The unexpected formation of a 2,2′-DI(N-ethyl-acetamino)substituted diphenyl disulfane on oxidation of 3-ethyl-2-methylbenzothiazolium tetrafluoroborate

Article abstract of DOI:10.1080/10426500307848

Attempts at the oxidation of 3-ethyl-2-methylbenzothiazolium salt 2 with a variety of oxidizing reagents did not lead to the desired isochiral S-oxide 3 or achiral S,S-dioxide 4, in some cases, however, unexpectedly to the ring-opened dimeric 2,2′-di(N-ethyl-acetamino)substituted diphenyl disulfane 5, the molecular structure of which was confirmed by x-ray analysis. The synthesis of 2-methylbenzothiazole-S,S-dioxide 14, reported by Zincke et al. in 1915, turned out to be not reproducible.

Full text of DOI:10.1080/10426500307848

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The Unexpected Formation of a 2,2′-Di( N -ethyl-
acetamino)substituted Diphenyl Disulfane on Oxidation
of 3-Ethyl-2-methylbenzothiazolium Tetrafluoroborate
Christian Reichardt a , Hans-Peter Erfurt a & Klaus Harms a
a Philipps University , Marburg, Germany
Published online: 27 Oct 2010.
To cite this article: Christian Reichardt , Hans-Peter Erfurt & Klaus Harms (2003) The Unexpected Formation of a 2,2′-
Di( N -ethyl-acetamino)substituted Diphenyl Disulfane on Oxidation of 3-Ethyl-2-methylbenzothiazolium Tetrafluoroborate,
Phosphorus, Sulfur, and Silicon and the Related Elements, 178:5, 1081-1092, DOI: 10.1080/10426500307848
To link to this article: http://dx.doi.org/10.1080/10426500307848
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Phosphorus, Sulfur and Silicon, 2003, Vol. 178:1081–1092
C
Copyright 2003 Taylor & Francis
1042-6507/03 $12.00 + .00
DOI: 10.1080/10426500390208910
THE UNEXPECTED FORMATION OF A
2,20-DI(N-ETHYL-ACETAMINO)SUBSTITUTED
DIPHENYL DISULFANE ON OXIDATION OF
3-ETHYL-2-METHYLBENZOTHIAZOLIUM
TETRAFLUOROBORATE
Christian Reichardt, Hans-Peter Erfurt, and Klaus Harms
Philipps University, Marburg, Germany
(Received August 12, 2002; accepted October 31, 2002)
Attempts at the oxidation of 3-ethyl-2-methylbenzothiazolium salt 2
with a variety of oxidizing reagents did not lead to the desired isochiral
S-oxide 3 or achiral S,S-dioxide 4, in some cases, however, unexpect-
edly to the ring-opened dimeric 2,20-di( N-ethyl-acetamino)substituted
diphenyl disulfane 5, the molecular structure of which was confirmed
by x-ray analysis. The synthesis of 2-methylbenzothiazole-S,S-dioxide
14, reported by Zincke et al. in 1915, turned out to be not reproducible.
Keywords: 3-Ethyl-2-methylbenzothiazolium salts; benzothiazolium
salts; heterocycles; oxidation; sulfur heterocycles
This article is part IX in the series “Chiral Polymethine Dyes.”—Part VIII: Reichardt
et al.3
X-ray crystal structure analysis by Klaus Harms.
The Fonds der Chemischen Industrie, Frankfurt (Main), is gratefully acknowledged
for their financial support of this work.
Address correspondence to Christian Reichardt, Department of Chemistry and Center
of Material Sciences, Philipps University, Hans-Meerwein-Strasse, D-35032 Marburg,
Germany. E-mail: Reichardt-Marburg@t-online.de
1081

