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New Organic Reactions Skip the Drip
5 June 2002 (All day)
If you think organic chemistry is a dry subject now, just wait. Researchers are trying to make it literally as dry as dust. In the 5 June issue of the Journal of the American Chemical Society, a team reports that it has carried out a battery of common organic chemistry reactions using solid compounds, without first dissolving them in the usual solvents. If the approach works for other reactions, it could propel "green chemistry" efforts to make everyday compounds without using toxic organic solvents.
Until now, few researchers suspected that scrapping solvents altogether was possible. For most reactions to occur, precursor compounds must mingle. That's easy in liquids, where ions and molecules move about freely. But in solids, molecules are frozen in place.
To get around that problem, a group at the Department of Energy's Ames Laboratory in Iowa, led by Vitalij Pecharsky--a materials scientist with a joint appointment at Iowa State University, Ames--started with powdery organic compounds, such as phosphonium salts, solid aldehydes or ketones, and anhydrous potassium carbonate. They placed them into 10-centimeter-long hardened steel vials loaded with steel balls the size of marbles and BBs. Then they flipped the switch on a mechanical mill, which shook each vial for between 3 and 20 hours. The mechanical energy broke down the crystalline solids and churned the starting compounds together, allowing the reactions to take place. When the team examined the resulting products with solid state nuclear magnetic resonance imaging and other tools, they found that between 70% and 99% of the starting compounds had transformed into the final products.
"It's an encouraging result," says Lawrence Scott, a synthetic organic chemist at Boston College in Massachusetts. The vast majority of organic reactions today require organic solvents, many of which are environmentally hazardous and costly to dispose of. Pecharsky says the novel method won't work for all reactions, and it would still require solvents to separate reaction products from unwanted byproducts. "It's no magic wand that will cover the entire field of organic chemistry," he says. But it might be enough to stir things up a bit.
Pecharsky's site at Iowa State