Mechanism of the Solution-Phase Reaction of Alkyl Sulfides Atomic Hydrogen. Reduction via a 9-S-3 Radical Intermediate

Article abstract of DOI:10.1021/jo9615615

The low selectivity of benzyl alkyl sulfide fragmentation subsequent to its reaction with atomic hydrogen is indicative of a reaction that proceeds via an early transition state. The competitive reduction of a series of substituted-benzyl alkyl sulfides was insensitive to the substituent on the aromatic ring (ρ = -0.13, r = 0.99). The relative rates of fragmentation of a series of the substituted-benzyl alkyl sulfides gave a V-shaped Hammett plot. Both electron-donating and electron-withdrawing groups destabilized the transition state (ρ = +0.99, r = 0.999; ρ = -0.82, r = 0.992). Since the relative rates of disappearance of the alkyl benzyl sulfides are not substituent dependent, but the relative rates of fragmentation are, a 9-S-3 intermediate is preferred as the structure leading to products.

Full text of DOI:10.1021/jo9615615

4210
J . Org. Chem. 1997, 62, 4210
Articles
Mech a n ism of th e Solu tion -P h a se Rea ction of Alk yl Su lfid es w ith
Atom ic Hyd r ogen . Red u ction via a 9-S-3 Ra d ica l In ter m ed ia te
Dennis D. Tanner,* Sudha Koppula,1 and Pramod Kandanarachchi2
Department of Chemistry, University of Alberta, Edmonton, Alberta T6G 2G2, Canada
Received August 12, 1996X
The low selectivity of benzyl alkyl sulfide fragmentation subsequent to its reaction with atomic
hydrogen is indicative of a reaction that proceeds via an early transition state. The competitive
reduction of a series of substituted-benzyl alkyl sulfides was insensitive to the substituent on the
aromatic ring (F ) -0.13, r ) 0.99). The relative rates of fragmentation of a series of the substituted-
benzyl alkyl sulfides gave a V-shaped Hammett plot. Both electron-donating and electron-
withdrawing groups destabilized the transition state (F ) +0.99, r ) 0.999; F ) -0.82, r ) 0.992).
Since the relative rates of disappearance of the alkyl benzyl sulfides are not substituent dependent,
but the relative rates of fragmentation are, a 9-S-3 intermediate is preferred as the structure leading
to products.
In tr od u ction
Fragmentation of a series of aryldialkylsulfuranyl
radicals generated by the reduction of their sulfonium
salts likewise showed low selectivity for competitive
ligand loss.10
Results obtained from the cyclic voltammetric study
of the one-electron transfer reductions of a series of
arylmethylalkylsulfonium salts suggested that the frag-
mentation of the reduced salts was evidence for simul-
taneous or nearly simultaneous electron transfer frag-
mentation.11a
Homolytic displacement reactions at sulfur have been
of mechanistic interest since displacement at sulfur may
proceed to products, as does phosphorus3 or iodine,4
through a hypervalent intermediate. Previous studies
of homolytic displacements of alkyl groups from sulfides
by carbon-centered radicals5-7 addressed the question of
the intermediacy of a 9-S-3 hypervalent radical.8 Dis-
placement of a series of alkyl groups by an aryl radical
exhibited very low selectivities as a function of leaving
group stability.5
The absolute rates of SHi displacement at sulfur have
been reported, and an analysis of their Arrhenius pa-
rameters suggested that displacement proceeds via a
trivalent transition state and not a 9-S-3 intermediate.
The authors stipulated, however, that a preequilibrium
involving a sulfuranyl radical and the starting radical
structure could not be ruled out.7
Although the results of Kampmeier,5,6 Beak,10 Saeva,11b
and Franz7 suggest that homolytic displacement at
sulfide sulfur is not likely to proceed through a sulfuranyl
radical of significant stability, the relative rate data that
have been measured for displacements by atomic hydro-
gen at the sulfur center of alkyl disulfides and unsym-
metric alkyl sulfides are compatible with reactions of a
trivalent intermediate.12 The displacements on the di-
sulfides and the sulfides show structure-reactivity re-
lationships where displacement on the sulfur of the
disulfide occurs at the sterically least hindered sulfur and
displacement at sulfur of the sulfide yields a thiol and
the most stable radical. Since the displacement by
atomic hydrogen at sulfur showed a structure-reactivity
relationship, the reduction provided a possible probe for
the involvement of a longer lived trivalent sulfuranyl
radical.
A number of sulfuranyl radicals have been generated;8,9
however, their stability appears to depend upon their
substituents having one or more electronegative ligands.
X Abstract published in Advance ACS Abstracts, May 15, 1997.
(1) NSERC, Undergraduate Research Fellowship.
(2) Postdoctoral Fellow, University of Alberta, 1994-1996.
(3) (a) Bentrude, W. G. In Free Radicals; Kochi, J . K., Ed.; Wiley
Interscience: New York, 1973; Vol. 2, Chapter 22. (b) Bentrude, W.
G. In Organic Free Radicals; Pryor, W. A., Ed.; ACS Symposium Series
69; American Chemical Society: Washington, DC, 1978.
