Triphenylethenethiol. Structure, equilibria with the thioketone, solvation, and association with DMSO

Article abstract of DOI:10.1021/jo9604651

The simple thioenols, triphenylethenethiol (12) and 2,2-diphenyl-1-anisylethenethiol (13) were prepared. Both are the only observed constituent of the thioenol ? thioketone equilibria and comparison and estimation suggested that the thiocarbonyl ? thioenol equilibrium constant K_enol for 12 and other simple thioenols is ≥10⁶ higher than for the corresponding carbonyl ? enol equilibria. The X-ray diffraction of 12, which is the first measured for a simple thioenol, shows a propeller arrangment of the three rings. The δ(SH) in the ¹H NMR spectrum increases with the increase in the hydrogen bonding accepting parameter β of the solvent. The association constant K_assoc of 12 with DMSO is 0.087, much lower than values of triarylethenols with DMSO. Reaction of diphenylacetaldehyde with Lawesson's reagent did not give the thioenol, but gave bis(2,2-diphenylvinyl) sulfide (16) and a substance (17) having a trithiaphosphorinane system.

Full text of DOI:10.1021/jo9604651

5462
J . Org. Chem. 1996, 61, 5462-5467
Tr ip h en yleth en eth iol. Str u ctu r e, Equ ilibr ia w ith th e Th iok eton e,
Solva tion , a n d Associa tion w ith DMSO†
Tzvia Selzer and Zvi Rappoport*
Department of Organic Chemistry, The Hebrew University, J erusalem 91904, Israel
Received March 7, 1996X
The simple thioenols, triphenylethenethiol (12) and 2,2-diphenyl-1-anisylethenethiol (13) were
prepared. Both are the only observed constituent of the thioenol h thioketone equilibria and
comparison and estimation suggested that the thiocarbonyl h thioenol equilibrium constant Kenol
for 12 and other simple thioenols is g106 higher than for the corresponding carbonyl h enol
equilibria. The X-ray diffraction of 12, which is the first measured for a simple thioenol, shows a
1
propeller arrangment of the three rings. The δ(SH) in the H NMR spectrum increases with the
increase in the hydrogen bonding accepting parameter â of the solvent. The association constant
K
assoc of 12 with DMSO is 0.087, much lower than values of triarylethenols with DMSO. Reaction
of diphenylacetaldehyde with Lawesson’s reagent did not give the thioenol, but gave bis(2,2-
diphenylvinyl) sulfide (16) and a substance (17) having a trithiaphosphorinane system.
In tr od u ction
(CH2)n
S
SH
Simple enols, defined as enols substituted by hydrogen,
alkyl, or aryl groups, but not by strongly electron-
withdrawing hydrogen bond-accepting substituents1 such
as carbonyl, are usually much less stable than their
carbonyl tautomers.2 When the double bond substituents
are bulky aromatic groups, such as mesityl, the enols are
frequently stable,3 and stability is also enhanced when
two â-aryl groups can become coplanar or close to
coplanar with the double bond. Appreciable keto h enol
equilibrium constants were determined in these cases,
and extensive structural and mechanistic investigations
on poly(bulky)aryl-substituted enols were conducted in
recent years.4
200 °C
13 mm
S
S
(2)
(CH2)n–1
+
(CH2)n
S
(CH2)n
(H2C)n
4
5
n = 4, 6
3
With phenyl-substituted systems the thioenol is the
only tautomer observed in several systems; e.g., only 6
was isolated from the reaction of benzhydryl benzyl
ketone with H2S/HCl, although the color of the thiocar-
bonyl compound was observed at an earlier reaction
stage,7 while 7 was the only product obtained from
dibenzyl ketone and Lawesson’s reagent.8
In contrast, the sulfur analogs, simple thioenols (1),
are, in comparison with the thiocarbonyl tautomers (2),
much more stable than are the enols vs the CdO
derivatives. Indeed, even simple thiocarbonyl compounds
2 exist in equilbria (eq 1) with appreciable amount of the
PhC(R)dC(SH)CH2Ph
6: R ) Ph
7: R ) H
Simple thioaldehydes with R-hydrogens also prefer to
be in the thioenol form, and no thioaldehyde was known
up to 1991, when Ando and co-workers prepared both 2,2-
di-tert-butylethanethial and its tautomer 2,2-di-tert-
butylethenethiol.9 In spite of the usual rapid thiocarbon-
yl to thioenol interconversion, the two species are nearly
stable to mutual interconversion, presumably due to the
high steric hindrance.
Although several preparative and quantitative studies
on thioenol/thioketone systems activated by a â-carbonyl
function had been conducted,10 quantitative equilibration
studies and physicochemical or structural information on
simple systems are scarce. The only kinetic/equilibrium
data known to us11 are for the diisopropyl and diisobutyl
systems 8/9 and 10/11 (eq 3). At 40 °C in CCl4 9 and 11
SH
S
C
H
C
C
C
(1)
2
1
thioenol.5 For example, the low-pressure pyrolysis of
spirotrithienes 3 gives mixtures of cyclic thioketones (4)
and their tautomeric cyclic thioenols 56 (eq 2). For five-
and seven-membered rings the percentage of 5 was ca.
3-fold higher than that of 4.
† Dedicated to Prof. Michael Hanack on the occasion of his 65th
birthday.
X Abstract published in Advance ACS Abstracts, J uly 15, 1996.
(1) Wheland, G. W. Advanced Organic Chemistry, 3rd ed.; Wiley:
New York, 1960; pp 663-702.
(2) Toullec, J . In The Chemistry of Enols; Rappoport, Z., Ed.; Wiley:
Chichester, 1990; Chapter 6, pp 323-398.
(7) Campaigne, E.; Edwards, B. E. J . Org. Chem. 1962, 27, 3760.
(8) Pedersen, B. S.; Scheibye, S.; Nilsson, N. H.; Lawesson, S.-O.
Bull. Soc. Chim. Belg. 1978, 87, 223.
