Alternative Solvents for Green Chemistry RSC Green Chemistry Book Series Series Editors: James H Clark, Department of Chemistry, University of York, York, UK George A Kraus, Department of Chemistry, Iowa State University, Iowa, USA GreenChemistryisoneofthemostimportantandrapidlygrowingconceptsin modern chemistry. Through national awards and funding programmes, nationalandinternationalcourses,networksandconferences,andadedicated journal,GreenChemistryisnowwidelyrecognisedasbeingimportantinallof thechemicalsciencesand technologies,and inindustryaswell asineducation and research. The RSC Green Chemistry book series is a timely and unique venture aimed at providing high level research books at the cutting edge of Green Chemistry. Titles in the Series: Alternative Solvents for Green Chemistry By Francesca M. Kerton, Department of Chemistry, Memorial University of Newfoundland, St. John’s, NL, Canada The Future of Glycerol: New Uses of a Versatile Raw Material ByMarioPagliaro,CNR,InstiuteofNanostructuredMaterialsandInstitutefor Scientific Methodology, Palermo, Italy and Michele Rossi, Department of Inorganic Chemistry, University of Milan, Milan, Italy Visitourwebsiteonwww.rsc.org/books Forfurtherinformationpleasecontact: SalesandCustomerCare,RoyalSocietyofChemistry,ThomasGrahamHouse, SciencePark,MiltonRoad,Cambridge,CB40WF,UK Telephone:+44(0)1223432360,Fax:+44(0)1223426017,Email:[email protected] Alternative Solvents for Green Chemistry Francesca M. Kerton Department of Chemistry, Memorial University of Newfoundland, St. John’s, NL, Canada ISBN: 978-0-85404-163-3 AcataloguerecordforthisbookisavailablefromtheBritishLibrary rFrancescaM.Kerton2009 Allrightsreserved Apart from fair dealing for the purposes of research for non-commercial purposes or for privatestudy,criticismorreview,aspermittedundertheCopyright,DesignsandPatents Act1988andtheCopyrightandRelatedRightsRegulations2003,thispublicationmaynot be reproduced, stored or transmitted, in any form or by any means, without the prior permission in writing of The Royal Society of Chemistry or the copyright owner, or in thecaseofreproductioninaccordancewiththetermsoflicencesissuedbytheCopyright LicensingAgencyintheUK,orinaccordancewiththetermsofthelicencesissuedbythe appropriate Reproduction Rights Organization outside the UK. Enquiries concerning reproduction outside the terms stated here should be sent to The Royal Society of Chemistryattheaddressprintedonthispage. PublishedbyTheRoyalSocietyofChemistry, ThomasGrahamHouse,SciencePark,MiltonRoad, CambridgeCB40WF,UK RegisteredCharityNumber207890 Forfurtherinformationseeourwebsiteatwww.rsc.org Preface Everyone is becoming more environmentally conscious and therefore, chemi- cal processes are being developed with their environmental burden in mind. Of course, this also means that more traditional chemical methods are being replaced with new innovations. This includes new solvents. Solvents are everywhere, but should they be? They are used in most areas includingsyntheticchemistry,analyticalchemistry,pharmaceuticalproduction and processing, the food and flavour industry and the materials and coatings sectors.But,theprinciplesofgreenchemistryguideustouselessofthem,orto use safer, more environmentally friendly solvents if they are essential. There- fore, we should always ask ourselves, do we really need a solvent? Chapter 2 explains some of the challenges and successes in the field of solvent-free chemistry, and the answer becomes apparent: not always! In the introductory chapter, some of the hazards of conventional solvents (e.g. toxicity and flammability) and their significant contribution to waste streamsarehighlighted.Thegeneralpropertiesofsolventsandwhyandwhere they are used are outlined. Additionally, EHS (Environmental, Health and Safety) assessments and life cycle analyses for traditional and alternative sol- vents are described. It becomes clear that often a less hazardous VOC is available and that although only ‘‘light green’’ (or at least ‘‘less black’’) in colour, they can be used as an interim measure until a more satisfying option becomes available. Ineachof thesubsequentchapters,wherepossible, theuse of an alternative solvent is described for a