Reaction products of methylene iodide with tertiary arsines

Article abstract of DOI:10.1007/s11176-005-0206-1

The reactions products of tertiary arsines with methylene iodide are (iodomethyl)trialkyl(aryl)-arsonium iodides. Treatment of the latter with lead(II) nitrate in aqueous ethanol solutions gives rise to an exchange reaction to form the corresponding nitra

Full text of DOI:10.1007/s11176-005-0206-1

Russian Journal of General Chemistry, Vol. 75, No. 2, 2005, pp. 240 243. Translated from Zhurnal Obshchei Khimii, Vol. 75, No. 2, 2005,
pp. 268 271.
Original Russian Text Copyright
2005 by Gigauri, Arabuli, Machaidze, Rusiya.
Reaction Products of Methylene Iodide with Tertiary Arsines
R. D. Gigauri, L. G. Arabuli, Z. N. Machaidze, and M. Sh. Rusiya
Dzhavakhishvili Tbilisi State University, Tbilisi, Georgia
Received April 22, 2003
Abstract The reactions products of tertiary arsines with methylene iodide are (iodomethyl)trialkyl(aryl)-
arsonium iodides. Treatment of the latter with lead(II) nitrate in aqueous ethanol solutions gives rise to an
exchange reaction to form the corresponding nitrates in high yields.
Tertiary arsines, both symmetrical and mixed-
radical, react with organyl halides to give tertiary
arsonium salts [1]. The fourth bond is formed by
coordination of antibonding 4s2 electrons of trivalent
arsenic with trivalent Lewis acids. As a result, ca-
tionic complexes are formed [2]. Nucleophilic pro-
perties of trialkyl(aryl)arsines depend not only on the
existence of the above-mentioned electron pair, but
also on the character of substituents on the central
atom, and, what is most important, on the composi-
tion and structure of the electrophilic reagent, that is
organyl halide [3].
R3As + CH2I2
[R3AsCH2I]I,
(1)
I
IIa IIf
R = C3H7 (a), iso-C3H7 (b), C4H9 (c), iso-C4H9 (d), C5H11
(e), C6H5 (f);
C6H5AsR2 + I
[C6H5AsR2CH2I]I,
(2)
IIg, IIh
R = C4H9 (g), C5H11 (h).
The synthesis of quaternary arsonium salts was
carried out at room temperature, except for triphenyl-
arsine. The latter was alkylated under Michaelis’s
conditions [4]. During reaction, coarse crystals pre-
cipitated and purified by precipitation from absolute
ethanol with diethyl ether until constant melting point.
Michaelis [4] has been the first to show that tri-
phenylarsine is alkylated with diiodomethane at
130 C to form an adduct with the following proposed
composition and structure.
The melting point of the adduct of methylene
iodide with triphenylarsine, obtained in the present
work, was 211 212 C, while, according to Mi-
chaelis’s data, it was 227 C. The reason for this dif-
ference evidently lies in the fact that Michaelis’s
sample of (iodomethyl)trialkyl(aryl)arsonium iodide
was purified by crystallization from aqueous ethanol.
Under these conditions, partial hydrolysis of the com-
pound cannot be excluded. (Iodomethyl)triphenyl-
arsonium iodide can be regarded as the salt of a strong
acid (HI) and a weak base (quaternary arsonium), and,
therefore, the above-mentioned crystallization may be
accompanied by the following equilibrium.
CH2I
(C6H5)3As
I
From this structure it follows that the arsenic atom
in it, as well as in all other five-coordinate arsenic
compounds should be sp3d-hybridized, and the
geometry of the product should be trigonal bipyramid
[5]. No more recent data on the alkylation with
methylene iodide of other trialkyl(aryl)arsines are
available.
To gain more information on the ability of diiodo-
methane to exhibit electrophilic properties in reaction
with tertiary arsines of various compositions and
structures, as well as to assess the structure of the re-
action products, in the present work we performed a
more thorough study of the reaction of trialkyl(aryl)-
arsines with methylene iodide.
[(C6H5)3AsCH2I]I + HOH
[(C6H5)3AsCH2I]OH + HI
Indirect evidence for this conclusion is provided
by physicochemical methods: The arsenic content of
a sample crystallized according to Michaelis increases
by 0.5 0.7 wt%, and its IR spectrum, a new absorp-
tion band in the range 3200 3400 cm , characteristic
of OH groups, appears [6].
1
It was found that methylene iodide reacts with
tertiary arsines, including those with mixed radicals,
to form tertiary arsonium iodides IIa IIh [reac-
tions (1) and (2)].
(Iodomethyl)trialkyl(aryl)arsonium iodides IIa IIh
are yellowish solids insoluble in benzene and diethyl
1070-3632/05/7502-0240 2005 Pleiades Publishing, Inc.

