Análisis nutrimental

M. Angell, J.P. Kassirer. N Engl J Med 1998; 339:839. 5. Ecology of Increasing Disease

D. Pimentel, M.L. Tort, L.D’Anna, A. Krawic, J. Berger, J. Rossman, F. Mugo, N. Doon, M. Shriberg, E. Howard, S. Lee, and J. Talbot. BioScience 1998; 48:817.

EXERCISES

1. Check the companies in your area in the Toxic Re- lease Inventory (or a comparable compilation; see preface for Web sites) Compare their releases with

2. Do you look at nuclear energy as a way to avert global warming or as a potential problem? 3. Are the Environmental Protection Agency and the

Food and Drug Administration (or comparable agencies in your country) impediments to progress or our guardians? Are they antiquated and unrealistic?

4. Check a year of Chem Eng News, Chem Ind (Lond), or other chemical news magazine for fires, explosions, spills, and other accidents.

5. Were there any fires, explosions, spills and acci- dents in your laboratory last year? If so, who goofed on what?

6. Do you contribute to air and water pollution? 7. Are there any Superfund or comparable sites near

you? If so, what led to them?

8. How do you feel about the use of tobacco, alcohol, salt, chemical pesticides, and being overweight and sedentary?

9. Should herbal teas, alternative medicines, and health food supplements be regulated by the government?

10. Do oil spills heal quickly or is there a long-term ef- fect on nature?

11. Should all rivers and lakes be fishable and swimmable?

12. Pick out some wastes of industry that have often been pollutants. How could they have been avoided or made into useful products? If you have trouble finding some, try lignin, fly ash, “red mud” (a waste from refining aluminum ore), spent sulfu- ric acid, chicken feathers, nitrogen oxides from making nylon, or calcium sulfite from scrubbing stack gases.

I. INTRODUCTION

The chemicals used as reagents are often highly reactive and are used because they are. As such, they may react readily with components of the human body, such as water, or the hydroxyl and amino groups of proteins and nucleic acids. The next chapters will deal with efforts to replace these toxic materials with inherently safer chemistry. It may not be possible to replace them completely. This leads to a hierarchy of approaches (a tiered approach follows), from the least change to the most change:

No change: Those using the process are confident that they can handle it. They may not have had any acci- dents recently.

Go to a closed system and carefully avoid leaks. Do not ship the chemical or store it in quantity. Prefer-

ably, generate it on site in situ as needed.

Farm out the work to specialist companies that are ex- perienced in handling it and are willing to do custom syntheses.

Replace the reagent with a less, but still toxic, reagent that may be easier to handle.

Replace the reagent with a nontoxic reagent.

Make the product by a different route, using nontoxic reagents.

Substitute other products for the ones made with the toxic reagent, preferably ones based on renewable

banned when the effect on children’s IQ was found. Chlorofluorocarbons are taxed, as well as being phased out, because they destroy the ozone layer. This scheme will be applied to phosgene (bp 7.56°C.),1

a reagent that is made by the reaction of carbon monoxide with chlorine (2.1) over activated carbon at elevated tem- peratures.2

CO  Cl2→ COCl2 ( 2.1)

Both the reagents and the product are quite toxic. Phosgene was used as a war gas in World War I. It causes irritation of the eyes and nose at 3 ppm or more. The effects are insidi- ous because the major discomfort comes not at first, but later. Current practice is to use it in closed systems and not to store or ship it. Workers wear indicator film badges to monitor their exposure and to alert them to danger. Custom phosgenations are offered by PPG Industries3, Hatco4, Rhone–Poulenc,5and SNPE6. SNPE has a plant that makes the phosgene as needed, so that at any one time only a few kilograms are present in the reactor and piping, an amount that can be handled by a scrubber using 10% sodium hy- droxide. This is fine unless something springs a leak. The company distributed a book on phosgene in 1998.7There has been some concern about the development of phosgene in chloroform that has been stored a long time.8 The best solution is to use solvents other than chloroform (a car- cinogen). The largest industrial use of phosgene is in the

Aldrich Chemical Co. catalog describes it as a moisture- sensitive lachrymator that should be handled with gloves in a hood.

Cl3COCOOCCl3

triphosgene (2.2)

Many investigators are studying ways to make iso- cyanates and polycarbonates without the use of phosgene. Their efforts will be reviewed in the following sections.

II. PREPARATION OF ISOCYANATES

The usual method of preparation can be illustrated by that of toluenediisocyanate (2.1) a reagent that is then reacted with diols to form polyurethanes10_{(see also reviews}11_).

Most of the weight of the phosgene is lost as hydrogen chloride, which is probably neutralized to form salts that are discarded. Other commonly used diisocyanates are also made by reacting the diamines with phosgene (2.2).

The diisocyanates are reacted with diols to produce polyurethanes that end up in consumer products, such as seat cushions, mattresses, insulation, car bumpers, swim suits, floor coatings, paints, and adhesives.12_{The aromatic} diisocyanates are cheaper, but yield less light-stable poly- mers than the aliphatic ones.

A. Other Ways to Make Isocyanates from