Reactions of thiols and organic disulfides with iron and its oxides

Article abstract of DOI:10.1007/s11172-006-0436-3

The influence of O₂ and H₂O on the formation of iron dithiolates (IDTs) by the reactions of thiols and organic disulfides with the iron powder was studied under the static (without mechanical activation of the reaction) and dynamic (

Full text of DOI:10.1007/s11172-006-0436-3

1
436
Russian Chemical Bulletin, International Edition, Vol. 55, No. 8, pp. 1436—1439, August, 2006
Reactions of thiols and organic disulfides with iron and its oxides
G. F. Pavelko
A. V. Topchiev Institute of Petrochemical Synthesis, Russian Academy of Sciences,
2
9 Leninsky prosp., 119991 Moscow, Russian Federation.
Eꢀmail: pavelko@ips.ac.ru
The influence of O and H O on the formation of iron dithiolates (IDTs) by the reactions
2
2
of thiols and organic disulfides with the iron powder was studied under the static (without
mechanical activation of the reaction) and dynamic (with mechanical activation of the reacꢀ
tion) conditions. Under the static conditions in the absence of O2 or H O, only BnSH and
2
PhSH give IDTs, whereas DdSH (Dd is dodecyl) produces IDTs in the presence of O or H O.
2
2
For the mechanical activation of the reactions of organic disulfides with the iron powder, the
formation of IDTs is possible if the reaction mixture contains H O. On the interaction with
2
iron oxides excess thiols are oxidized to organic disulfides and also afford IDTs.
Key words: butanediol, dodecanethiol, phenylmethanethiol, benzenethiol, dipropyl disulꢀ
fide, didodecyl disulfide, dibenzyl disulfide, diphenyl disulfide, iron dithiolates, iron, iron
oxides, mechanochemical reactions, Xꢀray photoelectron spectroscopy.
Organic disulfides are widely used as additives deꢀ
thiol 1c and disulfide 3a. The results are presented in
Table 1.
creasing friction and frictional wear of steel surfaces. In
this case, disulfides partially decompose to thiols under
Static conditions. Some IDTs are formed without
mechanochemical activation of the reactions of thiols with
the iron powder. For instance, the formation of IDTs
2b,d,e was visually observed by the appearance of the
color several minutes or hours after mixing the reactants.
When IDTs 2d,e were formed, hydrogen bubbles evolved
for several weeks. In the first case, in several months a
black product with metallic luster formed instead of brown
IDT 2d, whereas redꢀbrown IDT 2e did not change its
color. If the reaction mixture is sealed in an air atmoꢀ
sphere, thiols 1b—e initially turned to green. The brown
color characteristic of IDTs appears in several days.
1
boundary friction conditions. Mechanochemical reacꢀ
tions occurring via the reactions of organic disulfides and
thiols with iron favor continuous service of steel mechaꢀ
nisms. However, chemical methods for analysis of prodꢀ
ucts of mechanochemical reactions have not been develꢀ
2
oped up to recently. We have previously proposed the
method for studying mechanochemical reactions with
the help of a mechanochemical vibrational mill. It has
2
3,4
been shown that, contrary to the popular opinion,
IDTs appear from thiols rather than from organic disulꢀ
fides.
The purpose of the present work is to study the influꢀ
ence of O and H O on the formation of IDTs by the
reactions of thiols and organic disulfides with the iron
powder under the static and dynamic conditions.
In the absence of O , thiol 1c with the iron powder
2
forms no IDT 2c. No changes on the iron surface were
visually observed even after manyꢀyear contact of the reꢀ
actants in an evacuated ampule. However, if the ampule
containing thiol 1c and the iron powder was sealed off
under atmospheric pressure without degassing, then the
brown color characteristic of IDTs appears already in
2
2
Results and Discussion
The following reactions were studied:
3
0—60 min, and a brown precipitate is formed in 1 month.
An H O admixture acts similarly in a degassed reaction
2
medium. Probably, the reaction proceeds as follows:
where R = Pr (a), Bu (b), Dd (dodecyl, c), Bn (d),
and Ph (e).
