Anodic dissolution of tin in alcohols

Article abstract of DOI:10.1007/s11172-016-1387-y

Tin(II) alcoholates Sn(OR)₂ are formed upon the anodic galvanostatic dissolution of tin in alcohols in an undivided cell in the presence of minimum amounts of NaOAc as an electrolyte. Tin(II) alcoholates are easily hydrolyzed in air to form oxy

Full text of DOI:10.1007/s11172-016-1387-y

Russian Chemical Bulletin, International Edition, Vol. 65, No. 3, pp. 840—843, March, 2016
840
Anodic dissolution of tin in alcohols*
A. N. Vereshchagin,a M. N. Elinson,a A. S. Goloveshkin,b R. A. Novikov,a and M. P. Egorova
aN. D. Zelinsky Institute of Organic Chemistry, Russian Academy of Sciences,
47 Leninsky prosp., 119991 Moscow, Russian Federation.
Fax: +7 (499) 135 6390. Еꢀmail: vereshchagin@ioc.ac.ru
bA. N. Nesmeyanov Institute of Organoelement Compounds, Russian Academy of Sciences,
28 ul. Vavilova, 119991 Moscow, Russian Federation.
Fax: +7 (499) 135 5085. Еꢀmail: golovꢀ1@mail.ru
Tin(II) alcoholates Sn(OR)2 are formed upon the anodic galvanostatic dissolution of tin in
alcohols in an undivided cell in the presence of minimum amounts of NaOAc as an electrolyte.
Tin(II) alcoholates are easily hydrolyzed in air to form oxyhydroxide Sn3O2(OН)2 used as an
anode or its composite component in lithium cells.
Key words: electrolysis, anodic dissolution, tin(II) oxyalcoholates, tin(II) oxyhydroxide.
Metal alcoholates have found wide use in technoloꢀ
anode surface was passivated if nonꢀabsolutized alcohols
were used.
gy.1—3 They are applied in syntheses of highꢀpurity oxide
materials (alkoxo technology),1 in electrotechnical indusꢀ
try as semiconductors,4 and in the polymer chemistry.5
The following methods are used in the synthesis of
metal alcoholates3: (1) the reaction of metal with alcohol,
(2) the reaction of metal oxide or hydroxide with alcohol,
(3) alcoholysis of metаl halides MXn, (4) metathesis of
MXn with alkaline metal alkoxides or ammonia, and
(5) anodic oxidation of metals. Among the listed methꢀ
ods, electrochemical preparation of alcoholates are most
promising, cheap, and ecologically safe. The direct synꢀ
thesis of alcoholates by the anodic dissolution of metals in
alcohols should specially be mentioned.6—10 The electroꢀ
chemical preparation of titanium, germanium, zirconiꢀ
um, and tantalum ethylates was patented.11 Drawbacks of
these processes are the use of saturated solutions of amꢀ
monium chloride as supporting electrolytes and a sharp
current drop after several hours of electrolysis. We have
recently synthesized efficiently alkyl germanates by the
anodic dissolution of germanium using sodium acetate as
a supporting electrolyte.12
Scheme 1
R = Me (a), Et (b)
i. Electrolysis, NaOAc—ROH. ii. Hydrolysis with air moisture.
The yield of oxyhydroxide 2 increased insignificantly
with an increase in the current density. The electrolysis in
methanol was carried out at a high current density of
100 mA cm–2, and in ethanol the limiting current density
achieved 40 mA cm–2, which is related to the passivation
of the anode surface.
After the end of electrolysis, a white precipitate formed
was rapidly filtered off and dried in a desiccator over Р2О5.
Alcoholic solutions of the synthesized compounds were
The anodic dissolution of tin in alcohols was studied in
this work (Scheme 1, Table 1). The process was carried
out in an undivided electrolyzer in absolute methanol (or
ethanol) under an argon atmosphere at high dc densities
using minimum (necessary for electrical conductivity)
amounts of sodium acetate as a supporting electrolyte.
An iron plate served as a cathode. The electrolysis and
subsequent transformation of Sn(OR)2 (1) resulted in
the formation of tin oxyhydroxide Sn3O2(OН)2 (2). The
Table 1. Anodic dissolution of tina
Entry
R
j
Q/C
t/h
Δmb
/mmol
Yield of 2
/mA cm–2
(%)
1
2
3
4
Me
Me
Me
Et
120
140
100
140
1720
1720
1800
1720
2
1
1
1
3.99
3.98
9.84
3.96
38
40
44
37
a Undivided cell, argon, Fe cathode (5 cm2), Sn anode (5 cm2),
0.25 mmole (20 mg) of NaOAc, 20 mL of absolute ROH, 30 °С.
b Decrease in the weight of the anode.
* Dedicated to Academician of the Russian Academy of Sciences
V. M. Novotortsev on the occasion of his 70th anniversary.
Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 3, pp. 0840—0843, March, 2016.
1066ꢀ5285/16/6503ꢀ0840 © 2016 Springer Science+Business Media, Inc.

