摘要:

Green chemistry down under E D I T O R I A L Green chemistry in Australia had its origins in early February 1998 when Paul Anastas (then at the EPA Washington DC) and Terry Collins (Carnegie Mellon University) addressed the annual Royal Australian Chemical Institute (RACI) professors and heads of department of chemistry meeting. A great deal of enthusiasm for green chemistry was evident. The next major event was the Department of Chemistry at Monash University Melbourne embracing the principles of green chemistry and ultimately securing a Special Monash University Research Fund (SMURF) as a new research initiative. SMURF is open to all disciplines and interestingly the green chemistry proposal was ranked number one in the Faculty of Science then ranked number one across the University.Thus non-chemist scientists and non-scientists perceived green chemistry as a most worthwhile endeavour. This gave the Department seed funding for 1999 and a range of new projects started. The same year was an opportunity to apply for an Australian Research Council Special Research Centre. Applications for these are called for every 3 years across all disciplines (excluding medicine) and each university in Australia (38 in total) was allowed to submit 5 applications. Thankfully one of them was for green chemistry which ultimately was funded initially for three years with additional funding likely for a second 3-year period and even a third 3-year period funding being close to $1mAUS per year. The green chemistry proposal was one of only 11 successful ARCSRC applications and thus was a political winner in securing Federal funds.The Director of the Centre in the first instance is Roy Jackson (Sir John Monash Distinguished Professor) with Colin Raston as Deputy Director. Monash University has provided a lectureship in green chemistry which was filled by Janet Scott who worked in the Centre during 1999 and thus far has made significant advances in projects involved in developing solventless reactions and reaction in ionic liquids with two recent papers in Green Chemistry. In addition Monash University provided additional funding for the Centre as well as embarking on a refurbishment of a significant part of the Department of Chemistry as a focus for the Centre (offices meeting room and laboratories).The Centre has collaborative projects involving 12 faculty staff in the Department of Chemistry and increasing with staff in other Departments including Biochemistry and Materials Engineering and staff with contiguous Divisions of CSIRO (Commonwealth Scientific and Industrial Research Organisation)—Minerals Molecular Sciences and Forestry and Forest Products. Key projects include solventless reaction the replacement of organic Green Chemistry August 2000 G74 This journal is © The Royal Society of Chemistry 2000 solvents by water CO2 and ionic liquids the use of aqueous based catalyst systems the use of microwave energy in chemical reactions benign mineral processing new energy efficient materials together with the development of new appropriate analytical methods.As an ARC funded Centre there is a commitment to basic research with the expectation that the applied arena will be supported at least in part by industry. Even so the distinction between the two is fuzzy since success in green chemistry requires an understanding of processes at a molecular level. Thus far several companies are involved and gratifyingly some have come ‘knocking on the door’. In the Australian context this is an exciting development. An Advisory Committee with representation from other universities including overseas the EPA Industry and the Plastics and Chemicals Industry Association of Australia has been established. Through this Committee the Centre is committed to create strong collaborative links with research groups overseas noting that green chemistry is of global concern and the isolation of Australia.The Centre networks through the Green Chemistry Network and the Green Chemistry Institute for which Monash University is the Australian Chapter. The Centre is actively engaged in lobbying Government on key issues relating to Green Chemistry the environment and where possible striving to get relevant issues into our foreign policy. The Centre is also developing teaching programs in Green Chemistry. The first course was delivered last year and it proved very popular and resulted in a strong interest in research projects at the Honours and PhD levels in the Centre. At present there are over 12 postgraduates and 8 postdoctoral researchers in the Centre.Through community activities there is also a strong interest from the Teachers Association in getting aspects of Green Chemistry into the high school syllabus. The Victorian EPA and Envirolinx recently ran a highly successful half day workshop on green chemistry in Melbourne which attracted 50 engineers and process chemists predominantly from the chemical and waste industries utilities and processing industries. Ron Allison of Nufarm a large agricultural chemical manufacturer demonstrated a practical application of green chemistry in the production of 2,4-D herbicide. The Centre is planning a workshop early 2001 and green chemistry will feature in the IUPAC World Chemical Congress to be held in Brisbane 2–6 July 2000. The RACI is also committed to green chemistry with the establishiment of the Green Chemistry Challenge Award for excellence in industry and government/university research and teaching. The inaugural recipient in 1999 was Chris Strauss (CSIRO Molecular Sciences) in recognition of his research in eliminating the use of organic solvents and/or inorganic waste. The 2000 recipient is Eric Kennedy (University of Newcastle) in recognition of his new technology for converting halogenated wastes to useful chemicals. Another researcher in Australia who has embarked on green chemistry is Adam McCluskey (University of Newcastle) with a paper in Green Chemistry (1999 1 167) on water-based organic synthesis. We believe that green chemistry has a bright future in Australia and look forward to keeping you informed of future developments. Colin Raston Monash University Melbourne Australia

ISSN:1463-9262    

DOI:10.1039/b005199n

出版商:RSC    

年代:2000

数据来源: RSC

摘要:

