Chapter 3 Benign Synthesis

Benign Synthesis

  • Principle 3: Synthetic methods should minimize toxicity to human health and the environment.

3.1 Eliminating Toxins in Synthesis

  • Focuses on the chemical synthesis process.

  • Unlike Principle 2 (Synthetic Efficiency) which emphasizes waste elimination, Principle 3 emphasizes toxin elimination.

  • Importance of chemical processes, even involving experts, due to potential accidents leading to toxic releases.

  • Historical references to significant environmental disasters (e.g., Bhopal, Fukushima).

3.1.1 Ethical Responsibilities

  • Toxicity presents a crucial hazard for chemists.

  • Preventing chemical spills and leaks during transport, production, usage, and disposal is vital.

  • Eliminating harmful chemicals reduces risk.

  • Ethical responsibility to protect workers and communities from hazardous wastes, as exemplified by the Love Canal incident.

3.1.2 Economic Advantages of Eliminating Hazards

  • Cost-effectiveness of preventing toxic releases compared to remediation and legal liabilities.

  • Avoiding toxins enhances profitability and product affordability.

  • Roger Sheldon's E-factor concept highlights the financial burden of hazardous waste disposal.

3.2 Regulatory Frameworks

  • Worker exposure to toxic chemicals in production regulated by numerous organizations (e.g., OSHA, REACH).

3.2.1 European REACH Program

  • EU’s comprehensive legislation overseeing chemicals; includes assessment of risk.

  • Emphasizes shared efforts among member states regarding chemical behaviors and risks.

3.2.2 USA Toxic Substances Control Act (TSCA)

  • Initial regulations in the 1970s aimed to manage toxic chemicals.

  • Exemption of chemicals in use before 1979 impedes innovation towards safer alternatives.

  • Recent TSCA revision strengthened regulations based on public health rather than cost-benefit analysis.

3.2.3 Toxicity Databases

  • ECHA Database: Extensive source for chemical toxicity (accessed July 2019).

  • ToxCastDB and ExpoCastDB: Databases established by EPA in 2011 for toxicity forecasting and exposure studies.

  • PubChem Database: Offers comprehensive information on over 84 million compounds.

3.3 Toxicology

  • Study of chemical toxicity encompasses biological effects and mechanisms.

  • Definitions of toxins: acute vs chronic, severity, and potency importance.

3.3.1 Acute and Chronic Toxins

  • Acute toxins: Immediate health impact; symptoms range from mild (lachrymators) to severe (fatal).

  • Chronic toxins: Develop gradually with long-term exposure; harder to identify causative agents.

3.3.2 Severity of Toxins

  • Severity categorization based on health impacts varies from irritants to neurotoxins.

  • Example: Dimethylmercury, a slow-acting potent toxin with fatal consequences.

3.3.3 Potency of Toxins

  • Potency defined by required dose for affecting 50% of individuals (LD50).

  • LD50 values inform comparisons across chemicals.

3.3.4 Non-monotonic Dose–Response Curves

  • Some toxins demonstrate varied effects at different concentrations (e.g., endocrine disruptors).

  • Importance of proper dose-response curve models.

3.3.5 Reversibility

  • Certain toxins (lead, mercury) are nearly irreversible in their biological impacts.

3.3.6 Reactivity

  • Highly reactive materials can create more biologically harmful metabolites during detoxification.

3.3.7 Additivity and Synergy

  • Toxins interact in complex ways; understanding mixtures is essential for accurate toxicity assessments.

3.4 Classifications of Chemical Toxins

3.4.1 Globally Harmonized System (GHS)

  • UN-established system for classifying and labeling toxic chemicals, aimed at harmonization in commerce.

3.4.2 Health Hazards

  • Health hazards categorized focussing on acute toxicity, skin corrosion, eye damage, carcinogenicity, and reproductive toxicity.

3.4.3 Target Organ Toxicity

  • Toxins classified according to their target organ effects; useful for predicting impacts during exposures.

3.5 Case Study: Greener Quantum Dot Synthesis (QD Vision)

  • QD Vision Inc. won a PGCC Award in 2014 for its less toxic QLED synthesis process.

  • Highlights the shift from highly toxic precursors to less volatile carboxylate-based methods, reducing hazardous waste.

  • Improved energy efficiency through reduced cadmium and other toxic emissions.

  • Company advocates energy savings and less cadmium release justifies toxic material use in markets.

3.6 Redox Reactions

  • Redox reactions are classified by electron transfer mechanisms; aim to reduce hazardous by-products in industrial processes.

3.10 Summary

  • Less toxic synthesis necessitates familiarity with toxicology and utilizing available databases for safer alternatives.

  • The QD Vision case study showcases practical application of green chemistry principles.

3.11 Problems: Benign Synthesis

  • Various problems encourage critical thinking concerning toxicology, regulatory frameworks, and synthesis strategies.