Peroxyhydrocarbonate and peroxocarbonate ions as typical α-nucleophiles in phosphonyl transfer
In a search for novel, high-reactivity, α-nucleophiles we examined the kinetics of decomposition of 4-nitrophenyldiethyl phosphonate (NPDEPN) by Н₂О₂/NH₄HCO₃/HО⁻ at рН 7.7—10.4. This system generates HCO₄⁻ and CO₄²⁻, and their equilibrium concentrations were calculated with the corresponding equilib...
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Інститут загальної та неорганічної хімії ім. В.І. Вернадського НАН України
2011
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| Цитувати: | Peroxyhydrocarbonate and peroxocarbonate ions as typical α-nucleophiles in phosphonyl transfer / T.M. Prokop’eva, Yu.S. Sadovskii, V.A. Savyolova, T.N. Solomoichenko, Zh.P. Piskunova, C.A. Bunton, A.F. Popov // Украинский химический журнал. — 2011. — Т. 77, № 1. — С. 54-60. — Бібліогр.: 31 назв. — англ. |
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irk-123456789-1862292022-11-10T01:25:09Z Peroxyhydrocarbonate and peroxocarbonate ions as typical α-nucleophiles in phosphonyl transfer Prokop’eva, T.M. Sadovskii, Yu.S. Savyolova, V.A. Solomoichenko, T.N. Piskunova, Zh.P. Bunton, C.A. Popov, A.F. Органическая химия In a search for novel, high-reactivity, α-nucleophiles we examined the kinetics of decomposition of 4-nitrophenyldiethyl phosphonate (NPDEPN) by Н₂О₂/NH₄HCO₃/HО⁻ at рН 7.7—10.4. This system generates HCO₄⁻ and CO₄²⁻, and their equilibrium concentrations were calculated with the corresponding equilibrium constants, allowing estimation of second-order rate constants for nucleophilic reactions with NPDEPN, kHCO₄-= 0.006 and kCO₄²-= 0.18 M⁻¹×s⁻¹ (25 °C, μ=2.0 М). As shown by comparisons of Bronsted relationships of the rate constants with those for other anionic nucleophiles in dephosphonylation of NPDEPN, HCO₄⁻ and CO₄²⁻ ions are typical α-nucleophiles. These findings can be significant in selection of optimum conditions for decomposition of various ecotoxicants. С целью поиска новых высокореакционноспособных α-нуклеофилов изучена кинетика разложения 4-нитрофенилдиэтилфосфоната (NPDEPN) системой Н₂О₂/NH₄HCO₃/HО⁻ (рН 7.7—10.4). Данная система генерирует ионы HCO₄⁻ и CO₄²⁻ ; с использованием соответствующих констант равновесия были рассчитаны равновесные концентрации этих ионов, что дало возможность определить константы скорости второго порядка их нуклеофильных реакций с NPDEPN, kHCO₄ -=0.006 и kCO₄²-=0.18 M⁻¹×с⁻¹ (25 °C, μ=2.0 М). Сопоставление в рамках уравнения Бренстеда полученных величин и констант k для других неорганических анионов в реакции с NPDEPN позволило отнести ионы HCO₄⁻ и CO₄²⁻ к типичным α-нуклеофилам. Результаты могут иметь значение для выбора оптимальных условий разложения экотоксикантов различной природы. З метою пошуку нових високореакційноздатних α-нуклеофілів вивчено кінетику розкладу 4-нітрофенілдіетилфосфонату (NPDEPN) системою Н₂О₂/NH₄HCO₃/HО⁻ (рН 7.7—10.4). Дана система генерує йони HCO₄⁻ і CO₄²⁻; з використанням відповідних констант рівноваги було обчислено рівноважні концентрації цих йонів, що дало змогу визначити константи швидкості другого порядку їх нуклеофільних реакцій з NPDEPN, kHCO₄-=0.006 і kCO₄²-=0.18 M⁻¹×с⁻¹ (25 °C, μ= =2.0 М). Зіставлення в рамках рівняння Бренстеда одержаних величин і констант k для інших неорганічних аніонів у реакції з NPDEPN дозволило вважати йони HCO₄⁻ і CO₄²⁻ типовими α-нуклеофілами. Результати можуть мати значення для вибору оптимальних умов розкладу екотоксикантів різної природи. 2011 Article Peroxyhydrocarbonate and peroxocarbonate ions as typical α-nucleophiles in phosphonyl transfer / T.M. Prokop’eva, Yu.S. Sadovskii, V.A. Savyolova, T.N. Solomoichenko, Zh.P. Piskunova, C.A. Bunton, A.F. Popov // Украинский химический журнал. — 2011. — Т. 77, № 1. — С. 54-60. — Бібліогр.: 31 назв. — англ. 0041–6045 http://dspace.nbuv.gov.ua/handle/123456789/186229 547:541.127/.8 en Украинский химический журнал Інститут загальної та неорганічної хімії ім. В.І. Вернадського НАН України |
