摘要:

Evolution and growth in 2001 E D I T O R I A L The year 2001 sees a number of significant developments in the world of green chemistry. The year had an excellent start with the IUPAC International Symposium on Green Chemistry in Delhi in January. It is very important that developing countries with growing chemical manufacturing bases are at the forefront of the green chemistry revolution. We were delighted that IUPAC agreed to support this meeting and this helped to attract an international group of speakers from India the USA East and West Europe Africa and Japan. Green chemistry conferences later in the year include the first international conference organised by the Green Chemistry Network Green Chemistry Sustainable Processes and Products which is to be held in Swansea Wales in April.The 2001 Europacat conference in Ireland in September will also have a green chemistry theme. Green Chemistry hopes to include the latest information on and reports from green chemistry meetings around the world. The journal goes from strength to strength; institutional subscriptions have more than doubled since 1999 (the USA being the largest source of subscriptions) as have submissions. The quality of submissions continues to increase and we are pleased to have published work from many of the leading workers in this area of research and a variety of papers from institutions in so-called ‘Third World Countries’ where green chemistry may have its greatest application and impact. As a result of the increased submissions our natural rejection rate has increased to approximately 35%.Hardcopy publication times remain at an average of 120 days from receipt with web publication even faster. The journal now offers free contents alerts (www.rsc.org/is/journals/current/ej_update_form.htm); publication of supplementary information to your paper on the web (e.g. videos structures related data software) (www.rsc.org/esi); electronic submission by file upload (www.rsc.org/submissions) or e-mail attachment; and authors are sent free of charge electronic (.pdf) files of their papers instead of reprints allowing copies to be printed on demand. Whilst the web version of the complete journal remains free on a site-wide basis only to full-rate institutional subscribers the web news section is free to both subscribers and non-subscribers.Subscriptions to Green Chemistry were lower than we had planned for in 1999 and this led to caution and a minor cost-cutting exercise in 2000 which affected mainly the use of colour and the number of news pages we published. Colour will still be used in the back section wherever and whenever it is appropriate to do so. This measure had no deleterious effect on the quality of the science in the journal in fact the quality of work submitted has clearly improved. We are now confident of the financial viability of Green Chemistry even in a very competitive market. Green Chemistry February 2001 G2 This journal is © The Royal Society of Chemistry 2001 Nonetheless the continued success of the journal is dependent on encouraging new subscriptions and maintaining the large volume of high quality submissions we hope that you will continue to lend us your support in both of these areas.We welcome articles of various types from industrial and other non-academic organisations. We have been particularly pleased to publish articles from companies about green chemistry in practice and this issue sees further examples of this—these are the most powerful arguments to support all of our efforts to persuade more and more companies that green chemistry can achieve economic as well as environmental and societal benefit. Please encourage colleagues in industry to consider publishing their case studies in Green Chemistry. We should not lose sight of the fact that to represent properly what is important in the context of green chemistry we must continue to publish more than just articles on research and industrial application.Green Chemistry news pages continue to provide news on awards conferences and other activities as well as featuring highlights from the green chemistry literature. Supplementary news material will be available via the web —see also the Green Chemistry Network Site www.chemsoc.org/gcn for substantial information on what is happening in the world of green chemistry. We were very pleased to publish Neil Winterton’s authoritative review on chlorine (Green Chemistry 2000 2(5) 173). This exemplifies that not only are we interested in publishing long (critical) reviews but also that we welcome challenging controversial issues (though the latter would also be welcome in much shorter forms e.g.letters!). Educational issues are at least as important as any other aspect of green chemistry and we would very much like to publish more articles on innovative aspects of new courses and relevant educational material. For example at York we are starting a new Masters (“MRes”) course in Clean Chemical Technology this year and we hope to inform the community about how the course develops and the challenges that we encounter along the way. Therefore if you are running or planning a course module practical or workshop that you think may be relevant to the green chemistry community please let us know—as with industrial application the most effective means of persuasion is by example. We would like to extend our sincere thanks to all reviewers and authors of Green Chemistry papers for their hard work and contribution(s) to the journal. We look forward to your continued support and that of the growing community of green chemists to help ensure Green Chemistry is even more successful in 2001. James Clark York January 2001 DOI 10.1039/b100448o

ISSN:1463-9262    

DOI:10.1039/b100448o

出版商:RSC    

年代:2001

数据来源: RSC

摘要:

Fluorous techniques for the synthesis and separation of organic molecules Dennis Curran and Zhiyong (Robert) Lee of the Chemistry Department at the University of Pittsburgh USA describe how fluorous techniques provide strategic new green options for conducting organic reactions and for separating the resulting reaction mixtures. The technology is especially suitable for the preparation of combinatorial libraries. The yield of every chemical step is limited both by the efficiency of the reaction and the ability to recover the pure product from the reaction mixture. However most traditional solution phase synthesis methods are concerned only with conversion of starting materials to products (reactions) and not with product separations. Fluorous techniques provide strategic new options for conducting solution phase organic reactions and for separating the resulting reaction mixtures.Fluorous molecules typically contain at least one highly fluorinated domain attached to an organic domain. The fluorinated domain can be an integral part of the molecule (permanent attachment) if the intended use is as a reagent reactant or catalyst. A temporary attachment of a removable fluorous group is required to render a reaction substrate or product fluorous. Fluorous compounds can be separated from standard organic compounds by simple workup techniques Dennis Curran Distinguished Service Professor and Bayer Professor of Chemistry at the University of Pittsburgh USA and Chairman of the Scientific Advisory Board of Fluorous Technologies Inc.of liquid–liquid extraction (two- or three-phase) or solid–liquid extraction. Fluorous compounds can also be separated from each other based on fluorine content by fluorous chromatography. Four different types of techniques are summarized fluorous biphasic catalysis fluorous reagents and reactants fluorous substrates (fluorous synthesis) and fluorous mixture synthesis. The techniques differ in the size and nature of the fluorous tag in the reaction conditions and in the separation method. Fluorous techniques are applicable to both green chemical process development and chemical discovery research. Many of these new techniques are especially suited to the preparation of combinatorial libraries by solution phase parallel synthesis.Organic Compounds a typical organic tin hydride • mediates diverse radical reactions but. • is difficult to separate from organic products Fluorous molecules Fluorous molecules are designed to mimic organic molecules in terms of reactivity yet to still be readily separable from other organic molecules. In the technique of fluorous mixture synthesis fluorous molecules are also separated from each other. Fluorous molecules typically have two domains. The organic domain resembles a standard organic parent molecule and dictates the reactivity of the molecule. The fluorous domain is a highly fluorinated group that controls the separation features of the molecule.Fluorous domains are often perfluoroalkyl groups. Shown below are two simple examples of fluorous molecules designed after common organic parents. Fluorous tin hydrides have similar reactivity to the classical reagent tributyltin hydride. But Fluorous Compounds a typical fluorous tin hydride • mimics the reactivity of its organic parent and. • is easy to separate from organic products by liquid-liquid extraction • recover and reuse are routine DOI 10.1039/b100266j This journal is © The Royal Society of Chemistry 2001 a typical Boc protected amide • easy to prepare by amide coupling but. • is difficult to separate from the coupling reagents F E A T U R E a fluorous Boc protected amide • prepared by the same methods as the standard Boc-amide and.• is easy to separate from the coupling reagents by solid-liquid extraction G3 Green Chemistry February 2001 F E A T U R E unlike tributyltin compounds the fluorous tin compounds are readily separable from organic compounds by simple fluorous separation techniques like liquid–liquid extraction or solid–liquid extraction. The fluorous domain of the tin hydride is permanently attached because there is never any need to separate it from the organic domain. The tin compounds are simply recovered at the end of the reaction and recycled. Although only one fluorous tin hydride is shown in the table on page G3 a whole family is now available whose members differ from each other by the length and number of the fluorinated chains and the length of the spacer.This allows the separation properties and (sometimes) the reactivity properties to be tuned for particular needs. The fluorous Boc group is a typical example of a fluorous protecting group that is designed to be attached and removed by analogy with the standard Boc group. Such fluorous protecting groups are also called ‘fluorous tags’ and they allow rapid separation of all tagged molecules from non-tagged molecules by fluorous solid phase extractions. A growing assortment of fluorous tags is now available. Fluorous separation methods Liquid–liquid extraction Perfluorinated or very highly fluorinated solvents are called ‘fluorous solvents’ and they are typically immiscible with organic solvents and water.They are used in liquid–liquid extractions to quickly separate fluorous compounds from organic compounds in a two-phase liquid–liquid extraction or from organic and inorganic (or water soluble organic) compounds in a three-phase liquid–liquid extraction. The most popular fluorous Green Chemistry February 2001 G4 This journal is © The Royal Society of Chemistry 2001 solvent is probably 3M’s FC-72™ but a number of related solvents are available and these are all comparably priced. A photograph of a typical three-phase liquid–liquid extraction is shown above. Such extractions are readily automated and can be used to quickly partition reaction mixtures into organic water-soluble and fluorous fractions.In many cases the crude organic products are pure enough to be taken on to the next reaction and the fluorous products can usually be recycled if desired. Liquid–liquid extractions work best when fluorous domains are relatively large. In the best cases only a single separation is needed. With lower partition coefficients the organic fraction is washed several times with the fluorous solvent. Thanks to the exceedingly low solubilities of organic compounds in fluorous solvents the washing process can be conducted repeatedly without extractive loss of the organic product. Liquid–liquid extractive methods are typically used when the desired product is organic and some other reaction component (reactant reagent catalyst scavenged product) is fluorous.Solid–liquid extraction Silica gel with a fluorocarbon-bond phase (‘fluorous reverse phase silica gel’) can be used to adsorb fluorous molecules and free them from non-absorbed organic molecules by the simple process of solid–liquid extraction illustrated below. Examples of fluorocarbon bonded phases include –Si(Me2)CH2CH2C6F13 –Si(Me2)CH2CH2C8F17 and –Si(Me2)(CH2)3C(CF3)2C3F7. In the separation stage a crude reaction mixture is charged to a suitable amount of fluorous silica gel and the silica is eluted first with a ‘fluorophobic’ solvent to remove the organic compounds while leaving the fluorous compounds adsorbed. In cases where the fluorous products are desired a second elution with a ‘fluorophilic’ solvent then provides this material.These fluorous solid phase extractions are different from traditional chromatographies and this is advantageous in a parallel setting. In solid phase extractions relatively high loadings of substrate/silica are used and all of the mixtures in the synthesis behave identically. No fractionation is needed. In traditional chromatographies each mixture behaves differently and lower loadings and carefully monitoring of fractions are needed. The solid–liquid extractions are operationally filtrations and they are easy to conduct in parallel either manually (see the manual solid-phase extraction apparatus below) or by using various automated techniques. In addition to the operational convenience solid–liquid extractions succeed with many fewer fluorines in the fluorous domain compared to liquid–liquid extractions.For this reason solid–liquid extractions are especially useful when the desired product of the reaction bears a fluorous tag. The solid phase extraction is applicable in essentially all areas from traditional synthesis through parallel synthesis and is especially useful for parallel synthesis of intermediates. Solid–liquid extraction is currently the most general and most easily implemented fluorous–organic phase separation technique. It is useful for the gamut of fluorous methods. Fluorous solvents are rarely needed for the extractions and they are used only to wash the silica prior to reuse if desired.Fluorous chromatography The separation of fluorous molecules from each other can sometimes be accomplished by standard chromatographic techniques including traditional or reverse phase chromatography. However the best way to separate fluorous compounds from each other is usually by chromatography over fluorous silica. These separations capitalize on the unique feature of fluorous solid phases which is their ability to separate molecules primarily by fluorine content. An illustrative example of this is shown below with a family of fluoroacyl-tagged amides. The control compound lacking the fluorous tag (C7H15) comes off with the solvent front as do most other non-fluorinated organic compounds under these conditions.The fluorinated homologs then emerge strictly in order of fluorine content and a solvent gradient is needed to push the more highly fluorinated members of the series off the column. Many popular fluorous techniques involve fluorous–organic separations so preparative fluorous chromatography is not needed. However fluorous chromatography still has two major uses. First it can be used in methods development experiments to select suitable solvents for fluorous–organic solid phase extractions thereby ensuring in advance that separation conditions are suitable. Second it can be used to analyze the purity of essentially any kind of fluorous component and it provides information that is largely complementary to traditional chromatographic analyses.In contrast to other methods fluorous mixture synthesis techniques rely heavily on fluorous chromatography for the separation of tagged compounds by the fluorine content of the tag. Fluorous biphasic catalysis What we now call ‘Fluorous Biphasic Catalysis’ (FBC) was first introduced in the thesis of Dr. M. Vogt in Aachen in 1991. This work was known to almost no one and a seminal paper by Horváth and Rábai in 1994 introduced new concepts and results along with today’s terminology. Since that time fluorous biphasic catalytic methods have advanced rapidly and a large number of fluorous catalysts and ligands (especially phosphines) are known. The defining feature of FBC is the use of a fluorous reaction solvent and the technique is best viewed as a liquid phase catalyst immobilization method.Hydroformylation with a fluorous variant of Wilkinson’s catalyst provides a typical example of fluorous biphasic catalysis below. A toluene solution of an F E A T U R E enone and a silane is heated with a perfluoromethylcyclohexane solution of the catalyst. After the reaction is complete the mixture is cooled and the two phases are separated to provide the organic hydrosilylation products and the recovered catalyst immobilized in the fluorous phase. In an important variant of fluorous biphasic catalysis an organic solvent