Lignocelluloses Promise Improved Products for Materials Industries

SCIENCE/TECHNOLOGY

Lignocelluloses Promise Improved Products for Materials Industries Chemical modification of lignocelluloses may offer wood and lignin plastics, wood-based adhesives, and cellulose-fiber resin mats Ward Worthy, C&EN Chicago

"Lignocellulosic research is poised on the threshold of a new era of research breakthroughs," says David N.-S. Hon, director of Clemson University's Wood Chemistry Laboratory. In an era of uncertainties about oil supplies and prices and rising concern over environmental issues, he adds, wood and other lignocellulosic materials have become increasingly attractive to a variety of materials-based industries. At a PACIFICHEM '89 agrochemistry symposium on chemical modification of lignocellulosic materials, Hon noted that maximizing lignocellulosic productivity involves several sciences, including chemistry, silviculture, genetics, and biotechnology. Efficient methods for harvesting trees and processing them into primary and secondary wood products are essential. One important step is to improve the use of raw materials of lower quality by chemically converting them to highperformance value-added products. In an overview discussion of wood chemistry, Hon reminded his audience that wood is a biopolymer of cellulose, hemicelluloses, and lignins. As such, it possesses many active functional groups susceptible

to reaction: hydroxy Is (primary and secondary), carbonyls, carboxyls (ester), carbon-carbon, ether, and acetal linkages. In addition, lignins possess ethylenic and sulfur-containing groups. "Virtually every type of reagent capable of reacting with these functional groups can be applied to w o o d / ' Hon points out, noting that the literature is full of examples involving etherification, esterification, alkylation, hydroxyalkylation, graftcopolymerization, crosslinking, and oxidation. Those reactions have yielded a whole series of products with many applications. Unprecedented progress has been made in the past 15 years in developing new engineering materials from lignocellulosic wastes, including wood-polymer composites and wood plastics, according to the Clemson wood chemist. And there's more to come. Pioneering work on wood thermoplasticization promises to expand the utility of low-quality wood resources. New methods are leading to new cellulose products. Lignin, too, shows potential for use in the production of plastics. According to Nobuo Shiraishi, a professor of wood science and technology at Kyoto University, Japan, and one of the pioneers in thermoplasticization of wood, "Wood is an excellent natural composite." However, unlike metals, plastics, and glass, wood can't be melted, dissolved, or softened sufficiently for molding. This lack of plasticity often makes it less valuable as a material, Shiraishi says, adding that "once plastic properties are added to wood, it becomes more useful." One of the main reasons that wood isn't plastic, Shiraishi points out, is that crystalline cellulose has a melting point considerably higher than its decomposition tempera-

ture. However, if cellulose is derivatized, its thermal and other properties are altered—as demonstrated by cellulose nitrate, cellulose acetate, and benzyl cellulose, among others. It would seem reasonable, then, that if cellulose in wood were derivatized in situ, the wood itself might gain thermoplasticity. "Nevertheless," Shiraishi says, "no one thought to make such a trial until quite recently." That was perhaps natural, he continues, because for the past 40 years people have believed the accepted concept that a lignin molecule has a three-dimensional gel structure, which prevents derivatized wood from being thermally flowable. Shiraishi and associates did try, however, starting about 1979. They found that thermoplastic properties could indeed be imparted to wood, by esterification, etherization, and other derivatizations. For example, lauroylated wood meal could be molded to a pale yellow, transparent film by hot-pressing. Benzylation of the wood gave similar results. Derivatization by large substitu-

Esterification yields wood-based polymers with high water resistance January 15, 1990 C&EN

19

Science/Technology ents that provide "internal plasticization" appears to be among the easiest ways to confer thermoplasticity, Shiraishi says. In contrast, when small substituent groups and/or polar groups are introduced, fluidity cannot be achieved. In those cases, however, plasticity can be improved by additional external plasticization. For example, an allylated wood, not in itself completely thermoplastic, can be altered to a flowable, moldable material by blending with polymethyl methacrylate and dimethyl phthalate. Thermoplastic woods have been used to make films, sheets, and other types of moldings with various physical properties. Mechanical properties of films made from benzylated wood are comparable to those made from common synthetic polymers, Shiraishi says. Thermoset materials can also be made by using chemicals that can plasticize the modified wood and at the same time react to form crosslinks during molding. For example, wood board was made using phthaloylated wood together with bisphenol A diglycidyl ether, which served as the plasticizer and the crosslinking agent. The chemically modified woods can also be dissolved or liquefied in aqueous and organic solvents us-

