Discovery of practical production processes for arylsulfur pentafluorides and their higher homologues, bis- and tris(sulfur pentafluorides): Beginning of a new era of "super-trifluoromethyl" arene chemistry and its industry

Article abstract of DOI:10.3762/bjoc.8.53

Various arylsulfur pentafluorides, ArSF₅, have long been desired in both academic and industrial areas, and ArSF₅ compounds have attracted considerable interest in many areas such as medicines, agrochemicals, and other new materials, since the highly stable SF5 group is considered a "super-trifluoromethyl group" due to its significantly higher electronegativity and lipophilicity. This article describes the first practical method for the production of various arylsulfur pentafluorides and their higher homologues, bis- and tris(sulfur pentafluorides), from the corresponding diaryl disulfides or aryl thiols. The method consists of two steps: (Step 1) treatment of a diaryl disulfide or an aryl thiol with chlorine in the presence of an alkali metal fluoride, and (step 2) treatment of the resulting arylsulfur chlorotetrafluoride with a fluoride source, such as ZnF2, HF, and Sb(III/V) fluorides. The intermediate arylsulfur chlorotetrafluorides were isolated by distillation or recrystallization and characterized. The aspects of these new reactions are revealed and reaction mechanisms are discussed. As the method offers considerable improvement over previous methods in cost, yield, practicality, applicability, and large-scale production, the new processes described here can be employed as the first practical methods for the economical production of various arylsulfur pentafluorides and their higher homologues, which could then open up a new era of "super-trifluoromethyl" arene chemistry and its applications in many areas.

Full text of DOI:10.3762/bjoc.8.53

Discovery of practical production processes for
arylsulfur pentafluorides and their higher
homologues, bis- and tris(sulfur pentafluorides):
Beginning of a new era of “super-trifluoromethyl”
arene chemistry and its industry
Teruo Umemoto*§, Lloyd M. Garrick§ and Norimichi Saito§
Full Research Paper
Open Access
Address:
Beilstein J. Org. Chem. 2012, 8, 461–471.
IM&T Research, Inc./Ube America Inc., 6860 N. Broadway, Suite B,
Denver, Colorado 80221, USA
doi:10.3762/bjoc.8.53
Received: 09 November 2011
Accepted: 29 February 2012
Published: 29 March 2012
Email:
Teruo Umemoto* - teruoumemoto@comcast.net
* Corresponding author
Associate Editor: D. O'Hagan
§ Currently: Ube America Inc.
© 2012 Umemoto et al; licensee Beilstein-Institut.
License and terms: see end of document.
Keywords:
arylsulfur chlorotetrafluoride; arylsulfur pentafluoride;
pentafluorosulfanyl; sulfur pentafluoride; super-trifluoromethyl
Abstract
Various arylsulfur pentafluorides, ArSF5, have long been desired in both academic and industrial areas, and ArSF5 compounds have
attracted considerable interest in many areas such as medicines, agrochemicals, and other new materials, since the highly stable SF5
group is considered a “super-trifluoromethyl group” due to its significantly higher electronegativity and lipophilicity. This article
describes the first practical method for the production of various arylsulfur pentafluorides and their higher homologues, bis- and
tris(sulfur pentafluorides), from the corresponding diaryl disulfides or aryl thiols. The method consists of two steps: (Step 1) treat-
ment of a diaryl disulfide or an aryl thiol with chlorine in the presence of an alkali metal fluoride, and (step 2) treatment of the
resulting arylsulfur chlorotetrafluoride with a fluoride source, such as ZnF2, HF, and Sb(III/V) fluorides. The intermediate aryl-
sulfur chlorotetrafluorides were isolated by distillation or recrystallization and characterized. The aspects of these new reactions are
revealed and reaction mechanisms are discussed. As the method offers considerable improvement over previous methods in cost,
yield, practicality, applicability, and large-scale production, the new processes described here can be employed as the first practical
methods for the economical production of various arylsulfur pentafluorides and their higher homologues, which could then open up
a new era of “super-trifluoromethyl” arene chemistry and its applications in many areas.
Introduction
Pentafluorosulfanyl (SF5) is considered a “super-trifluoro- (ArSF5) are very thermally and chemically stable [2].
methyl group” as SF5 has the peculiarity of fluorine beyond a Pioneering work by Sheppard half a century ago on the syn-
trifluoromethyl (CF3) group [1]. Arylsulfur pentafluorides thesis and properties of arylsulfur pentafluorides revealed that
461