(9) Ando, W.; Ohtaki, J .; Suzuki, T.; Kabe, Y. J . Am. Chem. Soc.
1991, 113, 7782.
(3) E.g.: (a) Fuson, R. C.; Foster, R. E.; Shenk, W. J ., J r.; Maynert,
E. W. J . Am. Chem. Soc. 1945, 67, 1937. (b) Fuson, R. C.; Chadwick,
D. H.; Ward, M. L. J . Am. Chem. Soc. 1946, 68, 389. (c) Fuson, R. C.;
Armstrong, L. J .; Chadwick, D. H.; Kneisley, J . W.; Rowland, S. P.;
Shenk, W. J ., J r.; Sofer, Q. F. J . Am. Chem. Soc. 1945, 67, 386.
(4) For reviews see: (a) Rappoport, Z.; Biali, S. E. Acc. Chem. Res.
1988, 21, 442; (b) Hart, H.; Rappoport, Z.; Biali, S. E. in The Chemistry
of Enols; Rappoport, Z., Ed.; Wiley: Chichester, 1990; Chapter 8, pp
481-590.
(10) (a) Reyes, Z.; Silverstein, R. M. J . Am. Chem. Soc. 1958, 80,
6367, 6373. (b) Bleisch, S.; Mayer, R. Chem. Ber. 1967, 100, 53. (c)
Duus, F.; Pedersen, E. B.; Lawesson, S.-O. Tetrahedron 1969, 25, 5703.
(d) Duus, F. Tetrahedron 1972, 28, 5923. (e) Fabian, J . Tetrahedron,
1973, 29, 2449. (f) Duus, F.; Anthonsen, J . W. Acta. Chem. Scand. B
1977, 31, 40. (g) Duus, F. J . Org. Chem. 1977, 42, 3123. (h) Duus, F.
In Comprehensive Organic Chemistry; Barton, D., Ollis, W. D., Eds.;
Pergamon: New York, 1979; Vol. 3, pp 385-388.
(5) (a) Paquer, D.; Vialle, J . Bull. Soc. Chim. Fr. 1969, 3327; (b)
1969, 3595.
(6) Fraser, P. S.; Robbins, L. V.; Chilton, W. S. J . Org. Chem. 1974,
39, 2509.
(11) Paquer, D.; Vialle, J . Bull. Soc. Chim. Fr. 1971, 4407.
S0022-3263(96)00465-3 CCC: $12.00 © 1996 American Chemical Society

Triphenylethenethiol
J . Org. Chem., Vol. 61, No. 16, 1996 5463
(RR′CH)2CdS
8: R ) R′ ) Me
10: R ) i-Pr, R′ ) H
h RR′CdC(SH)CHRR′ (3)
9: R ) R′ ) Me
11: R ) i-Pr, R′ ) H
consist of 58% and 53% of the mixtures, respectively, and
the equilibration is accelerated by pyridine. Calculations
on the butane-2-thione and 2-methylbutane-3-thione
systems12 gave a 1 kcal mol-1 higher stability for the C)S
tautomer and a very high kinetic barrier of 85 kcal mol-1
for the tautomerization.
In addition to the lack of equilibrium data we know of
no crystal data or an association data with the solvent
for a simple thioenol. Consequently, we tried to prepare
a few aryl-substituted thioenols in order to obtain for
them data comparable to those available for the oxygen
analogs.4
Resu lts
Syn th esis. We attempted to prepare ethenethiols
with 2,2-di(bulky)aryl, 1,2,2-triaryl, and 2,2-diphenyl
substituents. The synthetic route to dimesityl and bis-
(2,4,6-triisopropylphenyl) systems that involved an initial
preparation of the thioketene led to polythio cyclic
compounds, which will be discussed elsewhere.
Triphenylethenethiol (12) and 1-anisyl-2,2-diphenyl-
ethenethiol (13) were prepared in two ways. (i) Reaction
of (2,2-diphenyl-1-aryl)magnesium bromides with sulfur
(S8) followed by hydrolysis with dilute H2SO4 solution
gave 12 and 13 (eq 4).
F igu r e 1. ORTEP drawing and numbering scheme for 17.
reagent, two other compounds were isolated instead, bis-
(2,2-diphenylvinyl) sulfide (16) and 1-(p-methoxyphenyl)-
2,4,6-trithia-1-phospha-3,5-bis(diphenylmethyl)-1-thio-
cyclohexane (17) (eq 6). 16 was identified by its mass
Ph2CHCH O + 14
S or Ph2C CHSH
PH2CHCH
toluene
15
1. Mg/solvent
(6)
CHPh2
CH
S
Ph2CdC(Br)Ar
8
2. S8
3. dilute H2SO4
S
S
Ph2C
C
C
CPh2
Ph2CHCH
S
Ph2CdC(SH)Ar
(4)
+
P
OCH3
H
H
12: Ar ) Ph, 44% (in ether)
13: Ar ) An, 42% (in THF)
S
16
17
(ii) Reaction of 2,2-diphenyl-1-arylethanone with an
equimolar amount of Lawesson’s reagent [bis(p-meth-
oxyphenyl)-1,3-dithiaphosphetane 2,4-disulfide (14)]8 in
toluene under reflux followed by chromatographic sepa-
ration of the product also gave 12 and 13 (eq 5).
spectral peaks at m/z 390 (M, B) and m/z 210 (Ph2CdCdS)
1
and its H and 13C NMR spectra. 17 was identified by
1
its mass spectrum, m/z (B, Ph2CHCHS), and its H NMR
spectrum, which showed signals at 3.85 (OMe), 6.98, 8.04
(Ar-H signals meta and ortho, respectively to the P, with
the proper PH and HH coupling), a doublet at 4.52 ppm
ascribed to the benzhydryl protons, and a doublet of
doublets at δ 6.07 ppm ascribed to the aliphatic ring
hydrogens, coupled by the phosphorous. The 13C NMR
spectrum displayed signals ascribed to the MeO group
(56.91 ppm), the aliphatic ring carbons (56.91 ppm, J PH
) 28.8 Hz), the benzhydryl carbons (59.57 ppm), and the
aromatic carbon signals.
