Toxic Organic Compounds

CHAPTER 10 Pesticides

Introduction DDT

The Accumulation of Organochlorines in Biological Systems Other Organochlorine Insecticides

Box 10-1: The Controversial Insecticide Endosulfan Principles of Toxicology Organophosphate and Carbamate Insecticides Natural and Green Insecticides, and Integrated Pest Management Green Chemistry: Insecticides That Target Only Certain Insects

Green Chemistry: A New Method for Controlling Termites Herbicides

Box 10-2: Genetically Engineered Plants Summary

Box 10-3: The Environmental Distribution of Pollutants Review Questions Green Chemistry Questions Additional Problems Further Readings Websites of Interest

CHAPTER 11 Dioxins, Furans, and PCBs

Introduction Dioxins

Box 11-1: Deducing the Probable Chlorophenolic Origins of a Dioxin PCBs

Box 11-2: Predicting the Furans That Will Form from a Given PCB Other Sources of Dioxins and Furans

Green Chemistry: H202, an Environmentally Benign Bleaching Agent for the Production of Paper The Health Effects of Dioxins, Furans, and PCBs Review Questions Green Chemistry Questions Additional Problems Websites of Interest

415 421 425 430

434 441 447

450 452 457 461 462

466 466

467 467

469 469

475 477

489 493

CHAPTER 12 Other Toxic Organic Compounds of Environmental Concern 507

Introduction 507

Polynuclear Aromatic Hydrocarbons (PAHs) 508

Box 12-!: More on the Mechanism of PAH Carcinogenesis 515

Environmental Estrogens 517

The Long-Range Transport of Atmospheric Pollutants 525

Brominated Fire Retardants 528

Perfluorinated Sulfonates 533

Review Questions 53 5

Additional Problems 535

Further Readings 535

Websites of Interest 536

Environmental Instrumental Analysis III: Electron Capture Detection of Pesticides 537

Environmental Instrumental Analysis IV: Gas Chromatography/Mass

Spectrometry (GC/MS) 540

Scientific American Feature Article: Tackling Malaria 544

part iv WATER CHEMISTRY AND

WATER POLLUTION 555

CHAPTER 13 The Chemistry of Natural Waters 557

Introduction 557

Oxidation-Reduction Chemistry in Natural Waters 559

Box 13-1: Redox Equation Balancing Reviewed 560

Green Chemistry: Enzymatic Preparation of Cotton Textiles 565

Acid-Base Chemistry in Natural Waters: The Carbonate System 578

Box 13-2: Derivation of the Equations for Species Diagram Curves 580

Ion Concentrations in Natural Waters and Drinking Water 589

Review Questions 598

Green Chemistry Questions 599

Additional Problems 599

Further Readings 600

Websites of Interest 600

CHAPTER 14 The Pollution and Purification of Water 601

Introduction 601

Water Disinfection 602

Box 14-1: Activated Carbon 603

Box 14-2: The Desalination of Salty Water 608 Box 14-3: The Mechanism of Chloroform Production in Drinking Water 614

Groundwater: Its Supply, Chemical Contamination, and Remediation 618 The Chemical Contamination and Treatment of Wastewater and Sewage 636 Box 14-4: Time Dependence of Concentrations in the Two-Step

Oxidation of Ammonia 639 Green Chemistry: Sodium Iminodisuccinate—A Biodegradable

Chelating Agent 642

Modern Wastewater and Air Purification Techniques 648

Review Questions 652

Green Chemistry Questions 654

Additional Problems 654

Further Readings 656

Websites of Interest 656

Environmental Instrumental Analysis V: Ion Chromatography of Environmentally Significant Anions 657

part v ME 1ALS, SOILS, SEDIMENTS, AND

WASTE DISPOSAL 661

CHAPTER 15 Toxic Heavy Metals 663

Introduction 663

Mercury 666

Lead 679 Green Chemistry: Replacement of Lead in Electrodeposition

Coatings 684

Cadmium 692

Arsenic 694

Box 15-1: Organotin Compounds 697

Chromium 705 Green Chemistry: Removing the Arsenic and Chromium from Pressure-Treated Wood 707

Review Questions 709

Green Chemistry Questions 710

Additional Problems 710

Further Readings 712

Websites of Interest 712

CHAPTER 16 Wastes, Soils, and Sediments 713

Introduction 713

Domestic and Commercial Garbage: Its Disposal and Minimization 714 Green Chemistry: Polyaspartate—A Biodegradable Antiscalant and Dispersing Agent 721

The Recycling of Household and Commercial Waste 723

Green Chemistry: Development of Recyclable Carpeting 732

Soils and Sediments 735

Box 16-1: The Superfund Program 748

Hazardous Wastes 758

Review Questions 766

Green Chemistry Questions 767

Additional Problems 767

Further Readings 768

Websites of Interest 769

Environmental Instrumental Analysis VI: Inductively

Coupled Plasma Determination of Lead 770

Scientific American Feature Article: Mapping Mercury 775

Appendix: Background Organic Chemistry AP-1

Answers to Selected Odd-Numbered Problems AN-1

Index 1-1

To the Student

There are many definitions of environmental chemistry. To some, it is solely the chemistry of Earth's natural processes in air, water, and soil. More commonly, as in this book, it is concerned principally with the chemical aspects of problems that humankind has created in the natural environment. Part of this infringement on the natural chemistry of our planet has resulted from the activities of our everyday lives. In addition, chemists, through the products they create and the processes used to create them, have also had a significant impact on the chemistry of the environment. •