range of chemical applications including extractions, synthetic and materials chemistry. At the beginning of each of these chapters, some of the advantages and disadvantages of that medium are laid out. Water is often described as Nature’s solvent; therefore Chapter 3 describes thesolventpropertiesofwater.Itisalreadyusedquitewidelyonanindustrial scale,particularlyinemulsionpolymerizationprocessesandhydrodistillations. However, some of the most exciting results have come in the field of synthetic RSCGreenChemistryBookSeries AlternativeSolventsforGreenChemistry ByFrancescaM.Kerton rFrancescaM.Kerton2009 PublishedbytheRoyalSocietyofChemistry,www.rsc.org v vi Preface chemistry.Recently,‘on-water’reactionshaveshownthathydrophobic(water insoluble)compoundscanachievehigherratesdispersedinwatercomparedto reactions in conventionalsolvents orundersolvent-free conditions. Water can alsobe usedatveryhightemperaturesandunderpressureinanear-criticalor supercritical state. Under these conditions, its properties are significantly alteredandunusualchemistrycanresult.ThisisfurtherdiscussedinChapter4, which describes supercritical fluids. The focus here is on the non-flammable options,thatis,carbondioxideandwater.Modificationsthatareperformedon substrates in order to make them soluble in supercritical carbon dioxide are described. Additionally, the benefits of the poor solvating power of carbon dioxide,e.g.selectiveextractions,arehighlightedanditsuseintuningreactivity through its variable density is described. Inadditiontowaterandcarbondioxide,thereisanincreasingavailabilityof solventssourcedfromrenewablefeedstocksincludingethanol,ethyllactateand 2-methyl-tetrahydrofuran. The properties of these solvents and their potential as replacements to petroleum-sourced solvents are discussed in Chapter 5. Renewable feedstocks and their transformations are a growing area of green chemistry and they have significantly impacted the solvent choice arena. In addition to renewable VOC solvents, non-volatile ionic liquid and eutectic mixture solvents have been prepared from renewable feedstocks and are lookingtobeverypromisingalternativesintermsoftoxicityanddegradation. These and other room temperature ionic liquids (RTILs) will be discussed in Chapter6.ThefieldofRTILshasgrowndramaticallyinthelasttenyearsand therangeofanions/cationsthatcanbeusedtomakethesenon-volatilesolvents iscontinuallyexpanding.Althoughsomeofthesemediamaybemoreexpensive thanotheralternatives,thechancetomaketask-specificsolventsforparticular processesisveryexciting.RTILs,alongsidefluoroussolvents,havealsomadea large impact in the area of recyclable homogeneous catalysts. Fluorous sol- vents, as described in Chapter 7, show interesting phase behaviour and allow the benefits of a heterogeneous and homogeneous system to be employed by adjustinganexternalvariablesuchastemperature.Recentadvancesinthisarea willbediscussed,forexample,supportedfluorouschemistry,whichavoidsthe use of large amounts of fluorous solvents and might be more amenable to industrial scale processes. Possiblytheleastexploredandnewestoptionsavailabletothegreenchemist are liquid polymer solvents (Chapter 8) and switchable and tunable solvents (Chapter9).Unreactivelowmolecularweightpolymersorthosewithlowglass transition temperatures can be used as non-volatile solvents. In particular, poly(ethyleneglycols) and poly(propyleneglycols) have been used recently in a range of applications. Probably the most important recent additions to our toolbox areswitchablesolvents.New molecularsolventshavebeendiscovered that can be switched from non-volatile to volatile or between polar and non- polar environments by the application of an external stimulus. Gas-expanded liquids will also be discussed in Chapter 9, as carbon dioxide can be used as a solubility switch and to reduce the environmental burden of conventional solvents. Preface vii Although many advances in the area of alternative solvents have originated in academia, many alternatives are already in use on an industrial scale. For example, supercritical carbon dioxide is used in coffee decaffeination and nat- ural product extractions, as an alternative solvent in dry-cleaning and as a solvent in continuous