Unequivocal structural evidence was obtained from
X-ray diffraction of 17. The ORTEP drawing is shown
in Figure 1, and selected crystallographic data are given
in Table 1.14
The six-membered 2,4,6-trithia-1-phospha ring dis-
plays a chair conformation. If the ring plane is defined
by atoms C(1), C(2), S(1), and S(2), the P and S(3) atoms
are on opposite sides of this plane. The four rings display
different torsional angles with the ring plane in the range
of 48.42-88.48°.
S
P
O
S
S
reflux, toluene
N2, xh
OMe
Ph2CHCAr + MeO
P
S
14
(5)
Ph2C C(SH)Ar
12: 15% (x = 50)
13: 34% (x = 48)
Thioenol 12 was previously prepared by method i by
Koelsch13 and was identified by microanalysis and its
reactions with methyl sulfate or benzoyl chloride. We
corroborated the thioenol structure by the mass spectra
in which the base peaks are the molecular peaks at m/z
288 (12) and 318 (13), by the νSH stretching at 2562 (12)
and 2578 cm-1 (13), by the SH signal in CDCl3 at 3.28
1
(12) and 3.27 (13) ppm in the H NMR spectra, by the
signals at 126.13 (CR) and 137.28 (Câ) for 12 in the 13C
NMR spectrum, and by X-ray diffraction of 12 (vide
infra).
Attem p ted Th ioen ol h Th iok eton e Equ ilibr a -
tion s. In order to determine the position of the equilib-
rium of the thiols 12 and 13 with their keto tautomers
(iii) In an attempt to obtain the 2,2-diphenylethene-
1-thiol (15) from diphenylacetaldehyde and Lawesson’s
(14) The authors have deposited atomic coordinates for this struc-
ture with the Cambridge Crystallographic Data Centre. The coordi-
nates can be obtained, on request, from the Director, Cambridge
Crystallographic Data Centre, 12 Union Road, Cambridge, CB2 1EA,
U.K.
(12) Bruno, A. E.; Steer, R. P.; Mazey, P. G. J . Comput. Chem. 1983,
4, 104.
(13) Koelsch, C. F.; Ullyot, G. J . Am. Chem. Soc. 1933, 55, 3883.

5464 J . Org. Chem., Vol. 61, No. 16, 1996
Ta ble 1. Bon d Len gth s a n d An gles for 17
Selzer and Rappoport
bond
length, Å
2.086(7)
2.094(8)
1.932(8)
1.836(2)
1.834(2)
1.809(2)
1.810(2)
angle
2PCS
deg
dihedral angleb
deg
S(1)-P(1)
S(2)-P(1)
S(4)-P(1)
S(1)-C(2)
S(2)-C(1)
S(3)-C(1)
S(3)-C(2)
C(1)-C(10)
C(2)-C(23)
4 C-C(Ph)
97.19 ( 0.21
103.8(1)
104.9(3)
113.7(4)
114.1(4)
A-An
75.28
88.48
67.21
48.42
68.60
109.4
90.54
C(1)S(3)C(2)
S(1)P(1)S(2)
S(1)P(1)S(4)
S(2)P(1)S(4)
2SP(1)C(3)
S(4)P(1)C(3)
2SC(1)S
A-Ph1
A-Ph2
A-Ph3
A-Ph4
Ph1-Ph2
Ph3-Ph4
102.8 ( 0.3
117.1(7)
1.546(3)
1.543(3)
1.520(3)-1.523(3)
113.65 ( 0.05
107.95 ( 0.17
113.7(1)
120.8 ( 0.8
108.9(2)-113.9(1)
117.6(2)-121.4(3)
SCC
S(1)C(2)S(3)
2PCC
Ar(C)-(C)
1.363(3)-1.401(4)a
6CS(sp3)C
ring CCC
a
b
Except for C(32)-C(33) ) 1.345(4) Å. A ) plane C(1)C(2)S(1)S(2); Ph1 ) C(11)-C(16); Ph2 ) C(17)-C(22); Ph3 ) C(24)-C(29); Ph4
) C(30)-C(35).
the R-Ph ring, all bond angles and the bond lengths are
close to those expected.
Associa tion of 12 w ith th e Solven t. We know of
no data on the conformation of the CdCsSsH moiety
that can be syn or anti, periplanar or clinal. Unfortu-
nately, the thioenolic hydrogen was not located in the
X-ray diffraction of 12. Also, we know of no association
data of the thioenolic SH with the solvent. We therefore
tried to learn about the CdCsSsH conformation by
1
comparing the δ(SH) values in the H NMR spectrum of
12 with the δ(OH) values of stable simple enols. The δ-
(SH) values in four solvents, together with the solvents’
hydrogen bond accepting parameters â of the Kamlet-
Taft solvatochromic equation,15 are given in Table 3. The
solvent dependence of the shift is relatively small, being
<1 ppm between solvents at the extremes of the â scale.
When the values were plotted against δ(OH) of the
stable enol 2,2-dimesitylethenol 20,15 a very approximate
F igu r e 2. ORTEP drawing and numbering scheme for 12.
Me2CdCHOH
Mes ) mesityl
20
18 and 19 from both sides, we tried to make the
thioketones from the corresponding ethanones and 14.
As mentioned above, these reactions gave only the
thioenols 12 and 13, suggesting that if the equilibration
is rapid, the thioenols are the exclusive equilibration
products within our detection limits.
linear relationship (eq 8) was obtained. The small slope
indicates a much lower sensitivity to the solvent change
than for 20. A plot of δ(SH) values vs â values also gave
an approximate linear relationship (eq 9).
