Experimental and Computational Evidence for the Formation of Iminopersulfinic Acids

Article abstract of DOI:10.1021/jo9800208

An experimental and computational study of the reactions of singlet oxygen with N-substituted sulfenamides is reported. Intermediates capable of epoxidizing norbornene were observed during the photooxidations of three sulfenamides. These results are used to argue for formation of iminopersulfinic acids. The structural integrity of two iminopersulfinic acids was supported by their successful location at the MP2/6-31G* level of theory. Furthermore, the inability to locate computationally significant persulfinimide precursors suggests that the iminopersulfinic acids form by enelike reactions involving near-simultaneous addition of singlet oxygen to sulfur and hydrogen abstraction.

Full text of DOI:10.1021/jo9800208

J . Org. Chem. 1998, 63, 3397-3402
3397
Exp er im en ta l a n d Com p u ta tion a l Evid en ce for th e F or m a tion of
Im in op er su lfin ic Acid s
Edward L. Clennan,*,† Ming-Fang Chen,† Alexander Greer,† and Frank J ensen‡
Department of Chemistry, University of Wyoming, Laramie, Wyoming 82071, and
Department of Chemistry, Odense University, DK-5230 Odense M., Denmark
Received J anuary 6, 1998
An experimental and computational study of the reactions of singlet oxygen with N-substituted
sulfenamides is reported. Intermediates capable of epoxidizing norbornene were observed during
the photooxidations of three sulfenamides. These results are used to argue for formation of
iminopersulfinic acids. The structural integrity of two iminopersulfinic acids was supported by
their successful location at the MP2/6-31G* level of theory. Furthermore, the inability to locate
computationally significant persulfinimide precursors suggests that the iminopersulfinic acids form
by enelike reactions involving near-simultaneous addition of singlet oxygen to sulfur and hydrogen
abstraction.
The formation of S-hydroperoxysulfonium ylides, 1,
was first proposed by Corey and Ouanne´s in 19761 in
order to rationalize the sulfur-carbon bond cleavage
observed during the photooxidations of a series of ben-
zylic sulfides. (Scheme 1) The transformation of 1 to the
fragmentation products was later described as a Pum-
merer rearrangement,2 and in support of that description
an R-hydroperoxy sulfide was isolated.3,4
produce a heteroatom-substituted analogue has been
reported. In this regard, iminopersulfinic acids 4 are
reasonable synthetic targets since they are isoelectronic
to S-hydroperoxysulfonium ylides 1. In addition, imi-
nopersulfinic acids could potentially form to a greater
extent in singlet oxygen reactions as a result of the lower
pKa of N-H in comparison to C-H bonds.8 We now
report the full details9 of an experimental and computa-
tional study that provides the first compelling evidence
for the formation of iminopersulfinic acids 4.
In 1991, Akasaka, Sakurai, and Ando5 reported that
epoxidation of norbornene occurred during photooxida-
tion of a thiazolidine (eq 1). Control reactions demon-
Resu lts a n d Discu ssion
Photooxidations of sulfenamides 5 and 6 were con-
ducted in oxygen-saturated benzene solutions by irradia-
tion with a 500 W tungsten-halogen lamp through 1 cm
of a 75 w/v % NaNO2 filter solution. Each reaction
mixture contained 2.3 mM of substrate, 5 × 10-5
M
strated that the R-hydroperoxy sulfide 3 was not a
competent oxygen donor under the reaction conditions
(1.5 h at 0 °C) and led to the suggestion that the
hydroperoxysulfonium ylide, 2, was acting as the epoxi-
dizing agent. Finally, in 1996, Ishiguro, Hayashi, and
Sawaki6 reported yet another facet of the chemistry of
S-hydroperoxysulfonium ylides when they suggested that
they were also capable of unimolecular rearrangements
to sulfones.
tetraphenylporphyrin (TPP), and an internal standard
appropriate for capillary GC analysis. In addition to the
anticipated formation of the sulfinamide 7 and sulfona-
mide 8, thiosulfonate 9, diphenyl disulfide 10, biphenyl
11, and several unidentified compounds were also de-
tected by capillary gas chromatography in the reaction
mixtures.
