Vanadium-catalysed oxidative bromination using dilute mineral acids and hydrogen peroxide: An option for recycling waste acid streams

Article abstract of DOI:10.1021/op000020l

Vanadium pentoxide, V₂O₅, catalyses the two-electron oxidation of Br^- to Br⁺, using aqueous hydrogen peroxide under dilute acidic conditions. In this system, kinetic studies show that HBr can be replaced with a combination of an alkali bromide salt (NaBr, KBr) and a dilute mineral acid (e.g., HCl, H₂SO₄, HNO₃, H₃PO₄). The salt/acid/peroxide system may be used for in situ or ex situ oxidative bromination, e.g. of various aromatic compounds. The application of the above concept towards the recycling of industrial acid waste is discussed. The cost effectiveness, E factors, and hazard factors for several bromination and oxidative bromination reagent systems are compared.

Full text of DOI:10.1021/op000020l

Organic Process Research & Development 2000, 4, 270−274
Vanadium-Catalysed Oxidative Bromination Using Dilute Mineral Acids and
Hydrogen Peroxide: An Option for Recycling Waste Acid Streams
Gadi Rothenberg and James H. Clark*
York Green Chemistry Group, Clean Technology Centre, Chemistry Department, The UniVersity of York,
Heslington, York YO10 5DD, UK
Abstract:
can reduce these risks. Several recent publications2a,4 cite
toxicity of Br and HBr as the incentive to investigate various
complex oxybromination reagents, but, in real life, two
situations have to be distinguished: (a) When molecular
bromine is available on-site (as in the Dead Sea Works in
Israel, for example), it is the cheapest and most enViron-
mentally friendly bromination reagent. Used in conjunction
Vanadium pentoxide, V
2 5
O
, catalyses the two-electron oxidation
2
-
+
of Br to Br , using aqueous hydrogen peroxide under dilute
acidic conditions. In this system, kinetic studies show that HBr
can be replaced with a combination of an alkali bromide salt
(NaBr, KBr) and a dilute mineral acid (e.g., HCl, H
2 4 3
SO , HNO ,
H
3
PO ). The salt/acid/peroxide system may be used for in situ
4
or ex situ oxidative bromination, e.g. of various aromatic
compounds. The application of the above concept towards the
recycling of industrial acid waste is discussed. The cost ef-
fectiveness, E factors, and hazard factors for several bromina-
tion and oxidative bromination reagent systems are compared.
with H
+ Br w 2 ArBr + 2 H
reagent has to shipped to the site, only four reagents are
2
O
2
, the stoichiometry would then be H
2
O
2
+ 2 ArH
1a
2
2
O. (b) When a bromine-containing
cheap enough to matter for large-scale manufacturing: Br
HBr (48% aqueous), KBr, and NaBr.
2
,
Obviously, it is much safer and cheaper to transport and
store large quantities of alkali bromide salts (NaBr, KBr)
Introduction
than either Br
2
or HBr. The drawback is that oxidation of
Bromination of organic compounds is one of the reactions
performed today on a very large scale, often resulting in
stoichiometric pollutant streams. Classical bromination of
aromatics, for example, utilizes only 50% of the halogen,
with the other half forming HBr waste (eq 1).
bromide to bromine requires acidic conditions (eq 2), so that
in the reaction H O + 2 Br w 2 BrO + 2 OH , only
2 2
small amounts of hypobromite are produced.
-
-
-
Although it is known that enzymes such as vanadium
bromoperoxidase (VBPO) catalyse brominations under sea-
5
water conditions, large-scale enzymatic bromination is
ArH + Br f ArBr + HBr
(1)
6
2
problematic. A more realistic industrial option in the near
future, would be to use simple catalysts and in-plant existing
technologies, especially considering the tight profit margins
associated with large-scale halogenation. For example, glacial
acetic acid was used, together with KBr and Mo(VI), to effect
Theoretically, it is possible to reoxidise the HBr, e.g. with
, and achieve high bromine utilization, between 90 and
2 2
H O
1
95% (eq 2).