(4) (a) Bunnett, J . F.; Wamser, C. C. J . Am. Chem. Soc. 1966, 88,
5534. (b) Brydon, D. L.; Cadogan, J . I. Chem. Commun. 1966, 744; J .
Chem. Soc. C 1968, 819. (c) Danen, W. C.; Saunders, D. G. J . Am.
Chem. Soc. 1969, 91, 5924. (d) Davis W. H., J r.; Gleaton, J . H.; Pryor,
W. A. J . Org. Chem. 1979, 42, 7. (e) Tanner, D. D.; Reed, D. W.;
Setiloane, B. P. J . Am. Chem. Soc. 1982, 104, 3917.
Resu lts a n d Discu ssion
The solution-phase reactions of atomic hydrogen with
a series of unsymmetric alkyl sulfides result in the
cleavage of an alkyl-sulfur bond with the formation of
a thiol and an alkyl radical (eq 1).
(5) Kampmeier, J . A.; Evans, T. R. J . Am. Chem. Soc. 1966, 88,
4096-4097.
(6) Kampmeier, J . A.; J ordan, R. B.; Liu, M. S.; Yamanaka, H.;
Bishop, D. J . In Organic Free Radicals; Pryor, W. A., Ed.; ACS
Symposium Series 69; American Chemical Society: Washington, DC,
1978; pp 275-289 and references therein.
(7) Franz, J . A.; Roberts, D. H.; Ferris, K. F. J . Org. Chem. 1987,
52, 2256.
(8) Perkins, C. W.; Martin, J . C.; Arduengo, A. J .; Lau, W.; Alegria,
A.; Kochi, J .K. J . Am. Chem. Soc. 1980, 102, 7753.
(9) (a) Perkins, C. W.; Clarkson, R. B.; Martin, J . C. J . Am. Chem.
Soc. 1986, 108, 3206-3210. (b) Perkins, C. W.; Martin, J . C. J . Am.
Chem. Soc. 1986, 3211-3214.
The relative rates of cleavage, k1/k2, favor the most
stable radical.12
S0022-3263(96)01561-7 CCC: $14.00 © 1997 American Chemical Society

Reaction of Alkyl Sulfides with Atomic Hydrogen
J . Org. Chem., Vol. 62, No. 13, 1997 4211
Ta ble 1. Rela tive Ra tes of th e Rea ction s of Alk yl
Su lfid es w ith Atom ic Hyd r ogen a t -78 °C in Aceton ea
b
1
c
alkyl sulfide R1SR2 (k/ko)disappearance
(k1/ko )
fragmentation
1. R1 ) R2 ) n-Hexyl
1
1
d
2. R1 ) n-C8H17
3.48 ((0.4)
3.70 ((0.5)
30.10 ((0.7)
1
R2 ) sec-C4H7
d
3. R1 ) n-C6H13
1.97 ((0.1)
R2 ) t-C4H9
4. R1 ) R2 ) n-propyl
5. R1 ) R2 ) i-C3H7
6. R1 ) R2 ) t-C4H9
7. R1 ) n-C8H17
R2 ) C6H5CH2
1
1.10((0.1)
e
1.68 ((0.03)f
4.56 ((0.25)g
a
The reactions were carried out with a hydrogen flow rate of 4
mL/min (4 Torr) using He as a makeup gas using a nonreactive
b
internal standard, 1 chloroheptane. n-Hexyl sulfide was used as
a reference substrate (ko) for entries 2, 3, and 7 and n-propyl sulfide
was used for entries 5 and 6 (1:1 mixture of alkyl sulfides, 0.01-
0.05 M). c The fragmentation ratio for unsymmetric sulfides were
F igu r e 1. Evans-Polanyi plot of the ratio of rates of
fragmentation of R•, kx°/the primary alkyl radical, k1°, versus
the difference in D(R-H).
1
obtained by product analysis. ko Represents the cleavage of the
d
primary alkyl-sulfur bond. An experiment performed with a 1:1
mixture of n-octyl sec-butyl sulfide and n-hexyl tert-butyl sulfide
(0.05 M) gave a relative rate of disappearance of (ksec/ktert) 1.60.
The calculated relative rate using entries 2 and 3 was 1.76. e This
compound did not show any appreciable reaction with hydrogen
atoms when reacted in a 1:1 mixture of n-propyl sulfide in which
n-propyl sulfide showed a 30.0% conversion. f The mole fraction
The stabilities of the radical products produced in these
competitive fragmentations were put on a quantitative
scale by applying the Evans-Polanyi relationship13 to
their relative rates of fragmentation. The plot showed a
slope of 0.25; see Figure 1.
A reaction series that has an Evans-Polanyi plot with
a slope of 0.25 can be interpreted as representing a
reaction with a transition state in which the carbon-
sulfur bond is 25% broken. The value of the slope is
consistent with an early transition state resulting either
from direct displacement (i) or from the fragmentation
of a trivalent, 9-S-3, intermediate (ii).
g
of n-hexyl sulfide was varied from 0.25-0.75. A value of 2.72
((0.1) was obtained at -42 °C ∆Ea (Ea(1°) - Ea(benzyl)) ) 1.27
kcal/mol.
relationship that was a combination of steric interactions
and leaving group stability; see Table 1.