is choosen such that on warming a homogeneous (one phase) solution results. After the reaction is complete the mixture is cooled to induce the phases to separate once again.In the hydrosilylation example the replacement of toluene by hexane allows for one phase reaction and two phase separation. FBC and related methods are ideally suited for economical and green chemical processes. A single liquid–liquid separation provides both the product and the recovered catalyst. The safety of fluorous solvents is also an attractive feature. For the single separation to succeed high partition coefficients are needed so the catalysts generally have large numbers of fluorines. Fluorous catalysts have advantages over solid-supported catalysts since they can be soluble in the reaction medium. Water-based biphasic catalysis reactions are also used but are obviously limited to water-tolerant processes.Fluorous catalysts do not share this limitation. Fluorous reagents reactants catalysts For many types of organic reactions it is desirable to use fluorous reaction components (reagents reactants catalysts) with fewer fluorines. Such molecules have advantages of lower molecular weight and increased solubility in organic solvents. With these types of molecules fluorous reaction solvents are not used and the fluorous phase (either solid or liquid) is used only in the separation stage. The reductive radical cyclizations with the family of fluorous tin hydrides shown below illustrate many of the features of this branch of fluorous chemistry. In general the substrate and the product are organic molecules and one of the other reaction components (in this case the tin hydride) is fluorous.The fluorous component can be used either catalytically or stoichiometrically and the reaction and separation stages are decoupled. After standard reactions members of the tin hydride family with more fluorines can be separated either by liquid–liquid extraction or by solid–liquid extraction while the solid–liquid Green Chemistry February 2001 G5 This journal is © The Royal Society of Chemistry 2001 F E A T U R E (C6F13CH2CH2)3SnH yes (3) (C4F9CH2CH2)3SnH yes (8–10) (C6F13CH2CH2CH2)3SnH yes (5–8) (C4F9CH2CH2CH2)3SnH yes (10–12) C10F21CH2CH2SnMe2H yes (3) C extraction is preferred for members with fewer fluorines.For the most highly fluorinated member of the series a fluorinated reaction co-solvent like benzotrifluoride (C6H5CF3) is needed. Benzotrifluoride is not a ‘fluorous’ solvent since it is miscible in all organic solvents (and indeed dissolves many types of organic compounds as well) but it still aids in the solubilization of fluorous compounds in the reaction medium. These types of methods are broadly useful for all types of organic synthesis from process chemistry (fluorous catalysts preferred) through traditional synthesis to solution phase parallel synthesis and combinatorial chemistry. Tuning of preferred reaction solvents and separation methods is accomplished by selecting a reagent with an appropriate fluorine content.The reagents with fewer fluorines are especially attractive since they often have excellent solubility in organic solvents yet can still be separated from standard organic compounds by solid–liquid extraction. Fluorous compounds are also soluble in supercritical CO2 and can be used in green chemical reactions in that solvent. The general solubility of the fluorous reaction components is an attractive feature in comparison to reagents quenchers and catalysts that are immobilized on insoluble polymers. The term ‘fluorous synthesis’ is often used to describe techniques in which the substrates and/or desired products are rendered fluorous. This technique is a phase tagging strategy that is conceptually analogous to ‘solid phase synthesis’ but with major operational Green Chemistry February 2001 differences.Making substrates and products fluorous necessarily involves cleavable tags (since the final product will not be tagged) and fluorous protecting groups or traceless tags can be used. Fluorous synthesis concepts were introduced with liquid–liquid separation methods coupled with very large fluorous tags (60–120 fluorines). These early ‘heavy’ fluorous techniques are quickly being replaced by ‘light’ techniques where tags with many fewer fluorines are used coupled with solid–liquid extraction. Amino acids are readily coupled to make amides by first tagging the amine with a fluorous acyl group or a fluorous Boc group and then coupling the acids with amines under standard conditions (below).In general only about 15–19 fluorines are needed and the resulting tagged molecules have solubility properties that are largely dominated by the organic domain. In other words they are soluble in organic not fluorous solvents. However the solid phase extraction (SPE) properties of the molecule are still dominated by the fluorous domain. The protected acids are coupled with amines under standard G6 tin hydride I-I extraction s-l fluorinated (no. of extractions) extraction rxn cosolvent? yes yes no yes no yes no yes no yes no yes no 8F17CH2CH2SnMe2H Summary Fluorous substrates products This journal is © The Royal Society of Chemistry 2001 conditions. The desired tagged products are then retained on the column in the first pass of the solid phase extraction (MeOH/water) while all the coupling reagents reactants and byproducts are eluted off.The coupled fluorous products are then eluted off in a second pass (MeCN) and are obtained in excellent purity. Fluorous synthesis is attractive because a single protecting group or tag can be used to render a library of organic molecules fluorous. The resulting library of soluble molecules can then be separated from broad classes of organic and inorganic reagents reactants side products etc. by solid phase extraction. Unlike polymer-bound molecules the fluorous-tagged compounds are small molecules that can be analyzed and characterized by standard small molecule techniques.The tagging methods are ideal for expedited parallel synthesis and for the gram-scale preparation of chemical intermediates in parallel. Because the tagged compounds have relatively few fluorines they can be reacted under typical conditions for non-tagged molecules and the solid phase extraction gives a fast yet substantive separation. In the final detagging step solid phase extraction can again be used to separate the organic product from the remnant of the fluorous tag. The tag can often be recovered in a form suitable for reuse if desired. In addition to fluorous acyl and Boc groups there are now a number of fluorous silyl groups fluorous THP groups fluorous benzyl groups etc. By directly addressing the separation problems inherent in the synthesis of small organic molecules fluorous techniques provide an array of powerful solutions that span the discipline of organic synthesis from large-scale chemical processes through traditional Fluorine Content Rxn Solvent Technique fluorous and organic Fluorous biphasic high catalysis low-medium Fluorous reagents organic or hybrid liquid–liquid or solid–liquid extraction organic low Fluorous substrates organic low variable Fluorous mixture synthesis fine synthesis to modern chemical discovery by combinatorial methods.The above Table summaries the four main fluorous methods outlined in this overview and compares and contrasts them. Fluorous methods are attractive and easy to apply because the experimental techniques (solution phase reactions liquid–liquid extractions solid phase extractions) are familiar to practicing organic chemists.What differs from standard organic techniques are the fluorous components that are used. The application of fluorous techniques has been limited to a few specialized laboratories due to the lack of availability of fluorous reagents reactants tags solvents silica etc. However a new company Fluorous Technologies (see box) intends to change this by providing laboratories worldwide with both the materials and the expertise that are needed to integrate fluorous methods into their ongoing discovery and production projects. Fluorous Technologies Inc.Fluorous Technologies Inc is a newly formed company based in Pittsburgh PA. It has licensed from the University of Pittsburgh several patents and pending patent applications for the use of fluorous organic chemistry for chemical synthesis isolation and purification. Investors in the company include Albany Molecular Research Inc Alfred Bader and retired founder of Aldrich Chemical Company and the University of Pittsburgh. Denis Curran is chairman of the Scientific Advisory Board for the company. See http://www. fluorous.com for further information. Uses Separation green chemical processes single liquid– liquid separation universal solid–liquid extraction chemical discovery intermediate synthesis fluorous chromatography leveraged chemical discovery Selected references Reviews D.P. Curran Combinatorial Organic Synthesis and Phase Separation Back to the Future Chemtracts—Org. Chem. 1996 9 75–87 D. P. Curran Strategy-level separations in organic synthesis From planning to practice Angew. Chem. Int. Ed. Engl. 1998 37 1175–1196. J. J. Maul P. J. Ostrowski G. A. Ublacker B. Linclau and D. P. Curran Benzotrifluoride and Related Solvents in Organic Synthesis In Topic in Current Chemistry Modern Solvents in Organic Synthesis; P. Knochel Ed.; Springer-Verlag Berlin 1999 206 80–104. D. P. Curran Parallel Synthesis with Fluorous Reagents and Reactants Med. Res. Rev. 1999 19 432–438. D. P. Curran S. Hadida A. Studer M.He S.-Y. Kim Z. Luo M. Larhed M. Hallberg and B. Linclau Fluorous Synthesis A User s Guide In Combinatorial Chemistry A Practical Approach (H. Fenniri Ed.) Oxford Univ. Press Oxford Vol. 2. in press. D. P. Curran Fluorous Techniques for the Synthesis of Organic Molecules A Unified Strategy for Reaction and Separation in Stimulating Concepts in Chemistry Wiley-VCH in press. Fluorous Biphasic Catalysis I. T. Horvath J. Rabai Facile catalyst separation without water Fluorous biphase hydroformylation of olefins Science 266 72–75. F E A T U R E I. T. Horvath Fluorous biphase chemistry Acc. Chem. Res. 1998 31 641–650. Y. Nakamura S. Takeuchi Y. Ohgo D. P. Curran Asymmetric alkylation of aromatic aldehydes with diethylzinc catalyzed by a fluorous BINOL-Ti complex in an organic and fluorous biphase system Tetrahedron Lett. 2000 41 57–60. Fluorous Reagents D. P. Curran S. Hadida Tris(2-(perfluorohexyl)ethyl)tin hydride A new fluorous reagent for use in traditional organic synthesis and liquid phase combinatorial synthesis J. Am. Chem. Soc. 1996 118 2531–2532. D. P. Curran S. Hadida S. Y. Kim Z. Y. Luo Fluorous tin hydrides A new family of reagents for use and reuse in radical reactions J. Am. Chem. Soc. 1999 121 6607–6615. Fluorous Synthesis A. Studer S. Hadida R. Ferritto S. Y. Kim P. Jeger P. Wipf D. P. Curran Fluorous synthesis A fluorous-phase strategy for improving separation efficiency in organic synthesis Science 1997 275 823–826. D. P. Curran Z. Y. Luo Fluorous synthesis with fewer fluorines (Light fluorous synthesis) separation of tagged from untagged products by solid-phase extraction with fluorous reverse-phase silica gel J. Am. Chem. Soc. 1999 121 9069–9072. Fluorous Mixture Synthesis Y Oderaotoshi Q. Zhang Z. Luo and D. P. Curran Fluorous Mixture Synthesis The First Strategy for the Synthesis of Mixtures of Organic Compounds that Provides Pure Individual Products through Demixing Controlled by the Fluorous Tag in preparation. Green Chemistry February 2001 G7 This journal is © The Royal Society of Chemistry 2001