4
b
oxybromination of various activated aromatics. An analo-
gous investigation using nitric acid and metal chloride salts,
however, required a 10-fold molar excess of acid and salt
2
HBr + H O f Br +2H O
(2)
2
2
2
2
Thus, activated aromatics, such as phenols, anisoles, and
7,3
for the oxidative chlorination of acetanilide.
2
anilines, may be oxybrominated without a catalyst, while
inactive (benzene, toluene) but not deactivated (e.g., ni-
trobenzene) ones, have been oxybrominated in the presence
of quaternary ammonium salts. In practice, however, HBr
recycling is rarely performed in industrial plants, as the
additional step and the corrosiveness of HBr necessitate
2
reactor costs that exceed those of purchasing more Br .
(
4) (a) Barhate, N. B.; Gajare, A. S.; Wakharkar, R. D.; Bedekar, A. V.
Tetrahedron Lett. 1998, 39, 6349-6350. (b) Choudary, B. M.; Sudha, Y.;
Reddy, P. N. Synlett 1994, 450.
3
(5) For a recent review, see Butler, A.; Walker, J. V. Chem. ReV. 1993, 93,
1937-1944.
(
6) Enzymatic oxybromination processes are popular research subjects, and
several novel ideas have been published. See, for example: (a) Sels, B.;
De Vos, D.; Butinx, M.; Pierard, F.; Kirsch-De Mesmaeker, A.; Jacobs, P.
Nature 1999, 400, 855-857. (b) Bhattacharjee, M.; Ganguly, S.; Mukherjee,
J. J. Chem. Res. (S) 1995, 80-81. (c) Martinez-Perez, J. A.; Pickel, M. A.;
Caroff, E.; Woggon, W.-D. Synlett 1999, 1875-1878. However, imple-
mentation of enzymatic processes has serious drawbacks, not least because
such reactions are carried out in very dilute solutions, and thus require
enormous reaction tanks, meaning high capital costs in a market where the
current technology is well-established and retains size advantage. Several
VBPO mimics have been reported, but it is unlikely that in the near future
they would lead to an enzymatic oxybromination process, which would have
to compete on a very narrow profit margin.
Transportation and storage of large quantities of molecular
bromine and HBr is extremely hazardous. Bromide recycling
*
Author for correspondence. E-mail: jhc1@york.ac.uk.
(
1) (a) Johnson, R.; Reeve K. Spec. Chem. 1992, 11, 292-299. (b) Ho, T.-L.;
Gupta, B. G. B.; Olah, G. A. Synthesis 1977, 676-677. (c) For a recent
monograph see Jones, C. W. Applications of Hydrogen Peroxide and
Derivatives; In RSC Clean Technology Monographs; Clark, J. H., Ed.; Royal
Society of Chemistry: Cambridge, 1999; pp 59-61.
(
2) (a) Barhate, N. B.; Gajare, A. S.; Wakharkar, R. D.; Bedekar, A. V.
Tetrahedron 1999, 55, 11127-11142. (b) Mukhopadhyay, S.; Ananthakrish-
nan, S.; Chandalia, S. B. Org. Process Res. DeV. 1999, 3, 451-454. (c)
L u¨ bbecke, H.; Boldt, P. Tetrahedron 1978, 34, 1577-1579.
(7) (a) Jerzy, G.; Slawomir, Z. Synth. Commun. 1997, 27, 3291-3299.
Generally, for oxychlorination a large excess of HCl is required, see: (b)
Thirumalai, P.; Bhatt, M. V. Tetrahedron Lett. 1979, 33, 3099-3100. (c)
Mukhopadhyay, S.; Chandalia, S. B. Org. Process Res. DeV. 1999, 3, 10-
16.
(3) Dakka, J.; Sasson, Y. J. Chem. Soc., Chem. Commun. 1987, 1421-1422.
