Heterogeneous permanganate oxidation of thiols

Article abstract of DOI:10.1055/s-1998-2190

The products that may be obtained from the oxidation of thiols by permanganate under heterogeneous conditions have been compared with those that are known to be produced by use of the same oxidant under homogeneous conditions. The products obtained from the oxidation of thiols under homogeneous and heterogeneous conditions are distinctively different. Sulfonic acids are obtained under homogeneous conditions, while disulfides are the only detectable products when the reactions are carried out heterogeneously. For example, a quantitative yield of dibutyl disulfide is obtained from the oxidation of butane-1-thiol, and oxidation of pentane-1,5- dithiol gives the corresponding cyclic disulfide, 1,2-dithiepane.

Full text of DOI:10.1055/s-1998-2190

November 1998
SYNTHESIS
1587
Heterogeneous Permanganate Oxidation of Thiols
Nazih A. Noureldin,* Marguerite Caldwell, Jennifer Hendry, Donald G. Lee
Department of Chemistry, University of Regina, Regina, SK, S4S 0A2, Canada
Received 10 February 1998
Abstract: The products that may be obtained from the oxidation
of thiols by permanganate under heterogeneous conditions have
been compared with those that are known to be produced by use
of the same oxidant under homogeneous conditions. The products
obtained from the oxidation of thiols under homogeneous and het-
erogeneous conditions are distinctively different. Sulfonic acids
are obtained under homogeneous conditions, while disulfides are
the only detectable products when the reactions are carried out
heterogeneously. For example, a quantitative yield of dibutyl di-
sulfide is obtained from the oxidation of butane-1-thiol, and oxi-
dation of pentane-1,5-dithiol gives the corresponding cyclic disul-
fide, 1,2-dithiepane.
material (Equation 3) and propane-1,3-dithiol gives about
0% cyclic disulfides and 50% polymeric material (Equa-
5
tion 4), while butane-1,4-dithiol gives only the cyclic di-
sulfide in 97% yield. In the case of 1,4-benzene-
dimethanethiol, intramolecular oxidation to a cyclic disul-
fide is obviously not possible, resulting in the formation
of only polymer, while for butane-1,4-thiol intramolecu-
lar oxidation takes place preferentially. For propane-1,3-
thiol, intramolecular and intermolecular oxidations ap-
pear to be of approximately equal probability.
Key words: heterogeneous permanganate oxidation, thiols, disul-
fides, cyclic disulfides
There is an accumulation of evidence which indicates that
heterogeneous permanganate oxidations yield significant-
ly different products from those obtained under homoge-
neous conditions. For example, alkenes readily react with
permanganate in homogeneous solutions to yield diols,
ketols, epoxides, diones or products derived from the ox-
1
idative cleavage of carbon–carbon double bonds. How-
A summary of the disulfides that have been prepared to
illustrate the scope of this reaction is presented in the Ta-
ble.
ever, under heterogeneous conditions, where permangan-
ate is adsorbed on a solid support, a very different selec-
2
, 3
tivity is observed.
In this paper we wish to describe a method for the oxida-
tion of thiols by permanganate under heterogeneous con-
ditions, to note the remarkable difference between the
products obtained under heterogeneous and homogeneous
Table. Isolated Yields of Disulfides Obtained from the Oxidation of
Thiols and Dithiols by Potassium Permanganate Adsorbed on Copper
Sulfate Pentahydrate.
conditions, and to comment on the potential synthetic use- Reactant
Product
Yield (%)
fulness of the heterogeneous reactions.
PhSH
PhSSPh
4-MeSC H SSC H Me-4
89
78
97
98
86
83
Although sulfides are oxidized to similar products by per-
manganate under both heterogeneous and homogeneous
4
4
-MeC H SH
6
4
6
4
6
4
-NO C H SH
4-NO C H SSC H NO -4
2 6 4 6 4 2
2
6
4
4, 5
conditions, the results obtained from the oxidation of
thiols are dramatically different. Under homogeneous
conditions, thiols are converted into sulfonic acids.6, 7
However, under heterogeneous conditions, thiols are oxi-
dized to the corresponding disulfides. As illustrated by the
reactions depicted in Equations 1 and 2, both aromatic and
BuSH
BuSSBu
CH (CH ) CH SH CH (CH ) CH SSCH (CH ) CH
3
2 3
2
3
2 3
2
2
2 3
3
3
CH (CH ) CH SH CH (CH ) CH SSCH (CH ) CH
3
2 7
2
3
2 7
2
2
2 7
98
73
aliphatic thiols are converted into disulfides in good HS(CH ) SH
2
5
yields.
HS(CH ) SH
97
45
2
4
HS(CH ) SH
2
3
The oxidation of dithiols results in the formation of cyclic An attempt was also made to use heterogeneous perman-
disulfides and/or polymers. The polymers result from in- ganate oxidations to prepare unsymmetrical disulfides,
termolecular oxidations, while the cyclic disulfides arise but with limited success. For example, the oxidation of an
from intramolecular oxidations. For example, the oxida- equimolar mixture of pentane-1-thiol and p-thiocresol re-
tion of 1,4-benzenedimethanethiol gives only polymeric sulted in the formation of three products, dipentyl disul-