1082
C. Reichardt et al.
Whereas chiral aromatics (e.g., helicenes) and chiral polyenes (e.g.,
carotinoids) are well-known conjugated -systems, chiral polymethinic
-systems have been studied in more detail only recently3,4 in spite of
the fact that chiral polymethine dyes have been already described in
5
1928 by Ko¨nig et al. and 1938 by G
o¨tze.6 Chiral polymethine dyes are
of potential interest as functional dyes7 because of their particular chi-
roptical properties. There are three possibilities to introduce chirality
into the conjugated -system of polymethine dyes: (a) introduction of
substituents with stereogenic centers into the polymethine chain8or
into the heterocyclic end groups;9,10 (b) the use of heterocyclic end
groups containing stereogenic centers within the heterocyclic ring
system;11,12 and (c) helical twisting of the polymethine chain by steric
effects.13–15 Recently having synthesized polymethine streptocyanine
dyes with sulfinyl groups as stereogenic centers in the two end groups,3
we thought that monochiral 2,3-dialkylsubstituted benzothiazolium-
S-oxide salts such as 3 (Scheme 1) with a stereogenic S O group would
be suitable candidates for the synthesis of new chiral tri- and pentame-
thinium thiacyanine dyes. To the best of our knowledge, up to now such
benzothiazolium-S-oxides are not known.17 Surprisingly, instead of the
SCHEME 1 Attempts at oxidation of benzothiazolium salt 2.
We prefer the designations monochiral (one-handed), isochiral (equal-handed), and
anisochiral (unequal-handed) in place of the ambiguous terms homochiral, racemic, and
scalemic, respectively, as recently recommended by H. Cornforth.1

Unexpected Formation of a 2,20-Disubstituted Diphenyl Disulfine
1083
desired S-oxide 3 (or S,S-dioxide 4), in two cases (oxidation with per-
acetic acid and with 3-chloroperbenzoic acid at higher temperature), the
ring-opened dimeric 2,20-disubstituted diphenyl disulfane 5 was unex-
pectedly obtained.
RESULTS AND DISCUSSION
We have tried to synthesize 3-ethyl-2-methylbenzothiazolium-S-oxide
salts such as 3 and the corresponding S,S-dioxide 4 by S-oxidation of
3-ethyl-2-methylbenzothiazolium tetrafluoroborate (2),18 which was ob-
tained from commercially-available 2-methylbenzothiazole (1) by alky-
lation with triethyloxonium tetrafluoroborate19 (Scheme 1).
Because there are reports that oxidation of N,S-heterocycles with-
out N-substituents leads preferably to the formation of the corre-
sponding N-oxides (see for example Ochiai and Hayashi20), we have
first protected the benzothiazol-nitrogen by alkylation. For oxidation
of the N-alkylated benzothiazolium salt 2 to the desired isochiral
(“racemic”)16 sulfoxide 3, the following oxidation reagents were ap-
plied at various temperatures:1,2 (a) hydrogen peroxide (without21a and
with Jacobsen’s catalyst22); (b) peracetic acid, formed in situ from hy-
drogen peroxide and acetic acid;21b (c) 3-chloroperbenzoic acid;21c,23
(d) sodium periodate;21d,24 and (e) hypofluorous acid in acetonitrile
(H3C–CN HOF).21e,25
A suspension of 2 in aqueous hydrogen peroxide (c = 30 cg/g)21a at
room temperature (rt) and at 50 C led only to the recovery of unreacted
2 with 85–90% yield.1 The same reaction in acetonitrile/water in the
presence of Jacobsen’s catalyst22 (2 mole-%) at rt and at 60 C afforded
likewise the unreacted educt 2 only with 84–87% yield.1
A suspension of 2 in acetic acid with an excess (4 equivalents) of
aqueous hydrogen peroxide (c = 30 cg/g)21b led at 10 C and at rt only
to the recovery of the educt with 85–90% yield. However, at higher tem-
peratures (i.e., 50 and 70 C), a highly viscous brownish oil was isolated,
which turned out to be neither the desired sulfoxide 3 nor the sulfone
4, but the diphenyl disulfane 5 (Scheme 1; see later).1 In order immedi-
ately to get sulfone 4, salt 2 was treated with an excess of 10 equivalents
of aqueous hydrogen peroxide in acetic acid at rt and at 70 C, however,
again without success. After treatment at rt, only the educt was recov-
ered, but at 70 C crude disulfane 5 could be again isolated as a highly
viscous light-brown oil.1
The oxidation of 2 with 3-chloroperbenzoic acid (1 equivalent)21c
in dichloromethane, according to a procedure given by Chioccara

