sufficient material for further work. Whether large or small scale, exercise precaution appropriate to the scale, as well as the inherent hazards, of the procedure.

Similarly, in many cases instrumental analyses—which require little reagent and generate very little waste in themselves—can be substituted for wet chemistry. Consider the waste reduction inherent in spectroscopic organic analysis versus chemical derivatization. And, hazardous waste reduction also reduces both compliance and disposal costs. When purchasing equipment to automate laboratory processes, choose equipment that is efficacious for the job at hand, but uses the least amount of reagents or solvents, or uses materials that are least hazardous. (See Vignette 5.1.)

5.B.2.1 Design Less Hazardous Laboratory Processes and Reaction Conditions

The third principle of green chemistry suggests that, where possible, syntheses should be designed using less toxic reagents. Although the use of a toxic reagent does not necessarily imply generation of a toxic waste, in line with the first principle, chemists should evaluate potential sources of hazardous waste expected from the proposed synthesis and incorporate strategies to minimize them.

VIGNETTE 5.1
Pollution prevention reduces solvent waste

A pollution prevention assessment of one organic chemistry research laboratory at a university revealed that each of the 25 researchers in the group used 1 L of solvent, usually acetone, every week to clean and/or rinse glassware, spatulas, and other items used in their procedures. For example, a researcher might rinse a spatula with acetone at the end of a procedure or use a solvent to speed the drying process after cleaning with soap and water. The excuses for using the solvent ranged from not having enough glassware available (thus the need to expedite drying) to lack of good brushes for cleaning residue to simply taking a shortcut to the cleaning process.

The lab purchased more glassware, better brushes, and an ultrasonicator that uses a mild detergent. The savings in solvent purchase and disposal paid back the price of the new purchases within 3 months. Later, the lab installed under-the-bench lab dishwashers, which resulted in even further reductions in solvent use for cleaning.

5.B.3 Use Safer Solvents and Other Materials

Traditionally, chemists have chosen reagents and materials to meet scientific criteria without always giving careful consideration to waste minimization or environmental objectives. In synthetic procedures, overall yield and purity of the desired product are important factors, because better yield implies lower cost. On the other hand, material substitution can be an important consideration in manufacturing process design because of the large quantity, and potential cost, of chemicals involved. The following questions should be considered when choosing a material to be used as a reagent or solvent in an experimental procedure:

   Can this material be replaced by one that will expose the experimenter, and others who handle it, to less potential hazard?

   Can this material be replaced by one that will reduce or eliminate the hazardous waste and the resulting cost of waste disposal?

   Can these steps be taken in conjunction with yield maximization and minimization of overall waste and cost?

All things being equal, laboratories are safer when they substitute nonhazardous, or less hazardous, chemicals where possible by considering alternative synthetic routes and alternative procedures for working up reaction mixtures. The following additional examples illustrate the application of this principle to common laboratory procedures:

   To reduce the amount of copper released to the sewer, use iron complexes rather than copper when studying spectrophotometry in general chemistry.

   In liquid scintillation counting of low-level radioactive samples, where possible, use nonflammable, lower toxicity, water-miscible solvents rather than xylene, toluene, or dioxane, so as to eliminate fire hazard and waste that must be incinerated.

   Substitute solid or liquid reagents for hazardous gases that must be used at elevated pressure. As an example, phosgene is a highly toxic gas occasionally used as a reagent in organic transformations. Its use requires proper precautions to contain the gas and handle and dispose of cylinders. Commercially available products such as diphosgene (trichloromethyl) chloroformate, a liquid, or triphosgene bis(trichloromethyl) carbonate, a low-melting solid, are often substituted for phosgene by appropriate adjustment of experimental conditions or are used to generate



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