Equilibrations of 0.13-0.14 mol L-1 solutions of 12 and
13 were attempted in hexane at 60 °C for up to 2 weeks,
δ(SH) (12) ) 0.18 δ(OH) (20) + 2.41 (R ) 0.937)
(8)
1
and the mixtures were analyzed by H NMR during this
period for the presence of 18 and 19 (eq 7). No traces of
δ(SH) (12) ) 1.06â + 3.20 (R ) 0.953)
(9)
hexane
In order to calculate an association constant (Kassoc) for
the intermolecular RSH‚‚‚DMSO hydrogen-bonded com-
plex we measured the δ(SH) values of 0.02 M of 12 in
binary CCl4-DMSO-d6 mixtures of varying compositions.
The data are given in Table 4.
Ph2CdC(SH)Ar
Ph2CHC(Ph)dS
(7)
8
2 weeks
Ar ) Ph
Ar ) An
18
19
12
13
For calculating Kassoc it is assumed, on the basis of a
similar study with 20,16 that only one DMSO-d6 molecule
is associated with 12 in the anti (a) CdCsSsH confor-
mation (eq 10), which is in equilibrium with an unasso-
the thioketone (estimated detection limit 1-2%) were
detected, and only 12 or 13 was observed. Likewise, no
tautomerization to 18 or 19 was observed in the presence
of 4% (v/v) of trifluoroacetic acid or up to 20% (v/v)
pyridine in hexane.
Solid Sta te Str u ctu r e of 12. Since no solid state
structure of a simple thioenol was determined so far, the
structure of 12 was determined by X-ray crystallography.
The ORTEP structure with atom numbering is given in
Figure 2, and selected bond lengths, angles, and dihedral
angles are given in Table 2.14 The thioenol has a
propeller conformation with different dihedral ArsCdC
angles in the range 44.5-62.3°. The torsional angle of
the double bond is 7°. Except for the bond angles around
Ph
Ph
S
Ph
Ph
Kassoc
Ph
Ph
(10)
+ DMSO
C
C
C
C
H
OSMe2
S
H
a
s
(15) Kamlet, M. J .; Abboud, J .-L. M.; Taft, R. W. Prog. Phys. Org.
Chem. 1981, 13, 485. Kamlet, M. J .; Doherty, R. M.; Abraham, M.;
Carr, P. W.; Doherty, R. F.; Taft, R. W. J . Phys. Chem. 1987, 91, 1996.
Kamlet, M. J ., Taft, R. W. Acta Chem. Scand. 1986, B40, 619.
(16) Biali, S. E.; Rappoport, Z. J . Am. Chem. Soc. 1984, 106, 5641.

Triphenylethenethiol
bond
J . Org. Chem., Vol. 61, No. 16, 1996 5465
Ta ble 2. Bon d Len gth s a n d An gles for 12
length, Å
1.803(3)
1.356(5)
angle
deg
120.4(3)
dihedral anglea
R-PhS(1)C(1)C(3)
deg
S(1)-C(1)
C(1)-C(2)
C(1)-C(3)
C(2)-C(9)
C(9)-C(15)
C-C(Ar)
S(1)C(1)C(2)
S(1)C(1)C(3)
C(2)C(1)C(3)
C(1)C(2)C(9)
C(1)C(2)C(15)
C(9)C(2)C(15)
CCC(Ar)
55.74
113.9(2)
1.503(5)
1.490(5)
1.473(4)
1.368(5)-1.399(5)
125.7(3)
119.5(3)
122.7(3)
117.8(3)
â-PhC(9)C(2)C(15)
44.54
62.27
â′-PhC(9)C(2)C(15)
116.7 (3)-122.2(4)
S(1)C(1)C(3)-C(9)C(2)C(15)
173.00
a
Key: R-Ph: C(3)-C(8); â-Ph: C(9)-C(14); â′-Ph: C(15)-C(20).
Ta ble 3. δ(SH) Va lu es (p p m ) for 12 in Sever a l Solven ts
Ta ble 5. Ka ssoc a n d δy Va lu es for 12 in CCl4-DMSO-d 6
a t 295 K
Mixtu r es a t 295 K
solvent
CCl4
CDCl3
CD3COCD3
DMSO-d6
â
δ(SH)
param
value
param
value
0
0
3.19
3.28
3.54
4.12
Kassoc
0.13
4.12
0.087
Rc
δa
0.815
4.7
0.62
a
b
δDMSO
0.48
0.76
Kassoc
Fa in DMSOd
b
a
b
According to eq 11, assuming that δa ) δDMSO
.
After one
iteration according to eq 13. c Correlation coefficient for eq 13.
Ta ble 4. δ(SH) (p p m ) a n d K Va lu es for 12 in
CCl4-DMSO-d 6 Mixtu r es a t 295 K
d
According to (δDMSO - δCCl )/(δa - δCCl ).
4
4
DMSO-d6:CCl4 (v/v)
DMSO-d6, M
δ(SH)
K
be the predominant or exclusive components of the
equilibria. This should be mainly ascribed to the large
difference in bond energies of CdO (177 kcal mol-1) and
CdS (115 kcal mol-1), which apparently more than
overcome the differences (in kcal mol-1) for CO (88)/CS
(61) and OH (110)/SH (82).17
Our results resemble the earlier ones. Only the
thioenol was obtained from 12 and 13 with no trace of
the thioketones 18 and 19. Since the two synthetic
methods that were designed to give the thioenols and the
thioketones, respectively, gave only the thioenols the
latter seem the thermodynamically more stable species
at equilibria.
0:100
2:98
10:90
50:50
100:0
0
3.19
3.25
3.33
3.64
4.12
0
0.28
1.42
7.07
14.14
0.069
0.177
0.937
∞
ciated syn (s) conformation. The association constant
Kassoc is then given by eq 11, where [DMSO]f is the free
Kassoc ) [a]/[s][DMSO]f ) K/[DMSO]f
(11)
DMSO and K ) [a]/[s]. When [DMSO]o is the free +
associated [DMSO] in the mixture, [DMSO]f ) [DMSO]o
- [a]. When δobs, δa, and δs are the observed SH chemical
shift and the unknown shifts for the anti and syn
conformations, respectively, K is given by eq 12, which
is based on the assumption of a rapid equilibrium
between the a and s conformations.