In order to remove the importance of these steric
interactions, the reaction kinetics of a series of benzyl
and meta- and para-substituted benzyl alkyl sulfides
were investigated; see Table 2.
As expected, the relative rates of disappearance of the
substituted benzyl alkyl sulfides were relatively insensi-
tive to the aromatic substituents, electron withdrawing
or electron donating. A linear free energy treatment of
the data showed a Hammett Fσ correlation of F ) -0.13
(σ+, r ) 0.99); see Figure 2.
Since the competitive rates of disappearance of the
substituted-benzyl alkyl sulfides did not appear to be
appreciably effected by substituents and the relative
rates of fragmentation of the dialkyl sulfides did show a
structure-reactivity relationship, the relative rates of
fragmentation (see eq 2) of the series of m- and p-
substituted benzyl alkyl sulfides were examined; see
Table 3.
Previous studies of displacement reactions on sulfur
or of the fragmentation of electrochemically generated
9-S-3 intermediates concluded that if a 9-S-3 intermedi-
ate was involved it would be extremely short lived.5-7,10-11
The low selectivity for displacement or fragmentation
was proposed to be the result of an early transition
state.5-7,10-12
The structure-reactivity relationship for displacement
can be probed by competitive kinetics since a mechanism
that proceeds by a biomolecular direct displacement
reaction predicts that a sulfide with two primary alkyl
groups would react more rapidly than a sulfide that
contained more highly substituted alkyl groups. Pre-
sumably, steric effects would inhibit the direct displace-
ment. Competitive rates of disappearance of diprimary
sulfides vs more highly substituted sulfides did not
confirm this prediction. The order of reactivity (1°,2° >
1°,3° > 2°,2° > 1°,1° >> 3°,3°) showed a reactivity
Although the benzyl group of the benzyl alkyl sulfide
fragmented much more slowly than expected, Table 1
(Figure 1), the relative rate of disappearance, k/ko, was
only marginally slower than the 3°/1° sulfide. Since it
had been suggested that a low selectivity for displace-
ment might be due to a pre-equilibrium between the
substrate and a 9-S-3 intermediate7 (Scheme 1, eqs 3-5),
the competitive reduction was investigated at several
concentrations of the di-primary-alkyl sulfide.
(10) Beak, P.; Sullivan, T. A. J . Am. Chem. Soc. 1982, 104, 4450-
4457.
(11) (a) Saeva, F. D.; Morgan, P. J . Am. Chem. Soc. 1984, 106, 4121-
4125. (b) Adcock, W.; Andrieux, C. P.; Clark, C. I.; Neudeck, A.;
Save´ant, J . M.; Tardy, C. J . Am. Chem. Soc. 1995, 117, 82851.
(12) Tanner, D. D.; Zhang, L.; Vigneswaran, M.; Kandanarachchi,
P. J . Org. Chem. 1995, 60, 4481.
When the mole fraction of R1SR1 was varied from 0.25
to 0.75, the relative rates of disappearance were un-
changed 1.68 ((0.03).
(13) Evans, M. G.; Polanyi, M. Trans. Faraday Soc. 1938, 34, 11.

4212 J . Org. Chem., Vol. 62, No. 13, 1997
Tanner et al.
Sch em e 1
demand for resonance stabilization it is not surprising
that the substituents do not have the expected effect, but
in fact promote a polarity that destabilizes the transition
state. The transition-state structure is summarized by
the three contributing cannonical forms (i-iii), eq 7. The
carbon-sulfur bond, usually polarized toward the more
electronegative sulfur, has an electropositive hydrogen
atom attached. The nonpolarized structure, ii, is now the
most important contributing form. Any added polarity,
due to aromatic substitution, appears to destabilize the
transition state. The decreased selectivity for benzyl vs
octyl radical fragmentation and its low activation energy
(∆∆Ea ) 1.27 kcal/mol) is entirely consistent with the
observed relative fragmentation rates of kbenzyl/kCH (15/
3
1, ∆∆Ea ) 1.6 kcal/mol) reported by Beak10 for the
reduction of the phenylbenzylmethylsulfonium salt (eq
8).
F igu r e 2. Hammett plot of the log of the relative rates of
reaction of a series of alkyl benzyl sulfides vs σ+: b, relative
rates of disappearance (kG/kH); O, relative rates of fragmenta-
tion (kG′/k1°)/(kH/k1°).
Assuming that k1 is not appreciably effected by the
substituent, the relative rates of fragmentation (eq 6) can
be presented on the same Hammett plot used for the
competitive intermolecular reactions; see Figure 2.
Con clu sion
Subsequent to their reaction with atomic hydrogen, the
relative rates of fragmentation of unsymmetric sulfides
show a structure-reactivity relationship that is consis-
tent with an SRN2 or a 9-S-3 fragmentation. The mecha-
nistic results suggest that the displacement proceeds by
an early transition state that is sensitive to steric
deactivation. In order to remove the importance of these
steric interactions, a series of substituted-benzyl alkyl
sulfides was treated with the hydrogen atom plasma.
