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  • Laser Copyrolysis of Chlorofluorocarbons with

    Metal Systems in the Gas Phase

    Grant Allen

    A dissertation submitted in partial fulfilment of the requirements for the degree

    of Bachelor of Science with Honours in Chemistry

    University of Auckland

    1996

  • ii

    Abstract

    The reaction mechanisms of the gas phase decomposition of Freon 12 (CF2Cl2), Freon

    22 (CF2HCl) and dichloromethane (CH2Cl2), induced by Infrared Laser Powered

    Homogeneous Pyrolysis (IR LPHP), are investigated and compared with

    decomposition when a volatile transition metal carbonyl compound is also present.

    The introduction of either Fe(CO)5 or W(CO)6 to each of the systems under study is

    found to alter the mechanism of decomposition with respect to that of the substrate

    alone. Halogen abstraction, (where the abstracting species, M(CO)x, is the product of

    metal carbonyl decomposition) occurs in preference to that mechanism normally

    associated with the decomposition of the selected compound.

    Freon 12 is found to decompose to the major product CF3Cl. In the presence of either

    Fe(CO)5 or W(CO)6, Freon 12 decomposes to give C2Cl2F4 and C2F4. The

    decomposition of Freon 22 is found to involve the elimination of HCl. Subsequent

    dimerisation of the resultant CF2 species yields C2F4. In the presence of either

    Fe(CO)5 or W(CO)6, the decomposition of Freon 22 does not involve the formation of

    either HCl or C2F4, suggesting an alternative mechanism. An initial Cl abstraction is

    proposed. Similarly the decomposition of dichloromethane in the presence of either

    Fe(CO)5 or W(CO)6, is found to yield products dissimilar to those obtained from the

    decomposition of dichloromethane alone. An initial Cl abstraction is occurring in

    preference to the elimination of HCl.

  • iii

    Statement of Originality

    The work presented herein contains no material that has been accepted for the award

    of any other degree or diploma at any university, and to the best of my knowledge

    contains no material previously published by another person except where due

    reference is made in the text.

    Grant Allen

  • iv

    Acknowledgements

    The author would like to express his gratitude to those people, without whose help,

    this dissertation would not have been possible. In particular Professor Douglas

    Russell, for his untiring assistance and enthusiasm, and to Dr Rebecca Berrigan for

    her constructive insight. Many thanks are also extended to those fellow researchers,

    namely Fergus Binnie, Janet Everett, Nathan Hore and to our technician Dr Noel

    Renner.

  • v

    Contents

    Abstract .... ii

    Statement of Originality .......................................................................................... iii

    Acknowledgements .................................................................................................. iv

    Contents ................................................................................................................... v

    List of Figures .......................................................................................................vii

    List of Tables ............................................................................................................ viii

    Chapter 1. Introduction ............................................................................... 1

    1.1 References and Notes for Chapter 1 .............................................. 5

    Chapter 2. Experimental ............................................................................. 6

    2.1 Introduction .............................................................................................. 6

    2.2 Infrared Laser Powered Homogeneous Pyrolysis ..............................6

    2.3 Equipment ..............................................................................................7

    2.3.1 Vacuum Line

    2.3.2 Pyrolysis Cell

    2.3.3 Window Material

    2.3.4 Photosensitiser

    2.3.5 CO2 Laser

    2.4 Chemicals.................................................................................................. 13

    2.5 Experimental Procedure ......................................................................... 13

    2.5.1 Introduction

    2.5.2 Procedure for Sample Preparation

    2.5.3 Pyrolysis Setup

    2.6 Experimental Analysis ......................................................................... 15

    2.6.1 Introduction

    2.6.2 Fourier Transform Infrared Spectroscopy

    2.6.3 Matrix Isolation ESR Spectroscopy

    2.6.4 X-ray Photoelectron Spectroscopy

    2.6.5 Attenuated Total Reflectance

    2.7 References and Notes for Chapter 2 ....................................................... 18

  • vi

    Chapter 3. Pyrolysis Results and Discussion ............................................. 19

