Applicability and mathematical verification of the reactivity-selectivity principle in the oxidation of thioanisoles by oxo(salen)manganese(v) complexes

Article abstract of DOI:10.1039/a604602i

The second-order rate constants for the oxidation of various para-substituted thioanisoles with substituted oxo(salen)manganese(v) complexes have been measured spectrophotometrically in acetonitrile at 25°C. Electron-withdrawing substituents in thioanisol

Full text of DOI:10.1039/a604602i

View Online / Journal Homepage / Table of Contents for this issue
Applicability and mathematical verification of the
reactivity–selectivity principle in the oxidation of thioanisoles by
oxo(salen)manganese(V) complexes†
Arunachalam Chellamani,*,a Naina Mohammed Ismail Alhajia and
Seenivasan Rajagopal*,b
a
Department of Chemistry, Manonmaniam Sundaranar University, Tirunelveli 627002, India
b School of Chemistry, Madurai Kamaraj University, Madurai 625021, India
The second-order rate constants for the oxidation of various para-substituted thioanisoles with
substituted oxo(salen)manganese(v) complexes have been measured spectrophotometrically in acetonitrile
at 25 ЊC. Electron-withdrawing substituents in thioanisoles and electron-releasing substituents in
oxo(salen)M nV complexes decrease the rate of oxidation. Correlation analyses show the presence of an
inverse relationship between reactivity and selectivity in the reactions of various thioanisoles with a given
oxo(salen)M nV complex and also in various oxo(salen)M nV complexes with a given thioanisole.
M athematical treatment of the results has also been carried out.
The validity of the concept that there is an inverse relationship
between the reactivity of a reagent and its selectivity among a
Results and discussion
The kinetics of oxygen atom transfer from oxomanganese()
set of similar substrates, known as the reactivity–selectivity
principle (RSP), has recently been subjected to critical
analysis.1–4 RSP has been tested with hydration, acid–base cata-
lysis, solvolysis, oxidation, reduction and other types of
reaction.3–6 However, applicability of RSP to biologically rele-
vant oxygen atom transfer (oxygenation) reactions has not yet
been reported. Oxygenation reactions7–9 have long been targets
for antibody catalysis as they mimic the metabolic activity of
biological enzymes10 such as cytochrome P-450 and xanthine
oxidase. Metal–porphyrin 11 and metal–salen 12–20 complexes
have been used to catalyse oxidation of alkenes,12–16 alkynes17
and sulfides18–20 by monooxygen atom donors, viz. PhIO,15–19
H2O2,14,20 hypochlorite12 or periodate.13
complexes 1–4 to various para-substituted thioanisoles has
been studied spectrophotometrically in acetonitrile at 25 ЊC.
The reaction is second-order overall, first-order each in the
complex and the substrate, which is evident from the k1 and k2
values reported in Table 1 for the reaction of methyl phenyl
sulfide (MPS) with the oxo complexes 1–4. A single electron
transfer (SET) mechanism 18 leading to the formation of a cat-
ion radical in the slow step has been proposed. The intermediate
1 decomposes to give LMnIII and sulfoxide as the products in a
fast step (Scheme 1). The postulation of this mechanism is sup-
O
O
+ •
Recently, we have investigated the oxidation of organic sulf-
ides by oxo(salen)manganese()18 and oxo(salen)chromium-
()19 complexes. Herein we report our results on the applic-
ability of RSP to the oxidation of aryl methyl sulfides by oxo-
(salen)manganese() complexes 1–4 (hereafter referred to as
slow
(salen)MnV + RSR′
(salen)MnIV + RSR′
R
+
S
O
oxo complexes) generated in situ from the corresponding [MnIII
(salen)]+PF6Ϫ complexes and PhIO as represented in eqn. (1).
-
O
(salen)MnIII + RSR′
R′
(salen)Mn
I
4
3
Scheme 1
–
PF6
5
Z
O
N
O
N
Z
2
+
Mn
6
1
ported by the study of substituent effects and the comparison
of experimental rate constants with the rate constant calculated
from the Marcus theory of electron transfer.