2
70
•
Vol. 4, No. 4, 2000 / Organic Process Research & Development
10.1021/op000020l CCC: $19.00 © 2000 American Chemical Society and The Royal Society of Chemistry
Published on Web 06/17/2000

Here, we examine the option of recycling mineral acid
waste streams for the oxidative generation of brominating
species, using bromide salts and hydrogen peroxide. The
relevance of this concept to industrial waste management
and sustainable development is discussed.
fast decomposition in the presence of bromine (vide infra).
The bromine could either be distilled by using a flash
distillation apparatus or bubbled directly through the desired
organic reaction mixture. It was found that other mineral
3 3 4
acids, viz., HNO , H PO , HBr (in which case KBr is
unnecessary), and even HCl, may also be as the source of
+
Results and Discussion
H ions.
Using HCl for bromination is interesting, as it seems
possible that companies engaged in chlorination processes
may also be interested in bromination, and might have waste
HCl streams available on-site. As chlorine is less soluble
Definitions. As this study deals mainly with application
of dilute acids, the term acid refers to a dilute acid of ∼1 M
in water. Where concentrated acid is used, the concentration
2 5
is specified. Similarly, the amounts of V O used in all
1
1a
than bromine in water, it is reasonable to suppose that the
absence of chlorinated products indicates either that no Cl
gas is formed when HCl is used as the source of protons
reactions, are 1-2 mol % relative to substrate, unless noted
otherwise. Reaction or reagent productivity is defined as
the amount of substance produced per unit reactor volume
2
-
-
8
(even though, initially, [Br ] ) [Cl ]), or that k
,
per unit time.
Vanadium-Catalysed Generation of Br
chlorination
11b
k
bromination
.
With the use of this system, ex situ bromination
of 1-octene gave >99% selectivity to 1,2-dibromooctane,
indicating that for the V -catalysed reaction 2HX + H
w X + 2H O, kX)Cl , kX)Br by at least 2 orders of mag-
2
Using KBr
and Mineral Acids. It was recently claimed that vanadium
pentoxide catalyses the oxidative bromination of various
activated aromatics, without the need for stoichiometric
2
O
5
2 2
O
2
2
9
nitude. Moreover, an ex situ process is advantageous in this
case, because in a one-pot reaction using HCl + KBr, attack
of chloride on the cyclic bromonium cation would result in
formation of a Vic-bromo-chloro-product (eq 4). Indeed,
amounts of acid. We found, however, that stoichiometric
2 5
V O , which dictates the acidic environment (pH 1-2) is
required for the reaction to proceed.
However, vanadium pentoxide may be used to catalyse
oxidative bromination in the presence of dilute mineral acids,
which may solve problems arising from the corrosiveness
of 48% HBr, or other combinations of bromide with
concentrated acids. This is important, because, although the
productivity of processes employing concentrated acids is
higher, it is partly due to corrosiveness that recycling of
bromides is shunned by the chemical industry. Since HBr is
+
-
used both as a source of H and Br in eq 2, it seems
reasonable that any Br o¨ nsted acid could be used in conjunc-
tion with a metal bromide salt. By far the cheapest and most
Barhate et al. showed that Vic-bromo-chloro-species were
the major products when a combination of concentrated HCl
and HBr was used (without a catalyst) in the oxidative
2
available alternative to Br and HBr would be the combina-
tion of NaBr (or KBr) and sulfuric acid.
When equivalent amounts of KBr and H
2
a
halogenation of alkenes.
1
0
2
SO
4
were
Comparison of HBr with KBr/Acid. The generation of
dissolved in 10 parts water, and added (in one batch) to
hydrogen peroxide (30-35 wt % in water), the solution
turned yellow-golden after a few minutes, but appreciable
amounts of bromine were not produced (<0.25% conversion
of bromide). Upon addition of catalytic amounts (1-2 mol
+
“
Br ” species from H
O
2 2
/HBr can be compared to that of
H
2
O
2
/KBr/acid by measuring the initial rates of H O
2 2
12
decomposition, as shown in Figure 1. Repeated experiments
evidenced good reproducibility (cf. the two plots for H PO ).
