Mesolysis Mechanisms of Aromatic Thioether Radical Anions Studied by Pulse Radiolysis and DFT Calculations

Article abstract of DOI:10.1021/acs.joc.5b00660

The mesolysis mechanisms for eight aromatic thioether radical anions (ArCH₂SAr′^?-) generated during radiolysis in 2-methyltetrahydrofuran were studied by spectroscopic measurements and DFT calculation. Seven of ArCH₂SAr′

Full text of DOI:10.1021/acs.joc.5b00660

Article
pubs.acs.org/joc
Mesolysis Mechanisms of Aromatic Thioether Radical Anions Studied
by Pulse Radiolysis and DFT Calculations
Minoru Yamaji,*,† Sachiko Tojo,‡ Mamoru Fujitsuka,‡ Akira Sugimoto,‡ and Tetsuro Majima*,‡
†Division of Molecular Science, Graduate School of Science and Engineering, Gunma University, Kiryu, Gunma 376-8515, Japan
‡The Institute of Scientific and Industrial Research (SANKEN), Osaka University, Ibaraki, Osaka 567-0047, Japan
S
* Supporting Information
ABSTRACT: The mesolysis mechanisms for eight aromatic
thioether radical anions (ArCH2SAr′•−) generated during
radiolysis in 2-methyltetrahydrofuran were studied by spectro-
scopic measurements and DFT calculation. Seven of
ArCH2SAr′•− underwent mesolysis via dissociation of the σ-
bond between the benzylic carbon and sulfur atoms, forming
the corresponding radical and anion with the stepwise
mechanism or concerted mechanism. Conversely, no mesolysis
in the benzyl β-naphthyl sulfide radical anion was found. From
the Arrhenius analysis of the mesolysis with the stepwise
mechanism, apparent activation energies (ΔEexp) were
determined and compared with those (ΔEcal) estimated by
the DFT calculations. Two types of C−S bond dissociation are
possible to give the C radical and S anion (ArCH2 /Ar′S−) and
•
the C anion and S radical (ArCH2 /Ar′S•). The dissociation energies (BDE(ArCH2 /Ar′S−) and BDE(ArCH2 /Ar′S•)) were
−
•
−
estimated by the DFT calculations, and BDE(ArCH2 /Ar′S−) were found to be smaller than BDE(ArCH2 /Ar′S•). The
•
−
formation of ArCH2 /Ar′S− was observed on the mesolysis of five ArCH2SAr′•−, while one ArCH2SAr′•− provided ArCH2 /
•
−
Ar′S•. Chemical properties governing the mesolysis mechanisms of ArCH2SAr′•− are discussed.
(B−). The other is the stepwise mechanism where the AB
INTRODUCTION
■
radical anion (AB•−) is produced on the electron attachment to
AB, yielding A• and B−. Scheme 1 illustrates two mesolysis
mechanisms.
Radical ions are important intermediates for understanding the
concept of reaction mechanism in modern organic chemistry.1
They are produced via one-electron attachment or detachment
to the parent neutral molecules, such as photoinduced electron
transfer between interacting substrates having well-defined
redox potential differences.2−4 In some molecules having two
aromatic groups linked with a σ-bond, intramolecular electron
transfer causes the σ-bond dissociation (dissociative electron
transfer) as a mesolysis.5−7 In a recent review, it was shown that
mesolysis plays a major role in controlling the chemoselectivity
and efficiency of various redox processes.8 Understanding the
mesolysis mechanism is, therefore, crucial toward designing
chemical reactions involving electron transfer and bond
dissociation. Experimental methodologies for producing radical
ions are few. Radiolysis of water and organic solvents is capable
of generating strong oxidizing and reducing agents toward the
solutes, yielding solute radical ions.9−16 Pico- and nanosecond
transient absorption measurements during pulse radiolysis
provide kinetic and mechanistic information on formation and
decay of the intermediates.13,17,18
Scheme 1. Two Mesolysis Mechanisms on One-Electron
Reductive Elimination of AB
In a previous paper, we reported mesolysis of α,α′-dinaphthyl
disulfide (αNpSSNpα) in 2-methyltetrahydrofuran (MTHF)
using radiolysis techniques.19 Formation of the αNpSSNpα
radical anion (αNpSSNpα•−) was observed in a MTHF rigid
matrix at 77 K and in fluid MTHF at low temperatures,
followed by the mesolysis resulting in the formation of αNpS• +