Hydrogen activation in supercritical fluids meeting in Mülheim Germany by colleagues from various backgrounds however there appeared to be a greater interest in this subject. Thus the originally planned COST meeting grew rapidly to a mini-symposium with over 60 participants. This extension was only possible with the generous support of the Max-Planck-Institute für Kohlenforschung the Foundation for the Advancement of Research in Inorganic Chemistry (BOAC) and Celanese Chemicals Europe GmbH. The broad interest was certainly peaked by the excellent scientific program put together by the Chairmen C. J. Elsevier and W. Leitner. It included oral contributions from network members as well as lectures from external experts. As highlighted below the topics covered preparative and mechanistic aspects of hydrogen activation in supercritical fluids The Max-Planck-Institute für Kohlenforschung in Mülheim was the venue for a two-day symposium on the “Activation of Hydrogen for Catalytic Chemical Synthesis in Supercritical Reaction Media” between 14–16 May 2000.This event was organised as part of the activities of a research network within the COST D 10 program of the European Community and its primary goal was to stimulate research activities collaborations and exchange of expertise within this COST D 10 group. Therefore the meeting was initially intended as an informal forum for the associated research groups of Professor Bargon/Dr Woelk (Bonn) Professor Dedieu (Strasbourg) Professor Elsevier (Amsterdam) Dr George (Nottingham) Professor Heaton (Liverpool) and Dr Leitner (Mülheim).After some inquiries A. M. Kluwer of the Institute of Molecular Chemistry at the University of Amsterdam The Netherlands describes a successful COST (SCFs) as well as theoretical calculations of their solvent properties and spectroscopic techniques to investigate reactions in SCFs. The presentations of the members of the COST group demonstrated nicely the mutual stimulation of their research within the network and many of the results originated from collaborations and exchange visits between the individual groups. Chemical reactions After an informal get-together on Sunday evening the program was opened on Monday by Dr Chr.Kohlpaintner of Celanese Chemicals Europe GmbH who presented examples from the industrial practice of aqueous two-phase catalysis. By using water-soluble catalysts he emphasized the possibility to reduce the Green Chemistry August 2000 NEWS & V I E W S G75 This journal is © The Royal Society of Chemistry 2000 NEWS & V I E W S amount of waste material (e.g. salts) obtain better product/catalyst separation and also sometimes higher activity. On basis of the Ruhrchemie/Rhône-Poulenc process for hydroformylation important issues of industrial applications of “unconventional” solvent systems were discussed. The topics of this opening lecture were nicely reflected in the closing lecture by Dr R.Karge from Hoffmann LaRoche who gave a detailed account on possible opportunities and problems associated with the industrial use of supercritical fluids with examples ranging from natural product extraction to hydrogenations in fine chemicals synthesis. The two presentations from industry thus framed the contributions directed towards the fundamental aspects of chemical reactions in SCFs. The opening lecture was followed by a presentation by Dr W. Leitner of the MPI providing an overview of homogeneous catalysis in compressed carbon dioxide. He started with a historical overview of the use of supercritical carbon dioxide in chemical synthesis and extractions. The major breakthrough came with the development of natural product extraction using scCO2 by K.Zosel at the host institute in Mülheim in the early 1960s. The use of supercritical fluids as an environmentally friendly alternative for organic solvents for homogeneous metal complex catalysed reactions has only been recently recognized but the number of examples has been growing fast. Leitner presented numerous examples of transition metal catalyzed reactions (e.g. enantioselective hydrogenation hydroformylation and rutheniumcatalyzed metathesis reactions) that were successfully adjusted to scCO2 as a solvent in his research group. A. M. Kluwer (University of Amsterdam) introduced selective palladium(0) catalyzed hydrogenations of alkynes to (Z)-alkenes in supercritical fluids. He showed that it has been possible to synthesize apolar palladium complexes comprising of a dinitrogen ligand and an electron poor alkene which are soluble in scCO2.These complexes have been tested for the hydrogenation of alkynes to (Z)-alkenes using various substrates. Product selectivities between 90 to 95% could be obtained and in some cases higher conversions were reported for supercritical media as compared to conventional solvents. Highly regio- and enantio-selective rhodium-catalysed asymmetric hydroformylation in scCO2 was the topic Green Chemistry August 2000 of G. Franció’s (MPI) lecture. The new perfluoroalkyl-substituted (R,S)-Rf-BINAPHOS allowed rhodium catalyzed hydroformylation to be carried out in compressed carbon dioxide as a solvent.The catalytic activity and the level of enantiocontrol was similar to the parent (R,S)-BINAPHOS/rhodium system but at the same time unprecedented high regioselectivity for the branched aldehydes was observed. Fluorinated catalysts for hydroformylation were also the theme of B. Heaton who presented recent results in this area obtained by him and J.