Despite the intense interest in the chemistry of S-
hydroperoxysulfonium ylides and the debate surrounding
their role in singlet oxygen reactions,7 no attempt to
† University of Wyoming.
‡ Odense University.
(1) Corey, E. J .; Ouannes, C. Tetrahedron Lett. 1976, 4263-4266.
(2) Ando, W.; Nagashima, T.; Saito, K.; Kohmoto, S. J . Chem. Soc.,
Chem. Commun. 1979, 154-156.
(3) Takata, T.; Hoshino, K.; Takeuchi, E.; Tamura, Y.; Ando, W.
Tetrahedron Lett. 1984, 25, 4767-4770.
(4) Takata, T.; Tamura, Y.; Ando, W. Tetrahedron 1985, 41, 2133-
2137.
(5) Akasaka, T.; Sakurai, A.; Ando, W. J . Am. Chem. Soc. 1991, 113,
2696-2701.
(6) Ishiguro, K.; Hayashi, M.; Sawaki, Y. J . Am. Chem. Soc. 1996,
118, 7265-7271.
(7) J ensen, F.; Greer, A.; Clennan, E. L. Submitted for publication.
(8) For example, pKa Et2NH 36 and pKa (CH3)2CH2 51. Scudder, P.
H. Electron Flow in Organic Chemistry; J ohn Wiley & Sons, Inc.: New
York, 1992.
(9) A preliminary account of the computational studies has ap-
peared: Greer, A.; Chen, M.-F.; J ensen, F.; Clennan, E. L. J . Am.
Chem. Soc. 1997, 119, 4380-4387.
S0022-3263(98)00020-6 CCC: $15.00 © 1998 American Chemical Society
Published on Web 04/30/1998

3398 J . Org. Chem., Vol. 63, No. 10, 1998
Clennan et al.
Sch em e 1
photooxidation was conducted in benzene-d6 provides
compelling evidence for this suggestion. The origin of
the small amount of biphenyl, 11, was further explored
by irradiation of 6 in benzene using our standard reaction
protocol (vide supra) followed by low-temperature re-
moval of the solvent, addition of benzene-d6, and subse-
quent analysis by GC-MS. This analysis revealed nearly
exclusive formation of biphenyl-d5 rather than biphenyl-
d0. Clearly, the small amount of biphenyl observed in
all of the reactions is formed by thermolysis of a yet
unidentified reaction component on the GC column.
Indeed, in separate experiments, we have shown that
thermal decomposition of AIBN in a benzene solution of
6 results in formation of biphenyl. Thioaminyl radicals
12 have previously been generated for ESR examinations
by a variety of methods, including hydrogen abstraction
from the parent sulfenamide with either PbO2 or tert-
butoxy radical.10 The products of their thermolysis,
however, have not been investigated. Examination of the
photooxidation of 6 by reversed-phase HPLC verified the
absence of biphenyl in the reaction mixture prior to GC
analysis and also confirmed the presence of the other four
products in addition to several unidentified components.
F igu r e 1. Product concentrations formed in the photooxida-
tions of 5 as a function of norbornene concentration.
We have previously demonstrated that N,N-disubsti-
tuted sulfenamides react with singlet oxygen quantita-
tively to give predominately the sulfinamide and a trace
of sulfonamide.11 In contrast, the N-monosubstituted
sulfenamides studied here undergo far more complex
reactions with singlet oxygen and give poor mass bal-
ances. In the photooxidation of 5, the identified products
account for only 67% of the SPh groups and 22% of the
NMe groups that were present in the starting material.
The recovery of the NR group improves to 33% in 6,
reflecting an increase in the yield of the sulfonamide,
PhS(O)2NH(n-Bu), and perhaps increased stability of the
iminopersulfinic acid intermediate (vide infra).
