Enhanced photocatalytic dehalogenation of aryl halides by combined poly-p-phenylene (PPP) and TiO2 photocatalysts

Article abstract of DOI:10.1016/j.jphotochem.2016.11.024

The abundant energy provided by sunlight makes visible-light driven photoredox catalysis an attractive means of performing chemical transformations. Titanium dioxide (TiO₂) and conjugated polymers are semiconducting materials that have been used as photoredox catalysts. Driving electron transfer process with photoredox catalysts and visible light has become a powerful method for achieving efficient chemical transformations. However, titanium dioxide does not readily absorb visible light, and conjugated polymers have not been extensively studied as photoredox catalysts for organic transformations. In this work, TiO₂ and the conjugated polymer poly-p-phenylene (PPP) were successfully used as heterogeneous co-catalysts for the dehalogenation of some simple aryl halides using triethylamine as a sacrificial electron donor. While PPP alone exhibited some photocatalytic activity upon irradiation with visible light, the efficiency of dehalogenation was enhanced by the addition of titanium dioxide. No reaction was observed in the absence of both photocatalysts or when TiO₂ was used as the sole photocatalyst. The optimum operating parameters were examined.

Full text of DOI:10.1016/j.jphotochem.2016.11.024

Accepted Manuscript
Title: Enhanced Photocatalytic Dehalogenation of Aryl
Halides by Combined Poly-p-phenylene (PPP) and TiO2
Photocatalysts
Author: John T. Petroff II Anh H. Nguyen Alex J. Porter
Fraisher D. Morales Michael P. Kennedy David Weinstein
Hossam El Nazer Ryan D. McCulla
PII:
S1010-6030(16)30815-2
DOI:
Reference:
http://dx.doi.org/doi:10.1016/j.jphotochem.2016.11.024
JPC 10448
To appear in:
Journal of Photochemistry and Photobiology A: Chemistry
Received date:
Revised date:
Accepted date:
3-10-2016
16-11-2016
22-11-2016
Please cite this article as: John T.Petroff II, Anh H.Nguyen, Alex J.Porter, Fraisher
D.Morales, Michael P.Kennedy, David Weinstein, Hossam El Nazer, Ryan D.McCulla,
Enhanced Photocatalytic Dehalogenation of Aryl Halides by Combined Poly-p-
phenylene (PPP) and TiO2 Photocatalysts, Journal of Photochemistry and Photobiology
A: Chemistry http://dx.doi.org/10.1016/j.jphotochem.2016.11.024
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Enhanced Photocatalytic Dehalogenation of Aryl Halides by
Combined Poly-p-phenylene (PPP) and TiO2 Photocatalysts.
John T. Petroff II, Anh H. Nguyen, Alex J. Porter, Fraisher D. Morales, Michael P. Kennedy,
David Weinstein, Hossam El Nazer*1, Ryan D. McCulla*
Photochemistry Dept., National Research Centre, 33 El Bohouth St., Dokki-Giza - Egypt -
P.O. 12622. Email: dr_hosamnazer@yahoo.com.
3501 Laclede Ave., Department of Chemistry, Saint Louis University, St. Louis, MO 63103,
United States of America.
Graphical abstract
Highlights
 Irradiation of poly-p-phenylene (PPP) with visible light resulted in the
dehalogenation of aryl bromides and chlorides.
 Combining PPP with TiO2 accelerated the photocatalyzed dehalogenation of the
aryl halides.
 Irradiation TiO2 alone resulted in no dehalogenation of the aryl halides.
Abstract
The abundant energy provided by sunlight makes visible-light driven photoredox
catalysis an attractive means of performing chemical transformations. Titanium dioxide (TiO2)
and conjugated polymers are semiconducting materials that have been used as photoredox
catalysts. Driving electron transfer process with photoredox catalysts and visible light has
become a powerful method for achieving efficient chemical transformations. However, titanium
1

