Green Chemistry To promote innovative chemical technologies that reduce or eliminate the use or generation of hazardous substances in the design, manufacture, and use of chemical products.
Green chemistry is about • Waste Minimisation at Source • Use of Catalysts in place of Reagents • Using Non-Toxic Reagents • Use of Renewable Resources • Improved Atom Efficiency • Use of Solvent Free or Recyclable Environmentally Benign Solvent systems
Green Chemistry = Responsibility Why is there no ‘Green Geology’ or ‘Green Astronomy’? Because chemistry is the science that introduces new substances into the world and we have a responsibility for their impact in the world.” - Ronald Breslow
Green Chemistry is also called… • A new approach to designing chemicals and chemical transformations that are beneficial for human health and the environment • An innovative way to design molecules and chemical transformations for sustainability • Meeting the needs of the current generation without compromising the ability of future generations to meet their own needs • Benign by design • Pollution prevention at the molecular level
What is Green Chemistry? • Green chemistry is the study of how to design chemical products and processes in ways that are sustainable and not harmful for humans and the environment. • Three components: catalysis, solvents, non-toxic • 12 principles of green chemistry
Green Chemistry Is About... Waste Materials Hazard Reducing Risk Energy Cost
Why do we need Green Chemistry ? • Chemistry is a very prominent part of our daily lives. • Chemical developments also bring new environmental problems and harmful unexpected side effects, which result in the need for ‘greener’ chemical products. • A famous example is the pesticide DDT.
The 12 Principles of Green Chemistry (7-12) • 7 Use of Renewable Feedstocks • A 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/de-protection, and temporary modification of physical/chemical processes) should be minimised 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. • 10 Design for Degradation • Chemical products should be designed so that at the end of their function they break down into innocuous degradation products and do not persist 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 a chemical process should be chosen to minimise the potential for chemical accidents, including releases, explosions, and fires.
What is “Green”? • Sustainable • Kinder and gentler to people and the planet
Conventional Heating vs Alternative Energy Source • Conventional Heating • Bunsen burner • Oil bath • Heating mantle • Alternative Energy Sources • Microwave • Ultrasound • Sunlight / UV • Electonchemistry
Clean Chemical Synthesis UsingAlternative Reaction Methods • Alternative Energy Sources • Microwave • Ultrasound • Sunlight / UV • AlternativeReactionMedia/Solvent-free • Supercritical Fluids • Ionic Liquids • Water • Polyethylene glycol (PEG) • Solvent free
History or how it all began… • While fire is now rarely used in synthetic chemistry, it was not until Robert Bunsen invented the burner in 1855 that the energy from this heat source could be applied • There is some controversy about the origins of the microwave power cavity called the magnetron – the high-power generator of microwave power. The British were particularly forward-looking in deploying radar for air defense with a system called Chain Home which began operation in 1937. Originally operating at 22 MHz, frequencies increased to 55 MHz. 1921 was published by A.W. Hull the earliest description of the magnetron, a diode with a cylindrical anode 1940 It was developed practically by Randall and Booth at the University of Birmingham in England ; they verified their first microwave transmissions: 500 W at 3 GHz. A prototype was brought to the United States in September of that year to define an agreement whereby United States industrial capability would undertake the development of microwave radar. 1940 the Radiation Laboratory was established at the Massachusetts Institute of Technology to exploit microwave radar. More than 40 types of tube would be produced, particularly in the S-band (i.e. 300 MHz). The growth of microwave radar is linked with Raytheon Company and P.L. Spencer who found the key to mass production.
History or how it all began… • 1946 Dr. Percy Spencer-the magnetron inventor; he has found a variety of technical applications in the chemical and related industries since the 1950s, in particular in the food-processing, drying, and polymer • surprisingly, microwave heating has only been implemented in organic synthesis since the mid-1980s. • Today, a large body of work on microwave-assisted synthesis exists in the published and patent literature. • Many review articles, several books and information on the world-wide-web already provide extensive coverage of the subject.
1969 “ Carrying out chemical reactions using microwave energy ” J.W. Vanderhoff – Dow Chemical Company US 3,432,413 • 1986 “The Use of Microwave Ovens for Rapid Organic Synthesis” Gedye, R. N. et alTetrahedron Lett. 1986, 27, 279 • 1986 “Application of Commercial Microwave Ovens to Organic Synthesis” Giguere, R. J. and Majetich, G. Tetrahedron Lett. 1986, 27, 4945
Energy Use in ConventionalChemical Processes • Heating • Stirring • Piping • Transporting • Cooling
Problem of Conventional Heating • You heat what you don’t want to heat. • Solvents for reactions, apparatus: heated up and cool it down. • Double energy penalty without any apparent “benefit”.
Energy Consumptions Three ways to get the reaction done, but different energy bills to pay
Microwaves • MW reactors operate at 2.45 GHz. • Electric field oscillates at 4.9 x 109 times/sec – 10oC/sec heating rate.
Electromagnetic Spectrum Neas, E.; Collins, M. Introduction to Microwave Sample Preparation: Theory and Practice, 1988, p. 8.