7
8
(salen)MnIII
PhlO
In an alternative mechanism 18 (Scheme 2), the formation of
O
ligand coupling
of O – & S +
RSOR′ + (salen)MnIII
(salen)MnV + RSR′
– O MnV(salen)
S +
–
PF6
O
Z
O
N
O
N
Z + Phl
(1)
R
R′
Mn+
II
Scheme 2
O
a hypervalent intermediate II either in a single step due to
electrophilic attack of Mn on the sulfide sulfur or in two
single electron transfer steps has been discussed. Sulfoxide is
(salen)MnV
1 Z = OMe
2 Z = H
3 Z = Cl
4 Z = NO2
† H2salen = N,NЈ-Bissalicylideneethylenediamine.
J. Chem. Soc., Perkin Trans. 2, 1997
299

View Online
Table 1 Rate constants for the oxidation of MPS by oxo complexes 1-4 in acetonitrile at 25 ЊC a
[MnV]/
10Ϫ3 
k1(obs)
/
k1(dec)
/
k1
/
k2 /
b
c
d
e
[MPS]/
10Ϫ2 
10Ϫ4 sϪ1
10Ϫ4 sϪ1
10Ϫ4 sϪ1
10Ϫ3 dm3 molϪ1 sϪ1
1
10.0
20.0
50.0
75.0
100.0
1.80
1.80
1.80
1.80
1.80
8.27 ± 0.23
12.6 ± 0.5
25.1 ± 1.2
34.3 ± 2.9
45.8 ± 2.5
3.90 ± 0.17
3.90 ± 0.17
3.90 ± 0.17
3.90 ± 0.17
3.90 ± 0.17
4.37 ± 0.06
8.70 ± 0.33
21.2 ± 1.0
30.4 ± 2.7
41.9 ± 2.3
4.37 ± 0.16
4.35 ± 0.17
4.24 ± 0.20
4.05 ± 0.36
4.19 ± 0.23
2f
4.0
4.0
4.0
4.0
4.0
10.0
14.0
20.0
50.0
100.0
0.83
1.24
1.65
1.80
3.04
1.80
1.80
1.80
1.80
1.80
7.79 ± 0.38
7.69 ± 0.37
7.32 ± 0.58
7.47 ± 0.42
7.73 ± 0.45
11.2 ± 0.8
13.7 ± 0.9
18.2 ± 1.1
36.2 ± 3.8
67.7 ± 6.5
5.27 ± 0.44
5.23 ± 0.24
4.72 ± 0.29
4.84 ± 0.32
5.05 ± 0.19
4.84 ± 0.32
4.84 ± 0.32
4.84 ± 0.32
4.84 ± 0.32
4.84 ± 0.32
2.52 ± 0.06
2.46 ± 0.13
2.60 ± 0.29
2.63 ± 0.10
2.68 ± 0.26
6.37 ± 0.48
9.12 ± 0.58
13.4 ± 0.8
31.4 ± 3.5
62.9 ± 6.2
6.30 ± 0.15
6.15 ± 0.33
6.50 ± 0.73
6.58 ± 0.25
6.70 ± 0.65
6.37 ± 0.48
6.51 ± 0.41
6.70 ± 0.39
6.27 ± 0.70
6.29 ± 0.62
3
2.0
5.0
10.0
15.0
20.0
1.80
1.80
1.80
1.80
1.80
7.92 ± 0.62
11.9 ± 0.9
19.8 ± 1.7
26.5 ± 1.5
32.9 ± 2.4
5.08 ± 0.42
5.08 ± 0.42
5.08 ± 0.42
5.08 ± 0.42
5.08 ± 0.42
2.84 ± 0.20
6.82 ± 0.48
14.7 ± 1.3
21.4 ± 1.1
27.8 ± 2.0
14.2 ± 1.0
13.6 ± 1.0
14.7 ± 1.3
14.3 ± 0.7
13.9 ± 1.0
4
2.0
5.0
10.0
15.0
20.0
1.80
1.80
1.80
1.80
1.80
13.3 ± 0.7
24.1 ± 1.0
45.6 ± 1.7
61.7 ± 1.6
86.7 ± 6.5
5.15 ± 0.32
5.15 ± 0.32
5.15 ± 0.32
5.15 ± 0.32
5.15 ± 0.32
8.15 ± 0.38
19.0 ± 0.7
40.5 ± 1.4
56.6 ± 1.3
81.6 ± 6.2
40.8 ± 1.9
38.0 ± 1.4
40.5 ± 1.4
37.7 ± 0.9
40.8 ± 3.1
a
As determined by a spectrophotometric technique following the disappearance of oxo complex at 680 nm; the error quoted in k values is the 95%
confidence limit of Student’s t test.21 b Estimated from pseudo-first-order plots over 20% reaction. c Estimated from first-order plots over 50-60%
reaction in the absence of sulfide. d Obtained as k1 = k1(obs) Ϫ k1(dec) e Individual k2 values estimated as k1/[S]. f Data taken from ref. 18.
