New sources of "active" halogen bis(dialkylamide)hydrogen dibromobromates, efficient reagents for destruction of ecotoxicants

Article abstract of DOI:10.1134/S1070428008050011

Bis(dialkylamide)hydrogen dibromobromates were synthesized and their reactivity was investigated in decomposition of diethylphosphonic, diethylphosphoric, and 4-toluenesulfonic acids 4-nitrophenyl esters. The nucleophilic reactivity of a typical α-nucleop

Full text of DOI:10.1134/S1070428008050011

ISSN 1070-4280, Russian Journal of Organic Chemistry, 2008, Vol. 44, No. 5, pp. 637−646. © Pleiades Publishing, Ltd., 2008.
Original Russian Text © T.M. Prokop'eva, V.A. Mikhailov, M.K. Turovskaya, E.A. Karpichev, N.I. Burakov, V.A. Savelova, I.V. Kapitanov, A.F. Popov, 2008,
published in Zhurnal Organicheskoi Khimii, 2008, Vol. 44, No. 5, pp. 649−658.
New Sources of “Active” Halogen Bis(dialkylamide)hydrogen
Dibromobromates, Efficient Reagents for Destruction
of Ecotoxicants
T. M. Prokop’evaa, V. A. Mikhailova, M. K. Turovskayaa, E. A. Karpicheva, N. I. Burakova,
V. A. Savelovaa, I. V. Kapitanovb, and A. F. Popova
aLitvinenko Institute of Physical Organic and Coal Chemistry, National Academy of Sciences of Ukraine
Donetsk, 83114 Ukraine
e-mail: prokopievaeuak@skif.net
bDonetsk State University, Donetsk, Ukraine
Received March 18, 2007
Abstract—Bis(dialkylamide)hydrogen dibromobromates were synthesized and their reactivity was investigated
in decomposition of diethylphosphonic, diethylphosphoric, and 4-toluenesulfonic acids 4-nitrophenyl esters. The
nucleophilic reactivity of a typical α-nucleophile, hypobromite ion, is independent of the source of the active
bromine. The cetyltrimethylammonium dibromobromate is a unique reagent for destruction of ecotoxicants. In
weakly alkaline media the half-life of 4-nitrophenyl diethylphosphonate did not exceed 6 s at [BrO–] 0.02 mol l−1,
and the apparent reaction rate compared to water increased ~40-fold. The main factor governing the micellar
effects of surfactants is concentrating the substrate in the micellar pseudophase.
DOI: 10.1134/S1070428008050011
The development of new efficient reagents for decom-
position of ecotoxicants in water requires a search for
universal systems operating by oxidative-nucleophilic
mechanism that can be applied to utilization of highly
toxic phosphorus acids esters, sulfides derivatives etc.
(pesticides, chemical warfare agents etc.) [1–3]. A good
combination of nucleophilic and oxidative properties is
inherent to hypobromites [4], but neither their solutions
nor solid salts are suitable for long storage [5]. An ideal
source of active bromine would be a safe solid substance
with a low pressure of bromine vapor, with a high content
of the active halogen, well soluble in water that would
furnish the necessary operating concentration of BrO–/
HOBr. As a source of active bromine for ecotoxicants
decomposition reagents with labile N–Br and C–Br bonds
and also molecular complexes of bromine with N- and
O-nucleophiles are widely used [6, 7]. However the com-
pounds of N-bromosuccinimide type as a rile are poorly
soluble in water [6]. The molecular complexes of bromine
with N- and O-nucleophiles (for instance, dioxane-
dibromide or the complexes with pyridine N-oxides) are
short-lived [7]. Especially interesting for practice are
compounds containing a tribromide anion.*
In water the tribromide anion undergoes a fast and
reversible dissociation [reaction (1)] to give a bromide
anion and a bromine molecule [8]; the latter in its turn
depending on the acidity of the environment generates
anion BrO–, HOBr, or BrO–/HOBr.