Competitive rates of reaction of the substituted- and
unsubstituted-benzyl alkyl sulfides were relatively in-
sensitive to substituents, F ) -0.13, while the relative
rates of fragmentation of the series of substituted-benzyl
alkyl sulfides were strongly influenced by the substitu-
ents. Since the relative rates of disappearance of the
alkyl benzyl sulfides are not substituent dependent, but
the relative rates of fragmentation are, a 9-S-3 interme-
diate is preferred as the structure leading to products.
It is apparent that all of the substituents, electron
withdrawing or electron donating, decrease the rate of
fragmentation of the benzyl groups compared to the
reference octyl groups. The substituent effects can be
rationalized if one considers the transition state for the
fragmentation of an 9-S-3 intermediate, eq 7.
Exp er im en ta l Section
Gen er a l P r oced u r e for th e Atom ic Hyd r ogen Rea c-
tion .12 An aliquot solution was placed in the U-shaped reactor.
The reactor was cooled to the desired temperature, and a
stream of hydrogen or deuterium was passed into the system
at a flow rate of 4 mL/min. The reaction system pressure was
controlled at 3-4 Torr by a make-up gas (helium). The
microwave generator was activated and the reaction allowed
to proceed for the desired time. After the reaction, the product
mixture was analyzed by GC. For each reaction, the products
were identified by comparison of their GC retention times, GC/
When the value kbenzyl/k1 (4.56) was added to the
Evans-Polanyi plot, it was apparent that the benzyl
radical was formed much more slowly then expected; see
Figure 1. Its rate of formation reflects a diminished
dependence on the resonance stabilization of the benzyl
radical, as expected for a transition state where the
radical is only partially (∼25%) formed. With so little

Reaction of Alkyl Sulfides with Atomic Hydrogen
J . Org. Chem., Vol. 62, No. 13, 1997 4213
Ta ble 2. P r od u ct Distr ibu tion in Aceton e of th e Rea ction of Atom ic Hyd r ogen w ith Or ga n ic Su lfid es of th e Typ ea ,b
a
b
R ) C6H13, R′ ) C8H17
.
The hydrogen flow rate was kept at 6 mL/min for all reactions. The reaction volume was 10 mL for reactions
at -78 °C and 5 mL for reaction at -42 °C. Substituted benzyl thiols were detected as products, but these appeared to react under the
reaction conditions. 1-Chloroheptane was used as an internal standard.
°C/15 mmHg; 1H NMR (200 MHz, DCCl3) δ 0.70-1.75 (m,
Ta ble 3. Rela tive Ra tes of Disa p p ea r a n ce a n d
F r a gm en ta tion of Alk yl Ar om a tic Su bstitu ted -Ben zyl
Su lfid es w ith Atom ic Hyd r ogen in Aceton e a t -78 °C
23H), 2.45 (t, 2H, J ) 7.5 Hz), 2.65 (t, 1H, J ) 7.5 Hz); IR
(vapor phase) ν 2934, 2869, 1460, 1381, 1296, 1225, 1140, 1005
cm-1; EI+ m/ z 201.9 (M+), 172.9, 144.9, 69.0, 57.0, 40.9. Anal.
Calcd for C12H26S: C, 71.22; H, 12.94. Found: C, 71.48 H,
12.87.
a
b
1
substituent G
(kG/kH)disappearance
(kG /kH)fragmentation
p-OCH3
p-CH3
p-C(CH3)3
p-F
m-CH3
H
0.168 ((0.02)
0.485 ((0.04)
0.572 ((0.03)
0.825 ((0.10)
0.895 ((0.04)
1
1.107 ((0.001)
1.101 ((0.001)
Syn th esis of n -Octyl Su bstitu ted-Ben zyl Su lfides. These
sulfides were prepared using a procedure similar to the one
used for dialkyl sulfides.14 n-Octanethiol (7.3 g, 0.05 mol) was
heated to reflux with the substituted-benzyl bromides or
chlorides (0.05 mol) in the presence of sodium hydroxide (2 g,
0.05 mol) in ethanol (50 mL) for 1 h. The cooled reaction
mixture was poured into ice-water (200 mL) and extracted
with diethyl ether. The sulfides were obtained as light yellow
oils after the column chromatography on silica gel. (Solvents
3:1 mixture of hexane:dichloromethane, yields 50-85%.) A
white solid was obtained in the case of p-cyano analog, and it
was recrystallized from ethanol.
n -Octylben zyl su lfid e: 1H NMR (200 MHz, CDCl3) δ 0.90
(t, 3H, J ) 7 Hz), 1.15-1.70 (m, 12H), 2.45 (t, 2H, J ) 8.3 Hz)
3.75 (s, 2H), 7.10-7.45 (m, 5H); IR (vapor phase) ν 3071, 2933,
2865, 1601, 1455, 1236, 1029, 701 cm-1; E+ m/ z 236.0 (M+),
145.1, 124.0, 91.1, 69.0, 55.1; bp 153-155 °C/4 mmHg. Anal.