ISSN:1463-9262    

DOI:10.1039/b100266j

出版商:RSC    

年代:2001

数据来源: RSC

摘要:

NEWS & V I E W S Highlights Duncan Macquarrie reviews the latest research in green chemistry Novel solvent systems The search for alternatives to traditional solvents continues to be an important goal and the three papers below illustrate quite different aspects of the search for novel solvent systems. Ionic liquids represent a class of solvents which are increasingly being found to be highly versatile. Based around imidazolium salts these solvents are liquid over a wide range but do not have any significant vapour pressure thus avoiding the difficulties and expense of VOC removal from waste gases. Examples of the versatility of these reaction media can be found in Green Chemistry (e.g. Green Chem. 2000 2 123; 1999 1 23; 1999 1 296).One of the latest examples of their utility has been published by Roger Sheldon of the Delft University of Technology (Org. Lett. 2000 2 4189). His group has shown that lipases are active in ionic liquids illustrated by the transesterification and ammoniolysis of ethyl octanoate and the epoxidation of cyclohexene by a combination of hydrogen peroxide and octanoic acid all catalysed by Candida antarctica in ionic liquids. Rates and yields were generally good in some cases better than in organic solvents. Fluorous biphasic catalysis is a second area which is receiving much attention with the possibility of using the thermally-controlled miscibility of fluorous and organic phases to effect separation of fluorous phase-soluble catalysts from organic-soluble product.Gianluca Pozzi from the University of Milan has recently described the oxidation of sulfides using fluorous Co-phthalocyanins (Eur. J. Org. Chem. 2001 181). He found that these catalysts were capable of the efficient oxidation of sulfides to sulfoxides with minimal Green Chemistry February 2001 G8 over-oxidation in most cases. The oxidant system was oxygen / dimethylpropanal taking advantage of the excellent solubility of oxygen in highly fluorinated media. Despite the excellent activity and selectivity achieved in the first run reuse of the fluorous phase proved problematic with either dramatic reductions in conversion or bizarrely extensive over-oxidation to sulfone. These changes were ascribed to oxidative changes to the catalysts something which was not observed in earlier work on epoxidation.Non-solvent reactions are becoming popular and many reactions can be carried out without solvent with obvious advantages. What is particularly rare is the successful translation of enantioselective reactions since the choice of solvent is often critical to achieving high selectivity. Kenso Soai of the Science University of Tokyo has published details of such a system (Chem. Commun. 2000 2471). He takes a b-aminoalcohol as chiral auxiliary in conjunction with diethylzinc and reacts this complex with benzaldehydes transferring the ethyl group to the carbonyl function giving chiral alcohols. Whereas these reactions run typically in hydrocarbon solvents Soai has shown that they can also be carried out very successfully without solvent.His group has used a series of catalysts each of which gave yields of !93% and ee’s of 85–89% with reaction rates greater than when solvents were used. The Heck reaction is one of the most important C–C bond forming reactions known and many variations have been published since the initial work in the 1960s. Jin-Xiang Wang and co-workers from Northwest Normal University in Lanzhou have now published details of the Heck reaction carried out in water with microwave irradiation (J. Chem. Res. (S) 2000 484). They found that the combination of water as solvent and microwaves afforded excellent yields (86–93%) of various coupling products from the reaction of aryl iodides (nitro carboxyl and methyl substituents) and substituted alkenes (phenyl acid and ester substituted).Only ten minutes irradiation was sufficient to complete the reactions as compared to 3–7 hours for conventional heating. Microwave reactions Two further papers concerning the use of microwaves have recently been published and are summarised below The group led by Majid Heravi at the Ferdowsi University of Mashhad in Iran have shown that microwaves can be used DOI 10.1039/b100267h This journal is © The Royal Society of Chemistry 2001 in conjunction with sulfuric acid / silica gel to effect the cyclisation of a series of alkynyl heterocycles to yield bi- and tricyclic thiazoles (J.Chem. Res. (S) 2000 482). Five to ten minutes reaction time were required to achieve good to excellent yields. The question of scale-up of microwave reactions is an important one and work relating to this key obstacle to commercialisation of microwave chemistry has been reported by A Loupy and co-workers from the CNRS in Gif-sur-Yvette and the Universite Paris-Sud (Org. Proc. R+D 2000 4 498). They have shown that using a commercial microwave reactor batch sizes of several hundred grams could be safely handled and rates and yields were comparable to those found in smaller ( < 5 g) scale operations. A range of different reaction types (alkylation of KOAc phenacylation of triazoles dealkylation of 2-ethylanisole; peracetylation glycosylation saponification halogenation and epoxidation of carbohydrates were also demonstrated).For a recent review on microwaves in synthetic chemistry see Green Chem. 1999 1 43. Oxidation reactions Shun-Ichi Murahashi and co-workers from Osaka University have published their results on the Ru catalysed oxidation This journal is © The Royal Society of Chemistry 2001 NEWS & V I E W S silica and compared its activity in the dioxirane-mediated epoxidation of alkenes. Homogeneous ketones catalyse this reaction but are deactivated by being oxidised themselves to esters via a Baeyer–Villiger oxidation. This side reaction is suppressed and the catalyst could be recovered and reused ten times with no loss in activity.Activity was comparable to the homogeneous version. A variety of substrates were epoxidised in yields > 90% with the catalyst. The oxidation of benzene to phenol is an important goal but is complicated by the greater reactivity of the product phenol leading to dihydroxybenzenes and their decomposition products. A team led by Daniele Bianchi and Rodolfo Vignola from EniChem in Novarra (Angew. Chem. Int. Ed. 2000 39 4321) has developed a biphasic iron-based catalyst system which give excellent selectivities to phenol at the (relatively) high conversion level of ca. 8%. Their catalyst is based on FeSO4 with a pyrazine carboxylic acid ligand and trifluoroacetic acid as cocatalyst. Working in a benzene–water–acetonitrile biphasic system (to partition the product away from the catalyst) they achieved 97% selectivity to phenol at 35 °C.The catalyst also displays activity in the oxidation of methane to formic acid. Green Chemistry February 2001 Homogeneous catalyst immobilisation The recently developed strategy for immobilisation of charged transition metal complexes developed by Augustine (Chem. Commun. 1999 1257) has been used as the basis of a novel and highly versatile ferrocenyl-rhodium hydrogenation catalyst by researchers at Chirotech (J. Org. Chem. 2000 65 8933). They prepared their catalyst by combining either alumina or silica and a heteropolyacid and then introducing the catalytic unit as a counterion to the charged heteropolyacid.The catalyst is stable to leaching unless there is a suitably competitive anion which can remove the catalyst from its interaction with the support. The catalyst was very active and selective towards a range of substrates often displaying much greater selectivity than either homogeneous versions or other more traditional heterogeneous hydrogenation catalysts. Sulfides are tolerated and do not poison the catalyst. A small amount of leaching was noted during the initial use of the catalyst but none was found after this and no reduction in activity was noted. Improvements to an epoxidation catalyst have been reported by the group led by Choong Eui Song of the Korea Institute of Science and Technology (Chem.Commun. 