F igu r e 2. Product concentrations formed in the photooxida-
tions of 6 as a function of norbornene concentration.
Two main lines of evidence support the involvement
of singlet oxygen in these reactions: (1) The product
Biphenyl, 11, was always a minor component of these
reactions as shown in Figures 1 and 2. In addition, it
was not found by capillary GC in photooxidations con-
ducted in chloroform, acetone, or methanol, suggesting
that the benzene solvent was incorporated into the
biphenyl product. Exclusive formation of biphenyl-d5
when the
(10) Bassindale, A. R.; Iley, J . In The Chemistry of Sulphenic Acids
and their Derivatives; Patai, S., Ed.; J ohn Wiley & Sons Ltd.: New
York, 1990; pp 101-186.
(11) Clennan, E. L.; Zhang, H. J . Am. Chem. Soc. 1995, 117, 4218-
4227.

Formation of Iminopersulfinic Acids
J . Org. Chem., Vol. 63, No. 10, 1998 3399
Ta ble 1. P r od u ct Ra tios in th e Ch em ica l a n d
P h otoch em ica l Oxid a tion s of Su lfen a m id e 6 (R ) n -Bu )
singlet oxygen source
TPPa,b
7
8
9
10
11
45.6
29.4
28.2
10.0
10.0
12.7
32.3
49.5
45.9
7.3
6.2
8.3
4.8
4.5
4.9
a,c
C60
endoperoxided
a
Reactions 3.04 mM in PhSNH(n-Bu) and 4.67 × 10-4 M in
b
the internal standard 4-tert-butylcyclohexanone. [Tetraphe-
nylporphyrin] ) [TPP] ) 5 × 10-5 M. [C60] ) 6.4 × 10-5 M.
c
d
100-fold molar excess of 1,4-dimethylnaphthalene endoperoxide.
ratios in the reaction of 6 as determined by capillary GC
were independent of the source of singlet oxygen.
A
comparison of the product ratios when using photochemi-
12
cal (TPP or C60 sensitization) or chemical (1,4-dimeth-
ylnaphthalene endoperoxide) generation of singlet oxygen
is shown in Table 1. (2) Both 5 and 6 quench the
emission of singlet oxygen at 1270 nm.13,14
The kT values measured by examining the abilities of
sulfenamides 5, 6, and N-tert-butylphenylsulfenamide 13
(PhSNH-t-Bu) to quench singlet oxygen emission are a
composite of all chemical, kr, and physical, kq, channels
of singlet oxygen deactivation induced by these sub-
strates. The observed values of (3.4 ( 0.5) × 108 M-1
s-1 for 5, (1.88 ( 0.06) × 108 M-1 s-1 for 6, and (1.0 (
0.2) × 108 M-1 s-1 for 13 are 2 orders of magnitude larger
than the kT (3.33 × 106 M-1 s-1) reported for PhCH2SN-
(CH2)5.11 We believe that the rate acceleration for the
N-monosubstituted sulfenamides reflect a decrease in
steric interaction upon approach of singlet oxygen to
sulfur. This difference in steric interaction can best be
seen by examination of Newman projections of the ab
initio-generated geometries of CH3SNHCH3, 14, and CH3-
SN(CH3)2, 15.9 Both compounds adopt geometries that
minimize electronic interactions between the lone pair
on nitrogen and the lone pairs on sulfur.15,16 In these
conformations, destabilizing steric interactions between
the methyl group on sulfur and the methyl(s) on nitrogen
are also minimized. Consequently, only in its approach
to the N-monosubstituted sulfenamide, 14, can singlet
oxygen avoid a destabilizing steric interaction with an
NMe group. In contrast, within the N-monosubstituted
sulfenamide series, the decrease in kT by a factor of 3.4
as the substituent is changed from t-Bu- to n-Bu- to
Me- is best described as an electronic effect. This
suggestion is supported by the observation that a plot of
log(kT(X)/kT(Me)) vs the Taft polar parameter, σ*, gives
an excellent straight line, r ) 0.9964, with a slope of F*
) -1.76.17
F igu r e 3. Concentrations of norbornene oxide formed in the
photooxidations of 5, 6, and 13 as a function of norbornene
concentration.
norbornene concentration. The data for 5 and 6 are
presented in Figures 1 and 2 and compared to the results
obtained with sulfenamide 13 in Figure 3. The concen-
tration profiles in these figures demonstrate that epoxide
was observed with as little as 5 mM norbornene, and its
yield increased with increasing norbornene concentration.