−SNpα. The decay kinetics of αNpSSNpα•− obeyed to an
Arrhenius expression from which the activation energy and
frequency factor were determined for the mesolysis. Generation
Mesolysis promoted by reductive electron transfer to a
molecule AB with A and B groups linked by a σ-bond may be
subjected to different mesolysis mechanisms.5−7 One is the
concerted mechanism where the electron attachment on AB
occurs together with dissociation to A radical (A•) and B anion
Received: April 6, 2015
© XXXX American Chemical Society
A
DOI: 10.1021/acs.joc.5b00660
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Article
of AB•− by radiolysis of AB in MTHF is well understood
according to eqs 1 and 220
MTHF ⇝ MTHF·+ + es−
(1)
AB + es− → AB•−
(2)
where MTHF•+ and es− represent MTHF radical cation and
solvated electron, respectively. In the present work, mesolysis
of thioethers (ArCH2SAr′) having various aromatic groups (Ar,
Ar′) (Chart 1) was investigated by γ-ray radiolysis in the
Chart 1. Molecular Structures and Abbreviations of
Aromatic Thioethers (ArCH2SAr′) Used in This Work
Figure 1. (a) Absorption spectrum observed after the γ-ray radiolysis
of AntCH2SBp in MTHF at 77 K. (b) Time-resolved absorption
spectra observed during a 8 ns electron pulse radiolysis of AntCH2SBp
(3 mmol dm−3) in MTHF at 180 K. Inset: time profiles of the
absorbance at 670 nm (solid) for AntCH2SBp•− and at 420 nm (blue)
•
•
for AntCH2 . (c) Reference absorption spectrum of AntCH2 in
acetonitrile.
spectral changes in Figure 1b, it can be inferred that
AntCH2SBp•− undergoes mesolysis, giving AntCH2 (Scheme
•
2).
p-Phenylthiophenolate anion (BpS−) as the counter fragment
•
of AntCH2 was not seen in the 400−800 nm wavelength
region since its absorption peak is probably located in a shorter
wavelength region than 330 nm. These results are also evident
for the stepwise mechanism being operative on the mesolysis of
AntCH2SBp•−.
MTHF rigid matrix at 77 K and pulse radiolysis in MTHF at
various temperatures. Kinetic analysis for the mesolysis of some
ArCH2SAr′•− provides apparent energy barriers for the
mesolysis via the stepwise mechanism. The concerted
mechanism is operative for some ArCH2SAr′•−. State energies
of radical anions are estimated by the density functional theory
(DFT) calculation for drawing the dissociation potential
surfaces as a function of the C−S bond distance.
Temperature dependence of the decay rate constant,
kd(670), of AntCH2SBp•− leading to the formation of AntCH2
•
and BpS− was examined in a temperature range of 160−220 K.
Figure 2 shows the Arrhenius plot of kd(670).
The plot of kd(670) vs T−1 gave a straight line according to
the Arrhenius equation
ln kd(670) = ln A − ΔEexp(RT)−1
(3)
where A and ΔEexp denote a frequency factor and an apparent
RESULTS
activation energy for the mesolysis of AntCH2SBp•−
,
■
Mesolysis via Stepwise Mechanism. Absorption spec-
trum observed during the γ-ray radiolysis of AntCH2SBp in
MTHF rigid matrix at 77 K is shown in Figure 1.
respectively. From the slope and intercept of the line, ΔEexp
and A for mesolysis of AntCH2SBp•− were determined to be
4.6 kcal mol−1 and 6.1 × 1011 s−1, respectively. Formation of the
corresponding ArCH2SAr′•− was also seen during the pulse
radiolysis of AntCH2SNpα, AntCH2SNpβ, AntCH2SPh, and
PhCH2SNpα in MTHF, followed by yielding the corresponding
radical and anion via the mesolysis. Consequently, the stepwise
mechanism governs the mesolysis of AntCH2SAr′•− and
PhCH2SNpα•‑. Their absorption spectral data and Arrhenius
plots are deposited in the Supporting Information (Figures S1−
4), whereas ΔEexp and A for the mesolysis of ArCH2SAr′•− are
listed in Table 1. Interestingly, PhCH2SNpα•− dissociates into
The absorption spectrum observed at 77 K is attributable to
AntCH2SBp•− as a stable intermediate. The absorption
spectrum having a peak at 670 nm resembles that of the
anthracene•−,21 indicating that the electron attached on
AntCH2SBp•− is localized on the anthracene (Ant) moiety.
