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Photochemistry of Chlorinated and Brominated
Diaryl Ether Environmental Contaminants
by
Sierra Rayne
B.Sc., Okanagan University College, 2000
A Dissertation Submitted in Partial Fulfillment of the
Requirements for the Degree of
DOCTOR OF PHILOSOPHY
in the Department of Chemistry
We accept this thesis as conforming to the required standard

Dr. P.C. Wan, Supervisor (Department of Chemistry)

Dr. D.J. Berg, Departmental Member (Department of Chemistry)

Dr. T.M. Fyles, Departmental Member (Department of Chemistry)

Dr. C.C. Helbing, Outside Member (Department of Biochemistry and Microbiology)

Dr. N. Bunce, External Examiner
(Department of Chemistry and Biochemistry, University of Guelph)
© Sierra Rayne, 2005
University of Victoria
All rights reserved. This dissertation may not be reproduced in whole or in part, by
photocopying or other means, without the permission of the author.

ii
Supervisor: Dr. Peter C. Wan
ABSTRACT
There is a need to better understand the fate of natural and anthropogenic organic
materials being released into terrestrial, aquatic, and atmospheric systems. For
halogenated aromatic compounds, environmental degradation via biological pathways is
generally ineffective. Hence, abiotic methods of transformation – including photolysis –
often play a significant role in the overall environmental fate of these compounds.
Among the various potential halogenated aromatic compounds for study, those with a
diaryl ether nucleus have been found to be of particular utility in industry, and are known
to be the stable products of a wide range of natural and anthropogenic processes. The
present work describes photochemical investigations on two representative classes of
diaryl ether contaminants – (1) chlorinated dibenzo[1,4]dioxins and representative model
analogs, and (2) brominated diphenyl ethers .

In order to better understand the underlying photochemistry of chlorinated
dibenzo[1,4]dioxins, photochemical studies on a range of model halogenated, alkoxy, and
alkyl dibenzo[1,4]dioxins have been performed in aqueous and organic solutions. The
compounds were found to undergo a photochemically initiated aryl-ether bond homolysis
that yields reactive 2-spiro-6’-cyclohexa-2’,4’-dien-1’-one and subsequent 2,2’biphenylquinone intermediates. Under steady-state irradiation, the 2,2’-biphenylquinones
were observed to participate in excited state hydrogen abstraction from the organic
solvent to give corresponding 2,2’-dihydroxybiphenyls. In the absence of continued
irradiation, 2,2’-biphenylquinones with electron donating substituents thermally

iii
rearrange to corresponding oxepino[2,3-b]benzofurans, whereas the unsubstituted 2,2’biphenylquinone and its derivatives with electron withdrawing groups thermally
rearrange to corresponding 1-hydroxydibenzofurans. The findings represent a possible
general photochemically initiated mechanism for the degradation of dibenzo[1,4]dioxins,
including the highly toxic chlorinated derivatives, that may shed insight into their fate in
natural systems and potential mechanisms for toxicological action.

The photochemistry of model brominated diphenyl ethers has been investigated in
organic and aqueous solution. These findings suggest that para brominated diphenyl
ethers with 1 or 2 bromine substituents will likely undergo exclusive photochemically
induced aryl-bromine bond homolysis in aqueous or organic solvents, followed by
hydrogen abstraction from organic solvents or similar impurities in natural aquatic
systems. No evidence of photochemical aryl-ether bond cleavage was observed with the
model para substituted mono- and di-brominated diphenyl ethers. In contrast, the
observed formation of brominated dibenzofurans and 2-hydroxybiphenyls from the
photolysis of a model hexabrominated diphenyl ether suggests that brominated diphenyl
ethers with >6 bromine substituents will undergo both photochemically induced arylether and aryl-bromine bond homolysis in organic solvents. When the brominated
diphenyl ether starting material has a bromine substituent in the ortho position relative to
the ether linkage, the findings demonstrate that photochemical aryl-bond homolysis can
lead to the production of brominated dibenzofurans.

