tistical approaches to the analysis of turbulent flows don't fully deal with these situations/' Reactor design is also changing. Rajamani Krishna, chairman of the department of chemical engineering at the University of Amsterdam, is an active proponent of systematizing reactor selection. "We have developed a systematic procedure for arriving at the 'ideal' reactor configuration for carrying out a desired chemical reaction," he told the symposium. The parameters involved in selection include maximum conversion, maximum selectivity, plant safety, and economic acceptability. Krishna's procedure involves three decision levels. In the first level, catalyst design is the main concern: optimizing the basic catalytic material and adapting it appropriately to the system. Because most of the systems used are fluid systems, often multiphasic fluid systems, a major design variable may be how to generate the maximum extent of a diffusion layer for catalysis. The type of gas-liquid contacting system can be crucial.
The second level looks at mass and energy flows into the reactor. "We must consider step inputs, periodically fluctuating inputs, serial flow introduction, staged- and parallel-flow introduction, [and] the use of membranes," Krishna says. At this level, it is also necessary to consider product dispositions. Sometimes, accumulating products for postreactor separations is the best strategy. At other times, removing the products as they are formed may be better. The final step in reactor selection is specifying the flow regime. The options are numerous and are not always determined by convention. After making the decisions, Krishna appends the "wish list of wants and musts" to arrive at a final reactor configuration. The engineers must still make "educated compromises" if incompatibilities appear. Some observers maintain that chemical reaction engineering came of age a decade ago, but others insist that routine, predictable engineering applications are a requisite for such maturity. ISCRE13 participants think that maturity has arrived. D
Highly electron-deficient porphyrin synthesized The most highly electron-deficient porphyrin known to date has been synthesized by chemists at the University of Pennsylvania, Philadelphia, and the University of Nebraska, Lincoln [/. Org. Chem., 59, 6943 (1994)]. The compound's unusual electrochemical properties suggest uses as a ligand in transition-metal oxidation-reduction catalysts.
Additionally, the perfluoroalkylated porphyrin may act as a catalyst in such unusual phases as supercritical fluids and fluorinated-nonfluorinated solvent mixtures. The generality of the porphyrin synthesis offers possibilities for making other members of this compound class. The new compound is 5,10,15,20-tetra-
Perfluoro substituents create electron deficiency H
0
+
(1)(CH3CH2)3N
C3F7COCI
H ,N
OH I CHC3F7
Available Fall 1995 The Fellowship places an ACS member in a staff position in Congress to • Gain firsthand knowledge of the operation of the legislative branch of the federal government, • Make scientific and technical expertise available to the government, and • Forge links between the scientific and government communities. Applications due January 1, 1995. For more information contact: Ms. Caroline Trupp Department of Government Relations and Science Policy American Chemical Society 1155 Sixteenth Street, N.W. Washington, DC 20036, (202) 872-4467. Applications consist of a letter of intent, a resume, and two letters of reference. Arrangements should be made to send the letters of reference directly to ACS. Candidates should contact ACS prior to submitting an application to determine the type of information needed in the letter of intent.
H+
(2)NaBH4
Carbinol C3F7
C3F7
V-NH F-,C„— r 7^3
ACS Congressional Fellowship
VNH
m~M HN-/ C3F7
Porphyrinogen
-C„F^ ^3r7
Oxidation
V-NH F7C:3-VV
VN
N—/ V C F
/ ° 3 ' 7
HN-/ C3F7 Porphyrin
NOVEMBER 28,1994 C&EN
39
SCIENCE/TECHNOLOGY SCIENCE/TECHNOLOGY
kis(heptafluoropropyl)porphyrin, made by inorganic chemistry professor Michael J. Therien at Pennsylvania and organic chemistry professor Stephen G. DiMagno and postdoctoral fellow R. Allen Williams at Nebraska. One upshot of the compound's very electron deficient state is a much less negative reduction potential for the zinc-porphyrin complex. The oneelectron reduction potential of the complex is -720 mV, compared with -1390 mV for the corresponding tetraphenylporphinatozincQI). Supercritical carbon dioxide is one medium the researchers are considering for catalytic reactions using the zinc-porphyrin complex. Carbon dioxide is compressible to densities as high as 0.5 g per mL above its critical temperature of 31 °C This fluidlike phase may dissolve the catalyst. Subsequently dropping the pressure to precipitate the catalyst would allow its recovery from products. The chemists speculate that the perfluoroalkylated ligand may lend selectivity to the derived complexes in reaction mixtures of fluorinated and nonfluorinated solvents. A fluorinated catalyst might reside preferentially in the fluorinated phase, while products separate from