In MTHF at 180 K, the absorption of AntCH2SBp•− at 670 nm
is seen at 50 ns after a 8 ns electron pulse (Figure 1b). With a
lapse of time, the absorption decayed showing an isosbestic
point at 435 nm with a first-order rate constant, kd(670) of 2.4
× 106 s−1 providing an absorption peak at 420 nm with the
same rate (see the insets in Figure 1b). The absorption
spectrum at 2.5 μs was similar to that of the 9-anthrylmethyl
−
PhCH2 and NpαS•, while AntCH2SAr′•− dissociate into
•
AntCH2 and thiolate anions (Ar′S−).
Mesolysis via the Concerted Mechanism. Absorption
spectral changes observed after the γ-ray radiolysis of
•
radical (AntCH2 ) as shown in Figure 1c. From the absorption
B
DOI: 10.1021/acs.joc.5b00660
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Article
Scheme 2. Mesolysis of AntCH2SBp•− via the Stepwise Mechanism
Figure 2. Arrhenius plots of the decay rate constant, kd(670), of the
transient absorption at 670 nm for AntCH2SBp•−
.
αNpCH2SPh in MTHF at 77 K upon annealing from 77 to 295
K are represented in Figure 3a.
Figure 3. (a) Absorption spectral changes upon annealing from 77 to
295 K after the γ-radiolysis of αNpCH2SPh (3 mmol dm−3) in MTHF
rigid matrix at 77 K for 60 min. (b) Transient absorption spectra
observed after a 8 ns electron pulse during the pulse radiolysis of
αNpCH2SPh in the MTHF solution at 200 K.
The absorption peaks at 330−380 nm are due to the α-
22
naphthylmethyl radical (αNpCH2 ). αNpCH2SPh•− with
•
absorption peaks at 380 and 770 nm21 was not observed in
α
the transient absorption spectra, indicating that NpCH2SPh•−
α
has a lifetime shorter than 50 ns. As temperatures of the matrix
Scheme 3. Mesolysis of NpCH2SPh via the Concerted
α
•
increase, the absorption spectrum for NpCH2 decayed. In
Mechanism
α
•
MTHF at 200 K, the absorption peaks of NpCH2 were seen
at 50 ns after a 8 ns electron pulse during the pulse radiolysis
(Figure 3b). With a lapse of time, the absorption peaks
decayed. From these observations, it is indicated that the
concerted mechanism is operative for the decomposition of
αNpCH2SPh upon one-electron reduction (Scheme 3).
Formation of the absorption peaks due to β-methylnaphthyl
radical (βNpCH2 ) was seen during a 8 ns electron pulse
•
radiolysis of −NpCH2SPh in MTHF at low temperatures. The
absorption spectral data are deposited in the Supporting
Information (Figure S5).
The absorption peak at 425 nm at 77 K ascribable to
PhCH2SNpβ•− diminished with a blue shift giving no
appreciable absorption in the wavelength region longer than
350 nm with increasing temperature from 77 K to room
temperature. The shape of the absorption spectrum observed at
50 ns after a 8 ns electron pulse radiolysis of PhCH2SNpβ in
MTHF at 180 K (Figure 4b) resembles that of PhCH2SNpβ•−
in Figure 4a. With a lapse of time from 50 ns to 1 μs, the
No Mesolysis in PhCH2SNpβ•−. During the radiolysis of
PhCH2SNpβ in MTHF, we found no mesolysis of
PhCH2SNpβ•−. Absorption spectral changes observed after
the γ-ray radiolysis of PhCH2SNpβ in MTHF at 77 K upon
annealing from 77 to 295 K are represented in Figure 4a.
