Green Chemistry Dr. C. H. GILL. (Prof. & Head) Dept. of Chemistry, Dr. Babasaheb Ambedkar Marathwada University, Aurangabad. firstname.lastname@example.org
GREEN CHEMISTRY GREEN CHEMISTRY PREVENTING POLLUTION SUSTAININGTHE EARTH
What is Green Chemistry? • It is better to prevent waste than to clear it up afterwards. • % Atom economy is the new % yield • The strive towards the perfect synthesis • Benign by design • Environmentally friendly and economically sound.
Why Chemical Manufacturing is Essential ? • Requirements of essential commodities on a very large scale such as:- • Synthetic Fibers • Plastic • Pharmaceuticals • Dyes • Fertilizers • Pesticides
The Need of Green Chemistry is due to Adverse Effect of Global Warming Deplication of Earth
Green Chemistry Is About... Waste Materials Hazard Reducing Risk Energy Environmental Impact COST
Some Aspects of Green Chemistry Catalysis Safer Reactions & Reagents Solvent Replacement Separation Processes Green Chemistry Use of Renewable Feedstocks Energy Efficiency Waste Minimisation Process Intensification
PREVENTING WASTES • Design experiments to Reduce or eliminate waste. • Incorporate materials used in a process into the final product.
The 12 Principles of Green Chemistry • Prevention of waste • Atom Economy • Less Hazardous Chemical Syntheses • Design Safer Chemicals • Safer Solvents and Auxiliaries • Design for Energy Efficiency • Use Renewable Feedstocks • Reduce Derivatives • Catalysis • Design for Degradation • Real-time Analysis for Pollution Prevention • Inherently Safer Chemistry for Accident Prevention
What is Atom Economy? Mass of Product % Atom economy = 100 ---------------------- Mass of Reactants
Example 98 % Atom economy = 100 -------------- = 44.1% 78 +144
Atom Uneconomic Reactions Example:- • Substitution • Elimination • Wittig • Grignard
Substitution Reaction (Atom Un-economic) 120.5 % Atom economy = 100 --------- = 54.5% 102+119 SO2 and HCl are unwanted by products reducing the overall atom economy.
Substitution Reaction(Atom Un-economic) 120.5 % Atom economy = 100 ----------- = 54.5% 102+119 SO2 and HCl are unwanted by products reducing the overall atom economy.
Elimination Reactions 56 % Atom economy = 100 ----------- = 45.9% 122
Atom Economic Reactions Example:- • Rearrangement • Addition • Diels-Alder • Other Concerted reactions. • ( Pericyclic)
Rearrangements Ex. Claisen Rearrangement 134 % Atom economy = 100 ------ = 100 % 134
Addition Reactions % Atom Economy = 100%
Diels Alder Reactions Atom Economy = 100%
Why Are Reactions Performed Using Solvents? • To dissolve reactants. • To slow or increase the rate of reactions. • To act as a heat sink or heat transfer agent. • To prevent hot spots and run-away reactions.
Issues with Organic Solvents • Organic solvents are of concern to the chemical industry because of the sheer volume used in synthesis, processing, and separation. • Organic solvents are expensive • Organic solvents are highly regulated. • Many organic solvents are volatile, flammable, toxic, and carcinogenic.
Solvent alternatives • Use of solvent less reactions • Use of “non-organic” solvents • Processing technology
Advantages to Solvent lessOrganic Reactions • There is no reaction medium to collect, purify, and recycle. • Reaction times can be dramatically shortened. • Lowered energy usage. • Considerable reduction in batch size volume. • Less expensive.
Ways to be Solvent-Free • Neat – reagents react together in the liquid phase in the absence of a solvent. • Solid-state synthesis – two macroscopic solids interact directly and form a third, solid product without the intervention of a liquid or vapor phase.
Potassium dihydrogen phosphate: an inexpensive reagent for the solvent-free, one-pot synthesis of α-aminophosphonates Ratnadeep S. Joshi, and Charansingh H. Gill* Green Chemistry letters & Reviews 2010, 3(3), 191-194.
