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Meeting Briefs from Houston
Method improves NMR studies of metal carbonyls The usefulness of 17 0 nuclear magnetic resonance to study transition metal carbonyl compounds can be increased by a technique developed by Robin L. Kump and Lee J. Todd of Indiana University that enriches the 1 7 0 isotope in these complexes. The researchers find that the large molecular size of complexes such as Ru3(CO)12 does not noticeably affect the line width of the carbonyl resonance, although broad bands are observed in organic compounds of large molecular size. They suggest that the high degree of symmetry in the metal carbonyl complex is the reason for the smaller line widths. Vitamin E enhances immune response Vitamin E, added to diets at a rate of 150 to 300 mg per kg, increases the resistance of young chickens and mice to bacterial infection, according to Robert P. Tengerdy and coworkers at Colorado State University. The vitamin supplement reduced mortality from 50% to 5% in Escherichia co/f-infected chickens and from 80% to 20% in mice infected with Diplococcus pneumoniae. Studies suggest that increases in immune response and phagocytosis are associated with depression of certain prostaglandin components, Tengerdy says. He notes that great caution must be exercised in extrapolating to humans the results of experiments with small animals. Hydrogen sulfide, carbon monoxide liquefy coal Unwanted by-products from coal hydrogenation or liquefaction—hydrogen sulfide and carbon monoxide—can be used to liquefy coal, according to researchers working at Allied Chemicals corporate research center, Morristown, N.J. Mahmoud B. Abdel-Basset and Charles T. Ratcliffe note that treatment of coal with only hydrogen sulfide causes incorporation of sulfur into the asphaltene fraction. But, says Ratcliffe, now at Apollo Technologies, Whippany, N J., use of hydrogen sulfide together with carbon monoxide allows conversion of coal to an ethyl acetate-soluble material with no increase in sulfur content. In their studies, the researchers treated coal tar under liquefaction conditions with labeled 13CO, which was incorporated as labeled aryl methyl groups in addition to hydrogenation of certain aromatic nuclei. The ability of the hydrogen sulfkje/carbon monoxide reagent to solubilize coal in the absence of hydrogen or a donor solvent, they say, could reduce the raw material cost of hydrogen in future liquefaction processes. High activity from intercalation catalysts Solid phase asymmetric hydrogenation catalysts have been made by intercalating homogeneous rhodium catalysts between layers of natural mineral clays, says Thomas J. Pinnavaia of Michigan State University. The catalysts, which have a chiral bidentate diphosphine ligand and a diene IIgand, make roughly the same products in homogeneous solution as they do when intercalated between the clay layers. However, the yield of optically active isomers shifts when the catalysts are intercalated. Sometimes these yields increase—as in the case of the hydrogenation of the aacylaminoacrylic acid precursor of the amino acid tyrosine, 42
C&EN April 7 ( 1980
and sometimes they decrease—as with the precursor of the amino acid phenylalanine. The optical activity of the most important amino acid investigated, L-dopa, remains the same (about 95%) for the intercalated and homogeneous catalysts, suggesting potential practical application for the intercalated compounds. Spectroscopy helps resolve yellow-cake caper Inductively coupled plasma (ICP) emission spectroscopy helped analytical chemists at Standard Oil (Ohio) to prove that samples of yellow cake, or triuranium octooxide, recovered by the FBI, had in fact been stolen during 1978 from the company's facilities in New Mexico. In all, 5 bbl of yellow cake, valued at $200,000, had been missing. ICP spectroscopy, which detects radiation emitted from a sample excited by a hot argon plasma, revealed that the stolen samples and those taken (legally) from company stocks for analysis differed in trace metal composition, particularly in sodium content, from samples obtained from neighboring companies. Although such analyses provided only circumstantial evidence, the suspects found it convincing enough to admit their guilt, thus expediting Sohio's efforts to recover the material from the FBI. New way to fabricate conducting polymers Researchers at Allied Chemical, Morristown, N.J., have found a new method for transforming monomers into highly conducting polymers. They find that crystalline oligomers such as biphenyl, terphenyl, or quaterphenyl will complex with oxidizing dopants such as arsenic pentaf luoride in the solid state, and then will polymerize into highly conducting, doped poly(p-phenylene). In practical terms this means that a monomer such as biphenyl can be deposited as a highly crystalline film, and only then polymerized. The current method is to make the poly(p-phenylene) film first, then dope it, which leads to a disruption of chain orientation and a considerable loss in the maximum potential conductivity (a problem common to all conducting polymers). In the new method, however, the crystalline structure of the monomer phase serves as a template to orient the chains as they form. Oxidized clays inhibit HCN oligomerization Ferric iron in montmorillonite clays markedly inhibits the oligomerization of hydrogen cyanide in aqueous solution, according to James P. Ferris and coworkers at Rensselaer Polytechnic Institute. This aspect of clay chemistry has not been recognized previously in experiments simulating preblotlc conditions on the primitive Earth, they say. The inhibitory effect is due to the rapid oxidation by Fe(lll) of dlaminomaleonitrile (DAMN), a critical intermediate in hydrogen cyanide oligomerization. The oxidation product, diiminosuccinonitrile, is readily hydrolyzed to hydrogen cyanide and derivatives of oxalic acid. When ferric iron in the clay is reduced to ferrous, the oligomerization pathway is no longer blocked. The researchers believe that since the Earth's early atmosphere contained little or no free oxygen, the iron present is more likely to have been in the ferrous state.
