Kinetics of the reactions of [Chloro(phenyl)arsanyl]acetic acid with bromo- and iodoacetic acids

Article abstract of DOI:10.1134/S1070363209030074

Quternization of [chloro(phenyl)arsanyl]acetic acid with bromo- and iodoacetic acids in aqueous alkali follows S_N2 mechanism and is accompanied by alkaline hydrolysis of haloacetic acids. The rate constants and thermodynamic parameters of the process were determined

Full text of DOI:10.1134/S1070363209030074

ISSN 1070-3632, Russian Journal of General Chemistry, 2009, Vol. 79, No. 3, pp. 378–382. © Pleiades Publishing, Ltd., 2009.
Original Russian Text © R.R. Rakhmatullin, O.A. Selyutina, V.I. Gavrilov, R.Z. Musin, 2009, published in Zhurnal Obshchei Khimii, 2009, Vol. 79, No. 3,
pp. 388–392.
Kinetics of the Reactions of [Chloro(phenyl)arsanyl]acetic Acid
with Bromo- and Iodoacetic Acids
R. R. Rakhmatullina, O. A. Selyutinaa, V. I. Gavrilova, and R. Z. Musinb
a Kazan State Technological University, ul. K. Marksa 68, Kazan, 420015 Tatarstan, Russia
e-mail: toons@kstu.ru
b Arbuzov Institute of Organic and Physical Chemistry, Kazan Research Center, Russian Academy of Sciences,
ul. Arbuzova 8, Kazan, 420088 Tatarstan, Russia
e-mail: musin@iopc.knc.ru
Received April 15, 2008
Abstract—Quternization of [chloro(phenyl)arsanyl]acetic acid with bromo- and iodoacetic acids in aqueous
alkali follows SN2 mechanism and is accompanied by alkaline hydrolysis of haloacetic acids. The rate constants
and thermodynamic parameters of the process were determined
DOI: 10.1134/S1070363209030074
We previously [1] studied the kinetics of the Meyer
reaction of [chloro(phenyl)arsanyl]acetic acid (I) with
chloroacetic acid in aqueous alkali at 25, 35, 45, and
55°C. In the present work we examined the kinetics of
the reactions of acid I with bromoacetic acid (II) and
iodoacetic acid (III) in aqueous sodium hydroxide.
PhAs(O)(CH2COO_ )2 + Cl_ + Hlg_ ,
PhAs(Cl)CH2COO_ + HlgCH2COO_
k
NaOH
I
II, III
IV
II, Hlg = Br; III, Hlg = I.
(2) The molecular ion peak had m/z 246, the ion
peak with m/z 210 corresponds to the rearrangement
ion [M – HCl]+, and the presence of a strong peak with
m/z 187 is related to formation of the fragment ion
peak [M – C2H3O2]+ as a result of cleavage of the As–
CH2 bond. The subsequent decomposition of the [M –
HCl]+ ion (m/z 210) with elimination of C2HO species
is responsible for the appearance of an intense ion peak
with m/z 169. The ion peak with m/z 91 belongs to the
rearrangement ion [C6H5CH2]+.
[Chloro(phenyl)arsanyl]acetic acid (I) was syn-
thesized according to the procedure described in [2].
SO2, HCl
KI
NaOH
PhAsCl2
PhAsO(OH)2
PhAsO
ClCH2COOH
PhAs(O)(OH)CH2COOH
PhAs(Cl)CH2COOH.
SO2, HCl
KI
The structure of I was additionally confirmed by
electron-impact mass spectrometry. The mass spectrum
(A) is given in Experimental. The mass spectrum of I
taken from “Wiley Registry of Mass Spectral Data
1988-2001, version 3.2.1” (B) is also given for
comparison.
The formation of 2,2'-(phenylarsoryl)diacetate (IV)
was proved by the formation of 2,2'-(phenyl-
arsamediyl)diacetic acid (V) via reduction of IV with
sulfur dioxide directly in the reaction mixture [2].
_
PhAs(O)(CH2COO )2 + SO2
IV
(1) The experimental mass spectrum (A) contains
all ion peaks given in B. The fragmentation pattern is
consistent with structure I.
HCl + KCl
PhAs(CH2COOH)2.
V
378