1084
C. Reichardt et al.
et al.,23 gave at 0 C only the unreacted educt (87%), but at 50 C in
trichloromethane as solvent, crude disulfane 5 again was isolated as
highly viscous brownish oil.1 After treatment of 2 with an excess of five
equivalents of 3-chloroperbenzoic acid in trichloromethane at 50 C, the
formation of disulfane 5 only could be detected.1
Oxidation of 2 with sodium periodate21d in acetone/water at 0 and
50 C, according to a procedure given by Leonard et al. for the oxidation
of sulfanes to sulfoxides,24 resulted likewise in the recovery of unreacted
educt only.1
Eventually, the oxidation of 2 at 0 C with the strongly oxidizing
hypofluorous acid/acetonitrile complex,21e,25 which oxidizes even thio-
phene easily to thiophene-S,S-dioxide, afforded with an equivalent
amount of oxidizing agent only the unreacted educt, however, with a
five-fold excess a nonseparated mixture of 2 (ca. 20%) and 5 (ca. 80%)
according to its 1H and 13C NMR spectrum.2
Obviously, the quaternary imonium cation of salt 2 is very resistant
to all five oxidation reagents, applied at various reaction conditions:
neither the sulfoxide 3 nor the sulfone 4 could be prepared this way.
However, in two cases (with peracetic acid and 3-chloroperbenzoic acid
at higher temperatures) a viscous brownish oil was unexpectedly iso-
lated, the molecular structure of which could not unambiguously de-
termined by its elemental analysis and spectroscopic measurements
alone. The oil, which did not crystallize by itself, was dissolved in small
amounts of various solvents and the solutions were slowly concentrated
by evaporation in vacuo in an exsiccator in the presence of silica gel or
P4O10. Finally, in one case, a slow crystallization process started under
high vacuum. After two days, the crystals were separated, washed with
petroleum ether (b.p. 40–60 C)/diethyl ether (5:1), and dried to afford
colorless needles with m.p. 104 C, resistant to air and water. One of
them was suitable for an x-ray analysis, the result of which is shown in
Figure 1.26
Unexpectedly, this oxidation product, mostly obtained as a poorly
crystallizing oil, turned out to be the ring-opened dimeric 2,20-di(N-
ethyl-acetamino)substituted diphenyl disulfane 5, crystallizing with a
half equivalent of water as semihydrate (Scheme 1). Elemental anal-
1
ysis, IR, mass, H, and 13C NMR spectra are in agreement with this
molecular structure (see Experimental). The bond lengths, bond angles,
and torsion angles around the C S S C moiety of 5 are practically
equal to that found for the unsubstituted diphenyl disulfane.27 Only
the torsion angle for C(1)–S(1)–S(2)–C(11) in 5 differs with 90.72
somewhat from that found for the unsubstituted diphenyl disulfane
(–85.99 ),27 the increase obviously caused by the two voluminous 2,20-
substituents.

Unexpected Formation of a 2,20-Disubstituted Diphenyl Disulfine
1085
FIGURE 1 Ball-and-stick-model of the molecular structure of disulfane
5 in the crystal. – Selected bond lengths [pm]: C(1)–S(1) 178.4(3), S(1)–
S(2) 202.07(15), S(2)–C(11) 179.0(3), C(2)–N(1) 141.9(5), N(1)–C(7) 133.4(9),
C(7)–O(2) 125.9(8), C(12)–N(2) 142.9(4), N(2)–C(17) 137.3(5), C(17)–O(1)
121.5(5). – Selected bond angles [ ]: C(1)–S(1)–S(2) 105.58(13), C(11)–S(2)–
S(1) 105.59(12), C(2)–C(1)–S(1) 115.0(3), C(12)–C(11)–S(2) 115.0(2), C(2)–
N(1)–C(7) 124.5(5), C(12)–N(2)–C(17) 121.6(3), N(1)–C(7)–O(2) 113.8(10),
N(2)–C(17)–O(1) 121.1(4). – Selected torsion angles [ ]: S(2)–S(1)–C(1)–C(2)
165.1(3), S(1)–S(2)–C(11)–C(12) –167.9(2), C(1)–S(1)–S(2)–C(11) –90.72(18),
S(1)–C(1)–C(2)–N(1) 1.5(5), S(2)–C(11)–C(12)–N(2) 0.5(4), C(2)–N(1)–C(7)–
O(2) –179.7(4), C(12)–N(2)–C(17)–O(1) 176.2(4). – The two 2,20-N-ethyl-
acetamino-substituents are disordered. O(3) represents the oxygen atom of the
water of crystallization, the H-atoms of which were not localized. For further
details see Experimental and ref.26
.
The diphenyl disulfane 5 was already described by Clark in 1925:
After treatment of an aqueous solution of the corresponding iodide (2
with I as anion) with ammonia, the mixture was kept in the dark, ex-
posed to atmospheric oxygen for two months and the crystalline deposit
formed (m.p. 103 C) was collected.28 However, at that time the molec-
ular structure of 5 was proven only by elemental analysis. The corre-
sponding bis(N-methyl-acetamino) derivative of 5 was isolated in 1968
by Vorsanger during his UV/Vis spectroscopical studies of the methy-
lene base obtained by deprotonation of 2,3-dimethylbenzothiazolium
salts.29,30 A plausible reaction path for the formation of disulfane 5 by
oxidation of 2 is given in Scheme 2. The quaternary imonium salt 2 is
at higher temperatures in equilibrium with its methylene base, which