The only value available for comparison is for tri-
phenylethanone/triphenylvinyl alcohol. In DMSO, the
best solvent for stabilizing the enol species, at 295 K Kenol
) ca. 0.06.18 For 12 (and 13) in hexane, the solvent that
least stabilizes enols, Kenol is g100 judged by the detection
limit of the NMR.
The higher the â value of the solvent,15 the higher is
K ) (δs - δobs)/(δobs - δa)
(12)
16,18,19
Kenol
,
e.g., Kenol (DMSO)/Kenol (H2O) for diphenyl-
acetaldehyde is ca. 50.18,19 The only comparison available
between DMSO and hexane is for 2-(2,4,6-triisopropyl-
A plot of K vs [DMSO]f should be linear with a slope )
K
assoc. Using the same analysis applied before16 we obtain
phenyl)acenaphthen-1-ol and its keto isomer where Kenol
-
eq 13, assuming as a first approximation that δa ) δDMSO
.
(DMSO)/Kenol(hexane) g 650-fold.19a From this value and
the Kenol values for 12 in hexane and for Ph2CdC(OH)-
Ph in DMSO,18 Kenol [Ph2CdC(SH)Ph]/Kenol [Ph2CdC-
(OH)Ph] g 650 × 100/0.06 ) g106. This estimation
involves the assumption that the PhsCd dihedral angles
that affect the stability of the enols and thioenols by
PhsCd conjugation4b,20 are the same in both systems,
but a ratio of 106 as a lower value seems reasonable.
If this is the case, the lack of observation of 15 in the
attempt to generate it is due to further reactions of the
formed 15 to give 16 and 17, since Kenol (Ph2CdCHOH)
is 5.06 in DMSO17 and ca. 0.1 in water.21
[DMSO]o/(δobs - δCCl ) ) ([12]o + [DMSO]o - [a])/
4
(δa - δ ) + 1/Kassoc (δa - δ ) (13)
CCl4
CCl4
A plot of the [DMSO]o/(δobs - δCCl ) values vs [12]o +
4
[DMSO]o - [a] should be linear with a slope of 1/(δa -
δ
CCl ) and an intercept 1/Kassoc(δa - δCCl ). Since the [a]
4
4
value is unknown, the [DMSO]o/(δobs - δCCl ) values were
4
plotted vs [12]o + [DMSO]o values, and from the observed
slope an approximate [a] value was calculated16 and then
used with eq 13. Since [a] , [DMSO]o for all the
solutions, one iteration of eq 13 gave convergence to the
δa and Kassoc values given in Table 5. Kassoc is low (0.087
L mol-1), and since Fa is 0.62, we conclude that both the
solvated anti conformer (62%) and the unsolvated cis
conformer (38%) are present in DMSO solution.
(17) For experimental values see: (a) March, J . Advanced Organic
Chemistry, 4th ed.; Wiley: New York, 1992; p 24. (b) Price, C. C.; Oae,
S. Sulfur Bonding: Ronald Press Co.: New York, 1962; pp 1-7. (c)
See also: Schaumann, E. In The Chemistry of Double Bonded
Functional Groups; Patai, S., Ed.; Wiley: Chichester, 1989; Chapter
17, pp 1269-1274. (d) For calculated CdS and C-S energies see:
Schleyer, P. v. R.; Kost, D. J . Am. Chem. Soc. 1988, 110, 2105.
(18) Rochlin, E.; Rappoport, Z. J . Am. Chem. Soc. 1992, 114, 230.
(19) (a) Miller, A. R. J . Org. Chem. 1976, 41, 3599. (b) Rappoport,
Z.; Nugiel, D. A.; Biali, S. E. J . Org. Chem. 1988, 53, 5361. (c) Nadler,
E. B.; Rappoport, Z. J . Am. Chem. Soc. 1989, 111, 213.
Discu ssion
Th ioen ol/Th iok eton e Equ ilibr ia . From examples
and references given above it is clear that thioenols are
more stable in relation to their thiocarbonyl compound
than their oxygen analogs and that simple thioenols may
(20) Nadler, E. B.; Rappoport, Z. J . Am. Chem. Soc. 1987, 109, 2112.
(21) Chiang, Y.; Kresge, A. J .; Krogh, E. T. J . Am. Chem. Soc. 1988,
110, 2600.

5466 J . Org. Chem., Vol. 61, No. 16, 1996
Selzer and Rappoport
The exclusive observation of 6 and 7 in their (presum-
(at 307 K) and 0.30 (at 305 K) L mol-1, respectively,28b
an order opposite to the order of the pKa’s of the thiols.27
However, the order of the Kassoc values in DMF [PhSH
(0.24 at 298 K), Me2CHSH (0.12 at 298 K), and Me3CSH
(0.084 at 309 K)] is the same as for the pKa’s (6.5, 10.86,
and 11.2, respectively).28b The acidity of 12 is probably
higher than that of the aliphatic thiols and closer to that
of thiophenol.
able) mixtures with the thiocarbonyl compounds7,8 is
consistent with these values. For PhCHdCHOH pKenol
-
(H2O) values are 3.35 (E) and 3.07 (Z).22 Using a Kenol
(EtOH)/Kenol (hexane) ratio of g619a (assuming that Kenol
(MeOH) ∼ Kenol (EtOH)), a pKenol (7) g2 in MeOH,8 and
a KR-CH Ph/KR-H ratio of ca. 30 (based on KR-Me/KR-H ratio
2
of 31 for the Mes2CdC(OH)R system in hexane),23 the
PhC(R)dC(SH)CH2Ph/PhC(R)dC(OH)CH2Ph ratio will
also be g106.