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| language |
English |
| topic |
Органическая химия Органическая химия |
| spellingShingle |
Органическая химия Органическая химия Prokop’eva, T.M. Sadovskii, Yu.S. Savyolova, V.A. Solomoichenko, T.N. Piskunova, Zh.P. Bunton, C.A. Popov, A.F. Peroxyhydrocarbonate and peroxocarbonate ions as typical α-nucleophiles in phosphonyl transfer Украинский химический журнал |
| description |
In a search for novel, high-reactivity, α-nucleophiles we examined the kinetics of decomposition of 4-nitrophenyldiethyl phosphonate (NPDEPN) by Н₂О₂/NH₄HCO₃/HО⁻ at рН 7.7—10.4. This system generates HCO₄⁻ and CO₄²⁻, and their equilibrium concentrations were calculated with the corresponding equilibrium constants, allowing estimation of second-order rate constants for nucleophilic reactions with NPDEPN, kHCO₄-= 0.006 and kCO₄²-= 0.18 M⁻¹×s⁻¹ (25 °C, μ=2.0 М). As shown by comparisons of Bronsted relationships of the rate constants with those for other anionic nucleophiles in dephosphonylation of NPDEPN, HCO₄⁻ and CO₄²⁻ ions are typical α-nucleophiles. These findings can be significant in selection of optimum conditions for decomposition of various ecotoxicants. |
| format |
Article |
| author |
Prokop’eva, T.M. Sadovskii, Yu.S. Savyolova, V.A. Solomoichenko, T.N. Piskunova, Zh.P. Bunton, C.A. Popov, A.F. |
| author_facet |
Prokop’eva, T.M. Sadovskii, Yu.S. Savyolova, V.A. Solomoichenko, T.N. Piskunova, Zh.P. Bunton, C.A. Popov, A.F. |
| author_sort |
Prokop’eva, T.M. |
| title |
Peroxyhydrocarbonate and peroxocarbonate ions as typical α-nucleophiles in phosphonyl transfer |
| title_short |
Peroxyhydrocarbonate and peroxocarbonate ions as typical α-nucleophiles in phosphonyl transfer |
| title_full |
Peroxyhydrocarbonate and peroxocarbonate ions as typical α-nucleophiles in phosphonyl transfer |
| title_fullStr |
Peroxyhydrocarbonate and peroxocarbonate ions as typical α-nucleophiles in phosphonyl transfer |
| title_full_unstemmed |
Peroxyhydrocarbonate and peroxocarbonate ions as typical α-nucleophiles in phosphonyl transfer |
| title_sort |
peroxyhydrocarbonate and peroxocarbonate ions as typical α-nucleophiles in phosphonyl transfer |
| publisher |
Інститут загальної та неорганічної хімії ім. В.І. Вернадського НАН України |
| publishDate |
2011 |
| topic_facet |
Органическая химия |
| url |
http://dspace.nbuv.gov.ua/handle/123456789/186229 |
| citation_txt |
Peroxyhydrocarbonate and peroxocarbonate ions as typical α-nucleophiles in phosphonyl transfer / T.M. Prokop’eva, Yu.S. Sadovskii, V.A. Savyolova, T.N. Solomoichenko, Zh.P. Piskunova, C.A. Bunton, A.F. Popov // Украинский химический журнал. — 2011. — Т. 77, № 1. — С. 54-60. — Бібліогр.: 31 назв. — англ. |
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Украинский химический журнал |
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UDC 547:541.127/.8
T.M. Prokop’eva, Yu.S. Sadovskii, V.A. Savyolova, T.N. Solomoichenko,
Zh.P. Piskunova, C.A. Bunton, A.F. Popov
PEROXYHYDROCARBONATE AND PEROXOCARBONATE IONS AS TYPICAL
α-NUCLEOPHILES IN PHOSPHONYL TRANSFER*
In a search for novel, high-reactivity, α-nucleophiles we examined the kinetics of decomposition of 4-nitrophenyldiethyl
phosphonate (NPDEPN) by Н2О2/NH4HCO3/HО– at рН 7.7—10.4. This system generates HCO4
– and CO4
2–,
and their equilibrium concentrations were calculated with the corresponding equilibrium constants, allowing estima-
tion of second-order rate constants for nucleophilic reactions with NPDEPN, kHCO4
−= 0.006 and kCO4
2−= 0.18 M –1⋅s–1
(25 oC, µ=2.0 М). As shown by comparisons of Bronsted relationships of the rate constants with those for other
anionic nucleophiles in dephosphonylation of NPDEPN, HCO4
– and CO4
2– ions are typical α-nucleophiles. These
findings can be significant in selection of optimum conditions for decomposition of various ecotoxicants.