Calcd for C15H24S: C, 76.21; H, 10.22; S, 13.56. Found: C,
75.98; H, 10.31; S, 13.35.
n -Octyl p-cya n oben zyl su lfid e: 1H NMR (200 MHz,
CDCl3) δ 0.90 (t, 3H, J ) 7 Hz), 1.10-1.80 (m, 12H), 2.40 (t,
2H, J ) 8.3 Hz), 3.75 (s, 2H), 7.35-7.65 (dd, 4H, J ) 40 Hz);
IR (vapor phase) ν 2934, 2866, 2234, 1608, 1508, 1235, 1022,
831 cm-1; E+ m/ z 261.1 (M+), 150.0, 145.2, 116.1, 89.1, 69.1,
55.1; mp 34-35 °C. Anal. Calcd for C16H23SN: C, 73.51; H,
8.86; S, 12.27; N, 5.38. Found: C, 73.12; H, 9.13; S, 12.29; N,
5.12.
1.050 ((0.01)
1
p-Cl
m-Cl
p-CN
0.971 ((0.04)
0.879 ((0.03)
0.822 ((0.01)
0.739 ((0.04)
0.557 ((0.04)
0.268 ((0.04)
a
The reactions were carried out in a 1:1 mixture of (0.01-0.05
M) substituted- and unsubstituted-benzyl alkyl sulfides in the
b
presence of chloroheptane as an internal standard. The relative
rates of fragmentation between primary alkyl and aromatic
substituted-benzyl fragments were determined by their product
distribution and were normalized by the relative rate of fragmen-
tation of the unsubstituted analog; see Table 2.
MS, and GC/IR with those of authentic samples. 2H NMR
spectra were also obtained for products of the reactions with
deuterium.
Ma ter ia ls. Commercially available tert-butyl sulfide (98%),
1-octanethiol (97+%) n-hexyl sulfide, and n-octane (99%)
(Aldrich Chemical Co.) and n-propyl sulfide (99.99%) and
isopropyl sulfide (99.99%) (American Petroleum Institute
Standards) were checked for purity by GC and used as
received. ter t-Bu tyl n -h exyl su lfid e was identical to the
material previously reported.12 The substituted toluenes were
identified by a comparison of their GC/IR, GC/MS, and GC
retention times with those of the authentic samples (Aldrich
Chemical Co.).
n -Octyl p-ch lor oben zyl su lfid e: 1H NMR (400 MHz,
CDCl3) δ 0.89 (t, 3H, J ) 7 Hz), 1.15-1.40 (m, 12H), 2.40 (t,
2H, J ) 8.0 Hz), 3.65 (s, 2H), 7.10-7.30 (m, 4H); IR (vapor
sec-Bu tyl n -octyl su lfid e was prepared using the standard
procedure14 using 1-bromooctane (0.15 mol) and sec-butane-
thiol (0.15 mol) in 87% yield (0.13 mol, 26.2 g): bp 120-124
phase) ν 2933, 2866, 1596, 1491, 1237, 1096, 1017, 821 cm-1
;
E+ m/ z 269.9 (M+), 145.0, 124.9, 89.0, 69.0, 55.0; bp 340 °C
dec. Anal. Calcd for C15H23SCl; C, 66.52; H, 8.55; S, 11.83.
Found: C, 66.73; H, 8.95; S, 11.87.
(14) Wagner, R. B.; Zook, H. D. Synthetic Organic Chemistry; J ohn
Wiley & Sons: New York, 1953; p 787.

4214 J . Org. Chem., Vol. 62, No. 13, 1997
Tanner et al.
n -Octyl m -ch lor oben zyl su lfid e: 1H NMR (400 MHz,
CDCl3) 0.90 (t, 3H, J ) 7 Hz), 1.15-1.65 (m, 12H), 2.35 (t,
2H, J ) 8.0 Hz), 3.65 (s, 2H), 7.10-7.40 (m, 5H); IR (vapor
phase) ν 2933, 2865, 1595, 1473, 1234, 1083, 876, 781, 692
cm-1; E+ m/ z 270.0 (M+), 157.9, 145.0, 124.9, 89.0, 69.0, 55.1;
bp 346 °C dec. Anal. Calcd for C15H23SCl; C, 66.52; H, 8.55.
Found: C, 66.59; H, 8.55.
1,2-Bis(m -ch lor op h en yl)eth a n e: 1H NMR (200 MHz,
CDCl3) δ 2.90 (s, 4H), 6.90-7.45 (m, 8H); IR (vapor phase) ν
3070, 2946, 2870, 1929, 1857, 1753, 1596, 1478, 1340, 1088,
1001, 667, 777 cm-1; E+ m/ z 252.2 (M+, 37Cl), 250.2 (M+, 35Cl),
178.3, 127.1; mp 97-99 °C (lit.16 mp 98-99 °C).
