摘要:

International Symposium on Green Chemistry The first International Symposium on Green Chemistry organised by the Royal Society of Chemistry and the Green Chemistry Network was held in Swansea, Wales in April 2001. The ‘international’ in the title was nicely reflected by the representation which included many delegates from the USA, Africa, Japan, Russia, India, Australia, Israel and Iran, as well as from Europe.The programme was put together with the intention of broadening the scope of the coverage from green chemistry to include green chemical engineering and technology, and educational issues—this worked very well. Thus while we were able to enjoy cutting edge research lectures from a number of distinguished chemists including Professor B. Trost (USA), Professor M. Poliakoff (UK), and Professor H.van Bekkum (The Netherlands), we also had presentations on energy analysis (J. Dewulf, Belgium), microreactors (K. F. Jenson, USA) and life cycle assessment (A. Azapagic, UK), as well as ones covering green chemistry education in Italy (A. Perosa, Italy) and teaching environmental chemistry in a sociotechnological context (V. Zoller, Israel).The applied nature of green chemistry was illustrated by a number of very interesting presentations from industry. These included ‘Biocatalysis from an Environmental Perspective’ (A. Zaks, USA), ‘Decolorable Printing Inks Suitable for Effective Paper Recycling’ (S. Nachida, Japan) and ‘Improving Routes to Improving Polymers’ (P. Williams, UK). The breadth of the conference and its participants was further illustrated by a presentation from Dr Warhurst of Friends of the Earth and Dr Anastas of the White House Office of Science and Technology Policy.The final session in the symposium was dedicated to award-winning academics and industrialists. This started with a remarkable lecture from the 2001 Academic US Green Chemistry Presidential Challenge award winner Professor C.-H.Wong on ‘Chemo-enzymate Approach to Carbohydrate-based Drug Discovery’. Three presentations by the first UK Green Chemistry Awards winner followed this: ‘Novel Recyclable Catalyst for Atom Economic Aromatic Nitration’ (C. Braddock) (Green Chem., 2001, 3, G26), ‘Super-efficient Dyes for the Coloration of Cotton, the Procion XL+ Range’ (W. J. Ebenezer) and ‘Oxazolidine Diluents: Reacting for the Environment’ (J.Peel) (Green Chem., 2001, 3, G40). Where next? Green chemistry has come a long way since the first Gordon Conference 5 years ago and it is now prominent in many national and international conferences. However, we believe that there is a need for a major international conference series. I am delighted that preliminary discussions on this are now underway involving some of the major green chemistry organisations in the world and we can look forward to hearing their decision later this year.James Clark York, March 2001 This journal is © The Royal Society of Chemistry 2001 E D I T O R I A L G34 Green Chemistry June 2001 DOI: 10.1039/b103990nInternational Symposium on Green Chemistry The first International Symposium on Green Chemistry organised by the Royal Society of Chemistry and the Green Chemistry Network was held in Swansea, Wales in April 2001.The ‘international’ in the title was nicely reflected by the representation which included many delegates from the USA, Africa, Japan, Russia, India, Australia, Israel and Iran, as well as from Europe. The programme was put together with the intention of broadening the scope of the coverage from green chemistry to include green chemical engineering and technology, and educational issues—this worked very well.Thus while we were able to enjoy cutting edge research lectures from a number of distinguished chemists including Professor B. Trost (USA), Professor M. Poliakoff (UK), and Professor H. van Bekkum (The Netherlands), we also had presentations on energy analysis (J. Dewulf, Belgium), microreactors (K.F. Jenson, USA) and life cycle assessment (A. Azapagic, UK), as well as ones covering green chemistry education in Italy (A. Perosa, Italy) and teaching environmental chemistry in a sociotechnological context (V. Zoller, Israel). The applied nature of green chemistry was illustrated by a number of very interesting presentations from industry.These included ‘Biocatalysis from an Environmental Perspective’ (A. Zaks, USA), ‘Decolorable Printing Inks Suitable for Effective Paper Recycling’ (S. Nachida, Japan) and ‘Improving Routes to Improving Polymers’ (P. Williams, UK). The breadth of the conference and its participants was further illustrated by a presentation from Dr Warhurst of Friends of the Earth and Dr Anastas of the White House Office of Science and Technology Policy.The final session in the symposium was dedicated to award-winning academics and industrialists. This started with a remarkable lecture from the 2001 Academic US Green Chemistry Presidential Challenge award winner Professor C.-H. Wong on ‘Chemo-enzymate Approach to Carbohydrate-based Drug Discovery’.Three presentations by the first UK Green Chemistry Awards winner followed this: ‘Novel Recyclable Catalyst for Atom Economic Aromatic Nitration’ (C. Braddock) (Green Chem., 2001, 3, G26), ‘Super-efficient Dyes for the Coloration of Cotton, the Procion XL+ Range’ (W. J. Ebenezer) and ‘Oxazolidine Diluents: Reacting for the Environment’ (J. Peel) (Green Chem., 2001, 3, G40). Where next? Green chemistry has come a long way since the first Gordon Conference 5 years ago and it is now prominent in many national and international conferences. However, we believe that there is a need for a major international conference series. I am delighted that preliminary discussions on this are now underway involving some of the major green chemistry organisations in the world and we can look forward to hearing their decision later this year. James Clark York, March 2001 This journal is © The Royal Society of Chemistry 2001 E D I T O R I A L G34 Green Chemistry June 2001 DOI: 10.1039/b103990n