Anodic dissolution of tin in alcohols
Russ.Chem.Bull., Int.Ed., Vol. 65, No. 3, March, 2016
841
I
11000
10000
9000
8000
7000
6000
5000
4000
3000
2000
1000
0
1, 2
3
20
30
40
50
60
70
80
90
2θ/deg
Fig. 1. Theoretical (1) and experimental (2) diffraction patterns of Sn3O2(OH)2 and their difference (3).
analyzed by 119Sn NMR spectroscopy. No 119Sn signals
were detected in alcoholic solutions. The elemental analꢀ
ysis results for the dried powders corresponded to comꢀ
pounds Sn3O2(OСН3)2 (3а) and Sn3O2(OСН2СН3)2 (3b)
isolated after electrolysis in methanol and ethanol, respecꢀ
tively. During further hydrolysis in air oxyalcoholates 3a,b
are hydrolyzed to oxyhydroxide Sn3O2(OH)2 (2), the
structure of which was confirmed by elemental and Xꢀray
phase analyses (Fig. 1). It was established that the oxyꢀ
hydroxide samples contained one crystalline phase.13 The
crystallite size of Sn3O2(OH)2 determined in terms of the
Williamson—Hall method14 was 28.7(5) nm.
alkaline medium was studied in detail earlier,15 and the
threeꢀstage mechanism of the process was proposed
(Scheme 2).
Scheme 2
In crystal Sn3O2(OH)2 forms clusters Sn6O4(OH)4
(Fig. 2) with hydrogen bonds between the bridging oxygen
atoms and OH groups.
Taking into account the obtained data and the results
of the anodic dissolution of tin in a waterꢀalkaline mediꢀ
It should be mentioned that nanocrystalline/amorꢀ
phous oxyhydroxide Sn3O2(OH)2 is used as an anode15 or its
composite component16 in lithium cells. Earlier Sn3O2(OH)2
was prepared by precipitation from SnCl2•2H2O (see
Ref. 15) or SnF2 (see Ref. 16) under the action of hydrꢀ
azine hydrate or sodium borohydride, respectively.
The surface of the tin anode before and after electrolyꢀ
sis in methanol was studied on a scanning electron microꢀ
scope (Fig. 3). Surface smoothening is observed as a result
of the dissolution of the anode. Large furrows formed by
the cleaning of the surface with emery paper (see Fig. 3, a)
disappear after anode etching (see Fig. 3, c), and the surꢀ
face becomes more developed (see Fig. 3, d).
Sn
O
It should be mentioned that the mechanism of anodic
dissolution of tin in alcohols was not described before the
present work. The anodic dissolution of tin in a waterꢀ
Fig. 2. Crystal structure of Sn3O2(OH)2.