The influence of O in the reaction medium was studꢀ
2
ied in the processes involving thiols 1b—e, and the effect
of an H O admixture was examined in the reactions of
2
Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 8, pp. 1383—1386, August, 2006.
066ꢀ5285/06/5508ꢀ1436 © 2006 Springer Science+Business Media, Inc.
1

Iron dithiolates
Russ.Chem.Bull., Int.Ed., Vol. 55, No. 8, August, 2006
1437
Table 1. Results of qualitative analysisa of IDTs formed upon the reactions of organosulfur compounds (OSC) with the
Fe powder and the results of XPS analysis of the surface of the Fe powders modified by OSC
OSC +
admixture
Atmosphere
In quartz ampules,
static conditions,
qualitative analysis
In steel reactor,
dynamic conditions
Qualitative analysis
ES2p/eV (XPS)
BuSH (1b)
Vacuum
Argon
Air
Vacuum
Argon
Air
Vacuum
Vacuum
Argon
Air
Vacuum
Argon
Air
Vacuum
Argon
Vacuum
Argon
Argon
Argon
+
—
+
–
—
+
+
+
—
+
+
—
+
–
—
–
—
—
—
—
+
—
—
+
—
—
—
+
—
—
+
—
168.6
—
—
168.7
—
—
—
1
b + O2
DdSH (1c)
1
1
c + O2
c + H O
2
BnSH (1d)
163.5; 168.8
1
d + O2
—
—
168.6
—
PhSH (1e)
1
e + O2
—
—
–
Pr S (3a)
—
2
2
168.8
—
b
3
a + H O
+
2
c
Dd S (3c)
–
–
–
—
2
2
Bn S (3d)
169.3
168.9
2
2
Ph S (3e)
2
2
a
Signs "+" and "–" indicate the qualitative reaction to IDTs (positive and negative, respectively), "—" means that no
experiment was carried out.
b
In quartz ampule.
No signal was detected by XPS.
c
The formation of dithiolate 2b is possibly related to a
higher reactivity of thiol 1b compared to that of thiol 1c
vation of the reaction. Probably, the process proceeds as
follows:
or to a higher concentration of O in the reaction medium
2
(
it is more difficult to remove O2 from lowꢀboiling
thiol 1b).
On contacting the reactants for several years disulfide
a forms no IDT 2a with the iron powder. No IDT 2a is
3
either formed under static conditions when the iron powꢀ
der, disulfide 3a, and two—three droplets of H O are
introduced successively into the ampule.
2
where Fe* is mechanically activated iron.
The overall process can be written as
Dynamic conditions. The reactions of thiols 1b—e
and disulfide 3a with the iron powder were carried
out in quartz ampules sealed in vacuo. All thiols 1b—e
react with Fe to form the corresponding IDTs 2b—e.
Soꢀcalled "selfꢀassembled monolayers" (SAM) of
When nꢀalkylthiols interact with the iron powder, the
5
Fe thiolates have been prepared earlier by ultrasonicaꢀ
presence of chemisorbed O on the iron surface does not
2
tion of solutions of thiols and amorphous iron. However,
SAM of Fe thiolates differ from IDTs, in our opinion, by
the fact that in the SAM the Fe atom is linked only with
one thiolate group, whereas IDTs are individual comꢀ
pounds.
prevent IDT formation, because oxygen forms water in
excess thiols in the reaction mixture.
Let us consider the results of XPS studies of the surꢀ
face of the iron powders obtained by the mechanochemiꢀ
cal reactions of thiols 1b—e and disulfides 3a,c—e with
the iron powder in a steel reactor in an argon atmosphere
(see Table 1).
Disulfide 3a forms no IDTs 2a with the iron powder.