ISSN:1463-9262    

DOI:10.1039/b103990n

出版商:RSC    

年代:2001

数据来源: RSC

摘要:

Highlights Duncan Macquarrie reviews the latest research in green chemistry Selective nucleophilic substitution The nucleophilic aromatic substitution of hydrogen (NASH) is a very important option in the synthesis of aromatic compounds. Nucleophilic aromatic substitution requires the formal elimination of X�C from the intermediate complex and, not surprisingly, halide and nitrite are favoured. This requires chlorination and nitration, to give the leaving group, processes which are rarely selective.The elimination of hydride, while attractive from an environmental point of view, is not a realistic option. NASH allows the elimination of hydride, by oxidatively removing the hydrogen, avoiding the halogenation and nitration steps. The group led by Illuminada Gallardo from the Universitat Autonoma de Barcelona have studied a particularly interesting electrochemical oxidation system (Chem., Eur.J., 2001, 7, 1759). They have carried out some mechanistic work, which has helped to unravel the mechanism of these reactions, and which they have then applied to the cyanation of aromatics. Yields were good with a wide range of substrates, and selectivity excellent, with no other products being detected.Oxidations The clean oxidation of secondary alcohols continues to be a challenge. Bimal Banik and colleagues from the Anderson Cancer Center at the University of Texas have provided a novel method for this transformation, which uses oxygen as the stoichiometric oxidant (J. Chem. Res (S), 2001, 28). In their system, they employ iodine as catalyst, under microwave conditions. 20mol% iodine was enough to obtain yields, typically > 75% in 6�C8 minutes in air. The authors speculate on the mechanism, which is not entirely clear, but conclude that the iodine oxidised the alcohol, followed by oxidation of the HI formed to iodine and water by oxygen. Sir John Meurig Thomas and Robert Raja of the Royal Institution and Cambridge University have published a Feature Article covering some of their work on the selective oxidation of a range of substrates using heterogeneous catalysts (Chem.Commun., 2001, 675). They describe the design of porous oxide-based catalytic systems for the oxidation of hydrocarbons such as cyclohexane, hexane and alkylaromatics, as well as other work including supported ferrocene-based enantioselective catalysts.Transesterification In the last Highlights, a paper on the use of metal alkoxides as transesterification catalysts was reported. Now the group led by B. P. Bandgar has reported the use of zinc dust as an efficient and general catalyst for the transesterification of b-ketoesters (J. Chem. Res (S), 2001, 16). t-Butyl esters can be prepared in reasonable yields, something which is generally difficult to achieve, primary and secondary alcohols give yields of ¡Ý 88%, and allylic alcohols can also be used with reasonable efficiency. The zinc dust can be recovered by filtration, but no data relating to reuse was presented.Selective electrophilic substitution The functionalisation of aromatics by electrophilic substitution is one of the most studied reaction systems, with significant challenges remaining in the replacement of homogeneous acids such as aluminium chloride and HF with more benign catalysts, and attempts to control selectivity.One of the more fruitful areas has been the use of zeolites to promote para-selectivity in a range of articles (see for example Green Chem., 1999, 1, 35, 75, 83).However, the Friedel�CCrafts reaction is generally considered to be worthless for the formation of meta isomers of aromatics, unless they are particularly electron-deficient. In a remarkable paper by Hendrikus van Herwijnen and Udo Brinker of the University of Vienna, just this sort of selectivity is found (J. Org. Chem., 2001, 66, 2874). They used a faujasite zeolite to dimerise benzyl chloride, with the logic being that the confinement in the pore structure of the zeolite would suppress the extensive polymerisation found in homogeneous systems.This was indeed the case, but the authors found that the isomer mixture obtained was surprisingly rich in meta isomer, with up to 65% of the product being meta. The authors ascribe this reversal of selectivity to the This journal is The Royal Society of Chemistry 2001 NEWS & V I E W S DOI: 10.1039/b103992j Green Chemistry June 2001 G35unusual “banana-shaped” cavities of this particular zeolite.How general this phenomenon is remains to be seen, but the changes from homogeneous phase are substantial. Aryl amine synthesis Clean methods for the preparation of aryl amines are being sought to replace the old tin-based methods, and improve on the more recent palladium-catalysed routes.Mayssam Ali and Stephen Buchwald of MIT have published their results concerning the Pd catalysed amination of aryl iodides (J. Org. Chem., 2001, 66, 2560). They found that the use of the biaryl ligand shown and NaOt-Bu as base is an excellent combination for many functional aryl iodides and aryl amines.Yields approach quantitative in most cases. In order to extend