At 40 mM norbornene, the yield of norbornene oxide was
between 10 and 15% based on the concentrations of the
sulfenamide substrates. Formation of norbornene oxide
did not occur if norbornene was added to the reaction
mixtures after the photolysis was complete except in the
case of N-tert-butylphenylsulfenamide, 13. The tert-butyl
group appears to sterically enhance the kinetic stability
of the oxygen-donating species, and epoxide yields were
always slightly higher using this sulfenamide.
The formation of an epoxide is reminiscent of the
behavior of hydroperoxy sulfonium ylides5 and implies
that an iminopersulfinic acid, 4, is formed in the reactions
of 5, 6, and 13 with singlet oxygen. To provide further
evidence for the formation of these new peracids, we have
conducted detailed ab initio searches for the iminoper-
sulfinic acids derived from the additions of singlet oxygen
to methylsulfenamide, 16 (CH3SNH2), and N-methyl-
methylsulfenamide, 17 (CH3SNHCH3).9 In both cases,
location of the iminopersulfinic acid was successful, and
a careful search of conformational space resulted in the
location of eight different conformers. Selected structural
features and the relative MP2/6-31G* energies of these
conformers for 16 and 17 are given in Tables 2 and 3,
respectively. Each conformer is related to three other
conformers by rotations around O-O, S-O, and S-N
bonds. These relationships are best depicted using a
conformational interconversion diagram, Scheme 2, with
the O-O, S-O, and S-N rotations depicted as diagonal,
horizontal, and vertical equilibria, respectively.
Photooxidations of sulfenamides 5, 6, and 13 in the
presence of norbornene resulted in formation of nor-
bornene oxide. The concentrations of all the products
including the epoxide were followed as a function of
(12) Arbogast, J . W.; Darmanyan, A. P.; Foote, C. S.; Rubin, Y.;
Diederich, F. N.; Alvarez, M. M.; Anz, S. J .; Whetten, R. L. J . Phys.
Chem. 1991, 95, 11-12.
(13) Clennan, E. L.; Noe, L. J .; Wen, T.; Szneler, E. J . Org. Chem.
1989, 54, 3581-3584.
(15) Craine, L.; Raban, M. Chem. Rev. 1989, 89, 689-712.
(16) Raban, M.; Kost, D. Tetrahedron 1984, 40, 3345-3381.
(17) Lowry, T. H.; Richardson, K. S. Mechanism and Theory in
Organic Chemistry; Harper & Row: New York, 1987.
(14) Clennan, E. L.; Noe, L. J .; Szneler, E.; Wen, T. J . Am. Chem.
Soc. 1990, 112, 5080-5085.

3400 J . Org. Chem., Vol. 63, No. 10, 1998
Ta ble 2. Selected Str u ctu r a l P a r a m eter s for Im in op er su lfin ic Acid Con for m er s, 16a
Clennan et al.