INTRODUCTION . Typical inorganic α-nucleo-
philes such as hypochlorite, hypobromite and hydro-
peroxide ions, neutral and anionic forms of hydro-
xylamine, exhibit abnormally high reactivity (α-effect),
as expected from Bronsted relationships for “nor-
mal” oxygen nucleophiles (aryloxide, alkoxide ions,
HO– and H2O) [1–4]. Possible applications of these
inorganic nucleophiles is their use in systems for effi-
cient destruction of ecotoxicants — pesticides, chemi-
cal warfare agents, etc. [5–7]. Of special interest are
mixtures of hydrogen peroxide with activators [6–
12], e.g., alkaline metal and ammonium hydrocarbo-
nates because aqueous H2O2/HCO3
–/HO– mixtures
contain the strong α-nucleophile, HO2
–, and an effi-
cient oxidant, HCO4
– [4, 6–12] allowing design of ver-
satile oxidizing-nucleophilic systems for “green” de-
composition of highly toxic phosphorus esters thro-
ugh nucleophilic attack by HO2
– and other peroxyions,
and of sulfide derivatives, e.g., Mustard Gas, by oxi-
dation with HCO4
– [5, 6]. There is evidence that both
HCO4
– and CO4
2–, which are formed in this system,
react as nucleophiles [13–16]. Until recently it was
uncertain whether these ions are normal oxygen or
α-nucleophiles. Structurally, CO4
2– meets the require-
ments of α-nucleophiles: i) the nucleophilic center
(oxygen) is anionic and is in the second period of the
Periodic Table; ii) there are no adjacent substituents
sterically hindering attack on the electrophilic center
in the substrate; iii) electronegative oxygen with un-
shared electron pairs is α- to the reaction center of the
reagent, which destabilizes the ground state and stabi-
lizes the transition state of the reaction [17, 18]. It is
difficult to predict, a priori, the kinetic behavior of
HCO4
– although it should be considerably less nuc-
leophilic than the dianion.
In this work we studied the decomposition kine-
tics of 4-nitrophenyldiethyl phosphonate (NPDEPN)
as a low-toxicity model of some pesticides and che-
mical agents with Н2О2/NH4HCO3/HО–, and estima-
ted nucleophilicities of aqueous HCO4
– and CO4
2– (c.f.
[16]). Such research can be useful in selection of opti-
mum conditions for decomposition of ecotoxicants.
As a source of HCO3
– we used ammonium hyd-
rogen carbonate because this compound is readily so-
luble in water, reasonably stable in the presence of
hydrogen peroxide, and leaves no inorganic residue
after reaction. However, we had to allow for reaction
of NH3 in these conditions.
EXPERIM ENTAL PART . Synthesis and purifica-
tion of NPDEPN are described [4]. The analytically
pure reagents were 25 % aqueous ammonia, ammo-
nium hydrogen carbonate and chloride, potassium hyd-
roxide and chloride, and bidistilled water. Concentra-
tions of hydrogen peroxide solutions were determi-
ned by titration with permanganate ion [19].
Hydrogen peroxide in the working solutions was
stabilized by Trilon B (10–4 M). Solutions of Н2О2—
NH4HCO3 were equilibrated for ca. 20 min at each
pH. The pH was controlled by KOH or by addition
of a certain volume of NH4OH of the known concen-
tration, pH was measured on a Metrohm 744. Kine-
tics were in water at 25 оС, ionic strength (µ) 2.0, main-
Органическая химия
© T.M. Prokop’eva, Yu.S. Sadovskii, V.A. Savyolova, T.N. Solomoichenko, Zh.P. Piskunova,
C.A. Bunton, A.F . Popov , 2011
* This research was made possible in part by Award UC2-2489-DO-03 of the U.S. Civilian Research & Development
Foundation (CRDF).
54 ISSN 0041-6045. УКР. ХИМ . ЖУРН . 2011. Т. 77, № 1
tained with NH4HCO3, NH4Cl, or, where necessary,
KCl. Reactions were monitored by following the
increasing absorbance of 4-nitrophenoxide ion at λ
410 nm on a Genesis 10 UV (Thermo Electron) spec-
trophotometer. Hydrogen peroxide was in large excess
over the substrate (≈ 5⋅10–5 M). Decomposition of H2O2
during the time of reaction did not cause problems,
but it increased slightly if KOH was used to control
pH. Calculation of the first-order rate constants was
as described [4]. After complete reaction the concen-
tration of 4-nitrophenoxide ion was that of the initial
substrate. The reported first-order rate constants are
averages of up to 12 results agreeing within 3 %.