Control reactions showed no generation of gas (<0.013
mmol) in the absence of V , nor was any gas produced
when either the KBr or the acid was absent, proving that
decomposition, catalysed by bromide and acid alone,
or by V alone, may be neglected. This is in agreement
with the early results of Mohammad and Liebhafsky, who
showed that oxygen evolution from H solutions using
KBr or KBr/acid is negligible on this time scale.
3
4
%) of vanadium pentoxide, an exothermic reaction occurred
2 5
O
and bromine was produced (eq 3).
2 2
H O
1
-2% V O5
2
2
KBr + H SO + H O
8 Br + 2H O + K SO
4
2 5
O
2
4
2
2
2
2
2
3
0 min, 25 °C
13
7
00 rpm stirring
(3)
2
O
2
14
Peroxide utilisation improved when the H
2 2
O was added
dropwise to the reaction mixture, as H itself undergoes
2
O
2
2 2
(11) (a) Compare 0.092 M [Cl ] with 0.214 M [Br ] at 25 °C, The Merck Index;
Merck & Co., Inc.: Rahway, 1989; pp 323; 211. (b) An indication of the
difference between the oxidation potentials of chloride and bromide may
be obtained by comparing the Standard Electrode Potentials (cf. -1.066 V
(
8) For a discussion, see Sheldon, R. A. Chem. Ind. 1992, 903-906;
CHEMTECH 1994, 38-47.
for 2 Br- w Br + 2e with -1.358 V for 2 Cl- w Cl
-
+ 2e , CRC
-
(
9) Bhattacharjee, M. Polyhedron 1992, 11, 2817-2818. See also ref 6b, and
Bhattacharjee, M.; Chaudhuri, M. K.; Islam, N. S.; Paul, P. C. Inorg. Chim.
Acta 1990, 169, 97-100.
2
2
Handbook of Chemistry and Physics, 76th ed.; CRC Press: Boca Raton,
1995; pp 8/29-8/31).
(
10) For the purpose of providing an acidic environment for bromide oxidation,
SO may be regarded as a dibasic acid, as pK ) 1.98 for the second
dissociation. With the weaker acid H PO , however, only the first dissocia-
tion is relevant, as pK ) 7.09 for the second dissociation (CRC Handbook
of Chemistry and Physics, 76th ed.; CRC Press: Boca Raton, 1995; pp
/44-8/45).
2
(12) Direct observation of Br generation kinetics, e.g., using spectroscopic
H
2
4
a
methods, is problematic, due to the fact that several of the possible
-
-
3
, and HOBr) evidence spectral changes
3
4
intermediate species (BrO , Br
similar to Br
a
2
.
(13) Mohammad, A.; Liebhafsky, A. H. J. Am. Chem. Soc. 1934, 56, 1680-
8
1685.
Vol. 4, No. 4, 2000 / Organic Process Research & Development
•
271

Figure 1. Vanadium-catalysed H
dilute acids/KBr. Conditions: 25 °C, 10.0 mmol acid, 10.0 g of
water, 10.0 mmol H (35 wt %), 10.0 mmol KBr, 1.5 mol %
2 2
O decomposition using
Figure 2. Decomposition of H
mmol H (35 wt %), 10.0 g of water; A 5.0 mmol of Br2(l)
2 5
no catalyst); B 10.0 mmol HBr (48 wt %), 1.5 mol % V O .
2 2
O at 25 °C. Conditions: 10.0
2 2
O
2 2
O
(
2 5
V O .
Table 1. Peroxide decomposition ratesa
2) the behaviour was similar to other KBr/acid systems. This
indicates that it is bromine, rather than HBr, that initiates
decomposition of hydrogen peroxide. Although not identical,
it can be seen that k1, bromine is of the same order of magnitude
3
3
entry
system
k
1
(× 10 )
k
2
(× 10 )
1
2
3
4
5
6
7
KBr/H
KBr/HNO
KBr/HCl
KBr/HClO
2
SO
3
4
3.37
2.95
2.03
0.49
0.51
1.96
35.21
24.1
20.7
10.1
2.1
2.3
9.8
1
6
as k2, acid/KBr for H
2
4 3
SO and HNO .