S-N
S-O1
HR-N
N-S-C
SO1O2
SO1O2HR
CSNH
CSO1O2
∆Eb
Ic
1.573
1.566
1.550
1.554
1.565
1.568
1.554
1.550
1.769
1.787
1.781
1.790
1.800
1.793
1.781
1.790
2.264
3.994
4.024
3.052
4.085
3.160
3.159
4.030
101.3
100.0
109.4
109.3
100.4
101.3
109.9
109.7
106.4
109.7
108.3
106.6
102.9
102.7
104.1
104.5
52.2
-120.7
-125.0
97.2
162.2
166.1
-34.2
-30.3
-166.9
-163.4
31.0
63.6
55.1
0
II
3.59
4.44
1.72
1.41
2.61
2.54
3.89
III
IV
V
VI
VII
VIII
60.0
66.4
-106.2
99.0
178.5
-175.1
170.5
174.5
91.3
-103.5
32.6
a
Distance in Å; angles in deg; the dihederal angles, WXYZ, are positive for a clockwise movement from W to Z as you look from X to
b
c
Y down bond XY. Relative MP2/6-31G* energies in kcal/mol. Conformers similar to those shown in Scheme 2 for 17 with NMe replaced
with NH.
Ta ble 3. Selected Str u ctu r a l P a r a m eter s for Im in op er su lfin ic Acid Con for m er s, 17a
S-N
S-O1
HR-N
N-S-C
SO1O2
SO1O2HR
CSNH
CSO1O2
∆Eb
Ic
1.566
1.563
1.546
1.550
1.563
1.565
1.552
1.548
1.808
1.816
1.804
1.805
1.827
1.819
1.803
1.812
2.876
4.029
4.126
3.337
4.073
3.338
3.254
4.023
100.9
100.0
111.3
111.4
100.5
100.9
111.2
111.3
108.2
109.5
109.5
108.2
102.2
102.1
104.2
104.6
79.7
-120.0
-127.1
106.9
166.3
169.6
-34.5
-31.0
-170.0
-167.2
33.0
55.6
55.0
0
II
2.46
2.68
0.94
1.41
0.72
0.72
1.58
III
IV
V
VI
VII
VIII
57.6
61.6
-105.5
106.0
-178.6
-177.1
166.7
173.7
95.0
-102.7
34.8
a
Distance in Å; angles in deg; the dihederal angles, WXYZ, are positive for a clockwise movement from W to Z as you look from X to
b
c
Y down bond XY. Relative MP2/6-31G* energies in kcal/mol. Refer to Scheme 2 for structure of conformer.
Sch em e 2
VII, are the most stable, with I representing the global
minimum. The nitrogen-peroxy hydrogen distance in
these four conformers is significantly shorter than in
their rotomeric partners, implying the existence of a
hydrogen bond. These hydrogen bonds in iminoper-
sulfinic acids, 16I and 17I, are similar to those observed
in peracids. Consequently, a lone pair on nitrogen is
optimally situated to accept the hydroperoxy proton
concomitantly with oxygen donation to an olefin via a
Bartlett “butterfly-like” mechanism.18
The epoxidation yields with the iminopersulfinic acids
derived from photooxidations of sulfenamides 5, 6, and
13, however, are considerably smaller than those ob-
served with peracids. The reduced epoxide yields reflect
the fact that the iminopersulfinic acids are formed in the
presence of sulfenamide substrates, which compete with
norbornene for the active oxygen. An induction period
for epoxide formation observed during photooxidation of
sulfenamide 6 is consistent with this suggestion (i.e.,
norbornene oxide was never observed during the photo-
oxidation of 6 until nearly 50% of the sulfenamide had
reacted).
It is tempting to suggest that the complex reaction
mixtures that are produced in these reactions are a result
of a variety of decomposition and rearrangement path-
ways open to the iminopersulfinic acid/S-hydroperoxy-
sulfonium ylides (Scheme 3). Thermal decompositions
(path a, Scheme 3) and induced decompositions (path b,
Scheme 3) are well-established routes for reactions of
peracids.19 Pummerer rearrangement of a hydroperoxy
In the conformers related by rotations about the S-O
bond, the structure with the peroxy hydrogen on the same
face of the S-O-O plane as the nitrogen, I, IV, VI, and
(18) March, J . Advanced Organic Chemistry. Reactions Mechanisms
and Structure, 4th ed.; J ohn Wiley & Sons: New York, 1992.