Laser irradiation converts cellulose to anhydrooligosaccharides 20

January 15, 1990 C&EN

Crosslinked wood board (left) is smooth, glossy, and dense compared with board made from untreated wood meal ing various methods. For example, aliphatic acid esterified woods will dissolve in such solvents as benzyl ether, styrene oxide, and phenol after treatment at 200 to 270 °C for 20 to 150 minutes. By using conditions that allow phenolysis of part of the lignin, liquefaction can be achieved under milder conditions, at temperatures around 80 °C. In addition, postchlorination of the modified wood markedly enhances its solubility. Shiraishi lists several potential applications for dissolution or liquefaction of chemically modified wood: fractionation of modified wood components, preparation of adhesives, preparation of woodbased foam-type moldings, and preparation of wood-based fibers for conversion to carbon fibers. A significant recent finding is that even untreated woods can be dissolved or liquefied in several organic solvents. For example, after treatment at 200 to 250 °C for 30 to 180 minutes, wood chips and wood meal can be dissolved by phenols, alcohols, glycols, ketones, and others. The process yields pastelike solutions with wood concentration as high as 70%. After dissolution, the wood components become reactive. In fact, almost the same range of products has been made from solutions of untreated wood as from solutions of modified wood, including adhesives, polyurethane foams, and carbon fibers. The new findings about dissolution of unmodi-

fied woods "will open a new and practical field for utilizing wood materials," Shiraishi says. Other research groups are pursuing related lines of research. For example, chemist Hideaki Matsuda, head of Okura Industrial Co/s research laboratory, notes that work in his lab has shown that carboxyl group-bearing esterified woods can be obtained efficiently by addition esterification of the wood with dicarboxylic acid anhydrides that react with the hydroxyl groups of the wood. Addition reactions of wood with anhydrides proceed with or without a solvent. These solventless reactions are "industrially advantageous," Matsuda says, adding that they yield esterified woods with a wide range of monoester content. The active carboxyl groups will in turn react with epoxide groups forming ester linkages. If a bisepoxide is used for the second addition reaction, ester linkages will be formed as above. In addition, crosslinks will be formed between the esterified woods. Under high temperature and pressure, the wood components plasticize to form reddish b r o w n , yellowish brown, or blackish brown crosslinked wood boards with smooth, glossy, and plasticlike surfaces. Of the boards of that type made so far, a phthalic anhydride board shows the best physical properties, Matsuda says, including very high compressive strength and water resistance.

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75.46 MH Z C NMR spectra of "curdlar ((1—»3)-p-D-glucan) in the solid state n veal chemical shifts indicating change fror single-chain form (anhydrous) to singk helix form (hydrate)

different orientations. The effect of both the proton-carbon spin-spin interactions and the chemical shift anisotropy is to broaden the spectral lines. In addition, carbon-13 (the carbon isotope with the magnetic dipole moment) is present in only about 1% natural abundance, so the carbon-13 absorption signal is weak and noise levels are high. Fortunately, special techniques are able to overcome the difficulties inherent in solid-state NMR. Applying strong radio-frequency radiation covering the range of proton absorption frequencies decouples the l H and 13C nuclei, eliminating the line-splitting proton-carbon spinspin interactions. Rotating the sample rapidly around an axis making an angle of 54.7° with the magnetic field—the so-called magic angle— cancels out the chemical shift anisotropics. And sensitivity can be increased by "cross-polarization"—simultaneously irradiating *H and 13 C nuclei with carefully matched power levels and frequencies that enhance the 13C signal. With the aid of such techniques and other new methods, scientists are gaining useful insights not only into the structures of complicated organic molecules but also into their dynamic interactions. For example, Saito and coworkers Motoko Yokoi and Yuko Yoshioka have been using high-resolution solid-state 13C NMR to study the conformation and dynamics of gel-forming polysaccharides. Specifically, Saito has recorded spectra for such compounds as (l-*3)-/3-D-glucans, agarose, and kappa- and zota-carrageenans in anhydrous powder, hydrate, and swollen gel states. He finds that hydration causes curdlan, a linear (l-^3)-/3D-glucan, to undergo "substantial conformational change," from single-chain to single-helix form. On the basis of these and other experiments, Saito concludes "the presence of a hydration-induced single helical conformation is an essential condition for gel-forming ability in linear (l-*3)-/3-D-glucans." In contrast, he notes, the network structure of branched (l-*3)-/3-D-glucans in the gel state arises mainly from a triple-helix conformation. For agarose and the carrageenans, on the other hand, there is no sub-

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Science/Technology stantial displacement in chemical mal history typical of this class of shifts as a result of changes among polymers/' Tonelli says. At 100 °C, the anhydrous powder, hydrate, and the polymer passes into a mesophase swollen gel states. However, Saito that doesn't become isotropic until says, hydration does result in sub about 200 °C. There's a "substantial stantial narrowing of the peaks. narrowing" of the 31P resonance in Alan E. Tonelli, a polymer physi the mesophase, compared with that cal chemist with AT&T Bell Labora seen in the room-temperature spec tories, notes that high-resolution trum of a semicrystalline sample. solid-state NMR spectra of polymers "Clearly a significant increase in are a source of two principal types backbone motion occurs at the of molecular information. The reso crystal-liquid crystal transition," nance frequencies or chemical shifts Tonelli observes. In 13C NMR stud provide a measure of the local con ies, measurements of relaxation formations and intermolecular pack times for crystalline spectra revealed ing of the polymer chains and also multiple resonances suggesting of interchain packing, particularly more than a single conformation or in crystalline domains. In addition, packing mode for the side chains. measurements of spin-lattice relax At Texas A&M University, chem ation times (Ti) for each resolvable istry professor James F. Haw and resonance can lead to estimates of associates Noel D. Lazo, Jeffrey L. the relative mobilities of the poly White, and Benny R. Richardson mer chain constituents (backbone have been developing high-resolu and side chains) in both crystalline tion solid-state NMR methods for and amorphous phases. studying chemical reactions in prog For instance, 13C and 31P spectra ress on heterogeneous catalysts. of a polyphosphazene show "ther Haw notes that mechanistic stud