Chemistry has played a major role in the advancement of society and in making our lives longer, healthier, more comfortable, and more enjoyable. The effects of human-made chemicals are ubiquitous and in many instances quite positive. Without chemistry there would be no pharmaceutical drugs, no computers, no automobiles, no TVs, no DVDs, no lights, no synthetic fibers. However, along with all the positive advances that result from chemistry, copious amounts of toxic and corrosive chemicals have also been produced and dispersed into the environment. Historically, chemists as a group have not always paid enough attention to the environmental consequences of their activities.

But it is not just the chemical industry, or even industry as a whole, that has emitted troublesome substances into the air, water, and soil. The fantastic increase in population and affluence since the Industrial Revolution has overloaded our atmosphere with carbon dioxide and toxic air pollutants, our waters with sewage, and our soil with garbage. We are exceeding the planet's natural capacity to cope with waste, and, in many cases, we do not know the consequences of these actions. As a character in Margaret Atwood's recent novel Oryx and Crake, stated, "The whole world is now one vast uncontrolled experiment."

During your journey through the chapters in this text, you will see that scientists do have a good handle on many environmental chemistry problems and have suggested ways—although sometimes very expensive ones—to keep us from inheriting the whirlwind of uncontrolled experiments on the planet. Chemists have also become more aware of the contributions of their own profession and industry in creating pollution and have created the concept of green chemistry to help minimize their environmental footprint in the future.

To illustrate these efforts, case studies of their initiatives have been included in the book. However, as a prelude to these studies, in the Introduction we discuss some of the history of environmental regulations—especially in the United States—as well as the principles and an illustrative application of the green chemistry movement that has developed.

Although the science underlying environmental problems is often maddeningly complex, its central aspects can usually be understood and appreciated with only introductory chemistry as background preparation. However, students who have not had some introduction to organic chemistry are encouraged to work through the Appendix on Background Organic Chemistry, particularly before tackling Chapters 10 to 12. Furthermore, the listing of general chemistry concepts that will be used in each chapter should assist in identifying topics from earlier courses that are worth reviewing.

To the Instructor

Environmental Chemistry, Fourth Edition, has been revised and updated in line with comments and suggestions from various users and reviewers of the third edition. In particular, where possible, we have fulfilled the request that larger chapters be split so that they can be covered in a week or two. In several places, some of the more advanced material has been placed in boxes that have been reordered to appear at the end of a series of related chapters.

Some instructors prefer to cover chapters in a different order than we have used, so the list of concepts that opens each chapter, describing material covered elsewhere in the hook, should help facilitate restructuring.

As in previous editions, the background required to solve both in-text and end-of-chapter problems is either developed in the book or would have been covered previously in a general chemistry course—as listed at the beginning of each chapter. Where appropriate, hints are given to start students on the solution. The Solutions Manual to the text includes worked solutions to all problems (except for Review Questions, which are designed to direct students back to descriptive material within each chapter).

New to This Edition

• All chapters now start with an outline of the concepts and methods from introductory chemistry and from previous chapters of the text that will be used in the chapter. This will give students a better idea of what background material to review, and it will give instructors a better idea of what is assumed in the material.

• Detailed applications of several of the newsworthy topics in the text have been formulated as Case Studies and are available on the website for this text (www. whfreeman.com/envchem4) •

• Much of the detail concerning CFCs (Chapter 2) has been cut, as it is now largely irrelevant since CFCs have been banned. However, the background and politics of the controversy about the remaining ozone-depleting substance have been documented in the new web-based Case Study Strawberry Fields—The Banning of Methyl Bromide.

• Material on converters and traps for diesel engines and lawn mowers, as well as the problems of two-stroke engines, together with the initiatives to produce low-sulfur gasoline and diesel fuel, have been added to Chapter 3.

• The relatively advanced material on the distribution of particle sizes in tropospheric air has been rewritten, with a new and more informative illustration, and placed in Box 3-2,

• A new green chemistry case concerning the use of ionic liquids has been added to Chapter 3.

• The information concerning the aqueous-phase oxidation of atmospheric S02 has been moved to a more relevant position in Chapter 3.

• Material concerning particulates in air as a health risk has been updated and reformulated as the web-based Case Study The Effect of Urban Air Particulates on Human Mortality, associated with Chapter 4.

• Material on the acid rain problem in China has been added and the concept of critical load introduced (Chapter 4).

• The Indoor Air Pollution section on benzene has been expanded to introduce the term air toxics and to discuss methylated benzenes as well as the parent compound (Chapter 4).

• The term albedo is now introduced early in Chapter 6, and sunlight reflection is further discussed.