REACTION PRODUCTS OF METHYLENE IODIDE WITH TERTIARY ARSINES
241
Table 1. Yields, melting points, molar electrical conductivities ( ), and elemental analyses of (iodomethyl)trialkyl(aryl)-
arsonium iodides
Found, %
Calculated
As
,
Comp.
no.
Yield,
%
mp,
C
Formula
1 cm2 mol
1
As
I
I
IIa
IIb
IIc
IId
IIe
IIf
99
97
93
95
78
98
92
89
149 150
155 156
166 167
215 216
122 123
211 212
152 153
129 130
71.7
70.3
69.5
67.2
62.7
59.9
64.5
63.4
15.60
15.58
14.08
14.11
13.02
12.52
13.49
12.86
54.45
53.27
48.91
48.88
45.06
43.54
48.09
44.42
C10H23AsI2
C10H23AsI2
C13H29AsI2
C13H29AsI2
C16H35AsI2
C19H17AsI2
C15H25AsI2
C17H29AsI2
15.89
15.89
14.59
14.59
13.49
13.07
14.04
13.35
53.77
53.77
49.38
49.38
45.65
44.22
47.53
45.16
IIg
IIh
ether, and most of aprotic organic solvents. They are
fairly readily soluble in acetone, DMF, and ethanol
and are poorly soluble in water. Their yields and some
physicochemical properties are listed in Table 1.
of iodine is quantitatively precipitated. This fact
provides unambiguous evidence for the conclusion
drawn from the IR spectra and electrical conductivity
data, that only one of the two iodine atoms is located
in the outer sphere of the complex. The reaction
results in formation of (iodomethyl)trialkyl(aryl)ar-
sonium nitrates IIIa IIIf.
The individuality and structure of (iodomethylene)-
trialkyl(aryl)arsonium iodides IIa IIh was established
by means of elemental analysis and IR spectroscopy.
The quaternization of the arsenic(III) atom by alkyla-
tion with methylene iodide is confirmed by the shift
of the As C(aliph.) absorption band from 580 to
IIa IIf + Pb(NO3)2
[R3AsCH2I]NO3 + PbI2 .
IIIa IIIf
1
620 cm , which suggests sp3 hybridization of the
Analogous results were obtained in the reactions of
(iodomethyl)phenyldialkylarsonium iodides IIg and
IIh with lead(II) nitrate. All the reactions were carried
out in aqueous ethanolic solutions (1:1 v/v). The
quaternary arsonium nitrates were precipitated from
the filtrate with diethyl ether and dried until constant
weight.
arsenic atom [7]. The spectra of the aromatic deriva-
tives all contain absorption bands due to phenyl
1
groups (700, 740, 1580, and 3000 3080 cm ) and
other substituents at the central atom [8].
Evidence for the ionic structure of (iodomethyl)tri-
alkyl(aryl)arsonium iodides comes from their molar
electrical conductivities ( ) in dilute DMF solutions
Arsonium nitrates IIIa IIIh colorless finely crys-
talline substances readily soluble (compared to the
starting iodide) in water, ethanol, and acetone, but
insoluble in ether, hexane, benzene, and other apolar
organic solvents. Their IR spectra (see figure, spec-
trum b) contain bands characteristic of starting arso-
(these compounds are insoluble in water). The
values vary within the range 59 72
1
1 cm2 mol ,
which corresponds to the electrical conductivity of
1:1 electrolytes [9].
The coordination formulas of complex compounds
are most frequently assessed by means of the double-
exchange reaction [10]. Hence, hydrolysis and anion
exchange in arsonium salts alter the function of the
arsenic-containing residue without altering the sub-
stituents on and the valence of the arsenic atom [3].
Previously we showed for the first time [1] that suc-
cessful exchange reactions for preparing quaternary
arsonium nitrates from corresponding halides can be
effected not only with silver(I) nitrate, but also with
lead(II) nitrate.
(b)
(a)
1
1500 1100
700 500 , cm
It was found that upon treatment of aqueous-etha-
nolic solutions of the alkylation products of tertiary
arsines IIa IIh with aqueous lead(II) nitrate only half
IR spectra of (iodomethyl)triphenylarsonium (a) iodide
and (b) nitrate.
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 75 No. 2 2005