-L. Xiao at the Leverhulme Centre for Catalysis at Liverpool. An elegant aqueous/supercritical fluid biphasic system was described by P. Jessop (University of California) for the complex or colloid catalyzed arene hydrogenation. This two-phase system comprising of an aqueous buffer and supercritical ethane gave high conversions and in some cases high selectivity for the hydrogenation of arenes and substituted arenes.This is the first successful example of an unsupported colloid-catalysed hydrogenation of a substrate in the supercritical fluid. In the Jessop group it was also found that the addition of subcritical carbon dioxide can have an accelerating effect on a solventless reaction with solid reactants. One of the examples that was presented was the hydrogenation of 2-vinylnaphthalene to 2-ethylnaphthalene which would not proceed without the presence of carbon dioxide. It was noted that the CO2 is not dense enough to dissolve any of the reagents except the hydrogen gas and that the carbon dioxide is not needed chemically for this reaction to proceed. The dramatic rate increase is caused at least partly by the lowering of the melting point of the vinyl naphthalene by the CO2.Theory Fluorination is known to be an efficient way of increasing the solubility of many compounds in supercritical carbon dioxide. A. Dedieu (CNRS Strasbourg) presented the latest results obtained in his group on the fundamental interactions between CO2 and perfluoroalkylsubstituted benzenes on a molecular level. Calculations performed at the MP2/6-31+G* level revealed an increased interaction of the carbon dioxide with fluoroalkyl-substituted benzenes compared to benzene. It is hoped that further analysis of the calculations can G76 This journal is © The Royal Society of Chemistry 2000 help to understand and analyse such weak interaction.Professor H. Huber (University of Basel) described in a very stimulating talk the state of the art in combining quantum chemistry and molecular dynamics to simulation and analysis of bulk properties and solvent effects of liquid and supercritical carbon dioxide. Spectroscopy The importance of spectroscopy as a powerful tool for the investigation of hydrogen activation in chemical synthesis was stressed during this meeting. Recent advances in IR spectroscopy of SCFs were presented by Mike George (University of Nottingham). C. J. Elsevier (University of Amsterdam) showed that supercritical media possesses beneficial features for NMR spectroscopy of solute molecules. Owing to their low bulk viscosity of these media the longitudinal relaxation times of quadrupole nuclei increase significantly and hence their line widths will be considerably reduced compared to those in common solvents like benzene and acetone.The use of toroid cavity detectors (TCD) for high-pressure NMR investigations was described by K. Woelk (University of Bonn). The unique cylindrical geometry and the confinement of the radio-frequency magnetic field to within the cavity predestined its simultaneous use as an NMR detector and high-pressure/temperature autoclave for in situ NMR studies. Spectroscopic results from catalytic hydrogenation reactions conducted with these probes in either conventional solvents or in supercritical fluids were presented by H.Niessen from the same group. The program ended on Tuesday with a visit to the high pressure laboratories of the MPI including some of the original equipment used by K. Zosel. The smooth and efficient local organisation which was mainly in the hands of Dr K. Beck was very important for the open and stimulating atmosphere throughout the meeting. There was ample time for scientific discussion with every contribution which could be continued in an informal atmosphere during the boat trip on the river Ruhr on Sunday afternoon and the conference dinner on Monday. In conclusion this COST D10 meeting was a fruitful and exciting event and provided an ideal opportunity for the exchange of new ideas existing know-how and theoretical background in this rapidly growing area of research.NEWS Producing resources to support education for sustainable development in schools The Council for Environmental Education (CEE) and the Environment Agency are holding a series of seminars on ‘Strategic Approaches to Supporting Education for Sustainable Development’ (ESD). The first seminar in the series focused on the changing climate within schools as the transition is made from environmental education to education for sustainable development and its position within the National Curriculum. The overwhelming message was that there is a lack of clarity at to what is requited from both teachers and resource producers alike. To resolve this the DfEE (Department for Education and Employment) have recently announced that new guidance notes will be issued but these will not be issued until early 2001.CEE have an extensive database available to members of environmental educational resources produced over the last 10 years. Reviewing the 1500 resources on the database Libby Grundy Director of CEE highlighted the almost complete lack of resources for the post 16 and special needs sectors. Most resources that have been produced fall in the Geography sector with over 100 resources devoted to ‘school grounds’ alone! Resources for science teaching in this area come a poor second with energy conservation dominating the field. As Nick Jones Education Officer at CEE pointed out aspects of sustainable development are statutory in Geography Science and Citizenship with a further five subjects Design & Technology History Art & Design Physical Education and ICT expected to promote the concepts.This cross curriculum aspect of ESD partly accounts for the lack of understanding of what is required according to Bill Scott (Centre for Research in Education and the Environment University of Bath). He called for the need for a focus of responsibility in schools and greater guidance as to what is required in terms of course content. Most educationalists believe the focus of ESD to be in Geography where the focus NEWS & V I E W S of teaching lies with conservation projects connected with school grounds. In the revised National Curriculum the contribution of Science to ESD is ‘through developing pupils’ skills in decision making on the basis of sound science the exploration of values and ethics relating to the applications of science & technology and developing pupils’ knowledge and understanding of some key concepts such as diversity and interdependence’.There is an obvious need for clarity and greater guidance and until this is forthcoming we are not likely to see much sustainable chemistry taught. Hopefully the situation will improve when the new guidelines are produced and that this will lead to a new impetus for producers of science resources. Without more involvement of science in ESD there is some danger that science is seen as the cause of environmental problems and Geography portrayed as the cure! Center is planning to support about 45 graduate students and postdoctoral fellows annually.Students are encouraged to visit their website to learn about possible positions http://www.nsfstc.unc.edu/. For further information contact Dr. Everett Baucom Deputy Director