• Material introducing the greenhouse effect and the discussion of Earth's energy balance, previously split between these two areas, has logically been combined and expanded by introducing a simple physical model for greenhouse warming in Chapter 6. A more sophisticated model of the greenhouse effect has been added as Box 6-1.

• A phase diagram for C02, showing the supercritical region, has been included to illustrate the green chemistry case in Box 6-2.

• The section on methane has been rewritten and updated, with new graphs provided, especially with regard to its current concentration plateau (Chapter 6).

• Updates on climate change based on the IPCC Fourth Assessment Report are included in Chapter 6.

• Chapter 7 now begins with a more extensive discussion of energy usage and C02 emissions by country, with an analysis of the factors that affect them globally and with particular reference to the United States and China.

• A separate Box 7-1, on fractional distillation of petroleum, has been added.

• Material on carbon sequestration—particularly on the chemistry involved—has been expanded and updated, given the growing importance of this technique (Chapter 7).

• Material in Chapter 8 concerning renewable energy sources—wind, hydroelectricity, biofuels, and geothermals—has been added, along with the web-based Case Study Mercury Pollution and the James Bay Hydroelectric Project (Canada).

• A new green chemistry case concerning the production of biodiesel has been added to Chapter 8.

• The chapter Radioactivity, Radon, and Nuclear Energy (now Chapter 9) has been repositioned into Part II, Energy and Climate Change.

• In the discussions about radioactivity (Chapter 9), definitions of the bequerel and the curie are now provided. The controversial hormesis theory is also introduced, and the debate about the existence of a threshold for health damage from radioactivity has been expanded. The material on the reprocessing of nuclear waste has been developed into a fuller discussion of the chemistry involved.

• The history of DDT, and an expanded discussion about banning it, have been incorporated into the web-based Case Study To Ban or Not to Ban DDT? Its History and Future, associated with Chapter 10.

• The term lethal concentration has been introduced in Chapter 10.

• The Chapter 10 material on organophosphate insecticides has been reorganized so that a description of their molecular structure now precedes explanation of their uses, etc. Pesticide toxicities are now discussed in terms of World Health Organization (WHO) categories.

• An extended treatment of the controversial insecticide endosulfan has been developed in the new Box 10-1.

• At the suggestion of several reviewers, a short discussion of the degradation of pesticides is now incorporated in Chapter 10.

• Chapter 11 now includes additional help for students in solving problems that involve the production of dioxins from chlorophenols.

• The section concerning PBDEs (Chapter 12) now incorporates a description of the chemical mechanism by which brominated fire retardants operate, and it has been extensively updated with new information concerning the uses and regulatory status of PBDEs.

• Following the suggestion of several reviewers, a new Environmental Instrumentation Analysis box on the widespread use of GC/MS for pesticide analysis has been added at the end of Part III.

• The new Box 13-1 reviews the assignment of oxidation numbers and the balancing of redox equations.

• The sections on sulfur compounds and acid mine drainage have been revised and repositioned (Chapter 13) so that the pE concept need not be coveted as background to them.

• At reviewer request, the species diagram for the C02-carbonate system and its derivation have been added (Chapter 13).

• A new web-based Case Study, Mercury Emissions from Power Plants, a topic of considerable current interest, has been added (Chapter 15).

• The information concerning the arsenic-contaminated drinking water in Asia has been updated, and more information has been added concerning the ways As can be removed from water (Chapter 15).

Scientific American Feature Articles

We are proud to feature several Scientific American articles in this edition. The topics discussed in these articles are highly relevant to topics covered in the book and allow students access to the most current thinking about contemporary environmental issues by active researchers.

Supplements

The Solutions Manual (1-4292-1005-2) includes worked solutions to virtually all problems (except for Review Questions, which are designed to direct students back to the appropriate material within each chapter).

Students and instructors interested in pursuing specific topics in more detail should consult the Further Readings section at the end of each chapter, as well as the Websites of Interest that are given for each chapter on the website, www.whfreeman.com/envchem4.

To All Readers of the Text

The authors are happy to receive comments and suggestions about the content of this book from instructors and students via e-mail: Colin Baird at [email protected] and Michael Cann at [email protected].

Acknowledgments

The authors wish to express their gratitude and appreciation to a number of people who in various ways have contributed to this edition of the book:

To Professor Thomas Chasteen of Sam Houston State University for masterfully writing the Environmental Instrumental Analysis boxes, which shed light on the perspective of scientists working in this discipline and add much to the book.

To Professor Brian D. Wagner of the University of Prince Edward Island, for supplying some of the Additional Problems included in the book.

To the students and instructors who have used previous editions of the text and who, via their reviews and e-mails, have pointed out subsections and problems that needed clarifying or expanding.

To W. H. Freeman and Company Senior Acquisitions Editor for the third and fourth editions, Jessica Fiorillo; Project Editor Vivien Weiss; and Assistant Editor Kathryn Treadway—for their encouragement, ideas, insightful suggestions, patience, and organizational abilities. To Margaret Comaskey for her careful copyediting and suggestions àgain in this edition, to Ted Szczepanski for finding the photographs, to Nancy Walker for obtaining permissions for figures and photographs, to Blake,Logan for design, and to Paul Rohloff for coordinating production.