Formation of Iminopersulfinic Acids
J . Org. Chem., Vol. 63, No. 10, 1998 3401
Sch em e 3
Ch a r t 1
Con clu sion
Intermediates formed in the photooxidations of sulfe-
namides 5, 6, and 13 have been shown to be competent
as epoxidizing agents for norbornene. The suggestion
that these intermediates are iminopersulfinic acids was
supported by computational studies that successfully
located these structures at the MP2/6-31G* level of
theory. In addition, a “concerted ene”-type mechanism
is implicated by the inability to computationally locate a
chemically significant persulfinamide. The intriguing
possibility that steric protection could provide a kineti-
cally stabilized iminopersulfinic acid was provided by the
observation that the epoxidizing agent formed in the
photooxidation of N-tert-butylmethylsulfenamide per-
sisted even after the photooxidation was complete. The
syntheses of sulfenamides with even larger groups on
nitrogen are currently being pursued to investigate this
possibility.
Sch em e 4
group from sulfur to an adjacent atom (path c, Scheme
3) is also well established.2 Decomposition of the N-
hydroperoxysulfenamide 18 followed by condensation of
phenylsulfenic acid and disproportionation of the thio-
sulfinate would give the observed thiosulfonate and
disulfide.20 Unfortunately, our inability to isolate and
identify all the products of these complex reactions
prevented the generation of quantitative evidence in
support of the mechanism depicted in Scheme 3.
Exp er im en ta l Section
Gen er a l Asp ects. Gas chromatographic data were col-
lected on a Hewlett-Packard GC/MS instrument consisting of
a 5890 series II GC and a 5971 series mass selective detector
or on a Perkin-Elmer Autosystem. An HP-5 (30 m × 0.25 mm
× 0.25 µm (length × inside diameter × film thickness))
capillary column was used on the GC/MS and a 5% diphenyl-
95% dimethyl polysiloxane (30 m × 0.32 mm × 1.0 µm (length
× inside diameter × film thickness)) fused silica column was
used on the Perkin-Elmer Autosystem. The HPLC analyses
were done on a HP 1090 liquid chromatograph with diode
array detection. A Hewlett-Packard 100 × 2.1 mm ODS
Hypersil C18 column was used with H2O-CH3CN (35:65) as
eluant at 0.2 mL/min. AIBN (2,2′-azobisisobutyronitrile) was
obtained from Aldrich and used without further purification.
Baker spectrophotometric-grade benzene was refluxed over
phosphorus pentoxide for 5 h under a nitrogen atmosphere
and distilled prior to use. N-Methyl-, N-n-butyl-, and N-tert-
butylphenylsulfenamides (PhSNHMe, PhSNHnBu, and Ph-
SNHtBu) were synthesized, isolated, and purified as described
in the literature.21 Sulfinimides 5SO22 and 6SO23 and sul-
An important mechanistic question that we have not
yet addressed is related to the mechanism of iminoper-
sulfinic acid formation. Two mechanistic extremes can
be identified; a stepwise path via a persulfinamide
intermediate, A, and a concerted pathway (Scheme 4).
To explore the stepwise pathway, we have attempted to
locate the persulfoxides A on the ab initio potential
energy surfaces for reactions of singlet oxygen with
sulfenamides 16, 17, and CH3SNMe2, 19.
A single persulfoxide conformer was located for addi-
tion of singlet oxygen to sulfenamide 19. In contrast,
both “out” and “in” conformers (Scheme 5) were identified
for the persulfoxides formed by addition of singlet oxygen
to 16 and 17. The nitrogen lone pair is syn to the S-C
bond in the “in” conformer but anti to the S-C bond in
the “out” rotomer. All of the persulfoxides, 16AI, 16AII,
17AI, 17AII, and 19AI (Chart 1), optimized to structures
in which the O-O bond nearly bisects the N-S-C bond
angle. Selected structural parameters for these persul-
foxides are given in Table 4.