KINETICS OF THE REACTIONS OF [CHLORO(PHENYL)ARSANYL]ACETIC ACID
379
After recrystallization from water, compound V had
mp 127°C (published data [2]: mp 126–127°C).
Anomalous relation between the reactivities of
bromo and iodo derivatives was observed for the first
time while studying reactions of methyl bromide and
methyl iodide with sodium methoxide in methanol [6].
The opposite directions in the variations of halogen
mobility and C–Hlg bond energy was also noted in the
reaction of ammonia with haloacetic acids in aqueous
solution [5], as well as in the alkaline hydrolysis and
ammonolysis of haloacetic acids in aqueous ethanol
and aqueous dioxane [7].
It was identified by mass spectrometry (EI). The
molecular ion peak (m/z 270, [M]+·) had low intensity
due to the presence of CH2COOH groups which
considerably reduced its stability. Ions with m/z 253
and 252 resulted from elimination of OH group and
water molecule, respectively, from the molecular ion.
Loss of CH2COOH from the molecular ion gives ion
with m/z 211. The most abundant peak was that with
m/z 169. Presumably, it is rearrangement ion [As(OH)
C6H5]+ formed via fragmentation of the ion with m/z
211 via elimination of C2H2O. Expulsion of water and
benzene molecules from [As(OH)C6H5]+ yields ions
with m/z 151 and 91, respectively. The other ion with
low m/z values originate from successive decom-
position of the above ions.
The kinetics of the reactions of [chloro(phenyl)
arsanyl]acetic acid (I) with bromoacetic acid (II) and
iodoacetic acid (III) were studied at 15, 20, 25, and
30°C. The reaction rate is described by kinetic Eq. (4).
ω = k cI cHlg + kh cHlg cNaOH
,
(4)
where ω is the rate of accumulation of halide ions; k is
the rate constant for the reaction of compound I with
haloacetic acid II or III; kh is the rate constant for
alkaline hydrolysis of haloacetic acid II or III; and cI,
cHlg, and cNaOH are the current concentrations of acid I,
haloacetic acid II or III, and sodium hydroxide,
respectively. Apart from argentometric tirtraion, the
reaction rate was also monitored by iodometric
titration, following the the consumption of arsinite ion.
The reaction of [chloro(phenyl)arsanyl]acetic acid
with haloacetic acids in aqueous alkali is complicated
by alkaline hydrolysis of the latter.
kh
HlgCH2COO_ + HO_
HOCH2COO_ + Hlg_ .
To estimate the contribution of the hydrolysis
process to the overall Meyer reaction rate we initially
studied the kinetics of alkaline hydrolysis of haloacetic
acids at 15, 25, 35, and 45°C. The progress of the
reaction was monitored following the concentration of
liberated halide ions by argentometric titration. The
rate constants of alkaline hydrolysis (kh) were
calculated using the second-order equation [3]. The
average values are collected in Table 1.
The As–Cl bond undergoes complete hydrolysis by
the action of alkali [8, 9] to produce chloride ion.
Dissolution of compound I in aqueous alkali was
accompanied by formation of an equivalent amount of
chloride ion, which was confirmed by argentometric
titration. Most probably, acid I is thus converted into
arsinite ion VI [10].
The temperature dependences of kh for chloroacetic
(1), bromoacetic (2), and iodacetic acids (3) were
determined:
_
_
PhAs(Cl)CH2COO + HO
PhAsCH2COO_ + Cl_.
logkh = 8.58 – 4.26×103/T; r = 0.982, s = 0.192;
logkh = 8.95 – 3.86×103/T; r = 0.999, s = 0.544;
logkh = 7.91 – 3.67×103/T; r = 0.999, s = 0.455.
(1)
(2)
(3)
O_
VI
The energy of activation E (kJ mol–1) and entropy
of activation –∆S (J mol–1 K–1) for alkaline hydrolysis
are as follows: chloroacetic acid, 82.1, 87.6 [4];
bromoacetic acid, 74.0, 82.0; iodoacetic acid, 70.2,
102. The rate constants of alkaline hydrolysis of
haloacetic acids change in the series Cl < I < Br. An
analogous dependence for the same reaction was reported
in [5], where the following rate constants were given
(60°C): kh×106 = 76.7, 2030, and 1575 l mol–1 s–1 for
chloro-, bromo-, and iodacetic acids, respectively. For
comparison, Table 1 also contains kh values calculated
by Eqs. (1)–(3) for the temperature 60°C.
Table 1. Average rate constants for alkaline hydrolysis of
haloacetic acids
kh × 106, l mol–1 s–1
Temperature,
ClCH2COOHa
BrCH2COOH ICH2COOH
°C
15
25
35
45
60b
0.650
1.83
5.45
16.0
57.5
29.0
92.1
13.9
43.3
282
109
770
257
776
2291
a
Data of [4]. b The rate constants kh at 60°C were calculated from
the corresponding temperature dependences [Eqs. (1)–(3)].
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 79 No. 3 2009