Supervisor: Dr. P.C. Wan, (Department of Chemistry)

iv

Dr. P.C. Wan, Supervisor (Department of Chemistry)

Dr. D.J. Berg, Departmental Member (Department of Chemistry)

Dr. T.M. Fyles, Departmental Member (Department of Chemistry)

Dr. C.C. Helbing, Outside Member (Department of Biochemistry and Microbiology)

Dr. N. Bunce, External Examiner
(Department of Chemistry and Biochemistry, University of Guelph)

v
TABLE OF CONTENTS
ABSTRACT.....................................................................................................................................ii
TABLE OF CONTENTS................................................................................................................. v
LIST OF TABLES.........................................................................................................................vii
LIST OF FIGURES ........................................................................................................................ix
LIST OF SCHEMES.....................................................................................................................xiv
LIST OF IMPORTANT ABBREVIATIONS................................................................................ xv
LIST OF STRUCTURES ............................................................................................................. xvi
CHAPTER 1 - INTRODUCTION................................................................................................... 1
1.1

Fundamentals of Environmental Photochemistry........................................................... 1

1.2
Dibenzo[1,4]dioxins ....................................................................................................... 4
1.2.1 General ....................................................................................................................... 4
1.2.2 Photochemistry........................................................................................................... 5
1.3
Brominated Diphenyl Ethers ........................................................................................ 23
1.3.1 General ..................................................................................................................... 23
1.3.2 Photochemistry......................................................................................................... 27
1.4

Proposed Research........................................................................................................ 30

CHAPTER 2 - PHOTOCHEMISTRY OF DIBENZO[1,4]DIOXINS .......................................... 34
2.1

Materials ....................................................................................................................... 34

2.2

Photoproduct Studies.................................................................................................... 36

2.3

UV-Vis Studies............................................................................................................. 60

2.4

Thermal Reactivity of the 2,2’-Biphenylquinones ....................................................... 72

2.5

Photochemical Reactivity of the 2,2’-Biphenylquinones ............................................. 89

2.6

Laser Flash Photolysis.................................................................................................. 92

2.7

Proposed Mechanism.................................................................................................. 115

2.8

Conclusions ................................................................................................................ 117

vi
CHAPTER 3 – PHOTOCHEMISTRY OF BROMINATED DIPHENYL ETHERS ................. 119
3.1

Materials ..................................................................................................................... 119

3.2
Product Studies........................................................................................................... 119
3.2.1 Photochemistry of 115 ........................................................................................... 119
3.2.2 Photochemistry of 41 ............................................................................................. 129
3.2.2.1
Photodegradation Kinetics and Product Identification/Quantification.......... 129
3.2.2.2
Photodebromination Product Distributions. .................................................. 146
3.2.2.3
Photochemical Formation of Brominated Dibenzofurans and 2Hydroxybiphenyls........................................................................................................... 153
3.3

Proposed Mechanism.................................................................................................. 162

3.4

Conclusions ................................................................................................................ 166

CHAPTER 4 - EXPERIMENTAL .............................................................................................. 168
4.1

General ....................................................................................................................... 168

4.2
Materials ..................................................................................................................... 169
4.2.1 Common Laboratory Reagents............................................................................... 169
4.2.2 Commercially Available Materials ........................................................................ 169
4.2.2.1
General .......................................................................................................... 169
4.2.2.2
Dibenzo[1,4]Dioxin Systems ........................................................................ 170
4.2.2.3
2,2’-Dihydroxybiphenyl Systems.................................................................. 170
4.2.2.4
Diphenyl Ether Systems ................................................................................ 170
4.2.3 Synthesis ................................................................................................................ 171
4.2.3.1
General .......................................................................................................... 171
4.2.3.2
Dibenzo[1,4]Dioxin Systems ........................................................................ 171
4.2.3.3
2,2’-Biphenylquinone Systems...................................................................... 174
4.3
Product Studies........................................................................................................... 175
4.3.1 Photochemical Product Studies.............................................................................. 175
4.3.1.1
General .......................................................................................................... 175
4.3.1.2
Results of Product Studies............................................................................. 177
4.3.1.2.1 Dibenzo[1,4]Dioxin Systems .................................................................... 177
4.3.1.2.2 2,2’-Biphenylquinone Systems ................................................................. 198
4.3.1.2.3 Diphenyl Ether Systems............................................................................ 198
4.3.2 Thermal Product Studies ........................................................................................ 213
4.4

UV-Vis Studies........................................................................................................... 214

4.5

Laser Flash Photolysis................................................................................................ 215