RESULTS AND DISCUSSION. Decomposition of
NPDEPN in the reaction conditions involves five
parallel pathways (scheme) and the very slow reac-
tion with H2O, which is not kinetically important:
The observed first-order rate constant with res-
pect to substrate, k, s–1 is given by equation:
k = kHO−[HO– ] + kHO2
−[HO2
– ] + kNH 3
[NH 3 ] +
+ kHCO 4
−[HCO4
– ] + kCO4
2−[CO4
2– ] , (1)
where kHO −, kHO 2
−, kNH 3
, kHCO 4
−, kCO4
2− are second-
order rate constants (M–1⋅s–1) of the corresponding
reactions, and quantities in square brackets are equi-
librium concentrations of the nucleophiles. Equation
(1) allows calculation of kHCO 4
− and kCO4
2− after allo-
wance for contributions of reactions of the other nuc-
leophiles, which are known from independent expe-
riments, and the corresponding concentrations can
be estimated with known equilibrium constants. The
overall reactions were followed over the pH range
7.67—10.4.
Values of kHO 2
− and kNH 3
were measured inde-
pendently, and kHO− =0.15 M–1⋅s–1 had been deter-
mined earlier [4].
Ammonolysis of NPDEPN was studied in
aqueous ammonia at µ =2.0 M (NH4HCO3 or KCl),
see table 1. Equilibrium concentrations [NH3] were
calculated [20] with the acid disso-
ciation constant [21] of NH4
+ Ka=
=5.66⋅10–10 and the experimental
pH and kinetics fitted equation (2):
k – kHO − [HO– ] = kNH 3
[NH3] . (2)
The rate constant of ammono-
lysis is kNH 3
= (6.29 ± 0.27)⋅10–5
M–1⋅s–1 (r =0.996, so=2.5⋅10–5, n=6) and fits the Bron-
sted equation (logkamine = –7.4 + 0.35pKa) for amine
reactions with NPDEPN [22].
The second-order rate constant kHO2
− and the
acid dissociation constant of hydrogen peroxide, K1,
were measured in aqueous NH4Cl (µ =2.0 М) and
fitted to eqn. (3) as in ref. [4], with allowance for re-
actions with OH– and NH3 :
k1 = kHO2
− – 1
K1
k1[H + ] , (3)
where k1, M–1⋅s–1 is the product of rate constant
kHO 2
− and the fraction of HO2
– :
k1 = kHO2
−
[HO2
− ]
[H2O2]o
=
=
k − k
HO −[HO −] − kNH 3
[NH 3]
[H 2O2]o
. (4)
The results are in table 2 and with equation (3)
fit equation (5):
k1 = (3.51 ± 0.17) – (3.42 ± 0.25)⋅1011k1[H +] , (5)
r =0.982, so =0.21, n=9,
T a b l e 1
Ammonolysis of 4-nitrophenyldiethyl phosphonate (water,
t=25 оС, µ =2.0 M (NH 4HCO3 or KCl)
рН
(k – k
HO−
[HO- ])
⋅105, s–1
[NH3]0 [NH4HCO3]0 [NH3]
M
9.60 16.6 2.66 2 3.23
10.22 39.1 5.33 2 6.63
10.56 61.9 7.99 2 9.53
10.79a 0.340 0.0266 — 0.0259
11.00a 0.600 0.0533 — 0.0524
11.49a 4.35 0.533 — 0.530
a Ionic strength was controlled by KCl.
ISSN 0041-6045. УКР. ХИМ . ЖУРН . 2011. Т. 77, № 1 55
and, k
HO 2
−= (3.51 ± 0.17) M–1⋅s–1, K1= (2.92 ± 0.21)⋅
10–12 M. These values are in reasonable agreement
with those in different conditions viz. kHO 2
− = 7.3
M –1s–1, K1= 3.16⋅10–12 M, µ =1.0 М (KCl) [4] and
kHO 2
– = 5.00 M–1⋅s–1, K1= 4.27⋅10–12 M, µ = 2.0 М
(KCl) [16].
The constants kHO 2
− and K1 in 2 M NH4Cl are
lower than those in 2 М KCl, probably due to speci-
fic interactions of Н2О2 and HO2
– with NH3, and
equilibrium formation of hydrogen bond complexes
by analogy with interaction of hydroperoxides with
tertiary amines [23]. A large excess of ammonia
([NH3] / [H2O2]0 ≈ 800, table 2) favors formation of
such complexes. As shown later, this formation does
not significantly affect values of kHCO 4
− and kCO 4
2−.