380
RAKHMATULLIN et al.
The argentometric titration curves for the reactions
The rate of the reaction of [chloro(phenyl)arsanyl]
acetic acid (I) with haloacetic acids in aqueous alkali
increases in the series Cl > Br < I, which may be
regarded as an evidence in favor of the SN2 mechanism
of this process.
of acid I with haloacetic acids II and III, plotted in the
EmV–Vml coordinates, showed two clearly defined
jumps. Model studies performed on KCl–KBr and
KCl–KI mixtures showed that the first jump
corresponds to bromide and iodide ion, respectively,
and that the second jump corresponds to chloride ion.
The current concentration of halide ion was calculated
at the equivalence point of the first jump. The rate
constants for the reactions of I with haloacetic acids II
and III were calculated using Eq. (5).
_OOCH2As
O_ + HlgCH2COO_
Ph
O_
H
H
_OOCCH2As
Ph
Hlg
COO_
C
ω – kh(c0Hlg – cHlg–)(c0NaOH – 2c0I – c0Hlg – cHlg– + cX)
.
k =
(5)
PhAs(O)(CH2COO_)2 + Hlg_ .
(c0Hlg – cHlg–)(c0I – cX)
EXPERIMENTAL
Here, cI0, c0Hlg, and c0NaOH are the initial concentrations of
acid I, haloacetic acid II or III, and sodium hydroxide,
respectively, and cHlg and cX are the current concentra-
tions of halide ion and 2,2'-(phenylarsoryl)diacetate.
The mass spectra (electron impact, 70 eV) were
recorded on a Finnigan Trace mass spectrometer
(USA); ion source temperature 200°C; batch inlet
probe was heated in a programmed mode from 35 to
250°C at a rate of 35 deg min–1. The spectral data were
processed using Xcalibur program; m/z values of ions
containing the most abundant isotopes are given below.
The reaction rate ω was determined from the slope
of the tangent at each point of the approximated time
dependence of the halide ion concentration. The rate
constant k almost did not change with time. Table 2
contains the result of the kinetic study on the reactions
of [chloro(phenyl)arsanyl]acetic acid (I) with
haloacetic acid II and III at different temperatures. For
comparison, average rate constants for the reaction of
compound I with chloroacetic acid in aqueous alkali
[1] are given, k×103 (l mol–1 s–1): 0.0158 (15°C),
0.0246 (25°C), 0.0424 (35°C), 0.101 (45°C). On the
basis of these data we constructed temperature
dependences of the rate constants k for the reactions of
I with chloroacetic, bromoacetic, and iodacetic acids
[Eqs. (6)–(8), respectively].
Bromoacetic acid (II) was distilled before use, bp
208°C; the distillate crystallized on cooling to form
colorless crystals with mp 49°C; published data [12]:
bp 209°C, mp 51°C. Iodoacetic acid was recrystallized
from water, mp 82–85°C; published data [13]: mp 83°C.
[Chloro(phenyl)arsanyl]acetic acid (I). mp 102–
103°C; published data [2]: mp 103°C. Found, %: As
30.03; Cl 14.27. C8H8AsClO2. Calculated, %: As
30.39; Cl 14.39. Mass spectrum, m/z (Irel, %): A: 246
(17.1) [M]+·, 248 (5.1), 229 (5.0), 210 (26.4) [M – HCl]+,
206 (4.5), 204 (15.5), 189 (75.0), 187 (95.0) [M –
C2H3O2]+, 169 (65.0), 140 (60.5), 119 (76.5), 91
(100.0), [C6H5CH2]+, 65 (40.0), 51 (73.3), 36 (70.0); B:
248 (3.2), 246 (12.1) [M]+·, 210 (26.4) [M – HCl]+, 206
(1.5), 204 (3.5) 189 (29.0), 187 (100.0) [M – C2H3O2]+,
169 (19.7), 140 (14.5), 91 (85.7) [C6H5CH2]+.
logk = 8.58 – 4.26×103/T; r = 0.998, s = 0.772; (6)
logk = 10.8 – 3.67×103/T; r = 0.999, s = 0.250; (7)
logk = 18.1 – 5.66×103/T; r = 0.999, s = 0.493. (8)
The energies of activation E (kJ mol–1) and
entropies of activation –∆S (J mol–1 K–1) are as
follows: chloroacetic acid, 69.9, 92.4 [1]; bromoacetic
acid, 70.3, 46.0; iodoacetic acid, 108.5, –93.3. Positive
value of the entropy of activation for the reaction of I
with iodoacetic acid must be noted. Increase in the
entropy of activation from negative values to positive
was also observed by us while studying the kinetics of
quaternization of 10-phenylphenoxarsinine with
methyl iodide in different solvents. The entropy of
activation increased from –143 to 9.9 J mol–1 K–1 in
going from acetone to propan-2-ol [11].
2,2′-(Phenylarsanediyl)diacetic acid (V). Mass
spectrum, m/z (Irel, %): 270 (2.8) [M]+·, 253 (0.42) [M –
OH]+, 252 (3.37) [M – H2O]+, 211 (40.0) [M – C2H3O2]+,
169 (100.0) [M – C2H3O2 – C2H2O]+, 152 (3.4)
[AsC6H5]+, 151 (11.0) [AsC6H4]+, 125 (1.3), 109 (2.6),
91 (29.4) [AsO]+, 77 (4.3) [C6H5]+, 75 (0.60) [As]+, 45
(0.90) [C2H5O]+, 43 (2.8) [C2H3O]+.
The kinetics of alkaline hydrolysis of bromo- and
iodoacetic acids were studied as described previously
for chloroacetic acid [4].
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 79 No. 3 2009