Whereas there is no Kassoc value for triphenylethenol,
Kassoc values with DMSO for Mes2CdC(OH)Ar are 1.82
for Ar ) Mes and 1.93 for Ar ) Ph and Kassoc ) 2.75 for
(Z)-MesC(Ph)dC(OH)Mes.19c Hence, the change from R-
or â-Mes to Ph increases Kassoc only slightly, suggesting
11
Finally, for 9 and 11, in CCl4 Kenol values are ca.
1-1.5. Comparison with the reliable pKenol value of 7.52
for diisopropyl ketone,24 correcting for the solvent effect
as done above and assuming that hexane resembles CCl4,
will give again a Kenol ratio of g106 for simple aliphatic
thioketone compared with the corresponding ketone.
pKenol value for methyl fluorene-9-thionocarboxylate
was recently determined in water as 5.80, and Kenol for
the ester was estimated to be 4 orders of magnitude
higher than that of the oxygen analogsmethyl fluorene-
9-carboxylate.25 This estimation is lower than in our
case, but the systems and solvents are sufficiently
different so that further discussion is unwarranted.
Th ioen ol-DMSO Associa tion . Whereas hydrogen
bond association of alcohols ROH with hydrogen bond
acceptors were extensively investigated,26 the corre-
sponding associations of thiols were much less investi-
gated. The lower boiling points of thiols as compared to
those of the analogous alcohols indicate that the associa-
tion is much weaker in RSH compared with ROH.27
The weak hydrogen bonds of thiols may be studied by
IR and NMR techniques. Kassoc values for association of
PhSH with various solvents in CCl4 at 26 °C range from
that the value for Ph2CdC(OH)Ph is close to 3 L mol-1
.
Consequently, the Kassoc of the thiol 12 is ca. 35 times
lower than that for the oxygen analog. The fraction of
associated thioenol (0.62) is much lower than those of the
triarylethenols (0.99).19c
Sid e P r od u cts fr om Dip h en yla ceta ld eh yd e. Nei-
ther diphenylethanethial nor its thioenol 15 were ob-
tained from Ph2CHCHO and 14. However, formation of
sulfide 16 and the heterocyclic compound 17 (eq 6) can
be accounted for by an initial reaction of diphenylacetal-
dehyde with 14 to give the corresponding thioaldehyde,
which immediately tautomerizes to 15. Reaction of 15
with the thioaldehyde, loss of H2S, and ketonization can
account for formation of 16, but the details of the process
are unknown. Likewise, Lawesson and co-workers29 had
observed that 2-R-cyclohexanones (R ) Me, Ph) gave with
14 the thioketones/thioenols, which after a few days gave
the bis(2-R-cyclohexen-1-yl) sulfides. The suggested
mechanism of nucleophilic attack of the thioenol on the
thioketone followed by a loss of H2S (eq 14) was proposed
earlier30 as a route for addition of thioenols to ketones.
0.039 (with C6H6) to 0.43 (with (n-Bu)3P)O) L mol-1 28a
.
Miller et al. determined thermodynamic parameters for
the association of aliphatic thiols with various solvents.28b
However, no analogous study on thioenols is available.
The main conclusion from Tables 3 and 4 is that the
solvent-dependent shift of δ(SH) is due to hydrogen
bonding association of the S-H bond with the solvent.
From the approximate linear correlation between δ(SH)
for 12 and δ(OH) for 20 (the latter being linear with δ-
(OH) values of other polyarylethenols)15 the two associa-
tion processes seem similar. Since the conformation of
the CdCsOsH moiety of 20 was deduced from the
3J HCOH values to be anti-clinal in hydrogen-bonding
solvents, syn-planar in non-hydrogen-bonding solvents,
and mixture of the two conformers in solvents of inter-
mediate â16 we assume without further evidence an
exclusive syn conformation of 12 in CCl4 and an equilib-
rium between the anti (clinal) conformation and the syn
conformation in the other solvents.
Ph
CH
Ph
O
Ph
CH
Ph
S
Ph
SH
–H2S
14
C
C
C
C
H
H
Ph
H
C
Ph
Ph
Ph
Ph
S
C
C
C
(14)
H
H
16
Trithiophosphorinane analogs of 17 from reaction of
14 and cycloalkanones were previously formed. Lawes-
son has suggested that 14 decomposes in solution to two
thionophosphine sulfide molecules 21.31 In our reaction
21 could react either with two molecules of 15 in a
concerted [2 + 2 + 2] cycloaddition (eq 15) or with one
S
S
+ S–
P
S
2 MeO
P
2 MeO
14
The Kassoc value for 12 with DMSO (0.087 L mol-1) is
of the same order of magnitude as the very few Kassoc
values available for the aliphatic and aromatic thiols. For
n-BuSH and t-BuSH, Kassoc values with DMSO are 0.17
21
(15)
Ph2HC
S
C
H
S
S
CH
S
S
S
Ph2HC
[2 + 2 + 2]
P
OMe
S
P
CH
Ph2HC
S
CH
(22) Chiang, Y.; Kresge, A. J .; Walsh, P. A.; Yin, Y. J . Chem. Soc.,
Chem. Commun. 1989, 869.
(23) Nugiel, D. A.; Rappoport, Z. J . Am. Chem. Soc. 1985, 107, 3669.
(24) Chiang, Y.; Hojatti, M.; Keeffe, J . R.; Kresge, A. J .; Schepp, N.
P.; Wirz, J . J . Am. Chem. Soc. 1987, 109, 4000.
CHPh2
17
OMe
(25) Chiang, Y.; J ones, J ., J r.; Kresge, A. J . J . Am. Chem. Soc. 1994,
116, 8358.
thioaldehyde molecule followed by reaction of the formed
zwitterion with a second thioaldehyde molecule (eq 16).
(26) Rochester, C. H. In The Chemistry of the Hydroxyl Group; Patai,
S., Ed.; Wiley: Chichester, 1971; Chapter 7, pp 327-392.