1,2-Bis(p-m eth ylp h en yl)eth a n e: 1H NMR (200 MHz,
CDCl3) δ 2.35 (s, 6H), 2.90 (s, 4H), 7.10 (s, 8H); IR (vapor
phase) ν 3024, 2934, 2873, 1888, 1783, 1515, 1449, 1341, 1211,
1108, 1022, 805 cm-1; E+ m/ z 210.1 (M+), 178.1, 165.1, 115.0,
105.1, 77.1; mp 83-84 °C (lit.16 mp 83-84 °C).
n -Octyl p-flu or oben zyl su lfid e: 1H NMR (400 MHz,
CDCl3) 0.90 (t, 3H, J ) 7 Hz), 1.10-1.70 (m, 12H), 2.40 (t,
2H, J ) 8.0 Hz), 3.65 (s, 2H), 6.90-7.40 (m, 4H); IR (vapor
phase) ν 2933, 2866, 1605, 1511, 1235, 1158, 1093, 831, 735;
E+ m/ z 254.0, 145.0, 109.0, 69.0, 54.7, 41.0; bp 300-301 °C/
749 mmHg. Anal. Calcd for C15H23SF: C, 70.82; H, 9.10; S,
12.61. Found: C, 71.03; H, 9.43; S, 12.84.
1,2-Bis(p -cya n op h en yl)et h a n e: 1H NMR (200 MHz,
CDCl3) δ 3.0 (s, 4H), 7.15 (d, J ) 9 Hz, 4H), 7.59 (d, J ) 9 Hz,
4H); IR (vapor phase) ν 3041, 2847, 2235, 1815, 1610, 1509,
1449, 1021, 827 cm-1; E+ m/ z 232.0 (M+), 203.1, 116.0, 89.0,
63.0; mp 202-204 °C.
p- or m -Su bstitu ted Ar yln on a n es. The arylnonanes were
prepared by the Grignard reaction of the magnesium salt of
1-bromooctane and a substituted benzyl bromide or chloride.
The products were purified by liquid chromatography on silica
gel (4:1 hexane:dichloromethane) in 10-30% yield.
1-F lu or o-4-n on ylben zen e: 1H NMR (200 MHz, CDCl3) δ
0.90 (t, J ) 6.9 Hz, 3H), 1.10-1.70 (m, 14H), 2.55 (t, J ) 8
Hz, 2H), 6.85-7.20 (m, 4H); IR (vapor phase) ν 3044, 2939,
1605, 1512, 1236, 1159, 1089, 1017, 822, 733 cm-1; E+ m/ z
222.2 (M+), 122.1, 109.1, 71.0, 57.0, 43.0 (GC/AED). Anal.
Calcd for C15H23F: C, 81.04; H, 10.42. Found: C, 80.88; H,
10.58.
n -Octyl m -m eth ylben zyl su lfid e: 1H NMR (400 MHz,
CDCl3) 0.90 (t, 3H, J ) 7 Hz), 1.15-1.70 (m, 12H), 2.35 (s,
3H), 2.40 (t, 2H, J ) 8.0 Hz), 3.65 (s, 2H), 6.95-7.30 (m, 5H);
IR (vapor phase) ν 3029, 2933, 2866, 1607, 1458, 1226, 1089,
779, 713; E+ m/ z 250.1 (M+), 145.1, 105.1, 68.9, 55.1; bp 307-
309 °C/749 mmHg. Anal. Calcd for C16H26S: C, 76.74; H,
10.46. Found: C, 76.56; H, 10.62.
n -Octyl p-m eth ylben zyl su lfid e: 1H NMR (400 MHz,
CDCl3) δ 0.90 (t, 3H, J ) 7.0 Hz), 1.10-1.07 (m, 12H) 2.35 (s,
3H), 2.40 (t, 2H, J ) 8.0 Hz), 3.65 (s, 2H), 7.20 (dd, 4H, J )
20.0 Hz); IR (vapor phase) ν 3025, 2933, 2866, 1513, 1234,
1022, 811 cm-1; E+ m/ z 150.2 (M+), 145.1, 105.1, 69.0, 54.2;
bp 300 °C dec. Anal. Calcd for C16H26S: C, 76.74; H, 10.46.
Found: C, 76.95; H, 10.76.
1-Ch lor o-4-n on ylben zen e: 1H NMR (200 MHz, CDCl3) δ
0.90 (t, 3H), 1.10-1.75 (m, 14H), 2.60 (t, J ) 8 Hz, 2H), 7.00-
7.40 (m, 4H); IR (vapor phase) ν 3033, 2935, 2866, 1493, 1352,
1096, 1016, 816 cm-1; E+ m/ z 240.2 (M+, 37Cl), 238.2 (M+, 35Cl),
167.1, 125.1, 91.2, 71.0, 57.0, 43.1. (GC/AED). Anal. Calcd
for C14H23Cl: C, 75.44; H, 9.70; Cl, 14.86. Found: C, 75.56;
H, 9.87; Cl, 14.53.
n -Octyl p-m eth oxyben zyl su lfid e: 1H NMR (400 MHz,
CDCl3) δ 0.95 (t, 3H, J ) 7.0 Hz), 1.15-1.65 (m, 12H) 2.45 (t,
2H, J ) 8.0 Hz), 3.70 (s, 2H), 3.80 (s, 3H), 7.05 (dd, 4H, J )
86.6 Hz); IR (vapor phase) ν 2934, 2865, 1609, 1511, 1250,
1173, 1041, 830; E+ m/ z 266.0 (M+), 153.0, 121.1, 91.3, 78.0;
bp 330 °C dec. Anal. Calcd for C16H26OS: C, 72.13; H, 9.83;
S, 12.04. Found: C, 71.98; H, 9.77; S, 11.65.