.
Table 2 Second-order rate constants and ρ values for the reactions of para-substituted thioanisoles (p-XC6H4SMe) with substituted oxo com-
plexes in acetonitrile at 25 ЊC a,b
Oxo complex k2/10Ϫ3 dm3 molϪ1 sϪ1
X
Z = OMe
H
Cl
NO2
ρd
(r)
OMe
Me
H
F
Cl
22.8 ± 2.1
26.4 ± 1.6
12.0 ± 0.8
6.70 ± 0.39
4.89 ± 0.12
2.67 ± 0.29
2.50 ± 0.11
1.28 ± 0.15
0.71 ± 0.08
0.24 ± 0.04
36.4 ± 2.5
21.7 ± 1.7
14.2 ± 1.0
11.6 ± 0.2
8.38 ± 0.38
7.36 ± 0.41
3.46 ± 0.03
2.34 ± 0.04
0.78 ± 0.08
52.0 ± 3.1
43.6 ± 1.8
40.8 ± 3.1
30.6 ± 1.5
19.0 ± 1.4
17.1 ± 0.2
9.15 ± 0.12
4.91 ± 0.25
1.65 ± 0.03
0.176 ± 0.042 (0.988)
0.332 ± 0.075 (0.989)
0.474 ± 0.078 (0.994)
0.477 ± 0.110 (0.989)
0.515 ± 0.192 (0.971)
0.520 ± 0.177 (0.976)
0.532 ± 0.141 (0.985)
0.533 ± 0.219 (0.965)
0.554 ± 0.228 (0.964)
9.25 ± 0.40
4.37 ± 0.18
3.27 ± 0.23
1.73 ± 0.12
1.48 ± 0.17
0.74 ± 0.11
0.40 ± 0.06
0.12 ± 0.03
Br
CO2H c
COMe
NO2
ρe
Ϫ2.06 ± 0.19
Ϫ1.85 ± 0.16
Ϫ1.52 ± 0.18
Ϫ1.44 ± 0.32
(r)
(0.995)
(0.995)
(0.992)
(0.970)
a
d
The errors quoted in k2 is 95% CL of the ‘Student t’.21 b General conditions: [oxo complex] = 0.0018 ; [sulfide] = 0.2 . c [sulfide] = 0.1 . The
values were obtained by correlating log k2 with 2σp for the reaction of various oxo complexes with a given thioanisole. e The values were obtained by
correlating log k2 with σp for the reaction of various thioanisoles with a given oxo complex.