1086
C. Reichardt et al.
SCHEME 2 Possible reaction path for the formation of disulfane 5 by oxida-
tion of 2, according to Vorsanger.29
dimerizes to 7,29,30 the oxidation of which leads to the semi-thioketal 8.
Its ring-opened isomer 9 is then oxidized to give the disulfane 5.
In conclusion, a selective or stereoselective S-oxidation of benzothia-
zolium salts such as 2 to the desired isochiral sulfoxide 3 or the sulfone
4 seems to be not possible by means of the aforementioned five reagents,
even not with rather strong oxidizing reagents. Under forced reaction
conditions, however, the ring-opened disulfane 5 is unexpectedly always
formed.1,2
In order to get at least sulfone 4, we have tried to synthesize 2-
methylbenzothiazole-S,S-dioxide 14, the N-alkylation of which should
easily lead to 4 (Scheme 3). Sulfone 14 was supposedly prepared in
1915 by Zincke et al. by heating the 2-(acetamino)phenyl methyl sul-
fone 13 with phosphorus oxytrichloride at 130 C for 1 h, to give 14 as
“gla¨nzende, glashelle Pla¨ttchen” with m.p. 149–150 C.31 The only proof
SCHEME 3 Attempt at the synthesis of 2-methylbenzothiazol-S,S-dioxide 14,
according to Zincke et al.31

Unexpected Formation of a 2,20-Disubstituted Diphenyl Disulfine
1087
for its molecular structure was an analysis of the sulfur content of the
product obtained (calculated 17.70% S; found 17.80% S30).
Starting with 2-aminothiophenol 10, we have synthesized the S,S-
dioxide 13 via the thioether 11 and its N-acetyl derivative 12 (Zincke
et al. used at that time a somewhat different route31). Unfortunately,
all attempts to reproduce the ring-closure reaction of 13 to 14 under
the given reaction conditions failed.1 The sulfone 14 obviously is not
available this way. To the best of our knowledge, this compound has not
been prepared up to now.
EXPERIMENTAL
General methods, equipment, and materials are the same as given in
Reichardt et al.3
Attempts at the Synthesis of 3 by Oxidation of 2
with Peracetic Acid21b
(a) At Room Temperature: Aqueous hydrogen peroxide (c = 30 cg/g;
1.3 mL, 32 mmol) was added with stirring to a suspension of tetraflu-
oroborate 2 (2.13 g, 8.0 mmol) in glacial acetic acid at rt. Stirring was
continued until a clear solution was formed (ca. 2 h). After neutraliza-
tion with a saturated aqueous NaHCO3 solution, the reaction mixture
was extracted with dichloromethane. The extract was dried with MgSO4
and the solvent was distilled off, to afford ca. 1.8 g (85%) of the starting
compound 2.
(b) At 70 C: Aqueous hydrogen peroxide (c = 30 cg/g; 1.5 mL, 37 mmol)
was added with stirring to a suspension of tetrafluoroborate 2 (2.50 g,
9.4 mmol) in glacial acetic acid (5 mL, 85 mmol) at rt. Stirring was con-
tinued until a clear solution was formed. Then, the reaction mixture
was heated slowly to 70 C and kept at this temperature for 2 h. After
cooling to rt and neutralization with saturated aqueous NaHCO3 solu-
tion, the diluted acetic acid was distilled off (after a negative peroxide
test) and the residue was dissolved in dichloromethane. After drying
with MgSO4, the solvent was distilled off to yield crude 5 (ca. 1.3 g, ca.
71%) as a highly viscous light-brown oil.
Attempts at the Synthesis of 3 by Oxidation of 2
with 3-Chloroperbenzoic Acid21c,23
(a) At 0 C: A solution of 3-chloroperbenzoic acid (1.50 g, 8.75 mmol) in
dry dichloromethane (50 mL) was added with stirring to a solution of
tetrafluoroborate 2 (2.45 g, 8.73 mmol) in dry dichloromethane at 0 C
during 60 min. Stirring was continued for ca. 30 min without cooling