Beilstein J. Org. Chem. 2012, 8, 461–471.
the SF5 group has absolutely unique properties [2,3]. SF5 is and reduction with zinc, giving pentafluorosulfanylacetylene
more electronegative (Hammet constants σI: +0.55 for SF5; (HC≡CSF5), which was then reacted with butadiene, followed
+0.39 for CF3) [2] and more lipophilic than CF3 (Hansch by an aromatization reaction at very high temperature, gave
hydrophobicity constants π: 1.51 for SF5; 1.09 for CF3) [4]. The phenylsulfur pentafluoride [35]. Recently, phenylsulfur penta-
high electronegativity results in high polarity in molecules. fluoride was prepared by reaction of 1,4-bis(acetoxy)-2-cyclo-
Thus, it is of significant note that there is no functional group hexene with SF5Br under 250 W sunlamp irradiation, followed
other than SF5 that has both high electronegativity and high by dehydrobromination and then aromatization reactions [36].
lipophilicity, because the two natures are generally in conflict. A triethylborane-catalyzed reaction of 4,5-dichloro-1-cyclo-
In addition, SF5 has high hydrolytic stability, which equals or hexene with SF5Cl followed by dehydrochlorination has also
exceeds CF3 [2]. These extraordinary properties render SF5 been reported [37]. The multistep method has recently been
compounds highly attractive particularly in medicinal [5-14], extended to the preparation of 2-naphthylsulfur pentafluoride
agrochemical [15-18], and new material [19-23] chemistry and and heteroarylsulfur pentafluorides [22,38-41].
industry. However, there have been no practical, economical
methods for the production of arylsulfur pentafluorides. In com- 5-Nitrophenyl-1,3-bis(sulfur pentafluoride) was prepared by
parison, trifluoromethyl arenes (ArCF3) have grown into a reaction of the corresponding polymeric disulfide with AgF2 in
significantly large field in chemistry and industry since their 12% yield [3]. Two isomers of phenyl tris(sulfur pentafluorides)
practical two-step production method was developed in the were synthesized by many steps starting from the reaction of
1930s through to the 1940s. The first step was chlorination of SF5Cl with acetylene via HC≡CSF5 [42]. Complex
ArCH3 to ArCCl3 with Cl2 and the second step was its conver- Co(CO)4(HC≡CSF5) derived from HC≡CSF5 and Co2(CO)8
sion to ArCF3 with HF or SbF3 [24-26]. A large number of tri- was decomposed in the presence of Br2 to give phenyl-1,2,4-
fluoromethyl arenes are currently produced on a large scale and tris(sulfur pentafluoride). Photoreaction of HC≡CSF5 in the
used in many areas such as medicines, agrochemicals, dyes, ma- presence of SF5Cl gave phenyl-1,3,5-tris(sulfur pentafluoride),
terials for electronics, and others [27-30]. Accordingly, many but in low yield (19%) [42].
chemists have long desired to have easy access to the “super-tri-
fluoromethyl” arenes; however, there have been no economical All of the previous methods described above suffer from
methods for their production until now.
multiple drawbacks of low yields, the necessity of costly and
dangerous fluoro-reagents, and the quite limited scope and ap-
In 1961, Sheppard first reported the synthesis of phenylsulfur plicability. In response to these, we now report practical, inex-
pentafluoride by stepwise fluorination of diphenyl disulfide pensive, and widely applicable methods suitable for the large-
with expensive silver difluorides (AgF2) in a fluorocarbon scale production of arylsulfur pentafluorides and their higher
solvent [3]. However, the yield was only 9%. Since then, many homologues, which have the potential to open up a new era of
substituted phenylsulfur pentafluorides have been prepared by sulfur pentafluoride chemistry and its industry. These new
this method, but still with very low yields [3,20,31,32]. In 2000, methods have been described in patents and patent applications
a new method using molecular fluorine (F2) was reported [33]. [43-48].
Thus, bis(p- or m-nitrophenyl) disulfide was treated with F2
diluted with nitrogen (F2:N2 = 1:9 v/v) at low temperature in Results and Discussion
acetonitrile to give the nitrophenylsulfur pentafluoride in ca. Recently we synthesized various arylsulfur trifluorides (ArSF3)
40% yield. However, in addition to the low yields, this method by treatment of diaryl disulfides with chlorine in the presence of
requires F2, which is a highly toxic, corrosive and explosive potassium [49,50] or cesium fluoride [50] and thus discovered
gas, and it applies only for the case of electron-deficient nitro- 4-tert-butyl-2,6-dimethylphenylsulfur trifluoride (Fluolead
phenylsulfur pentafluorides, due to the extremely high reactiv- reagent) as an excellent fluorinating agent with high thermal
ity of F2. These factors significantly limited the scope and stability, ease of handling, and wide applicability [50,51].
application of this method. Another method reported used During the research, we unexpectedly discovered that an aryl-
expensive xenon difluoride to fluorinate diphenyl disulfide sulfur chlorotetrafluoride (ArSF4Cl) is formed when a diaryl
giving phenylsulfur pentafluoride, but its yield was only 25% disulfide is treated with an excess of chlorine in the presence of
[34].
an excess of the alkaline metal fluoride. Janzen et al. reported
that cis- and trans-phenylsulfur chlorotetrafluoride and its
Multiple-step methods have previously been developed for the p-methyl- and p-nitro-derivatives were formed by reaction of
preparation of arylsulfur pentafluorides. In 1964, it was reported diaryl disulfide with XeF2 and tetraethylammonium chloride
that the reaction of sparsely available and toxic gaseous SF5Cl [52]. However, the physical properties of the arylsulfur chloro-
with acetylene, followed by bromination, dehydrobromination, tetrafluorides were not determined since they were not isolated,
462