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Science/Technology The Texas A&M chemists have also studied the conversion of methanol to gasoline on the zeolite catalyst H-ZSM-5. These studies provide support for suggested mechanisms involving surface-bound methoxy intermediates, Haw says, and show that methyl ethyl ether and ethylene are intermediates in the reaction. Isai Ando, a polymer chemist at Tokyo Institute of Technology, presented results of studies of conformation and dynamics aspects of polypeptides with long alkyl side chains, in the solid and the liquid crystalline state. Some of the studies involved 13C cross-polarization/ magic-angle spinning NMR experiments with poly(L-glutamate) (POLG) and poly(L-aspartate) (POLA), exam i n i n g the effects of c h a n g i n g temperatures. For POLG, the main chain is found to have a right-handed a-helical conformation over the temperature range of 27 to 200 °C, Ando

says. He notes that this change allows the formation of thermotropic liquid crystals. In contrast, POLA's main chain changes from a righthanded to a left-handed a-helical conformation chain within the same temperature range. POLA doesn't form thermotropic liquid crystals in that temperature range, and, according to Ando, it's the conformational change that prevents their formation. At a later PACIFICHEM '89 session, Teruo Yagashita of Fujitsu Laboratories described the use of 13C NMR to study the structure of synthesized diamond films, made by chemical vapor deposition, and to compare their NMR spectra with those of natural diamonds. In the case of the natural diamonds, the NMR spectra showed a single sharp peak with a chemical shift of 34.9 ppm. The Ti for that peak was a very long 14.5 hours, Yagashita notes. On the basis of those findings, Yagashita and co-

workers Motonobu Kawarada and Toshisuke Kitakoji assigned the chemical shift of 34.9 ppm to carbons forming C—C single bonds, corresponding to the diamond lattice structure. The NMR spectra of the synthesized diamond film contained the 34.9 ppm chemical shift observed for the natural diamonds. It also contained a smaller peak at 29.5 ppm. That chemical shift corresponds to that for the methine carbon of adamantane, Yagashita points out, but it could be something else, too. However, relaxation time measurements for the 34.9 ppm chemical shift revealed, in addition to the very long Ti found with the natural sample, a middle-length Ti and also a very short Ti. The short relaxation times indicate that there are carbon radicals as well as carbon in the synthetic diamond films, Yagashita says, adding that that finding has been confirmed by electron spin resonance experiments. •

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Science/Technology

Oxidative coupling routes for methane proposed by peroxide anions, but further reactions of the resulting surface alkyl groups are affected strongly by gaseous oxygen. The alkyl groups would react with the adsorbed oxygen or directly with the gaseous Although Japanese chemists have oxygen, promoting "deep oxidation" over the years engaged in many to carbon monoxide and carbon dicatalysis research projects, basic as oxide. This may explain the comwell as applied, few currently common observation that oxidative coumand more interest than does di- pling of light alkanes cannot be obrect catalytic conversion of meth- served at low temperatures in the ane. At PACIFICHEM '89, research- presence of gaseous oxygen. ers described progress in this area Methane is also capable of being ranging from mechanisms of basic aromatized under certain conditions, interest to process development for and this aspect is being investigated commercial chemicals. at the University of Tokyo's departA major topic of interest at all ment of synthetic chemistry by a levels is the direct conversion of group under Kaoru Fujimoto. Remethane to C2 compounds through cently it has been found that galliumthe oxidative coupling of methane. supported ZSM-5 type zeolite is an At Tokyo Institute of Technology's extraordinarily effective catalyst for department of chemical engineer- this type of reaction. Gallium and ing, for example, Kiyoshi Otsuka zinc are also effective promoters has been studying direct coupling when used in the impregnated form, to elucidate the mechanism of this the ion-exchanged form, the physireaction on the basis of kinetic and cally mixed form, or even when inisotopic labeling data. corporated in the zeolite framework. Otsuka is particularly interested Fujimoto and his colleagues have in the oxygen species responsible found that the added oxygen gas in for activation of the C—H bonds of the propane or butane conversion m e t h a n e . He proposes that the on H-ZSM-5 selectively oxidizes hymechanism for activation and oxi- drogen on the zeolite to promote dative coupling of methane is: conversion of the feed and especially the formation of aromatic hyCH 4 + S — CH 4 * • • • S drocarbons. They claim that the CH 4 * • • • S — CH 4 + S H-ZSM-5 displays excellent ability CH 4 * • • • S + CH 4 — 2CH 4 + S CH 4 * • • • S + 0 2 — CH 3 + H 0 2 + S for paraffin conversion and aromatics formation if the hydrogen atom 2CH3 —• C2H6 —• C2H4 on the zeolite is effectively removed. CH3 + O2 — C O , C 0 2 Furthermore, the hybrid catalyst in where S is a surface location on the the simple compressed physical mixcatalyst. The vibrationally active ture, as well as alumina-supported CH 4 * reacts with diatomic oxygen Ga 2 03, exhibits aromatic selectivity to give adsorbed methyl groups or methyl radicals in the gas phase. Catalyst effective for Otsuka says that this mechanism conversion of paraffins has been confirmed with isotope experiments using DH 4 . The rate determining step is that of the C—H bond breaking. The results show that the reaction proceeds via a methyl species as a reaction intermediate. It is still open to question whether the methyl intermediate is a methyl radical in the gas phase or a methyl group adsorbed on the surface. The experiments indicate that the activation of methane is caused only 30