The calculations were made with equilibria equ-
ations (6)—(9), largely with data from the cited lite-
rature:
H 2O2
K1 H + + HO2
– , K1= 2.92⋅10–12 M ; (6)
H 2O2 + HCO3
–
K
2 HCO4
– + H 2O,
K2= 0.33 M–1 [9] ; (7)
HCO4
–
K3 H + + CO4
2– , K3= 3.98⋅10–10 M (8)
HCO3
–
K4 H + + CO3
2– , K4= 4.68⋅10–11 M (9)
and material balance:
[HCO3– ]0 = [HCO3
– ] + [CO3
2– ] +
+ [HC4
– ] + [CO3
2– ] , (10)
[H 2O2]0 = [H 2O2] + [HO2
– ] +
+ [HCO4
– ] + [CO4
2– ] . (11)
Equilibrium concentrations of peroxoanions
HO2
–, HCO4
– and CO4
2– together with related rate
constants, k, equilibrium concentrations of ammonia
and initial concentrations of hydrogen peroxide are
in table 3.
The second-order rate constants for contributi-
ons of the peroxocarbonate reactions are given by
equation (12), which is derived from equation (1):
∆k = k
HCO 4
−[HCO4
– ] + k
CO 4
2−[CO4
2– ] , (12)
where ∆k = k – kHO −[HO– ] – kHO 2
−[HO2
– ] –
– kNH 3
[NH 3] , (13)
and table 3 includes values of ∆k, equation (13).
It is significant that the overall contribution from
the peroxycarbonate ion reactions to the observed ra-
te constant [i.e. ∆k/k ratio, see eqns. (12) and (1)] is
generally 70—90 %, indicating that uncertainties in
contributions of the other reactions, eqn. (1), are not
very important. Comparison of ∆k, for reactions of
[HCO4
– ], and [CO4
2– ] at similar initial [H2O2]o
shows (table 3) that an increase in рН , and therefore
in [CO4
2– ], increases ∆k , while [HCO4
– ] decreases it
(runs 2—9, 10 and 16, and 12, 14, and 22). Therefore
the main contribution to ∆k [equation (12)] is, as exрес-
pted, from kCO 4
2−[CO4
2– ]. Linear correlation, ∆k ver-
sus [CO4
2– ] neglecting the contribution of reaction
with HCO4
– gives:
∆k = (0.13 ± 0.14)⋅10–3 + (0.181 ± 0.007)[CO4
2– ] , (14)
r=0.983, so=6⋅10–4, n=29,
and k
CO 4
2−=0.18 M–1⋅s–1.
Rate constant kHCO 4
− can be estimated by the two-
parameter correlation equation (12), of ∆k versus
[HCO4
– ] and [CO4
2– ] giving equation:
∆k = –(0.00024 ± 0.00020) + (0.0063 ± 0.0025)⋅
⋅[HCO4
– ] + (0.183 ± 0.006)[CO4
2– ] , (15)
R=0.986, so=5⋅10–4, n=29.
As expected, the value of rate constant, kCO 4
2−,
from this equation is essentially that from eqn. (14).
Elimination of the most strongly deviating points
does not significantly affect constants for reactions
involving [HCO4
– ] and [CO4
2– ].
Thus, estimated rate constants are kHCO 4
− =
=(0.006 ± 0.002) M –1⋅s–1 and kCO 4
2− = (0.18 ± 0.01)
T a b l e 2
Observed rate constants k of decomposition of 4-nitrophe-
nyldiethyl phosphonate in H2O2/NH4Cl/HO– ([H2O2]0
0.00246 M, µ =2.0 M (NH 4Cl), KOH, 25 oC)
рН [NH3], M k ⋅103, s–1
10.25 1.82 0.622 ± 0.010
10.50 1.89 0.882 ± 0.010
10.75 1.94 1.28 ± 0.02
11.00 1.97 2.30 ± 0.01
11.25 1.98 3.30 ± 0.02
11.50 1.99 4.86 ± 0.02
11.75 1.99 6.68 ± 0.07
12.00 2.00 8.13 ± 0.05
12.25 2.00 9.82 ± 0.07
Органическая химия
56 ISSN 0041-6045. УКР. ХИМ . ЖУРН . 2011. Т. 77, № 1
M–1⋅s–1. There apparently is a contribution of a re-
action with HCO4
– but it is not large and the value
of kHCO 4
− is uncertain. Slightly different values were
given earlier [16], because here we use a revised va-
lue of kHO 2
− and K1 was determined with ionic
strength maintained with 2 М NH 4Cl rather than
with KCl. The observed rate constants k agree with
kcalc calculated from equation (1) with values of
kHCO 4
− and kCO 4
2− (fig. 1):
k = –(0.23 ± 0.13)⋅10–3 +
+ (1.01 ± 0.02)kcalc , (16)
r=0.992, so=5⋅10–4, n=29.
