine.
• Chlorine during the process also reacts with
aromatic rings of the lignin to form chlorinated
dioxins and chlorinated furans.
• These compounds being carcinogens, cause
health problems. Terrence Collins of cambegie
mellon university developed a green bleaching
agent which involves use of H2O2 as a
bleaching agent in the presence of some
activators such as TAML which catalysis the
fast conversion of H2O2into hydroxyl radicals
that cause bleaching.
• This bleaching agent breaks down lignin in a
shorter time and at much lower temperature.
• It can be used in laundry and results in lesser
use of water.
3.Eco Friendly Paints:
• Oil based ‘alkyd ’paints give off large amount
of volatile organic compounds (VOCs) as it
dries and cures.
• These VOC's have many environmental effects.
Procter & Gamble and Cork composites &
polymers established a mixture of soya oil and
sugar to be used in place of petroleum
petrochemicals derived paints resins and
solvents which reduced the hazardous
volatiles by 50%.
• Chermpol MPS, paint formulation uses these
bio basedsepose oils to replace petroleum-
based solvents and create paint which is safer
to use.
• Sherwin William established water based
acrylic alkyd paints from recycled soda bottle
plastic (PET), acrylics and soya bean oil. These
paints give performance benefits of alkyds and
low VOC content of acrylics.
3. Putting Out Fires the Green Way:
• The conventionally used chemical firefighting
foams used worldwide discharge toxic
substances into environment contaminating
water and deleting ozone layer.
• A new foam called pyro cool has now been
invented to put out fires effectively without
producing toxic substances as in other
firefighting materials.
 4. Turning Turbid Water Clear in Green Way:
• Conventionally, municipality and industrial
waste water is made clear by the use of Alum.
Alum is found to increase toxic ions in treated
water which causes Alzheimer’s disease.
• The tamarind seed kernel powder which is
discarded as agriculture waste has been found
as effective and economic agent to make
municipal and industrial waste water clear as
with alum.
• Tamarind kernel powder is non-poisonous,
biodegradable and economic. In a study, four
flocculants tamarind seed kernel powder,
mixture of the powder and starch, starch and
alum were taken.
5.Biodegradable plastics:
• large dumps of non-biodegradable waste
plastic. Many companies have been working in
this direction.
• A method has been discovered by the
scientists at Nature Works in which
microorganisms convert corn-starch into a
resin just as strong as the petroleum-based
plastic presently used for making containers,
water bottles etc.
 6. Solar Cell:
• The solar cell is most important example of
green technology.
• It directly converts the light energy into
electrical energy by the process of
photovoltaics.
• Solar photovoltaic technology has been found
to be one of the few renewables, low-carbon
producers with both the scalability and the
technological development to congregate the
ever-growing global demand for electricity.
• The use of solar photovoltaics has been rising
at an average of 43% per year since 2000.
Generation of electricity from solar energy
results in less consumption of fossil fuels,
reduction of pollution and greenhouse gas
emissions.
Conclusion:
• Though many exciting green chemical
processes are being developed but there are
far greater number of challenges lie ahead.
• A lot of efforts are being undertaken to design
non-polluting starting materials and to get
safer products without side products.
• The greatest challenge is too incorporate the
green chemistry in day-to-day life.
• Many successful efforts have been made but
still a lot has to be done.