1-Meth yl-4-n on ylben zen e: 1H NMR (200 MHz, CDCl3) δ
0.90 (t, J ) 6.9 Hz, 3H), 1.10-1.70 (m, 14H), 2.32 (s, 3H), 2.60
(t, J ) 8 Hz, 2H), 7.10 (s, 4H); IR (vapor phase) ν 3023, 2934,
2866, 1515, 1460, 1351, 1118, 1022, 802 cm-1; E+ m/ z 218.2
(M+), 203.0, 175.3, 147.1, 132.0, 105.1, 77.0. (GC/AED). Anal.
Calcd for C16H26: C, 88.01; H, 11.99. Found: C, 87.97; H,
12.03.
n -Octyl p-ter t-bu tylben zyl su lfid e: 1H NMR (200 MHz,
CDCl3) δ 0.90 (t, 3H, J ) 7.0 Hz), 1.10-1.75 (m, 12H) 1.40 (s,
9H), 2.45 (t, 2H, J ) 7.3 Hz), 3.71 (s, 2H), 7.10-7.50 (dd, 4H,
J ) 10.7 Hz); IR (vapor phase) ν 2934, 2866, 1463, 1368, 1267,
1100, 1020, 824 cm-1; E+ m/ z 292.1 (M+), 147.0, 132.0, 117.0,
105.0, 91.0, 57.1; bp 335 dec. Anal. Calcd for C19H32S: C,
78.01; H, 11.03; S, 10.96. Found: C, 78.00; H, 11.14; S, 10.99.
1,2-Di-p- or -m -Su bstitu ted Ar yleth a n es. The bibenzyls
were prepared using substituted benzyl bromides or chlorides
by their Grignard substitution reactions according to the
literature procedure.15 1,2-Bis(p-methoxyphenyl)ethane was
identified by its GC/IR and GC/MS spectra.16
1-Ch lor o-3-n on yl ben zen e: 1H NMR (200 MHz, CDCl3)
δ 0.85 (t, J ) 7 Hz, 3H), 1.10-1.70 (m, 14H), 2.55 (t, J ) 8
Hz, 2H), 6.90-7.25 (m, 4H); IR (vapor phase) ν 2935, 2866,
1598, 1471, 1351, 1206, 1086, 878, 776, 600 cm-1; E+ m/ z 240.2
(M+ 37Cl), 238.2 (M+, 35Cl), 203.2, 167.1, 126.1, 91.1, 57.1, 43.1.
(GC/AED). Anal. Calcd for C15H23Cl: C, 75.44; H, 9.69; Cl,
14.86. Found: C, 75.32; H, 9.67; Cl, 15.01.
1,2-Bis(m -m eth ylp h en yl)eth a n e: 1H NMR (200 MHz,
CDCl3) δ 2.45 (s, 6H), 3.00 (s, 4H), 6.95-7.45 (m, 8H); IR (vapor
phase) ν 3030, 2994, 2871, 1607, 1489, 1090, 882, 775, 699
cm-1; E+ m/ z 209.0 (M+), 105.0, 77.0, 51.0. (GC/AED). Anal.
Calcd for C16H18: C, 91.38; H, 8.62. Found: C, 91.21; H, 8.78.
1,2-Bis(p-ch lor op h en yl)eth a n e: 1H NMR (200 MHz,
CDCl3) δ 2.85 (s, 4H), 6.95-7.35 (m, 8H); IR (vapor phase) ν
3034, 2939, 2869, 1499, 1097, 1016, 816, 638 cm-1; E+ m/ z
251.8 (M+, 37Cl), 249.8 (M+, 35Cl), 125.0, 88.9, 63.0; mp 110-
111 °C (lit.17 mp 112 °C).
1-ter t-Bu tyl-4-n on ylben zen e: 1H NMR (200 MHz, CDCl3)
δ 0.89 (t, J ) 6.9 Hz, 3H), 1.15-1.70 (m, 23H), 2.55 (t, J ) 8
Hz, 2H), 7.05-7.40 (m, 4H); IR (vapor phase) ν 3026, 2934,
2867, 1465, 1368, 1267, 1100, 1019, 825 cm-1; E+ m/ z 260.2
(M+), 245.4, 231.1, 173.1, 147.1, 132.0, 117.1, 91.0, 41.0. (GC/
AED). Anal. Calcd for C19H32: C, 87.63; H, 12.37. Found:
C, 87.51; H, 12.49.
1-Meth yl-3-n on ylben zen e: 1H NMR (200 MHz, CDCl3) δ
0.90 (t, J ) 6.9 Hz, 3H), 1.10-1.70 (m, 14H), 2.35 (s, 3H), 2.55
(t, J ) 8 Hz, 2H), 6.90-7.30 (m, 4H); IR (vapor phase) ν 3023,
2936, 2869, 1461, 1352, 1263, 725, 652 cm-1; E+ m/ z 218.4
(M+), 175.2, 147.2, 119.0, 106.2, 91.0, 77.1. (GC/AED). Anal.
Calcd for C16H26: C, 88.01; H, 11.99. Found: C, 88.07; H,
11.92.