For the reaction of disulfide 3a with the iron powder in
6
the presence of two—three drops of H O, the formation
According to published data, the bond energies of the
2
of IDT 2a is observed several days after mechanical actiꢀ
S(2p) level (E) indicated by XPS for Fe modified by thiols

1438
Russ.Chem.Bull., Int.Ed., Vol. 55, No. 8, August, 2006
G. F. Pavelko
and organic disulfides, are associated with the compounds
presented below.
time, whereas the other products of the incomplete oxiꢀ
dation of IDTs 2b,c,e under similar conditions are oxiꢀ
dized very rapidly. Evidently, the thiolate bond is not
detected by Xꢀray photoelectron spectroscopy when the
iron powder is modified by thiols 1b,c,e.
Organic disulfides form no IDTs upon the interaction
with the iron powder as indicated by negative qualitative
reactions to IDTs and the absence of a maximum with an
energy of 161.5—162.4 eV in the Xꢀray photoelectronic
spectra. The signals of the S(2p) level with the energy
Compound
E/eV
Alk—S—Fe
161.5—162.4
162.8—163.9
166.1—167.1
168.6—169.2
Alk—S—H/Alk—S—S—Alk
–
Alk—SO2
Alk—SO3
–
An analysis of these and our results shows that the
signal of the S(2p) level of the thiolate bond is characterꢀ
istic only of the iron powder modified by thiol 1d. Indeed,
after this spectrum was decomposed to the components,
two maxima with energies of 162.7 and 164.2 eV are obꢀ
served (Fig. 1, a). As can be seen from the data in Fig. 1,
the Xꢀray photoelectronic spectrum of the iron powꢀ
der modified by thiol 1d is similar to the spectrum of
Oꢀcontaining thiolate 4d in which the presence of thiolate
bonds was confirmed by the formation of FeS upon therꢀ
mal decomposition in vacuo.
1
68.6—169.3 eV indicate that the oxidation products of
organic disulfides rather than of IDTs are present on the
iron powder surface.
Reactivity of iron oxides toward thiols. Since O is highly
2
reactive, the interacting steel surfaces are always covered,
to this or another extent, by iron oxides, which actively
reduce friction and wear at a certain concentration.
7
According to published data , Fe O oxidizes thiols to
2
3
disulfides. In the present work, it is shown for the first
time that iron oxides oxidize thiols and, moreover,
form IDTs. When thiol 1b reacts with FeO in the abꢀ
The IDT samples in the individual state are very sensiꢀ
tive to the presence of O . Some of them are ignited in air.
2
However, the partial oxidation of IDT 2d forms Oꢀconꢀ
taining thiolate 4d, which is stable for unrestrictedly long
sence of O , IDT 2b is formed in 8 days; the reaction with
2
Fe O affords 2b in 10 days; in the presence of an H O
2
3
2
admixture IDT 2b is formed already in 1 h. Thiol 1c reacts
with iron oxides much more slowly than thiol 1b. Selfꢀ
assembled monolayers of iron dithiolates have been preꢀ
I (rel. units)
6
4
2
0
0
0
0
a
5
4
pared previously by ultrasonication of solutions of thiols
and amorphous Fe O . In authors´ opinion, in these SAM
2
3
III
the AlkS radical is bonded to Fe
.
Thus, it is shown in the work that under the static
conditions IDTs 2d,e appear already at room temperature
as a result of the reactions of thiols 1d,e with the iron
powder. The presence of O and H O in catalytic amounts
3
2
1
2
2
favors the formation of IDTs 2b,c under the static condiꢀ
tions. It is confirmed by Xꢀray photoelectron spectroscopy
that no ITD is formed by the mechanical activation of the
reaction of organic disulfides with iron. The reaction of
disulfide 3a with the iron powder under the dynamic conꢀ
1
70
165
160 E/eV
I (rel. units)
ditions in the presence of H O was established to afford
2
IDT 2a. When reacting with excess thiols, iron oxides
oxidize them to organic disulfides and also give IDTs.
b
1
50
Experimental
1
Experiments under the dynamic conditions were carried out
in an M35L vibrational mill (vibration amplitude ~4 mm, vibraꢀ
tional frequency 48 Hz, electric engine power 1.7 kW). A steel
cylindrical reactor (height 35 mm, diameter 46 mm) was held in
a vertical position and accomplished virtually circular motion
without rotation around its axis in the horizontal plane.