Colin Baird wishes to express his thanks. . .

To Ron Martin and Martin Stillman, his colleagues at the University of Western Ontario who used the first two editions and have made valuable suggestions for improvement, and to his colleagues at Western and elsewhere who supplied information or answered queries on various subjects: Myra Gordon, Duncan Hunter, Roland Haines, Edgar Warnhoff, Marguerite Kane, Currie Palmer, Rob Lipson, Dave Shoesmith, Felix Lee, Peter Guthrie, Geoff Rayner-Canham, and Chris Willis.

To his secretaries through the years—Sandy McCaw, Clara Fernandez, Darlene McDonald, Diana Timmermans, Elizabeth Moreau, Shannon Woodhouse, Wendy Smith, and Judy Purves—for their brave attempts to decipher his writing and for dealing with the always-urgent problems that authors seem to have.

To his daughter Jenny—and others of her generation, and those following them—for whom this subject matter really matters.

Mike Cann wishes to express his thanks ...

To his students (especially Marc Connelly and Tom Umile) and fellow faculty at the University of Scranton, who have made valuable suggestions and contributions to his understanding of green chemistry and environmental chemistry.

To Joe Breen, who was one of the pioneers of green chemistry and one of the founders of the Green Chemistry Institute.

To Paul Anastas (Center for Green Chemistry and Green Engineering at Yale) and Tracy Williamson (U.S. Environmental Protection Agency), whose boundless energy and enthusiasm for green chemistry are contagious.

To Debra Jennings, who for over 30 years as the chemistry department secretary has, to his amazement, managed to decode his handwriting and simply put up with him, always in good spirit.

To his loving wife, Cynthia, who has graciously and enthusiastically endured countless discussions of green chemistry and environmental chemistry.

To his children, Holly and Geoffrey, and his grandchildren, McKenna, Alexia, Alan Joshua, Samantha, and Arik, who, along with future generations, will reap the rewards of sustainable chemistry.

Both authors wish to express thanks to the reviewers of the fourth edition of the text for their helpful comments and suggestions:

Ann Marie Anderssohn, University of Portland

D. Neal Boehnke, Jacksonville University

Nathan W. Bower, Colorado College

Michael Brabec, Eastern Michigan University

Patrick J. Castle, U.S. Air Force Academy

Jihong Cole-Dai, South Dakota State University

Arlene R. Courtney, Western Oregon University

James Donaldson, University of Toronto'Scarborough

Jennifer DuBois, University of Notre Dame

Robert Haines, University of Prince Edward Island

Yelda Hangun-Balkir, California University of Pennsylvania

Michael Ketterer, Northern Arizona University

John J. Manock, University of North Carolina-Wilmington

Steven Mylon, Lafayette College

Myrna Simpson, University of Toronto

Chuck Smithhart, Delta State University

Barbara Stallman, Lourdes College

Steven Sylvester, Washington State University, Vancouver

Brian Wagner, University of Prince Edward Island

Feiyue Wang, University of Manitoba

Z. Diane Xie, University of Utah

Chunlong (Carl) Zhang, University of Howston-Ciear Lake

ENVIRONMENTAL CHEMISTRY

Introduction

In this book you will study the chemistry of the air, water, and soil, and the effects of anthropogenic activities on the chemistry of the Earth. In addition, you will learn about green chemistry, which aims to design technologies that lessen the ecological footprint of our activities.

Environmental chemistry deals with the reactions, fates, movements, and sources of chemicals in the air, water, and soil. In the absence of humans, the discussion would be limited to naturally occurring chemicals. Today, with the burgeoning population of the Earth, coupled with continually advancing technology, human activities have an ever-increasing influence on the chemistry of the environment. To the earliest humans, and even until less than a century ago, humans must have thought of the Earth as so vast that human activity could scarcely have any more than local effects on the soil, water, and air. Today we realize that our activities can have not only local and regional but also global consequences.

There are now many indications that we have exceeded the carrying capacity of the Earth, i.e., the ability of the planet to convert our wastes back into resources (often called nature's interest) as quickly as we consume its natural resources and produce waste. Some say that we are living beyond the "interest" that nature provides us and dipping into nature's capital. In short, many of our activities are not sustainable.

As we write these introductory remarks, we are reminded of the environmental consequences of human activities that impact the areas where we live and beyond. Colin spends his summers on a small island just off the North Atlantic coast in Nova Scotia, while Mike spends a few weeks each winter on the west coast of southern Florida a few kilometers from the Gulf of Mexico. Although these locations are a great distance apart, if predictions are correct, both may be permanently submerged by the end of this century as a result of rising sea levels brought about by enhanced global warming (see Chapters 6 and 7). The public footbridge that links Colin's island to the mainland is treated with creosote, and the local residents no longer harvest mussels from the beds below for fear they may be contaminated with PAHs (Chapter 12). Colin's well on this island was tested for arsenic, a common pollutant in that

If mankind, is to survive, we shall require a substantially new manner of thinking.

