Penny le Couteur & Jay Burreson

by Napoleon's Buttons: How 17 Molecules Changed History

  FABULOUS FREONS

  The ideal refrigerant molecule has special practical requirements. It must vaporize within the right temperature range; it must liquefy by compression—again within the required temperature range; and it must absorb relatively large amounts of heat as it vaporizes. Ammonia, ether, methyl chloride, sulfur dioxide, and similar molecules satisfied these technical requirements as good refrigerants. But they either decomposed, were fire hazards, were poisonous, or smelled terrible—sometimes all of these.

  Despite the problems with refrigerants, the demand for refrigeration, both commercial and domestic, grew. Commercial refrigeration, developed to meet the demand of trade, preceded home refrigeration by fifty or more years. The first refrigerators for in-home use became available in 1913 and by the 1920s had begun to replace the more traditional icebox, supplied with ice from industrial ice plants. In some early home refrigerators the noisy compressor unit was installed in the basement, separate from the food box.

  Looking for an answer to concerns about toxic and explosive refrigerants, mechanical engineer Thomas Midgley, Jr.—already successful as the developer of tetraethyl lead, a substance added to gasoline to reduce engine knock—and chemist Albert Henne, working at the Frigidaire Division of General Motors, considered compounds that were likely to have boiling points within the defined range of a refrigeration cycle. Most of the known compounds that fitted this criterion were already in use or had been eliminated as impractical, but one possibility, compounds of fluorine, had not been considered. The element fluorine is a highly toxic and corrosive gas, and few organic compounds containing fluorine had ever been prepared.

  Midgley and Henne decided to prepare a number of different molecules containing one or two carbon atoms and a varying number of fluorine and chlorine atoms instead of hydrogen atoms. The resulting compounds, chlorofluorocarbons (or CFCs, as they are now known), admirably fulfilled all the technical requirements of a refrigerant and were also very stable, nonflammable, nontoxic, inexpensive to manufacture, and nearly odorless.

  In a very dramatic manner Midgley demonstrated the safety of his new refrigerants at a 1930 meeting of the American Chemical Society in Atlanta, Georgia. He poured some liquid CFC into an open container, and as the refrigerant boiled, he put his face in the vapor, opened his mouth, and took a deep breath. Turning to a previously lit candle he slowly exhaled the CFC, extinguishing the candle flame—a remarkable and unusual demonstration of the nonexplosive and nonpoisonous properties of this chlorofluorocarbon.

  A number of different CFC molecules were then put into use as refrigerants: dichlorodifluoromethane, which was more usually known by its Du Pont Corporation trade name of Freon 12; trichlorofluoromethane, or Freon 11; and 1,2-dichloro-1,1,2,2,-tetrafluoroethane, or Freon 114.

  The numbers in the Freon names were a code developed by Midgley and Henne. The first digit is the number of carbon atoms minus one. If this is zero it does not get written; thus Freon 12 is really Freon 012. The next number is the number of hydrogen atoms (if any) plus one. The last number is the number of fluorine atoms. Any remaining atoms are chlorine.

  CFCs were the perfect refrigerants. They revolutionized the refrigeration business and became the basis for a huge increase in home refrigeration especially as more and more homes were connected to electricity. By the 1950s a refrigerator was considered a standard home appliance in the developed world. Shopping for fresh foods on a daily basis was no longer necessary. Perishable items could be stored safely and meals readied ahead of time. The frozen food industry blossomed; new products were developed; ready-to-eat meals—TV dinners—were introduced. CFCs changed how we bought food, how we prepared food, and even what food we ate. Refrigeration allowed heat-sensitive antibiotics, vaccines, and other medications to be stored and shipped around the world.

  A plentiful supply of safe refrigerant molecules also gave people the means of cooling something other than food—their surroundings. For centuries capturing natural breezes, moving air by means of fans, and using the cooling effect of evaporating water had been the main ways of coping with the temperature of hot climates. Once CFCs arrived on the scene, the fledgling air-conditioning industry expanded rapidly. In tropical regions and other places where summers were extremely hot, air-conditioning made homes, hospitals, offices, factories, malls, cars—anywhere people lived and worked—more comfortable.