the reaction to include a wider range of functional groups, they also found that replacing the alkoxide base with cesium carbonate allowed a wider range of functionality to be incorporated, including esters, ketones and nitriles, with yields ranging from 62–91%. Solvents The search for alternative solvents encompasses ionic liquids and supercritical fluids, but it is important not to lose sight of new “conventional” solvents.Diethoxymethane (DEM) is one such solvent, which has now been commercially available for a short period. It has a good liquid range (–66 °C to 88 °C) relatively low toxicity, and is immiscible with water. Some of its benefits have been reported in a paper by Neil Boaz and Bhaskar Venepalli of Eastman Chemical Company in Tennessee (Org.Proc. R and D, 2001, 5, 127). They describe the solvent as being superior to THF and dichloromethane in organometallic reactions and phase transfer applications. The solvent is hydrophobic; it thus does not need to be dried, and can be very easily separated from water and recycled. It is stable to bases, does not form peroxides as easily as some other ethers, and even has some stability towards mild aqueous acids.The addition of CO2 to propylene glycol has been studied using ionic liquids as catalyst and solvent. Jiajian Peng and Youquan Deng of the Chinese Academy of Sciences in Langzhou have shown that the reaction is highly efficient and the solvent recyclable in a straightforward process (New.J. Chem., 2001, 25, 639). They showed that, using BMIM BF4 – (BMIM = 1-n-butyl-3-methyl imidazolinium) as solvent and catalyst, CO2 would add very efficiently to propylene oxide, giving the carbonate in high yield in an autoclave under modest CO2 pressure. Release of the CO2 followed by distillation gave the product and the solvent, which could be used directly for a further batch.Asymmetric synthesis The use of simple chiral ligands and auxiliaries was mentioned in the last Highlights, and the use of phase transitions to drive equilibria has also been described recently in Green Chem., 2000, 2, 49. Now a group of workers from DSM Research Life Sciences in Groningen, led by Quirinus Broxterman has published details of the asymmetric Strecker synthesis of amino acids using a combination of a simple chiral auxiliary and selective crystallisation to drive equilibria selectively to the desired product (Org.Lett., 2001, 3, 1121). They use (R)-phenylglycine amide, along with a ketone and HCN to produce the Strecker intermediate as a pair of diastereoisomers. Only one of these is soluble in the reaction solvent (aqueous methanol or even water) and the other precipitates selectively.The soluble diastereomer re-equilibrates and the precipitation of one of the two drives the reaction to completion, and the formation of one diastereoisomer in > 99% selectivity. This is then converted to novel amino acids using known methods. Hydroformylation Hydroformylation is a relatively clean method for the production of aldehydes, and has been the subject of intense effortstly.One of the latest describes research aimed at the functionalisation of acrylates, rather then the usual simple alkenes. Jianliang Xiao and co-workers at the Leverhulme Centre for Innovative Catalysis in Liverpool and at the University of Leicester have published details of the use of supercritical CO2 in the hydroformylation of alkyl acrylates, highly functional compounds, useful as intermediates in organic chemistry (Chem.Commun., 2001, 725). They show that, using rhodium catalysts coupled This journal is © The Royal Society of Chemistry 2001 NEWS & V I E W S G36 Green Chemistry June 2001with fluorinated phosphine ligands, the hydroformylation proceeds in excellent selectivity, with turnovers an order of magnitude higher than in conventional solvent systems.Materials chemistry While the majority of chemistry reported as green relates to organic synthesis, materials chemistry is also an area where the same principles apply, and which is experiencing a time of remarkable and exciting growth (see, for example, Green Chem., 1999, 1, 169; 2000, 2, 79; 2000, 2, 93).Guanghou Wang and co-workers at Nanjing University have developed a remarkably simple and clean route to copper oxide nanorods, useful as sensors and in semiconductor applications (Chem. Commun., 2001, 727). They found that copper chloride and sodium hydroxide could be simply ground together in the presence of PEG 400, following by washing and recovery of the PEG, resulting in copper oxide nanorods, without high temperatures or prolonged reaction periods.Typical dimensions of the wires were 8 nm across and up to 400 nm long. NEWS Green Chemistry Network Symposium The next Green Chemistry Network symposium will be held on 26 September 2001 at the University of Strathclyde in Glasgow, UK. The Keynote speaker will be Professor Stan Roberts from the Department of Chemistry, University of Liverpool whose presentation will be entitled ‘Biotransformations using Natural and Non-natural Catalysts’.If you would like to attend the symposium, please contact Dr Helen Coombs, Green Chemistry Network, University of York, Heslington, York YO10 5DD, UK. Tel/Fax: + 44 (0)1904 434550. Email: greennet@york.ac.uk Emerging technologies—sustainable development The 1st Binational RSC/SACI International Conference on Organic Chemistry was held at the University of Cape Town, South Africa (http://www.uct.ac.za) in January 2001.This outstanding meeting, chaired by Professor J. R. Bull, included a post-conference workshop on emerging technologies at which one presentation was by Professor Keith Smith, University of Wales Swansea, UK, on ‘Sustainable Development.’ In particular, Professor Smith described work taking place in his laboratories on electrophilic aromatic substitution with zeolites: This journal is © The Royal Society of Chemistry 2001 NEWS & V I E W S Green Chemistry June 2001 G37A Powerpoint file of Professor Smith’s slide presentation is available as Electronic Supplementary Information (ESI) at http://www.rsc.org/suppdata/ gc/b1/b103992j/ Further details on Professor Smith’s work can be found in Green Chem., 2001, 3, G13.Green Chemistry Stall The Green Chemistry Stall at the Royal Society’s summer exhibition 2001 will be a multifaceted view of the progress of Green Chemistry. The growing interest in Green Chemistry will be illustrated through the work of the Green Chemistry Network, both in the UK and abroad.A video will be screened throughout the day highlighting the chemical industry as it is now, current research and the future ‘greener’ chemical industry. The heterogeneous catalysis work carried out here at York in the Clean Technology Centre will be represented by video, posters and interactive models to demonstrate the nature of catalyst surfaces.The value of collaboration between chemistry and chemical engineering will be demonstrated through a working model of a novel catalytic reactor. We hope that the stall will have something to offer for visitors of all ages and of all backgrounds. Reducing the use of organic solvents US Department of Agriculture (USDA) Agricultural Research Service (ARS) scientists in Peoria, Illinois, USA, are coupling two environmentally friendly techniques to reduce or eliminate the use of toxic organic solvents in the processing of agricultural commodities.The U.S. Environmental Protection Agency has called for a reduction in the amount of toxic solvents released into the environment, which has impacted industrial manufacturers.Solutions called ionic liquids, salt-like fluids at room temperature, are safer to use than organic solvents like hexane in research laboratories, according to ARS biochemist Joseph A. Laszlo at the National Center for Agricultural Utilization Research in Peoria. In the past, researchers had to use solvents to get enzymes to act as a catalyst for chemical reactions.Now, ionic liquids can be used in place of solvents. Laszlo and ARS chemist David L. Compton made ionic liquids in their laboratory. They are the first researchers to perform enzymatic reactions in ionic liquids in combination with supercritical CO2. They tested the liquids as a solvent for the enzyme chymotrypsin with a commonly used laboratory substrate. This enzyme may catalyze reactions needed to manufacture important chemical ingredients in drugs and skin care products.Laszlo says that combining ionic liquids and supercritical CO2 results in a superior processing method, which is better than either one alone. In the technique, CO2 is heated and compressed to the point that it becomes both liquid and gas, which is the supercritical state. Laszlo reported these findings at the 221st annual meeting of the American Chemical Society meeting in San Diego, April 1–5, 2001, where he participated in a 5-day symposium on the development of ionic liquids.New Faraday for a greener chemical industry A Government funded multi-partner initiative for a ‘Greener Chemical Industry’ has recently been established in the UK. The initiative is funded under the Faraday Partnership programme which provides funding for research, training, networking and technology translation.The partnership, called CRYSTAL will be administered by the Institution of Chemical Engineers with the Royal Society of Chemistry and the Chemical Industries Association being the other hub partners. Other CRYSTAL partners include 18 academic institutions, 8 companies and 12 other networks and similar organisations representing most of the UK chemical industry.CRYSTAL’s mission is to become the lead UK body, for the research, development, implementation and promotion of green chemical technology and practices, by leveraging and synergising the resources of all the partners for the benefit of the UK chemical industry. CRYSTAL’s major objectives are: • Technology transfer: use CRYSTAL’s experienced Technology Translators, TCS, and partner organisations to promote the widest uptake of existing, emerging and future technologies.