Rhubarb to the Rescue

Saturday, June 01, 1996
The chemicals destroying Earth’s ozone layer are some of the most unreactive substances known, which is why they make it through the lower atmosphere to wreak havoc higher up. The manufacture of chlorofluorocarbons, or CFCs, was banned in the United States as of January 1. But eliminating stockpiles of the refrigerant gases is no easy matter. Some 100 million pounds, including illegal imports confiscated by the Justice Department and Customs Service, are in storage tanks. The days of perpetual storage, however, may finally be over. Robert Crabtree and Juan Burdeniuc, chemists at Yale, have discovered a simple, safe method for disposing of the ozone-eating chemicals.

The obvious approaches to getting rid of CFCs have involved using extremely high temperatures, which proved to be expensive, or highly reactive substances, which are dangerous and difficult to handle. The carbon atoms in CFCs form very strong bonds with fluorine and chlorine atoms--thus their unwillingness to react with other materials. But Burdeniuc, a graduate student working with Crabtree, suggested trying sodium oxalate, a common laboratory chemical that is also found in rhubarb leaves, just to see what would happen. It didn’t seem likely, because sodium oxalate is a very mild substance, says Crabtree. But I said, ‘What the hell, we’ll give it a whirl.’

Burdeniuc’s hunch was right. The researchers passed CFCs over a bed of powdered sodium oxalate. Both were heated to about 520 degrees. The two compounds reacted to form four harmless substances--carbon, carbon dioxide, sodium fluoride (used in toothpaste), and sodium chloride (which is salt). Crabtree isn’t sure what the exact mechanism of the reaction is; by rights sodium oxalate should not be able to break CFC bonds at all. I think the mechanism is going to be very surprising, he says.

However the reaction works, Crabtree thinks it can provide a safe and probably inexpensive method of reducing CFC stockpiles. With an easy way to destroy CFCs, he says, industries might be dissuaded from plans to sell their excess to countries where their use is permitted.
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