  Other uses for CFCs were also found. As they reacted with virtually nothing, they made ideal propellants for virtually everything that could be applied through a spray can. Hair sprays, shaving foams, colognes, suntan lotions, whipped cream toppings, cheese spreads, furniture polish, carpet cleaners, bathtub mildew removers, and insecticides are just a few of the huge variety of products that were forced through the tiny holes of aerosol cans by expanding CFC vapor.

  Some CFCs were perfect for foaming agents in the manufacture of the very light and porous polymers used as packing materials, as insulating foam in buildings, as fast food containers, and as “Styrofoam” coffee cups. The solvent properties of other CFCs, such as Freon 113, made them ideal cleaners for circuit boards and other electronic parts. Substitution of a bromine atom for a chlorine or a fluorine in the CFC molecule produced heavier compounds of higher boiling point, such as Freon 13B1 (the code is adjusted to indicate bromine), just right for use in fire extinguishers.

  By the early 1970s almost a million tons of CFCs and related compounds were being produced annually. It seemed that these molecules were indeed ideal, perfectly suited to their roles in the modern world, without a drawback or a downside. They seemed to make the world a better place.

  FREONS REVEAL THEIR DARK SIDE

  The glow around CFCs lasted until 1974, when disturbing findings were announced by researchers Sherwood Rowland and Mario Molina at another meeting of the American Chemical Society in Atlanta. They had found that the very stability of CFCs presented a totally unexpected and extremely disturbing problem.

  Unlike less stable compounds, CFCs don’t break down by ordinary chemical reactions, a property that had originally made them so appealing. CFCs released into the lower atmosphere drift around for years or even decades, then eventually rise to the stratosphere, where they are ruptured by solar radiation. Within the stratosphere there is a stratum stretching from about fifteen to thirty kilometers above the surface of the earth known as the ozone layer. This may sound like a fairly thick cover, but if this same ozone layer were to exist at sea level pressures, it would measure only millimeters. In the rarefied region of the stratosphere, the air pressure is so low that the ozone layer is vastly expanded.

  Ozone is an elemental form of oxygen. The only difference between these forms is the number of atoms of oxygen in each molecule—oxygen is O2 and ozone is O3—but the two molecules have very different properties. High above the ozone layer intense radiation from the sun breaks the bond in an oxygen molecule, producing two oxygen atoms:

  These oxygen atoms float down to the ozone layer, where each reacts with another oxygen molecule to form ozone:

  Within the ozone layer ozone molecules are broken up by high-energy ultraviolet radiation to form an oxygen molecule and an oxygen atom.

  Two oxygen atoms now recombine to form the O2 molecule:

  Thus in the ozone layer ozone is constantly being made and constantly being broken down. Over millennia these two processes have achieved a balance, so that the concentration of ozone in the Earth’s atmosphere remains relatively constant. This arrangement has important consequences for life on earth; ozone in the ozone layer absorbs the portion of the ultraviolet spectrum from the sun that is most harmful to living things. It has been said that we live under an umbrella of ozone that protects us from the sun’s deadly radiation.

  But Rowland and Molina’s research findings showed that chlorine atoms increase the rate of breakdown of ozone molecules. As a first step, a chlorine atom collides with ozone to form a chlorine monoxide molecule (ClO), and leaves behind an oxygen molecule:

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bsp; In the next step ClO reacts with an oxygen atom to form an oxygen molecule and regenerates the chlorine atom:

  Rowland and Molina suggested that this overall reaction could upset the balance between ozone and oxygen molecules, as chlorine atoms hasten the breakup of ozone but have no effect on the making of ozone. A chlorine atom, used up in the first step of the ozone breakdown and produced anew in the second step, acts as a catalyst; that is, it increases the rate of reaction but is not itself consumed. This is the most alarming aspect of the effect of chlorine atoms on the ozone layer—not just that ozone molecules are being destroyed by chlorine but that the same chlorine atom can catalyze this breakdown again and again. One estimate is that, on average, every chlorine atom that finds its way to the upper atmosphere via a CFC molecule will destroy a hundred thousand ozone molecules before it is deactivated. For every 1 percent of ozone layer depletion, an additional 2 percent of damaging ultraviolet radiation might penetrate the Earth’s atmosphere.