flow hydrogenation reactions. An overview ofthese and someotherindustrialprocessesthatusealternativesolventswillbedescribedin Chapter 10. Unfortunately, as will become clear to readers, there is no universal green solvent and users must ascertain their best options based on prior chemistry, cost, environmental benefits and other factors. It is important to try and minimize the number of solvent changes in a chemical process and therefore, the importance of solvents in product purification, extraction and separation technologies has been highlighted. There have been many in-depth books and reviews published in the area of greensolvents.Hopefully,readerswillfindthisbookareadableintroductionto the field. However, some cutting-edge results from the recent literature have beenincludedinanattempttogiveaclearerpictureofwheregreensolventsare today. For more comprehensive information on a particular solvent system, readersshouldlooktotheprimaryliteratureandthemanyexcellentreviewsof relevance to this field in journals such as Green Chemistry and Chemical Reviews. Certainsolventmediacanbefascinatingintheirownright,notjustas‘green’ solvent alternatives! Therefore, we must not be blind to our overall goal in reducing the environmental burden of aparticular process.Hopefully, readers of this book will be able to make up their own minds about the vast array of solvents available for a greener process, or even come up with a new addition for the green chemistry toolbox. Although many advances have been made during the past decade, the most exciting results are surely yet to come. IwouldliketothanktheeditorsoftheRSCGreenChemistrySeries,James Clark and George Kraus, for the opportunity to contribute a book to this importantgroupofbooks.Also,IwouldliketoacknowledgeMerlinFox(the commissioningeditor)andthestaffatRSCPublishinginvolvedwiththisseries, particularly,AnnieJacob,whohasbeenadvisingandhelpingmeallalongthe way.Finally,Iwouldliketothankmyhusband,ChrisKozak,forhispatience, support and motivational input during the writing of this book. Francesca Kerton St. John’s, Newfoundland, Canada Contents Chapter 1 Introduction 1.1 The Need for Alternative Solvents 1 1.2 Safety Considerations, Life Cycle Assessment and Green Metrics 4 1.2.1 Environmental, Health and Safety (EHS) Properties 4 1.2.2 Life Cycle Assessment (LCA) 5 1.2.3 Solvents in the Pharmaceutical Industry and Immediate Alternatives to Common Laboratory Solvents 12 1.3 Solvent Properties Including Polarity 14 1.4 Summary 20 References 21 Chapter 2 ‘Solvent free’ Chemistry 2.1 Introduction 23 2.2 Chemical Examples 25 2.2.1 Inorganic and Materials Synthesis 25 2.2.2 Organic Synthesis 27 2.2.2.1 Enantioselective Catalysis 36 2.2.2.2 Microwave assisted Reactions 39 2.2.2.3 Photoreactions 39 2.3 Summary and Outlook for the Future 39 References 41 RSCGreenChemistryBookSeries AlternativeSolventsforGreenChemistry ByFrancescaM.Kerton rFrancescaM.Kerton2009 PublishedbytheRoyalSocietyofChemistry,www.rsc.org ix x Contents Chapter 3 Water 3.1 Introduction 44 3.1.1 Biphasic Systems 46 3.2 Chemical Examples 49 3.2.1 Extraction 49 3.2.2 Chemical Synthesis 51 3.2.2.1 Metal-mediated and Catalysed Reactions 54 3.2.2.2 Microwave Assisted Reactions 56 3.2.2.3 Biocatalysis 57 3.2.2.4 Carbon Dioxide Fixation 58 3.2.3 Materials Synthesis 60 3.3 HighTemperature,SuperheatedorNearCriticalWater 63 3.4 Summary and Outlook for the Future 64 References 65 Chapter 4 Supercritical Fluids 4.1 Introduction 68 4.2 Chemical Examples 71 4.2.1 Supercritical and Liquid Carbon Dioxide 71 4.2.1.1 Solubility in Supercritical Carbon Dioxide 71 4.2.1.2 Extraction 74 4.2.1.3 Chemical Synthesis 76 4.2.1.4 MaterialsSynthesisandModification 82 4.2.2 Supercritical Water and Near Critical Water 84 4.2.2.1 Extraction and Analytical Chemistry 84 4.2.2.2 Chemical Synthesis 86 4.2.2.3 Materials Synthesis 89 4.2.2.4 Supercritical Water Oxidation (SCWO) 90 4.3 Summary and Outlook for the Future 91 References 92 Chapter 5 Renewable Solvents 5.1 Introduction 97 5.2 Chemical Examples 100 5.2.1 Alcohols including Glycerol 100 5.2.2 Esters 103 5.2.2.1 Biodiesel 105 5.2.3 2-Methyltetrahydrofuran (2-MeTHF) 108 5.2.4 Terpenes and Plant Oils 109 5.2.5 Renewable Alkanes 113