Br–3 ' Br– + Br2
(1)
We report here on the study of the nucleophilic
reactivity of BrO– ion toward 4-nitrophenyl diethyl-
phosphonate (I), diethylphosphate (II), and 4-toluene-
sulfonate (III), the α-effect values of BrO– ions in the
cleavage processes of these substrates were estimated,
optimum conditions for the reactions were chosen, and
the effect of surfactant micelles on the rate of the
nucleophilic attack of hypobromite anion on the electron-
deficient site of substrate I was investigated.
* Dibromobromates according to the IUPAC nomenclature.
637

PROKOP’EVA et al.
638
for a long time* without applying any special precautions;
EtO(Et)P(O)OC6H4NO2-p
(EtO)2P(O)OC6H4NO2-p
they are not irritant for mucous membranes and dry skin
at a short contact.
I
II
TsOC6H4NO2-p
III
At the quantitative evaluation of the reactivity of the
hypobromite ion it is necessary to take into consideration
that BrO– anion operates as an efficient nucleophile in
the cleavage of acyl-containing substrates, and that its
conjugate acid HOBr is a strong oxidant. Kinetic curves
demonstrating the variation in time of absorption of
p-nitrophenolate ion formed in the reaction of complex
IV with ester I at different pH values are presented in
Fig. 1. The ascending branch of the curve corresponds
to the accumulation in the system of p-nitro-phenolate
ion formed at the attack of BrO– anion on the electron-
deficient site of the substrate, and the descending branch
of the curve reflects the oxidation of the p-nitrophenolate
ion [reaction (2)]; thus in this process p-nitrophenolate
ion is an intermediate compound.
As a source of active bromine bis(dialkylamide)-
hydrogen dibromobromates IV–VII were used, and also
a micelle-formative cetyltrimethylammonium dibromo-
bromate (VIII) was employed.
O
O
O
.
.
N
HBr
3
N
N
HBr
3
CH
H C
3
CH
3
3
2
IV
V
H C
3
O
H C
3
O
.
.
N
HBr Cl
N
HBr
2
3
H C
3
CH
H C
3
CH
3
3
2
2
BrO_
VII
VI
AcylO
NO2
+
_
3
.
C H N(CH ) Br
16 33
3 3
_
k2BrO
VIII
_O
NO2
(2)
AcylOBr
These compounds possess a number of advantages
compared to the other known tribromides. They are solid
substances easily obtained in an analytically pure state,
they dissolve quickly in water solutions of alkali
providing relatively stable hypobromites solutions; they
are stable under common conditions and can be stored
koxidation
Oxidation
H2O
AcylOH
BrO_
products
Acyl = EtO(Et)P(O), (EtO)2P(O), Ts.
D
1
The nucleophilic reactivity of hypobromite anion
generated by various sources of bromine was studied
under the conditions when the contribution of the
oxidation of the p-nitrophenolate ion was close to zero:
during 5–10 half-times of the reaction the p-nitropheno-
late ion concentration did not decrease. Therewith the
choice of pH depended on the ratio of the rate constants
of the nucleophilic attack on the electron-deficient site
of the substrate and of the oxidation of the p-nitropheno-
late ion. With the reactive ester I pH was maintained on
the level ≥11.15, with compounds II and III pH was set
at >11.35. The apparent rate constant (kapp, s–1) under
these conditions was described by equation (3).
1
0.5
2
3
4
5
0
0
5
10
15
20
25
30
, min
_
_
_
kB2 rO
_
αBrO
kapp = kHO aHO
[HOBr]0
(3)
Fig. 1. Variation in time of absorption of p-nitrophenolate ion
(λ 420 nm) during the reaction of BrO–/HOBr generated by
complex IV with ester I. [HOBr]0 0.01 mol l−1, pH 11.5 (1),
10.8 (2), 10.40 (3), 10.00 (4) 9.60 (5); water, μ 1.0, 25°C.
*
After 10 years the decrease in the content of active bromine in
compound VI did not exceed ~5%.
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NEW SOURCES OF “ACTIVE” HALOGEN
The term kHO– aHO–, s–1, in equation (3) corresponds
639
to the contribution of the alkaline hydrolysis; [HOBr]0,
mol l−1, is the analytical concentration of hypobromic
acid; αBrO– is the fraction of BrO–, and kB2 rO− l mol–1 s–1
is the second order rate constant characterizing the
nucleophilicity of hypobromite anion in water. Inasmuch
as the constant of the acid ionization of hypobromic acid
pKa is 8.69 [9], the value αBrO– → 1 (pH 11.15, α 0.996;
pH 11.35, α 0.998), equation (3) may be written in the
form (4).
