CH5 Slides: Metrics - E-Factor and PMIA PDF

METRI CS Image: Wikimedia Commons, Life Cycle Thinking, DAY 3 SESSION www.greenchemistry-toolkit.org  METRI CS Image: Wikimedia Commons, Life Cycle Thin...

METRI CS Image: Wikimedia Commons, Life Cycle Thinking, DAY 3 SESSION www.greenchemistry-toolkit.org  METRI CS Image: Wikimedia Commons, Life Cycle Thinking, DAY 3 SESSION www.greenchemistry-toolkit.org  Topics To Be 1. Covered Why do we need metrics in green chemistry? 2. Established Metrics in Green Chemistry Atom Economy Atom Utilization 3. Additional Metrics Used in Green Chemistry Process Mass Intensity Life Cycle Assessment Ecological Indicator/Ecological Footprint CONVENTIONAL METRICS: PERCENT YIELD Percent yield: % yield = (actual yield/theoretical yield) x 100 What is missing? What co-products are made? How much waste is generated? Is the waste benign waste? How much energy is required? Are purification steps needed? What solvents are used? (are they benign and/or reusable?) Is the “catalyst” truly a catalyst? (stoichiometric vs. catalytic)  ESTABLISHED GREEN CHEMISTRY METRICS 1. Atom economy (atom efficiency) Mass of desired product∗ Atom Economy = Mass of all reactants∗ *including the stoichiometric coefficient 2. Environmental (E) factor E-factor = total waste (g) / product (g) 3. Atom utilization (variation of atom economy) % Atom Utilization = (MW of desired product/MW of all products) X 100 4. Reaction mass efficiency (RME) (mass of product C/(mass of A + mass of B)) X 100 ADDITIONAL METRICS USED IN GREEN CHEMISTRY 5. Process Mass Intensity (PMI) The total mass of materials to the mass of the isolated product. 6. Life Cycle Assessment (LCA) An assessment of environmental impacts associated with all of the stages of a product's life. ATOM ECONOMY Atom-Economy is a calculation based on the overall balanced chemical equation. It is simply the mass of desired product divided by the total mass of products. Or, since the mass of products equals the mass of reactants in a balanced chemical equation, atom economy is the mass of desired product divided by the total mass of reactants. Barry M. Trost Stanford University ATOM ECONOMY – THE PROCESS Single Stage Process: A+B C m.w. = molecular weight  ATOM ECONOMY Multi-Stage Process: (1) A + B C (2) C + D E (3) E + F G ATOM ECONOMY EXAMPLE TWO: IBUPROFEN SYNTHESIS The Problem: The Solution: BHC Company has developed and was developed and patented by the Boots implemented new greener synthesis is (U.S. 3,385,886). This synthesis is a six-step process Patents 4,981,995 and in and results in large quantities of unwanted ). In this process, most of the atoms of the chemical byproducts that must be are incorporated into the desired product (ibuprofen). This results in only small waste that is generated is a result of many of the of unwanted byproducts (very good atoms of the reactants not being incorporated atom economy/atom utilization) thus lessening unwanted byproducts (poor atom products. There are other environmental economy/atom utilization). process also advantages the are not used in stoichiometric amounts. - from Cann, M.C.; and Connelly, M.E. Real World Cases in Green Chemistry, American Chemical Society: Washington, DC, 2000 Ibuprofe n Synthesis ATOM ECONOMY – CONVERGENT ARM SYNTHESIS (1) A + B (1) F + G C H (2) C + D (2) H + I E J E+J P  EXERCISE: CALCULATE AE OF THE GREENER SYNTHESIS OF IBUPROFEN  EXERCISE: CALCULATE AE OF THE GREENER SYNTHESIS OF IBUPROFEN  EXERCISE: CALCULATE AE OF THE GREENER SYNTHESIS OF IBUPROFEN  EXERCISE: CALCULATE AE OF THE GREENER SYNTHESIS OF IBUPROFEN THE BROWN SYNTHESIS OF IBUPROFEN “INHERENT” ATOM ECONOMY OF REACTION CLASSES Some Atom Economic Some Atom Un-Economic Reactions Reactions Rearrangemen Substitution t Additio Eliminatio n n Diels- Wittig Alder Other concerted Grignar reactions d ENVIRONMENTAL FACTOR (E-FACTOR) Depends on the definition of waste Non-recoverable starting materials, solvent, catalysts. Undesired side products. Smaller E-factor means closer to zero waste E-factor can be used to estimate/calculate the total waste generated: Amount of Waste = Amount of Product x E-factor E-factor = total waste (g) / product (g) Annual production (t) Industry sector E-factor Waste produced (t) Oil 10 6-10 8 Ca. 0.1 105 – 10 7 refining Bulk 10 4-10 6 C Hydrogenation Chlorination or Bromination on alkene Hydration  Diels Alder Reactions An excellent way of forming 2 C-C bonds simultaneously. Concerted mechanism; highly regio- and stereoselective. Some reactions can be carried out in water or ionic liquids, which may also act as catalyst. Low atom economy reactions The “Bad”  Wittig Reactions A versatile method of preparing alkenes with an unambiguously placed double bond - gives high yields and takes place under mild conditions. Used Expensive because of poor atom economy, which is due to production of triphenylphosphine oxide (MWt 278).  Substitution Trading some parts of the molecule with another molecule AB + CD ---> AC +BD Friedel-Craft (Electrophilic ReactionAromatic Substitution)  Eliminatio n Taking part of a molecule out A ---> B + C or more Dehydrogenation Dehydroxylation Dehalogenation