1088
C. Reichardt et al.
until rt was reached. The reaction mixture was washed with saturated
aqueous NaHCO3 solution and water (100 mL), dried with MgSO4, and
the solvent was distilled off (after a negative peroxide test). The residue,
partly oily and partly colorless crystals, was dried in vacuo, to give crude
educt 2 (ca. 2.0 g, ca. 87%), according to its 1H and 13C NMR spectrum.
(b) At Room Temperature with a Five-Fold Excess of Oxidizing
Reagent: A solution of 3-chloroperbenzoic acid (11.52 g, 67.0 mmol) in
dry trichloromethane was added with stirring to a solution of tetraflu-
oroborate 2 (3.54 g, 13.4 mmol) in dry trichloromethane (50 mL) at rt
during 2 h. Within 1 h, the reaction mixture was heated to 50 C and
kept at this temperature for 2 h with stirring, to give a clear yellow so-
lution. After cooling to rt the mixture was neutralized by washing with
saturated aqueous NaHCO3 solution (150 mL) and eventually with wa-
ter (150 mL). The organic phase was dried with MgSO4, the solvent was
distilled off (after a negative peroxide test), and the residue was dried
in vacuo to give crude 5 (1.95 g, 75%) as highly viscous brownish oil,
identical with that obtained after oxidation of 2 with peracetic acetic at
70 C, according to its 1H and 13C NMR, IR, and mass spectra.
Analytical Data of Disulfane 5
The viscous brownish oil obtained, which did not crystallize by it-
self, and the crystalline compound (colorless needles with m.p. 104 C;
ref.28 103 C), obtained from this oil as described in the general sec-
tion, gave the following results, which are in complete agreement with
1
the molecular structure of 5: H NMR (CD3COCD3): = 1.13 (t, 6H,
3 J = 7.2 Hz, CH2 CH ), 1.72 (s, 6H, CO CH ), 3.29 (d of q, 2H,
3
3
3 J = 7.1 Hz, CH CH3; additional splitting because of restricted ro-
2
tation for steric reasons), 4.08 (d of q, 2H, 3 J = 7.1 Hz, CH CH3;
2
additional splitting because of restricted rotation for steric reasons),
7.29–7.64 (m, 8H, aromatic H). – 13C NMR (CD3COCD3): = 13.4
(CH2 CH3), 22.6 (CO CH3), 43.4 (CH2 CH3), 127.5, 129.0, 130.3, and
131.2 (aromatic C), 136.0 (C S S C), 141.1 (C N), 169.6 (CO CH3). –
–1
IR (KBr): = 1663 cm (C O). – MS (FD): m/z(%) = 388 (100) [M+]. –
C20H24N2O2S2 (388.5): calcd. C 61.83, H 6.23, N 7.21; found C 61.54,
H 6.41, N 7.19.
X-Ray Molecular Structure of 5 (Figure 1)*
(a) Crystal data: C20H24N2O2S2 0.5 H2O with M = 388.54 + 9.00 =
r
397.54 g/mol; crystal habitus: colorless needle; crystal size: ca.
Further crystallographic data (excluding structure factors) have been deposited with
the Cambridge Crystallographic Data Centre (CCDC) as supplementary publication
no. CCDC–169579. Copies of the data can be obtained free of charge on application to
CCDC.26