KINETICS OF THE REACTIONS OF [CHLORO(PHENYL)ARSANYL]ACETIC ACID
381
Table 2. Kinetic data for the reactions of [chloro(phenyl)arsanyl]acetic acid (I) with bromoacetic acid (II) and iodoacetic acid
(III) in aqueous sodium hydroxide
Temperature,
°C
Reaction time,
cI0 × 102, M
c0Hlg × 102, M
c0NaOH, M
Conversion, % k × 103,a l mol–1 s–1
s × 10–2
Bromoacetic acid
0.8262
15
15
15
20
20
20
25
25
25
30
30
30
0.617
0.682
0.525
0.735
0.732
0.745
0.820
0.892
0.650
0.442
0.475
0.338
0.891
0.785
0.777
0.908
0.902
0.979
0.565
0.524
0.612
0.389
0.432
0.483
162
180
186
54
59.9
57.5
55.2
50.3
46.3
48.7
44.5
40.1
51.5
30.5
41.8
36.3
10.8
9.7
0.8262
0.8160
9.8
0.8262
21.7
22.2
20.9
29.8
30.7
27.3
45.6
46.0
44.0
0.8262
54
0.8262
54
0.8691
87
0.8691
54
0.8660
132
54
0.8262
0.8262
54
0.8160
96
Iodoacetic acid
15
15
15
20
20
20
25
25
25
30
30
30
0.545
0.694
0.470
0.539
0.550
0.550
0.686
0.825
0.735
0.422
0.196
0.237
0.454
0.527
0.436
0.640
0.508
0.393
0.605
0.719
0.463
0.200
0.245
0.237
0.8262
0.8262
0.8160
0.8262
0.8262
0.8160
0.8262
0.8262
0.8262
0.8262
0.8262
0.8160
162
162
180
54
63.3
58.3
72.9
58.0
64.6
62.5
72.1
80.2
64.6
46.8
62.6
64.7
26.7
26.0
29.7
62.4
78
64.4
93
61.9
63
119.9
110.5
121.2
214.6
226.2
280.9
63
75
57
57
96
The average k×103 values, l mol–1 s–1, for bromoacetic acid are 10.1 (15°C), 21.6 (20°C), 29.3 (25°C), and 45.2 (30°C); for iodoacetic
a
acid: 27.5 (15°C), 62.9 (20°C), 116.9 (25°C), and 240.6 (30°C).
Kinetic study on the reaction of [chloro(phenyl)
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definite time intervals, and the concentrations of
arsinite ions and halide ions were determined by
iodometric and argentometric titration, respectively,
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