(27) Crampton, M. R. In The Chemistry of the Thiol Group; Patai,
S., Ed.; Wiley: Chichester, 1974; Chapter 8, pp 379-415.
(28) (a) Mathur, R.; Becker, E. D.; Bradley, R. B.; Li, W. C. J . Phys.
Chem. 1963, 67, 2190. (b) Hu, S. J .; Goldberg, E.; Miller, S. I. Org.
Magn. Reson. 1972, 4, 683.
(29) Scheibye, S.; Shabana, R.; Lawesson, S.-O.; Roemming, C.
Tetrahedron 1982, 38, 993.
(30) Campaigne, E.; Moss, R. D. J . Am. Chem. Soc. 1954, 76, 1269.
(31) Campaigne, E. In The Chemistry of the Carbonyl Group; Patai,
S., Ed.; Wiley: Chichester, 1966; Chapter 17, pp 917-959.

Triphenylethenethiol
J . Org. Chem., Vol. 61, No. 16, 1996 5467
petroleum ether:ether as eluent. The triphenylethenethiol
obtained (130 mg, 46%) was identical with the product
obtained by method a.
S
S–
Ph2HC CH
Ph2CH( S)H
Ph2HC
C
H
(16)
17
S
+
P
2,2-Dip h en yl-1-a n isyleth en eth iol (13). A mixture of 2,2-
diphenyl-1-anisylvinyl bromide (0.95 g, 2.6 mmol) and Mg (0.07
g, 2.7 mmol) in dry THF (20 mL) was refluxed for 5 h. Sulfur
(65 mg, 0.25 mmol) was added, and the mixture was refluxed
for an additional 2 h. After addition of 10% H2SO4 solution
(20 mL) at 0 °C, the phases were separated, the organic phase
was dried (MgSO4), and the ether was removed, leaving 2,2-
diphenyl-1-anisylethenethiol (13) (0.35 g, 55%). Crystalliza-
tion from CHCl3 gave 13, mp 109 °C.
S
S
S
An
P
An
The Cambridge Structural Database contains only one
trithiaphosphorinane structure that was determined by
X-ray diffraction, i.e., 2-(p-methoxyphenyl)-4,6-bis(pen-
tafluorophenyl)-1,3,5,2-trithia 2-thiophosphorinane.32 It
has a chair conformation with P-S bond lengths of
2.102-2.117 Å, C-S bond lengths of 1.816-1.851 Å, PdS
bond length of 1.937 Å, and S-P-S and P-S-C bond
angles of 103.9° and 96.4-98.2°, respectively. The
structure of 17 resembles this structure.
Microanalysis: C, 78.98; H, 5.62. Anal. Calcd for C21H18
OS: C, 79.24; H, 5.65.
-
MS m/z (relative abundance, assignment): 318 (100, M+),
285 (7, M - SH), 254 (5, C20H14), 239 (9, C15H11OS), 165 (12,
C13H9), 151 (97, AnCdS+), 108 (5, AnH), 77 (5, C6H5).
IR νmax(Nujol): 2578 (SH), 1604 (CdC) cm-1
.
1H NMR (CDCl3) δ: 3.27 (1H, s, SH), 3.77 (3H, s, OCH3),
6.87-6.91 (10H, m, PhH), 6.73 (2H, d, AnH), 7.02 (2H, d, AnH).
13C NMR (CDCl3) δ: 55.17 (OCH3), 113.53 (CAn), 125.95,
127.57, 128.66, 130.29, 130.46, 130.86 (CAr), 130.41 (CdC),
134.36 (CdC), 136.62, 141.97, 143.30 (CAr), 158.80 (COMe).
(b) A solution containing 2,2-diphenyl-1-anisylethanone
(0.38 g, 1.3 mmol) and Lawesson’s reagent (0.55 g, 1.35 mmol)
in toluene (15 mL) was refluxed for 48 h under nitrogen. After
being cooled to rt and absorbed on silica, the mixture was
chromatographed on a dry silica column using 95:5 petroleum
ether: ether as eluent. The 2,2-diphenyl-1-anisylethenethiol
obtained (0.14 g, 34%) has spectral properties identical with
those of the sample obtained above.
Exp er im en ta l Section
Gen er a l Meth od s. Melting points are uncorrected. For
X-ray diffraction Mo KR (λ ) 0.170 69 Å) radiation with a
graphite crystal monochromator in the incident beam was
used. All crystallographic computing was done on a VAX 9000
computer using the TEXSAN structure analysis software.
Solven ts a n d Ma ter ia ls. Ether, THF, hexane, benzene,
and toluene were kept over metallic sodium, distilled, and used
immediately. Pyridine was kept over KOH and distilled before
use. Commercial DMSO-d6 (Aldrich) was used without further
purification. Lawesson’s reagent and diphenylacetaldehyde
were purchased from Aldrich. Triphenylvinyl bromide, mp
114-5 °C, was prepared according to Koelsch.33 Triphenyl-
ethanone, mp 37 °C,34 was prepared by a Grignard reaction of
diphenylketene with PhMgBr. 2,2-Diphenyl-1-anisylethanone
(mp 130 °C) was prepared by a modification of the reaction
for the preparation of the mesityl analog.35 1-Anisyl-2,2-
diphenylvinyl bromide, mp 137-139 °C, was prepared accord-
ing to Gal.36
Rea ction of Dip h en yla ceta ld eh yd e w ith La w esson ’s
Rea gen t. A solution containing diphenylacetaldehyde (5 mL,
28 mmol) and Lawesson’s reagent (8.5 g, 21 mmol) in toluene
(40 mL) was refluxed for 21 h under nitrogen. The green oil
obtained after evaporation of the solvent was chromatographed
on a silica column using 80:20 ether:CH2Cl2 eluent. Two
products were separated.
(a ) Bis(2,2-d ip h en ylvin yl) Su lfid e (16). Crystallization
from petroleum ether (60-80 °C) gave 0.93 g (17%) of the
yellow sulfide, mp 116-117 °C.
