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.”