Iron powder samples obtained after the mechanical modifiꢀ
cation of iron in the steel reactor by thiols and organic disulꢀ
fides were studied by Xꢀray photoelectron spectroscopy in an
XSAMꢀ800 twoꢀchamber instrument (Kratos Analytical Ltd).
The characteristic line MgꢀKα (hν = 1253.6 eV) was used as the
exciting radiation. The instrument was calibrated using standard
2
5
0
4
3
1
70
165
160
E/eV
Fig. 1. Xꢀray photoelectronic spectra of the S(2p) level of the
iron powder obtained by the mechanical modification of iron
with thiol 1d in the steel reactor (a) and compound 4d (b):
, Bn—S—Fe (162.6 eV); 2, Bn—S—S—Bn (164.1 eV);
, Bn—SO2 (167.1 eV); 4, Bn —SO3– (169.1 eV).
1
3
–

Iron dithiolates
Russ.Chem.Bull., Int.Ed., Vol. 55, No. 8, August, 2006
1439
samples using the lines Au4f (84.0 eV), Ag3d (368.3 eV), Cu2p
reaction mixture was degassed, and the ampule was sealed off.
The duration of mechanical activation was 1 h.
(
932.7 eV), and CuLMM (918.7 eV).
Spectra of powders of modified iron and compound 4d were
Reaction of thiols 1b with iron oxides. A. A mixture of FeO or
Fe O (0.10 g) and thiol 1b (2.0 mL) in 15ꢀmL ampules in vacuo
recorded in vacuo (~10– Pa) at room temperature.
8
2
3
The spectra were processed, including smoothening, subꢀ
traction of the background, quantitative analysis, and decompoꢀ
sition of complicated peaks to particular spectral components,
using the Spectra Presenter program. Recharge of samples was
taken into account by the carbon component with the lowest
bond energy (285.0 eV).
All experiments under the static and dynamic conditions
were carried out at room temperature. Experiments on synthesis
of IDTs in the absence of O2 were conducted with freshly reꢀ
were degassed by freezing—thawing out in liquid nitrogen, and
the ampules were sealed off. After 8 or 10 days, respectively,
a brown color appeared, which turned green upon contact with air.
B. Water (0.04 g) was introduced into an ampule containing
a mixture of Fe O (0.40 g) and thiol 1b (2.0 mL). The content of
the ampule was degassed, and the ampule was sealed off in vacuo.
After 1 h, the ampule was shaken several times, after which thiol
1b turned brown; it turned then green upon contact with air.
Synthesis of Oꢀcontaining thiolate 4d. A degassed and argonꢀ
2
3
duced iron without contact with O . Oxygen was preliminarily
saturated solution of thiol 1d (2.0 mL, 17 mmol) and Et N
2
3
removed from the reactants and solvents.
(1.5 mL, 10.8 mmol) in acetonitrile (25 mL) was added with
stirring to a degassed solution of FeCl •4H O (0.30 g, 1.5 mmol)
Thiols 1b—e and disulfide 3a were purity grade, Fe (carboꢀ
nyl iron) was specialꢀpurity grade 6ꢀ2, Fe (metallic reduced
iron) and FeO were purity grade, and Fe O was specialꢀpurity
2
2
and Bn S (1.0 g, 4 mmol) in acetonitrile (25 mL). Acetonitrile
2
2
immediately turned brown, and an amorphous precipitate of the
same color was formed.
2
3
grade 2ꢀ4. Thiols 1b—e and disulfide 3a were purified by fracꢀ
tional distillation prior to use. Disulfides 3c—e were synthesized
The reaction mixture was magnetically stirred for 3 h under
argon and then in air until MeCN became completely colorꢀ
less. A dark green precipitate was filtered off on a porous glass
filter suitable for separation of volatile solvents by pressingꢀout
with gas, washed with ether (4×15 mL), and dried in vacuo. The
yield of compound 4d was 0.55 g (77.5%). Found (%): C, 53.25;
H, 5.05; Fe, 13.06; S, 20.40. C21H21FeO S . Calculated (%):
8
by described procedures.