formed due to ligand coupling of S+ and OϪ in the intermediate
II.‡
The second-order rate constants for the reactions of various
para-substituted thioanisoles with each of the oxo complexes are
listed in Table 2. The rate data in Table 2 show that introduction
of substituents in the oxidant and the substrate has the opposite
effect on the rate of reaction i.e. electron-releasing substituents
in the oxo complex as well as electron-withdrawing substituents
in the sulfide retard the rate of oxidation. The kinetic data for
the reactions of various thioanisoles with a given oxo complex
and various oxo complexes with a given sulfide have been cor-
related with Hammett substituent constants. The correlation
is better with σp values rather than with σ+/σϪ values. A better
correlation of log k2 with σ+ or σϪ values rather than with σ
values has been postulated earlier for an electron-transfer
mechanism 26,27 for the oxidation of organic sulfides. However,
Miller et al. 28 have cautioned against deciding a reaction mech-
anism simply based on the correlation of log k with σ+/σϪ or on
the magnitude of ρ value. Thus the correlation of log k with σ+/
‡ One of the referees suggested another possibility of a direct oxygen
transfer from the oxo complex to sulfur without the formation of an
intermediate. But we have not considered this aspect as the dialkyl
sulfides are oxidized much more slowly than thioanisoles (cf. ref. 18),
which is in favour of SET and against direct oxygen transfer. A similar
explanation has been offered in the CeIV oxidation of organic sulfides.22
Further, for the reactions where a larger reactivity of dialkyl sulfides
compared to thioanisole has been observed, a direct oxygen transfer
mechanism has been suggested.23–25
300
J. Chem. Soc., Perkin Trans. 2, 1997

View Online
Table 3 Results of correlation between log kF i and log kSi according to eqn. (2)
Oxo complexes (F and S)
Results
2 and 1
3 and 1
3 and 2
4 and 1
4 and 2
4 and 3
r
0.999
0.992
0.993
0.963
0.969
0.985
b
∆
0.900 ± 0.022
0.194
0.733 ± 0.085
0.585
0.816 ± 0.084
0.392
0.689 ± 0.172
0.933
0.770 ± 0.177
0.739
0.954 ± 0.149
0.348
where kF i and kSi are the second-order rate constants for the
reactions of fast and slow reagents (oxo complexes) respectively
with each sulfide and εi is the error of the log kF i vs. log kSi
correlation. Since the difference between the reagents is variable
along the series of substrates, the mean difference ∆ can be
calculated using eqn. (3).
∆ =
ͩ
log kF i Ϫ
log kSi
ͪ
/N
(3)
͚
͚
i
i
Based on the values of b and ∆, four types of RSP have been
discussed.4 (i) A valid RSP [RSP(+)] when b < 1 and ∆ is not
too small. (ii) Anti-RSP [RSP(Ϫ)] when b > 1. (iii) Indifferent
behaviour [RSP(?)] when b = 1. (iv) A cross-over RSP i.e. RSP is
valid in one part of the series and invalid in the other [RSP(±)]
when ∆ is too small.
With the rate data available in Table 2, log kF i values were
plotted against log kSi values according to eqn. (2) to find slope
b and the values of ∆ were calculated using eqn. (3) for all the
six possible combinations of one fast and one slow reagent
(among the four oxo complexes) with a series of similar sub-
strates (nine thioanisoles) (Fig. 1). The results summarized in
Table 3 show a valid RSP in all cases as the value of b is less
than unity and ∆ is not too small.
Fig. 1 Log kF i vs. log kSi plots for the reactions of substituted thio-
anisoles with (a) 2 and 1, (b) 3 and 1, (c) 3 and 2, (d) 4 and 1, (e) 4 and
2 and (f) 4 and 3 (for clarity, only five points are shown for each line)
In a system involving more than one reagent and the same set
of substrates, the existence of a ‘magic point’4 in the log kF i vs.
log kSi plots is an indication for a strong RSP. The magic point
represents some limiting value of reactivity in which, for a par-
ticular substrate, the reaction rate is independent of the reagent
and vice versa. In this aspect, the present system reveals interest-
ing results (Fig. 1). The correlations involving nitro-substituted
oxo complex 4 (lines d–f) produce one magic point, y0(1)
and the correlations involving other oxo complexes (lines
a–c) produce another magic point, y0(2). Both magic points are
situated on the side of high reactivity, as expected for a strong
RSP as observed in the solvolysis4,30 of various meta- and para-
substituted allyl benzenesulfonates with various alcohols. Also,
it can be seen from Table 3 (the last three columns) that the
correlations involving 4 have b values with high error (>10%).
Hence, the reason for the different behaviour of 4 may be an
insufficiently precise linearity, rather than chemical differences
between the reagents.