Schematic of a Microwave E= electric field H= magnetic field l= wavelength (12.2 cm for 2450 MHz) c= speed of light (300,000 km/s)
Microwaves Application in Heating Food 1946: Original patent (P. L. Spencer) 1947: First commercial oven 1955: Home models 1967: Desktop model 1975: U.S. sales exceed gas ranges 1976: 60% of U.S. households have microwave ovens
Spectrum Electromagnetic • Electric field component • Responsible for dielectric heating • Dipolar polarization • Conduction • Magnetic field component
Microwaves – Dipolar Rotation • Polar molecules have intermolecular forces which give any motion of the molecule some inertia. • Under a very high frequency electric field, the polar molecule will attempt to follow the field, but intermolecular inertia stops any significant motion before the field has reversed, and no net motion results. • If the frequency of field oscillation is very low, then the molecules will be polarized uniformly, and no random motion results. • In the intermediate case, the frequency of the field will be such that the molecules will be almost, but not quite, able to keep in phase with the field polarity. • In this case, the random motion resulting as molecules jostle to attempt in vain to follow the field provides strong agitation and intense heating of the sample. • At 2.45 GHz the field oscillates 4.9 x 109 times/s which can lead to heating rates of 10 °C per second when powerful waves are used
MW Heating Mechanism Continuous electric field Alternating electric field Withhigh frequency Noconstraint • Two mechanisms: • Dipolar rotation / polarization • Ionic Conduction mechanism
Microwave Dielectric HeatingMechanisms Conduction Mechanism Dipolar Polarization Mechanism Dipolar molecules try to align to an oscillating field by rotation Ions in solution will move by the applied electric field Mingos, D. M. P. et al., Chem. Soc. Rev. 1991, 20, 1 and 1998, 27, 213
Microwave vs Oil-bath Heating J.-S. Schanche, Mol. Diversity 2003, 7, 293. www.personalchemistry.-com; www.biotage.com.
Conventional Heating byConduction Conductive heat Heating by convection currents Slow and energy inefficient process temperature on the outside surface is in excess of the boiling point of liquid
Direct Heating by MicrowaveIrradiation • Solvent/reagent • absorbs MW energy • Vessel wall transparent to MW • Direct in-core heating • Instant on-off Inverted temperature gradients!
Microwave Ovens Cooking Food! Cooking Chemistry ??? Household MW ovens The Use of Microwave Ovens for Rapid Organic Synthesis R. Gedye et al., Tetrahedron Lett. 1986, 27, 279.
Publications on MW-AssistedOrganic Synthesis 7 Synthetic Journals: J.Org.Chem.,Org.Lett.,Tetrahedron Lett.,Tetrahedron, Synth.Commun., Synlett, Synthesis All Journals (Full Text): Dedicated instruments only (Anton Paar, Biotage, CEM, Milestone, Prolabo)
Industrial /Chemical / Applications of Microwave Heating Food Processing + Defrosting + Drying / roasting / baking + Pasteurization Plasma + Semiconductors Waste Remediation + Sewage treatment Drying Industry + Wood, fibers, textiles + Pharmaceuticals + Brick / concrete walls Analytical Chemistry + Digestion + Extraction + Ashing Polymer Chemistry + Rubber curing, vulcanization + Polymerization Biochemistry / Pathology + Protein hydrolysis + PCR, proteomics + Tissue fixation + Histoprocessing Ceramics/Materials + Alumina sintering + Welding, smelting, gluing Medical + Diathermy, tumor detection + Blood warming + Sterilization (Anthrax) + Drying of catheters
Books on Microwave-Assisted Synthesis (ACS Professional Reference Book) H. M. Kingston, S. J. Haswell (eds.) Hayes, B. L., CEM Publishing, Matthews, NC, 2002 Microwaves in Organic and Medicinal Chemistry Kappe, C. O. and Stadler, A. Wiley-VCH, Weinheim, 2005, ISBN: 3-527-31210-2 410 pages, ca 1000 references, Fundamentals of Microwave Application Alternative Laboratory Microwave Instruments Chemistry Applications Biochemistry Applications Laboratory Microwave Safety
Books on Microwave-Assisted Synthesis Lidstöm, P.; Tierney, J. P. (Eds.), Blackwell Scientific, 2005 Loupy Andre (Ed.) Wiley-VCH, Weinheim, 2003, ISBN: 3-527-30514-9 523 pages, 2000 refs. Book (2 volumes) Wiley-VCHA. Loupy edit Second Edition (2006) 22 Chapters
Books on Microwave-Assisted Synthesis Practical Microwave Synthesis for Organic Chemists - Strategies, Instruments, and Protocols Edition - 2009, X, 310 Pages, Hardcover, Monograph Astra Zeneca Research Foundation Kavitha Printers, Bangalore, India, 2002 email@example.com
Monomodal instrument Piccoli volumi processabili - Onde Stazionarie (Hot Spots) - Difficoltà nello Scale-up + Alta densità d’energia Images adapted from: C.O. Kappe, A. Stadler: Microwaves in Organic and Medicinal Chemistry, Wiley, 2005
Multimodal instrument + Alta densità d’energia (maggior potenza disponibile) + Maggiori volumi processabili (cavità a MW più grande) + No Onde Stazionarie (No Hot-spots) + Semplice Scale-up - Volume minimo processabile