comparable to that of galliumsupported H-ZSM-5. The researchers postulate that the hydrogen atoms on the zeolite surface exit through the gallium sites. This phenomenon has resulted in what they say is a "spillover mechanism," in which hydrogen spills over from zeolite to the Ga/Al203. Fujimoto's work is aimed at trying to clarify the role of gallium on the ZSM-5 from the standpoint of spillover and reverse spillover of hydrogen. In the conversion of n-butane over H-ZSM-5 and Ga-ZSM-5, a small amount of C2 to C 4 products appears in any case. With the addition of 5% oxygen in the feed stream, selectivity to aromatic hydrocarbons quadruples to 16.4%. The data indicate that the higher conversion should not be attributed to oxidation of the butane. Similarly, the low hydrogen production should be attributed to direct oxidation of hydrogen on the zeolite surface. The results further show that, if hydrogen atoms on the zeolite surface are removed, H-ZSM-5 exhibits a high selectivity to aromatics. Addition of metals to the zeolite increases selectivity to aromatics, Fujimoto found. Platinum was particularly useful in this respect, and gallium seemed to have a comparable effect around 500 °C. The most probable explanation of the promotional power of gallium should be attributed to the reverse spillover effect. In this case, the gallium acts as the exit for hydrogen on the zeolite surface. This means that hydrogen atoms generated in the aromatization do not leave the zeolite surface for the gas phase but, rather, hydrogenate ethylene or propylene, which are intermediates in the paraffin-to-aromatic conversion. With the gallium-supported ZSM5 zeolite, on the other hand, hydrogen atoms on the zeolite surface migrate to the gallium site, are recombined to form hydrogen molecules, and then desorb into the gas phase. This is the reverse phenomenon of spillover and has thus been called reverse spillover. Fujimoto believes that the concept of spillover reasonably interprets the fact that selectivity of aromatic hydrocarbons on the Ga-ZSM-5 was suppressed

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Science/Technology by hydrogen in the gas phase in spite of its low h y d r o g e n a t i o n activity. A subject related to direct coupling of methane is that of methylation of various compounds. At the department of materials science and chemical engineering of Yokohama National University, Y. Osada is interested in oxidative methylation of toluene with methane to form ethylbenzene and styrene. This would provide a new route to the synthesis of styrene from natural gas and the distillates of coal tar as an alternative to petroleum. Osada's group has some initial results illustrating that the toluene methylation to form ethylbenzene and styrene with an oxygen molecule certainly involves the coupling of methyl and benzyl radicals, which are generated on the alkali-promoted basic oxide catalysts. As the partial pressure of the methane is raised the Cs selectivity has sometimes reached 72%. Another type of methylation is under investigation at Chiba University's department of industrial chemistry by Toshiaki Sodesawa. Oxidative methylation of some olefins, aromatics, and nitriles having a methyl group in the alpha position is of particular interest. Sodesawa found that N a 2 0 / L a 2 0 3 catalysts are the most effective for the formation of C4 hydrocarbons by oxidative methylation. It is clear, he says, that the oxidative methylation occurs on the surface of the catalyst, while the oxidation to carbon monoxide and carbon dioxide occurs in the gas phase. He suggests that a possible reaction scheme may be: CH 4 + C 3 H 6 +V 2 0 2 -> CH 2 =CHCH 2 CH 3 + H 2 0 CH 4 + C 3 H 6 + 0 2 CH2=CHCH=CH2 + 2H20 CH 2 =CHCH 2 CH 3 — CH3CH=CHCH3 Hydrocarbons + 0 2 -* CO + C 0 2 Thus, the primary C4 hydrocarbon formation may be considered as the reaction of choice via methyl addition to propylene. It may be concluded, Sodesawa says, that the surface of the Na 2 0/La 2 0 3 catalyst plays a significant role in C4 formation. Another approach to methane coupling has been explored by

