In presenting the dissertation as a partial fulfillment of the requirements for an advanced degree from the Georgia Institute of Technology, I agree that the Library of the Institute shall make it available for inspection and circulation in accordance with its regulations governing materials of this type. I agree that permission to copy from, or to publish from, this dissertation may be granted by the professor under whose direction it was written, or, in his absence, by the Dean of the Graduate Division when such copying or publication is solely for scholarly purposes and does not involve potential financial gain. It is under­ stood that any copying from, or publication of, this dis­ sertation which involves potential financial gain will not be allowed without written permission. 7/2^/68 THE REACTION OF ATOMIC OXYGEN WITH ORGANIC COMPOUNDS A THESIS Presented to The Faculty of the Graduate Division by Arthur Joseph Mosher In Partial Fulfillment of the Requirements for the Degree Doctor of Philosophy in the School of Chemistry Georgia Institute of Technology March 1970 THE REACTION OF ATOMIC OXYGEN WITH ORGANIC COMPOUNDS Approved: Uhaiaraan •9 Date Approved by Chairman ACKNOWLEDGMENTS I would like to thank Dr. Erling Grovenstein, Jr. for acting as my research advisor; without his penetrating analysis this thesis would not have been possible. I would also thank Drs. Thomas F. Moran and Charles J_. Liotta for serving on the reading committee. Discussions with the latter were quite beneficial to this thesis. Special recognition is due to John McKelvey, whose exciting mind and cheerful disposition are a source of inspiration to all. Dr. Robert A. Pierotti is also to be thanked for patient application of his pedagogical ability. The National Center for Air Pollution Control supplied extensive financial support. My parents and sisters deserve special mention for their un­ failing confidence in my abilities and their prayers which helped me complete this work. Fellow students and friends are also to be thanked for both help and the pleasure of their company. The James Graham family provided both culinary and secretarial assistance. Among the least known contributors to this thesis are the warm people who re­ peatedly went out of their way to lend support. The secretaries (especially W. C. and E. B.), librarians (especially A. E. and F. K.) and chemistry staff (especially D. L. and M. R. ) are to be commended. But there remains one whom must not go unmentioned; one who contributed to my welfare as only a woman can. I would thank Red. TABLE OF CONTENTS Page ACKNOWLEDGMENTS ii LIST OF TABLES vi LIST OF FIGURES viii SUMMARY ix CHAPTER I INTRODUCTION AND HISTORICAL BACKGROUND Ground State Atomic Oxygen, O(^P) 1 Excited Atomic Oxygen, 0(-*-D) 9 Atomic Oxygen from Electrical Discharges .... 14 II REAGENTS AND MATERIALS Organic Substrates 18 Gases 19 Products of Oxidation 20 Solvents 28 GLC Columns 30 III EXPERIMENTAL TECHNIQUES Mercury Photosensitized Decomposition of N2O . 35 Microwave Glow Discharge 40 Photolysis of Nitrogen Dioxide 44 Photolysis of Ozone 45 Photolysis of Nitrous Oxide 47 Kinetic Isotope Effect 47 Product Analysis 48 IV THE REACTION OF 0(3P) WITH AROMATICS AT 30°C Product Distribution in Neat Hydrocarbons .... 51 Relative Reactivity Runs and Partial Rate Factors . 63 V THE REACTION OF 0(3P)WITH AROMATICS AT 100°C Product Distribution in Neat Hydrocarbons .... 