Ethics and Responsibility in Science 1 Flashcards
Define Metrology?
- Meterology is the scientific study of measurement
- It establishes a common understanding of units
- (crucial for linking/comparing human activities)
Metrology is divided into three basic overlapping activities
These are…
- The definition of units of measurement - magnitude
- The realisation of these units of measurement in practice
- Traceability - linking measurements made in practice to the reference standards (similar to quality assessment/assurance)
What is the difference between accuracy vs precision
- Accuracy refers to how close a measurement is to the true or correct value
- While precision refers to how consistent or repeatable multiple measurements are, regardless of their correctness
The following is a chemical process to make Naproxen
Identifying some issues with the cleanness of this process…
- Despite a high yield (95%) you make a lot of phosphine oxide side product
- This phosphine oxide will go into landfill + depletes phosphorous
- Can control sterochemistry but a racemic mixture is made, which requires the removal of 50% of product to meet FDA standards
- Uses bromine, as it is a liquid and an aggressive + corrosive material - consideration over materials in reactors
What things would we might want to consider within metrics for the sustainability of a chemical process?
- Energy
- Material’s including plant
- Waste
- Risk and Hazards
- Toxicity
- Impact on environment
- Cost
Two of the most common metrics are Atom Economy and E-factor
Both methods focus on what?
Both methods concentrate on reducing waste
(other factors like toxicity, risks, energy consumption are ignored)
What is the equation for Percentage yield
What is a key issue with percentage yield?
You may have a high yielding reaction however produce a lot of waste
An example of this is the Wittig reaction with an average 86% yield but produces 2446g of waste per 1000g of starting material
What is the equation for atom economy?
What types of reactions have a 100% atom economy
- Rearrangements (e.g. Claisen rearrangement)
- Hydrogenations
- Carbonylations
- Cycloadditions
The Diel-Alder reaction makes the pesticide ‘Aldrin’ with high efficiency
With around an overall Atom Economy of 82.2%
What is the issue however?
Aldrin is whats called a persisten pollutant as it stays in the soil for years and is now band worldwide
Exposure linked to health problems such as Parkinson’s, breast cancer and immune, reproductive and nervous system damage (it accumulated in fatty tissue)
What types of reaction classes have a low Atom Efficiency?
- Substitutions
- Eliminations
What is the formula for E-factors
What industry has a suprising low E-factor
Oil-refinery’s E-factor is really low as all parts of the crude oil are used hence is pretty efficient
What is the advantage of using E-factors over other metrics
It takes into account solvent use
What are the disadvantages of using E-factors over other metrics
- What if large volumes of solvent are water, or if the waste consists of dilute aqueous solutions of benign inorganics (doesn’t include process water e.g for cooling/steaming)
- Still concentrates of waste rather than other factors which could also contribute to Greeness (for example if a small amount of highly toxic byproduct was formed)
- Green Chemistry Principle 9: “Catalytic reagents are superior to stoichiometric ones” (E-factor only focuses on stoichiometric)
What is the equation for Atom Efficiency?
What is the equation for Reaction Mass Efficiency?
This was the original pantented process to make Ibuprofen by boots
What are some flaws with the process?
- Formation of by-products + stoichiometric amounts of waste
- Lots of acids + bases which are salting out creating waste problems
- Solvent for this process is CCl₄ (carcinogen)
This is the newer process used to form Ibuprofen once the Boots patent finished
Why is it better?
- Got a smaller number of telescoped step - fewer seperations+purification - smaller amount of energy goes into the process + waste which comes out
- More sustainable process due to a higher degree of catalysis
- There is a lower degree of stoichiometric and super stoichiometric transformations
This is the newer process used to form Ibuprofen once the Boots patent finished
How could we characterised it is a better process?
- It would prove better against the 12-Principles of Green Chemistry
- Also moving towards a more circular economy e.g. vapourised HF can be caputred and recirculated + decompressed AND same for nickek which can also be recovered + reprocessed + reused
What is the core benefit of conducting a Life Cycle Assessment (LCA)
The benefit of a Life Cycle assessment is that is provides a comprehensive evaluation of the environmental impact of product, process, or system from raw material extraction to disposal
Why are metrics are part of LCA similar to different lens
- We change the lens to fit the question which changes the focal length of the interrogation of our process
- Are we looking at the molecule, bond, aggregate, or product etc?
- Are we looking at the community who uses it?
What part of a metric cannot be measured?
- The ethical bounds of a process
- e.g. how you feel about a molecule, what you feel about a product or is it the right thing to do?
- Does out process/foundation industries actually help us to achieve the sustainable development goals
How do the 9 Planetary Boundaries relate the metrics?
- This paper uses the 9 different domains which are critical-life systems which we need for quality life on the planet
- And uses indicators, so of which can be measured using metrology while some are difficult to measures
- And uses those as indicators of activity and health/well-being of the planet
- DDT was dubbed the “ideal pesticide”
- Is was inexpensive to prepare with a wide spectrum in activity to control insects/pests/beetles/flys and mosquitos
- Why was it so benefical
- Important to control the population size of aerial vectors
- For the viability of food and agriculture
- And also the spread of diseases like malaria + typhoid
What were the concerns with DDT found in the 1950s?
- Peregrine falcons (UK) were found to be laying thinner eggs
- Decline in bird populations - later shown due to DDE (other insecticides)
- It was subsequently banned in 1972 - concerns of individuals who still suffer from vector born diseases however
How does the DDT problem relate to metrology?
- When the biological effects of DDT were seen, we could not detect materials are very low biologically active concentrations (pg/fg)
- Appreciation of toxicity - changes very rapidly
Thomas Midgely Jnr invented Freon 21 which was the first chlorofluorocarbon (CFCs). They were later employed as refrigerants, polymer blowing agents and propellants
Although future issues with CFCs were found, why were they revolutionary at the time?
- To avoid significant reheat costs, the fluid should evaporate close to operating temperature, i.e. room temperature
- The compression fluid is circulated continually, the only input is the energy to run the compressor motor and pump the fluid
- Early refrigeration (air conditioning) units were based upon SO₂, CH₃Cl, Propane or NH₃ - smelly, flammable and toxic - safer coolant
- STGs
Why did CFC prove to be an issue?
- Radical cleavage of C-X bonds leads to catastrophic chain reaction with atmospheric ozone (O₃)
- O₃ is cricual for life/shields harmful solar irradiation
- CFCs were Banned under the Montreal Protocol
- Midgely was also the inventor, in the 1920’s of the fuel additive to petroleum to ensure that fuel burned efficiently - avoiding pre-combustion/pinking
- This was tetraethyl lead (TEL) which as added to petrol for 80yrs
- What was the issue?
- Resulting in the lead poisoning of thousands globally as a result of TEL
- Was completely removed from fuel by 1996
Why do questions around chemical synthesis have multiple answers?
- Metric systems tend to emphasis one specific facet of a process, multiple metrics must be used to build a picture of the relative interactions and impacts
- planetary boundaries as an example
- They are multi-impact - requiring complex network analysis - LCA - all are retrospective and require data, often large data to inform choice