1
588
Short Papers
SYNTHESIS
fide, pentyl p-tolyl disulfide and di-p-tolyl disulfide in a
molar ratio of 1:2:1.5.
Bis(p-nitrophenyl) Disulfide:
p-Nitrothiophenol is sparingly soluble in CH Cl . Oxidation was
2
2
achieved by stirring a finely powdered suspension of somewhat im-
pure p-nitrothiophenol (0.615 g, 2.5 mmol) with oxidant, as in the
general procedure, for 140 min. The product precipitated; yield:
Delaude and Laszlo have recently reported that the heter-
ogeneous oxidation of thiols by potassium tetraoxofer-
rate(VI), K FeO , adsorbed on K10 montmorillonite clay,
0
.373 g (97%); mp 177–178°C (lit.11 182°C).
2
4
1
H NMR: δ = 8.25–8.13 (m, 4H), 7.70–7.56 (m, 4H).
MS: m/z (%) = 308 (M , 100), 171 (14), 155 (07), 138 (15), 124 (14),
also results in the formation of disulfides in quantitative
+
8
yields. Although both experimental methods are similar,
108 (26), 69 (27).
the use of potassium permanganate offers one practical
advantage; it is an inexpensive, commercially available
product while ferrate(VI) must be prepared and purified
prior to use. On the other hand, the use of iron-based oxi-
dants is attractive from an environmental viewpoint be-
cause iron, unlike most other transition metals, including
Dibutyl Disulfide:
Oxidation of butane-1-thiol (0.271 g, 3.01 mmol) following the gen-
eral procedure gave dibutyl disulfide (0.263 g, 98%) in 21 min; ηD
1
.4938 (lit.11 1.4926).
1
H NMR: δ = 2.66 (t, 4H, J = 7 Hz), 1.73–1.54 (m, 4H), 1.51–1.32 (m,
4H), 0.98–0.88 (m, 6H).
8
, 9
manganese, is considered to be nontoxic.
IR (neat): ν = 2957, 2929, 2872, 1464, 1413, 1378, 1272, 1217, 1131,
–1
1089, 912, 743 cm .
Possible mechanisms for these and other heterogeneous
permanganate oxidations have been previously consid-
+
MS: m/z (%) = 178 (M , 31), 122 (26), 57 (100), 41 (63), 29 (57).
4
, 10
ered.
Dipentyl Disulfide:
Oxidation of pentane-1-thiol (0.315 g, 3.02 mmol) following the gen-
eral procedure gave dipentyl disulfide (0.267 g, 86%) in 2 h; ηD
The oxidant used in these experiments was prepared by placing equal
amounts (typically 5 g) of KMnO and CuSO •5 H O in a mortar and
11
1.4888 (lit. 1.4889).
4
4
2
1
grinding until homogeneous. The solvent, CH Cl , was purified by
H NMR: δ = 2.61 (t, 4H, J = 7 Hz), 1.71–1.52 (m, 4H), 1.41–1.20 (m,
2
2
stirring over KMnO , using a small amount of phase transfer agent
8H), 0.92–0.77 (m, 6H).
4
(
Bu NBr) to solubilize the oxidant, and distilled. The purity of the
IR (neat): ν = 2956, 2925, 2958, 1465, 1412, 1378, 1329, 1271, 1209,
4
–1
solvent treated in this way was confirmed, by use of GC, to be 99.9%
or better. The thiols and sulfides were obtained from the Aldrich
Chemical Co. The liquids were distilled before use to ensure that no
alkene impurities were present. The products were identified by com-
parison of spectroscopic data with published data for the same com-
pounds. Purity was confirmed by mp, refractive indices and/or GC
analysis.
1131, 729, 502, 488, 474 cm .
+
MS: m/z (%) = 206 (M , 19), 136 (15), 103 (14), 71 (39), 43 (100), 39
(12).
Dinonyl Disulfide:
Oxidation of nonane-1-thiol (0.393 g, 2.39 mmol) following the gen-
eral procedure gave dinonyl disulfide (0.317 g, 83%) in 3 h; ηD
1
.4773.
1
Oxidation of Thiols; General Procedure:
H NMR: δ = 2.62 (t, 4H, J = 7 Hz), 1.70–1.50 (m, 4H), 1.50–1.15 (m,
