phosgene only on demand. Both chemicals are highly toxic themselves, and their use in any event should be considered carefully, but solids avoid the problems associated with handling a toxic gas.
• Consider carefully the use of reagents containing toxic heavy metals. For example, proprietary detergents for glassware (used, if necessary, with ultrasonic baths) are a safer substitute for chromic acid cleaning solutions. Various chromium(VI) and other metal oxidants have been important in synthetic organic chemistry, but other oxidants are possible substitutes. When planning a reaction, consider the cost of disposal of heavy metal waste in addition to its utility. Search the literature for other oxidation reagents tailored to the specific needs of a given transformation. (For information about reducing the use of mercury in laboratory equipment, see section 5.B.8.)
• F-TEDA-BF4, or 1-chloromethyl-4-fluoro-1,4-diazoniabicyclo[2.2.2]octane bis(tetrafluoroborate), substitutes for more hazardous reagents in many fluorination procedures. To reduce the reactivity and toxicity risks associated with perchloryl fluoride, fluorine, and other fluorinating reagents, search the literature for appropriate substitutes.
• Avoid solvents listed as select carcinogens (for a definition of select carcinogens, see Chapter 4, section 4.C.3.4), reproductive toxins, or hazardous air pollutants. Choose solvents with relatively high American Conference of Governmental Industrial Hygienists threshold limit values. Recognizing that not all hazards can always be reduced simultaneously, the best substitute solvent meets needed experimental constraints but has physiochemical properties, such as boiling point, flash point, and dielectric constant that are similar to the original solvent. Although cost can be a factor, consider the benefits of safety, health, and the environment as well. For example, heptane is more costly than hexane, but is very similar physiochemically and is not listed by the U.S. Environmental Protection Agency (EPA) as a hazardous air pollutant. Toluene usually can substitute for the carcinogen benzene. Chemical suppliers now highlight solvents with lower hazards including reduced flammability and potential for peroxide formation.
• Supercritical fluids present an interesting case in conflicting green chemistry principles. Supercritical CO2 as a solvent involves a chemically relatively benign material, carbon dioxide. Reaction workup requires only ambient heat, and there is no hazardous waste. On the other hand, it requires elevated pressure. Supercritical solvents for chromatography and synthesis require specialized equipment for handling, but because of the ubiquity of chromatography methods operating at elevated pressure and the common nature of the pumps and vessels necessary, much of the hazard has been mitigated. The technology for using supercritical fluids has developed rapidly in recent years. Consider use of these materials, but with appropriate precaution and dedicated permanent equipment.
5.B.4 Design Experimental Products for Degradation After Use
Green chemistry practitioners plan synthesis and other processes so that, as part of the experiment, the products and byproducts are rendered safe or less hazardous. For example, they include in the experimental plan reaction workup steps that deactivate hazardous materials or reduce their toxicity.
5.B.5 Include Real-Time Controls to Prevent Pollution
To cut costs, firms are increasingly asking for justin-time delivery of raw materials and using other real-time controls. Green chemistry laboratories can borrow this strategy. A quantity of hazardous chemical not ordered is one to which trained laboratory personnel are not exposed, for which appropriate storage need not be found, which need not be tracked in an inventory control system, and which will not end up requiring costly disposal when it becomes a waste.
Part of acquiring a chemical is a life-cycle analysis. All costs associated with the presence of each chemical at an institution must be considered. The purchase cost is only the beginning; the handling costs, human as well as financial, and the disposal costs must be taken into account. Without close attention to these aspects of managing chemicals in a laboratory, orders are not likely to be minimized, and unused chemicals become a significant fraction of the laboratory’s hazardous waste.
The American Chemical Society’s booklet Less Is Better: Laboratory Chemical Management for Waste Reduction (Task Force on Laboratory Waste Management, 1993) gives several reasons for ordering chemicals in smaller containers, even if that means using several containers of a material for a single experiment:
• Consequence of breakage is substantially reduced for small package sizes.
• Risk of accident and exposure to hazardous material is less when handling smaller containers.
• Storeroom space needs are reduced when only a single size is inventoried.