_
kB2 rO
_
_ aHO
[HOBr]0
kapp = kHO
(4)
The second order rate constants were estimated
from the linear dependence kapp – [HOBr]0 (Fig. 2) and
were presented in Table 1. In all events the segment cut
on the ordinate corresponded to the contribution of the
acid hydrolysis estimated by taking into account kOH−,
l mol–1 s–1, determined in independent experiments [4].
The reactivity of hypobromite ion generated by
various sources of the active bromine IV–VII virtually
coincided. This was not unexpected: the amides contain-
ed in the bromine complexes do not react with esters,
and the operating concentrations of dibromo-bromates
IV–VII are not sufficiently high to affect the environment
properties and the nucleophilicity of BrO– anion. The
hypobromite ion is a typical α-nucleophile. Although it
is by 7 orders of magnitude less basic than the hydroxide
ion (pKa of the conjugate acids is 8.69 [9] and 15.74
[10] respectively), it reacts with substrates I–III at a rate
close to that of the alkaline hydrolysis (Table 1). The
value of the α-effect is usually evaluated either from the
ratio of the second order rate constants kα2-nucl/k2nucl, or
from the difference Δ = log kα2-nucl – kn2ucl at the comparable
values of constants of acid ionization of the conjugate
acids of the α-nucleophile and a “normal” oxygen-
containing nucleophile. With the use of Bro/nsted equa-
tions for arylate (alcoholate) ions (5–7) [11] it was
possible to calculate the value of the α-effect of the
hypobromite ion in reactions with esters I–III.
Fig. 2. Dependence of kapp, s–1, on [BrO–], mol l−1, in reactions
of esters I, straight line 1, pH 11.35; II straight line 2, pH
11.35, and III, straight line 3, pH 11.60, with hypobromite
ion generated by complex IV; water, μ 1.0, 25°C.
be equal to 2.5 × 10–4 (I), 2.3 × 10–5 (II), and 3.1 × 10–5
(III) l mol−1 s−1. Therefore the magnitude of the α-effect
characterized by the ratio of the second order rate
constants k2α-nucl/k2nucl is ~600, 500, and 400 and is
independent of the source of the active bromine. In the
case of ClO– anion the increase in the reaction rate
estimated in similar way amounted to kα2-nucl/k2nucl ≥ 103
(pKaHOCl = pKaArOH = 7.4) [4].
Table 1. Nucleophilic reactivity of hypobromite ion toward
4-nitrophenyl diethylphosphonate (I), diethylphosphate (II),
and toluenesulfonate (III); water, μ 1.0 (KCl), 25°Ca
_
_
, RO
)
log k2(ArO
log k2(ArO
(I) = 0.50pKa _ 7.95
(5)
(6)
(7)
_
_
, RO
)
(II) = 0.57pKa _ 9.60
_
_
, RO
)
log k2(ArO
(III) = 0.59pKa _ 9.64
The reactivity of “normal” oxygen-containing nucleo-
phile, arilate ion with pKaArOH = pKaHOBr = 8.69 should
a Rate constants of alkaline hydrolysis equal: 0.15 (I), 0.009(II),
0.008 (III) l/(mol−1 s−1) [4].
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PROKOP’EVA et al.
640
We already demonstrated formerly [4] that the
p- (or π-) antibonding and lower bonding molecular
orbitals [18, 20]. This interaction character is reflected
in the physicochemical properties of these compounds
[18, 19, 21]. This is beyond question that the higher
occupied orbital should interact stronger with the lower
unoccupied orbital of the substrate that the nonperturbed
p- (or π-) orbital of the nucleophile. Therewith the closer
in the energy the reacting orbitals of the nucleophile and
substrate, the stronger is the stabilization of the transition
state of the reaction and consequently the higher is the
rate of the process. These nucleophiles should exhibit
the α-effect both in reactions with saturated and
unsaturated substrates. Obviously BrO– anion can be
classed in this group.
hypobromite ion is a typical α-nucleophile.Although the
cause of the abnormally high reactivity of α-nucleophiles
has been under investigation for over 50 years, it is still
under discussion [12]; and the α-effect in all likelihood
has no unique nature. The high reactivity of α-nucleo-
philes is commonly regarded as the result of the stabiliza-
tion of the transition state of the reaction caused, e.g., by
intramolecular general acid-base catalysis [13], by the
elevated thermodynamic stability of reaction products
[14]; solvation effects of the solvent play a special part
[12].