NSF Science and Technology Center for Environmentally Responsible Solvents and Processes 300 Venable Hall University of North Carolina-Chapel Hill Chapel Hill NC 27599-3290 USA. New NSF Science and Technology Center The National Science Foundation (NSF) has funded a new Science and Technology Center dedicated to studying Environmentally Responsible Solvents and Processes. The key mission of the Center is to establish the fundamental understanding necessary to enable liquid and supercritical CO2 to replace aqueous and organic solvents in a large number of key industrial processes (in later years other supercritical fluids may be investigated).If successful the Center should have significant impact on reducing pollution and energy usage in the U.S. and elsewhere. The Center involves the University of North Carolina-Chapel Hill (lead institution) NC State University NC A&T University of the University of Texas (Austin). The Center is developing a very extensive website which has recently become operational. It has many hyperlinks to websites related to development of sustainable technology. They are interested in establishing as many mutual hyperlinks as possible with appropriate websites to facilitate students’ learning about “green chemistry”.They currently have a hyperlink to the RSC’s Green Chemistry Network website. The Aluminium chloride in decline It is rare to go to any green chemistry meeting without at least one speaker putting forward a green alternative to the use aluminium chloride in Friedel–Crafts alkylation and acylation. Evidence that green chemistry is working can be found from the rapid decline in anhydrous aluminium chloride (AAA) production in recent years. The UK’s only producer Elementis recently closed its production facility in Durham whilst in the US the number of producers has fallen from 6 to 3 in the last 15 years.Today AAA sales are only around 1000,000 tpa with processes such as styrene and ibuprofen manufacture being recent converts to green technology. More efficient p-xylene production IFP have unveiled a new efficient catalyst for converting ethyl benzene to p-xylene. The new zeolite based catalyst called Oparis gives yields of 93% compared to 88% achieved with the conventional mordenite catalyst. Pilot studies have shown that loss of aromatics due to transalkylation have been cut by 50% whilst activity has been increased by 25%. He higher reactivity will result in significant opex and capex savings. Cargill Dow start to build new PLA plant Building work has started at Cargill Dow’s Blair site on the world’s first G77 Green Chemistry August 2000 This journal is © The Royal Society of Chemistry 2000 Biopesticide for Australian Sugar The first biopesticide for sugar cane called BioCane has recently been launched in Australia.The product is based on a naturally occurring fungus that has been cultured on broken rice grains to provide a medium for distribution. BioCane granules are claimed to be particularly effective against grayback canegrub which cost the industry A$10 million pa. NEWS & V I E W S large-scale facility for manufacturing plastics from corn. The plant should be operational in early 2002 and is expected to consume 14 million bushels of corn per year. The plant will produce polylactide (PLA) sold under the name NatureWorks PLA which can be used to manufacture a wide range of biodegradable consumer goods from food packaging and furnishings such as cups to textiles.Production capacity will be 300 million pounds of PLA a year. The company plans to build a similar facility in Europe at some time in the future. The Round Table makes the following recommendations • The Government should initiate processes of updating the Sustainable Development Strategy and integrate these more closely with the Budget and spending planning processes. • Economic and policy analysis should identify where and to what extent economic instruments including taxes would be the most efficient and effective means of delivering the targets. • The Treasury should always give sympathetic consideration to using at least some environmental taxes to provide incentives for relevant environmental improvements when it introduces a new sustainable development tax proposal.• The Government should consider before introducing any sustainable development economic instrument its possible impact on the competitiveness of UK firms (including the UK as a whole). • Where there is real evidence of likely damage to competitiveness the Government should adopt measures which give firms some flexibility in how to respond. • The Government should consider before introducing a sustainable development economic instrument what equity problems arise (undertaking research into its net impact on identified potentially vulnerable groups in terms not only of costs but also of benefits) and what measures might be taken to overcome them.Further research should be undertaken after the introduction of a new economic instrument to assess its actual impact on relevant groups. • Economics instruments should be assessed for effectiveness in delivering Economic instruments “Not too difficult!” says UK Sustainable Development Round Table The UK Government must be bolder in moving the economy in more sustainable directions its key independent environment advisers have urged. Green chemistry in New Zealand Kathleen Crisley from the University of Canterbury describes the areas of green chemistry research being investigated in New Zealand In 1999 the University of Canterbury in Christchurch launched a campus-wide initiative known as Green Products and Processes.This research group Green Chemistry August 2000 G78 acknowledges the fact that effective research into “sustainability” requires a wide range of specialist skills each contributing to the study of pertinent sustainability issues. The initiative encourages interdisciplinary and industry collaborations by involving dedicated project management and organisational This journal is © The Royal Society of Chemistry 2000 sustainable development objectives. Where the instrument by itself is likely to be less than fully effective associated measures aimed at increasing the effectiveness of delivery of the objective should be introduced.