Tomoyuki Inui, of the department of hydrocarbon chemistry at Kyoto University. He and his colleagues are looking at oxidative coupling as well as dehydrogenative coupling by applying novel metallosilicate catalysts and a series reactor concept. The dehydrogenative coupling is carried out using a newly developed platinum-modified gallium silicate catalyst. Oxidative coupling is done using a modified S m 2 0 3 catalyst coated on the inner surface of a ceramic foam and on honeycombformed ceramic supports. Methaneair mixtures are then passed through at very high space velocities. The products are introduced successively into a second reactor, which is connected in series to the S m 2 0 3 catalyst and packed with the gallium silicate to perform aromatization of the light olefins. In the case of dehydrogenative coupling, the methane is converted almost exclusively—about 90%—to aromatic hydrocarbons at a reaction temperature of 650 to 700 °C. Benzene/toluene/xylene make up 65% of the aromatics, with the remainder being higher molecular weight compounds. Inui believes this indicates that ethylene is formed from the methane by very strong hydrogen abstraction of the dispersed gallium component, and the subsequent transformations of olefins, oligomers, and cycloolefins. For oxidative coupling, cesium-based catalysts are effective in producing the usual selection of C 2 and C 3 compounds. Selective oxidation of lower alkanes has focused almost exclusively on methane conversion, with good reason. However, there are other alkanes of interest, especially for the formation of organic chemicals. One case in point is the conversion of propane, which has been under investigation by Yoshihiko Moro-oka at the Research Laboratories of Resources Utilization at Tokyo Institute of Technology. Morooka has been looking into catalysts for the conversion of propane to both acrolein and acrylonitrile. Trials with many catalyst compositions have shown that the most effective catalyst for oxidation of propane to acrolein is a composite metal oxide with the gross formula Ag0.oiBi0.85Vo.54Mo0.4504. Oxidation

of propane started at 400 °C and the highest conversion is achieved at that temperature. Propene, carbon monoxide, carbon dioxide, and lower hydrocarbons also are formed. The catalyst does not appear to participate in the activation of propane. The general conclusion is that propane is the intermediate to acrolein, and mixed-oxide catalysts mainly promote the oxidation of propane to acrolein in this reaction. The same catalysts have been shown to be active in the ammoxidation of propene to acrylonitrile. Moro-oka and his colleagues have looked into their use in the ammoxidation of propane to acrylonitrile. A number of catalysts evaluated show high activity and selectivity to acrylonitrile. The same catalyst that is the best for acrolein formation was also the best for formation of acrylonitrile. At this point, conversion of propane is unsatisfactory for commercial purposes, and improvements are needed. However, compared with the oxidation or ammoxidation of propene, the possibilities of improvements are there. Moro-oka expects that this work will stimulate further interest. Joseph Haggin

Microwave reactor is faster, more efficient

A continuous-flow reactor that uses microwave energy to speed reactions and increase yields has been developed at Australia's Commonwealth Scientific & Industrial Research Organisation (CSIRO), Clayton, Victoria. According to CSIRO chemist Christopher R. Strauss, the benchtop units are in production commercially at Industrial Microwave Applications, Mortlake, New South Wales, and will sell in the U.S. for $15,000. Working with Alan F. Faux and Teresa Cablewski, Strauss designed the reactor around a coil of microJanuary 15, 1990 C&EN 33

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34 January 15, 1990 C&EN

Science/Technology

CSIRO's Strauss (left) and IMA's Wellink with benchtop microwave reactor wave-transparent polytetrafluoroethylene fitted into a microwave cavity. This reactor processes 20 mL of reaction mixture per minute at programed temperatures up to 200 °C and pressures up to 210 psi. A heat exchanger cools the liquid rapidly on leaving the cavity. Industrial Microwave p r o d u c t m a n a g e r Stephan Wellink says the company is also developing reactors that will process 4, 20, 30, and 40 L per minute for industrial scaleups. Reactions demonstrated on the reactor to date include nucleophilic substitutions, additions, eliminations, esterifications, transesterifications, transketalizations, acetylations, amidations, hydrolyses, isomerizations, condensations, and decarboxylations. For example, yields of isopropyl acetate from isopropanol, ace-

tic acid, and catalytic mineral acid were 85% at 154 to 158 °C, 150 psi, and a residence time of 2.3 minutes. Saponification of methyl benzoate emulsified with 5% aqueous sodium hydroxide was quantitative at 174 to 182 °C, 100 to 150 psi, and a residence time of 1.6 minutes. And yields of benzyl phenyl ether from benzyl chloride and sodium phenoxide in methanol were 67% at 146 to 147 °C, 150 psi, and a residence time of 1.6 minutes. The high pressures make possible the use of such low-boiling reagents as aqueous ammonia, formaldehyde, and methylamine. The reactor cannot handle solids or viscous liquids, however, or reactions that require low temperatures or evolve copious amounts of gases. Stephen Stinson

New method for synthesizing chiral drugs

Syntheses of chiral a-arylpropionic acids as nonsteroidal anti-inflammatory drugs (NSAIDs) have been devised by chemists at Merck & Co., Rah way, N.J. This achievement may help medicinal chemists in meeting demands of the U.S. Food & Drug Administration that drugs of the future consist of the enantiomers that are more pharmacologically active.