2000 2415). They have immobilised a trifluoromethyl ketone on G9 NEWS & V I E W S of alkanes with peroxy species (J. Org. Chem. 2000 65 9186). They first studied the oxidation of cyclohexane to a mixture of alcohol and ketone and found that Ru-charcoal with peracetic acid gave excellent selectivities and reasonable yields. Yields could be improved substantially by the addition of trifluoroacetic acid (up to 90% conversion of cyclohexane could be achieved. A second area of investigation was the room temperature oxidation of alkyl aromatics where the optimum system was Ru(PPh3)2Cl2 and t-BuOOH. With this combination conversions ranging from 46–100% were achieved for a range of alkyl aromatics with selectivities of 54–95%.The related oxidation of methylpyridines to pyridine carboxylic acids has been investigated by Yasutaka Ishii and his group based at Kansai University in Osaka (Org. Proc. R+D 2000 4 505). In the latest in a series of Green Chemistry February 2001 papers on the use of N-hydroxyphthalimide (NHPI) as an oxidation catalyst they report the efficient oxidation of 3-methylpyridine to the corresponding acid in 77% yield using 10 mol% NHPI 2 mol% Co(ii) acetate and 1 atmosphere of oxygen at 100 °C. The addition of 0.5 mol% Mn(ii) acetate allowed the reduction of the Co level to 0.1 mol% thus reducing the total amount of metal present. Thus the use of NHPI allows milder conditions to be used for this type of oxidation than the normal high temperature and pressure systems currently in use.G10 Transesterifications Transesterification is an important reaction type catalysed either by strong acids or by strong bases particularly Super-efficient dyes for the coloration of cotton —the Procion® XL+ range Dr. W. J. Ebenezer and Dr. M. G. Hutchings of DyStar UK Ltd. describe the environmental benefits available from the Procion XL+ range of reactive dyes for cotton commercial technical and crucially environmental pressures. Over the last 5 years our team has invented and ultimately commercialised the new Nevertheless after a further 144 years of intensive dye research and development there still remains a need for yet more innovation in response to today’s The discovery of the first synthetic textile dyestuffs half way through the 19th century heralded the beginning of the modern organic chemical industry.This journal is © The Royal Society of Chemistry 2001 alkoxides in the corresponding alcohol. Rebecca Kissling and Michel Gagné of the University of North Carolina have extended their previous work on alkoxides in non-protic solvents by optimising the structures of the inorganic clusters formed (Org. Lett. 2000 2 4209). They have found that in non-protic solvents clusters of alkoxides form which are more reactive than the species found in alcohols. By modifying the clusters such that insoluble (and therefore inactive) clusters do not form they have successfully extended the lifetime of these catalysts.This involved the use of both aryloxides and alkoxides to give the clusters shown in the diagram. With these clusters essentially quantitative transesterifications could be achieved with as little as 0.5 mol% catalyst compared with the 5–10 mol% (and multiple addition strategies) normally required. Procion XL+ range of dyes for cotton. Their outstanding technocommercial properties are augmented by a combination of notable environmental advances which together have been recognised by the 2000 UK Green Chemistry Award. This article gives an overview of this technology. Technical Reactive dye molecules are characterised by a chromophore to impart colour attached to a reactive group.The latter is invariably an electrophilic species capable of reacting with cellulose and thereby binding the chromophore to the cellulose covalently. Such dyes are water soluble by virtue of sulfonation and are applied to cellulose from aqueous solution under conditions which induce covalent bond formation between dye and cellulose. The subject of this innovation is a new range of dyes for application to cotton by so-called exhaust dyeing. Although the industrial technology of dye application is highly advanced and can be complex the easiest picture of the dyeing process of relevance here is a solution of the dye plus the cotton to be dyed to which are usually added salt to force the dye onto the fibre and base to induce cellulose nucleophile–dye electrophile reaction.The heterogeneous mixture is heated for a period to induce reaction. A major concern is competing hydrolysis of the dye electrophile by water at elevated pH yielding dye which can no longer be attached permanently to the substrate but which must nevertheless be removed in a wash-off sequence and then discarded to effluent. Coloured effluent generated in this way can give rise to environmental problems. No commercially available reactive dye avoids the unfortunate hydrolysis problem despite some claims to the contrary. Despite this drawback reactive dyes are attractive to the textile dyer because of their ease of use fastness properties brightness and the wide range of shades. In general they are used at the higher quality end of the cellulosics market.Current main areas of commercial expansion are in sportswear for example knitted cotton T-shirts. An important concept to understand is that dyers rarely use a single dye when dyeing cotton with reactive dyes. Under most circumstances a mixture of dyes is utilised to achieve the desired shade. This makes it possible to achieve an infinite number of shades with a small number of dyes. Achieving the exact shade requires Background The target • 4 3 106 te p.a. of cotton is exhaust dyed with reactive dyes; • 4 3 108 te p.a. of fresh water is used in the overall process and all of this is ultimately discarded in a contaminated state; • 2.8 3 106 te p.a.of salt is used in the process; and all of this is ultimately discarded in the aqueous effluent; • 8 3 104 te p.a. of reactive dye is applied with an average fixation yield of 70% thus • 2.4 3 104 te p.a. of dye is discarded in the aqueous effluent. This journal is © The Royal Society of Chemistry 2001 NEWS & V I E W S some skill and re-dying is sometimes necessary with a shading addition to correct the shade. In extreme cases the cloth may be stripped of colour and completely re-dyed but this is both a commercial and environmental last resort. One of the root causes of problems in achieving the required shade is that if the dyes in a mixture have different dyeing profiles the shade and depth may change with time. Therefore the timing of the dyeing process is critical.Historical – scope of the environmental problem Reactive dyes for cotton were invented and commercialised by ICI in the mid-1950s. The superb level of wet fastness properties exhibited by these dyes led to their rapid acceptance and increasing popularity. Over the following decades research into new patented reactive dyes allowed incremental improvements in the gamut of shades available fastness properties and especially the fixation efficiency. Currently the total world-wide production of cotton is estimated at 21 3 106 te p.a. (metric tonnes per annum) The corresponding amount of reactive dye used for cotton coloration is estimated to be 120,000 te p.a. Of this about two thirds is dyed by exhaust technology.Salient statistics which follow from these figures include Most aqueous effluent is discarded via local watercourses. The dyer at the dyehouse removes some colour but not salt and other additives. Nevertheless a large amount of colour finds its way to waste water treatment works and possibly further. The environmental load is therefore appreciable and has a wide impact. The reactive dye business due to its maturity is extremely competitive and price sensitive. As older dye technologies have moved out of patent these have been taken up by manufacturers in the developing world driving down manpower costs and total production costs. Therefore a large proportion of cotton processing has also moved to the cheaper and currently less environmentally conscious economies of the developing world.In 1995 our research and technical marketing departments outlined the technical profile for a new prospective range of reactive dyes to compete effectively against cheap non-patented commodity reactive dyes. The new range should enable build-up to unprecedented depths of shade on cotton i.e. the maximum depth of colour attained on the cloth should be much greater than conventionally observed. This would allow very strong colours to be obtained using less dye. The cost on the cloth should be at least 25% less than the market leading dyes in the individual shade ranges. In addition to the economy of coloration the total cost of production should exhibit a step change improvement on the current state of the art.The principal method of approach toward production cost reduction was to enable Right-First-Time production and improve dyehouse productivity. This involved molecular engineering of the new range of dyes to exhibit almost Green Chemistry February 2001 G11 NEWS & V I E W S range of dyes should exhibit no shade change during the course of the dyeing. The graph below shows the virtually superimposable exhaustion (upper traces; total dye fixed and unfixed on the fibre) and fixation (lower traces; dye covalently bound to the fibre) profiles for the new dyes on cotton versus time during the course of a dyeing. Additionally the dyes were required to be insensitive to changes in dyeing