Among the factors governing the α-effect the basicity
of the nucleophile [15], hybridization type of the electro-
philic site [12, 16] etc. [12] should be mentioned. In the
case of hypohalogenite ions it is presumed that the
cleavage of esters occurs through a rate-determining state
A, where the hypohalogenite ion being a Lewis acid func-
tiones as intramolecular general acid-base catalyst [13],
namely, the phosphoryl (or sulfonyl) oxygen atom is in-
volved into an interaction with the unoccupied d-orbitals
Nonetheless, the explanation of the α-effect based
on the destabilization of the initial state has certain
drawbacks. Thus if the α-nucleophile is destabilized due
to the energetically unfavorable interactions between the
unshared electron pairs or by solvation effect of the
solvent [12, 22] its nucleophilic reactivity should increase
when the degree of destabilization diminishes in the
transition state. However simultaneously the basicity of
this supernucleophile should also grow for the addition
of a proton thereto should even greater decrease its
destabilization. Therewith it is expectable that the parallel
increase in the reaction rate and basicity of the α-nucleo-
phile should be described by Bro/nsted relation for the
“normal” nitrogen- and oxygen-containing nucleophiles.
However actually it is not the case. It is therefore sug-
gested that the protonation of the nucleophile is a process
controlled by the charge, whereas the nucleophilic
substitution is apparently orbital-controlled [18, 23].
O
P
O
S
Hlg
O
Hlg
O
O
A
of the halogen atom in the hypohalogenite ion.
However the hypohalogenite ions, in particular, ClO–
anion, demonstrate the α-effect toward a saturated carbon
atom in reactions with benzyl bromide [17] where this
assistance id hardly possible.
The systems based on the organic complexes of
tribromide ion are versatile, i.e., they can be used as
oxidants and nucleophiles for neutralization of toxic
substrates [4, 24]. The optimum pH value for cleavage
of esters I–III is that where the apparent rates of
In [18] based on the extended version of perturbation
theory of molecular orbitals another understanding of
the nature of the α-effect is developed proceeding from
the destabilization of the initial state. All α-nucleophiles
may be divided in two groups. The first group includes
ions of ROO–, ClO–, and RSS– type possessing high
repulsion energy of the unshared electron pairs of the
α-atom and nucleophilic center in the ground state of
the reaction. The second group of nucleophiles includes
NH2NH2, NH2OH, hydroxamate and highly basic
oximate ions, pyridines N-oxides, and azide ion. The
conformations of the latter have a structure where the
electron repulsions in the ground state of the reaction
are negligible [19]. In the α-nucleophiles of the first
group should occur a splitting of hypohalogenite ion
p- (or π-) levels and an appearance of higher occupied
_
oxidation
BrO
(8)
k
k
.
=
app
app
nucleophilic substitution and oxidation are equal:
2
_
Ka
Ka + aH+
aH+
k2BrO
= koxidation [HOBr]0
,
[HOBr]0
Ka + aH+
(9)
Accounting for the established laws of these processes
[4, 24] expression (8) transforms into (9).
RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 44 No. 5 2008

NEW SOURCES OF “ACTIVE” HALOGEN
641
where [HOBr]0, mol l−1, is the analytical concentration
12
10
of hypobromic acid; Ka is the constant of acid ionization;
Ka/(Ka + aH+) and aH+/(Ka + aH+) are fractions of hypo-
bromite ion and of hypobromic acid at pH = –log aH+;
koxidation, l2/(mol2 s) is the rate constant of oxidation.