• Strategic research: develop step change green chemical technology and practices through industry identified core research programmes bringing together innovative chemistry and chemical engineering and other relevant disciplines (biotech, IT) in new collaborative partnerships. • Training: develop and run both inter and intra company courses (including MRes and PhD) for postgraduate chemists and chemical engineers, CRYSTAL structure This journal is © The Royal Society of Chemistry 2001 NEWS & V I E W S G38 Green Chemistry June 2001industry technologists and business managers. This will enable the culture change to allow future research and development work to be undertaken in a more eco-efficient and competitive way.• Awareness/Best Practice: increase the awareness in industry, government and academia of opportunities for developing sustainable products and processes. Initially the main focus of research will cover: • Metrics: given the complexity of the concept, there is a recognised need for a set of metrics to underpin the paradigm shift implied by sustainable development by providing operational guidelines. The overall objective is to develop and test a comprehensive set of sustainable development metrics, from which specific sectors and companies can identify and use the metrics with most significance for their particular businesses. • Catalysis: the prime route to chemical manufacturing processes with the required degree of selectivity, energy efficiency and atom economy is to develop new catalytic systems.This approach offers the best way to avoid stoichiometric reactions, use of protection for sensitive functionalities, and employing hazardous or toxic reagents.Significant emphasis will be placed on enhancing the ease of recovery and reuse of both homogeneous and heterogeneous catalytic systems of proven activity and selectivity • Eco-efficient solvents: VOC’s remain a key issue for most chemistry-based industries and eco-friendly solvent alternatives for many processes and product formulations are required. Many classical reactions still employ ‘unfriendly’ solvents such as dichloromethane, acetone or dimethylformamide and a ‘toolkit’ of alternatives is required which are cost effective, have ease of handling and are recyclable.This toolkit of solvents is likely to include supercritical fluids, biphasic systems, ionic liquids, bio-solvents as well as solvent free technologies. Each of these provides challenging scale-up, cost and supply issues which need to be overcome before they will be more widely adopted by industry.• Alternative feedstocks: the potential for using crops as a chemical feedstock is huge, but largely untouched due to barriers such as cost, quality and availability. For example a recent IENICA report suggests that at least 12.5% of the EU solvents market (currently 4 million tpa) could be supplied from bio-based sources; the current figure is less than 1.5%.Initial processing can account for much of the costs, hence by developing innovative, clean extraction and separation technologies the cost of the raw chemical feedstocks can be significantly improved, facilitating wider use. • Energetic chemistry: CRYSTAL will systematically explore alternative ways of introducing energy into catalytic chemical reactions in ways which use it most cleanly and effectively.In particular many of the problems associated with waste in chemicals manufacture could be avoided if electrons could be used to drive the processes. Small scale reactors, easily replicated for scale out of manufacturing, are available: the keys are (i) to find electrodes capable of enacting the desired chemistry and (ii) to expand the culture of synthetic and manufacturing chemists to include electrochemistry • Reaction engineering: All the above areas require underpinning by innovations in reaction engineering.In particular significant environmental and cost benefit are to be realised from the redesign of conventional reactors to accommodate new and existing technologies.Through obtaining a more thorough understanding of reaction kinetics reactors can be designed to take advantage of the underlying chemistry leading to more efficient processes. Much of the training will be provided by the Green Chemistry Network at York and the Centre for Environmental Studies at Surrey. Emphasis will be placed on meeting industry requirements and will include training on general aspects of Green Chemical Technology as well as specific technologies. A particular important aspect of CRYSTAL is technology translation. Initially process types and industry sectors will be road-mapped to identify best practice and identify gaps. Technology translation will also be required to convert the outcomes of the research process into useful technology and to transfer this technology to a cross-section of industry. This journal is © The Royal Society of Chemistry 2001 NEWS & V I E W S Apology We wish to offer our apologies to Dennis Curran and Zhiyong Luo for allowing the Feature article on ‘Fluorous techniques for the synthesis and separation of organic molecules’ (Green. Chem., 2001, 3, G3–G7) to be published without being being checked by the authors. We very much regret the embarrassment and inconvenience that this has caused the authors. Revised procedures should prevent any similar occurrence in the future. Green Chemistry June 2001 G39

