Photodegradation of 2-Substituted Benzimidazole Fungicides by Ultraviolet Radiation by Dong Chen A Thesis Submitted to the Faculty of The College of Science in Partial Fulfillment of the Requirements for the Degree of Master of Science Florida Atlantic University Boca Raton, Florida August 1994 PHOTODEGRADATION OF 2-SUBSTITUTED BENZIMIDAZOLE FUNGICIDES BY ULTRAVIOLET RADIATION BY DONG CHEN This thesis was prepared under the direction of the candidate's thesis advisor, Dr.Cyril Parkanyi, Department of Chemistry, and has been approved by the members of the supervisory committee. It was submitted to the faculty of the College of Science and was accepted in partial fulfillment of the requirements for the degree of Master of Science in Chemistry. SUPERVISORY COMMITTEE Thesis Advisor Chairman, Department of Chemistry D an, College of Sc1ence I I Date II Acknowledgments I wish to express my sincere thanks to my thesis advisor, Dr. Cyril Parkanyi, Professor and Chairman of the Department of Chemistry, for his guidance, suggestions and enthusiastic support. His patience and keen interest throughout this study are greatly appreciated. I would also like to acknowledge the valuable suggestions of my committe members Dr. Russell G. Kerr, Assistant Professor, and Dr. Earl W Baker, Professor, Department of Chemistry. Special thanks are due to my dear friend and colleague, Ms. Guoping Deng, for her constant support and help with NMR data. I am most grateful to Dr. J William Louda for the mass spectra, without his help this work would not have been completed. My deepest and sincerest thanks go to my parents, Mrs. & Mr. Chen, for their love, encouragement and support. Also, I thank all my friends who have helped me with this project. Finally, I thank DuPont (benomyl), Merck Sharp & Dohme (thiabendazole) and Bayer (fuberidazole) for supplying the samples of fungicides for this research. Ill Abstract Author: Dong Chen Title: Photodegradation of 2-Substituted Benzimidazole Fungicides by Ultraviolet Radiation Advisor: Dr. Cyril Parkanyi Institution: Florida Atlantic University Degree: Master of Science in Chemjstry Year: 1994 The photodegradation of benzimidazole-based fungicides: benomyl ( { 1- [ (butylamine) carbonyl]-1 H-benzimidazol-2-yl} carbamic acid methyl ester), thiabendazole (2-( 4-thiazolyl)-1 H-benzimidazole) and fuberidazole (2-(2-furyl)-1 H-benzimidazole) by ultraviolet radiation has been studied. Benomyl in an organic solvent (chloroform) undergoes a rapid degradation even without any UV radiation; UV radiation and air agitation will increase the rate of the reaction. The degradation product was found to be methyl 2-benzimidazolecarbamate (MBC) in all cases. The degradation of thiabendazole and fuberidazole in methanol was also studied under different conditions but degradation was observed only under UV radiation and in the presence of oxygen, 7-8 Photodegradation products were found in the mixture after irradiation of thiabendazole but only 2 of them were separated from the rruxture and identified. Benzimidazole-2- carboxamide and dimethyl oxalate were two of the final photodegradation products of thiabendazole in methanol. It is clear that the thiazole ring is the most vulnerable part of the molecule and suffers ring cleavage. No photodegradation products of fuberidazole were identified so far. IV TO MY DEAR PARENTS Contents Chapter 1. Introduction 1. 1 Light and Energy . 1 1.2 Laws ofPhotochemistry .. 4 1.3 Ultraviolet Spectroscopy . ... ... 5 14 The Excited States ... ... .. .. ... .......... ........... .. 7 1.5 Fate ofthe Excited Species .... .... ... ... .... .. ... .... .9 1.6 Light Sources in Photochemistry . 11 1. 7 Fungicides ............ 13 1.7.1 Fate ofFungicides in Soil ... ............ .. .. ..... .. .... 13 1. 7.2 Benzimidazoles as Fungicides . ............ ............ 15 Chapter 2. Literature Review 2. 1 Introduction . 18 2.2 Photochemistry ofHeterocyclic Fungicides .... ... .. .. ..... ..... .. .. 19 2.2.1 Carboxamides ..... .. ............ .. .. ........... ...... 19 2.2.2 Pyrimidines and Pyridines . .. 20 2.2.3 Thiophanates . ... 21 v 2.2.4 Benzimidazoles ........ .............. ........ .... .... 22 Chapter 3. Experimental 3 . I Materials . .... .. .. 28 3.2 Instrumentation ... ... .. ............... 28 3.2.1 Photolysis ..... .. ... .. .. ......... 28 3.2.2 Monitoring of the Photodegradation .... ... .. 36 3. 3 Identification and Isolation . .. ... .. .... .. 36 3.3 .1 TLC ............... .. .... .. ..... 36 3.3.2 Column Chromatography ..... ................. ............ 36 3.4 Analytical Methods . .............. 36 3 .4. 1 Infrared Spectroscopy ................ 36 3.4.2 Nulear Magnetic Resonance Spectroscopy ... 36 3.4.3 Mass Spectrometry .... .......... .. 36 3. 5 Procedure . 3 7 3. 5. 1 Photodegradation . 