NEWS OF THE WEEK
From the ACS meeting
One-step process carbonylates ethylene Scientists at Eastman Chemical, Kingsport, Term., have found a low-pressure, low-temperature catalytic process that produces propionic acid or propionic anhydride by ethylene carbonylation. The process—which uses a catalyst system involving a group 6 metal, a halide salt, and an organic halide in a singlestep reaction—may lead to a benign alternative to the currently used hydroformylation-oxidation process. Eastman research associate Joseph R. Zoeller described the process to the Division of Petroleum Chemistry. Support for the research was shared by Eastman and the Department of Energy. Propionic acid and its derivatives are chemical intermediates with rising importance in applications ranging from food preservation to plastics making. The potential is growing rapidly for use of propionate derivatives, especially as chemical feedstocks to make methacrylic acid derivatives. "The most direct process for generating these intermediates is hydrocarboxylation," Zoeller said. "The process is well known, but only a single producing unit is now onstream at BASF" in Mannheim, Germany. Major drawbacks, he noted, are the highly toxic volatile catalyst, Ni(CO)4, and the extreme operating conditions. The alternatives are precious-metal catalysts, none of which have been used commercially. Zoeller's group discovered that halide-promoted group 6 metals—preferably in the form of an iodide-promoted molybdenum catalyst—provide very high rates of carbonylation at low pressures (25-70 atm) and temperatures (150-200 °C). 'This represents the first demonstration of an efficient carbonylation catalyst utilizing a group 6 element as the catalytically active metal component," he noted. Such a catalyst should simplify current commercial processes, removing many of the potential toxic dangers. Other than the BASF process, nearly all propionate derivatives are made by a circuitous hydroformylation-oxidation sequence that generates the propionic acid, which is then converted to derivatives. For the Eastman catalyst system, mo8
APRIL 1,1996 C&EN
lybdenum is the most active group 6 metal and the halide may be bromide or iodide, but iodide is preferable. The catalyst is added as Mo(CO)6—a readily available and easily handled, but highly toxic, solid, Zoeller points out. Ethyl propionate is present in a steadystate concentration of less than 2% of the product mixture; other products appear only in trace amounts. The mechanism, not yet totally elucidated, probably proceeds via a freeradical pathway that is initiated by rate-limiting dissociation of CO from Mo(CO)6, with subsequent halide extraction from the ethyl halide. The ethyl radical is scavenged by the complex [.Mo(CH 3 CH 2 CO)(CO) ? ]. This complex allows entry into a chain-propagation sequence that is responsible for catalysis. Addition of iodide to the complex generates CH3CH2COI, a precursor to the propionate derivatives, and allows eventual regeneration of the complex. Joseph Haggin
TV series spotlights minority scientists A television miniseries spotlighting the careers of 20 black, Hispanic, and Native American scientists and engineers will air on three consecutive Mondays, starting April 8, on Public Broadcasting Service stations. Entitled "BreakThrough: The Changing Face of Science in America" and running a total of six hours, the series is a celebration of science. In segments previewed by C&EN, chemists, physicists, computer scientists, engineers, biologists, and geologists palpably transmit their passion for their discipline. Aimed at encouraging minority students to consider a career in science by providing positive role models, "BreakThrough" likely will appeal to a broad audience. Physicists and a physical chemist kick off the series. For example, from a telescope high atop a mountain in Chile, Neiï Tyson, a research astrophysicist at Princeton University, probes the Milky Way "like an unborn child trying to figure out what its mother looks like." Astrophysicist France A. Cordova, chief scientist at the National Aeronautics & Space Administration, testifies at congressional hearings, seeking support for NASA. And chemist George Castro, a senior scientist at IBM Research Divi-
Tyson:from the Bronx to the Milky Way sion's Almaden Research Center, San Jose, Calif., smiles when the X-ray microscope he designed successfully images a single molecule. In another segment, the spotlight is on environmental scientists. For instance, Mario J. Molina, professor of atmospheric chemistry and chemistry at Massachusetts Institute of Technology, gives a historical tour of the chlorofluorocarbon research that made him cowinner of the 1995 Nobel Prize for Chemistry. And Karen K. Medville, an environmental research scientist at Arizona State University West, Phoenix, discusses her efforts to teach Native Americans about water pollution. Other series segments feature scientists working at the cutting edge of medical research, academic scientists striving for tenure, and engineers who are reaping the rewards of entrepreneurship. Many of the scientists come from humble backgrounds and happened into science through chance encounters. For example, Tyson, who is black, grew up in the Bronx and embarked on his stargazing course after glimpsing the moon through binoculars. Cordova, who is Hispanic, first majored in English and discovered science through substitute teaching. Medville, who is a Cherokee Indian, became a single parent early in life. Now writing a thesis for a Ph.D. in environmental toxicology from Cornell University, she poignantly describes how she doggedly navigated her way through college, starting with remedial courses. "BreakThrough" is narrated by actor Andre Braugher, a star of the NBC TV series "Homicide: Life on the Street." Funding was provided by the Alfred P. Sloan Foundation, the National Science Foundation, and the Intel Foundation. Check local TV listings for exact times and dates of airing. Mairin Brennan