ISSN:1463-9262    

DOI:10.1039/b103992j

出版商:RSC    

年代:2001

数据来源: RSC

摘要:

Oxazolidine diluents: reacting for the environment Neil G. Carter, Research & Development Manager, describes the work at Industrial Copolymers Ltd† which won the industrial category of the UK Green Chemistry Awards, 2000 Introduction Over the last decade, there has been a considerable transformation in the solvent-borne industrial coatings market. Major developments have taken place in water-based coatings technology, which has now expanded from the consumer housepaint market into industrial sectors.Increasingly stringent volatile organic compounds (VOCs) regulations have led to the development of a more viable water-based alternative to solvent-borne technology. However, some limitations still exist, particularly with the key characteristics of chemical and abrasion resistance in coating performance.Alongside the advances in water-based technology, has been the development of high-solids coatings. These are usually formulated with lower-molecular-weight components to achieve the lowest possible viscosity with the minimum use of solvent. However, there is a limit to molecular weight reduction, as this can lead to problems associated with loss of coating performance.An example of a market that has seen the trends as described above is 2-pack polyurethane OEM coatings. Typically, these systems are comprised of an acrylic (or acrylic and polyester) polyol and an HDI-based polyisocyanate (usually biuret or trimer). These form polyurethanes possessing unique performance properties including excellent chemical resistance and weather exposure, as well as good abrasion resistance.One possible solution to maintaining the coating benefits of solvented systems, whilst reducing the VOC, is to incorporate a reactive diluent. Incozol LV1, a low viscosity bisoxazolidine reactive diluent, has been specifically designed to achieve high performance coatings compliant with even the strictest environmental legislation.Incozol LV: reactive diluent Incozol LV (I) is a low-viscosity bisoxazolidine designed as a co-reactant in polyurethane coatings to achieve low VOC levels. Incozol LV is comprised of two oxazolidine rings (five-membered heterocyclic rings containing nitrogen and oxygen) linked by a carbonato bridge, which affords low viscosity by restricting intermolecular hydrogen bonding.Incozol LV has the ability to reduce the viscosity of the polyol component of the 2-pack system in which it should be incorporated, in a similar way to solvent (Fig. 1). Incozol LV possesses key properties demanded of a good reactive diluent,2 namely: • Good polyol and solvent compatibility • Low intrinsic viscosity: 50 mPa at 20 °C • Reasonably high equivalent weight: 90 (functionality of 4) • Low colour (essential for clear lacquer finishing) • Workable pot life and cure response • No adverse effect on coating properties (including film hardness development and resistance, gloss and weathering properties) Chemistry of oxazolidine diluents Activation of oxazolidine reactivity with polyurethanes : ring opening hydrolysis reaction The ability of Incozol LV to co-react into the polyurethane backbone of the coating is activated by the ring opening hydrolysis of the two oxazolidine rings, resulting from the reaction of water present as moisture contamination in both the solvent and polyol components.Moisture in the atmosphere during spraying application also aids the activation of the oxazolidine rings. Consequently, the inclusion of Incozol LV has the dual benefit of scavenging moisture, as well as lowering the VOC.Polyurethane coatings can be adversely affected by moisture, through the reaction of water with the polyisocyanate component, forming carbon dioxide gassing. This can often result in pinholing defects in the coating or hazing problems with clear lacquer finishes. Hence, pre-mixing Incozol LV with the polyol and solvent component to scavenge the moisture prior to polyisocyanate mixing is clearly an advantage towards improving the coating.Indeed, repeated opening of containers will serve to further activate the oxazolidine prior to hardener (polyisocyanate) mixing. Activation of Incozol LV results from the hydrolytic ring opening of the oxazolidines yielding hydroxyl and amino † Industrial Copolymers Limited, PO Box 347, Primrose Hill, London Road, Preston, UK PR1 4LT.Fig. 1 Viscosity-reducing effect of Incozol LV. This journal is © The Royal Society of Chemistry 2001 AWARD G40 Green Chemistry June 2001 DOI: 10.1039/b103991cThis journal is © The Royal Society of Chemistry 2001 functionalities on each ring. Consequently, with Incozol LV, four sites (two hydroxyl and two amino) are available for reaction with polyisocyanate (Scheme 1).Recently, research has been conducted in conjunction with the University of Central Lancashire in Preston, UK3, to determine quantitatively the hydrolysis reaction, both from the point of view of extent and rate of hydrolysis. Practically, this has been achieved by determining the concentration of residual Incozol LV (if any) detectable using gas chromatography, with respect to the amount of water added in different stoichiometric mixes of Incozol LV and water.Furthermore, the rate of hydrolysis has been studied by following the residual Incozol LV depletion with respect to mixing time. The extent of hydrolysis (Fig. 2), indeed the driving force for reacting the diluent, indicates that Incozol LV is almost completely ring opened and available for reaction with isocyanate after only 30 minutes mixing; 