dioxide does not readily absorb visible light, and conjugated polymers have not been
extensively studied as photoredox catalysts for organic transformations. In this work, TiO2 and
the conjugated polymer poly-p-phenylene (PPP) were successfully used as heterogeneous co-
catalysts for the dehalogenation of some simple aryl halides using triethylamine as a sacrificial
electron donor. While PPP alone exhibited some photocatalytic activity upon irradiation with
visible light, the efficiency of dehalogenation was enhanced by the addition of titanium dioxide.
No reaction was observed in the absence of both photocatalysts or when TiO2 was used as the
sole photocatalyst. The optimum operating parameters were examined.
Keywords: Conjugated polymer photocatalyst; semiconductor photocatalyst; photoredox
catalysis
1. Introduction
Decreasing the environmental impact of organic reactions is a laudable objective that
has been taken up by many researchers.[1] One way to achieve this aim is to use an abundant
and renewable energy source, such as sunlight, to drive these reactions. Harnessing energy
from the visible region of the solar spectrum is attractive because most organic compounds do
not absorb visible light, which limits the occurrence of undesirable side reactions. For this
reason, photocatalysts that absorb visible light have the potential for numerous applications in
organic synthesis.
Visible-light driven photoredox catalysis has experienced a surge of interest since the
work by MacMillan, Stephenson, and Yoon was published in 2008 and 2009.[2-4] The use of
photoredox catalysts for organic transformations was made possible by the excellent stability,
visible light absorption, and redox properties of Ru(II) and Ir(III)polypyridine complexes.[5]
Irradiation of these organometallic complexes is typically used to induce electron transfer
2

reactions to generate reactive ion-radicals that subsequently transform into products. For
example, Ru(II) and Ir(III) complexes have been used to develop a tin-free methodology for the
generation of radicals from compounds with activated carbon-halogen bonds.[6]
The replacement of toxic tin hydrides with photoredox catalysts provides more benign
conditions for the generation of radicals. In 2009, the benefits of this methodology were
demonstrated through the reductive dehalogenation of alkyl bromides and chlorides by the visible-
light photocatalyst Ru(bpy)3Cl2.[4] Radical generation through reduction of the organic halide by the
reduced catalyst [Ru(I)] followed by hydrogen abstraction was suggested as the reaction
mechanism. The robustness of the method was soon exploited for radical cyclizations, malonate
addition to heterocycles, dehalogenation of vicinal halides, coupling with alkynes, coupling allylic
bromides, and as part of the total synthesis of (+)-Gliocladin C.[7-13] The versatility of generating
radicals from organohalides has prompted the investigation of organic photoredox catalysts capable
of facilitating dehalogenations.[14-16]
One limiting feature of the aforementioned reactions is the substrates must be activated
towards reduction. This limitation can be overcome by the use of photoredox catalysts with higher
reduction potential. Recently, this was demonstrated by the use of a poly-2-phenylpyridine Ir
complex used to generate radicals from unactivated alkyl, alkenyl, and aryl iodides.[17] Thus, more
substrates could be accessed with photoredox catalysts with even higher reduction potentials.
Inorganic semiconductors have been used as photocatalysts for water treatment and to a
lesser extent to drive organic reactions.[18] The irradiation of semiconductors excites electrons into
the conduction band and concomitantly produces holes in the valence band. This allows the
oxidation or reduction of adsorbed species with the proper redox potentials as shown in Scheme 1.
To catalyze organic reactions, photocatalytic systems are designed to take advantage of the
reactivity of the transient radical-anion (A-•) or radical-cation (D•+) to generate new products (P)
through unimolecular rearrangements or reactions with other species at the surface or in bulk
solution.
3