σϪ is not a necessary condition for the proposal of an electron
transfer mechanism.§ It is pertinent to point out here that a
good correlation of log k with σ has been observed in the CrVI
oxidation of organic sulfides29 where a SET mechanism has
been established.
The last row of Table 2 contains ρ values for substituent
variation in thioanisole for each oxo complex while the last
column shows reaction constants for substituent variation in
oxo complex for each thioanisole. The ρ values in Table 2
show that there is a significant variation of reaction constants
(selectivity) when we vary the nature of substituent either in
the oxo complex or in the sulfide. Also, it is apparent that as the
reactivity of either sulfide or oxo complex decreases the ρ value
increases i.e. there is an inverse relationship between reactivity
and selectivity in both cases. However, the ρ values shown in the
last column of Table 2 deserve an explanation. Though it
changes significantly when p-OMe is introduced in place of H,
little change is observed if p-NO2 is substituted. We have used
only four points in the correlation of log k2 vs. 2σ and the r
values observed in the case of sulfides containing electron-
withdrawing groups (except p-F and p-CO2H) are only satisfac-
tory. Further, the error associated with ρ values for these
sulfides is high compared to that observed for sulfides having
electron-releasing groups. Thus the ρ value measured for
p-NO2C6H4SMe is less reliable compared to that for
p-OMeC6H4SMe.
In a detailed analysis of RSP, Exner 4 has concluded that
although RSP was evidently disproved as a general rule, investi-
gations of selectivity and its relation to reactivity should be
continued and used possibly to characterise a certain type of
reaction or a certain mechanism. The operation of RSP has
been attributed to the factors3,5 that (i) absence of solvent
effects, (ii) no appreciable structural change near the reaction
site, and (iii) no change in mechanisms. Hence, the fact that the
present system obeys RSP may be considered as evidence that
the same mechanism is operating in all reactions.
Mathematical verification
When two reagents (fast F and slow S) and a series of similar
substrates (i = 1, 2 … n) can be chosen in such a way that the
greatest difference in reactivity within the substrate set is greater
than between the reagents the RSP then requires a more or less
precise linear relationship 4 between the two series, as in eqn. (2)
Experimental
All the thioanisoles were prepared according to the reported
procedure.31,32 The purity of the sulfides was checked by HPLC
analyses which showed the presence of a single entity in each
sulfide. Acetonitrile (GR, E. Merck) was first refluxed over P2O5
for 5 h and then distilled. Iodosylbenzene was prepared from
(diacetoxyiodo)benzene by a standard method.33
log kF i = a + b log kSi + εi
(2)
Ϫ
The [MnIII(salen)]+PF6 complexes were synthesised accord-
§ For a detailed discussion on the mechanism see ref. 18.
J. Chem. Soc., Perkin Trans. 2, 1997
301

View Online
ing to a known procedure.16,18 The IR and UV–VIS spectral
studies of all the complexes were found to be identical with
literature data.16 The oxo complexes 1–4 were generated 18 in situ
by stirring magnetically 0.15 mmol of finely powdered PhIO in
5 ml acetonitrile solution containing 0.015 mmol of corre-
sponding MnIII(salen) complex for 5 min under nitrogen
followed by filtration at ice temperature to remove the undis-
solved iodosylbenzene. The conversion of MnIII to MnV may be
considered quantitative in the sense that prolonged stirring
causes no change in the initial absorption spectrum of MnV
solution.
ance in the form of a project. Also, N. M. I. A. thanks the CSIR,
New Delhi for the award of a Senior Research Fellowship.
References
1 C. D. Johnson, Chem. Rev., 1975, 75, 755.
2 A. Pross, Adv. Phys. Org. Chem., 1977, 14, 69.
3 C. D. Johnson, Tetrahedron, 1980, 36, 3461 and references cited
therein.