24H), 0.990–0.75 (m, 6H).
Thiol (2.5 mmol) was placed in a 50-mL round-bottomed flask.
CH Cl (20 mL) and oxidant (0.8 g) were added and the heteroge-
IR (neat): ν = 2918, 2851, 1465, 1412, 1377, 1333, 1300, 1262, 1228,
2
2
–1
neous mixture was stirred at r.t. for several hours. The progress of the
reaction was monitored by TLC or GC until no thiol was detected.
The contents of the flask were then filtered through Celite and washed
with CH Cl (2 × 10 mL) and Et O (10 mL). The product was isolated
1132, 722, 520, 488, 454 cm .
+
MS: m/z (%) = 318 (M , 20), 192 (18), 159 (22), 85 (37), 71 (66), 57
(64), 43 (100), 41 (62), 29 (34).
2
2
2
by evaporation of the solvent under reduced pressure, and identified
from spectroscopic analysis. Although the yields determined by GC
analysis were usually quantitative, isolated yields were somewhat
less. It was found that the reaction time could be decreased without
any reduction in yield by using more oxidant and/or by refluxing the
solution.
1,2-Dithiolane:
Oxidation of propane-1,3-dithiol (0.283 g, 2.61 mmol) following the
general procedure gave 1,2-dithiolane (0.124 g, 45%) in 30 min.
1
H NMR: δ = 2.89–2.67 (m, 4H), 2.18–1.95 (m, 2H).
–1
IR (KBr): ν = 2918, 1440, 1410, 1331, 1290, 1234, 825, 753 cm .
+
MS: m/z (%) = 106 (M , 100), 78 (37), 64 (52), 45 (53), 41 (95).
The remainder of the product was an insoluble, polymeric sheet on the
inside of the reaction flask.
Diphenyl Disulfide:
Oxidation of thiophenol (0.275 g, 2.5 mmol) following the general
procedure gave diphenyl disulfide (0.242 g, 89%). The reaction was
1,2-Dithiane:
1
1
complete in 33 min; mp 60.7–60.9 ˚C (lit. 61–62°C).
The oxidation of butane-1,4-dithiol (0.303 g, 2.48 mmol) following
the general procedure gave 1,2-dithiane (0.289 g, 97%) in 80 min.
1
H NMR: δ = 7.63–7.49 (m, 4H), 7.42–7.20 (m, 6H).
–
1
1
IR (KBr): ν = 1573, 1474, 1436, 736, 686, 471, 461 cm .
H NMR: δ = 2.90–2.62 (m, 4H), 2.05–1.71 (m, 4H).
+
MS: m/z (%) = 218 (M , 82), 185 (20), 154 (27), 109 (100), 65 (48).
IR (neat): ν = 2924, 2846, 1432, 1407, 1323, 1302, 1279, 1225, 1131,
–1
912, 731, 712, 514, 450 cm .
+
MS: m/z (%) = 120 (M , 61), 64 (21), 55 (100), 45 (27).
p-Ditolyl Disulfide:
Oxidation of p-thiocresol (0.313 g, 2.52 mmol) following the general
procedure gave a partially soluble, faintly yellow product after
1,2-Dithiepane:
3
2 min. Because of the insolubility of the product in CH Cl , several
The oxidation of pentane-1,5-dithiol (0.332 g, 2.44 mmol) following
the general procedure gave 1,2-dithiepane (0.239 g, 73%) in 1 h.
H NMR: δ = 2.70 (t, 4H, J = 6.4 Hz), 1.82–1.64 (m, 4H), 1.61–1.44
2
2
Et O washes of the Celite were required to obtain a yield of 0.241 g
2
1
1
1
(
78%); mp 44.5–44.8°C (lit. 47–48°C).
H NMR: δ = 7.60–7.35 (m, 4H), 7.25–7.07 (m, 4H), 2.33 (s, 6H).
1
(m, 2H).
–
1
–1
IR (KBr): ν = 3029, 2913, 1488, 1396, 800, 489, 480 cm .
MS: m/z (%) = 246 (M , 77), 123 (100), 91 (17), 79 (26), 77 (26), 45
IR (neat): ν = 2925, 2849, 1654, 1636, 1458, 669, 486, 458 cm .
MS: m/z (%) = 134 (M , 56), 101 (8), 87 (18), 69 (56), 45 (27), 41
+
+
(47).
(100), 27 (25).

November 1998
SYNTHESIS
1589
The authors are pleased to acknowledge financial support from the
Natural Sciences and Engineering Research Council of Canada.
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1