Aftert Einstein area of abandoned gold mines (Chapter 15). To the north, the once robust cod fishing industry of Newfoundland has collapsed due to overfishing. Mike lives in northeastern Pennsylvania on a lake where the wood in his dock is preserved with the heavy metals arsenic, chromium, and copper (Chapter 15). Within a short distance are two landfills (Chapter 16), which take in an excess of 8000 tonnes of garbage per day (from municipalities as far as 150 kilometers away), two Superfund sites (Chapter 16), and a nuclear power plant that generates plutonium and other radioactive wastes for which there is no working disposal plan in the United States (Chapter 9). Colin's home in London, Ontario, is within an hour's drive of Lake Erie, famous for nearly having "died" of phosphate pollution (Chapter 14), and nuclear power plants on Lake Huron. Nearby farmers grow corn to supply to a new factory that produces ethanol for use as an alternative fuel (Chapter 8); in Ottawa, a Canadian company has built the first demonstration plant to convert the cellulose from agricultural residue to ethanol (Chapter 8).

On sunny days we apply extra sunscreen because of the thinning of the ozone layer (Chapters 1 and 2). Three of the best salmon rivers in North America in Nova Scotia must be stocked each season because the salmon no longer migrate up the acidified waters. Many of the lakes and streams of the beautiful Adirondack region of upstate New York are a deceptively beautiful crystal clear, only because they are virtually devoid of plant and animal life, again because of acidified waters (Chapters 3 and 4).

Environmental issues like these probably have parallels with those that exist where you live; learning more about them may convince you that environ' mental chemistry is not just a topic of academic interest, but one that touches your life every day in very practical ways. Many of these environmental threats are a consequence of anthropogenic activities over the last 50 to 100 years.

In 1983 the United Nations charged a special commission with developing a plan for long-term sustainable development. In 1987 the report titled "Our Common Future" was issued. In this report (more commonly known as the The Brundtland Report), the following definition of sustainable development is found:

Sustainable development is development that meets the needs of the present without compromising the ability of future generations to meet their own needs.

Although there are many definitions of sustainable development (or sus-tainability), this is the most widely used. The three intersecting areas of sustainability are focused on society, the economy, and the environment. Together they are known as the triple bottom line. In all three areas, consumption (particularly of natural resources) and the concomitant production of waste are central issues.

The concept of an "ecological footprint" is an attempt to measure the amount of biologically productive space that is needed to support a particular human lifestyle. Currently there are about 4-5 acres of biologically productive space for each person on the Earth. This land provides us with the resources that we need to support our lifestyles and to receive the waste that we generate and convert it back into resources. If the entire population of 6.5 billion people lived like Colin and Mike (rather typical North Americans), the total ecological footprint would require five planet Earths. Obviously, everyone on the planet can't live in as large and inefficient a house, drive as many kilometers in such an inefficient vehicle, consume as much food (particularly meat) and energy, create as much waste, etc., as those living in the most developed regions. As countries such as China and India, the two most populous countries in the world (with a combined total of over 2.3 billion people) and two of the fastest growing economies in the world, continue to develop, they look to the lifestyles of the 1 billion people on the planet who live in already developed countries. Factor in the expected increase in population to 9 billion by 2050, and clearly this is not sustainable development.

The people of the world (in particular, those in developed countries) must strive to lead a lifestyle that is sustainable. This does not necessarily mean a lower standard of living for those in the- developed world, but it does mean finding ways (more efficient technologies along with conservation) to reduce our consumption of natural resouces and the concomitant production of waste. A widespread movement toward the development and implementation of sustainable technologies or green technologies currently seeks to reduce energy and resource consumption, to use and develop renewable resources, and to reduce the production of waste. In chemistry, these developments are known as green chemistry, which is described later in this Introduction and which we will see as a theme throughout this text.

A Brief History of Environmental Regulation

In the United States, many environmental disasters came to a head in the 1960s and 1970s. In 1962, the deleterious effects of the insecticide DDT were brought to the forefront by Rachel Carson in her seminal book, Silent Spring. In 1969, the Cayahoga River, which runs through Cleveland, Ohio, was so polluted with industrial waste that it caught fire. The Love Canal neighborhood in Niagara Falls, New York, was built on the site of a chemical dump; in the mid-1970s, during an especially rainy season, toxic waste began to ooze into the basements of area homes, and drums of waste surfaced. The U.S. government purchased the land and cordoned off the entire Love Canal neighborhood. These distressing events were brought into the homes of Americans on the nightly news and, along with other environmental disasters, became rallying points for environmental reform.

This era saw the creation of the U.S. Environmental Protection Agency (EPA) in 1970, the celebration of the first Earth Day, also in 1970, and a mushrooming number of environmental laws. Before 1960, there were approximately 20 environmental laws in the United States; now there are over 120. Most of the earliest of these were focused on conservation, or setting aside land from development. The focus of environmental laws changed dramatically, starting in the 1960s. Some of the most familiar U.S. environmental legislation includes the Clean Air Act (1970) and the Clean Water Act (originally known as the Federal Water Pollution Control Act Amendments of 1972). One of the major provisions of these acts was to set up pollution control programs. In effect, these programs attempted to control the release of toxic and other harmful chemicals into the environment. The Comprehensive Environmental Response, Compensation and Liability Act (also known as the Superfund Act) set up a procedure and provided funds for cleaning up toxic waste sites. These acts thus focused on dealing with pollutants after they were produced and are known as "end-of-the-pipe solutions" and "command and control laws."