Vinyl chloride detector sensitive to below ppb The ability to detect traces of vinyl chloride has been extended a thousandfold to measure levels below parts per billion, report scientists at the University of Colorado and National Oceanic & Atmospheric Administration Aeronomy Laboratory in Boulder. The development depends on a conventional nickel-63 electron capture detector in which the nitrogen carrier gas is doped with nitrous oxide (N 2 0). The "dramatic improvement" in sensitivity is due to a reaction in the detector of vinyl chloride with 0~, which forms when nitrous oxide reacts with electrons at 350° C. Because of the high sensitivity, air samples could be collected in cigarette-pack-sized devices worn by workers. If applied, the method could eliminate "all of the complex handling, storage, and desorption procedures" now being used to measure vinyl chloride in industrial settings. Zirconium binds antimicrobial agents to cotton A number of organic antimicrobial agents such as pyrithione and tetracycline can be durably bound to cotton fabric in the form of zirconium complexes. Cletus E. Morris and coworkers at USDA's Southern Regional Research Center in New Orleans find that fabric containing such complexes continues to inhibit the growth of bacteria and fungi after a series of launderings. In the most effective process, fabric is treated first with a solution of zirconyl acetate and then with a solution of a salt of the antimicrobial agent. Fabric treated in this way with pyrithione, for instance, completely inhibits the growth of two strains of odor-causing bacteria after 50 launderings. It also completely inhibits the growth of a fungus that causes athletes foot after 20 launderings. Highly selective resin extracts lithium from brines A highly selective, one-pass method for removing lithium chloride from brines has been developed by chemists at Dow Chemical. The method, described by Alan Cisar. uses a hydrous lithium aluminate as an ion exchange resin to remove lithium selectively (present at concentrations of less than 1500 ppm) from brines containing as much as 25% dissolved salts. Once the brine has been passed through the resin bed, the bed is washed with fresh water and the lithium chloride extracted. Key to the process is the ion exchange resin (LiCI)x- 2AI(OH)3. 2H 2 0. Its structure, the chemists find, consists of layers of edge-sharing AI(OH)3 octahedra with only two thirds of the octahedral holes filled. These layers alternate with intercalated lithium salts and water molecules. The chemists think the resin picks up additional lithium chloride in the unfilled holes in the AI(OH)3 layers. Anomalies point to multilayered supernova For several years now, nuclear chemists have interpreted isotopic anomalies in chondritic meteorites as evidence that a nearby supernova injected foreign material into the presolar nebula shortly before the solar system formed. The latest anomaly-ridden element is titanium, which appears to mark various meteorite samples as coming not just from a supernova, but from different layers within that supernova. California Institute of Technology scientists Gerald J.
Wasserburg, Franz Niederer, and Dimetri Papanastassiou find titanium anomalies ranging from 0.5 to —0.5%, indicating that the samples originated under varying conditions of nucleosynthesis. Titanium is especially significant in this work because it is relatively abundant and because its oxide is refractory, implying that it condensed before the supernova material had a chance to mix thoroughly with the rest of the presolar nebula. Photoelectrochemical cell stability improved A photoetching technique that helps protect electrodes in photoelectrochemical cells against photocorrosion has been developed by David Cahen and his group at Weizmann Institute of Science, Rehovot, Israel. Using cells consisting of thin, polycrystalline cadmium chalcogenide-based layers on metallic substrates in polysulfide electrolytes, the researchers reported achieving an 8 % solar to electrical conversion efficiency. But increasing the conversion efficiency, says Cahen, is not so important as finding a way to make photoelectrochemical cells stable and inexpensive. Cadmium chalcogenide crystals, he adds, are cheaper than gallium arsenide, and they can be made using reagent-grade materials. Theory of alkylidene reactions takes shape A theoretical framework to explain the unusual chemistry of alkylidene complexes of electron-deficient transition metals is beginning to take shape, says Roald Hoffmann of Cornell University. A molecular orbital analysis of these complexes shows that an electrophilic interaction of acceptor orbitals on the metal with the lone pair of electrons on the carbene causes the carbene ligand to pivot in place while a second interaction weakens the bond attaching the hydrogen atom to the carbene carbon. Bulky substituent groups on the metal and on the carbene protect the metal center from intermolecular reactions and control the extent of carbene pivoting. The metal-hydrogen interaction guides the hydride to a neighboring alkyl group, thus facilitating the a -elimination reaction characteristic of the reactions of these compounds. Synthesis gives higher yields for lactulose The disaccharide lactulose now can be synthesized from milk sugar, or lactose, in greater than 8 0 % yields, by a process developed by scientists at the USDA Eastern Regional Research Center in Philadelphia. The procedure, which involves using triethylamine in the presence of boric acid, gives such high yields because borate forms a preferential complex with the ketose portion of the product lactulose, explain Kevin Hicks, F. W. Parrish, and Philip E. Pfeffer of the USDA research group. The product crystallizes readily once the amine and the boric acid are removed. Lactulose is probably noncariogenic and nonnutritive; its low sweetness, however, makes it an unlikely candidate for the nonnutrient sweetener market. The laxative properties of the sugar are the basis of Richardson-Merrell's product Chronulac, introduced into the prescription laxative market late in 1979—another factor that makes lactulose a less than ideal sweetener. April 7, 1980 C&EN
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