conditions—i.e.mistakes by the process operator would still yield a dyeing within specification. The exhaust reactive dyeing market for cotton is segmented broadly into two areas warm dyeing (60 °C) and hot dyeing (80 °C) with warm dyeing accounting for the majority (60%) share principally due to lower recipe costs. Perversely a project decision was made to target the new dye range for 90 °C dyeing; this decision subsequently yielded a large number of non-intuitive benefits. Green Chemistry February 2001 After 4 years of intensive effort involving cross-functional project teams new patentable dyes had been invented and production processes developed. These products were commercialised in 1999 as the Procion XL+ range of reactive dyes.Reactive dyes consist of chromophoric units to provide the colour plus various non-coloured functionality. The non-coloured weight consists of reactive groups linking functionality holding the various parts of the molecule together and other groups which are used to alter the application properties. A major goal of our synthetic effort was to minimise the proportion of non-coloured organic weight in the dye molecules and thus use the carbon atoms within to produce colour more efficiently. The effect of this was to make dyes with high colour strength such that less dye is utilised to achieve a particular level of shade. The dyes are based on monochlorotriazine reactive groups attached to carefully designed chromophores.The reactivity of the chlorotriazine unit toward cellulose has intentionally been tuned to the desired 90 °C application profile by selection of appropriate aliphatic di- and tri-amine linking units L. The linkers used in the various dyes also contribute to the compatibility of dye combinations. Commercial confidentiality inhibits more detailed disclosure of the chemistry underpinning the Procion XL+ dyes. The first derives from a reduction in the overall length of the dyeing process. The normal exhaust dyeing process for cotton is in three stages; preparation of the fibre (including removal of knitting oils i.e. scouring); dyeing; and finally wash-off plus any after-treatment.The higher dyeing temperature allows a shorter and simpler application profile. Of particular note is the ability to combine the scouring and dyeing processes in a single stage. The net effect of this is a load-to-unload time of as little as 3 hours less than half that of a conventional exhaust reactive dyeing process. This can double the productivity of a dyer i.e. one dyeing machine does the work of two. The second productivity benefit originates from the reliability of the dyes. Reproducibility levels approaching 100% (i.e. a Right-First-Time level of 100%) may be achieved both in G12 perfect compatibility—such that any combination of the dyes will behave as if it were a single component. The new • 6 3 105 te p.a.of cotton requiring redyeing • 6 3 107 te p.a. more fresh water • 4.2 3 105 te p.a. more salt utilised Benefits The beauty of the Procion XL+ system is that it provides productivity benefits from two distinct sources. Reactive dyeing of cotton uses a large amount of water typically 100 litres per kg of cotton. As a result of the telescoped dyeing process which removes the This journal is © The Royal Society of Chemistry 2001 laboratory-to-bulk and batch-to-batch due to the near perfect compatibility and robustness to process variables of the dyes. Customers are achieving many months of fault free dyeing. This eliminates the environmental drawbacks of reworking unacceptably dyed goods such as more chemicals (including hydrosulfite for dye stripping) more energy and more water.A reasonable estimate of the average proportion of exhaust dyed product which falls outside the desired specification with conventional reactive dyes is 15%. Thus figures which follow from this include Use of Procion XL+ dyes negates the necessity to use these resources as well as the extra dye and associated chemical auxiliaries. In addition the time manpower and financial resources of the dyehouse not being used in reworking can also be directed more profitably. The combined effect of these two features is a step change in dyehouse productivity with enormous seen and unseen environmental benefits particularly around maximising the use of resources. Thus fewer dyeing machines are needed and used in fewer dye works requiring less manpower.The resultant increase in dyeing efficiency should mean that the most antiquated and environmentally unfriendly “low tech” dyehouses suffer disproportionately and disappear thus having large environmental benefits although not necessarily where the technology is employed. This new faster technology leads to up to 50% reduction in energy usage for the dyeing of cotton (independently audited) despite the use of a higher dyeing temperature. separate pre-treatment stage coupled with efficient wash-off of unfixed dye (after-treatment step) the new dyes require up to 40% less water. Water usage and effluent discharge are a very high environmental priority particularly in dry countries as fresh water is an increasingly scarce and valuable resource.Thus this property is a major benefit to the dyer and surrounding community. A typical value for salt usage is 700 g per kg of cotton. Procion XL+ dyes have been designed to have higher affinity for the cotton in concert with superior migration properties and therefore the total salt use is reduced by up to 33%. This impacts very favourably on aqueous effluent being discarded into local fresh watercourses. Higher dye fixation has been designed successfully into Procion XL+ dyes. This obviously results in a reduction in colour in effluent leading to less ‘coloured rivers’ or less need for treatment to remove the colour from the effluent.A related benefit is the reduced COD BOD and TDS of the aqueous effluent because of less dye and also less chemical auxiliaries used to remove colour from the effluent. Keith Smith’s initial involvement with clean technology arose almost accidentally nearly 20 years ago. At that stage Smith’s main interest lay in organoboron chemistry and it was during the study of the synthesis of chloroalkanes from reaction of alkylboranes with dichloramine-T that one of his observant students noticed a strange reaction occurring during column chromatography of the reaction products. The Procion XL+ range also meets all of the product safety standards required of new dyestuffs. Outlook An unexpected benefit of the Procion XL+ dyes was discovered through an Focus On… Professor Keith Smith University of Wales Swansea The University of Wales Swansea will be the venue for the first major conference on Green Chemistry to be held in the UK (3–6 April 2001).Mike Lancaster continues the Focus On … series of articles by highlighting some of the work being carried out there by Professor Keith Smith Isomerically pure chloroaromatics are valuable intermediates for fine and This journal is © The Royal Society of Chemistry 2001 NEWS & V I E W S examination of the bioadsorption of reactive dyes onto activated sewage sludge. The most important colour when considering pollution is red as the eye is very sensitive at this wavelength. It was discovered that the red Procion XL+ dye which exhibits some novel chemical functionality is very highly bioadsorbed up to 20 times more than other commercial red reactive dyes.This means that any Procion Rubine XL+ dye in dyehouse effluent is efficiently removed at sewage works virtually eliminating the possibility of colour pollution of rivers by this most visible dye. Traditionally very deep bright red and wine shades on cotton are dyed using azoic dyes. This very old procedure involves the synthesis of the azo dye chromophore within the cotton fibre. It is an extremely inefficient process and environmentally very undesirable. It is also notoriously difficult to control the resulting shade which exacerbates the environmental impact of this process.The exceptional build up characteristics of the Procion XL+ dyes now enable a number of deep red shades to be dyed without the use of azoic dyes. The reliability and efficiency of the Procion XL+ process has already led to a number of reactive dyers gaining business in traditional azoic Some new products that were not present in the crude reaction mix were formed during column chromatography on silica. After careful examination it became evident that the silica was acting as a catalyst for chlorination. This was proven by chlorination of toluene with reagents such as tert-butyl hypochlorite as well as dichloramine-T in the presence of silica. These findings aroused Smith’s interest in the whole area of heterogeneous catalysis shade areas and it is reasonable to assume that this trend will continue thus contributing to the