Chapter 16: Chlorocarbon Compounds By: Isabella Barnett

There has been a lot of controversy on the subject of chlorocarbons in the past and even today. Chlorocarbon compounds have been used in a wide variety of things from refrigerators and air-conditioning to propellants in canisters and Styrofoam. Before our modern version of refrigeration people used solid ice to keep things cool. However, a refrigerator needs a compound that undergoes the evaporation-compression cycle, a refrigerant. Early on people used ether, ammonia, methyl chloride, and sulfur dioxide as refrigerants. After successful land-based refrigerants was established in Australia, James Harrison tried his ether-based evaporation-compression mechanical system at sea, it failed at first but was later proven effective. Meat was able to be transported across the seas in 1877 and on. As a result, refrigeration made an important impact on the economies of meat-producing countries like Australia, New Zealand, Argentina, and South Africa. While the early refrigerants vaporized in the required temperature range, liquefied by compression in the required temperature range, and absorbed relatively large amounts of heat as it vaporizes they had their faults. They either decomposed, were fire hazards, were poisonous, or smelled awful. Then Midgley and Henne prepared compounds with one or two carbon atoms and a varying number of fluorine and chlorine atoms instead of hydrogen atoms, chlorofluorocarbons (CFC). They fit all of the refrigerant requirements and they were very stable, nonflammable, nontoxic, inexpensive to manufacture, and had little odor.  CFCs were used in other things as well such as air-conditioning units, propellants in aerosol cans, circuit board cleaners, and in porous polymers. When a bromine atom replaces a chlorine or fluorine atom, it produced a heavier compound perfect for fire extinguishers. But like with almost all good things, problems arose. CFCs do not break down by ordinary chemical reactions; they increase the rate of breakdown of ozone molecules. First, a chlorine atom collides with ozone to form a chlorine monoxide molecule and an oxygen molecule. Next, ClO reacts with an oxygen atom to form an oxygen molecule and regenerates the chlorine atom. Rowland and Molina realized this would upset the balance between ozone and oxygen molecules, as chlorine atoms speed up the breakup of ozone they do nothing in the making of ozone. Basically, not only was the ozone molecules are being destroyed by chlorine but the chlorine atoms also catalyze this breakdown again and again. This breakdown causes harmful ultraviolet radiation to penetrate the atmosphere and reach the Earth’s surface. The Montreal Protocol required the nations who signed it to phase-out the use of CFCs. Today hydrofluorocarbon and hydrochlorofluorocarbon compounds are used as refrigerants instead of chlorofluorocarbons. PCBs also turned out to be more trouble than they were worth. PCBs caused chloracne, one of the first signs of PCB poisoning. PCBs are considered the most dangerous compounds ever synthesized; there danger is not only in their direct toxicity but in the fact that they are so stable they persist in the environment and accumulate in concentration along the food chain. DDT is another example of unintended consequences. DDT is a potent insecticide and was used to stop the spread of typhus and to kill mosquito larvae by the military during WWII. The “bug bombs” used caused a release of CFCs as well as DDTs. DDT and its breakdown product accumulate in animal tissues, which in birds inhibits the enzyme that supplies calcium to their eggshells leading to a decline in the species population. Chloroform also lead to advances in anesthetics but even they caused problems. Chlorocarbons are extremely important even today. While today most countries have discouraged the use of chlorocarbons, we are still dealing with the consequences of their overuse in the past. Chlorocarbons lead to many achievements and sparked many revolutionary ideas but the side effects have caused maybe more long-term damage than they were worth. The environmental damage has left a mark that can never be erased. It is hard to comprehend that something that seems so good and so helpful can turn out to cause irreversible destruction. The problem with a great success is that people are too busy marveling at it to notice the problems that come from that success. Chlorocarbons have done a lot to improve living conditions but we will never fully comprehend the lasting damage these molecules have left in the environment and for our future. It is very clear in this chapter how chlorocarbons have shaped our past. The chapter shows both the good and the bad these molecules have caused. It is stated several times that while they have led to many great accomplishments, chlorocarbons have caused health hazards such as medical issues, defects, environmental complications, and future disasters that we cannot even foresee. The author states that refrigeration would not have been successful without them and anesthesia would not be as effective if it wasn’t for the help of chlorocarbons. Nevertheless, were these achievements worth the consequences that are not just occurring now or in our near future but way down the road?