Acknowledgements...................................................................................................................... 218
References.................................................................................................................................... 220

vii
LIST OF TABLES

Table 2.1. Contributions of the individual 2,2’-dihydroxybiphenyl, dibenzo[1,4]dioxin,
and 2-phenoxyphenol analytes towards the photochemical mass balance of 3 in H2O
after 60 min irradiation. ............................................................................................ 56
Table 2.2. Contributions of the major photoproduct classes towards the photochemical
mass balance of 3 after 60 min irradiation in 19:1 (v/v) H2O:CH3CN and H2O. ..... 57
Table 2.3. Hammett constants used in the current work.................................................. 68
Table 2.4. Σσ+ and Σσ values for the 2,2’-biphenylquinones used in constructing Figure
2.10 and Figure 2.11. ................................................................................................ 68
Table 2.5. Σσ values for the 2,2’-biphenylquinones used in constructing Figure 2.12 and
Figure 2.13. ............................................................................................................... 75
Table 2.6. Rate constants (in s-1) and deuterium isotope effects for the first-order thermal
decays of 16, 19, 26, 28, and 75 in acetonitrile (kH) and acetonitrile-d3 (kD). Error
bars are the range of duplicate trials. ........................................................................ 86
Table 2.7. Rate constants (in s-1) and deuterium isotope effects for the first-order thermal
decays of 16, 19, 26, 28, and 75 in benzene (kH) and benzene-d6 (kD). Error bars are
the range of duplicate trials....................................................................................... 87
Table 2.8. Rate constants (in s-1) and deuterium isotope effects for the first-order thermal
decays of 16, 19, 26, 28, and 75 in toluene (kH) and toluene-d8 (kD). Error bars are
the range of duplicate trials....................................................................................... 87
Table 2.9. F and R values for the 2-spiro-6’-cyclohexa-2’,4’-dien-1’-ones used in the
Swain-Lupton modeling approach.......................................................................... 104
Table 2.10. Sum of the field (F) and resonance (R) substituent constants and absolute
and relative pseudo first-order rate constants for the rearrangement of 18, 24, 25, 27,
111, 112, and 113 into the corresponding 2,2’-biphenylquinones used in the SwainLupton modeling approach. .................................................................................... 104
Table 2.11. Activation energies (Ea) and log10 pre-exponential factors (log A) for the
rearrangements of 2-spiro-6’-cyclohexa-2’,4’-dien-1’-ones 18, 24, 25, and 111 into
the corresponding 2,2’-biphenylquinones in CH3CN. Error bars on Ea and log A are
95% confidence intervals about the mean. Because of the logarithmic method by
which A is determined in the Arrhenius plots, conventional plus/minus error bars on
A cannot be assigned. ............................................................................................. 112
Table 4.1. Absolute quantities (in pg; uncorrected for the recovery standard) of 3 and its
mono- through tri-chlorinated photodechlorination products over the course of a 60
min irradiation period in 19:1 CH3CN:H2O (v/v). Percent recoveries of the 13Clabeled recovery standard (13C-3) are also shown. ................................................. 188
Table 4.2. Absolute quantities (in pg; uncorrected for the recovery standard) of monothrough tetra-chlorinated 2,2’-dihydroxybiphenyl photoproducts of 3 over the course
of a 60 min irradiation period in 19:1 CH3CN:H2O (v/v). Percent recoveries of the
13
C-labeled recovery standard (13C-3) are also shown............................................ 194
Table 4.3. Absolute quantities (in pg; uncorrected for the recovery standard) of monothrough tetra-chlorinated 2-phenoxyphenol photoproducts of 3 over the course of a

viii
60 min irradiation period in 19:1 CH3CN:H2O (v/v). Percent recoveries of the Clabeled recovery standard (13C-3) are also shown. ................................................. 197
Table 4.4. Absolute quantities (in pg; uncorrected for recovery standards) of 41 and its
penta- and tetra-brominated photodebromination products over the course of a 60
min irradiation period in 100% CH3CN. Percent recoveries of the three 13C-labeled
recovery standards are also shown.......................................................................... 205
Table 4.5. Absolute quantities (in pg; uncorrected for recovery standards) of 41 and its
penta- and tetra-brominated photodebromination products over the course of a 5 min
irradiation period in 100% CH3CN. Percent recoveries of the three 13C-labeled
recovery standards are also shown.......................................................................... 206
Table 4.6. Absolute quantities (in pg; uncorrected for recovery standards) of 41 and its
penta- and tetra-brominated photodebromination products over the course of a 5 min
irradiation period in 100% H2O. Percent recoveries of the three 13C-labeled recovery
standards are also shown......................................................................................... 207
Table 4.7. Absolute quantities (in pg; uncorrected for recovery standards) of 41 and its
penta- and tetra-brominated photodebromination products over the course of a 5 min
irradiation period in seawater. Percent recoveries of the three 13C-labeled recovery
standards are also shown......................................................................................... 208
Table 4.8. Absolute quantities (in pg; uncorrected for recovery standards) of 41 and its
pentabrominated photodebromination products over the course of a 15 min
irradiation period in 100% CH3CN under solar irradiation. Note that no
tetrabrominated diphenyl ethers photoproducts were detected over the irradiation
period. Percent recoveries of the three 13C-labeled recovery standards are also
shown. ..................................................................................................................... 209
Table 4.9. Absolute quantities (in pg; uncorrected for recovery standard) of the
brominated dibenzofuran photoproducts following a 1 min irradiation period (302
nm) of 41 in 100% dry CH3CN. The percent recovery of the 13C-42 recovery
standard was 72%. .................................................................................................. 211
13