    3.1 Introduction .............................................................................................. 19

    3.2 IR LPHP of Freon 12................................................................................ 19

    3.2.1 Literature

    3.2.2 Experimental

    3.3 IR LPHP of Freon 22 ............................................................................... 24

    3.3.1 Literature

    3.3.2 Experimental

    3.4 IR LPHP of Dichloromethane ................................................................ 26

    3.5 IR LPHP of Transition Metal Carbonyl Compounds .......................... 30

    3.5.1 Introduction

    3.5.2 IR LPHP of Fe(CO)5

    3.5.3 IR LPHP of W(CO)6

    3.6 References and Notes for Chapter 3 ....................................................... 33

    Chapter 4. Copyrolysis Results and Discussion ........................................ 34

    4.1 Introduction .............................................................................................. 34

    4.2 Copyrolysis of Freon 12 with Fe(CO)5 ................................................... 34

    4.3 Copyrolysis of Freon 12 with W(CO)6 ................................................... 36

    4.4 Copyrolysis of Freon 22 with Fe(CO)5 ................................................... 44

    4.5 Copyrolysis of Freon 22 with W(CO)6 ................................................... 45

    4.6 Copyrolysis of Dichloromethane with Fe(CO)5 .................................... 47

    4.7 Copyrolysis of Dichloromethane with W(CO)6 .................................. 48

    4.8 References and Notes for Chapter 4 .................................................. 49

    Chapter 5. Conclusions and Future Work ................................................ 50

  • vii

    List of Figures

    1.1 The Cl free-radical catalysis of O3 decomposition as proposed by Molina

    and Rowland ................................................................................................. 1

    1.2 The role of polar stratospheric clouds in ozone depletion ............................... 3

    1.3 Mechanism of reaction between atomic potassium and a halogenated

    compound, RX ................................................................................................. 4

    2.1 Schematic diagram of the conventional pyrolysis cell ................................. 8

    2.2 Schematic diagram of the pyrolysis cell used for ATR analysis ..................... 9

    2.3 Energy level diagram for the CO2 laser ........................................................... 11

    2.4 Schematic diagram of the ATR setup .............................................................. 17

    3.1 The decomposition scheme of CF2Cl2 as proposed by Zitter et al .................. 20

    3.2 The decomposition scheme of CF2Cl2 as proposed by Hill et al ..................... 21

    3.3 FTIR spectra of Freon 12 before and after IR LPHP ....................................... 22

    3.4 The proposed high temperature decomposition scheme of CF2Cl2.................. 23

    3.5 The decomposition scheme of CF2HCl ........................................................... 24

    3.6 FTIR spectra of Freon 22 before and after IR LPHP ....................................... 25

    3.7 The decomposition scheme of CH2Cl2 ............................................................ 27

    3.8 FTIR spectra of CH2Cl2 before and after high temperature IR LPHP ............. 28

    3.9 The decomposition scheme of CH2Cl2 in the presence of oxygen .................. 29

    3.10 ATR/FTIR spectrum of a film deposited after W(CO)6 pyrolysis ................... 32

    4.1 FTIR spectra of Freon 12 with W(CO)6 before and after IR LPHP ................. 38

    4.2 The decomposition scheme of CF2Cl2 ............................................................. 39

    4.3 XPS spectrum of a film deposited after Freon 12/W(CO)6 copyrolysis .......... 41

    4.4 XPS spectrum of the W 4f photoelectrons ....................................................... 42

    4.5 ATR/FTIR spectrum of a film deposited after Freon 12/W(CO)6

    copyrolysis ....................................................................................................... 43

    4.6 FTIR spectra of Freon 22 with W(CO)6 before and after IR LPHP ................ 46

  • viii

    List of Tables

    2.1 Aperture diameters ........................................................................................... 12

    2.2 Chemicals u

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