1 Concepts of Green Chemistry

Concepts of Green Chemistry (SB p.207) Sustainable Development “ Meeting the needs of the present without compromising the ability of future generations to meet their own needs.” United Nations 1987,

Concepts of Green Chemistry (SB p.207) Sustainable Development 1. Economic sustainability 2. Social sustainability 3. Environmental sustainability Closely related to Green Chemistry

Concepts of Green Chemistry (SB p.208) Green Chemistry During the early 1990s,  the US Environmental Protection Agency (EPA) coined the phrase “green chemistry”  promote innovative chemical technologies  reduce or eliminate the use or generation of hazardous substances in the design, manufacture and use of chemical products

Concepts of Green Chemistry (SB p.208) Green Chemistry Green chemistry is about the design of chemical products and processes that reduce or eliminate the use and generation of hazardous substances. Environmental chemistry is the chemistry of the natural environment, and of pollutant chemicals in nature. Green chemistry seeks to reduce and prevent pollution at its source.

6 Green Chemistry can also be described as 1.Sustainable chemistry 2.Chemistry that is benign by design 3.Pollution prevention at the molecular level 4.All of the above

7 Green chemistry can be regarded as a reduction process. It aims at reducing the cost, waste, materials, energy, risk and hazard. Cost Energy Waste Materials Risk and hazard Reducing

8 The Twelve Principles of Green Chemistry: 1.Waste Prevention 2.Maximizing Atom Economy 3.Using Less Hazardous Chemical Syntheses 4.Producing Safer Chemical Products 5.Using Safer Solvents and Auxiliaries 6.Designing for Energy Efficiency 7.Using Renewable Raw Materials 8.Reducing Derivatives (fewer steps)

9 The Twelve Principles of Green Chemistry: 9.Using Catalysts 10.Designing Degradable Chemical Products 11.Developing Real-time Analysis for Pollution Prevention 12.Minimizing the Potential for Chemical Accidents

10 1.Waste prevention It is better to prevent the formation of waste than to treat or clean up the waste. Chemical wastes are undesirable products from chemical reactions. They are usually hazardous to the environment. Industrial processes should be designed to minimize the generation of waste.

11 2.Maximizing atom economy Traditionally, the success of a chemical reaction is judged by the percentage yield of product. It is possible to achieve 100% yield but the reaction may generate waste that is far greater in mass and volume than that of the desired product.

12 Consider the following reaction: AgNO 3 (aq) + KCl(aq)  AgCl(s) + KNO 3 (aq) ~100% yield undesirable Suggest reactions that have no undesirable products. Na(s) + Cl 2 (g)  2NaCl(s) N 2 (g) + 3H 2 (g)  2NH 3 (s) CH 2 =CH 2 (g) + H 2 (g)  C 2 H 6 (g) Direct combination Addition reaction

13 Concept of atom economy The greater the value of the atom economy, the better is the reaction to convert all the reactant atoms to the desired product.  Less waste

14 Calculate the atom economy of each of the following conversions C 4 H 9 OH + KBr + H 2 SO 4  C 4 H 9 Br + KHSO 4 + H 2 O 3C 4 H 9 OH + PBr 3  3C 4 H 9 Br + H 3 PO 3 = 47.0%  = 83.4% Non-S N S N 1  side products Greener

15 + 2HOCl + Ca(OH) 2 + CaCl 2 + 2H 2 O + H 2 O 2 catalyst + H 2 O 2   = 44.1% = 76.3%

16 + 2HOCl + Ca(OH) 2 + CaCl 2 + 2H 2 O + H 2 O 2 catalyst + H 2 O 2   Greener More harmful Less harmful harmless

17 3. Using less hazardous chemical syntheses Chemical syntheses should be designed to use or generate substances that possess little or no toxicity to humans and the environment.

18 Adipic acid is the essential feedstock for making synthetic fibres such as nylon. Consider the synthesis of adipic acid (HOOC(CH 2 ) 4 COOH). C 6 H 6 HOOC(CH 2 ) 4 COOH Traditional method C 6 H 12 O 6 HOOC(CH 2 ) 4 COOH New method

19 Traditional Method benzene (1) H 2, Ni-Al 2 O 3, 25  55 atm cyclohexane (2) Co/O 2, 8  9.5 atm cyclohexanone cyclohexanol (3) conc. HNO 3 adipic acid dinitrogen oxide

20 Traditional Method benzene (1) H 2, Ni-Al 2 O 3, 25  55 atm cyclohexane (2) Co/O 2, 8  9.5 atm cyclohexanone cyclohexanol (3) conc. HNO 3 adipic acid dinitrogen oxide In step 1, the starting material for the synthesis is benzene, which is a known carcinogen. The synthesis has the following risks and hazards:

21 Traditional Method benzene (1) H 2, Ni-Al 2 O 3, 25  55 atm cyclohexane (2) Co/O 2, 8  9.5 atm cyclohexanone cyclohexanol (3) conc. HNO 3 adipic acid dinitrogen oxide In step 2, the oxidation of cyclohexane with air may lead to an uncontrolled reaction. It has the risk of explosion. Not all of the cobalt catalysts can be recovered. This may lead to the disposal of a heavy metal to the environment.

