Diss. ETH No. 12700 Reduction of Polyhalogenated Alkanes by an Iron Porphyrin as Electron Transfer Mediator: System and Product Analysis A dissertation submitted to the SWISS FEDERAL INSTITUTE OF TECHNOLOGY ZURICH for the degree of DOCTOR OF NATURAL SCIENCES presented by JOHANNA BUSCHMANN Dipl. Chem. ETH born February 12, 1969 citizen of Arbon (TG) accepted on the recommendation of Prof. Dr. Rene Schwarzenbach, examiner Dr. Werner Angst, co-examiner Prof. Dr. Bernhard Krautler, co-examiner Zilrich 1998 Der Schauende Ich sehe den Baumen die Sttirme an, die aus laugewordenen Tagen an meine i:ingstlichen Fenster schlagen, und hore die fernen Dinge sagen, die ich nicht ohne Freund ertragen, nicht ohne Schwester lieben kann. Da geht der Sturm, ein Umgestalter, geht <lurch den Wald und <lurch die Zeit, und alles ist wie ohne Alter: die Landschaft, wie ein Vers im Psalter, ist Ernst und Wucht und Ewigkeit. Wie ist das klein, womit wir ringen, was mit uns ringt, wie ist das gross; liessen wir, ahnlicher den Dingen, uns so vom grossen Sturm bezwingen, wir wurden weit und namenlos. Was wir besiegen, ist das Kleine, und der Erfolg selbst macht uns klein. Das Ewige und Ungemeine will nicht von uns gebogen sein. Das ist der Engel, der den Ringern des Alten Testaments erschien: wenn seiner Widersacher Sehnen im Kampfe sich metallen dehnen, fi.ihlt er sie unter seinen Fingern wie Saiten tiefer Melodien. Wen dieser Engel uberwand, wekher so oft auf Kampf verzichtet, der geht gerecht und aufgerichtet und gross aus jener harten Hand, die sich, wie formend, an ihn schmiegte. Die Siege laden ihn nicht ein. Sein W achstum ist: der Tiefbesiegte von immer Crosserem zu sein. Rainer Maria Rilke Acknowledgements I want to thank Prof. Rene Schwarzenbach for letting me work in his group and for advising this research. Special thanks to Dr. Werner Angst and Dr. Judith Perlinger for their discussions where many ideas were evaluated and thought over. I thank Dr. Angst and Prof. Krautler for being my co-examiners. Dr. Angst, Prof. Krautler, Janet Kessel- mann and Prof. Anderson are kindly acknowledged for reviewing this dissertation. I would like to thank people in the ,,Dehalo"-meetings: Guy Glod, Wolfram Schu- macher, Christoph Holliger, Werner Angst, Judith Perlinger and Rene Schwarzenbach. For the interesting presentations and discussions the people from the ,,ET" -meetings are kindly acknowledged: Stephan Hug, Silvio Canonica, Iganz Bilrge, Thomas Hofstetter, Werner Angst and Rene Schwarzenbach. Numerous people assisted me in parts of my work. I would like to acknowledge Adrian Amman and Thomas Ri.ittimann for their help with the IC-measurements, Roland Hany for the NMR-measurements, John Westall for the discussions about the right use of FITEQL, Vesna Klingel for the contributions in her diploma work, Martin Schwarz for his help in the syntheses of the cyclopropanes and Christian Saxer and Etienne Michel for performing a number of kinetic measurements. I would like to express my thanks to the Schwaba-crew for creating a pleasant wor- king atmosphere: Werner Angst, Cedric Arnold, Michael Berg, Thomas Bucheli, Andrea Ciani, Rick Devlin, Dieter Diem, Urs Domman, Martin Elsner, Beate Escher, Claudia Pesch, Guy Glod, Kai-Uwe Goss, Andreas Gerecke, Franca Gri.iebler, Edi Hohn, Stefan Haderlein, Thomas Hofstetter, Rene Hunziker, Jorg Klausen, Markus Meier, Ji.irg Mi.ihle- mann, Markus Millier, Stephan Muller, Klaus Pecher, Judith Perlinger, Csaba Reisinger, Kenny Weissmahr, Markus Ulrich, Thomas Waxweiler, Andre Weidenhaupt and Hans- ruedi Zweifel. I also like to thank Verena Cajochen, Sabine Hilger, Donald Tillman and many others for the common joggings at ,,a quarter to twelve". Warm thanks to my colleages outside EAWAG: Andrea, Annie, Bettina, Birgit, Edmee, Felix, Gabi H. and Gabi A., Marcel, Susi, Ulrich and Ursi. Finally, I would like to express my gratitude to my family for their love and support during all those years. Table of Contents List of Figures V List of Tables VIII Abbreviations X Summary XII Z usammenfassung XV 1. Introduction 1 2. Evaluation of the Iron Porphyrin/ Cysteine System 9 2.1 Introduction 9 2.2 Meso-tetrakis-(N-methyl-pyridyl)iron porphin 9 2.3 Kinetics of PHA reduction: determination of rate constants 12 2.4 Effect of pH on the reduction rates of CC14 and C2Cl6 14 2.4.1 Effect of pH on iron porphyrin with respect to redox potential and spin state 15 2.4.2 Effect of pH on cysteine 16 2.4.3 Buffers 21 2.5 Effect of cysteine and phosphate concentration on the reduction rates of CC14 and C2Cl6 22 2.5.1 Effect of