Unexpected Formation of a 2,20-Disubstituted Diphenyl Disulfine
1089
0.4 0.2 0.1 mm; monoclinic crystal system with space group C2/c
and Z = 8, a = 2794.9(2), b = 737.5(1), and c = 2041.4(1) pm,
=
30
= 90 and = 94.470(10) ; V = 4195.0(7) 10
m3;
= 1.259
calcd.
–1
Mg/m3; F(000) = 1688; linear absorption coefficient = 2.453 mm
.
(b) Data collection: Type of diffractometer: Enraf-Nonius CAD 4;
Cu-K radiation [ = 154.178 pm at 293(2) K] with software CAD4-
EXPRESS for data collection and cell refinement and XCAD4 (Harms,
1993) for data reduction; scan method: ω- -scans, scan angle: 0.75 ;
range for data collection: 3.17 to 65.10 ; index ranges 0
8, –23 23.
h
32, 0
k
l
(c) Solution and refinement: Reflections collected 3644, symmetry-
independent reflections 3563 (R = 0.0469), observed reflections 2647
int
[I > 2 (I)], reflections used for refinement 3563, extinction coefficient
X = 0.00034(11). Program system used: SHELXS-97, SHELXL-97, and
SHELXTL. Empirical absorption correction, direct methods, difference
Fourier analysis, full-matrix refinement at F2 with all independent re-
flections, weighting scheme w = [ 2(F02) + (0.1246 P)2 + 3.0398 P]
,
1
with P = (F2 + 2F2)/3. Goodness-of-fit parameter (based on F2) S =
c
0
1.036. Hydrogen atoms were introduced in calculated positions with
fixed isotropic U ’s; non-hydrogen atoms were refined anisotropically.
R index (all data): wR2 (based on F2) = 0.2069; R index conventional
[I > 2 (I)] = 0.0630. Completeness to = 65.10 : 99.6%.
Attempts at the Synthesis of 2-Methylbenzothiazole-
S,S-dioxide 14
See Scheme 3.
(2-Aminophenyl) Methyl Sulfane (11)
In a three-necked, round-bottomed 500-mL flask, equipped with two
dropping funnels, reflux condenser, and magnetic stirrer, a solution of
NaOH (60.0 g, 1.50 mmol) in distilled water (100 mL) and methanol
(100 mL) was placed under a nitrogen atmosphere. At rt, 2-
aminothiophenol (10) (62.6 g, 0.50 mmol) was added dropwise with stir-
ring within 1 h. Through the second dropping funnel, freshly distilled
dimethyl sulfate (70.0 g, 0.56 mmol) was added at 30–40 C with stirring
and the mixture was heated at reflux for 2 h. After cooling to rt, the pre-
cipitate formed was filtered off and the red-violet filtrate was extracted
three times with diethyl ether (3 100 mL). The combined red-violet
ethereal extracts were dried with MgSO4 and the solvent was distilled
off until the boiling point reached ca. 65 C. The fractional distillation
was continued in vacuo with a glass filter pump to yield 11 (36.5 g, 52%)