• The Government should take a pro-active approach to establishing the public perception of the policy ‘baseline’ against which proposals for economic instruments should be judged. • Effective processes should be considered and adopted based on the practical experience gained from past exercises in the consideration of environmental taxes. • The Government should establish an independent standing advisory body on sustainable development economic instruments reporting to HM Treasury. • The Government and the proposed advisory body should give further consideration to whether powers to introduce economic instruments to tackle issues of sustainable development might appropriately be given to the devolved administrations or to local government.• The UK Government should initiate further discussion between groups of countries about the way in which appropriate economic instruments introduced in each country might contribute to the joint solution of common problems of sustainable development. UK Round Table in Sustainable Development publication “Not too difficult! – economic instruments to promote sustainable development within a modernised economy” (see http://www.open.gov.uk/roundtbl/ hometb.htm or telephone +44 207 944 4964 for further information). inputs to programme and team development. Green Products and Processes team members are involved in the following research areas that are particularly relevant to the green chemistry movement Natural products and clean synthesis We have a research team who are involved in the identification and production of new pharmaceutical agents and enzyme inhibitors that are derived from New Zealand’s indigenous estuarine fungi.The team is combining the biochemical and microbial characterisation of the source material with novel process engineering techniques for separation and purification and where necessary or appropriate the total synthesis of the new compounds. The identification and development of enzymatically catalysed processes are also being undertaken for the development of cleaner production techniques for a range of chemical and food products. Such products include high performance machine oils edible oils and food supplements.Key green chemistry staff at the University of Canterbury. TOP ROW Professor Laurence Weatherley Head of the Chemical and Process Engineering Department and leader of the Green Products & Processes Group; Professor Murray Munro co-leader of the Marine Chemistry research project; Professor Ken Marsh co-leader (with Laurence Weatherley) of the new ionic solvents research initiative. BOTTOM ROW Dr John Blunt Reader in Chemistry and Head of the Department of Chemistry and co-leader of the Marine Chemistry research project; Associate Professor Tony Cole Head of the Plant and Microbial Sciences Department. Ionic solvents Ionic solvents are the subject of a new research programme for which international collaborations are actively being sought.Ionic liquids are a family of inorganic solvents that exhibit a high degree of catalytic activity. Such liquids also exhibit no significant vapour pressure and high solvating power for a wide range of compounds. They are interesting because their structure can be readily adapted to achieve desired physical and catalytic properties of interest to chemists and to engineers. The prime purpose of the proposed research programme is to study the thermophysical properties of these liquids as well as liquid–liquid equilibria and partitioning with organic solvents to develop tailored ionic liquids for specific separation processes. We are also studying novel methods of dispersing ionic liquid media for the enhanced separation and recovery of biological products which is a cross-over between this research programme and the natural products research programme described earlier.NEWS & V I E W S An important aspect of the ionic solvents project is the strengthening of international collaborative links with inorganic chemistry groups in the UK and the USA who will provide support with respect to the synthesis and to modification of the solvent chemistry. Current links exist with the Group headed by Professor Ken Seddon at Queens University Belfast Dr Tom Welton Imperial College London and Professor Robin Rogers Center for Green Manufacturing at the University of Alabama. These linkages will facilitate an iterative research process between chemists biologists and chemical engineers to understand the relationship between chemical structure and performance of these liquids.The Green Products and Processes Group is actively seeking collaborations with offshore colleagues. To inquire about the possibilities for collaboration contact Kathleen Crisley Project Manager Green Products & Processes University of Canterbury Private Bag 4800 Christchurch New Zealand. Tel. +64-3-364-2217; Fax +64-3-364-2063; e-mail k.crisley@research.canterbury. ac.nz Green Chemistry August 2000 G79 This journal is © The Royal Society of Chemistry 2000 NEWS & V I E W S Perspectives The Heck reaction – remarkable improvements to turnover numbers and frequencies The Heck reaction remains one of the most useful and versatile C–C bond forming reactions known.Recently effort has been expended in making heterogeneous versions of the Pd catalysts (see for example Green Chem. 2000 2 53) and in the development of Pd catalysts with very high efficiencies. The group led by Jean Michel Brunel in Marseille has now reported that a new class of phosphapalladacycles (generally the best type of catalyst) display enormous turnover numbers and turnover frequencies (Angew. Chem. Int. Ed. 2000 39 1946). The catalysts structure is as shown in the scheme and the novelty lies in the use of the bisalkylaminophosphane unit in place of the more usual bisaryl or bisalkyl unit.In test reactions with iodobenzene and norbornene turnover numbers of up to ca. 1010 were achieved with > 108 being regularly found. These numbers are substantially higher than any seen before and allow the Heck reaction to be done with vanishingly small quantities of catalyst. The Mannich reaction is an efficient method for the coupling of three components in one step. This is typically achieved using Lewis acid catalysts such as AlCl3 and boron species leading to acidic spent catalyst waste. Recently lanthanides have been employed as water stable Lewis acids for the transformation an approach which may