71 Relative Reactivity and Partial Rate Factors ... 75 Nitrobenzene Oxidations 75 iv CHAPTER Page VI MISCELLANEOUS OXIDATIONS OF AROMATIC COMPOUNDS Microwave Discharge 81 Photolysis of NOz 89 Photolysis of O3 91 VII OXIDATION OF ALIPHATIC COMPOUNDS Cyclohexene 93 Cyclohexane 96 Propane and n-Butane 102 VIII DISCUSSION Reaction of 0( P) with Aromatic Compounds at 30°C Product Distribution of Neat Hydrocarbons .... 104 Relative Reactivity Runs and Partial Rate Factors. 109 Correlation of Partial Rate Factors with (7~+. 115 Ortho Partial Rate Factors 117 Test of Additivity Principle for Polymethylbenzenes 119 Free Energy Correlations with Related Reactions . 122 Molecular Orbital Calculations 126 Kinetic Isotope Effect and Postulated Mechanism . 129 Reaction of 0(3P) with Aromatic Compounds at 100°C Product Distribution in Neat Hydrocarbons .... 132 Relative Reactivities and Partial Rate Factors . 133 Nitrobenzene 136 Free Energy Quantities 142 Microwave Glow Discharge Product Distributions 143 Variation of Products with Travel Time and Temperature 147 Lifetimes of Atomic Oxygen 152 Miscellaneous Oxidations of Toluene 157 Oxidation of Non-Aromatic Compounds Cyclohexene 161 Cyclohexane 163 Propane and n-Butane 165 IX RECOMMENDATIONS FOR FUTURE WORK Kinetic Isotope Effects 166 Nitrobenzene System 167 Identification of Possible Products I69 Identity of Oxygen Atoms from mgd 170 0(3P) Oxidations at 100°C 172 V APPENDICES Page 1 KINETIC ISOTOPE EFFECT Hydrocarbon Ratio 174 Phenol Ratio 177 2 PRODUCT YIELD OF TOLUENE - 0(3P) RUN ... 180 3 RELATIVE REACTION RATES TOWARD 0(3P) Derivation of Rate Equation 185 Sample Calculation of Relative Reactivity 187 Sample Calculation of Partial Rate Factors 189 Derivation of Alternate Rate Equation 191 BIBLIOGRAPHY 196 VITA 202 vi LIST OF TABLES Table Page 1 Hydrocarbons Used 18 2 Gases 19 3 GLC Standards 20 4 GLC Columns Used 30 5 Separation of Parent Hydrocarbons 50 6 Experimental Quantities at 30°C for Relative Rate Equation 66 7 Relative Rate Data for Mono substituted Benzenes at 30°C 68 8 Relative Rate Data for Methylbenzenes at 30°C . 69 9 Total Reactivity of Methylbenzenes at Calculated from Toluene for C-H Insertion Only 7 0 o 10 Relative Rate Data for Aromatics at 100 C . 76 11 Experimental Data for Nitrobenzene Runs at 100°C 80 12 Toluene Yields at Different Travel Times .... 87 13 Partial Rate Factors From 0(3P) at 30°C .... 110 14 Calculated Electron Density of Aromatics .... 127 15 Partial Rate Factors From 0(3P) at 100°C . 134 16 Product Composition for Oxidation of Nitrobenzene 138 17 Toluene Product Distribution at Different Travel Times and Temperatures 148 vii LIST OF TABLES (Continued) Table Page 18 Apparent Lifetimes of Atomic Oxygen in a CO2 Atmosphere 156 19 Toluene Blank Runs 159 20 Oxidation Products of Aliphatic Compounds .... 162 21 Mass Spectral Intensities of Hydrocarbons in B-UV5. 176 22 Mass Spectral Intensities of Phenols in B-UV5 . 178 23 Sample Data of Toluene Yield 183 24 Summation of Data for T-UV99 184 viii LIST OF FIGURES Figure Page 1 Experimental Apparatus for Hg, N20 Runs 38 2 Experimental Apparatus for Microwave Glow Discharge Runs 42 3 Hammett Plot at 30°C 116 4 Logarithm (para-prf) vs. Logarithm (ortho-prf). ... 118 5 Logarithm [Experimental vs. Calculated Relative Reactivity for 0(3p)] ~ 120 6 Logarithm [Experimental vs. Calculated prf's for 0(3P)] ~~. 