Chemoselectiveacylation of amines, thiols and phenols using 2,4,6-triacyloxy-1,3,5 triazine (TAT) as a new and effective reagent under mild condition. Somnath S. Gholap and Charansingh H. Gill* J. Indian Chem. Soc. 2009, 86, 179-182
Ammonium metavanadate: an efficient catalyst for synthesis of - hydroxyphosphatesS. S. Sonar and C. H .GillArkivoc ii, (2009), 138-148
Synthesis of 1,5-benzodiazepines using silica perchloric acid: An effective reusable heterogeneous catalyst under mild condition.Somnath S. Gholap and C. H .GillRasayan Journal of chemistry 1(2), (2008), 331-336
SILICA DICHLOROPHOSPHATE [SiO2-POCl2] AS A EXPEDITIOUS REUSABLE CATALYST FOR THE SYNTHESIS OF BIS-(INDOLYL) METHANES UNDER SOLVENTFREE CONDITIONS Charansingh H. Gill and Somnath S. Gholap Bulletin of the catalysis Society of India, 8 (2009) 126-130 33
Limitations • Not all reactions will work in the absence of solvent. • Function of catalysts. • Exothermic reactions are potentially dangerous. • Specialized equipment needed for some procedures. • If aqueous quench and organic extraction are performed, this reduces green benefits.
Use of non-organic solvents • Water
Organic Reactions in Aqueous Media • Water–Isn’t that bad for my organic reaction?
Organic Reactions in Aqueous Media • Most of the world’s chemistry occur in aqueous media.
Why Water? • Cost - water is the world’s cheapest solvent. • Safety – doesn’t get any safer than water. • Some reactions work better in water.
Green Concerns of Water • The product may need to be extracted into an organic solvent to purify it. • This generates aqueous effluent containing solvent, which must be properly disposed.
Eco-friendly and facile synthesis of 2-substituded -1H-imadazol [4, 5-b] pyridine in aqueous media by air oxidation Rajesh P. Kale and C.H.Gill Tetrahedron letters 50, (2009), 1780-1782
Limitations of Water as a Solvent • Some reactions will never work in water. • Poor solubility of most organic compounds. • Solubility may be increased by use of organic co-solvents, PH control, surfactants, and hydrophilic auxiliaries.
Use safer solvents for chemical processes • Return safe substances to the environment • Design for biodegradability • Eliminate the use of toxic solvents to dissolve reactingmaterials
Microwaves. • Microwaves have wavelengths between 1cm to 1 meter, located between IR and Radio/Radar frequencies. • The mechanism of how energy is impacted to a substance under microwave irradiation is complex. • Microwaves may be considered a more efficient source of heating than conventional source of heating, the energy is directly imparted to the reaction medium rather than through the walls of a reaction vessel.
The combination of solvent free procedures and MW irradiation can be used to carryout a wide range of reaction within short reaction times and with high conversions selectively. • This approach is efficient, easy to perform, economic and less polluting as solvents are avoided.
Benefits of Microwave • Very rapid reactions ( few minutes) • Higher degree of purity achieved due to short residence time at high temperature • No local Overheating • Yields often better. • Pure Products
Microwave Induced Synthesis of 3-methyl-4-[(Chromon-3-yl)-methylene]-1-Phenyl Pyrazolin-5(4H) ones with Alumina Support and in Solvent free Conditions B.K.Karale and C.H.Gill Synthetic Communications, 32(4), (2002), 497. Stereochemistry determined by NOE
One Pot Synthesis of Substituted [1,2,4]-Triazolo [1’,2’:1,2]pyrimido [6,5-b]-quinoline and Its Antibacterial Activity Ratnadeep S. Joshi and Charansingh H. Gill Bulletin of Korean Chemical Society, 31(8), (2010), 2341-2344 48
Thiamine hydrochloride (VB1) promoted one-pot synthesis of 2,4,5-triphenyl-1H-imidazole using microwave irradiation Priyanka G. Mandhane and C.H.Gill Chinese Chemical Letter (doi:10.1016/j.cclet.2010.11.021) 49
Microwave Induced Synthesis of Flavones N.R.Dalvi and C.H.Gill Chemistry an Indian Journal, 1(8), 582-83, 2004