lead to cleaner processes. A new method has also been developed by researchers in Ibaraki led Green Chemistry August 2000 G80 by Akira Hosomi which uses base catalysis to carry out the transformation (Angew.Chem. Int. Ed. 2000 39 1958). Reactions are run at low temperature and give high yields. A range of substituents can be employed in the reaction. Anti syn ratios are also generally high often > 90 10. Such a method may broaden the scope of the reaction to acid-labile reagents and gives a valuable alternative to undesirable catalysts such as aluminium trichloride. One of the most intensively researched areas of chemistry is the search for novel epoxidation methods. Many exist but few are genuinely environmentally acceptable. A recent contribution to this area has come from Oliver Weichold and his colleagues at the university of Würzburg (J.Org. Chem. 2000 65 2897). Their system is based on the well known combination of methyl rhenium trioxide (MTO) and hydrogen peroxide. This couple can be used to carry out a number of oxidations but often suffers from lack of selectivity and typically requires mild base buffers to control side reactions. If hydrogen peroxide is replaced with the urea–hydrogen peroxide complex (UHP) then these problems can be ameliorated. However this generates urea as by-product as well as the water from the peroxide. Weichold and co-workers have got round this hurdle by employing a NaY zeolite to act as a host for the oxidations. The NaY provides a suitable Two novel catalytic systems for the epoxidation of alkenes New catalytic method for the Mannich reaction This journal is © The Royal Society of Chemistry 2000 environment for the reaction to take place without the incursion of significant side-reactions and without the use of soluble basic buffer or significant amounts of urea.For example the epoxidation of a range of alkenes was shown to proceed in excellent conversions and almost complete selectivity. As indicated above the use of hydrogen peroxide and its complexes as oxidants is an active area of research as the oxidant is both clean and cheap. The drive to replace high volatility solvents with more easily handled materials such as ionic liquids is likewise a vigorously active field. Gregory Owens and Mahdi Abu-Omar of the Department of Chemistry and Biochemistry at UCLA have now combined the two areas with a new protocol for the epoxidation of alkenes (Chem.Commun. 2000 1165). They used the catalyst methyl trioxorhenium for the transformation. Cyclic styrenic and allylic alkenes were oxidised in a few hours at room temperature in excellent conversions and selectivities but linear alkenes suffered from lower conversion (but still excellent selectivity). The solvent used was a cationic imidazolium tetrafluoroborate which is easily synthesised and is stable under the reaction conditions. Products can be extracted with organic solvents leaving the catalyst in the ionic liquid layer. Oxidations in supercritical carbon dioxide A further epoxidation method this time using oxygen and aldehyes as the oxygen transfer couple has been demonstrated by Frank Loeker and Walter Leitner of the Max Planck Institute in Mülheim (Chem.Eur. J. 2000 6 2011). They have discovered that the epoxidation of alkenes using aldehydes and oxygen can be carried out without the addition of catalysts. Typically this type of oxidation which uses an aldehyde as oxygen carrier via peroxyacid-type intermediates requires transition metal catalysts such as iron or nickel to take place. In an interesting twist to this chemistry they have found that the interior stainless steel walls of their reactor provide the catalytic sites required without the requirement of any further catalyst making the reactor the ultimate heterogeneous catalyst! Excellent conversions were achieved for several epoxidations.Whether this process has any implications for the lifetime of the vessel was not discussed. Many attempts are being made to revamp hydroformylation chemistry. This reaction type represents an extremely valuable route to aldehydes from alkenes but the traditional approaches have significant drawbacks especially for higher olefins. These include the separation of the expensive rhodium catalyst or forcing conditions and poor selectivity if the cheaper cobalt is used. The ratio of linear to branched aldehyde is often another difficult parameter to control. Murielle Sellin and David Benzene hydroxylation Entrapped biocatalysts New routes for the functionalisation of hydrocarbons Cole-Hamilton of the University of St Andrews have now published an interesting method based on supercritical fluids (J.Chem. Soc. Dalton Trans. This journal is © The Royal Society of Chemistry 2000 NEWS & V I E W S 2000 1681). Their process deliberately utilises catalysts which are insoluble in the reaction medium so that the product-containing solution can be swept from the vessel into a second reactor where it is depressurised to isolate the product. Their catalyst system is based on Rh complexes of triarylphosphites and their reaction conditions can be chosen such that selectivity to the more valuable linear isomer is highly favoured. No rhodium could be detected in the product and the catalytic system could be re-used several times.The hydroxylation of aromatic feedstocks is a second important goal in the functionalisation of hydrocarbon feedstocks. This allows the direct formation of valuable raw materials directly from hydrocarbons and is especially exciting when an oxidant such as hydrogen peroxide is used. The 1980’s saw the advent of TS-1 a zeolitic material capable of such reactions under mild conditions. One of the major drawbacks of this material is its very small pore size which precludes the majority of aromatics from reaching the active sites. Corresponding MCM-type catalysts have been studied and some promising results have been achieved. Another approach described by Nomiya’s group from Kanagawa university in Japan involves the use of vanadium substituted polyoxomolybdates as catalysts (J.Mol. Cat. A 2000 156 143). They have presented results which demonstrate that these materials are active catalysts for the conversion of benzene to phenol using hydrogen peroxide. Since access to active sites in such polyoxomolybdates is easier larger molecules should also be