The mechanism of bromide oxidation/H
2
2
O decomposition
4
1
7
is complex. In presence of vanadium oxides, mechanistic
studies have shown that this system is sensitive to changes
in solvent, and that different reaction pathways may domi-
nate, depending on the coordination environment of the
KBr/H
HBr
3
PO
4
Br
2
0.6
a
In mmol s-1. Values are the least-squares fit of at least 10 observations,
2
18
with r > 0.96. Conditons are as shown in Figures 1 and 2.
catalyst. Different mechanisms have been proposed for
19
20
V
2
O
5
-catalysed bromide and iodide oxidations. However,
on the basis of our results and the elegant and conclusive
1
9
Strong and weak acids evidenced different behaviour in
mechanistic studies reported by Butler et al., we suggest
that (a) in the presence of V O , the behaviour of H O /HBr
15
this system. In fact, when acetic acid was used, no reaction
was detected on this time-scale even in the presence of V
2
5
2
2
2 5
O .
2 2
is nearly identical to that of H O /KBr/acid; and (b) regard-
Experimental values of initial decomposition rates are given
in Table 1. For each acid, it was possible to distinguish
2 2 2
less of the mineral acid used, both Br formation and H O
decomposition depend on two-electron oxidation and the
formation of the common intermediate HOBr.
between two regions. Initially, the rate of gas generation (k
1
)
was low and constant. Then, a much higher rate (k ) was
2
Oxidative Bromination Using the MBr/H SO /H O
2
2
4
2
observed. We suggest that this change is effected when the
concentration of bromine increases above a certain level.
Experimental evidence supporting this hypothesis was ob-
tained using HBr and Br2(l) as “Br” sources. As shown in
Figure 2, decomposition of hydrogen peroxide in the presence
of bromine (without a catalyst) was extremely fast initially.
Then, almost no gas was released, showing a behaviour
System. Oxidative bromination of various aromatics was
tested using the above method (eq 5). Results are presented
in Table 2. Results were comparable to those obtained using
hydrogen peroxide and concentrated HBr. Both NaBr and
KBr can be used with equal facility. Only traces (<0.5%)
3 2 4
(16) Theoretically, one would expect that HCl, HNO , H SO , and HBr would
all dissociate completely under the aqueous conditions employed. Thus,
the differences shown in Figure 1 may reflect possible participation of the
inorganic anions in the catalytic decomposition process.
typical of acid/KBr systems that contain no V
was used as the bromide source, no reaction occurred in the
absence of V (not shown). In the presence of V (Figure
2 5
O . When HBr
(17) Atkins, P. W. Physical Chemistry, 5th ed.; Oxford University Press: Oxford,
O
2 5
2 5
O
1994; p 915.
(
18) (a) Butler, A.; Clague, M. J.; Meister G. E. Chem. ReV. 1994, 94, 625, and
references therein; (b) Bortolini, O.; Di Furia, F.; Scrimin, P.; Modena, G.
J. Mol. Catal. 1980, 7, 59.
(14) However, in all cases (even when using KBr/AcOH in the absence of
catalyst), enough bromine was generated to cause coloration of the samples.
cf. Maass, O.; Hiebert, P. G. J. Am. Chem. Soc. 1924, 46, 290-308.
15) The slow reaction observed with perchloric acid is probably a result of its
low solubility in the reaction medium. Significant amounts of solid
perchlorates were observed even when the amount of water was doubled.
(19) (a) Clague, M. J.; A. Butler, A. J. Am. Chem. Soc. 1995, 117, 3475-3484.
(b) de la Rosa, R. I.; Clague, M. J.; Butler, A. J. Am. Chem. Soc. 1992,
114, 760-761.
(
(20) Secco, F. Inorg. Chem. 1980, 19, 2722-2725.