Semiconductor photocatalysts have been used for various organic transformations. [18]
Irradiation of the common inorganic semiconductor photocatalyst TiO2 is typically used for oxidative
transformations; however, unmodified TiO2 photocatalytic systems often suffer from poor selectivity.
For example, photocatalytic oxidation of benzene with commercial TiO2 leads to over-oxidation and
yields only 2% phenol.[19] This poor yield was slightly improved to 34% by using mesoporous TiO2.
[19] Also, the addition of Pd and Au as co-catalysts to TiO2 improved the yield of phenol to
~30%.[20] Improvement of the oxidation of alcohols to the corresponding aldehydes and ketones
has also been improved with modified TiO2.[21] Irradiation of aerated water containing 4-
methoxybenzyl alcohol and nanostructured TiO2, made by boiling an aqueous solution containing
TiCl4, produced the corresponding aldehyde with relatively good yields of the aldehyde (42% after
65% substrate conversion). Commercially available TiO2 (Degussa P25) yielded poorer results (12%
in 40% substrate conversion). This same oxidation was improved to 78% yield by the use of rhodium
ion-modified TiO2 as the photocatalyst.[22]
Compared to TiO2, which only has a moderate conduction band potential (–0.5 V vs. NHE),
the conjugated polymer poly(p-phenylene) (PPP) has a much higher conduction band potential of –
2.0 vs. NHE.[23] Electron transfer to an acceptor can only occur easily if the reduction potential of
the acceptor is less negative than the conduction band potential of the photocatalyst. Thus, PPP is
expected to be a much stronger reductive photocatalyst than TiO2 and most other inorganic
semiconductors. The potential use of conjugated polymer photocatalysts in synthetic applications
was illustrated by the visible-light driven pinacol coupling of benzaldehyde by using PPP as the
photoredox catalyst.[23-25] The reaction required the use of a sacrificial electron donor triethylamine
(Et3N) and was accelerated by the addition of Lewis and Brønsted acids.
One drawback of PPP system was the need for several days of irradiation for the reaction to
complete. While not used for organic transformation, improvement in the degradation of organics by
conjugated polymer and TiO2 nanocomposites has been observed. For example, polyaniline/TiO2
and poly(3-hexythiophene)/TiO2 nanocomposites were shown to improve the photocatalytic
degradation of phenol and methyl orange, respectively.[26,27] As detailed above, co-catalysts and
4

the formation of composites has been shown improve the photocatalytic performance of TiO2 and
PPP. These observation suggested use of PPP and TiO2 as co-catalysts or as part of a composite
could lead to an improvement in photocatalysis. In the present work, the photocatalytic
dehalogenation of some simple aryl halides was performed to test the hypothesis that an
increase in photocatalytic activity would be observed when PPP and TiO2 were used as co-
catalysts.
2. Methods and Materials
2.1 Materials: All aryl halides and solvents were obtained from Sigma-Aldrich Chemical
Company or Fisher Scientific and were used as received without further purification. The
solvents used were HPLC grade (99.9+%). Titanium (IV) oxide, anatase (98%) was purchase
from Acros chemical and was used as received.
2.2 Poly-(p-phenylene) preparation: Poly-(p-phenylene) was prepared using a procedure similar
to Yamamoto’s method.[28] Briefly, 1,4-dibromobenzene (11.8 g) and magnesium turnings (1.22
g) were combined in dry THF (40 mL) under a dry argon atmosphere and stirred at room
temperature for 1 hour. Next, 50 mg of Ni(bpy)Cl2 was added at room temperature. The reaction
was allowed to proceed at reflux for another 16-30 hours before being cooled to room
temperature. The reaction was quenched by adding the reaction mixture to ethanol (600 mL).
The resulting polymer solid was collected by filtration, and then washed sequentially with 0.1 M
HCl(aq), water, and ethanol prior to being dried under reduced pressure. The solids were purified
by Soxhlet extraction with toluene for 30 hours.
2.3 General photocatalytic reaction procedures: Photocatalytic reduction reactions were carried
out using a LZ4-X Luzchem Photoreactor with eight fluorescent bulbs generating approximately
5

70 W/m-2 from 400-440 nm. Reaction solutions were added to disposable borasillicate test tubes
and sealed with rubber septa. Prior to photolysis, all of the samples were sparged with argon for
at least 30 minutes and sonicated to break up the heterogeneous photocatalyst powder. During
the photoreaction, the samples were stirred and the temperature held constant at 25-30 ˚C. The
product analysis was performed using an Agilent 1200 Series HPLC fitted with a UV-Vis diode
array detector.
3. Results and Discussion
The addition of Brønstead acids had been shown to quicken the pinacol coupling of
simple aryl aldehydes using PPP. However, even with the addition of acid, the photoreaction of
benzaldehyde (107 mg) to hydrobenzoin still required 36 hours to reach an 81% isolated yield of
benzyl alcohol.[24,25] The long irradiation times were hypothesized to result from poor
adsorption of the substrates to the PPP surface.[24,25] Titanium dioxide has many
photocatalyst applications and often has good adsorption properties, and thus, it was posited
that using TiO2 as a co-catalyst would improve the performance of the PPP photocatalytic
system.
3.1 Optimization of catalyst loading. The dehalogenation of methyl 4-chlorobenozate (1) to
methyl benzoate (2) by PPP acting as the photoredox catalyst was chosen to test if the addition
of TiO2 as a co-catalyst would accelerate the reaction. In the typical photoreaction, a 5 mL
solution of acetonitrile containing 1 (9 mM), and triethylamine (1 M), was prepared in a glass
test-tube. The PPP and TiO2 were then added as insoluble powders. The effect of formic acid
(200 mM) on the reaction was also examined.
6