Table 1. Frequency Factors (A), Activation Energies (ΔEexp and ΔEcal), Bond Dissociation Energies (BDE), and Mesolysis
Mechanism for ArCH2SAr′•‑
a
b
c
A (s−1
1.6 × 109
)
ΔEexp (kcal mol−1
)
ΔEcal (kcal mol−1
)
BDE(ArCH2 /Ar′S−) (kcal mol−1
)
BDE(ArCH2−/Ar′S•) (kcal mol−1
)
mechanism
•
compd
d
PhCH2SNpα
PhCH2SNpβ
αNpCH2SPh
βNpCH2SPh
AntCH2SPh
AntCH2SBp
AntCH2SNpα
AntCH2SNpβ
2.2
∼0
∼0
e
−14.2
−15.5
25.1
S/W
no
37.4
48.5
47.8
33.7
22.1
20.4
34.4
d
N/A
N/A
N/A
5.6
1.4
conc
conc
S/W
S/W
S/W
S/W
d
N/A
e
1.0
d
2.4 × 1012
6.1 × 1011
3.6 × 1012
1.2 × 1012
1.7
e
−8.0
−7.9
−9.1
−8.7
d
4.6
d
4.9
e
d
4.8
2.1
a
b
Obtained from the Arrhenius analysis of ArCH2SAr′•− decay rates. The difference between the minimal and the maximal of state energies of
c
ArCH2SAr′•− estimated by the DFT calculation. S/W and conc are abbreviated for the stepwise and concerted mechanisms, respectively. “No”
indicates the absence of mesolysis. Applicable to the actual formation of the radical and the anion. Not obtained.
d
e
C
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differences between the minimal and maximal values are
calculated to be activation energies for the mesolysis (ΔEcal).
The positive ΔEcal for AntCH2SPh•− and AntCH2SNpβ•−
indicate that these ArCH2SAr′•− have definite lifetimes for
the mesolysis on the stepwise mechanism. ΔEcal for
PhCH2SNp•− was close to zero (Table 1).
Bond dissociation energies (BDE) of the benzylic C−S bond
of ArCH2SAr′•− can be estimated according to eq 4
ΔHf(RA) = ΔHf(R) + ΔHf(A) − BDE
(4)
where ΔHf(RA), ΔHf(R), and ΔHf(A) denote the formation
heat of ArCH2SAr′•− (RA), radical (R), and anion (A),
respectively. ΔHf(RA), ΔHf(R), and ΔHf(A) calculated by
DFT calculations using UB3LYP at the 6-31G(d) level are
deposited in the Supporting Information (Tables S1 and 2).
For the mesolysis of ArCH2SAr′•−, two BDE are calculated for
Figure 4. (a) Absorption spectral changes on annealing from 77 to
295 K after the γ-radiolysis of PhCH2SNpβ (3 mmol dm−3) in MTHF
rigid matrix at 77 K for 60 min. (b) Absorption spectral changes
observed after a 8 ns electron pulse during the pulse radiolysis of
PhCH2SNpβ in MTHF at 180 K.
the formation of ArCH2 /Ar′S− and ArCH2 /Ar′S• (Table 1).
•
−
ArCH2 /Ar′S− were produced in the mesolysis of
•
AntCH2SAr′•− and NpCH2SPh•−, while ArCH2 /Ar′S• was
−
produced for PhCH2SNpα•−. It is noteworthy that BDE-
•
−
(ArCH2 /Ar′S−) are smaller than BDE(ArCH2 /Ar′S•).
absorption peak of PhCH2SNpβ•− at 400 nm decreased without
a wavelength shift. On the decrease of PhCH2SNpβ•−, no
absorption peaks, such as β-naphthylthiyl radical (βNp S•),23
evolved in the wavelength longer than 350 nm. From these
observations, we concluded that no mesolysis occurs in
DISCUSSION
■
In the present work, mesolysis mechanisms of ArCH2SAr′•− via
the stepwise or concerted mechanisms are examined. All
AntCH2SAr′•− undergo mesolysis via the stepwise mechanism.
The apparent activation energies, ΔEexp, obtained from the
Arrhenius plots are as large as ca. 5.0 kcal mol−1 and larger than
those (ΔEcal) estimated by the DFT calculations (∼2.0 kcal
mol−1). For AntCH2SBP•− and AntCH2SNpα•−, definite ΔEcal
were not obtained. Moreover, the absence of ΔEcal for
NpCH2SPh•− suggests that the mesolysis is governed by the
concerted mechanism. No mesolysis was observed for
PhCH2SNpβ•−, although the potential surface of ΔERA predicts
the mesolysis via the concerted mechanism. Next, we elucidate
the relationship between the calculated BDE and the mesolytic
PhCH2SNpβ•−
.