272
•
Vol. 4, No. 4, 2000 / Organic Process Research & Development

Table 2. Oxidative bromination using MBr/acid/hydrogen peroxidea
b
entry
substrate
acid (mmol, mol/kg)
H
2 2
O /mmol
V
O
2 5
/mol %
time/min
conv./%
products (% selectivity)
1
2
3
4
5
6
7
8
9
anisole
HBr (10, 0.52)
HBr (10, 0.52)
AcOH (84, 5.28)
11
11
20
25
25
25
25
25
25
None
1.0
2.5
1.5
3.1
2.0
2.5
2.0
3.0
100
100
140
90
15
68
30
85
83
60
45
35
90
4-BA (>99)
anisole
anisole
4-BA (>99)
c
4-BA (>99)
anisoled
H SO
2
H SO
2
H SO
2
H SO
2
H SO
2
H SO
2
4
4
4
4
4
4
(5, 0.33)
(5, 0.33)
(5, 0.33)
(5, 0.33)
(5, 0.33)
(5, 0.28)
4-BA (93); 2,4-DBA (7)
4-BA (94); 2,4-DBA (6)
4-BT (95); 2-BT (3)
4-BT (95); 2-BT (4)
4-BEB (60); 2-BEB (7)
4-BP (69); 2-BP (31)
anisole
35
toluene
900
220
180
60
toluened
ethylbenzene
phenold
d
a
Standard reaction conditions: 10.0 mmol substrate; 10.0 g water; 700 rpm stirring; 25 °C. Yields based on GC area, corrected by the presence of an external
standard (n-decane). b BA ) bromaoanisole; DBA ) dibromoanisole; BT ) bromotoluene; BP ) bromophenol; BEB ) bromoethylbenzene. Repeating the reaction
c
d
in presence of 10 mol% TEAB did not affect conversion or selectivity. 10.0 mmol NaBr used instead of KBr.
Table 3. Raw material costs, E factors, and risk factors of industrial bromine alternativesa
b
Br
source
bromine
mol %
content
wt %
stoichiometric
reagents required
total price
waste
stream
E
factor
hazard
factor
-
1
c
entry
$ ton ArBr
d
1
2
3
4
5
6
7
Br2(l)
Br2(l)
HBr(aq)
KBr(s)
NaBr(s)
MgBr2(s)
NaBrO3(s)
100.0
100.0
98.7
67.1
73.3
86.7
52.9
100.0
100.0
47.4
67.1
73.3
86.7
52.9
Br
Br
2
2
1300
840
3920
4160
3600
9990
4820
HBr
0.51
0.11
0.23
0.78
2.00
0.61
0.56
high
d
+ H
2
O
2
2
2H
4H
4H
2
2
2
O
O
O + K
high
d
2HBr + H
O
O
2
high
2KBr + H
2
2
O
O
+ H
+ H
+ H
SO
2
SO
4
2
SO
4
low
low
low
2NaBr + H
2
2
2
SO
4
4H2O + Na
4H
2
SO
4
MgBr
2
+ H
+ 2H
2
2
2
SO
4
2
O + MgSO
4
e
f
2NaBrO
3
2
4
2NaHSO
4
+ 3O
2
high
a
+
+
b
Based on the reaction “Br ” + ArH w ArBr + H . For example, for entry 1, the reaction is Br
2
+ ArH w ArBr + HBr. Prices from CMR and industrial sources
-1
(
(
2 3
$ ton ): bromine (liq) 1300; HBr (48 wt % aq) 1500; KBr (powder) 2200; NaBr 1600; MgBr 7600; sulfuric acid 100; hydrogen peroxide (35 wt % aq) 600; NaBrO
1 c
2 5
powder) 2500. V O
approximated at $10 kg- , using 1 mol% relative to bromide. Comparison excludes aromatic substrate prices. kg waste/kg product, comparison
d f
based on 100% theoretical bromination of benzene (see Supporting Information for details). Transportation/storage risks. e For a recent study, see ref 22. Reaction
risks (possible explosion/runaway reaction).
of benzyl bromide were obtained in the oxidative bromination
of toluene, ruling out an SET free-radical process. Oxybro-
mination of deactivated aromatics using this method, how-
ever, was unsuccessful, which points to a drawback of the
dilute acid option s it is necessary to find a Lewis acid
catalyst, that is stable under acidic aqueous conditions, to
promote this reaction. Such catalysts are currently under
research in our laboratory.
can be utilised. The latter option is increasingly relevant, as
the chemical industry moves towards waste minimisation and
zero-emission plants.