cysteine concentration 22 2.5.2 Effect of phosphate concentration 25 2.6 Ionic strength 28 2.7 Rereduction of the iron porphyrin 31 2.8 Blank reactions 34 2.8.1 Porphyrin ring as electron transfer mediator 35 2.8.2 Reactions without iron porphyrin 36 2.9 Summary and conclusions 38 3. Reaction Intermediates and Reaction Products 39 3.1 Introduction 39 3.2 Degradation of CC14: product analysis 41 II 3.2.1 Product distribution between different phases 43 3.2.2 Ion chromatographic analysis 45 3.2.3 Product analysis by NMR and MS 47 3.3 Degradation of CC14: reaction intermediates 50 3.3.1 Trapping of CC4-radicals 50 3.3.2 Trapping of carbenes 52 3.4 Degradation of CC14: proposed reaction mechanism in the iron porphyrin/ cysteine system 54 3.5 Degradation of CC14: proposed reaction mechanism in the reaction with cysteine (blank system) 57 3.6 Degradation of CBr4, CBr2Cl2, CBrC13: comparison with CC14 58 3.7 Degradation of polyhalogenated methanes containing one hydrogen: CHBr3, CHBr2Cl, CHBrC12 63 3.8 Degradation of fluorinated methanes: CFBr31 CF2Br2, CFC13 66 3.9 Degradation of polyhalogenated ethanes 77 3.10 Summary and conclusions 84 4. Kinetics and Reaction Mechanisms. Structure-Reactivity Considerations 86 4.1 Introduction 86 4.2 Competition 86 4.3 Activation parameters 94 4.4 Comparison of degradation mechanisms of polyhalogenated methanes in different model systems 100 4.5 Structure- Reactivity Considerations 111 4.5.l Polyhalogenated methanes 111 4.5.2 Polyhalogenated ethanes 113 5. Conclusions 114 6. References 117 III Appendix A A-1 Al Chemicals A-1 A.2 Syntheses A-2 A.2.1 Meso-tetrakis(N-methyl-pyridyl)iron porphin A-2 A.2.2 N-formylcysteine A-3 A.2.3 3-methyl-3-butenoic acid A-4 A.2.4 Diazomethane A-4 A.2.5 2-(2,2-dichloro-1-methyl cyclopropyl)-ethanoic acid A-5 A.2.6 2-(2,2-dibromo-1-methyl cyclopropyl)-ethanoic acid A-5 A.2.7 2-(2-bromo-2-chloro-1-methyl cyclopropyl)-ethanoic acid A-6 A.3 Stock solutions and buffers A-6 A.4 Experimental procedures: Kinetic experiments A-7 A.4.1 Standard procedure for kinetic experiments A-7 A.4.2 Determination of rate constants A-10 A.4.3 pH variation A-10 A.4.4 Variation of cysteine concentration A-11 A.4.5 Variation of phosphate concentration A-12 A.4.6 Variation of ionic strength A-12 A.4.7 Variation of ligand concentration A-13 A.4.8 Reactions without porphyrin A-14 A.4.9 Variation of initial concentration of CBr2Cl2 A-15 A.4.10 Competition experiments: CBr2Cl2 versus CBrCl3 A-17 A.4.11 Competition experiments: CC14, CHBrClv CHBr2Cl A-18 A.4.12 Competition experiments: CC14 versus 4-chloro- nitrobenzene A-19 A.4.13 Determination of activation parameters A-20 IV A.5 Experimental procedures: Analysis of products and reaction intermediates A-21 14 A.5.1 Distribution experiments with C-CC14 A-21 13 A.5.2 C-CC14 experiments A-22 A.5.3 D' abstraction experiments A-22 A.5.4 Carbene trap experiments A-23 A.5.5 Quantification of products: methods of analyses A-26 A.5.6 Product studies of polyhalogenated ethanes A-26 A.6 Analytical prodedures A-27 A.6.1 GC-ECD A-27 A.6.2 GC-MS A-27 A.6.3 IC A-28 A.6.4 HPLC A-28 A.6.5 Scintillation counter A-29 A.6.6 NMR A-29 Appendix B B-1 B.1 UV-VIS experiments B-1 B.1.1 Cysteine-ligated iron porphyrin at different pH B-1 B.1.2 Effect of oxygen: Formation of superoxide radical B-2 B.1.3 Azide and cyanide as ligands B-3 B.1.4 Effect of cysteine concentration B-4 B.1.5 Effect of substrates B-4 B.1.6 UV-VIS spectrum of porphyrin ligand B-5 B.2 Polarographic measurements B-6 v List of Figures Figure 1.1: Worldwide production of some polyhalogenated alkanes (Fisher and Midgley, 1993i Rippen, 1988). 2 Figure 1.2: Half-reaction reduction potentials of organic redox couples (left side), various electron transfer mediators (middle) and some biogeochemically important redox couples (right side). Standard reduction potentials are indicated at environmentally relevant conditions: 25°C, pH 7.0, [Ci-)= [HCO;] = 10-3 M, [Br'] = lff' M. (Figure adopted from Schwarzenbach et al., 1997). 3 Figure 1.3: A mediator catalyses the electron transfer from the bulk electron donor to the pollutant. Typical bulk electron donors are iron(O), iron carbonate, hydrogen sulfide, hydrogen or iron sulfides. Mediators include surface- complexed iron, reduced cobalamins, reduced quinones or iron porphyrins. Organic pollutants that can be reduced are for example azo-dyes, nitroaromatic compounds or polyhalogenated alkanes (Figure adorpted from Schwarzenbach et al., 1997). 4 Figure 2.1: Meso-tetrakis(N-methyl-pyridyl)iron porphyin, an artificial water-soluble iron porphyrin.