Transforming expression (9) into equation
8
6
_
log(koxidation/k2BrO ) + pKa
,
(10)
pH =
2
4
2
0
it is possible to determine the pH, corresponding to pHopt;
considering koxidation [4, 24] and k2BrO− for substrates I–
III it is 10.0–10.7. It should be stressed that ion BrO–
being an α-nucleophile makes it possible at concentration
1 mol l−1 to achieve half-conversion time (τ1/2) of
compounds I–III into the reaction products not exceeding
5 s (substrate I) and 50 s (substrates II and III).
(12)
20
0
5
10
15
25
× 103, mol/l
c0
Fig. 3. Dependence of the apparent pseudofirst order rate
constants (kapp, s–1) on the initial concentration of
cetyltrimethylammonium dibromobromate (CO, mol l−1) in
decomposition of ester I; pH 11.14–11.20, water, 25°C, ionic
force not fixed.
In designing reagents ensuring efficient decomposi-
tion of ecotoxicants it is important not only to obtain
high apparent reaction rates but to provide the solubiliza-
tion of substrates poorly soluble in water. The latter factor
is often the governing one in substantiation of the routes
to modification of the systems for ecotoxicants destruc-
tion. We formerly demonstrated that in the micelles of
cetyltrimethylammonium bromide (IX) the rate of reac-
tion between BrO– anion and esters I–III grew 20–30-
fold [24]. Unique reagents generating BrO–/HOΒr and
operating as micelle-fomative compounds are quaternary
ammonium salts of VIII type. Recently compounds IV–
VIII were widely used in selective bromination of
phenols and anilines [25], and also for selective oxidation
of sulfides to sulfoxides [26]. However we found no
publications on detailed kinetic studies of nucleophilic
substitution in the presence of compound VIII.
Micellar effects of surfactant VIII were studied by
an example of the cleavage of ester I. The dependence
of kapp on co is of a pattern typical for the reactions of
anionic nucleophiles with electroneutral substrate
(Fig. 3). The quantitative relationships of the cleavage
of ester I can be understood in the framework of a simole
pseudophase model [27]. Assuming that both in water
(w) and in the micellar pseudophase (m) the substrate
(HO_)w
(S)w
(BrO_)w
w
w
_
_
k2,HO
k2,BrO
_
_
PBrO
POH
PS
(S)m
Reaction products
(11)
Reaction products
m
m
_
(HO_ )m
(BrO_)m
_
k2,BrO
k2,HO
_[HO_]m[S]mcVm + k2m,BrO
_
(S) reacted by two concurrent paths, alkaline hydrolysis
and reaction with BrO– anion, the overall scheme of the
process may be described by equation (11).
m
_[BrO ]m[S]mcVm,
vm = k2,HO
(12)
The distribution of the substrate and reagents is
described by the corresponding distribution factors: PS =
[S]m/[S]w, PBrO– = [BrO–]m/[BrO–]w, and PHO– = [HO–
]m/[HO–]w, and the rate of substrate cleavage in the
micellar pseudophase, by equation
in water, by equation
_[HO_]w[S]w(1 _ cVm)
w
vw = k2,HO
_
_
+ kw2,BrO [BrO ]w[S]w(1 _ cVm),
(13)
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PROKOP’EVA et al.
642
Table 2. Nucleophilic reactivity of hypobromite ion (km2,BrO– )
generated by cetyltrimethylammonium dibromobromate,
constants of binding of substrate (KS) and nucleophile
(KBrO–) in the course of decomposition of 4-nitrophenyl
diethylphosphonate (I), 25°C
where the values km2 ,HO–, k2m, BrO– and k2w, HO–, k2w, BrO– =
k2BrO¯, l mol−1 s−1, are second order rate constants
corresponding to the reactivities of the hydroxy and
hypobromite anions in the micellar pseudophase and in
water; c = cO – CCM, mol l−1, is the concentration of the
surfactant involved in the micelle formation (CCM,
mol l−1, is the critical concentration of micelle formation),
Vm, l mol−1 is the partial molar volume of the sur-
factant ; cVm and (1 – cVm) are volume fractions of the
micellar and water phases.
a Calculated by equation (16).
b Calculated without accounting for the contribution of alkaline
The overall rate of the process (Scheme 11) averaged
over the total volume of the system may be expressed
through the reaction rates in the micellar and water phases
by equation (14).
hydrolysis.