Conclusions
Vanadium-catalysed oxidative bromination by means of
dilute mineral acids, hydrogen peroxide, and alkali bromides
is an effective method for the bromination of activated and
nonactivated (but not deactivated) aromatic substrates.
2 4 3 3 4
H SO , HNO , HBr, HCl, and (to a lesser extent) H PO may
be used, making this an option for recycling industrial acid
waste. Furthermore, this method has the advantages of low
transportation and storage risks and employs the relatively
2 2
safe 35% H O . The drawbacks are high prices and low
productivity (compared to using molecular bromine), and the
fact that concurrent unwanted decomposition of the peroxide
occurs.
Experimental Section
Cost Effectiveness of Aromatic Bromination Processes.
The raw material costs, E factors,2 and risk factors for
various industrial bromination reagents, are presented in
Table 3.22 As a result of the low cost and high productivity
of molecular bromine, the MBr/acid/H O option will be
2 2
economically viable only if bromine transportation costs
become prohibitive, or if in-plant bromide and acid waste
Materials and Instrumentation. Unless stated otherwise,
chemicals were purchased from commercial firms (>98%
pure) and used without further purification. GC analyses were
performed using an HP-5890 gas chromatograph with an HP1
capillary column (25 m/0.25 mm). A standard sample of 1,2-
dibromooctane was prepared according to the literature.23
Products were identified by comparison of their GC retention
1
(
21) Sheldon, R. A. Chem. Ind. 1997, 12-15; J. Chem. Technol. Biotechnol.
997, 68, 3181-388.
22) Groweiss, A. Org. Process Res. DeV. 2000, 4, 30-33.
1
(23) Vogel, A. I., Vogel’s Textbook of Practical Organic Chemistry, 5th ed.;
Longman: Essex, 1989; pp 509-511.
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times with standard reference samples. CAUTION! There
are hazards associated with using hydrogen peroxide (see
ref 1c, pp 21-27).
35 wt % soln) was added dropwise using a pressure-
equalizing dropping funnel. The reaction was stirred (700
rpm) at 25-30 °C for 90 min, after which time the organic
phase was separated and analysed by GC (n-decane external
standard).
2 2
General Procedure for Measuring Initial H O De-
composition Rates. Example: using HCl and KBr, 10.0
mmol (1.19 g) KBr was dissolved in 10.0 g of distilled water,
to which was added 10.0 mmol (1.0 g of 35 wt % solution)
Acknowledgment
G.R. thanks the European Commission for a Marie Curie
Individual Research Fellowship and gratefully acknowledges
the support of the Leo Baeck (London) lodge. J. H. C. thanks
the RAEng-EPSRC for a Clean Technology fellowship. We
thank Dr. M. Bhattacharjee (Indian Institute of Technology,
Kharagpur) for discussions.
HCl, and 0.15 mmol (28.0 mg) V
2
O
5
. After stirring for 1
min at 25 °C, 10.0 mmol H
2 2
O
(∼1.0 mL of 35 wt %
solution, exact amount determined by iodometric titration)
was added in one batch using a syringe. Gas generation was
monitored by measuring the volume of water displaced from
an upturned biuret connected to the reaction vessel.
General Procedure for in situ Oxybromination. Ex-
ample: For the oxybromination of anisole, 10.0 mmol (1.19
g) KBr was dissolved in 10.0 g distilled water, to which was
Supporting Information Available
Two examples detailing the calculation of E factors
presented in Table 3. This material is available free of charge
via the Internet at http://pubs.acs.org.
added 5.0 mmol (0.49 g of 98 wt % solution) H
mmol (1.08 g) anisole, and 0.14 mmol (26.0 mg) V
stirring for 1 min at 25 °C, 100 mmol H
(∼10.0 mL of
2
SO
4
, 10.0
2
O . After
5
O
2 2
OP000020L
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