842
Russ.Chem.Bull., Int.Ed., Vol. 65, No. 3, March, 2016
a
Vereshchagin et al.
b
100 μm
1 μm
c
d
100 μm
1 μm
Fig. 3. Surface of the tin anode before (a, b) and after (c, d) electrolysis in methanol.
um,17 we can present the mechanism of anodic dissoluꢀ
tion of tin in alcohols in the general form as follows
(Scheme 3). Dihydrogen is evolved and alcoholate anions
are formed at the cathode, and the dissolution of the tin
anode results in the formation of Sn2+ reacting in solution
with alcoholate anions. The formed tin(II) alcoholate is
hydrolyzed in air to form first tin oxyalcoholate 3 and then
tin(II) oxyhydroxide (2).
Thus, we carried out the efficient synthesis of Sn3O2(OH)2
using available materials and solvents at high current denꢀ
sities. It should specially be emphasized that minimum
amounts of available sodium acetates were used as a supꢀ
porting electrolyte.
Experimental
Solidꢀstate 119Sn NMR spectra were recorded on a Bruker
AMXꢀIII 400 spectrometer using BBI and BBF standard liquid
sensors without sample rotation at a magic angle. Chemical shifts
in the NMR spectra are presented relative to SnМе4.
Scheme 3
Xꢀray phase analysis was carried out on a Bruker D8 Adꢀ
vance Xꢀray powder diffractometer equipped with a LynxEye
linear detector, a Ni filter, and variable slits (λ(CuKα) = 1.5418 Å,
θ/2θ scan mode, recording range 10—100°, increment 0.02°) in
the Bragg—Brentano geometry, and a sample was deposited on
the silicon sample holder.
The SEM images of samples were obtained on a Hitachi
SU8000 scanning electron microscope with field emission. To
obtain microscopic images, samples (cross sections of the anode
i. Partial hydrolysis. ii. Complete hydrolysis.

Anodic dissolution of tin in alcohols
Russ.Chem.Bull., Int.Ed., Vol. 65, No. 3, March, 2016
843
9—10 mm thick) were placed on an aluminum stage (25 mm)
and fixed with a conducting silver glue. The images were obꢀ
tained at an accelerating voltage of 30 kV (working distance
8—10 mm) in the secondary electron detection mode.9,20
A ТЕСꢀ13 laboratory stabilizer with the stabilization of the
outlet current at 0.005—1 A served as a power supply. A tin rod
(diameter 6.5 mm, height 55 mm, working surface area 5 cm2,
purity of tin 99.99%) was used as an anode. The cathode was an
iron plate (working surface area 5 cm2). Methanol and ethanol
(Acros) were used without additional drying.
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Anodic dissolution of tin in alcohols (general procedure). Diꢀ
rect current (the current density and amount of passed electriciꢀ
ty are indicated in Table 1) was passed in an argon atmosphere at
30 °C through an alcoholic solution (20 mL) of sodium acetate
(20 mg, 0.25 mmol) in an undivided cell with external cooling
equipped with a tin anode and iron cathode (surface area of the
electrodes 5 cm2). After the end of electrolysis, the electrodes
were carefully taken from the cell and purified. A white precipiꢀ
tate formed in the volume was rapidly filtered off and dried in
a desiccator over Р2О5.
Tin(II) oxymethylate (3а). Found (%): Sn, 78.72; С, 5.52;
Н, 1.42. С2H6O4Sn3. Calculated (%): Sn, 79.11; С, 5.34; Н, 1.34.
Readily hydrolyzed with air moisture.
Tin(II) oxyethylate(3b). Found (%): Sn, 74.14; С, 10.17; Н, 2.17.
C4H10O4Sn3. Calculated (%): Sn, 74.47; С, 10.05; Н, 2.11.
Readily hydrolyzed with air moisture.
Tin(II) oxyhydroxide (2). 119Sn NMR (CD2Cl2, 149.2 MHz),
δ: –74 (s, J = 1200 Hz). Found (%): Sn, 84.12; Н, 0.52. H2O4Sn3.
Calculated (%): Sn, 84.36; Н, 0.48. The diffraction patterns were
refined by the Rietveld method in the TOPAS 4.2 program.18 All
observed peaks corresponded to the structure of Sn3O2(OH)2
described in the literature.13 Line broadening was refined using
the Williamson—Hall method,14 and the predominant orientaꢀ
tion of the sample was described by spherical harmonics of the
fourth order. The final refinement has the following R factors:
RWP/RWP´/RBragg are 3.68/12.62/1.05%, respectively.
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The authors are grateful to coworkers of the departꢀ
ment of Structural Research of the N. D. Zelinsky Instiꢀ
tute of Organic Chemistry (Russian Academy of Sciences)
for studies of samples by electron microscopy.
This work was financially supported by the Russian
Foundation for Basic Research (Project No. 13ꢀ03ꢀ12237ꢀ
ofiꢀm).
19. V. V. Kachala, L. L. Khemchyan, A. S. Kashin, N. V. Orlov,
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in revised form January 25, 2016