3 7 3. 5. 2 Detection and Isolation . 3 7 3. 5. 3 Characterization . .... ........ 37 Chapter 4. Results and Discussion 4.1 Study of the UV Spectra .................... .. .... ....... ... 38 4.2 Photodegradation ...... ... ........ .. ............. .......... 43 4.2. 1 Degradation ofBenomyl in Chloroform ...... .. ...... .......... 43 VI 4.2.2 Degradation ofThiabendazole and Fuberidazole in Methanol ... 43 4.3 Detection, Isolation and Analysis ... ... .... .... ....... 50 4.3.1 Benomyl . .. ........ ......... .......... .. .. ....... 50 4.3 . 2 Thiabendazole . 55 4.3.3 Fuberidazole ...... .... .. ... ..... .... .. .. .. 67 Chapter 5. Conclusions . ...... ................. ... .. 69 References ....... ....... .... .. ........................ 71 VII List of Figures Chapter 1. Introduction 1.1 Electromagnetic Spectrum .... .. 2 1.2 Potential Energies of a Molecule . ... .. .. ... .... ...... .6 1. 3 Scheme of Electronic Levels . .8 1.4 The Several Routes to Loss of Electronic Excitation . 10 1.5 Structural Formulas ofBenzimidazole-Based Fungicides .... ..... .. ... 16 Chapter 2. Literature Review 2. 1 Structural Formulas of Carboxin and Oxycarboxin . 19 2.2 Degradation ofCarboxin and Oxycarboxin . ... ......... ... .. ... 20 2.3 Structural Formulas ofDimethirimol and Pyroxychlor . ... .... ... .. 20 2.4 Photodegradation of Thiophanates .. .... .... ....... .. .. ...... 21 2.5 Structural Formulas ofBenzimidazole and its Photoproducts A and B .. .... 23 2.6 Degradation ofBenomyl. .... ... ..... 24 2. 7 Degradation of Thiabendazole . ........ .. .. 24 2.8 Degradation ofFuberidazole . ... ... ... ..... .. ...... .... ... 25 2.9 Degradation ofBenzimidazole-2-amine . .. .. ... .. ... ... 26 Vlll 2. 10 Degradation of 2-Chlorobenzimidazole .. ... ..... ..... ... 27 Chapter 3. Experimental 3.1 IR Spectrum ofBenomyl .... 29 3.2 IR Spectrum ofThiabendazole ..................... ... ....... 30 3.3 IR Spectrum ofFuberidazole ........ .. ..... .. ... 31 3.4 NMR Spectrum ofBenomyl ... .......... .. ....... .... ... 32 3.5 NMR Spectrum ofThiabendazole .. ... ......... ..... .. .... .. .. .. 33 3.6 NMR Spectrum ofFuberidazole ... .. .. .... .... ..... .... .. ... .. 34 3.7 Mass Spectrum ofThiabendazole .. ... ...... .. .... ... .. .. 35 Chapter 4. Results and Discussion 4.1 UV Spectrum ofBenomyl in Chloroform . .......... .............. 39 4.2 UV Spectrum ofThiabendazole in Methanol. .................... .. 40 4.3 UV Spectrum ofFuberidazole in Methanol ... ... .. .. ..... .. 41 4.4 UV Spectrum ofBenzimidazole in Methanol ......... ... ........... 42 4.5 UV Spectrum ofReaction 1 ofBenomyl in Chloroform .... ... .. .. ... 44 4.6 UV Spectrum ofReaction 2 ofBenomyl in Chloroform ............... 45 4.7 UV Spectrum ofReaction 3 o(Benomyl in Chloroform ... ..... .. 46 4.8 UV Spectra of Reaction 4 ofBenomyl in Chloroform .... ...... ........ 47 4.9 UV Spectra ofReaction of Thiabendazole in Methanol ................ .. 48 4.10 UV Spectra ofReaction ofFuberidazole in Methanol . 49 4.11 IR Spectrum ofBenomyl Degraded Product ........ ... .. .. ......... 52 IX 4.12 NMR Spectrum ofBenomyl Degraded Product ..... .... .. 53 4. 13 Degradation Pathway of Benomyl . 54 4.14 Thin-Layer Plate Resulting from Two-Dimensional Chromatography of Thiabendazole Photolysis Reaction Product ... .. .. 55 4. 15 IR Spectrum efFraction 2 ofThiabendazole Degradation . 57 4.16 NMR Spectrum efFraction 2 ofThiabendazole Degradation .. ... ... 58 4.17 Mass Spectrum efFraction 2 ofThiabendazo1e Degradation . .... ..... 59 4.18 UV Spectrum efFraction 2 ofThiabendazole Degradation .. ............ 61 4.19 IR Spectrum ofUnknown of Thiabendazole Degradation . .. .. .. .. .. .. 63 4.20 NMR Spectrum ofUnknown ofThiabendazole Degradation . ... 64 4.21 Mass Spectrum of Unknown of Thiabendazole Degradation .... .......... 65 4.22 Photodegradation Pathway ofThiabendazole ............. ...... ... 68 X List of Tables Chapter 1. Introduction 1.1 Typical Bond Dissociation Energies .. ............... .. ...... ... 3 1.2 Properties ofthe n~1t* and 7t~7t* States .. ...... .. .. .... ... .. .. 9 1.3 Properties ofBenzimidazole-Based Fungicides .... ............ ... .. 17 Chapter 4. Results and Discussion 4.1 "-max Values ofBenzimidazole and Benzimidazole-Based Fungicides .........3 8 4.2 Rf Values for Benomyl Products ...... ... .. .. .. ... 51 4.3 NMR Data of Benomyl Degradation Product . 51 4.4 IR Data ofBenomyl Degradation Product ............ ... ....... .. 54 4.5 NMR Data ofFraction 2 of Thiabendazole Degradation .................. 56 4.6 IR Data ofFraction 2 of Thiabendazole Degradation ......... .... .. .. 62 4.7 NMR Data ofUnknown of Thiabendazole Degradation ..................62 4.8 IR Data ofUnknown of Thiabendazole Degradation .... .... .. ..... .67 XI Chapter 1 Introduction