Mesolysis Mechanism and Bond Dissociation Ener-
gies by DFT Calculation. State energies (ΔERA) of
ArCH2SAr′•− were estimated by the DFT calculations at the
UB3LYP/6-31G(d) level. The state energies (ΔERA) as a
function of the C−S bond distance, r(C−S), are represented in
Figure 5.
As r(C−S) increases, ΔERA for PhCH2SNp•− uniformly
decreases, which is characteristic for the concerted mechanism.
As for AntCH2SPh•− and AntCH2SNpβ•−, the minimum and
maximum values were clearly seen on ΔERA. The energy
features. The calculated BDE values for the ArCH2−/Ar′S−
•
formation are greater than those for the ArCH2 /Ar′S•
formation. From an energetic viewpoint, mesolysis of
ArCH2SAr′•− forms the ArCH2 /Ar′S− type intermediates.
•
We have obtained that NpCH2SPh•− subjected to the
concerted mesolysis have small positive BDE values for the
ArCH2 /Ar′S− formation in contrast to negative ones of the
•
other thioethers preferring stepwise mesolysis. This finding
would provide a criterion that the calculated BDE values for the
ArCH2 /Ar′S− formation may predict the mesolysis mecha-
•
•
nism. The calculated negative BDEs for ArCH2 /Ar′S− indicate
that the C−S bond in the corresponding ArCH2SAr′•− is
dissociative in nature. However, PhCH2SNp•− having BDE of
ca. −15 kcal mol−1 for ArCH2 /Ar′S− are exceptional. No C−S
•
bond cleavage in PhCH2SNpβ•− was observed whereas the
formation of αNpS• and PhCH2− was seen on the mesolysis of
−
PhCH2SNpα•‑. The calculated BDE(ArCH2 /Ar′S•) (25.1 kcal
mol−1) for PhCH2SNpα•‑ is substantially greater than the
BDE(ArCH2 /Ar′S−) (−14.2 kcal mol−1). From the energetic
•
viewpoint, the mesolysis of PhCH2SNpα•− is much endother-
mic compared to those of AntCH2SAr′•−.
ArCH2SAr′•− are three-electron-bonded radicals where the
C−S σ−bonding molecular orbital is occupied by two
electrons, and the C−S antibonding σ* orbital is singly
occupied. The orbital occupation between the benzylic carbon
and sulfur atoms is expressed as σ(2)σ*(1). The antibonding
σ* electron is responsible for the bond weakening and facile
Figure 5. State energies of ArCH2SAr′•− calculated at the UB3LYP/6-
31G(d) level considering the dielectric constant of THF.
D
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130.3, 129.3, 129.0, 127.9, 127.8, 127.7, 127.5, 127.1, 126.4, 125.2,
124.2, 32.3. Anal. Calcd for C27H20S: C, 86.13; H, 5.35. Found: C,
85.95; H, 5.46.
bond dissociation. The concerted mechanism for the reductive
dissociation of the C−S bond of ArCH2SAr′•− is interpreted by
considering a direct occupation of the attached electron on the
σ* orbital of NpCH2SPh. Conversely, for the stepwise
mechanism, ArCH2SAr′•− having definite lifetimes undergo
mesolysis with definite activation energies. The absorption
spectral shapes of AntCH2SAr′•− and PhCH2SNpα•− are similar
to those of radical anions of anthracene and naphthalene thiols,
respectively.21 These results indicate the attached electron is
localized on the larger aromatic group in ArCH2SAr′•−. The
captured electron intramolecularly moves from the aromatic
group to the σ* orbital during the molecular motion, which
may affect A and ΔEexp.