To examine the effect of TiO2, the initial rate of the reaction was estimated by
determining the concentration of 2 by HPLC after four hours of irradiation with different catalyst
loadings. A representative HPLC trace is shown in Figure 1. Each reaction was performed at
least three times, and the total amount of photocatalyst used was always equal to 6 mg. The
average concentration of 2 after four hours of irradiation is given in Table 1. In the absence of
PPP (Table 1, entries 9-12), 2 was not detected by HPLC. However, the formation of 2 was
detected after 4 hours of irradiation when only PPP was used as a photocatalyst (Table 1,
entries 1 & 2). This indicated that PPP itself was capable of acting as a photocatalyst for this
reaction. Compared to PPP alone, a mixture of PPP and TiO2 consistently yielded higher
concentrations of 2.
The optimal ratio of PPP to TiO2 for the production 2 was 1:1. When 3 mg of both PPP
and TiO2 was used, the measured concentrations of 2 after fours hours of irradiation were 1.0
and 1.4 mM in the absence and presence of formic acid, respectively. This was over three times
larger than for PPP alone, which yielded 0.29 and 0.4 mM of 2 in the absence and presence of
formic acid, respectively. Adjusting the ratio to favor PPP or TiO2 while keeping the total amount
of photocatalyst constant yielded less 2 (Table 1, entries 3,4,7, and 8). However, in both cases,
about double the amount of 2 was observed compared to PPP alone. As reflected in confidence
intervals, the variation of the measured concentrations of 2 from reaction to reaction was
relatively large for all of the different catalyst loadings.
7

The addition of formic acid resulted in the production of more 2 on average for a given
photocatalyst loading ratio. For example, at the optimal ratio of PPP to TiO2 (3 mg: 3 mg), 1.4
mM of 2 was generated when 200 mM of formic acid was added to the solution compared to
only 1.0 mM when formic acid was absent. These results were consistent with those observed
in the pinacol coupling of benzaldehyde; except in the present work, formic acid had a lesser
effect.[24] In fact, the 95% confidence intervals in some cases (Table 1, entries 5 & 6) indicated
that there was no significant difference with and without formic acid.
3.2 Effect of varied electron donor concentration. For semiconductor photoredox catalysts,
charge recombination of the electron promoted to the conduction band (e-cb) and the valence
band hole (h+vb) decreases the efficiency of photoredox catalysis. Therefore, increasing the
concentration of the sacrificial electron donor (Et3N) was expected to accelerate the reaction.
After four hours of irradiation, the concentration of 2 increased linearly with increasing
concentration of Et3N as shown in Figure 2. This result was consistent with the role of the
triethylamine acting as the primary electron donor in the photocatalyzed dehalogenation
reaction.
3.3 Dehalogenation of aryl chlorides and bromides with varied redox potentials. The initial
reaction optimization studies indicated that PPP catalyzed the dehalogenation of 1 by facilitating
electron transfer from the triethylamine to 1. Therefore, it was hypothesized that any aryl halide
with a reduction potential more positive than the conduction band potential of PPP (–2.0 vs.
NHE)[23] would undergo dehalogenation under these conditions. To test this hypothesis, aryl
halides with reported reduction potential values, which ranged from –2.16 to –1.15 V vs.
Ag/AgBr (Et4NBr supporting electrolyte),[29,30] were chosen to examine the effect of aryl halide
reduction potential on the photocatalytic dehalogenation reaction using PPP/TiO2 co-catalysts.
For the chosen aryl halides, all reported reduction potential values were determined using the
same Ag/AgBr system, in which the potential of the Ag/AgBr system was estimated at –520 mV
8