4 O. Exner, J. Chem. Soc., Perkin Trans. 2, 1993, 973.
5 (a) C. Srinivasan, P. Kuthalingam and N. Arumugam, J. Chem. Soc.,
Perkin Trans. 2, 1980, 170; (b) D. Bethell, A. E. Graham, J. P. Heer,
O. Markopoulou, P. C. B. Page and B. K. Park, J. Chem. Soc., Perkin
Trans. 2, 1993, 2161; (c) I. Lee, H. J. Koh, Y. S. Park and H. W. Lee,
J. Chem. Soc., Perkin Trans. 2, 1993, 1575.
Kinetic measurements
Reaction mixtures for kinetic runs were prepared by quickly
mixing the solutions of the oxo complex and sulfide in varying
volumes so that in each run the total volume was 5 ml. The
kinetics was followed in a Perkin-Elmer UV–VIS spectro-
photometer (Lambda 3B) fitted with thermostatted cell
compartments under pseudo-first-order conditions ([sulfide] >
[oxo complex]) in acetonitrile at 25 ± 0.1 ЊC by monitoring the
decay of oxo complex at 680 nm.16,18
The rate constants were computed from the linear least-
squares plots of ln(At Ϫ A∞) vs. time, where At is the absorb-
ance at time t and A∞ is the experimentally determined infinity
point. The values of k1 were obtained 18,23 as k1 = k1(obs) Ϫ k1(dec)
where k1(dec) represents the first-order rate constants for the
auto-decomposition of oxo complex and k1(obs) represents the
pseudo-first-order rate constants for the decay of oxo complex
in the presence of sulfides. The second-order rate constants, k2,
were obtained by the relation k2 = k1/[sulfide].
The reaction mixture from an actual kinetic run was sub-
jected to vacuum evaporation and the residue was then
extracted with diethyl ether. The ethereal extract was dried over
anhydrous Na2SO4 and the solvent evaporated. The product
was dissolved in CH2Cl2 and the GC analyses of the samples
showed the presence of sulfoxide and iodobenzene. The yield of
sulfoxide (60–70%) depended on the sulfide and oxo complex
employed. The lower yield of sulfoxide may be attributed to the
competitive self-decomposition of oxomanganese() complex
to MnIII complex, which is confirmed by the near quantitative
recovery of MnIII complex from the reaction mixture.
The reaction carried out under stoichiometric conditions
([2] = 0.0018 ; [PhSMe] = 0.018 ) gave sulfoxide in ca. 70%
yield and MnIII (salen) complex in ca. 95% yield with negligible
amount of sulfone. Accordingly, the stoichiometry for the
oxidation of sulfides with oxo complexes can be represented
by eqn. (4).
6 E. Buncel and C. J. Chanqui, J. Org. Chem., 1980, 45, 2825.
7 R. H. Holm, Chem. Rev., 1987, 87, 1401.
8 B. Meunier, Chem. Rev., 1992, 92, 1411.
9 R. S. Drago, Coord. Chem. Rev., 1992, 117, 185.
10 (a) R. Sato and Y. Omuru, Cytochrome P-450, Kodansa, Tokyo and
Academic Press, New York, 1980; (b) H. L. Holland, Chem. Rev.,
1988, 88, 473; (c) A. G. Cochran and P. G. Schultz, J. Am. Chem.
Soc., 1990, 112, 9414; (d) M. H. Gelb, W. A. Toscano, Jr., and S. C.
Sligar, Proc. Natl. Acad. Sci., 1982, 79, 5758; (e) J. Amesz, Biochim.
Biophys. Acta, 1983, 1, 726.
11 (a) E. Guilmet and B. Meunier, Tetrahedron Lett., 1982, 23, 2449; (b)
1980, 21, 4449; (c) J. T. Groves and M. K. Stern, J. Am. Chem. Soc.,
1988, 110, 8628; (d) P. L. Anelli, S. Banfi, F. Montanari and S. Quici,
J. Chem. Soc., Chem. Commun., 1989, 779.
12 W. Zhang and E. N. Jacobsen, J. Org. Chem., 1991, 56, 2296.
13 P. Pietikainen, Tetrahedron Lett., 1995, 36, 319.
14 P. Pietikainen, Tetrahedron Lett., 1994, 35, 941.
15 E. G. Samsel, K. Srinivasan and J. K. Kochi, J. Am. Chem. Soc.,
1985, 107, 7606.