120 7 Logarithm (Relative Reactivity towards Cl2) vs. Logarithm [Relative Reactivity towards 0(3p)] Logarithm (Relative Stability of HC 1 complexes) vs. Logarithm [Relative Reactivity towards 0(3P)] .... 123 8 Logarithm (Relative Reactivity for Cl* ) vs. Logarithm [prf for 0(3P)] Logarithm (prf for C^H5# ) vs. Logarithm [prf for 0( P)] 125 9 Logarithm [prf for 0(3P)] vs. Calculated Electron Density 128 10 Hammett Plot at 100°C 135 11 Lifetimes of Atomic Oxygen 154 ix SUMMARY The purpose of this research was to study the reaction of hydro­ carbons with atomic oxygen; the major emphasis was placed on product determination and reaction rates. The majority of work concerned the oxidation of aromatic compounds with ground state atomic oxygen, 0( P). The experimental technique of choice was the mercury photosensitized decomposition of nitrous oxide at 2537J§; a flow system at atmospheric pressure and 30°C was found to be convenient for most aromatic com­ pounds studied. The compounds successfully oxidized were: benzene, toluene, ethylbenzene, tert-butylbenzene, ortho;- meta-and para-xylene, mesitylene, 1, 2, 3-trimethylbenzene, anisole, fluorobenzene, benzotri- fluoride and nitrobenzene. In every case the main products were phenols. When ortho-methyl groups were present, methyl cleavage (resulting in phenols) became an important reaction. No evidence for formation of anisoles was found in the most favorable case, that of 1, 2, 3-trimethylbenzene. After the identity of the primary volatile addition products had been established, kinetic analysis of the relative reactivity (and attend­ ant partial rate factors) was made. The logarithm of the partial rate factors gave a satisfactory Hammett relationship when plotted versus <7~+ constants; this confirms the electrophilic nature of oxygen atoms. IT WAS ALSO FOUND THAT THE LOGARITHM OF THE PARTIAL RATE FACTORS GAVE A FAIR STRAIGHT LINE WHEN PLOTTED AGAINST THE CALCULATED GROUND STATE ELECTRON DENSITIES OF THE AROMATIC HYDROCARBONS. THIS WAS INTERPRETED AS GOOD EVIDENCE FOR AN EARLY RATE-DETERMINING TRANSITION STATE IN THE 3 0( P) OXIDATION OF HYDROCARBONS. THE ACTIVATING EFFECT OF METHYL GROUPS WAS FOUND TO BE A FUNCTION OF THEIR POSITION AND NUMBER. A PLOT OF CALCU­ LATED REACTIVITY (BASED UPON TOLUENE) VERSUS THE EXPERIMENTAL REACTIVITY OF THE POLYMETHYLBENZENES AS ORDINATE GIVES A STRAIGHT LINE WITH A FALL- OFF FACTOR (SLOPE) OF 0. 84. LINEAR FREE ENERGY CORRELATIONS WITH RELATED REACTIONS WERE ALSO FOUND. D A KINETIC ISOTOPE EFFECT (~ OF 1. 14) WAS DETERMINED FOR AN EQUIMOLAR MIXTURE OF BENZENE AND DEUTEROBENZENE. THIS IS IN AGREE- 3 MENT WITH THE MECHANISM OF 0( P) OXIDATION OF BENZENE SHOWN BELOW: ,3 S SLOW FAST FAST +0( P) » -H- +H- OH (J -COMPLEX SINCE THE PARTIAL RATE FACTORS FOR 0( P) CORRELATE WELL WITH CALCULATED ELECTRON DENSITIES OF THE GROUND STATE HYDROCARBON, THE RE­ ACTION IS BELIEVED TO HAVE AN EARLY TRANSITION STATE. THE ABSENCE OF ANISOLES ARGUES FOR TWO FAST STEPS FOLLOWING ^"-COMPLEX FORMATION RATHER THAN AN INTRAMOLECULAR HYDROGEN SHIFT. HOWEVER, A ONE-STEP REARRANGE- XI MERIT FROM THE CT-COMPLEX TO THE PRODUCT PHENOL IS NOT RULED OUT. OXIDATION OF AROMATICS VIA A MICROWAVE GLOW DISCHARGE THROUGH C02> O^ OR N^O GAVE SUBSTANTIALLY DIFFERENT PRODUCT DISTRIBUTIONS THAN DID THE MERCURY-NITROUS OXIDE TECHNIQUE.