vs. SCE or –276 mV vs. NHE.[31,32] In addition to 1, the aryl halides (3-10) used in this study are
shown in Scheme 2.
The effect of aryl halide reduction potential was investigated using the general
photocatalytic reaction procedure described in the section 2.3. Experimental solutions were
composed of 1 M triethylamine, 200 mM formic acid, 3 mg of TiO2, 3 mg of PPP, and 10 mM
aryl halide in 5 mL of acetonitrile. Photolysis of each experimental solution was repeated a
minimum of three times. After irradiation, the concentration of the dehalogenated products was
determined. The results of these experiments are given in Table 2.
The salient result of these experiments was that aryl halides with a reduction potential
more negative than –1.5 V vs. Ag/AgBr did not undergo dehalogenation under these conditions
(Table 2, entries 1-4). Conversely, if the reduction potential of the aryl halide was more positive
than –1.5 V vs. Ag/AgBr, then the aryl halide underwent dehalogenation. As a point of
reference, the potential of PPP can be approximated as –1.7 V vs. Ag/AgBr.
The resulting dehalogenated products of 1,3-dibromobenzene (7), 4-chlorobenzonitrile
(8), methyl 4-chlorobenzoate (1), 4-bromobenzonitrile (9), and methyl 4-bromobenzoate (10) are
shown in Figure 3. All of these have a literature reported reduction potential at least 0.2 V more
positive than the conduction band potential of PPP. The inability of PPP/TiO2 to dehalogenate
aryl halides with reduction potentials more negative than –1.5 V vs Ag/AgBr indicates that PPP
initiates the dehalogenation by a single electron transfer to the aryl halide in the reactions
containing aryl halides 7-10 and 1. Single electron transfer to the aryl halides 3-5 from the
conduction band of PPP (–1.7 vs. Ag/AgBr) would be thermodynamically unfavorable, and thus, the
failure of 3-5 to dehalogenate was expected. Electron transfer to 6 (–1.54 V vs. Ag/AgBr) from the
conduction band of PPP should be thermodynamically favorable; however, the kinetics of this
9

reduction may not be slow when the potential difference between PPP and the aryl halide is smaller
than 0.2 V.
After 4 hours of irradiation, the average concentration of the resulting dehalogenated
product ranged from 0.92 to 1.8 mM for the aryl halides with reduction potentials more positive
than –1.5 V vs. Ag/AgBr (Table 2, entries 5-9). However, the significance of these differences
could not be established due to the large 95% confidence intervals relative to the determined
concentrations. The average concentrations and corresponding confidence intervals in Table 2
were calculated using data from three to five experiments. The relatively large errors associated
with the measured concentrations likely arise from the heterogeneous nature of the reaction
conditions.
Given the heterogeneous nature of the reaction solution, a scale up of the reaction to
give similar yields could not be assumed. Therefore, in order to test the scale-up potential, 150
mg of each respective reactant were irradiated with 420 nm light in a sonicated, rapidly stirring
mixture containing 6 mg PPP, 6 mg TiO2, and the appropriate concentrations of formic acid (200
mM) and Et3N (1 M) in acetonitrile totaling 5 mL. All samples were sparged with argon prior to
irradiation. This photoreaction took place in a 13 mm borosilicate test tube and lasted for one
month with each reaction giving a product with a yield between 31% and 79%. These yields
were only loosely correlated to the reduction potential of the reactants, likely because as the
magnitude of the reduction potential increases the yield decreases.
3.4 Mechanistic Implications. The increasing rate with additional sacrificial electron donor and
the dependence on the reduction of the aryl halides to undergo dehalogenation allow for the
inference that PPP acted as a photoredox catalyst in these reactions. This indicates the reaction
proceeds first by excitation of PPP, followed by electron transfer from Et3N to PPP, and then
from the PPP to the aryl halide, forming a radical-anion. The aryl halide radical-anion
dehalogenates by releasing a halide anion, resulting in the putative aryl radical. In a final step,
the aryl radical abstracts a hydrogen atom from the solvent or triethylamine. This proposed
10

process is depicted in Scheme 3. Although the presence of TiO2 does increase the rate of the
reaction, its exact role is unknown.
4. Conclusions: The conjugated polymer PPP and TiO2 were successfully used as
heterogeneous co-catalysts for the dehalogenation of aryl halides. Only aryl halides with
reduction potential values 0.2 V more positive than the conduction band potential of PPP
underwent dehalogenation. The rate of reaction increased with an increasing concentration of
the sacrificial electron donor triethylamine. The effect of 200 mM formic acid on the reaction was
unclear. Results were consistent with a mechanism involving a single electron transfer (SET)
from the PPP to the aryl halide, leading to the loss of a halide ion and the formation of the
corresponding radical, which subsequently yields the dehalogenation product via abstraction of
a hydrogen atom. While PPP exhibits some photocatalytic activity upon irradiation with visible
light, the rate of dehalogenation was enhanced by the addition of TiO2, though the exact role of
TiO2 is unclear at this time. No reaction was observed in absence of both photocatalysts or
when TiO2 was used as the sole photocatalyst, and the optimal ratio of PPP to TiO2 was 1:1.
Acknowledgements
This work is based upon work supported by the National Science Foundation under grant no.
(CHE-1255270). The authors thank the National Science Foundation for support under grant
CHE-0963363 for renovations to the research laboratories in Monsanto Hall. H.E.N. was
supported by the U.S. – Egypt Science and Technology Junior Scientist Visits Program.
11