amenable to this treatment. Although no results were presented in this article relating to bulkier substrates such an extension to this system may be of interest. The formation of amines such as tert-butylamine has recently been revolutionised by the advent of the BASF process. This replaces the harsh corrosive Ritter reaction with a much cleaner direct amination of the alkene with ammonia over zeolites.Extension of this concept to the direct amination has been attempted by the group of Wolfgang Hölderich at the RWTH Aachen (J. Mol. Cat. A 2000 156 255). They found that using the BASF conditions the reaction was hindered by thermodynamic difficulties and that the polymerisation of styrene restricted their choice of operating parameters. Undeterred they found that the hydration of styrene under similar conditions followed by a nucleophilic displacement of the alcohol with ammonia gave the desired product in relatively low yields. More success was found with a-methyl styrene where the direct amination proceeded in good yield. The use of enzymes as catalysts in organic synthesis is a very attractive area of research with excellent selectivities and mild conditions being commonplace.However the use of enzymes is often complicated by the sensitivity of enzymes to non-biological conditions. In organic solvents the use of CLICs or powdered enzymes is possible but can lead to substantial loss of activity. In aqueous solution the enzyme is typically homogeneous but this can lead to difficulties in recovery of the enzyme and the product. The group of Manfred Reetz in Mülheim has now developed a system whereby a lipase is entrapped in a hydrophobic silica matrix (Synthesis 2000 781). The trick here was to have a functionalised silica containing hydrophobic methyl or propyl groups.This led to lipases which were substantially more active than the powdered enzyme in organic solvents. Recovery and reuse of the enzyme–silica composite was demonstrated. Green Chemistry August 2000 G81 Green Chemistry Network Symposium at the University of Leicester NEWS & V I E W S Lanthanides have recently been the subject of intense interest due to their excellent Lewis acid characteristics coupled with their very flexible Following a successful first symposium at York towards the end of 1999 the GCN’s ‘Young Persons’ symposium series moved to Leicester. On this occasion the presentations covered a wide breadth of green chemistry topics including selective synthesis benign solvents fluorous biphase systems for efficient separations fuel cells and clean electrochemical synthesis.Abstracts of the talks can be seen on the GCN web site http://www.chemsoc.org/gcn. Ayhan Celik from Leicester discussed the design of enzymes for carrying out specific selective chemical transformations particularly oxidations. The concept was illustrated with the ascorbate peroxidase (APX) catalysed oxidation of aromatic substrates. APX efficiently catalyses the hydrogen peroxide oxidation of aryl alkyl sulfides but with little R:S selectivity. By replacing an active tryptophan site in APX with alanine the R:S selectivity can be as high as 4:1 (for R = Et). The selectivity theme was continued by Colin Hayman from Loughborough who Green Chemistry August 2000 coordination chemistry allowing them to function in Lewis basic solvents such as water and to behave catalytically in discussed stereoselective approaches to Phorbol esters.Phorbol esters are co-carcinogens and an efficient synthesis of these materials is needed to further study their biological properties. The talk focussed on a key intramolecular Diels–Alder reaction introducing stereocontrol the Diels–Alder reaction being potentially highly green producing no waste. Approaches to activating the diene and dieneophile to speed up the slow reaction were discussed. The next two presentations from Richard Major and Jie Ke of Nottingham University discussed aspects of supercritical CO2 technology. Dispersion polymerisation in supercritical fluids is currently a very active research area.AIBN initiated polymerisation of methyl methacrylate. Stabilisers are an essential part of such systems being required to control particle size and prevent reactor fouling. The Nottingham group have been studying the effects of Krytox 157FSL an acid terminated perfluoropolyether and have show that particle size can be controlled by both the concentration and MWt of the stabiliser. Since phase behaviour may have a significant influence on the reaction it is important to ensure that so called supercritical reactions actually remain in the supercritical state throughout the reaction. Acoustic measurements have been shown to offer a simple effective means of monitoring the phase behaviour of reactions.Using hydroformylation of G82 This journal is © The Royal Society of Chemistry 2000 Friedel–Crafts acylations. The group led by Tony Barrett (Green Chem. 1999 1 G97) has now published a new method which combines a ytterbium catalysts with fluorous biphasic conditions allowing the Friedel–Crafts acylation of anisole and the efficient recycling of catalyst (Synlett 2000 847). They chose as catalyst the fluorous Yb catalyst containing three carbanionic ligands each of which has three perfluorosulfonyl chains imparting fluorous phase solubility. This catalyst is active in the acylation of anisole with acetic anhydride and can be recovered and reused. propene in CO2 as an example the critical temperature shifts from well below that of CO2 to well above as the reaction proceeds due to the effect of varying concentration of products and reactants.The next two presentations discussed green aspects of fluorous biphasic systems which exploit the temperature dependant miscibility of highly fluorinated solvents and normal organic solvents. Adrian Dobbs (Open University) discussed ‘greening’ of the Wittig reaction. Although very versatile the Wittig reaction is not widely uses in industry one reason for this is the difficulty of removing triphenyl phosphine oxide residues from the product. However by using phosphines such as 1 containing a perfluoro alkyl group the resulting phosphine oxide can be readily extracted into a perfluorinated hydrocarbon solvent and recycled.Alison Stuart from Leicester discussed some catalytic applications of fluorous soluble phosphorous ligands