KS = (PS – 1)Vm
KBrO– = (PBrO– – 1)Vm
KHO– = (PHO– – 1)Vm
_ [BrO_]m[S]mcVm
m
v = vm + vw = k2,BrO
(17)
_ [HO_]m[S]mcVm
m
In processing the experimental data by equation (16)
we assumed that km2,HO– ≈ kw2,HO– = 0.15 l/mol [4], KHO– ≈
30 l/mol [28]; [BrO–] = Co, mol l−1 (pH ≈ const = 11.14–
11.20), and Vm = 0.37 l/mol [29]. The optimized values
were km2,BrO–/Vm, KS, and KBrO– that are compiled in Table
2. There are also presented the values of the same kinetic
and thermodynamic parameters estimated without
accounting for the contribution of the alkaline hydrolysis
in water and micelles of compound VIII.
w
+ k2,HO
+ k2,HO
_ [HO_ ]w[S]w(1 _ cVm)
_
+ k2w,BrO
_[BrO ]w[S]w(1 _ cVm)
(14)
Taking into account the relations between the overall
concentrations of reagents and their real concentrations
in the respective phases described by the distribution
factors and the material balance equations the apparent
rate constant can be represented by equation (15).
The attention is engaged by the fact that the values
km2,BrO– and KBrO– estimated along two approaches are
close to each other, whereas the constants of binding the
substarate are essentially different. Therewith the KS
value estimated from the kinetic data without accounting
for the contribution of alkaline hydrolysis was determin-
ed with ~50% error and seemed overestimated.Actually,
the constant of binding ester I with micelles of functional
[30] and cationic [24, 28] surfactants calculated from
kinetic data amounted to 150–300 l/mol. This value is
consistent with the distribution factor of substrate II
which is close to ester I by the hydrophobicity: from the
data on solubility [31] PS(II) ≈ 350, and KS(II) = PS(II) Vm ≈
150 l/mol (Vm = 0.37 l/mol). Therefore the account-ing
for the reaction of the hydroxide ion in water and in
micelles provided more correct description of the micellar
effects of the surfactant.
_ PSPBrO_ cVm
k2m,BrO
_ (1 _ cVm)
kw2,BrO
[BrO_]
v
[S]
kapp
=
=
_
[1 + (PS _ 1) cVm][1 + (PBrO _ 1) cVm]
_cVm
kw2,HO
k 2,HO PSPHO
_ (1 _ cVm)
_
m
_
[HO_]o
+
[1 + (PS _ 1) cVm][1 + (PHO _ 1) cVm]
(15)
In event of dilute solutions of surfactant where the
volume fraction of the micellar phase is small (CVm << 1)
[27] and an efficient uptake of the reagents by the
surfactant micelles exists (PS, PBrO–, PHO– >> 1) it is
possible to simplify equation (16):
_
k2m,BrO_/V )
kw2,BrO
KSKBrO_ c
[BrO_ ]o
m
v
kapp
=
=
It should be stressed that the analysis of experimental
data was based on the simplest pseudophase model not
accounting for the exchange of the reactive ions (HO–,
BrO–) and inert anion (Br–) between water and the micel-
lar pseudophase. The consideration of these equilibria is
obviously very important for the description of the
micellar effects of a surfactant since it makes possible to
more accurately estimate the concentration of the reactive
(1 + KSc)(1 + KBrO_ c)
[S]
k2m,BrO_/V )
k2,HO
w
_
KSKHO_ c
m
[HO_ ]o
(16)
(1 + KSc)(1 + KHO_ c)
where the binding constants have the following appear-
ance:
RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 44 No. 5 2008

NEW SOURCES OF “ACTIVE” HALOGEN
643
and kmapp = 9.16 × 10–2, then kmapp/kwapp kwapp ≈ 30–40. The
reason of it is the effect of substrate concentration in the
micellar pseudophase. Actually, the maximum catalytic
ions in water and the micellar pseudophase [32]. However
this approach requires the estimation of a number of
constants of ion exchange that is frequently a very
difficult task.