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15

Figure 1. Representative HPLC trace of sample analyzed after 4 hours of irradiation carried out
at 420 nm on a 5 mL acetonitrile solution containing 9 mM 1, 1.5 mg of TiO2, 4.5 mg PPP, and
1M Et3N. Peaks at 1.652, 8.856, and 11.263 minutes are Et3N, 2, and 1, respectively.
16

Figure 2. Affect of Et3N concentration on the PPP/TiO2 photocatalyzed dehalogenation of
methyl 4-chlorobenozoate (1). Irradiations were carried out at 420 nm on 5 mL acetonitrile
solutions containing 9 mM 1, 200 mM formic acid, and 3 mg of TiO2 and PPP, and a variable
amount of Et3N. The concentration of 2 was after 4 hours of irradiation determined by HPLC
analysis.
17

Figure 3. Dehalogenation of aryl halides by TiO2/PPP photocatalysis
18

Scheme 1
19

Scheme 2
20

Scheme 3
21

Table 1. Optimization of catalyst loading for the dehalogenation of 1.a
Entry
1
Catalyst(s)
Formic acid (mM)
[2]b
6.0 mg PPP
0
0.29 ± 0.15c
0.4 ± 0.3c
0.5 ± 0.2c
0.9 ± 0.3c
1.0 ± 0.3c
1.4 ± 0.6c
0.34 ± 0.17c
0.8 ± 0.3c
n.d.d
2
6.0 mg PPP
200
0
3
4.5 mg PPP + 1.5 mg TiO2
4.5 mg PPP + 1.5 mg TiO2
3 mg PPP + 3 mg TiO2
3 mg PPP + 3 mg TiO2
1.5 mg PPP + 4.5 mg TiO2
1.5 mg PPP + 4.5 mg TiO2
6.0 mg TiO2
4
200
0
5
6
200
0
7
8
200
0
9
10
11
12
6.0 mg TiO2
200
0
n.d.d
n.d.d
n.d.d
None
None
200
a. Solutions containing formic acid, 1 M triethylamine, and 9 mM of MCB, and the photocatalysts
were sonicated and sparged with argon for 30 minutes prior to irradiation with eight 420 nm
bulbs. b.Concentration of methyl benzoate (2) after 4 hours of irradiation as determined by HPLC
analysis. c. 95% confidence intervals. d. not detected.
22

Table 2. Dehalogenation of aryl halides.a
Reduction
potential
Yieldc
Entry
Aryl halide
[product]b
-2.16d
-1.84d
-1.81d
-1.54d
-1.45d
-1.36d
-1.32e
-1.26d
n.d.f
--
1
2
3
4
5
6
7
8
9
4-chlorotoluene (3)
--
4-bromotoulene (4)
n.d.
--
4-bromobenzene (5)
n.d.
--
1,4-dibromobenzene (6)
1,3-dibromobenzene (7)
4-chlorobenzonitrile (8)
Methyl 4-chlorobenzoate (1)
4-bromobenzonitrile (9)
n.d.
56
31
39
79
68
1.4 ± 0.4
1.4 ± 0.5
1.4 ± 0.6
1.8 ± 0.9
0.92 ± 0.05
Methyl 4-bromobenzoate (10) -1.15d
a.
Irradiation of solutions containing 200 mM formic acid, 1 M triethylamine, and 9 mM of aryl
halide for four hours at 420 nm. Solutions were sonicated and sparged with argon for 30
minutes prior to irradiation. b. Concentration of dehalogenated product after 4 hours of irradiation
c.
as determined by HPLC analysis. Yield of dehalogenated product on large-scale reactions
d.
e.
(150 mg) in 13 mL of CH3CN. Reduction potential values from reference 25 vs. Ag/AgBr.
Reference 26. f. not detected.
23