The core of the Merck technology, Merck organic chemist Robert D. Larsen told a session at PACIFICHEM '89, is reaction of ketenes made from racemic acids with such chiral alcohols as ethyl (R)- or (S)-lactate. Other researchers have worked on reactions of racemic ketenes with chiral alcohols, but the Merck approach is the first to combine use of cheap, practical chiral alcohols with achievement of such high optical purities. The key to success is a-hydroxycarbonyl compounds as chiral alcohols reacting in nonpolar solvents CIRCLE 8 ON READER SERVICE CARD

Science/Technology

Spectroscopic Characterization of Minerals and Their Surfaces

H

ere is an overview of the powerful spectroscopic methods in use today for characterizing crystal structure, chemistry, morphology, and excited states of minerals. With a triple focus, this new summary of the latest techniques emphasizes: • the structural and physical properties of minerals that have been associated with promotion of chemical reactions on their surfaces • the fact that most naturally occurring minerals store electronic energy in quantities sufficient to significantly alter some of their properties, and • the spectroscopic means by which biologically deposited minerals can be distinguished from geologically deposited ones

Twenty-three chapters describe a variety of new applications of mineral spectroscopy to determine composition, purity, interaction with energy, characterization of active centers, and adsorbate interactions. A discussion of nonoptical methods includes instruction on how to describe a mineral and its surface before studying it. Other chapters focus on energy storage within minerals. A section on active centers uses clays as a model, because in spite of its complexity, it is one of the most important classes of natural reactive minerals. If you are a physicist, chemist, geologist, or fuel, soil, agricultural, and environmental scientist interested in interfacial chemistry of geological surfaces, this book will stimulate your thinking and inspire you to try these new characterization methods. Lelia M. Coyne, Editor, San Jose State University Stephen W.S. McKeever, Editor, Oklahoma State University David F. Blake, Editor, NASA-Ames Research Center Developed from a symposium sponsored by the Division of Geochemistry of the American Chemical Society ACS Symposium Series No. 415 492 pages (1989) Clothbound ISBN 0-8412-1716-5 LC 89-27755 $94.95

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such as hexane, heptane, or toluene. Nonpolar solvents apparently promote a necessary intermolecular hydrogen bonding with the ketene. Larsen developed the technique with Edward G. Corley, Paul Davis, Paul J. Reider, and Edward J. J. Grabowski of Merck's process engineering group, headed by Ichiro Shinkai. They demonstrated the method with ibuprofen and naproxen. As with most NSAID's, the (S)-isomer is the more pharmacologically active of each of these. For example, the Merck group converted ibuprofen [a-(p-isobutylphenyl)propionic acid] to the acid chloride with thionyl chloride, the acid chloride to the ketene with trimethylamine or dimethylethylamine, the ketene to chiral ester with ethyl (S)-lactate and 3-dimethylaminopropylamine in heptane, and the chiral ester to (S)-ibuprofen by hydrolysis with dilute hydrochloric acid or lithium hydroxide. The product was 94.5% (S)-isomer and 5.5% (R)-isomer. For drug categories in which the (R)-isomer is desirable, esters of (K)-lactic acid are also cheaply available. Indeed, the highest selectivity attained in Rahway was 99.5% (R)ibuprofen with (R)-pantolactone as chiral alcohol. Though this lactone is costly, it is available from naturally occurring pantothenic acid, and Larsen suggests that the price might come down if a high-volume use were found. Stephen Stinson

Novel route to bimetal cluster catalysts

Bimetallic clusters have long been touted as catalysts of promise for the improvement of selectivity in numerous types of Q chemistry. A new approach has been investigated by Masaru Ichikawa of the Catalysis Research Center at Hokkaido University in Japan. The method involves trapping

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35

Science/Technology

Synthesis provides zeolite/bimetallic cluster catalyst : Pink

Rhfi(CO)16 NaY CO • H?

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120-200 C 1 atm

lr 6 (COU NaY

NaY

| Pink-yellow Yellow

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Rh6_Jrx NaY Gra

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CO

CO

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NaY zeolite

the bimetallic catalysts in zeolitic cages. Ichikawa notes that surface organometallic chemistry and intrazeolitic synthesis of metal clusters provide the possibility for more sophisticated control of the multinuclear frameworks. This approach should permit preparation, at the molecular level, of well-characterized metal centers that are catalytically active and of desired specificity. The University of Hokkaido group has made tailored bimetallic catalysts using SiC>2-bound Rh 4 Fe2, Rh 5 Fe, Pt 3 Fe 3 , Ir4Fe, and Pd 6 Fe 6 carbonyl clusters as the precursors. They all exhibit high activities and selectivities toward methanol and ethanol in a synthesis gas reaction and C3+ alcohols in olefin hydroformylation. Ichikawa believes that the iron promotion for alcohol production is remarkable, compared with that from homometallic clusters. The structures and locations of the clusters in the zeolites have been studied at considerable length with a great variety of instrumentation. Iron promotion is proposed by 36 January 15, 1990 C&EN