positive environmental impact.Additionally Procion XL+ dyes exhibit very high tolerance to the levels of calcium and magnesium ions in the water used for dyeing. This removes the need for sequestrants which would ultimately be discharged to effluent and also improves the robustness of the process to variations in source water quality. Within 5 years of the start of the research phase of the project Procion XL+ dyes are already making major inroads into the cotton dyeing market and have enormous potential to reduce the visible and invisible environmental impact of one of the most basic and fundamental industrial processes used world-wide.Nevertheless there remain environmental hurdles to overcome in the colouration of cotton and investigations at the DyStar research facility in Cheadle continue to address these issues and further improve the environmental profile of this important industry. and supported reagents. In particular his initial thoughts turned to improving selectivity (and hence reducing waste) of the chlorination process by using zeolites in place of silica. This in turn generated significant industrial interest and sponsorship from companies such as BP. Selective halogenation Green Chemistry February 2001 G13 NEWS & V I E W S pharmaceutical chemicals. However traditional synthetic methods usually suffer from lack of selectivity resulting in the production of significant amounts of unwanted products and waste etc.Zeolites with their active sites embedded in well-defined pores of molecular size should be capable of selectively delivering mono-chlorinated positional isomers from simple aromatic substrates such as toluene. Smith’s group has extensively explored such reactions looking at parameters such as zeolite type solvent and chlorinating agent. Using toluene as substrate and tert-butyl hypochlorite as chlorinating agent studies showed that zeolites need to contain acidic sites in order to catalyse the ring chlorination reaction. However the A-type zeolites which have small pore sizes were ineffective. The best results were obtained with the largest pore sized zeolite tested - partially proton exchanged faujasite X (HNaX) in acetonitrile solvent.In this case the p/o ratio was over 4.5:1. In addition the reaction occurred rapidly at 25 °C in quantitative conversion. This reaction proved quite general with even better selectivities being obtained with other monosubstituted benzenes. The methodology has also been adapted to the selective para-bromination Green Chemistry February 2001 of phenyl acetate using bromine. In this case it was observed that HBr evolved during the reaction was catalysing both para and ortho bromination leading to low selectivities. By using zeolites with low acidity such as NaY very high selectivities could be obtained. In addition to providing an appropriate catalyst size within the pore these zeolites also mop up HBr formed during the reaction thus preventing the more general acid catalysed process from taking place.Aromatic nitro compounds are of significant commercial interest being useful intermediates for the pharmaceutical agrochemical dye and explosives industries. The technology normally employed involves use of nitric acid and stoichiometric amounts of sulfuric acid which is required to generate the active nitronium ion. Whilst this process is economical it suffers from two major problems; the first is the generation of large amounts of spent acid for disposal and the second is poor selectivity especially to the para isomer which is often required. Smith’s initial involvement with nitration chemistry was aimed at solving the second problem using his zeolite expertise.An extensive study of the catalytic effect of zeolites of varying pore size and acidity on the nitration of toluene using acetyl nitrate (generated in situ from nitric acid and acetic anhydride) was undertaken. As expected zeolite activity varied enormously the best overall results being obtained using zeolite Hb which has a relatively large pore size to aid diffusion but small enough to give high para selectivity as well as high acidity. By optimising catalyst loading temperature and acetic anhydride quantities (stoichiometric amounts are needed) p/o selectivities of 4:1 could be obtained—a considerable improvement over previous methods.Smith readily admits however that this process is still not ideal for example stoichiometric amounts of acetic acid are produced which although easily removed by distillation and potentially reused in another process adds to the cost and detracts somewhat from the eco-efficiency of the process. G14 ArH + 2N O + æ O catalyst ææÆ 2 4 2 4ArNO + 2H O 2 2 Aromatic nitrations Keith Smith Professor of Organic Chemistry at the University of Wales Swansea. Aromatic alkylation This journal is © The Royal Society of Chemistry 2001 More recently Smith has started to work on a nitration process which would largely overcome the issue of waste production. In terms of atom efficiency a process based on dinitrogen tetroxide would have many advantages as shown by the equation below.In preliminary work zeolite Hb has again proved an effective catalyst. For example in the nitration of chlorobenzene p/o selectivities of over 6.5 have been achieved. This novel technology will undoubtedly be further explored and offers good potential for a highly selective waste-free cost-effective process that many sectors of the chemical industry would be interested in. This is one area in which Smith would like to make a commercially valuable breakthrough. Smith’s ability to spot commercially relevant problems is amply demonstrated by his work on the clean synthesis of 2,6-dialkylnaphthalene. Naphthalene- 2,6-dicarboxylic acid is used to prepare poly(ethylene naphthalenedicarboxylate) (PEN) which is increasingly finding use in films liquid crystal polymers packaging and coatings for example.Although market growth is increasing the high cost of the dicarboxylic acid is preventing more rapid growth. This high cost is due to unselective and sometimes complex synthetic procedures. An ideal synthesis would involve selective dimethylation of naphthalene followed by oxidation; although this method is used the methylation procedure results in a complex mix of dimethylnaphthalenes (10 isomers are possible!) which need separating. Zeolites were again looked at to provide the answer. Although some improvements can be made there is difficulty in obtaining the 2,6-isomer in preference to the 2,7-isomer.The simplistic diagram below illustrates the problem; in a typical zeolite both isomers require roughly the same diameter of channel. Smith is happy to point out that solving the methylation problem with current commercially available zeolites is unlikely. Instead he has concentrated his efforts on higher alkyl derivatives. Using the synthesis of di-tert-butylnaphthalene as a model system yields of the 2,6-isomer of over 60% with a 2,6 2,7 ratio of over 50 have been obtained with dealuminated HM zeolite as catalyst and tert-butanol as the alkylating agent. The ultimate aim of this approach would be to produce selectively a 2,6-dialkyl product which when oxidised would either produce another valuable co-product (cf.phenol production from cumene) or would produce the minimum amount of waste. In September 2000 the UK Department of the Environment Transport and the Regions (DETR) launched its second environmental expenditure survey. The survey—conducted by environmental consultants URS Dames & Moore—involves over 7000 UK firms and the results are due to be published in May 2001. The survey will not only provide information that the European Union requires under its Regulation on structural business statistics. By providing an estimate of how much UK firms spend on environmental protection the survey will also help assess the impact of this spending on the UK’s competitiveness and the effect of environmental policy and regulation.According to the DETR “We need this information . . . to see if there is a shift to using within process or K. Smith et al. A novel method for nitration of simple aromatic compounds J. Org. Chem. 1998 63 8448–8454. K. Smith and S. D. Roberts Regioselective dialkylation of naphthalene Catal. Today 2000 60 227–233. K. Smith Highly regioselective Lewis Education Like at most universities there are a variety of chemistry courses on Acid-free electrophilic aromatic substitution J. Chem. Tech. Biotechnol. 