16 K. Srinivasan, P. Michuad and J. K. Kochi, J. Am. Chem. Soc., 1986,
108, 2309.
17 B. Rihter, S. SriHari, S. Hunter and J. Masnovi, J. Am. Chem. Soc.,
1993, 115, 3918.
18 A. Chellamani, N. M. I. Alhaji, S. Rajagopal, R. Sevvel and
C. Srinivasan, Tetrahedron, 1995, 51, 12677.
19 R. Sevvel, S. Rajagopal, C. Srinivasan, N. M. I. Alhaji and
A. Chellamani, submitted for publication.
20 M. Palucki, P. Hanson and E. N. Jacobsen, Tetrahedron Lett.. 1992,
33, 7111.
21 C. Srinivasan, S. Rajagopal and A. Chellamani, J. Chem. Soc.,
Perkin Trans. 2, 1990, 1839.
22 E. Baciocchi, D. Intini, A. Piermattei, C. Roe and B. Ruzziconi,
Gazz. Chim. Ital., 1989, 119, 646.
23 R. Curci, S. Giannattasio, O. Sciacovelli and L. Troisi, Tetrahedron,
1984, 40, 2763.
24 F. Ruff and A. Kucsman, J. Chem. Soc., Perkin Trans. 2, 1985,
683.
25 H. G. Hanthal, H. Onderka and W. Pritzkow, J. Prakt. Chem., 1969,
82, 311.
26 (a) S. Oae, Y. Watanabe and K. Fujimori, Tetrahedron Lett., 1982,
1189; (b) Y. Watanabe, T. Numata, T. Iyanagi and S. Oae, Bull.
Chem. Soc. Jpn., 1981, 54, 1163.
27 J. H. Acquaye, J. G. Muller and K. J. Takeuchi, Inorg. Chem., 1993,
32, 160.
28 A. E. Miller, J. J. Bischoff, C. Bizub, P. Luminoso and S. Smiley,
J. Am. Chem. Soc., 1986, 108, 7773.
29 C. Srinivasan, A. Chellamani and S. Rajagopal, J. Org. Chem., 1985,
50, 1201.
30 R. V. Sendega, R. V. Vizgert and M. K. Mikhalevich, Reakts.
Sposobnost Org. Soedin. (Tartu), 1970, 7, 512.
31 H. Zahn and H. Zuber, Chem. Ber., 1953, 86, 180.
32 V. Baliah and M. Uma, Tetrahedron, 1963, 19, 455.
33 H. Saltzman and J. G. Sharefkin, Organic Syntheses, Vol. V,
New York, Wiley, 1973, 658.
34 T. Takata, R. Tajima and W. Ando, Phosphorous and Sulfur, 1983,
16, 67.
35 W. Ando, R. Tajima and T. Takata, Tetrahedron Lett., 1982, 23,
1685.
O᎐MnV(salen)+ + PhSMe →
᎐
MnIII(salen)+ + PhSOMe (4)
Ando and co-workers34,35 have reported the direct oxidation
of sulfides by PhIO in CH2Cl2. To check whether there is any
reaction between the dissolved PhIO and sulfide under the
present experimental conditions we have carried out the reac-
tion as described below. A solution of PhIO was prepared by
stirring 33 mg (0.15 mmol) of finely powdered PhIO in 5 ml of
acetonitrile for 5 min followed by filtration. The concentration
of PhIO in the solution was too low to be detected by iodo-
metric estimation (the solubility of PhIO in acetonitrile16 is
very low, 10Ϫ4 m). To the PhIO solution thus prepared ca. 0.2
 MPS was added and the product analyses showed negligible
amount of sulfoxide. This experimental observation led us to
conclude that the reported sulfoxide yield is mainly due to the
reaction between oxo complex and sulfide.
Acknowledgements
We thank Professor C. Srinivasan for constant encouragement.
We thank the CSIR, New Delhi for providing financial assist-
Paper 6/04602I
Received 2nd July 1996
Accepted 18th October 1996
302
J. Chem. Soc., Perkin Trans. 2, 1997