To conduct some experiments in quartz ampules, iron
was synthesized by the reduction of Fe O with hydrogen at
2
3
6
00—610 °C. Hydrogen was purified from an admixture of H O
2
vapor by passing over Mg chips at 600 °C.
Formation of IDTs under the static conditions in the absence
2
3
of O . An Fe powder (2.00 g, 0.36 gꢀat.) was placed in a 15ꢀmL
C, 53.28; H, 4.47; Fe, 11.80; S, 20.32. The elemental composiꢀ
tion of compound 4d depends on the duration of contact of
dithiolate 2d with O2 in organic solvents. The substance is inꢀ
soluble in organic solvents, and in the solid state in air it keeps
for unrestrictedly long time. In the individual state IDT 2d in air
is oxidized with heating to red heat.
2
quartz ampule and additionally reduced with hydrogen. Then
argonꢀsaturated thiol 1b—e or disulfide 3a (4.0 mL) was added
to the ampule under an argon atmosphere, and the ampule was
sealed off in vacuo (~0.5 Torr). The formation of IDT was visuꢀ
ally monitored by the appearance of color. When experiments
were carried out in the presence of H O, 0.09 g of H O was
Qualitative determination of IDTs. The reaction mixture conꢀ
2
2
introduced into the ampule containing the reaction mixture,
after which the contents of the ampule was degassed, and the
ampule was sealed off in vacuo.
taining IDTs contacted with air O . In this case, IDTs containing
2
nꢀalkyl or phenylmethyl substituents instantly changed the brown
9
color to green forming a bulky amorphous dark green color.
Formation of IDTs under the static conditions in the presence
The author is grateful to I. O. Volkov (A. N.
Nesmeyanov Institute of Organoelement Compounds,
Russian Academy of Sciences) for recording and discusꢀ
sion of Xꢀray photoelectronic spectra.
of atmospheric O . Ampules (15 mL) with mixtures of carbonyl
2
Fe (2.00 g, 0.36 gꢀat.) and thiol 1d or 1e (4.0 mL) were sealed off
in air. After 9 months, 7.8% 1d and 53.0% 1e reacted with Fe,
which corresponds to the formation of 3.9% 2d and 26.5% 2e.
Mechanochemical synthesis of IDTs in argon. Three steel
balls 12.7 mm in diameter and three steel balls 7.9 mm in diamꢀ
eter, reduced Fe (purity grade) (2.00 g, 0.36 gꢀat.), thiol 1b—e
or disulfide 3a in the individual state (10.0 mL), or disulfide
References
1
2
. S. Plaza, ASLE Trans., 1987, 30, 493.
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3
c—e (0.01 mol) in purified heptane (10.0 mL) were placed in a
4
12 (in Russian).
steel reactor. The reactor was purged with argon and hermetiꢀ
cally closed. After mechanical activation of the reaction for 3 h,
the iron powder was repeatedly washed with hexane by decantaꢀ
tion, filtered off, and dried in vacuo. Xꢀray photoelectronic specꢀ
tra were recorded after several days.
Mechanochemical synthesis of IDTs in the absence of O2.
Unlike experiments under the static conditions, five quartz balls
—7 mm in diameter were placed into the ampule before the
additional reduction of the Fe powder (2.00 g, 0.36 gꢀat.). After
Fe was reduced, degassed and argonꢀsaturated thiol 1b—e or
disulfide 3a (4.0 mL) was added to the ampule under an argon
atmosphere, the contents of the ampules were degassed, and the
ampules were sealed off in vacuo. The duration of mechanical
activation of the reaction was 1 h. In experiments with disulꢀ
3
4
5
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1
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8
. T. J. Wallace, J. Org. Chem., 1966, 31, 1217.
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9
. G. F. Pavelko, Izv. Akad. Nauk, Ser. Khim., 1998, 2388 [Russ.
Chem. Bull., 1998, 47, 2316 (Engl. Transl.)].
Received July 25, 2005;
fide 3a, H O (0.09 g) was introduced into the ampule. The
in revised form July 21, 2006
2