it into the nonfluorinated phase. Researchers at Exxon Research & Development, Annandale, N.J., have shown that fluorinated solvents such as perfluoromethylcyclohexane become immiscible with nonfluorinated liquids like hexane and toluene when mixtures are warmed. They use this phase separation as the basis for a hydroformylation of olefins to aldehydes. To make their ligand, the Pennsylvania-Nebraska team begins with condensation of pyrrole with heptafluorobutyryl chloride. The product is reduced with sodium borohydride to heptafluoropropyl-2-pyrrolylcarbinol. Treatment of the carbinol with acid cyclizes four molecules to a porphyrinogen. Oxidation of that precursor with DDQ (2,3-dichloro5,6-dicyanoquinone) produces the completely conjugated porphyrin. Future work at Pennsylvania will include study of the effectiveness of this compound's complexes in catalytically activating carbon-hydrogen bonds to convert alkanes to oxygenates. The Nebraska workers will study use of the porphyrin complexes in epoxidation of olefins and reduction of dioxygen. Stephen Stinson 40
NOVEMBER 28,1994 C&EN
SOFTWARE/DATABASE UPDATE • Chemical Patentlmages and PatentBBS (MicroPatent; Chemical Patentlmages subscriptions are $2,750, and PatentBBS is free; circle 301) provide patent information of chemical interest. Chemical Patentlmages is a collection of U.S. chemical patents, including full text and structures, on CD-ROM. PatentBBS is a free on-line service that provides access to information on new patents worldwide in polymers, biotechnology, environmental science, fiber optics, pharmaceuticals, and other areas. • Eco-Chem Network (Eco-Chem Network Inc.; $1,500 annual fee to buyers or sellers, plus 2 to 5% charge per transaction; circle 302) is a subscriber-based, on-line computer network that connects chemical manufacturers and consumers. The netw o r k p r o v i d e s a m e c h a n i s m for chemical companies to deal directly with interested buyers. • N e w Chem-X Substituent Database (Chemical Design, pricing available from company, circle 303) provides data on quantitative structureactivity relationships for the presence of any of 318 aliphatic and aromatic substituents on a set of active analogs. Properties important for activity can then be identified. The database is a module of Chem-X, a chemical structure visualization and computation p r o g r a m that r u n s on W i n d o w s , Macintosh, and UNIX platforms. • ChemNovel (Chemical Design, pricing available from company, circle 304) is a program for pharmaceutical lead generation. Based on a p h a r m a c o p h o r e (a description of structural features required for activity), the software invents new molecules that meet the requirements. ChemNovel is a module of Chem-X, which runs on Windows, Macintosh, and UNIX computers. • Echoice (Chemical Daily Co., $1,500, circle 305), a database of chemical products and producers in China, serves as a buyer's guide for China's chemical industry. It is produced by Chemical Daily Co., Tokyo, the publisher of Japan Chemical Week. The database includes about 15,000 chemical products and 10,000 manufacturers. It runs on IBM compatibles.
• Title V Software (ERM, $9,500 single user, circle 306) helps users collect and manage air emissions inventory data, produce reports on emissions, and develop "what-if" scenarios. The package helps clients prepare Title V operating permit applications u n d e r the Clean Air Act amendments. It is a Windows application. • Icarus Process Evaluator (Icarus, pricing available from company, circle 307) prepares detailed designs, cost estimates, and schedules of process design concepts based on process simulation results. It runs on IBM compatibles a n d n e t w o r k e d computers. • Molecular Images Software (US Science, $195 academic, circle 308) is a Windows-based program for searching, viewing, and rendering Protein Data Bank (PDB) files. It can search for keywords in directories of PDB files, produce realistic images, and calculate distances, angles, and nearest neighbor contacts. The software includes viewing options and fitting functions. • M u l l i k e n ( C A C h e Scientific, $25,000 commercial, circle 309) is a quantum chemistry program developed at IBM's Almaden Research Center, San Jose, Calif. It includes four methods for studying molecular properties: molecular mechanics, semiempirical and ab initio quantum chemistry, and density functional theory. CAChe Scientific's graphical user interface eases prediction and visualization of molecular properties. The program runs on workstations and parallel platforms. • N e w g e r (FIZ C h e m i e , pricing available from company, circle 310) is a d a t a b a s e of p h a r m a c e u t i c a l tradenames, structural and molecular formulas, CAS Registry N u m bers, and pharmacological effects. It is b a s e d on " O r g a n i c - C h e m i c a l Drugs and Their Synonyms" by Berlin pharmacist Martin Newger. The database is available for PCs, workstations, mainframes, and network servers. • For information on these items, see Reader Service Card CIRCLE 7 ON READER SERVICE CARD