The risk due to a hazardous substance is a function of the exposure to and the hazard level of the substance:

risk = f (exposure X hazard)

The end-of-the-pipe laws attempt to control risk by preventing our exposure to these substances. However, exposure controls inevitably fail, which points out the weakness of these laws. The Pollution Prevention Act of 1990 is the only U.S. environmental act that focuses on the paradigm of prevention of pollution at the source: If hazardous substances are not used or produced, then their risk is eliminated. There is also no need to worry about controlling exposure, controlling dispersion into the environment, or cleaning up hazardous chemicals.

Green Chemistry

The U.S. Pollution Prevention Act of 1990 set the stage for green chemistry. Green chemistry became a formal focus of the U.S. EPA in 1991 and became part of a new direction set by the EPA, by which the agency worked with and encouraged companies to voluntarily find ways to reduce the environmental consequences of their activities. Paul Anastas and John Warner defined green chemistry as the design of chemical products and processes that reduce or eliminate the use and generation of hazardous substances. Moreover, green chemistry seeks to

• reduce waste (especially toxic waste),

• reduce the consumption of resources and ideally use renewable resources, and

reduce energy consumption.

Anastas and Warner also formulated the 12 principles of green chemistry. These principles provide guidelines for chemists in assessing the environmental impact of their work.

The 12 Principles of Green Chemistry

1. It is better to prevent waste than to treat or clean up waste after it is formed.

2. Synthetic methods should be designed to maximize the incorporation of all materials used in the process into the final product.

3. Wherever practicable, synthetic methodologies should be designed to use and generate substances that possess little or no toxicity to human health and the environment.

4. Chemical products should be designed to preserve efficacy of function while reducing toxicity.

5. The use of auxiliary substances (solvents, separation agents, etc.) should be made unnecessary whenever possible and innocuous when used.

6. Energy requirements should be recognized for their environmental and economic impacts and should be minimized. Synthetic methods should be conducted at ambient temperature and pressure.

7. A raw material feedstock should be renewable rather than depleting whenever technically and economically practical.

8. Unnecessary derivatization (blocking group, protection/deprotection, temporary modification of physical/chemical processes) should be avoided whenever possible.

9. Catalytic reagents (as selective as possible) are superior to stoichiometric reagents.

10. Chemical products should be designed so that at the end of their function they do not persist in the environment and ultimately break down into innocuous degradation products.

11. Analytical methodologies need to be further developed to allow for real-time in-process monitoring and control prior to the formation of hazardous substances.

12. Substances and the form of a substance used in a chemical process should be chosen so as to minimize the potential for chemical accidents, including releases, explosions, and fires.

In many of the chapters that follow, real-world examples of green chemistry are discussed. During these discussions, you should keep in mind the 12 principles of green chemistry and decide which of them are met by the particular example. Although we won't consider all of the principles at this point, a brief discussion of some of them is beneficial.

• Principle 1 is the heart of green chemistry and places the emphasis on the prevention of pollution at the source rather than cleaning up waste after it has formed.

• Principles 2-5, 7-10, and 12 focus on the materials that are used in the production of chemicals and the products that are formed.

° In a chemical synthesis, unwanted by-products are often formed in addition to the desired product(s); these compounds are usually discarded as waste. Principle 2 encourages chemists to look for synthetic routes that maximize the production of the desired product(s) and at the same time minimize the production of unwanted by-products (see the synthesis of ibuprofen discussed later).

° Principles 3 and 4 stress that the toxicity of materials and products should be kept to a minimum. As we will see in later discussions of green chemistry, Principle 4 is often met when new pesticides are designed with reduced toxicity to nontarget organisms.

0 During the course of a synthesis, chemists employ not only compounds that are actually involved in the reaction (reactants) but also auxiliary substances such as solvents (to dissolve the reactants and to purify the products) and agents that are used to separate and dry the products. These materials are usually used in much larger quantities than the reactants, and they contribute a great deal to the waste produced during a chemical synthesis. When chemists are designing a synthesis, Principle 5 reminds them to consider ways to minimize the use of these auxiliary substances.

° Many organic chemicals are produced from petroleum, which is a nonrenewable resource. Principle 7 urges chemists to consider ways to produce chemicals from renewable resources such as plant material (biomass).

° As we will see in Chapter 10, DDT is an effective pesticide. However, a major environmental problem is its stability in the natural environment. DDT degrades slowly. Although it has been banned in most developed countries since the 1970s (in the United States since 1972), it can still be found in the environment, particularly in the fatty tissues of animals. Principle 10 stresses the need to consider the lifetimes of chemicals in the environment and the need to focus on materials (such as pesticides) that degrade rapidly in the environment to harmless substances.

• Many chemical reactions require heating or cooling and/or a pressure higher or lower than atmospheric pressure. Performing reactions at other than ambient temperature and pressure requires energy; Principle 6 reminds chemists of these considerations when designing a synthesis.