with particular reference to hydroformylation. Hydroformylation of terminal with catalysts such as HRh(CO)L3 where L is triphenyl phosphine give aldehydes with a normal+iso chain ratio of around 2.5. Since it is the normal aldehyde which is usually required reactions which produce more of the desired product are both greener and more efficient. By replacing triphenyl phosphine with a series of fluorinated phosphine ligands the normal+iso ratio has been increased to over 6. Fuel cells are of current topical interest and offer tremendous potential as a more efficient and cleaner method of energy generation than conventional methods.Robert Cunningham (Keele) described work on the direct internal fuel reforming in solid oxide fuel cells. SOFCs have several advantages over other fuel cell systems not least because they operate at high temperatures and can therefore use a variety of fuels including natural gas. There are several problems however mainly concerned with carbon deposition on the anode and sintering of the anode during the high temperature operation. In the first international meeting dedicated to the study and application of ionic liquids as solvents forty-one scientists and engineers from academia industry and government research laboratories met in Heraklion on the island of Crete from 12-16 April 2000 to discuss the current and future status of the application of ionic liquids to new green industrial technologies.They were joined by six industry observers and four student/staff helpers. The full program scientific abstract attendee list and group picture can be accessed via the website create for this ARW at http://bama.ua.edu/ ~ rdrogers/NATO. The workshop began with a plenary lecture on green chemistry by Professor John Warner (University of Massachusetts-Boston) followed by three-and-a-half days of intensive lectures and discussion on the current status of ionic liquid research and application. Topics covered included industrial needs in green chemistry current industrial applications of ionic liquids separations electrochemistry novel chemistries in ionic liquids green catalysis and the status of East–West collaborations.Electrochemistry?’ was given by Professor Keith Scott (Newcastle). The usefulness of electrochemical techniques Green Industrial Applications of Ionic Liquids—a NATO advanced research workshop Further information on this research workshop can be obtained at the Green Chemistry website at http://www.rsc.org/greenchem The last day-and-a-half were devoted to roundtable discussions meant to distill the workshop’s content into major This journal is © The Royal Society of Chemistry 2000 NEWS & V I E W S The Keele group has developed a unique test system based on thin walled yttria-stabilised zirconia (electrolyte) tubular reactors for studying anode performance.By modifying the nickel/zirconia anode significant lowering of the carbon deposition rate can be obtained incorporation of Mo into the anode is proving especially beneficial. Stephanie Livermore (Keele) continued the SOFC theme concentrating on cells that run at intermediate temperatures (600 °C). Ceria-gadolina based cells have high ionic conductivity and therefore can operate at lower temperatures than the cells discussed above. This gives the potential advantage of producing less carbon deposits. The Keynote speech ‘How Green is recommendations of the ionic liquid research community. The three roundtables included a) outlining industrial priorities needs and challenges in green chemistry b) drafting ionic liquids research priorities to meet the green needs of the chemical industry and c) developing protocols to enhance East–West collaborations in ionic liquids research.The major outcomes of the workshop included the following • Ionic liquids are intrinsically interesting and worthy of study for advancing science (ionic vs. molecular solvents) with the expectation that something useful may be derived from their study. • Combined with green chemistry a new paradigm in thinking about synthesis in general ionic liquids provide an opportunity for science/engineering/business to work together from the beginning of the field’s development. • Readily available well characterized ionic liquids free of intellectual property are needed to encourage development of applications. • Toxicity biodegradation bio-accumulation safety health and environment (SHE) impact data are needed immediately. in areas as divers as fuel cells organic synthesis and waste remediation were discussed. Some of the synthetic applications highlighted includes naphthalene oxidation synthesis of 3-bromothiophene (avoiding zinc acetate waste) and hydrogenation of vegetable oil. By way of an excellent conclusion Scott highlighted the relevance and potential areas of application to all the 12 Principles of Green Chemistry. Potentially electrochemical reactions are also relatively inexpensive with electrons costing £8/te equivalent much less expensive than most other redox reagents. However the cost of the electrochemical cells are relatively high preventing investment in all but ‘secure’ long-term chemical production. So is electrochemistry green? Well it certainly can be but like most things it depends on how it is applied. • Ionic liquid research should include cost/benefit economic and life-cycle analyses. • Regulatory road blocks to ionic liquid implementation should be tackled now. • A public (free) verified web-based database of physical thermodynamic and related data (i.e. not process specific) is needed and work should start immediately on identifying the best methods to accomplish this. • There is an urgent need to increase the number but especially the areas of expertise of ionic liquids researchers. A model of open collaboration needs to be encouraged. • International collaboration and communication/education regarding the results are needed. • A brochure should be developed to advance the understanding of ionic liquids and their applications. • A NATO Advanced Study Institute should be held dedicated to all facets of the study and application of ionic liquids from scientific engineering and business perspectives. This meeting should occur no earlier than Spring 2002. Green Chemistry August 2000 G83

ISSN:1463-9262    

DOI:10.1039/b005200k

出版商:RSC    

年代:2000

数据来源: RSC