24
25
fonamides 5SO2 and 6SO2 are all known compounds, and
their spectral data including their mass spectra are consistent
with their assigned structures.26 Norbornene oxide was
synthesized as reported in the literature27 and purified by slow
sublimation at 70 °C to give needlelike crystals. Tetraphe-
nylporphyrin (TPP), 4-tert-butylcyclohexanone, and nor-
bornene were obtained from Aldrich, dodecane was obtained
from J . T. Baker, and 85% m-CPBA was obtained from
ACROS, and all were all used without further purification.
The barriers for collapse of these persulfoxides to the
iminopersulfinic acids at the MP2/6-31G* level are
extremely small. The “out” rotomer, 16AI, for example,
has little chemical significance because its barrier to
collapse to iminopersulfinic acid, 16I, is only 0.0015 kcal/
mol.
(21) Armitage, D. A.; Clark, M. J .; Kinsey, A. C. J . Chem. Soc. C
1971, 3867-3869.
(22) Schroeck, C. W.; J ohnson, C. R. J . Am. Chem. Soc. 1971, 93,
5305-5306.
(19) Sawaki, Y. In Organic Peroxides; Ando, W., Ed.; J ohn Wiley &
Sons: New York, 1992; p 425-477.
(20) Koch, P.; Ciuffarin, E.; Fava, A. J . Am. Chem. Soc. 1970, 92,
5971-5977.
(23) Maricich, T. J .; Angeletakis, C. N. J . Org. Chem. 1984, 49,
1931-1934.
(24) Challis, B. C.; Iley, J . N. J . Chem. Soc., Perkin Trans. 2 1985,
699-703.

3402 J . Org. Chem., Vol. 63, No. 10, 1998
Ta ble 4. Selected P er su lfoxid e Str u ctu r a l P a r a m eter sa
Clennan et al.
S-N
S-O1
S-O2
O1-O2
HR-O2
N-S-C
S-O1-O2
O2-O1-S-N
16AI
16AII
17AI
17AII
19AI
1.665
1.655
1.665
1.666
1.666
1.651
1.646
1.621
1.599
1.599
2.490
2.465
2.474
2.495
2.495
1.442
1.454
1.463
1.470
1.470
1.649
1.710
1.800
1.821
104.3
97.9
106.3
100.8
100.8
107.0
105.2
106.6
108.6
108.6
42.5
36.9
48.5
58.2
58.2
a
b
Distance in Å. Refer to Scheme 5 for conformer identification; CH3SNH2, 16, CH3SNHCH3, 17, CH3SN(CH3)2, 19.
Com p u ta tion a l Meth od s. Ab initio calculations were
performed using the Gaussian-94 program package28 incorpo-
rating standard notations and procedures.29 All geometry
optimizations were done at the MP2/6-31G* level of theory.
The nature of stationary points was verified by harmonic
vibrational frequency calculations. A previous theoretical
study has demonstrated that electron correlation is necessary
to adequately describe the sulfide-1O2 potential energy surface
(PES).30,31
R ) Me, n-Bu, and t-Bu), 5 × 10-5 M TPP, 1-50 mM
norbornene, and an internal standard (4-tert-butylcyclohex-
anone or dodecane) were irradiated for 20-25 min with a
500-W tungsten halogen lamp through a 1 cm 75 w/v % NaNO2
filter solution. The reaction mixtures were analyzed im-
mediately by gas chromatography, and the concentrations of
the reaction components were measured by reference to
calibration curves constructed with authentic samples of the
products.
P h otooxid a tion s. Tubes containing 1 mL of an oxygen-
saturated benzene solution of 2.3 mM sulfenamides (PhSNHR;
AIBN Rea ction . An excess of AIBN (2,2′-azobisisobuty-
ronitrile) was added to a 2 mL benzene solution, which was
2.2 mM in 6. This mixture was then refluxed for 4 h and
analyzed by GC/MS.