AntCH2SNpα. Yield: 75% (580 mg). Colorless prism. Mp: 200−202
1
°C. H NMR (400 MHz, CDCl3): δ 8.45−8.43 (m, 2H), 8.22−8.20
(m, 2H), 8.02−7.99 (m, 2H), 7.89−7.85 (m, 1H), 7.78 (d, 1H, J = 8.2
Hz), 7.69 (d, 1H, J = 7.1 Hz), 7.55−7.44 (m, 6H), 7.39 (t, 1H, J = 7.6
Hz), 5.13 (s, 2H). 13C NMR (100 MHz, CDCl3): δ 134.4, 133.9,
133.1, 131.5, 130.2, 129.2, 128.6, 127.9, 127.8, 127.7, 126.5, 126.3,
126.2, 125.7, 125.2, 125.1, 124.1, 32.4. Anal. Calcd for C25H18S: C,
85.68; H, 5.18. Found: C, 85.46; H, 5.40.
AntCH2SNpβ. Yield: 78% (600 mg). Colorless prism. Mp: 173−175
°C. 1H NMR (400 MHz, CDCl3): δ 8.44 (s, 1H), 8.30 (t, 2H, J = 9.2
Hz), 8.02 (d, 2H, J = 9.2 Hz), 7.93 (s, 1H), 7.84−7.78 (m, 3H), 7.54−
7.44 (m, 7H), 5.23 (s, 2H). 13C NMR (100 MHz, CDCl3): δ 135.4,
134.0, 131.7, 130.3, 129.3, 128.6, 128.0, 127.9, 127.7, 127.31, 127.26,
126.8, 126.5, 125.9, 125.2, 124.2, 32.1. Anal. Calcd for C25H18S: C,
85.68; H, 5.18. Found: C, 85.49; H, 5.25.
CONCLUSIONS
■
The mesolysis mechanisms of ArCH2SAr′•− generated in
MTHF have been investigated on the basis of the absorption
measurements and DFT calculations. Mesolysis of
NpCH2SPh•− (C−S bond dissociation) occurs via the
concerted mechanism, while no mesolysis of PhCH2SNpβ•− is
found. Mesolyses of AntCH2SAr′•− and PhCH2SNpα•− occur
2-Methyltetrahydrofuran (MTHF, Tokyo Kasei) was distilled over
CaH2 before use. MTHF solutions of the compounds were degassed
by several freeze−pump−thaw cycles on a high vacuum line (5 × 10−4
Torr) and sealed in a 1 cm path length quartz cell. The concentration
of the thioethers was 3 × 10−3 mol dm−3 throughout this work.
Instruments. γ-Ray radiolysis was carried out for 30 min with a
60Co source at Osaka University. The dose rate was 4 kGy h−1. Visible
absorption spectra after the γ-radiolysis of ArCH2SAr′ in MTHF rigid
matrix were recorded on a spectrophotometer (Shimadzu Multispec-
1500). Transient absorption spectra were measured during the pulse
radiolysis of ArCH2SAr′ in MTHF using a linear accelerator at Osaka
University (28 MeV, 8 ns, 0.87 kGy pulse−1). The details of the
detection system for transient absorption have been described
elsewhere.27 Transient absorption spectra were taken by using a
photodiode array (Hamamatsu Photonics, S3904-1024F) with a gated
image intensifier (Hamamatsu Photonics, C2925-01) as a detector.
The temperature effects were examined using a cryostat (Oxford
DN704) with a digital temperature controller (DTC-2) with precision
of 1.0 °C. 1H and 13C spectra were recorded on an NMR System 400
MHz spectrometer.
via the stepwise mechanism, yielding AntCH2 /Ar′S− and
•
PhCH2 /αNpS•, respectively. On the basis of the Arrhenius
−
analysis for the decay kinetics of ArCH2SAr′•−, ΔEexp and A
were determined to be compared with ΔEcal estimated by the
DFT calculation. BDE(ArCH2 /Ar′S−) and BDE(ArCH2 /
Ar′S•) were evaluated by the DFT calculations. The former
values provide a criterion for the mesolysis mechanism and the
positive and negative values for the concerted and stepwise
mechanisms, respectively. As for the BDE, PhCH2SNp•− are
exceptional. The mesolysis of PhCH2SNpα•− provides
•
−
−
−
ArCH2 /Ar′S• where BDE(ArCH2 /Ar′S•) is substantially
larger than BDE(ArCH2 /Ar′S−). Consequently, the mesolysis
•
mechanism of ArCH2SAr′•− strongly depends on the varieties
of the aromatic groups (Ar and Ar′).
