W5 L3 - Green Chemistry and Sustainability Flashcards
Steps in Environmental Life Cycle Assessment of a medicine
- API formulation and formulation
- best not to use fossil fuel to prepare API - device production
- packaging
- distribution
- biologic drugs need to be kept cold, so may need air travel - patient use
- drug metabolised to chemicals that end up in urine/faeces - disposal (end-of-life or reuse)
- if not disposed safely, it may end up in landfill
Environmental Hazards of Clozapine (for schizophrenia)
ECOTOXICITY:
This product may be harmful to contaminated plant and animal life, especially in large quantities. All releases to terrestrial, atmospheric and aquatic environments should be avoided.
ENVIRONMENTAL EXPOSURE CONTROLS:
Controls should be engineered to prevent release to the environment, including procedures to prevent spills, atmospheric release and release to waterways.
Environmental Hazards of antibiotics
Low levels of antibiotics in the environment can cause AMR (Anti-Microbial Resistance)
Environmental Hazards of hormones
Can impact on reproduction of wildlife on land and sea
12 Principles of green chemistry
- prevent waste
- atom economy
- less hazardous synthesis
- design benign chemicals
- benign solvent and auxiliaries
- design for energy efficiency
- use of renewable feedstocks
- reduce derivatives
- catalysis (vs stoichiometric)
- design for degradation
- real-time analysis for pollution prevention
- inherently benign chemistry for accident prevention
Prevent Waste
- It is better to prevent the formation of waste than to treat or clean up waste after it is formed.
- Redesign chemical transformations to minimize the generation of hazardous waste.
- By preventing waste generation, hazards associated with waste storage (pollution), transportation and treatment are minimised
Atom Economy
- Atom Economy evaluates the efficiency of a chemical transformation.
- Atom economy is a ratio of the total mass of atoms in the desired product to the total mass of atoms in the reactants.
- Design chemical transformations that maximize the incorporation of all materials used in the process into the final product, resulting in few if any wasted atoms.
- Choosing transformations that incorporate most of the starting materials into the product is more efficient and minimizes waste.
Less Hazardous Synthesis
- Syntheses should be designed to use and generate substances that possess little or no toxicity to human health and the environment.
- Use less hazardous reagents whenever possible
- Design processes that do not produce hazardous by-products.
- Choosing reagents that pose the least risk.
Design Benign (Safer) Chemicals
New chemicals and products should be designed to have their desired function, while minimizing their toxicity and ecotoxicity.
Use Safe Solvents & Reagents
-The use of solvent & separation agents leads to considerable waste.
- Reduction of solvent volume or complete elimination of the solvent is often possible.
- Use less hazardous solvents/reagents.
- Purification steps generate large quantities of solvent & waste (e.g. chromatography supports).
- Avoid purifications when possible and minimize the use of solvents.
Safer Solvents: criteria for selection
- Chemical efficiency (for the reaction).
- Safety: AVOID low boiling point, low flash point, risk of peroxides. FIRE
- Health: acute, long term.
- Environment: Biodegradability, ecotoxicity, solubility in water, volatility, odour, life cycle analysis, effect on ozone layer (CFCs in inhalers now banned).
- Quality (important for last stage of synthesis, e.g. crystallisation of the drug)
- Cost & Recyclability
recommended solvents
- water is the best but can’t always be used as it can react with reagents
Banned solvents
- ethers as they are a fire hazard
- halogenated solvents as they are dangerous for ozone
Design for Energy Efficiency
- Energy requirements of chemical processes should be minimised for their environmental and economic impacts.
- Synthetic and purification methods should be designed for room temperature and pressure: avoids high energy costs associated with high temperature and pressure.
Energy in a chemical process
- Heating (electric)
- Cooling (water condensers, water circulators)
- Stirring
- Distillation
- Filtering
- Equipment (lab fume cupboard)
- Photochemistry
- Microwave chemistry
Source of energy:
Power plant – coal, oil, natural gas
Try use renewable non-fossil fuel based energies, to minimise global warming….Wind Farms or Solar Energy
Use of Renewable Feedstocks
- Chemical transformations should be designed to utilize raw materials and feedstocks that are renewable.
- Renewable feedstocks: agricultural products or the waste from other processes. (good)
- Depleting feedstocks: raw materials that are mined or generated from fossil fuels (petroleum, gas, coal). (bad)
Reduce Derivatives (Avoid Chemical Derivatisation)
- Unnecessary derivatization: for example adding & removal of protection groups
- Protection steps require additional reagents and can generate waste, lowering both chemical yield and atom efficiency.
- Synthetic transformations: more selective may eliminate the need for protecting groups.
Catalysis (vs Stoichiometric)
- Catalytic reagents are superior to stoichiometric reagents.
- Catalysts can serve several roles:
Enhance the selectivity of a reaction.
Reduce the temperature of a transformation (save energy & avoid unwanted side reactions).
Enhance the extent of conversion to products (increase yield)
Reduce reagent-based waste (catalysts are not consumed during the reaction).
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.
- Molecular-level design is required to develop products that will degrade into hazardless substances when they are released into the environment.
Environmental Persistence & Damage
- Sulfonated detergents
Alkylbenzene sulfonates – 1950’s & 60’s
Foam in sewage plants, rivers and streams
Persistence was due to long alkyl chain
Introduction of alkene group into the chain increased degradation - Chlorofluorocarbons (CFCs)
Do not break down, persist in atmosphere & destruction of ozone layer
Now banned as a refrigerant & in inhalers - DDT (4,4’-dichlorodiphenyltrichloroethane)Pesticide: NOW BANNED
Bioaccummulate and caused thinning of egg shells, decreasing bird
Real-Time analysis for Pollution Prevention
- Monitor the progress of a reaction to know when the reaction is complete or to detect the formation of any unwanted by-products.
- Analytical methodologies should be developed and used to allow for real-time, in-process monitoring and control to minimize the formation of hazardous substances.
Inherently Benign (safe) Chemistry for Accident Prevention
- Choose reagents and solvents that minimize the potential for explosions, fires and accidental release.
- Risks associated with these types of accidents can sometimes be reduced by altering the form (solid, liquid or gas) or composition of the reagents.