22 Traditional Method benzene (1) H 2, Ni-Al 2 O 3, 25  55 atm cyclohexane (2) Co/O 2, 8  9.5 atm cyclohexanone cyclohexanol (3) conc. HNO 3 adipic acid dinitrogen oxide In step 3, dinitrogen oxide or nitrous oxide (N 2 O) gas is produced as a by- product. It is a greenhouse gas with an effect which is 200 times the effect of carbon dioxide.

23 biosynthetic pathway D-glucose (1) E. coli 3-dehydroshikimic acid (3) Pt/H 2, 3  4 atm muconic acid adipic acid (2) E. coli Much greener 1. the starting material, glucose, is harmless. shikimic acid 1 2 3

24 biosynthetic pathway D-glucose (1) E. coli 3-dehydroshikimic acid (3) Pt/H 2, 3  4 atm muconic acid adipic acid (2) E. coli Much greener 2.E. coli is used to catalyse two steps of the reaction. This reduces the use of certain chemical reagents with significant toxicity.

25 biosynthetic pathway D-glucose (1) E. coli 3-dehydroshikimic acid (3) Pt/H 2, 3  4 atm muconic acid adipic acid (2) E. coli Much greener 3.there are no by-products generated during the synthesis.

26 4. Producing safer chemical products The chemical products synthesized should be safe to use. For example, chemicals called organotin compounds(Anti-biofouling agent) were used in large ships to prevent accumulation of barnacles( 藤壺 ) and marine plants traditionally.

27 The accumulation of barnacles( 藤壺 )on the ship may increase the resistance to its movement.

28 However, organotin compounds are highly toxic to the surrounding marine life. Then, Rohm and Haas Company developed a non-toxic alternative called Sea-Nine TM. It degrades quickly in the marine environment and is not toxic to the surrounding marine life.

29 5. Using safer solvents and auxiliaries The solvents and auxiliaries (e.g. drying agent, blowing agent, etc.) used in chemical syntheses will become part of the wastes. They may cause environmental pollution and health hazard.

30 CFCs : - unreactive volatile liquids or easily liquefied gases low flammability low toxicity  Cleaning solvents Propellants Refrigerants Blowing agents They were eventually banned because they deplete the ozone layer.

31 Screening of UV radiations by ozone layer = nm =250 nm ~99% of UV radiation from the sun are screened out

32 They were eventually banned because of their ability to deplete the ozone layer. One Cl  free radical can destroy ozone molecules Cl  + O 3 → ClO + O 2 ClO + O 3 → Cl  + 2O 2 CFCl 3 → CFCl 2 + Cl  uv chain reaction

33 Nowadays, CO 2 is used to replace CFCs as the blowing agent. CO 2 is non-toxic and non-flammable. It does not deplete the ozone layer. STYROFOAM produced with carbon dioxide as the blowing agent

34 Many solvents currently used in the chemical industry are harmful and volatile They are known as Volatile Organic Compounds (VOCs) E.g. Propanone, benzene, dichloromethane, dibromomethane, chloroform and carbon tetrachloride. VOCs + NO x photochemical smog UV

35 1.Using ionic liquids as solvents Low m.p. due to poor packing between ions of significantly different sizes High b.p. due to ionic nature  Low volatility E.g.

36 By modifying the structures and charges of the ions, More viscous ionic liquids can exhibit specific properties such as m.p., viscosity, volatility & hydrophobicity to meet the particular needs of a synthesis. Designer solvents

37 Na 2 WO 4 as catalyst [CH 3 (n-C 8 H 17 ) 3 N]HSO 4 as phase transfer agent  C, 8h 30% 93% yield The reaction can be carried out in aqueous medium Sato, K.; Aoki, M.; Noyori, R. Science, 1998 A “Greener” Route to Adipic Acid  18.0 Atom economy == 67.0%

38 Advantages of using ionic liquids over using VOCs as solvents (2010 AL Paper 1 Q.6) 1.Tailor-made 2.Low b.p. Not easily escape to the environment Volatile organic reactants/products can be easily removed by simple distillation. The solvents can be easily recycled and reused 3.Low flammability due to their low vapour pressure

39 Advantages of using ionic liquids over using VOCs as solvents 4.Wide liquid range due to low m.p. and high b.p. Organic syntheses can occur at higher temperatures 5.Ionic nature can allow organic syntheses involving ionic species.

40 2.Using supercritical CO 2 as solvent in decaffeination Coffee beans decaffenation with caffeine without caffeine In the past, solvents used for decaffeination are harmful to the environment and human beings E.g. CHCl 3, CH 2 Cl 2, benzene

41 T /  C P / atm Solid Liquid Vapour A T B C P c = 73atm T c = 31  C Gas Supercritical fluid As dense as a liquid As mobile as a gas CO 2

42 T /  C P / atm Solid Liquid Vapour A T B C P c = 73atm T c = 31  C Gas Supercritical fluid Decaffeination using supercritical CO 2 CO 2