(25) Burchill, P.; Herod, A. A.; Marsh, K. M.; Pirt, C. A.; Pritchard,
E. Water. Res. 1983, 17, 1891-1903.
kT Mea su r em en ts. The kT values were obtained in ben-
zene using the apparatus and procedure previously de-
scribed.13,14 Sulfenamide concentrations were chosen in order
to observe decreases in lifetime of singlet oxygen over a range
of approximately 25-15 µs. The kT values were obtained from
the experimental lifetimes by plotting kobsd vs the concentration
of sulfenamide used for the particular experiment. Each kT
value was determined at least twice with a precision of (15%.
Ch em ica l Oxid a tion . 1,4-Dimethylnaphthalene 1,4-en-
doperoxide32 (ca. 40 mg) was added to a 1 mL volumetric flask
(26) N-Methylphenylsulfenamide, 5: EI/MS (m/z) 139 (M+, 100), 124
(PhSNH+, 22.9), 109 (PhS+, 94.5), 97 (34.7), 80 (22.1), 69 (29.9), 65
(45.1). N-n-Butylphenylsulfenamide, 6: EI/MS (m/z) 183 (M + 2, 28.1),
181 (M+, 55.1), 138 (PhSNHCH2+, 91.0), 109 (PhS+, 100), 94 (15.3), 77
(C6H5+, 69), 65 (21.0). N-tert-Butylphenylsulfenamide, 13: EI/MS (m/
z) 181 (M+, 44.2), 166 (M+ - CH3, 26.7), 125 (PhSNH2+, 100), 109
(PhS+, 60.9), 93 (42.7), 65 (27.8). N-Methylphenylsulfinamide, 5SO:
EI/MS (m/z) 155 (M+, 7.4), 125 (PhSO+, 46.6), 107 (100), 97 (48.6), 77
(31.4), 51 (22.2). N-n-Butylphenylsulfinamide, 6SO: EI/MS (m/z) 197
(M+, 0.5), 180 (28.5), 154 (6.6), 149 (13.9), 125 (PhSO+, 100), 106 (19.8),
97 (21.9), 77 (C6H5+, 25.1). N-Methylphenylsulfonamide, 5SO2: EI/
containing a benzene solution 2.3 mM in 6 and 2.01 × 10-4
M
MS (m/z) 171 (M+, 29.7), 141 (PhSO2+, 17.5), 107 (33.7), 77 (C6H5
,
+
100), 51 (35.9). N-n-Butylphenylsulfonamide, 6SO2: EI/MS (m/z) 213
in 4-tert-butylcyclohexanone. The resulting solution was then
allowed to sit in the dark for 20 h and then analyzed by gas
chromatography to give the results shown in Table 1.
(M+, 6.8), 171 (8.2), 170 (PhSO2NHCH2+, 88.8), 158 (11.2), 141 (PhSO2
,
+
92.7), 77 (C6H5+, 100), 51 (28.8).
(27) Budnik, R. A.; Kochi, J . K. J . Org. Chem. 1976, 41, 1384-1389.
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G. A.; Montgomery, J . A.; Raghavachari, K.; Al-Laham, M. A.;
Zakrzewski, V. G.; Ortiz, J . V.; Foresman, J . B.; Cioslowski, J .;
Stefanov, B. B.; Nanayakkara, A.; Challacombe, M.; Peng, C. Y.; Ayala,
P. Y.; Chen, W.; Wong, M. W.; Andres, J . L.; Replogle, E. S.; Gomperts,
R.; Martin, R. L.; Fox, D. J .; Binkley, J . S.; Defrees, D. J .; Baker, J .;
Stewart, J . P.; Head-Gordon, M.; Gonzalez, C.; Pople, J . A. Gaussian,
Inc., Pittsburgh, PA, 1994.
Ackn owledgm en t. This work is supported by Grants
from the Danish National Science Research Council
(F.J .). We also thank the National Science Foundation
and the donors of the Petroleum Research Fund, ad-
ministered by the American Chemical Society, for their
generous support of this research (E.L.C.).
(29) Hehre, W. J .; Radom, L.; Schleyer, P. v. R.; Pople, J . A. Ab Initio
Molecular Orbital Theory; J ohn Wiley & Sons: New York, 1986.
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