The plot in fig. 1 has unit slope and a
near zero intercept, as expected from equation
(16), and is based on the data in table 3.
The value of K3 =3.98⋅10–10 is reasonable
in terms of similarities in рKа of HCO4
– and
HSO5
– (that of HSO5
– is 9.4 [8]). An approxi-
mate рKа of HCO4
– can also be estimated
from pH-rate profiles for oxidations of orga-
nic sulfides, 2-hydroxyethylphenyl [10], diethyl
[11] and methylphenyl sulfide [12] in Н2О2/
NH4НCO3/HO–. The rates of oxidation by
HCO4
– are almost pH-independent in the
range ~7—9, consistent with рKа>рН , follo-
wed by rate decreases with increasing pH,
with oxidations by HCO4
– and CO4
2–, ten-
ding to a constant rate at рН 10—11 with
рKа< рН and the weaker oxidant, CO4
2–,
being the dominant species. The point for
рKа=рН is in the pH-range of decreasing
rates. The mid-point of the pH-rate profile
should approximate the рKа of HCO4
– giving
values of рKа~10 [10], ~9.8 [11], ~9.0 [12]
and therefore рKа of HCO4
– should be in the
range 9.0 —10.0. These results are consistent
with K3 =3.98⋅10–10.
Thus, the reactivity of CO4
2– ion (as a
nucleophile) toward NPDEPN is ca. 20 fold
lower than that of HO2
– (kHO 2
− =3.51 M–1⋅s–1).
However, the estimated rate constant of the
reaction of CO4
2– and triphenyl phosphinate
in aqueous alcohol, kCO 4
2− = 210 M –1⋅s–1 is
≈ 2.3 fold higher than kH O 2
− [15] indica-
ting that effects of substrate structure and
solvent composition on nucleophilicities of
CO4
2– and HO2
– have to be considered.
It is useful to examine Bronsted relation-
ships in comparing nucleophilicities of
HCO4
– and CO4
2– with those of “normal” anionic
oxygen nucleophiles [3] and anionic inorganic α-nuc-
leophiles [4], provided that appropriate basicities can
be established.
Kinetic parameters for decompositions of peroxy-
carbonic acid (to hydrogen peroxide and carbon di-
oxide) and carbonic acid (to water and carbon di-
oxide) are similar, and Richardson et al. [8] sugges-
ted that this is also the situation for the first-stage
T a b l e 3
Peroxohydrolysis of 4-nitrophenyldiethyl phosphonate in Н2О2/
NH4HCO3/HO– (water, t=25 oC, µ =2.0 M, [NH 4HCO3]0 = 2.00 M)
pH [H2O2]0,
М
k ⋅103,
s–1
[NH3]
[HO2
– ]
⋅104 ∆k ⋅103,
s–1
[HCO4
–
] ⋅102
[CO4
2– ]
⋅103
M M
7.67 0.242 1.22 0.0516 0.202 1.15 9.26 1.72
7.76 0.242 0.891 0.0656 0.248 0.800 9.24 2.12
7.78 0.242 0.973 0.0695 0.259 0.878 9.24 2.22
7.88 0.242 1.01 0.0878 0.326 0.890 9.21 2.78
7.90 0.242 1.10 0.0929 0.341 0.974 9.21 2.91
7.93 0.242 1.24 0.102 0.365 1.11 9.20 3.12
8.09 0.242 1.45 0.151 0.525 1.26 9.13 4.47
8.10 0.242 1.31 0.151 0.537 1.11 9.13 4.57
8.15 0.242 1.60 0.176 0.601 1.38 9.10 5.12
8.22 0.121 0.951 0.206 0.349 0.815 4.60 3.04
8.50 0.178 2.66 0.488 0.963 2.29 6.54 8.22
8.56 0.237 3.15 0.477 1.47 2.60 8.57 12.4
8.60 0.227 3.81 0.515 1.54 3.24 8.16 12.9
8.65 0.236 3.36 0.565 1.78 2.70 8.41 14.9
8.73 0.483 8.12 0.715 4.44 6.52 16.4 35.1
8.90 0.120 2.89 1.03 1.53 2.29 4.09 12.9
8.97 0.125 2.38 1.15 1.85 1.66 4.16 15.5
9.00 0.116 2.66 1.12 1.82 1.95 3.83 15.2
9.16 0.110 3.53 1.62 1.88 2.59 3.39 19.5
9.19 0.0581 2.19 1.81 1.32 1.61 1.78 10.9
9.50 0.219 16.4 2.57 9.07 13.1 5.31 66.8
9.50 0.236 17.2 2.57 9.80 13.6 5.71 71.8
9.56 0.0588 3.83 3.14 2.63 2.70 1.38 19.9
0.72 0.0283 2.91 3.89 1.64 2.08 0.564 11.8
9.75 0.0579 5.27 3.90 3.55 3.77 1.11 24.8
9.90 0.0214 3.01 5.00 1.65 2.11 0.340 10.7
10.08 0.0155 2.86 6.39 1.57 1.89 0.188 8.99
10.40 0.00933 2.74 9.34 1.56 1.57 0.180 6.41
10.40 0.00860 2.23 9.34 1.43 1.10 0.0591 5.91
ISSN 0041-6045. УКР. ХИМ . ЖУРН . 2011. Т. 77, № 1 57
acid dissociation constants, рKа, which would give,
as a base, рKа (HCO4
– ) = 3.45, i.e. close to the true
рKа of HCO3
– rather than the apparent value in wa-
ter for HCO3
– 6.35 [24].