15% residual Incozol LV is detected when a stoichiometric amount of water was mixed with the oxazolidine.At 0.5 moles of water, which would represent a more typical level of water present in polyol and solvent components, a majority (about 80%) of Incozol LV has been activated after six hours mixing.This indicates that some interaction with atmospheric moisture must also contribute to the oxazolidine ring opening. The rate of hydrolysis (Fig. 3) for 0.5 moles of water showed a large proportion of oxazolidine activated by the water present initially in the mixture. The rate of hydrolysis then declined as Incozol LV was consumed by the atmospheric moisture.After 12 hours the oxazolidine ring has fully opened and the amino alcohol generated is fully available for reaction with polyisocyanate. Reaction of ring opened oxazolidine (aminoalcohol) with polyisocyanate Once activation of Incozol LV has been completed, the aminoalcohol generated is then available for reaction into the polyurethane backbone.This takes place through the formation of urea couplings formed from isocyanate reaction with the secondary amine sites and urethane linkages via the terminal OH groups (Scheme 2). A second study4 by the University of Central Lancashire examined the interaction of the aminoalcohol with HDI polyisocyanates (Tolonate HDT™) using Fourier Transform infra-red spectrophotometry (FTIR).Incozol LV was added to a large excess of Tolonate HDT™ (20% w/w Incozol LV to 80% w/w Tolonate HDT™). Quantitative FTIR analysis in absorbance mode of the depleting NCO peak was performed for the following reaction combinations: • Tolonate HDT™ • Tolonate HDT™ + water • Tolonate HDT™ + Incozol LV • (Incozol LV + water) + Tolonate HDT™ N.B. - Tolonate is a trademark of Rhodia Ltd.Differences in NCO peak depletion, at different mixing times up to 150 minutes, with respect to the mix combinations, was compared to determine the influence of the ring opened Incozol LV (Fig. 4). It was discovered that 40% of the available isocyanate was consumed immediately on addition of Incozol LV (Fig. 7). Addition of a small quantity of water did not greatly increase the extent of reaction with isocyanate. Since reaction mixtures were exposed to the atmosphere during mixing, the results suggest that water activates the oxazolidine ring opening, in preference to the reaction with isocyanate.This is a fair assumption, since no bubbling (resulting from the formation of CO2 from the isocyanate–water reaction) was observed on incorporation of Incozol LV.The amount of Tolonate HDT™ Scheme 1 Hydrolysis reaction ring opening Incozol LV. Fig. 2 Extent of hydrolysis of Incozol LV. Fig. 3 Rate of hydrolysis for 0.5 moles of water. Scheme 2 Reaction of Incozol LV with isocyanate. AWARD Green Chemistry June 2001 G41This journal is © The Royal Society of Chemistry 2001 consumed represents the maximum concentration that can react with Incozol LV at the chosen mix ratio, with the residual Tolonate HDT™ being the reaction excess.Incorporation of Incozol LV into 2-pack polyurethane coatings Having demonstrated the reactivity of activated (ring-opened) oxazolidine with polyisocyanate, a further study5 was conducted to determine the practical implications of isocyanate reactivity in 2-pack polyurethane lacquers.This involved investigating how much Incozol LV is reacted into a 2-pack acrylic/polyurethane lacquer formulation, Desmophen A365/Desmodur N3390, throughout the duration of film curing. The amount of unreacted Incozol LV was quantitatively determined by gas chromatography of a Soxhlet extract of the film. The amount of Incozol LV incorporated into the polyurethane backbone can be calculated by subtracting the result from the known concentration of Incozol LV in the formulation.Extraction of Incozol LV was performed on films cured for 0 hours (uncured), 24 hours, 48 hours, 72 hours and 1 week. N.B. - Desmophen / Desmodur are trademarks of Bayer PLC. At 22 °C/23% humidity (Fig. 5), almost complete reaction of Incozol LV into the lacquer was observed after 2 days curing the film.At a higher temperature (40 °C) and humidity, (88%) (Fig. 6) incorporation of the oxazolidine was a much faster process, with very little (0.5%) Incozol LV extracted from the film after only 1 hour. The studies described so far have shown that complete utilisation of Incozol LV is possible in the polyurethane lacquer, but how does the level of Incozol LV incorporated influence the VOC of the lacquer? Fig. 7 shows the effect on VOC for clear lacquer formulations (Formulations 1 and 2) and primer paint (Formulation 3) (Table 1). In each case, up to 30% polyol has been replaced by Incozol LV reactive diluent. At 30% Incozol LV, considerable reductions in VOC are possible, with VOC as low as 250 g/l achievable for a clear lacquer depending on selection of a suitable formulation.This is certainly a favourable figure when compared to the present European legislation demand for a top coat clear lacquer of 420 g/l. VOC regulation-compliant paints can also be achieved incorporating Incozol LV. Fig. 4 Reduction in isocyanate percentage for 80:20 w/w Tolonate HDT: Incozol LV at ambient temperature. Note 1 - Constant Mix Ratio Tolonate HDT: Incozol LV 80% : 20%.Note 2 - Water content, where added, is equivalent to one quarter of the stoichiometric amount of Incozol LV Fig. 5 Rate of incorporation of Incozol LV into 2K Polyurethane Lacquer. Fig. 6 Rate of incorporation of Incozol LV into 2K polyurethane lacquer. Fig. 7 VOC reduction for up to 30% w/w polyol replacement with Incozol