Low-cost route to C2 products from methane

Rh6_xlrx(CO)16

Ichikawa to be associated with the heteronuclear activation of carbon monoxide with the adjacent Rh-Fe +3 , Pd-Fe +3 , and Ir-Fe +3 located at the metal cluster/SiC>2 interfaces, in order to enhance migratory insertion of carbon monoxide into metal-metal and metal-alkyl bonds. Ichikawa's group has prepared a series of bimetallic catalysts from the hexanuclear carbonyl clusters, which were presynthesized o inside NaY zeolite supercages (13 A in diameter). The researchers showed that derived bimetallic crystallites— consisting of ensembles of less than 10 A in size, with uniform metal compositions similar to those of the original carbonyl clusters—formed inside the NaY zeolite. To test the activity of the catalysts, the hydrogenolysis reactions of w-butane and benzene dehydrogenation were employed as exploratory reactions. Depending on the identity of the cluster, different C-C bonds could be cleaved. Iron promotion seemed to be most effective on the terminal C-C bond. Joseph Haggin

A novel approach to the oxidative coupling of methane has been proposed by a group headed by Kohji Omata of the department of synthetic chemistry at the University of Tokyo. He previously reported that lead oxide supported on magnesia exhibits a high activity and selectivity to C2 hydrocarbons, and he has further clarified that bulk oxygen in the lead oxide is largely responsible for the formation of the C2 hydrocarbons. Now he provides a possible means for using an inexpensive oxidant in the oxidative coupling of methane. Omata and his colleagues are developing a new type of inorganic membrane reactor that has the capacity of producing ethane from methane with oxygen extracted from air. The reactor is made from a porous alumina tube, on which a membrane is deposited. The membrane is made by coating the tube surface repeatedly with magnesium oxide and then lead oxide from their aqueous nitrate solutions. When the membrane is thick enough, the entire assembly is calcined at 600 °C in air. In operation, the support tube and the catalytic membrane on the surface are placed inside a concentric quartz tube. The ends of the annular space are sealed. Air is passed through the central alumina tube, and methane is passed through the annular space where it contacts the catalyst surface. Omata has shown that oxygen diffuses from the central space and through the membrane to the annular space, where it reacts with the methane to form C2 hydrocarbons. He concludes that oxygen is incorporated into the membrane at the inside surface and reacts with the methane at the outside surface. The reactor sustained catalytic reactions for a prolonged period.

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Science/Technology thermodynamically unstable relative to nitrogen and oxygen at low temperatures. But at the high temperatures of exhaust gas streams, cataAir lytic decomposition seems to him to be the simplest and cheapest means for removing nitric oxide from the streams. Catalysts have been used before with less than complete success. Most of the work has employed noble metals and metal oxides. Some of these materials are active in the reduced state, but the oxygen in the exhaust gas usually competes with the nitric oxide for adsorption sites on the surface and effectively poisons the catalyst. Numerous nitric oxide removal processes are in use with varying Quartz tube degrees of effectiveness. These include catalytic decomposition and Colloidal silica reduction, adsorption, absorption, t Porous alumina oxidative adsorption, and combined Air oxidative adsorption and reduction. Iwamoto suggests that copper-exThe membrane reactor exhibits changed zeolites offer promising greater activity and selectivity to C2 properties for the catalytic decomhydrocarbons than is normally ex- position of nitric oxide. Of particular interest in this reperienced with the usual methane/ oxygen-mixed system. Selectivity to gard is the zeolite ZSM-5, which is C2 hydrocarbons is more than 99% best known for its role in the proat temperatures above 750 °C. The duction of gasoline from methanol. principal product is ethane. Still un- The active sites for nitric oxide adder investigation are the details of sorption are, apparently, Cu + ions, the mechanisms involved in the oxy- which function as electron-donating gen transport through the mem- sites for the nitric oxide. Furtherbrane and the surface reactions with more, the catalytic cycle of the nitric oxide decomposition includes the methane. + Joseph Haggin Cu ions as active centers and N O " and/or (NO) 2 ~ species as reactive intermediates. At low temperatures, the active catalytic sites would be poisoned by oxygen. At higher temperatures, oxygen can desorb from the zeolite surface, and the regeneration of the active site permits continued catalysis. It is still not entirely clear why the Cu-ZSM-5 catalysts function as they do. However, the evidence sugIn the drive to clean the atmosphere, gests that among the reasons are nitric oxide is a major target. Chem- the atomic dispersion of the copper ist Masakazu Iwamoto of the de- as a result of the ion-exchange proppartment of industrial chemistry at erties of the zeolite, the easy deMiyazaki University in Japan has sorption of oxygen at relatively low been investigating the problem for temperatures, and the reduction of many years and at PACIFICHEM the Cu 2 + to Cu + being more diffi'89 offered some new possibili- cult in the zeolite than is the case ties. for other transition metals. Iwamoto notes that nitric oxide is Joseph Haggin

Membrane reactor produces ethane from methane

Protein drug delivery system nears approval

i

Polyethylene-glycol-modified adenosine deaminase (PEG-ADA) may be on the verge of gaining Food & Drug Administration approval. If, as the manufacturer expects, that approval comes in the next month or two, it will mark not only a new therapy for children with ADAdeficient severe combined immunodeficiency, it will also herald what may well be the start of a more broadly applicable new drug delivery technology. PEG-ADA would be the first product to be marketed by Enzon Inc., a South Plainfield, N.J., company set up in 1981 to develop PEG technology. It is being developed as an orphan drug for the disease associated with an inherited deficiency of ADA, in which the immune system fails to develop. The disease is usually fatal unless a child is kept in protective isolation. With approval near, Enzon president Abraham Abuchowski sketched for a PACIFICHEM '89 session the current activity involving PEGmodified drugs. Abuchowski notes