The calculation was carried out at the DFT level using the Gaussian
09 software package. The geometries of the thioethers were fully
optimized by using the 6-31G(d) base set at the UB3LYP method
considering a dielectric constant of tetrahydrofuran in the CPCM
model.
EXPERIMENTAL SECTION
■
General Synthesis Procedures for PhCH2SNpα, PhCH2SNpβ,
αNpCH2SPh, and βNpCH2SPh. Aryl thiol (10 mmol) was added to a
solution of the corresponding arylmethyl halide (5 mmol) and K2CO3
(50 mmol) in 50 mL of acetone. After the reaction mixture was
refluxed for 12 h, it was cooled to room temperature and filtrated.
After the solvent was evaporated by reduced pressure, the crude
product was purified by flash column chromatography using a hexane/
chloroform eluent. The NMR data of PhCH2SNpα, PhCH2SNpβ,
ASSOCIATED CONTENT
* Supporting Information
The Supporting Information is available free of charge on the
ACS Publications website at DOI: 10.1021/acs.joc.5b00660.
■
S
Mesolysis profiles of radical anions of AntCH2SPh,
AntCH2SNpα, AntCH2SNpβ, PhCH2SNpα and
βNpCH2SPh; results of DFT calculation including tables
of atom coordinates for the optimized geometries; and
1H and 13C NMR spectra of AntCH2SPh, AntCH2SBp,
AntCH2SNpα, and AntCH2SNpβ (PDF)
β
αNpCH2SPh, and NpCH2SPh were consistent with those reported
previously.24−26
General Synthesis Procedures for Anthrylmethyl Sulfides.
An acetone (30 mL) solution of 9-(chloromethyl)anthracene (500 mg,
2.2 mmol) and aryl thiol (3.5 mmol) in the presence of K2CO3 (1.2 g,
8.7 mmol) was refluxed for 12 h. After being cooled to room
temperature, the solution was filtrated, and the solvent was evaporated
under reduced pressure. The product was purified by GPC using
chloroform eluent and recrystallized from ethanol. Melting points were
measured by a Yanaco micro melting point apparatus and uncorrected.
AntCH2SPh. Yield: 80% (530 mg). Colorless leaflet. Mp: 152.5−153
°C. 1H NMR (400 MHz, CDCl3): δ 8.43 (s, 1H), 8.27 (d, 2H, J = 8.7
Hz), 8.02 (d, 2H, J = 9.2 Hz), 7.54−7.45 (m, 6H), 7.35−7.23 (m, 3H),
5.13 (s, 2H). 13C NMR (100 MHz, CDCl3): δ 131.6, 130.3, 130.0,
129.3, 129.1, 127.9, 127.7, 126.6, 126.4, 125.2, 124.2, 32.2. Anal. Calcd
for C21H16S: C, 83.96; H, 5.37. Found: C, 83.94; H, 5.45.
AUTHOR INFORMATION
Corresponding Authors
*E-mail (M.Y.): yamaji@gunma-u.ac.jp.
*E-Mail (T.M.): majima@sanken.osaka-u.ac.jp.
■
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
AntCH2SBp. Yield: 79% (650 mg). White powder. Mp: 192.5−194
°C. 1H NMR (400 MHz, CDCl3) δ 8.44 (s, 1H), 8.29 (d, 2H, J = 8.7
Hz), 8.03 (d, 2H, J = 8.2 Hz), 7.61−7.45 (m, 12H), 7.37−7.39 (m,
1H), 5.17 (s, 2H). 13C NMR (100 MHz, CDCl3) δ 131.7, 130.4,
We thank Dr. Takumi Kimura for performing the experiments
and the staff for running the pulse radiolysis facilities in the
Radiation Laboratory, The Institute of Scientific and Industrial
E
DOI: 10.1021/acs.joc.5b00660
J. Org. Chem. XXXX, XXX, XXX−XXX

The Journal of Organic Chemistry
Article
Research, Osaka University. This work has been partly
supported by a Grant-in-Aid for Scientific Research
(25220806, 25288035, 25390125, 26288032, and others)
from the Ministry of Education, Culture, Sports, Science and
Technology (MEXT) of Japanese Government.
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