In the micelles of surfactant the hypobromite ion
behaves like a typical α-nucleophile, and the transfer of
the reaction from water into micelles of compound VIII
results in an increase of the apparent reaction rate. Thus
at [BrO–]o 0.02 mol l−1 the value kwapp = 3.10 ×10–3 –2.2 ×
10–3 (calculated based on the values of kw2,BrO–, Table 1),
(18)
micellar effect can be evaluated also be equation (18)
[27] and it amounts to 30–40.
Table 3. Reaction conditions and apparent rate constants in reactions of BrO– ion with 4-nitrophenyl diethylphosphonate (I),
diethylphosphate (II), and toluenesulfonate (III); water, μ 1.0, 25°C
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PROKOP’EVA et al.
Inasmuch as km2,BrO– ≤ kw2,BrO–, obviously just the
644
4-toluenesulfonyl chloride respectively in anhydrous
dioxane in the presence of triethylamine. After isolation
ester I was twice ditilled in a vacuum at a pressure of
0.05 mm Hg. Ester III was thrice recrystallized from
anhydrous ethanol. The physicochemical characteristics
(mp, nD20) and UV spectra were in full agreement with
the published data. Substrate II was purchased from
Aldrich and used without further purification.
concentrating of ester I in the micellar pseudophase
governs the observed increase in the reaction rate. There-
with already at the concentration of [BrO–]o 0.02 mol l−1
the half-conversion time of substrate I into the reaction
products would reach ~6 s, and it is comparable with τ1/2
value at the decomposition of the ester with water
solutions of hypobromite ion at [BrO–]o 1 mol l−1.
Kinetic relationships of substrate decomposition and
the micellar effects in the micelles of compounds VIII
and IX are practically similar. However the obvious
advantage of organic complex VIII is its being simul-
taneously a source of the active bromine and micelle
formative compound. Considering that the micelles of
compound IX accelerate the oxidation of p-nitro-
phenolate ion [24]* the generalized facility based on
compound VIII is undoubtedly interesting for the
practice of decomposition and utilization of ecotoxicants
by the oxidative-nucleophilic mechanism of action.
Inorganic reagents of “specially pure” and “chemical-
ly pure” grades were used without additional purification.
Bis(N,N-dimethylacetamide)hydrogen dibromo-
bromate (VI). A solution of 225 ml (1.5 mol) of 40%
hydrobromic acid was mixed at cooling with 78 ml
(1.5 mol) of bromine. To this mixture was poured at
vigorous stirring 225 ml (3 mol) of N,N-dimethylacet-
amide. A heavy red oily substance separated and slowly
crystallized at cooling and stirring. The precipitate was
filtered off and dried in air. The yield was commonly no
worse than 570 g (91%). The reaction product was
recrystallized from methanol (~1 ml per 1 g of dibromo-
bromate) avoiding strong heating of the solution, or it
was distilled in a vacuum of an oil pump equipped with
a liquid nitrogen trap at bp 86–90°C (0.05 mm Hg), mp
Just similar surfactants may be regarded as an alterna-
tive to the “green” systems “hydrogen peroxide–
activator”. Although the hydroperoxide anion is among
the strongest α-nucleophiles, the hydrogen peroxide is
relatively weak oxidant that demands the necessary
application of activators of acid nature increasing the
oxidative ability of H2O2 [2, 3]. It commonly requires
the reaction to be performed in weakly alkaline media
(pH < 10). But in this case the fraction of the hydro-
peroxide ion as nucleophilic reagent is small, and it is
necessary to use high concentrations of the unstable
hydrogen peroxide (≥1mol l−1). The organic complexes
IV–VIII at pH ≈ 10.0 and [HOBr]o << 1 mol l−1 ensure
the desired rate of decomposition of organophosphorus
compounds.
1
81–83°C. The H, 13C, and 17O NMR spectra of com-
pound VI were published in [34].
Bis(N-acetylpiperidine)hydrogen dibromo-
bromate (IV) was obtained similarly, mp 80–82°C.