Presidential Green Chemistry Challenge Awards

To recognize outstanding examples of green chemistry, the Presidential Green Chemistry Challenge Awards were established in 1996 by the U.S. EPA. Generally five awards are given each year at a ceremony held at the National Academy of Sciences in Washington, D.C. The awards are given in the following three categories.

1. The use of alternative synthetic pathways for green chemistry, such as:

• catalysis/biocatalysis,

• natural processes, such as photochemistry and biomimetic synthesis, and

• alternative feedstocks that are more innocuous and renewable (e.g., biomass).

2. The use of alternative reaction conditions for green chemistry, such as:

• solvents that have a reduced impact on human health and the environment and

• increased selectivity and reduced wastes and emissions.

3. The design of safer chemicals that are, for example:

• less toxic than current alternatives and

• inherently safer with regard to accident potential.

Real-World Examples of Green Chemistry

To introduce you to the important and exciting world of green chemistry, we provide you with real-world cases of green chemistry throughout this book. These examples are winners of Presidential Green Chemistry Challenge Awards. As you explore these examples, it will become apparent that green chemistry is very important in lowering the ecological footprint of chemical products and processes in the air, water, and soil.

We begin our journey into this important topic by briefly exploring how green chemistry can be applied to the synthesis of ibuprofen, an important everyday drug. We will see how the redesign of a chemical synthesis can eliminate a great deal of waste/pollution and reduce the amount of resources required.

Before discussing the synthesis of ibuprofen, we must first take a brief look at the concept of atom economy. This concept was developed by Barry Trost of Stanford University and won a Presidential Green Chemistry Challenge Award in 1998. Atom economy focuses our attention on Green Chemistry Principle 2 by asking the question: How many of the atoms of the reactants are incorporated into the final desired product and how many are wasted? As we will see in our discussion of die synthesis of ibuprofen, when chemists synthesize a compound, not all the atoms of the reactants are utilized in the desired product. Many of these atoms may end up in unwanted products (by-products), which are in many instances considered waste. These waste by-products may be toxic and can cause considerable environmental damage if not disposed of properly. In the past, waste products from chemical and other processes have not been disposed of properly, and environmental disasters such as the Love Canal have resulted.

Before we take on the synthesis of ibuprofen, let us look at a simple illustration of the concept of atom economy using the production of the desired compound, 1 -bromobutane (compound 4) from 1-butanol (compound 1).

H-jC— CH2— CHi— CH2—OH + Na—Br + H2S04->

If we inspect this reaction, we find that not only is the desired product formed, but so are the unwanted by-products sodium hydrogen sulfate and water (compounds 5 and 6). On the left side of this reaction, all the atoms of the reactants that are utilized in the desired product are printed in green and the remainder of the atoms (which become part of our waste by-products) in black. If we add up all of the green atoms on the left side of the reaction, we get 4 C, 9 H, and I Br (reflecting the molecular formula of the desired product, 1 -bromobutane). The molar mass of these atoms collectively is 137 g/mol, the molar mass of 1-bromobutane. Adding up all the atoms of the reactants gives 4 C, 12 H, 5 O, 1 Br, 1 Na, and 1 S, and the total molar mass of all these atoms is 275 g/mol. If we take the molar mass of the atoms that are utilized, divide by the molar mass of all the atoms, and multiply by 100, we obtain the % atom economy, here 50%. Thus we see that half of the molar mass of all the atoms of the reactants is wasted and only half is actually incorporated into the desired product.

% atom economy = (molar mass of atoms utilized/molar mass of all reactants) X 100

This is one method of accessing the efficiency of a reaction. Armed with this information, a chemist may want to explore other methods of producing 1-bromobutane that have a greater % atom economy. We will now see how the concept of atom economy can be applied to the preparation of ibuprofen.

Ibuprofen is a common analgesic and anti-inflammatory drug found in such brand name products as Advil, Motrin, and Medipren. The first commercial synthesis of ibuprofen was by the Boots Company PLC of Nottingham, England. This synthesis, which has been used since the 1960s, is shown in Figure In-1. Although a detailed discussion of the chemistry of this synthesis

ÇH,

CH 5 f"^

y-T

ibuprofen

co2c2h5

co2c2h5

Step 5

Step 5

FIGURE In-1 The Boots Company synthesis of ibuprofen. [Source: M, C. Cann arid M. E. Connelly, Real-World Cases in Green Chemistry (Washington, D.C.: American Chemical Society, 2000).|

is beyond the scope of this book, we can calculate its atom economy and obtain some idea of the waste produced. In Figure In-1, the atoms printed in green are those that are incorporated into the final desired product, ibupro-fen, while those in black end up in waste by-products. By inspecting the structures of each of the reactants, we determine that the total of all the atoms in the reactants is 20 C, 42 H, 1 N, 10 O, 1 CI, and 1 Na. The molar mass of all these atoms totals 514.5 g/mol. We also determine that the number of atoms of the reactants that are utilized in the ibuprofen (the atoms printed in green) is 13 C, 18 H, and 2 O (the molecular formula of ibuprofen). These atoms have a molar mass of 206.0 g/mol (the molar mass of the ibuprofen). The ratio of the molar mass of the utilized atoms to the molar mass of all the reactant atoms, multiplied by 100, gives an atom economy of 40%:

% atom economy = (molar mass of atoms utilized/molar mass of all reactants) X 100

Only 40% of the molar mass of all the atoms of the reactants in this synthesis ends up in the ibuprofen; 60% is wasted. Because more than 30 million pounds of ibuprofen are produced each year, if we produced all the ibuprofen by this synthesis, there would be over 35 million pounds of unwanted waste produced just from the poor atom economy of this synthesis,

A new synthesis (Figure In-2) of ibuprofen was developed by the BHC Company (a joint venture of the Boots Company PLC and Hoechst Celanese Corporation), which won a Presidential Green Chemistry Challenge Award in 1997. This synthesis has only three steps as opposed to the six-step Boots synthesis and is less wasteful in many ways. One of the most obvious improvements is the increased atom economy. The molar mass of all the atoms of the reactants in this synthesis is 266.0 g/mol (13 C, 22 H, 4 O; note that the HF, Raney nickel, and the Pd in this synthesis are used only in catalytic amounts and thus do not contribute to the atom economy), while the utilized atoms (printed in green) again weigh 206.0 g/mol. This yields a % atom economy of 77%.

% atom economy = (molar mass of atoms utilized/molar mass of all reactants) X 100

A by-product from the acetic anhydride (reactant 2) used in step 1 is acetic acid. The acetic acid is isolated and utilized, which increases the atom economy of this synthesis to more than 99%. Additional environmental advantages of the BHC synthesis include the elimination of auxiliary materials (Principle 5), such as solvents and the aluminum chloride promoter

CH3

CH,

f-

r^^COOH

7

ibuprofen

FIGURE ln-2 The BHC Company synthesis of ibuprofen. (Source: M. C. Carin and M. E. Connelly, Real-World Cases in Green Chemistry (Washington, D.C.: American Chemical Society, 20001.1

(replaced with the catalyst HF, Principle 9), and higher yields. Thus the green chemistry of the BHC Company synthesis lowers the environmental impact for the synthesis of ibuprofen by lowering the consumption of reac-tants and auxiliary substances while simultaneously reducing the waste.

Other improved syntheses that are winners of Presidential Green Chemistry Cha llenge Awards include the pesticide Roundup, the antiviral agent Cytovene, and the active ingredient in the antidepressant Zoloft.

Green chemistry provides a paradigm for reducing both the consumption of resources and the production of waste, thus moving toward sustainability. One of the primary considerations in the manufacture of ehcmicals must be the environmental impact of the chemical and the process by which it is produced. Sustainable chemistry must become part of the psyche of not only chemists and scientists, but also business leaders and policymakers. With this in mind, real-world examples of green chemistry have been incorporated throughout this text to expose you (our future scientists, business leaders, and policymakers) to sustainable chemistry.

Further Readings

1. P. T, Anastas and J. C. Warner, Green Chemistry Theory and Practice (New York: Oxford University Press, 1998).

2. M. C. Cann and M. E. Connelly, Real-World Cases in Green Chemistry (Washington, D.C.: American Chemical Society, 2000).

3. M. C. Cann and T. P. Umile, Real-World Cases in Green Chemistry, vol. 2 (Washington, D.C.: American Chemical Society, 2008).

4. M. C. Cann, "Bringing State of the Art, Applied, Novel, Green Chemistry to the Classroom, by Employing the Presidential Green Chemistry Challenge Awards," Journal of Chemical Education 76 (1999): 1639-1641.

5. M. C. Cann, "Greening the Chemistry Curriculum at the University of Scranton," Green Chemistry 3 (2001): G23^G25.

6. M. A. Ryan and M. Tinnesand, eds., Introduction to Green Chemistry (Washington, D.C.: American Chemical Society, 2002).

7. M. Kirchhoff and M. A Ryan, eds., Greener Approaches to Undergraduate Chemistry Experiments (Washington, D.C.: American Chemical Society, 2002).

8. World Commission on Environment and Development, Our Common Future [The Bruntland Report] (New York: Oxford University Press, 1987).

9. M. Wackernagel and W. Rees, Our Ecological Footprint: Reducing Human Impact on the Earth (Gabriola Island, BC: New Society Publishers, 1996).

Websites of Interest

1. EPA "Green Chemistry": http://www.epa.gov/greenchemistry/index.html

2, The Green Chemistry Institute of the American Chemical Society website: http://www.chemistry.Org/portal/a/c/s/l/acsdisplay.html?DOC = greenchemistryinstitute\index.html

3. University of Scranton "Green Chemistry": http://academic.scranton.edu/ faculty/CANNM 1/greenchemistry.html

4. American Chemical Society Green Chemistry Educational Activities: http://www.chemistry.org/portal/a/c/s/l/acsdisplay.html?DOC=education\ greenchem \ index.html

5. Owr Common Future (Report of the World Commission on Environment and Development): http://ringofpeace.org/environment/brundtland.html

6. Ecological Footprint: http://www.myfootprint.org/

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