1,2-Bis(p -flu or op h en yl)et h a n e: 1H NMR (200 MHz,
CDCl3) δ 2.90 (s, 4H), 6.85-7.30 (m, 8H); IR (vapor phase) ν
3044, 2939, 2869, 1877, 1605, 1512, 1236, 1159, 1089, 1017,
822, 732 cm-1; E+ m/ z 218.0 (M+), 109.0, 83.0, 57.0; mp 85-
86 °C. (GC/AED). Anal. Calcd for C14H12F2: C, 77.05; H, 5.54.
Found: C, 77.05; H, 5.51.
1-Cya n o-4-n on ylben zen e: 1H NMR (200 MHz, CDCl3) δ
0.90 (t, J ) 7 Hz, 3H), 1.10-1.75 (m, 14H), 2.65 (t, J ) 8 Hz,
2H), 7.55 (d, J ) 9 Hz, 2H), 7.85 (d, J ) 9 Hz, 2H); IR (vapor
phase) ν 3040, 2938, 2867, 2233, 1912, 1609, 1507, 1022, 824
cm-1; E+ m/ z 229.1 (M+), 158.0, 130.1, 117.1, 89.0, 71.1, 57.0.
(GC/AED). Anal. Calcd for C16H23N: C, 83.79; H, 10.10.
Found: C, 83.62; H, 10.19.
n -Octyl d isu lfid e was prepared by the I2 oxidation of
1-octanethiol (5 g, 0.035 mol):18 1H NMR (200 MHz, CDCl3) δ
0.89 (t, J ) 7 Hz, 6H), 1.10-1.80 (m, 24H), 2.65 (t, J ) 8 Hz,
4H); IR (vapor phase) ν 2994, 2865, 1461, 1294 cm-1; E+ m/ z
290.3 (M+), 178.0, 145.2, 115.1, 71.1, 57.1; bp 295-296 °C/750
mm Hg.
1,2-Bis(p-ter t-bu tylp h en yl)eth a n e: 1H NMR (200 MHz,
CDCl3) δ 1.35 (s, 18H), 2.92 (s, 4H), 7.10-7.40 (m, 8H); IR
(vapor phase) ν 3027, 2987, 2877, 1514, 1369, 1267, 1195, 1108,
1019, 821 cm-1; E+ m/ z 294.2 (M+), 279.2, 147.1, 132.1, 116.8,
105.1, 91.0, 57.0, 40.9; mp 150-152 °C. (GC/AED). Anal.
Calcd for C22H30: C, 89.74; H, 10.26. Found: C, 89.70; H,
10.31.
(15) Trahanovsky, S. W.; Brixins, D. W. J . Am. Chem. Soc. 1973,
95, 6778.
(16) The NIST/EPA/NIH Mass Spectral Library, Version 1.1a,
National Institute of Standards and Technology, Gaithersburg, MD,
1995.
(17) Kade, R. J . Prakt. Chem. 1879, 19, 461.
(18) Vogel, A. I. J . Chem. Soc. 1948, 1822.

Reaction of Alkyl Sulfides with Atomic Hydrogen
J . Org. Chem., Vol. 62, No. 13, 1997 4215
Deter m in a tion of th e Rela tive Ra te of F r a gm en ta tion
of Su bstitu ted Ben zyl n -Octyl Su lfid es. Solutions of
n-octyl-substituted benzyl sulfides (0.025-0.05 M) in acetone
(10 mL) were subjected to a hydrogen plasma (H2 flow rate; 6
mL/min, 3.5 Torr, 5-15 min), and the product mixtures were
analyzed by gas chromatography. The relative rates were
calculated by determining the amounts of n-octane, nonyl-
arenes, n-octanethiol, and n-octyl disulfide formed.
The relative rates of fragmentation between primary alkyl
1
and substituted-benzyl groups (kG /k1°) were calculated using
eq 9, and the relative rates of fragmentation between substi-
tuted- and unsubstituted-benzyl sulfides were calculated using
eq 11.
It was assumed that the rate of fragmentation to form the
primary radical (k1°) was not affected by the substituent G in
the benzylic fragment.
Deter m in a tion of th e Rela tive Ra tes of Disa p p ea r a n ce
of n -Octyl Su bstitu ted -Ben zyl Su lfid es. Acetone solutions
(10 mL) of a 1:1 mixture of (0.01-0.05 M) n-octyl benzyl
sulfide, n-octyl substituted-benzyl sulfide, and 1-chloroheptane
(internal standard) were subjected to hydrogen plasma (hy-
drogen flow rate ) 6 mL/min, 3.5 Torr, 5-15 min) at -78 °C.
The initial and final product mixtures were analyzed by gas
chromatography using a 105 m × 0.25 mm × 0.5 µm Rtx-1 glass
capillary column fitted to a Varian 6000 chromatograph
equipped with a hydrogen flame detector interfaced to a Varian
vista CDS 401 chromatography data system. The rates of
disappearance of n-octyl substituted-benzyl sulfides (G) rela-
tive to the unsubstituted analog (H) were calculated (eq 12)
using the area ratios of those compounds (AG, AH) with respect
to the internal standard (AS).
Ack n ow led gm en t. The authors thank the Depart-
ment of Chemistry, the University of Alberta, the
Natural Science and Engineering Research Council of
Canada, CANMET of Canada, and Alberta Energy for
their generous support of this work.
J O9615615