Zeolite catalyst breaks down nitric oxide

38 January 15, 1990 C&EN

Abuchowski: PEG technology

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Science/Technology

SOFTWARE/DATABASE UPDATE

that protein-based drugs have great potential as therapeutic agents for diseases such as cancer and for genetic disorders, with the proteins being derived from genetic engineering, fermentation, or animal sources. Protein-based drugs have the benefits of site specificity and low incidence of side effects. But there also are obstacles to use: poor uptake into the bloodstream, short blood-circulating life, and potential for eliciting an immune (allergic) reaction. Abuchowski points out that more than 24 different types of drug delivery systems are now under development for proteins. These include liposomes, bioerodible polymers, encapsulation, osmotic pumps, and others. The technology being developed at Enzon employs covalent attachment o( the inert polymer PEG to the proteins. PEG appears to block access to sites on the surfaces of the proteins, thus inhibiting clearance from the circulation and attack by the immune system. More than 40 proteins have been modified with PEG, Abuchowski says. Enzon has three in clinical trials: PEG-ADA (being developed by Enzon as an orphan drug); PEGL-asparaginase for treatment of acute lymphoblastic leukemia; and PEGuricase for treatment of hyperuricemia associated with chemotherapy. Two other PEG products—PEGsuperoxide dismutase (PEG-SOD) for use in destroying excess oxygen that may damage injured tissue, and PEG-catalase, another antioxidant— have been licensed to Sterling Drug for clinical development. PEG-L-asparaginase provides an example of the difference PEG modification can make. Abuchowski notes that L-asparaginase has been used in treating acute lymphoblastic leukemia since the early 1970s. But it has the serious side effects of short lifetimes and of eliciting immune reactions. Modification with PEG, he says, increases circulating half-life from 30 hours to two weeks and significantly decreases immune reaction. Another application of PEG technology is development of a blood substitute, PEG-hemoglobin. It is still in the research stage. James Krieger

• LCASreact and NBSfluids (STN International, Circle 301) are now available on the STN International online network. L C A S r e a c t (from C h e m i c a l Abstracts Service) is a learning file for the CASreact chemical reaction search system. NBSfluids (produced by the National Institute of Standards & Technology) contains Miprops, a program that calculates thermophysical and transport properties over a wide range of temperatures and pressures for 12 cryogenic fluids.

40


• Biological Abstracts on Compact Disc (Biosis; $7660 annual subscription, discounted for Biological Abstracts subscribers; Circle 302), to be issued quarterly beginning this March, includes software from SilverPlatter Information Inc. that enables users to search the database by title, author, abstract, concept codes, and several other parameters. • Equil (MicroMath Scientific Software, $199, Circle 303), an IBM PC-based p r o g r a m t h a t solves chemical e q u i l i b r i u m problems, can be used as an educational tool in secondary schools and colleges and for lab calculations. The user selects reagents and specifies solution properties (pH, ionic strength) and problem to be solved. The program then retrieves equilibrium reaction data from a modifiable, internal database and generates titration curves, species concentration diagrams, complex formation curves, and other types of output. • S.I. Plus (Geocomp Corp., $79, Circle 304), for IBM PCs and compatibles, makes unit conversions—meters to feet, pascals to p o u n d s per square inch, and more than 90,000 other conversions commonly used by scientists and engineers. • ChemDraft II (C Graph Software; $295, $100 for optional computational package; Circle 305) facilitates creation of chemical and mathematical drawings

for import into word processors s u c h as W o r d P e r f e c t a n d Microsoft Word. The program, which runs on IBM PCs and compatibles, handles both two- and three-dimensional chemical structures, has interactive ring and substituent libraries, and stores user-defined structures. The c o m p u t a t i o n a l package (MM2 and MNDO) can be used to optimize geometries and to calculate molecular properties. • Spectrafile IR Plus (Heyden & Son, $1600 and up, Circle 306) is instrument control software for use with in-place IR and FTIR s p e c t r o m e t e r s . The p r o g r a m , which runs on IBM PCs and compatibles, provides spectral manipulation, quantitative analysis, searching, archiving, plotting, and, in many cases, computer control of commercial IR and FTIR spectrometers. • HerbicideStack (Scientific Software, $150, Circle 307), for Apple Macintosh computers, is an educational HyperCard stack describing approximately 300 herbicide products. The stack can be readily expanded or modified by the user.

Literature • Laboratory and Science Handbook (Digital Equipment Corp., free, Circle 308) provides detailed information on Digital and thirdparty hardware/software products for scientific research. • Brochure (Fisons Instruments, free, Circle 309) describes Astral, a computerized laboratory information management system. • Bulletin (Beckman Instruments, free, Circle 310) details EasyLIMS software, a laboratory information management system for IBM PCs a n d P S / 2 s t h a t h a s a Microsoft Windows user interface. For information on these items or numbered ads, see Reader Service Card

Lignocelluloses Promise Improved Products for Materials Industries

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