Tr ip h en yleth en eth iol (12). (a) To a solution of triphen-
ylvinyl bromide (4 g, 12 mmol) in dry ether (70 mL) were added
magnesium turnings (0.4 g, 16 mmol) and a crystal of iodine.
The mixture was refluxed for 6 h, during which time most of
the magnesium had disappeared. Sulfur (0.4 g, 1.5 mmol) was
then added, and the mixture was refluxed for an additional 2
h. A dilute H2SO4 solution (50 mL) was then added, the
mixture was cooled to 0 °C, the aqueous and the organic phases
were separated, the organic phase was dried (MgSO4) and
filtered, and the ether was removed, leaving a yellow solid.
Crystallization from benzene gave triphenylethenethiol (2.3
g, 48%), mp 110-112 °C (lit.13 mp 110-111 °C).
MS m/z (relative abundance, assignment): 390 (100, M+),
313 (3, M - Ph), 210 (14, Ph2CdCdS), 178 (56, C14H10), 165
(41, C13H9), 134 (6, C8H6S), 102 (8, C8H6), 77 (23, C6H5).
IR νmax(Nujol): 1598 (CdC) cm-1
.
1H NMR (CDCl3) δ: 6.81 (2H, s, CdCH), 7.18-7.40 (20H,
m, PhH).
13C NMR (CDCl3) δ: 124.53 (CdCS), 127.18, 127.23, 127.66,
128.27, 128.38, 129.67, 138.94, 139.88 (CPh), 141.67 (PhCd).
Microanalysis: C, 85.98; H, 5.80; S, 7.81. Anal. Calcd for
C28H22S: C, 86.11; H, 5.68; S, 8.21.
(b ) 1-(p -Met h oxyp h en yl)-2,4,6-t r it h ia -1-p h osp h a -3,5-
bis(d ip h en ylm eth yl)-1-th iocycloh exa n e (17). Crystalliza-
tion from a 4:6 CH2Cl2:petroleum ether mixture gave white
crystals of 17, mp 200-202 °C (0.17 g, 2%).
MS m/z (relative abundance, assignment): 212 (100, Ph2-
CHCHS), 197 (10), 178 (42, C14H10), 165 (26, C13H9), 152 (13,
C12H8), 134 (16, C8H6S), 121 (16), 89 (15, C7H5), 77 (14, C6H5).
MS m/z (relative abundance, assignment): 288 (100, M+),
253 (7, C20H13), 165 (10, C13H9), 121 (41, PhCdS+).
IR νmax(Nujol): 2562 (SH), 1607 (CdC), 1589 (CdC) cm-1
.
1H NMR (CDCl3) δ: 3.28 (1H, s, SH), 6.89-7.42 (15H, m,
PhH).
13C NMR (CDCl3) δ: 126.13 (CdC), 127.36, 127.46, 127.59,
128.20, 128.67, 129.56, 129.83, 130.37, 130.53 (Ph-C), 137.28
(CdC), 141.69, 142.24, 142.98 (CPh).
Microanalysis: C, 82.80; H, 5.17; S, 9.53. Anal. Calcd for
C20H16S: C, 83.29; H, 5.17; S, 11.11.
Crystallographic data: space group Pna2, a ) 9.305(2) Å, b
) 19.351(3) Å, c ) 8.592(1) Å, V(Å3) ) 1563.1(5), Z ) 4, Fcalcd
) 1.23 g cm-3, µ (Cu KR) ) 16.94 cm-1, R ) 0.033, Rw ) 0.051.
(b) Triphenylethanone (0.35 g, 3 mmol) and Lawesson’s
reagent (0.55 g, 1.4 mmol) were dissolved in toluene (15 mL),
the solution was refluxed under nitrogen, and the progress of
the reaction was followed by TLC. After 50 h, when no more
changes were observed, the mixture was cooled, absorbed on
a dry silica column, and then chromatographed using 95:5
IR νmax(Nujol): 1595 (CdC) cm-1
.
1H NMR (CDCl3) δ: 3.85 (3H, s, OCH3), 4.52 (2H, d, Ph2-
CH), 6.07 (2H, dd, CHS2), 6.89 (2H, dd, AnH). 7.23-7.31 (10H,
m, PhH), 8.04 (2H, dd, AnH).
13C NMR (CDCl3) δ: 55.58 (OCH3), 56.91 (CHS2, d, J ) 7.2
Hz), 59.57 (Ph2CH), 114.37 (m-AnH, d, J ) 13 Hz), 122.5 (p-
CAn, d, J ) 100 Hz), [127.19, 127.35, 128.40, 128.52, 128.95]
(CPh), 133.73 (o-AnH, d, J ) 14 Hz), 139.50, 139.99 (CPh),
164.08 (COMe).
Microanalysis: C, 67.12; H, 5.15. Anal. Calcd for C35H31
OPS4: C, 67.02; H, 4.98.
-
Crystallographic data: space group P21/n, a ) 13.492(1) Å,
b ) 19.837(2) Å, c ) 11.897(1) Å, â ) 92.95(1)°, V(Å3) ) 3179.9-
(7), Z ) 4, Fcalcd ) 1.31 g cm-3, µ(Cu KR) ) 33.88 cm-1, R )
0.032, Rw ) 0.050.
(32) Hasserodt, J .; Pritzkow, H.; Sundermeyer, W. Chem. Ber. 1993,
126, 1701.
(33) Koelsch, C. F. J . Am. Chem. Soc. 1952, 74, 2047.
(34) Ley, H.; Manecke, W. Ber. 1923, 56B, 777.
(35) Fuson, R. C.; Rachlin, A. I. J . Am. Chem. Soc. 1946, 68, 343.
(36) Rappoport, Z.; Gal, A. J . Am. Chem. Soc. 1969, 91, 5246.
Ack n ow led gm en t. We are indebted to Professor S.
E. Biali for helpful discussions.
J O9604651