(N,N'-Diacetylpiperazine)hydrogen dibromo-
bromate (V). To a solution of 1 g (5.9 mmol) of N,N'-
diacetylpiperazine in 5 ml of water was added a mixture
of 0.42 ml (3.9 mmol) of 40% hydrobromic acid and
0.16 ml (3.0 mmol) of bromine, the separated precipitate
was filtered off, washed with methanol, and dried, mp
183–184°C.
It should be noted in conclusion that the possible
applications of complexes of type IV–VIII are not
limited to the problem under discussion. They can find
and already have found application as was mentioned
above in the fine organic synthesis [26], as disinfectants
(to suppress the unwanted microflora in closed reservoirs,
purification of sweet water under stringent conditions)
[33] etc. showing once more that these compounds are
unique.
Bis(N,N-dimethylacetamide)hydrogen chloro-
bromobromate (VII). To a solution of 4.5 ml (56 mmol)
of 38% hydrochloric acid was added 2.8 ml (55 μmol)
of bromine, the mixture was cooled, and 10 ml
(0.11 mol) of dimethylacetamide was added at vigorous
stirring. The precipitated yellow-orange crystals were
filtered off and recrystallized from methanol, mp 81–
83°C.
Cetyltrimethylammonium dibromobromate
(VIII). Into a desiccator over a beaker containing ~1 ml
(20 mmol) of bromine was placed 2.35 g (6.07 mmol) of
cetyltrimethylammonium bromide. Within 24 h an oily
red substance formed that was left in air till it solidified.
It was crushed and maintained in a vacuum of a water-
jet pump. Yield 3.15 g (5.7 mmol).
EXPERIMENTAL
Substrates I and III were obtained by acylation of
4-nitrophenol with diethyl chlorophosphonate and
* The effect of compound VIII on the oxidation of p-nitro-
phenolate ion was not investigated in this study.
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NEW SOURCES OF “ACTIVE” HALOGEN
645
Langmuir, 2001, vol. 17, p. 4809; Menger, F.M. and Rourk,
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In all organic complexes IV–VIII the content of active
bromine corresponded to the stoichiometric composition.
The method of kinetic experiments was described
in detail in [4, 30]. The solutions of reagents were
prepared just before each series of kinetic measurements.
Double distilled water was used. When the initial con-
centration of the nucleophile was less than 0.02 mol l−1,
sodium carbonate was applied as a buffer at the con-
centration 0.05–0.005 mol l−1. The required pH of buffer
solutions was adjusted by KOH and HCl solutions. The
acidity of the medium was checked before and after each
kinetic run with a pH-Meter-744, Metrohm; when the
change in pH after the end of the run exceeded 0.05 pH
unit, the run was rejected. The hydrobromic acid
concentration was estimated by iodometry. Ionic force
was adjusted with 1 Μ potassium chloride solution
(except the experiments with dibromobromate VIII).All
reactions were studied in water. The reaction progress
was monitored by measuring the absorption of the formed
p-nitrophenolate ion at λ 400–440 nm on spectro-
photometers Specord UV VIS and Genesys 10UV. The
substrate was charged into the cell from a capillary as
a concentrated solution in anhydrous dioxane. In the
kinetic runs the initial concentration of substrate (<5 ×
10–5 mol l−1) was always far less than the initial con-
centration of the nucleophile. The values kapp, s–1, were
calculated from the variation in time of the optical density
by equation (19).
2. Richardson, D.E., Yao, H., Frank, K.M., and Bennett, D.A.,
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(19)
ln(D∝ – Dô) = ln(D∝ – Do) – kappô ,
where Do , Dτ, and D∝ are optical densities at the initial,
running, and final moment of the reaction respectively.
In Table 3 conditions are compiled of reactions of BrO–
generated by complexes IV–VII with esters I–III, and
the apparent pseudofirst order rate constants are
presented. Linear plots were processed by the least-mean-
squares procedures, and their accuracy was shown by
the mean square deviations.
8. Dancaster, E.A., J. Phys. Chem., 1932, vol. 36, p. 1712;
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The authors are grateful to Professor C.A.Bunton
(University of California in Santa Barbara, U.S.A.) for
taking part in discussing the results and for valuable
suggestions regarding the published article.
The study was carried out under a financial support
of the Civil Research and Development Foundation
(CRDF) USA (grant UC2-2489-DO-03).
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