Bronsted plots for dephosphonylation of NPD-
EPN with our values of kHCO 4
− and kCO 4
2− are shown
in fig. 2, line 2, with data for reactions with other ani-
onic inorganic nucleophiles. The reactions with
HCO4
– and CO4
2– are much faster those of NPDE-
PN with aryloxide/alkoxide ions (line 1), a standard
reaction series [3]. Rate differences correspond to
∆logkHCO 4
− =3.8 and ∆logkCO 4
2− =2.5 with and respec-
tively, with the behaviour typical of α-nucleophiles
with supernucleophilic reactivity toward NPDEPN.
Reactivities towards NPDEPN of the anionic
α-nucleophiles, including ClO–, BrO– and NH2O–,
and F– *, which is a strong nucleophile in dephos-
phorylations [4], are described by the Bronsted re-
lationship, where kNu is the appropriate second-order
rate constant:
logkNu = –(2.9 ± 0.2) + (0.25 ± 0.02)pKa . (17)
Introduction of rate constants for HCO4
– and
CO4
2– into the equation also gives a single Bronsted
relationship (line 2 in fig. 2):
logkNu = –(3.06 ± 0.14) + (0.26 ± 0.02)pKa , (18)
r=0.992, so=0.14, n= 6.
The fact that kHCO 4
− and kCO 4
2− fit on the corre-
lation line, with little change in the coefficients, indi-
cates that possible specific solvation of HCO4
– and
CO4
2– ions by NH4
+ and NH3 or its complexation
with H2O2 have little effect on the reactivity of the
peroxocarbonate ions.
The simple relationship equation (18) indicates
that common features control the kinetic behavior of
these inorganic nucleophiles towards NPDEPN, with
rates of phosphonyl transfer being sensitive to nucleo-
phile basicities [4]. The slope of the plot of logkNu
against pKa is consistently lower for α- than for
simple nucleophiles as in fig. 2, lines 2 and 1 (the slopes
are 0.26 and 0.50 [3] respectively).
The point for HO2
– falls above line 2. This ap-
parent high reactivity of HO2
– may be due to tran-
sition state stabilization by hydrogen bonding with
the equatorial oxygen atom [4] (I). The correspon-
ding hydrogen bonding by N H 2 in N H 2O– wo-
uld be less important and this nucleophile fits on
line 2 (fig. 2).
The reactivity of HCO4
– and the fit to the Bron-
sted relationship, are interesting because X-ray crys-
tallography indicates that the resonance stabilized
structure II, is НООС(О)О–, in the solid and probab-
ly also in solution [25], rather than –ООС(О)ОН . If
this structure solely governed reactivity the nucleo-
Органическая химия
Fig. 1. Observed rate constants k versus calculated kcalc.
F ig. 2. Bronsted plots for reactions of aryloxide/alkoxide
ions (1) and inorganic α-nucleophiles (2) with 4-nitrophe-
nyldiethyl phosphonate. Values of k Nu, M –1⋅s–1 for ClO–,
BrO–, NH2O– and F– are from ref. [4]. Statistical correction
for pKa of HCO4
– and CO4
2– is 0.30. Line 1 is from data
in ref. [3]; line 2 is from the solid points, see text.
* While F – ion is not an α-nucleophile, in nucleophilic substitutions at phosphoryl and phosphonyl centers it
has reactivities similar to that of anionic inorganic α-nucleophile of the same basicity [4].
