Glaser's "Chemistry is in the News"
To Accompany Wade Organic Chemistry 4/e.
Chapter 6. Alkyl Halides: Nucleophilic Substitution and Elimination.
Scientists have understood the mechanism of elimination reactions for many years. When they created refrigerants and coolants, however, scientists did not realize the amount of stress they were placing on the atmosphere. In recent years, most people have become aware of the depletion of the ozone layer and the various problems it is causing. However, few of these people understand that the E1 reaction is the mechanism that allows bromine and chlorine ions to break up ozone in the stratosphere. One ion of bromine can destroy ozone molecules for over twenty years. Because of the urgency of this problem the Montreal Protocol was formed in 1989 capping the production of chloroflourocarbons (CFCÕs) and methyl bromides. Even though the agreement to protect the disappearing ozone layer was of utmost importance at the beginning of negotiations, the interest for the issue has gradually decreased and the energy seen in the project has weakened. (To see pictures of Ozone Layer depletion, click on the GIF files on this link.)
The production of CFCÕs and methyl bromides are worldwide industries, these compounds are used in aerosol propellents, refrigerants, air conditioners, and fumigants. Their use leads to the projection of harmful chemicals into the atmosphere. While CFC's have been the main focus, it has been found that in fact, bromine atoms remove ozone more effectively than chlorine atoms. The chemistry of the bromine in the stratosphere is analogous to that of chlorine except that bromine reaches its radical state much quicker enabling it to react faster with the oxygen. It has also been found that a greater proportion of bromine from the methyl bromide stays in the atmosphere in its reactive form as compared to chlorine. This makes the destruction of the ozone by bromine on a mole-per-mole basis more important.
A coupling reaction can also occur with BrO and ClO producing Br and Cl atoms that both lead to depletion of the ozone. The combination of the two can enhance the depletion of the ozone by 5% to 20%. Another harmful fact about methyl bromide is that it is not only produced by man, but it also occurs naturally. The sources for methyl bromide are oceans, fumigation of buildings and containers, various agricultural activities, and the burning of biomass. These facts of ozone depletion make one realize that many things are hindering the restoration of the atmosphere, which makes the problem larger. Negotiations and agreements between both the industrialized nations and the third world countries must be made to limit the release of these gases.
Question 1: Methyl bromide is responsible for what percent of ozone depletion?
A. About 10%.
Question 2: Draw the structure of methyl bromide. (If you cannot remember use ChemFinder.)
Question 3: Write the reactions that lead methyl bromide to destruct one molecule of ozone, while leaving the bromine ion free to do more damage.
MeBr + UV light ==> methyl cation + bromide
bromide + ozone ==> BrO and dioxygen
4 BrO + 2 O2- ==> 4 bromide + 3 dioxygens
Question 4: In 1990 25% of the countries in the world agreed to pay for 75% of poorer countries obligations to a treaty. Is it fair for the richest countries to be responsible for helping the poor countries fulfill these requirements?
A. Personal opinion.