  Based on their experimental results, Rowland and Molina predicted that chlorine atoms from CFCs and related compounds would, on reaching the stratosphere, start the decomposition of the ozone layer. At the time of their research billions of CFC molecules were being released into the atmosphere every day. The news that CFCs posed a real and immediate threat of depletion of the ozone layer and to the health and safety of all living things prompted some concerned reaction, but it was a number of years—and further studies, reports, task forces, voluntary phaseouts, and partial bans—before CFCs were completely banned.

  Data from an entirely unexpected source provided the political will to ban CFCs. In 1985 studies from the Antarctic showed a growing depletion in the ozone layer above the South Pole. That the largest so-called “hole” in the ozone layer could appear in winter above a virtually uninhabited continent—there was little call for refrigerants or aerosol hair sprays in Antarctica—was baffling. It obviously meant that the release of CFCs into the environment was a global concern and not just a local problem. In 1987 a high-altitude research plane flying above the south polar region found chlorine monoxide (ClO) molecules in the low-ozone areas—experimental verification of the predictions of Rowland and Molina (who eight years later shared in the 1995 Nobel Prize in chemistry for their recognition of the long-term effects of CFCs on the stratosphere and the environment).

  In 1987 an agreement called the Montreal Protocol required all the nations who signed it to commit to a phaseout of the use of CFCs and ultimately a complete ban. Today hydrofluorocarbon and hydrochlorofluorocarbon compounds are used as refrigerants instead of chlorofluorocarbons. These substances either do not contain chlorine or are more easily oxidized in the atmosphere; few reach the high stratospheric levels that the less reactive CFCs did. But the newer replacements for CFCs are not as effective refrigerants, and they require up to 3 percent more energy for the refrigeration cycle.

  There are still billions of CFC molecules in the atmosphere. Not every country has signed the Montreal Protocol, and even in those countries that have there are still millions of CFC-containing refrigerators in use and probably hundreds of thousands of old abandoned appliances leaking CFCs into the atmosphere, where they will join the rest of the CFCs on the slow but inevitable journey upward to wreak havoc on the ozone layer. The effect of these once-lauded molecules may be felt for hundreds of years to come. If the intensity of high-energy ultraviolet radiation reaching the Earth’s surface increases, the potential for damage to cells and their DNA molecules—leading to higher levels of cancer and greater rates of mutation—also increases.

  THE DARK SIDE OF CHLORINE

  Chlorofluorocarbons are not the only chemical group that were considered wonder molecules when first discovered but later revealed an unexpected toxicity or potential for environmental or social damage. What is perhaps surprising, however, is that organic compounds containing chlorine have shown this “dark side” more than any other group of organic compounds. Even elemental chlorine displays the dichotomy. Millions of people around the world depend on chlorination of their water supplies, and while other chemicals may be as effective as chlorine in purifying water, they are a lot more expensive.

  One of the major public health advances of the past century has been the effort to bring clean drinking water to all parts of the world—something we have still to achieve. Without chlorine we would be a lot further from this goal; yet chlorine is poisonous, a fact well understood by Fritz Haber, the German chemist whose work on synthesizing ammonia from nitrogen in the air, and on gas warfare, was described in Chapter 5. The first poisonous compound used in World War I was the yellowish-green chlorine gas, whose initial effects include choking and difficulty breathing. Chlorine is a powerful irritant to cells and can cause fatal swelling of tissues in the lungs and airways. Mustard gas and phosgene, compounds used in later poisonous gas releases, are also chlorine-containing organic compounds, with effects as horrifying as those of chlorine gas. Although the mortality rate for exposure to mustard gas is not high, it does cause permanent eye damage and severe, lasting respiratory impairment.