242
GIGAURI et al.
Table 2. Yields, melting points, molar electrical conductivities ( ), and elemantal analyses of (iodomethylene)tri-
lkyl(aryl)arsonium nitrates
Found, %
Calculated
Comp.
no.
Yield,
%
,
mp,
C
Formula
1
1 cm2 mol
As
N
As
N
IIIa
IIIb
IIIc
IIId
IIIe
IIIf
90
88
87
93
79
96
87
84
69 70
120 121
87 88
130 131
97 98
175 176
77 78
91 92
137.6
131.7
124.8
124.0
121.6
118.2
120.1
119.0
18.01
17.95
16.88
16.21
14.82
14.32
15.36
14.60
3.21
3.08
2.97
2.95
2.28
2.73
2.79
3.01
C10H23AsINO3
C10H23AsINO3
C13H29AsINO3
C13H29AsINO3
C16H35AsINO3
C19H17AsINO3
C15H25AsINO3
C17H29AsINO3
18.43
18.43
16.70
16.70
15.27
14.73
15.99
15.09
3.44
3.44
3.12
3.12
2.85
2.75
2.99
2.82
IIIg
IIIh
nium iodides IIa IIh, as well as those due to the
nitrate ions. Analysis of the IR spectra of compounds
IIa IIh shows that the NO3 ions in them are outer-
sphere. No bands due to inner-sphere NO3 ions were
found [1, 11]. Actually, the IR spectra contain bands
(Iodomethyl)tripropylarsonium iodide (IIa). Tri-
propylarsine, 28.0 g, was placed in an Erlenmeyer
flask and treated with 38.6 g of methylene iodide. The
homogeneous liquid phase was kept at room tempe-
rature for 10 days. Crystals formed and were filtered
off, washed on the filter with dry diethyl ether, twice
precipitated with diethyl ether from absolute ethanol,
and dried in a vacuum dessicator over phosphorus
pentoxide and paraffine until constant weight. Yield
64.0 g (99%).
1
at 1360 ( ) and 850 cm ( ) due to antisymmetric
3
2
stretching vibrations and out-of-plane deformation
vibrations of the nitrate ion, which confirms existence
of cationic complexes.
The ionic composition of (iodomethyl)trialkyl(aryl)-
arsonium nitrates IIIa IIIh is proved by the molar
conductivities of their aqueous solutions (Table 2).
Other quaternary arsonium iodides were prepared
analogously, except for (iodomethyl)triphenylars-
onium iodide (Table 1).
1
The values span the range 118 138 1 cm2 mol ,
which corresponds to the electrical conductivity of
1:1 electrolytes [10]. The fact that the electrical
conductivities of nitrates IIIa IIIh as compared to
respective (iodomethyl)trialkyl(aryl)ammonium
iodides IIa IIh in DMF is probably explained by the
higher degree of electrolytic dissociation in water.
(Iodomethyl)tripropylarsonium nitrate (IIIa).
A solution of 3.2 g of (iodomethyl)tripropylarsonium
iodide in a mixture of distilled water and ethanol
(1:1) was treated with a solution of 1.18 g of lead(II)
nitrate containing 2 3 drops of nitric acid (added to
prevent hydrolysis of the salt). A yellow precipitate
immediately formed. A day after, it was filtered off,
the filtrate was evaporated on a water bath to obtain a
viscous material. It was dissolved in ethanol until
saturation and then treated with ether to obtain
crystals that were dried in a vacuum dessicator over
phosphorus pentoxide until constant weight. Yield
2.49 g (90%), colorless fine crystals.
IIIa IIIf
[R3AsCH2I]+ + NO3.
EXPERIMENTAL
The IR spectra were measured on a UR-20 spec-
trometer in the range 400 3700 cm 1 in KBr pellets.
The specific electrical conductivities in DMF and
water were measured on an Impuls conductometer
with the accuracy 1.5%. The temperature was
maintained with the accuracy 0.5 C. The molar
(Iodomethyl)trialkyl(aryl)arsonium nitrates IIIb
IIIh were obtained in a similar way (Table 2).
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