LV.VOC limit for a topcoat clear lacquer 420 g/l. VOC limit for pre-coat / primer paint 250 g/l. (EC Directive April 1998.) AWARD G42 Green Chemistry June 2001This journal is © The Royal Society of Chemistry 2001 Effect of incorporating Incozol LV on 2-pack polyurethane clear lacquer film properties6,7 Film curing properties Ideally, the true benefit of using a suitable reactive diluent is to achieve a reduction in VOC without adversely affecting the cure properties of the coating.The influence on pot life (Fig. 8) and cure response (Fig. 9) is shown for the three formulations in Table 1. Pot life was measured as the time taken for the initial mix viscosity of the lacquer to double. Viscosity was measured at 20 °C using a Ford No 3 flow cup. Cure response was determined using a Sheen Model B-K dry time recorder.In each of the formulations up to 30% w/w polyol has been replaced by Incozol LV without greatly influencing the cure properties. Furthermore, for the two clear lacquer and the paint formulations, incorporating up to 30% w/w Incozol LV as polyol replacement did not significantly alter the Persoz film hardness development (Fig. 10). Dry coating properties Cured panels of the three formulation case studies were evaluated for chemical resistance using a variety of solvents including isopropyl alcohol, methyl ethyl ketone, petrol and skydrol (aviation brake fluid). The method used for measurement was a Satra rub fastness tester (Model STM 61), comprising of a felt pad which had been pre-soaked in the test reagent/solvent, and rotated for 100 revolutions under a constant applied force of 24.5 N.The effect on the film is Table 1 Formulations used in performance property studies. Formulation Composition Formulation 1 A 2K acrylic/polyurethane lacquer - G-Cure 109 HE75 + up to 30% w/w replacement Incozol LV/Tolonate HDT90 Formulation 2 A 2K acrylic/polyurethane lacquer - Desmophen A365/Desmodur N3390 Formulation 3 A 2K acrylic/polyurethane paint - Joncryl SCX-922/Tolonate HDB75MX N.B.G-Cure is a trademark of Henkel PLC and Joncryl is a trademark of S.C. Johnson & Sons B.V. Fig. 8 Effect on pot life with incorporation of Incozol LV. Fig. 9 Effect on cure response over time with incorporation of Incozol LV. Fig. 10 Film hardness using ASTM D4366-95 Method B for formulation 1 (Table 1).AWARD Green Chemistry June 2001 G43This journal is © The Royal Society of Chemistry 2001 recorded as an observation and graded according to the scale defined with the results in Table 2. Formulating with bisoxazolidine reactive diluent appears to have no significant influence on coating chemical resistance. Table 3 shows the effect on the gloss retention of the clear lacquer formulations after weathering trials by QUV B after 500, 1000 and 3000 hours.No significant influence on the level of gloss retention by incorporating up to 20% Incozol LV was observed. Summary Incozol LV is a low viscosity bisoxazolidine reactive diluent that is activated by moisture contamination present in both the polyurethane coating components (polyol and solvent) and in the atmosphere during application.The moisture triggered ring opening allows Incozol LV, via chemical reaction with polyisocyanate, to be successfully incorporated into the polyurethane coating. Incozol LV offers the benefit of reducing the VOC of polyurethane coatings beyond the present legislative demands without adversely altering cure and coating properties. Acknowledgements The author acknowledges Alexis Holden and Robert Clarke of the University of Central Lancashire, Preston, UK, and Alex Thrift and Elaine Whalley of Industrial Copolymers Limited, Preston, UK.References 1 G. A. Howarth. Oxazolanes—Old Chemistry, New Applications, Proceedings of the 23rd Waterborne High Solids and Powder Coatings Symposium, New Orleans, February 1996. 2 Incozol LV, Oxazolidine - Reactive Diluent, Industrial Copolymers Product Literature, September 1997. 3 A. Holden and R. Clarke. University of Central Lancashire Internal Report to Industrial Copolymers, November 1997. 4 A. Holden and R. Clarke. University of Central Lancashire Internal Report to Industrial Copolymers, April 1998. 5 A. J. Thrift and E. Whalley. Internal Report, Industrial Copolymers, April 1998. 6 D. P. Moore and N. G. Carter. From Cars to Transport Bridges, Proceedings of 4th Nürnberg Congress, April 1997. 7 D. P. Moore and N. G. Carter. The Versatility of Oxazolidines as Reactive Diluents in Two-Component Polyurethanes, Pitture & Vernici. Paints and Varnishes, 20, September 1997. Table 2 Effect on chemical resistance of a clear lacquer incorporating up to 20% w/w Incozol LV. Formulation 1 Formulation 2 % Replacement with Incozol LV 0 5 20 0 5 20 Chemical Resistance to IPA 10 10 10 10 10 10 Chemical Resistance to MEK 10 9 10 10 10 9 Chemical Resistance to Petrol 10 9 9 10 10 10 Chemical Resistance to Skydrol 9 10 10 9 9 10 Key:- 0 = film fully removed, 4 = film softened, significantly marked, 8 = slight gloss reduction / marked, 9 = film very slightly marked, 10 = film unaffected. Table 3 Incorporating Incozol LV results in high gloss retention after QUV B weathering. Method used to determine gloss was a sheen gloss meter at 20° using ASTM D523-89. Formulation 1 Formulation 2 % Polyol Replacement with Incozol LV 0 5 20 0 5 20 % Gloss Retention after 500 hr QUV B 96 94 100 80 88 88 % Gloss Retention after 1000 hr QUV B 94 91 100 73 80 80 % Gloss Retention after 3000 hr QUV B 93 90 98 70 76 78 AWARD G44 Green Chemistry June 2001

ISSN:1463-9262    

DOI:10.1039/b103991c

出版商:RSC    

年代:2001

数据来源: RSC