1090
C. Reichardt et al.
as colorless liquid of b.p. 126 C/15 Torr (ref.32 141.5–143.0 C/36 Torr). –
1H NMR (CDCl3): = 2.34 (s, 3H, CH3), 4.26 (broad s, 2H, NH2), 6.67–
7.37 (m, aromatic H). – 13C NMR (CDCl3): = 18.1 (CH3), 115.0 (C-3),
118.9 (C-5), 120.3 (C-1), 129.0 (C-4), 133.5 (C-6), 147.3 (C-2). – IR (KBr):
= 3359 (NH2) cm–1.– MS (FD): m/z (%) = 139 (100) [M+]. – C7H9NS
(139.2): calcd. C 60.39, H 6.52, N 10.06; found C 60.24, H 6.48, N 9.95.
2-( N-Acetamino)phenyl Methyl Sulfane (12):
In a three-necked, round-bottomed 1 L-flask with stirrer, reflux con-
denser, and dropping funnel, a solution of sulfane 11 (35.4 g, 25.4 mmol)
in dry benzene (400 mL) was placed. Under cooling with an ice-bath,
acetyl chloride (24.0 g, 25.3 mmol) was added dropwise with stirring.
The mixture was then stirred at 90 C for 1 h. After cooling to rt, the
precipitate formed was filtered off, and washed in succession with water
(200 mL), aqueous HCl (c = 5 cg/g; 200 mL), aqueous NaOH (c = 5 cg/
g; 200 mL), and water (200 mL). After two-fold recrystallization from
ethanol and drying in vacuo, 12 (31.3 g, 68%) was obtained as colour-
1
less needles with m.p. 104 C (ref.33 104–106 C). – H NMR (CDCl3):
= 2.18 (s, 3H, CH3 CO), 2.33 (s, 3H, CH3 S), 7.02–8.21 (m, aromatic
H), 8.22 (broad s, 1H, NH). – 13C NMR (CDCl3): = 18.8 (CH3 S),
24.8 (CH3 CO), 120.9 (C-3), 124.4 (C-5), 125.5 (C-1), 128.6 (C-4), 132.5
(C-6), 138.2 (C-2), 168.4 (C O). – IR (KBr): = 3228 (NH) cm 1, 1656
(C O). – MS (EI): m/z (%) = 183 (2) [M+ + 2H], 182 (5) [M+ + H], 181
(55) [M+], 139 (82) [M+–CH3CO + H], 134 (42) [M+–SCH3], 124 (100)
[M+–CH3CO + H CH3], 43 (32) [CH3CO+]. – C9H11NOS (181.3): calcd.
C 59.64, H 6.12, N 7.73; found C 59.68, H 5.88, N 7.83.
2-( N-Acetamino)phenyl Methyl Sulfone (13)30
To a solution of sulfane 12 (14.5 g, 78.8 mmol) in glacial acetic acid
(65 mL), placed inside a three-necked, round-bottomed 250-mL flask
equipped with stirrer, dropping funnel, and reflux condenser, was added
with stirring aqueous hydrogen peroxide (c = 30 cg/g; 65 mL, 1.7 mol).
The mixture was slowly heated to 85 C within 1 h and kept at this tem-
perature for 2 h. The reaction mixture was given in an open Erlenmeyer
flask and concentrated by heating it at 40 C. The brownish, partly
crystalline residue was three times recrystallized from 2-propanol and
dried in vacuo, to afford sulfone 13 (9.8 g; 58%) as colorless needles
1
with m.p. 139 C (ref.31 139–140 C). – H NMR (CDCl3): = 2.18 (s,
3H, CH3 SO2), 3.00 (s, 3H, CH3 CO), 7.19–8.39 (m, 4H, aromatic H),
9.43 (broad s, 1 H, NH). – 13C NMR (CDCl3): = 25.1 (CH3 CO), 44.3
(CH3 SO2), 123.0, 124.2, 127.2, 129.3, 135.4, and 137.1 (aromatic C),
168.6 (C O). – IR (KBr): = 3320 (NH) cm 1, 1683 (C O), 1306 and
1148 (SO2). – MS (EI): m/z (%) = 214 (2) [M+ + H], 213 (20) [M+], 171

Unexpected Formation of a 2,20-Disubstituted Diphenyl Disulfine
1091
(100) [M+–CH3CO + H], 134 (30) [M+–SO2CH3], 43 (32) [CH3CO+]. –
C9H11NO3S (213.3): calcd. C 50.69, H 5.20, N 6.57; found C 50.46, H
5.10, N 6.43.
Attempts at the Synthesis of
2-Methylbenzothiazole-1,1-dioxide (14)31
Sulfone 13 (1.0 g, 4.8 mmol) and phosphorus oxytrichloride (3 mL,
32 mmol) were slowly heated to 130 C within 2 h and kept at this tem-
perature for 1 h, to give an orange-yellow solution. After cooling to RT,
the reaction mixture was poured onto ice (ca. 10 g) in order to hydrolyze
unreacted POCl3. The flocculent brownish precipitate formed (ca. 5 mg
only), which should be 14 according to Zincke et al.,31 was filtered off
and dried. Its FD mass spectrum does not show the peak of the molec-
ular ion at m/z = 181, corresponding to M = 181.2 for C8H7NO2S (14).
r
The aqueous filtrate was extracted with dichloromethane, the extract
was dried with MgSO4, and the solvent was distilled off, to give unre-
acted educt 13 (0.87 g, 85%) as brownish solid. The reaction was several
times repeated, also with longer reaction times, but always with the
same negative result.1
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