1997 68 432–436. Pipe dreams? Shifting the balance towards clean technology September 2000 saw the launch of the UK Government’s second environmental expenditure survey. Becky Allen looks at the results being generated by similar surveys elsewhere in the world and asks how industry can persuaded to spend on more on cleaner technology.Environmental expenditure surveys One of the major problems associated with the survey was the ability of UK This journal is © The Royal Society of Chemistry 2001 NEWS & V I E W S offer at Swansea. Of particular relevance is the Chemistry with Environmental Chemistry degree which includes a module on the Chemistry of Waste. Typical subjects covered in this module include sources of waste waste minimisation waste treatment and recycling potential. Several other modules within this course have discussion of topics relevant to green chemistry including Consumer Chemistry and Chemistry & Man.Professor Smith will be presenting a keynote lecture on aspects of his work at Green Chemistry— Sustainable Products and Processes (Swansea 3–6 April 2001) (for further information contact www.rsc. org/conferences). ‘clean’ technologies to protect the environment during the production process rather than end-of-process spending (‘end-of-pipe’).” The first such survey was conducted by ECOTEC and published in 1999. Kate Martin of URS Dames & Moore told Green Chemistry “We are building on the ECOTEC report and hope to improve and extend it.” Despite being a rough and ready estimate of environmental expenditure by UK industries ECOTEC’s survey did reveal some interesting patterns of expenditure particularly in the chemical sector.The ECOTEC survey estimated total gross environmental expenditure at between £3,540 million and £5,010 million in 1997. Of this 73% represented operating expenditure and 27% was capital expenditure including both end-of-pipe and integrated capital expenditure. When the latter is in turn Further reading K. Smith et al. Selective mono-chlorination of aromatic compounds under mild conditions by tert-butyl hypochlorite in the presence of zeolites Green Chem. 1999 1 83–90. broken down ECOTEC estimates that almost three quarters (71%) of capital spending is on end-of pipe and that only 8% of total gross environmental expenditure is on integrated processes. By far the largest spending sector was the chemical industry accounting for 24% of the UK total and the chemical sector spent a larger proportion (35%) of its total expenditure on capital spending.The ECOTEC survey put environmental spending by UK industry at 0.5% of gross domestic product (GDP) which would if accurate be far below other European member states. However figures from the Organisation for Economic Cooperation and Development (OECD) put the figure at 1.5% of GDP in 1996 compared with 1.4% in the USA 1.5% in the Netherlands and 1.7% in Switzerland. Green Chemistry February 2001 G15 NEWS & V I E W S End-of-pipe equipment UK top ten • Effluent treatment plant equipment • Air filters • Extraction systems • Solid waste compactors • Air scrubbers • Noise reduction • Waste management and recycling facilities • Bunding • Thermal oxidation plant or firms to supply environmental information.ECOTEC admit that “[Our] expenditure estimates can only be indicative of broad orders of magnitude because many firms are still unfamiliar or have difficulties with the definitions of environmental expenditure and few firms have the information on environmental expenditure readily available.” Securing improvements in this area will be an important test of the second survey which has provided firms taking part with extensive background information. The DETR told Green Chemistry “Companies are starting to be aware that environmental information in company reporting is important. In future we will be able to link into initiatives on company accounting.There are moves to identify environmental expenditure separately in company accounts so tying the two together is the way forward.” Data aside the question remains how best to promote spending on clean technology instead of end-of-pipe measures? The ECOTEC survey found that regulatory compliance was by far the most influential factor driving environmental expenditure being cited by 79% of UK companies followed by securing health and safety improvements (35%) and saving money (21%). Most experts however believe that a complex mixture of policy instruments set in a stable long-term framework are required to stimulate clean technology. According to Reinhard Coenen and Sigrid Klein-Vielhauer of the Karlsruhe Research Centre “End-of-pipe technologies are rapidly coming to their limits.Moreover end-of-pipe technologies are often connected with the shifting of environmental medium to another for example the application of Green Chemistry February 2001 G16 control technologies for sulfur dioxide or waste water purification technologies leads to creation of solid waste and thus to waste management problems. A more ecological sustainable development requires a change of a paradigm in the engineering approach from an emission-orientated or end-of-pipe approach to a source-orientated approach.” Coenen and Klein-Vielhauer argue that although integrated environmental technology has both economic and ecological advantages over end-of-pipe technology in theory in practice end-of-pipe technology still dominates.“Against this background one has to raise the question of why the use of end-of-pipe technologies still dominates environmental protection,” they say. Coenen and Klein-Vielhauer believe that one of most important barriers to clean technology is the dominance of inflexible command and control regulation as instruments of environmental policy in most industrialised nations whose standards are orientated towards performance of end-of-pipe technologies. They also point to the higher investment and transaction costs of integrated environmental technologies. To overcome these barriers they argue that environmental policies must be made more flexible that economic incentives —such as eco taxes input or emission charges or emission trading—should be used to encourage a move away from end-of-pipe technologies and that industry will need guidance for entrepreneurial planning through long-term environmental goals and norms.The UK government appears to agree. In a report on clean technology issued in April 2000 the Parliamentary Office of Science and Technology said “Innovation flourishes where regulation is flexible and policies stable. No one instrument on its own can stimulate companies to innovate successfully. Rather a mixture of instruments (and flexibility in the style in which they are implemented) is needed depending on the specific factors and circumstances of the firms and sectors involved.Also the policy climate needs to be stable and credible over a protracted period to minimise risks faced by industry.” incineration • Water metering Source ECOTEC 1999. References UK Environmental Expenditure Survey DETR 2000 www.environment. detr.gov.uk/envsurvey/ Environmental protection expenditure by UK industry a survey of 1997 expenditure ECOTEC 1999 www. environment.detr.gov.uk/ expenditure97/index.htm R. Coenen and S. Klein-Vielhauer The significance of environmental technology for economically and ecologically sustainable development www.jrc.es/iptsreport/vol14/english/ ENV1E146.htm Cleaning up? Stimulating innovation in environmental technology Parliamentary Office of Science and Technology 2000 www.parliament.uk/post/report.htm The end of the road for end-of-pipe? Environmental protection by Finnish industry in 1997 Statistics Finland www.stat.fi/ Environmental expenditure Swiss Some countries seem to be moving in the right direction. In a similar pattern to Federal Statistical Office 1997 www.statistick.admin.ch/ Statistics Canada www.statcan.ca/ Eurostat europa.eu.int/comm/eurostat/ This journal is © The Royal Society of Chemistry 2001 the UK 80% of German environmental spending goes on end-of-pipe technology. In Finland however an increasing amount is being spent on clean technology. In 1997 Finnish industries spent a total of FIM 3.3 billion on environmental protection approximately 42% of which was capital expenditure as opposed to operating expenditure. Unlike both the UK and Germany process-integrated environmental investment accounts for over half (52%) of capital expenditure a proportion that has been rising steadily compared to end-of-pipe spending in Finland since 1992. Part of this may be due to structural differences in Finnish industry says Katja Hietikko a senior statistician at Statistics Finland “We have a lot of forestry and basic metal industries. Their processes are quite modern and thus investments are typically process-integrated.” But Hietikko suggests that the differences may also reflect attitudinal differences “Finnish industry has a long history of done end-of-pipe investments and if they want to minimize the environmental impacts they have to do something to the processes because the end-of-pipe investments are not good enough anymore.”

ISSN:1463-9262    

DOI:10.1039/b100267h

出版商:RSC    

年代:2001

数据来源: RSC