  Poisonous gas molecules used in World War I. The chlorine atoms are bolded.

  Phosgene gas is colorless and highly toxic. It is the most insidious of these poisons; it is not immediately irritating, so fatal concentrations may be inhaled before its presence is detected. Death usually results from severe swelling of tissues in the lungs and airways, which leads to suffocation.

  PCBS-FURTHER TROUBLE FROM CHLORINATED COMPOUNDS

  Still more chlorocarbon compounds that were initially greeted as wonder molecules have, like CFCs, turned out to pose a serious health hazard. Industrial production of polychlorinated biphenyls, or PCBs as they are most commonly known, began in the late 1920s. These compounds were considered ideal for use as electrical insulators and coolants in transformers, reactors, capacitors, and circuit breakers, where their extreme stability, even at high temperatures, and their lack of flammability were highly prized. They were employed as plasticizers—flexibility-enhancing agents—in the manufacture of various polymers, including those used for wrapping in the food industry, for liners in baby bottles, and for polystyrene coffee cups. PCBs also found a use in the manufacture of various inks in the printing business, carbonless copying paper, paints, waxes, adhesives, lubricants, and vacuum pump oils.

  Polychlorinated biphenyls are compounds where chlorine atoms have been substituted for hydrogen atoms on the parent biphenyl molecule.

  The biphenyl molecule

  This structure has many possible arrangements, depending on how many chlorine atoms are present and where they are placed on the biphenyl rings. The following examples show two different trichlorinated biphenyls, each of which has three chlorines, and one pentachlorinated biphenyl with five chlorines. More than two hundred different combinations are possible.

  Not long after the manufacture of PCBs began, reports of health problems among workers at PCB plants emerged. Many reported a skin condition now known as chloracne, where blackheads and suppurating pustules appear on the face and body. We now know that chloracne is one of the first symptoms of systemic PCB poisoning and can be followed by damage to the immune, nervous, endocrine, and reproductive systems, and by liver failure and cancer. PCBs are anything but a wonder molecule and, in fact, are among the most dangerous compounds ever synthesized. Their menace lies not only in their direct toxicity to humans and other animals but, like CFCs, in the very stability that made them so useful in the first place. PCBs persist in the environment; they are subject to the process of bioaccumulation (or biomagnification), where their concentration increases along the food chain. Animals at the top of the food chain, such as polar bears, lions, whales, eagles, and humans, can build up high concentrations of PCBs in the fat cells of their bodies.

  In 1968 a devastating episode of human PCB poisoning epitomized the direct effects of ingestion of these molecules. Thirteen hundred residents of Kyushu, Japan, became ill—initially with chloracn
e and respiratory and vision problems—after eating rice-bran oil that had accidentally become contaminated with PCBs. The long-term consequences included birth defects and liver cancer fifteen times the normal rate. In 1977 the United States banned the discharge of PCB-containing materials into waterways. Their manufacture was finally outlawed in 1979, well after numerous studies had reported the toxic effects of these compounds on human health and the health of our planet. Despite regulations controlling PCBs, there are still millions of pounds of these molecules in use or awaiting safe disposal. They still leak into the environment.

  CHLORINE IN PESTICIDES-FROM BOON TO BANE TO BANNED

  Other chlorine-containing molecules have not just leaked into the environment; they have been deliberately put there in the form of pesticides, sometimes in huge amounts, over decades, and in many countries. Some of the most effective pesticides ever invented contain chlorine. Very stable pesticide molecules—those that persist in the environment—were originally thought to be desirable. The effects of one application could perhaps last for years. This indeed has turned out to be true, but unfortunately the consequences were not always as foreseen. The use of chlorine-containing pesticides has been of great value to humanity but has also caused, in some cases, totally unsuspected and very harmful side effects.