ix
LIST OF FIGURES

Figure 1.1. Literature convention numbering system for substituted dibenzo[1,4]dioxins.
................................................................................................................................... 19
Figure 2.1. Contributions of the individual 2,2’-dihydroxybiphenyl photoproducts
towards the overall photochemical mass balance for 3 over a 60 min irradiation
period in 19:1 (v/v) H2O:CH3CN: 10 ({), 57 (…), 63 (isomer 1) (‹), 63 (isomer 2)
(S), 64 (z), and 58 („). Error bars show the range of duplicate photolyses where
available. ................................................................................................................... 45
Figure 2.2. Contributions of the individual dechlorination photoproducts towards the
overall photochemical mass balance for 3 over a 60 min irradiation period in 19:1
(v/v) H2O:CH3CN: 9 ({), 30 (…), 59 (‹), 115 (S), 61 (z), and 62 („). Error bars
show the range of duplicate photolyses where available. ......................................... 49
Figure 2.3. Contributions of the individual 2-phenoxyphenol photoproducts towards the
overall photochemical mass balance for 3 over a 60 min irradiation period in 19:1
(v/v) H2O:CH3CN: 12 ({), 65 (‹), 66 (S), 67 („), and 68 (z). Error bars show the
range of duplicate photolyses where available. ........................................................ 50
Figure 2.4. Solution mass balance ({) and contributions of unreacted starting material
(…), the sum of photodechlorination photoproducts (‹), the sum of 2,2dihydroxybiphenyl photoproducts (S), and the sum of 2-phenoxyphenol
photoproducts (z) towards the overall photochemical mass balance for 3 over a 60
min irradiation period in 19:1 (v/v) H2O:CH3CN. Error bars show the range of
duplicate photolyses where available........................................................................ 52
Figure 2.5. UV-Vis spectra taken at 60 s intervals following photogeneration of 16 in dry
CH3CN. Inset shows transient decay traces taken at 10 s intervals at the λmax=522
nm of the 2,2’-biphenylquinone. The intensity of the absorption band at λmax=522
decreased continuously over the monitoring period. ................................................ 61
Figure 2.6. UV-Vis spectra taken at 60 s intervals following photogeneration of 75 in dry
CH3CN. Inset shows transient decay traces taken at 10 s intervals at the λmax=548
nm of the 2,2’-biphenylquinone. The intensity of the absorption band at λmax=548
decreased continuously over the monitoring period. ................................................ 62
Figure 2.7. UV-Vis spectra taken at 60 s intervals following photogeneration of 26 in dry
CH3CN. Inset shows transient decay traces taken at 10 s intervals at the λmax=530
nm of the 2,2’-biphenylquinone. The intensity of the absorption band at λmax=530
decreased continuously over the monitoring period. ................................................ 63
Figure 2.8. UV-Vis spectra taken at 60 s intervals following photogeneration of 28 in dry
CH3CN. Inset shows transient decay traces taken at 10 s intervals at the λmax=607
nm of the 2,2’-biphenylquinone. The intensity of the absorption band at λmax=607
decreased continuously over the monitoring period. ................................................ 64
Figure 2.9. UV-Vis spectra taken at 60 s intervals following photogeneration of 19 in dry
CH3CN. Inset shows transient decay traces taken at 10 s intervals at the λmax=566
nm of the 2,2’-biphenylquinone. The intensity of the absorption band at λmax=566
decreased continuously over the monitoring period. ................................................ 65


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