I
58 ISSN 0041-6045. УКР. ХИМ . ЖУРН . 2011. Т. 77, № 1
philicity of HCO4
– should be similar to that of weakly
nucleophilic HCO3
– and less than of CO3
2–, also a
weak nucleophile, e.g., in the reaction of CO3
2– with
4-nitrophenyl acetate there is a significant negative
deviation from the Bronsted plot for other “normal”
oxygen and nitrogen nucleophiles [1]. As suggested for
the abnormally high reactivity of the neutral hyd-
roxylamine [4, 26, 27] and amidoxime [28, 29] deriva-
tives and hydroxamate ions [29—31], this “non-
conventional” kinetic behavior of HCO4
– may be due
to stabilizing intramolecular hydrogen bonding in
the transition state III:
Hydrogen bonding and proton transfer are shown
in an energetically favorable seven-membered ring
and, as with oxidation [8, 9], peroxy oxygen is at the
reaction center. Formation of the transition state,
III, could be preceded by proton transfer from pero-
xide to carboxylate oxygen (general base catalysis)
concerted with peroxy oxygen attack on phosphorus:
Richardson et al. [8], in discussing these systems,
point out that proton transfer could involve a solvent
molecule (water or alcohol):
Regardless of the detailed mechanism of dephos-
phonylation by HCO4
– the data point in the Bron-
sted relationship (fig. 2) involves the pKa for deproto-
nation of the carboxylic, rather than the hydroperoxy
group, and the fit in this relationship apparently
involves cancellation of effects in hydrogen and oxy-
gen transfers. There is uncertainty in the extent of
contribution of reaction with HCO4
– which in so-
me conditions is small, and the value of kNu is un-
certain (equation (15)), and lower than expected (fig.
2). The low slope of the Bronsted plot for these α-nu-
cleophiles also obscures deviations from the line plot-
ted for other nucleophiles which, except for HO2
–,
have no readily exchangeable hydrogen and do not
involve the cancellations noted earlier.
CONCLUSIONS. Dephosphorylation kinetics of
NPDEPN in Н2О2/NH4HCO3/HО– show that HCO4
–
and CO4
2– are efficient α-nucleophiles, more reactive
by several orders of magnitude than “normal” anio-
nic oxygen nucleophiles of similar basicities. Of all
known inorganic anionic α-nucleophiles HCO4
– ion
has the lowest basicity (рKа =3.45). Intramolecular
general acid-base catalysis appears to be a factor in the
abnormally high reactivity of the peroxyhydrocarbo-
nate ion.
РЕЗЮМЕ . С целью поиска новых высокореакци-
онноспособных α-нуклеофилов изучена кинетика раз-
ложения 4-нитрофенилдиэтилфосфоната (NPDEPN) сис-
темой Н2О2/NH4HCO3/HО– (рН 7.7—10.4). Данная систе-
ма генерирует ионы HCO4
– и CO4
2– ; с использованием
соответствующих констант равновесия были рассчита-
ны равновесные концентрации этих ионов, что дало
возможность определить константы скорости второго по-
рядка их нуклеофильных реакций с NPDEPN, kHCO4
−=
=0.006 и kCO4
2−=0.18 M –1⋅с–1 (25 oC, µ=2.0 М). Сопостав-
ление в рамках уравнения Бренстеда полученных вели-
чин и констант k для других неорганических анионов
в реакции с NPDEPN позволило отнести ионы HCO4
–
и CO4
2– к типичным α-нуклеофилам. Результаты могут
иметь значение для выбора оптимальных условий разло-
жения экотоксикантов различной природы.
РЕЗЮМЕ. З метою пошуку нових високореакцій-
ноздатних α-нуклеофілів вивчено кінетику розкладу 4-ні-
трофенілдіетилфосфонату (NPDEPN) системою Н2О2/
NH4HCO3/HО– (рН 7.7—10.4). Дана система генерує йо-
ни HCO4
– і CO4
2–; з використанням відповідних кон-
стант рівноваги було обчислено рівноважні концен-
трації цих йонів, що дало змогу визначити константи
швидкості другого порядку їх нуклеофільних реакцій
з NPDEPN, kHCO4
−=0.006 і kCO4
2−=0.18 M –1⋅с–1 (25 oC, µ=
=2.0 М). Зіставлення в рамках рівняння Бренстеда одер-
жаних величин і констант k для інших неорганічних
аніонів у реакції з NPDEPN дозволило вважати йони
HCO4
– і CO4
2– типовими α-нуклеофілами. Результати
можуть мати значення для вибору оптимальних умов
розкладу екотоксикантів різної природи.
II
III
ISSN 0041-6045. УКР. ХИМ . ЖУРН . 2011. Т. 77, № 1 59
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L.M. Litvinenko Institute of Physical Organic & Coal Reseived 18.10.2010
Chemistry, NAS of Ukraine, Donetsk
Department of Chemistry and Biochemistry, University
of California, Santa Barbara, USA
Органическая химия
60 ISSN 0041-6045. УКР. ХИМ . ЖУРН . 2011. Т. 77, № 1
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