Beilstein J. Org. Chem. 2012, 8, 461–471.
presumably because the chlorotetrafluorides were considered to
be unstable. Instead, their chemical structures were assigned by
19F- and 13C NMR spectroscopy of the reaction solution.
Arylsulfur chlorotetrafluorides were prepared in high yield by
the reactions of diaryl disulfides with an excess amount of
chlorine (ca. 7 mol or more per mole of the disulfide) in the
presence of an excess amount of potassium or cesium fluoride
(ca. 16 mol or more per mole of the disulfide) in dry acetoni-
trile at ice-bath temperature to room temperature. Although
conventionally dried and powdered potassium fluoride can be
used satisfactorily, spray-dried potassium fluoride, having a
large surface area, is preferable. The normal dry potassium fluo-
ride must be used in greater quantities than the spray-dried
potassium fluoride. When the reaction is not taken to comple-
tion, the distilled product (ArSF4Cl) is contaminated with its
Scheme 1: Preparation of ArSF4Cl 2.
intermediate ArSF3. By this method, many arylsulfur chloro- methanesulfonyl group, were prepared in good to high yields
tetrafluorides 2a–o having different substituents on the aromatic from the corresponding diaryl disulfides. 2-Fluoro and 2,6-
ring were prepared, as summarized in Scheme 1 and Table 1. difluorophenylsulfur chlorotetrafluoride were formed in high
The products were trans isomers, except for in the case of poly- yields due to the small steric effect of fluorine atom(s).
fluorinated arylsulfur chlorotetrafluorides, which formed a mix- However, bis(2-bromophenyl) disulfide gave a 11:1 mixture of
ture of trans and cis isomers. The products were distilled under 2-bromophenylsulfur trifluoride and chlorotetrafluoride.
reduced pressure or crystallized and then characterized.
2-Bromophenylsulfur chlorotetrafluoride was a minor product
due to the steric hindrance of the relatively large bromo
Arylsulfur chlorotetrafluorides having an electron-donating substituent at the ortho position. Arylsulfur chlorotetrafluorides
alkyl group, such as methyl or tert-butyl, or an electron-with- were also prepared from the corresponding aryl thiols in high
drawing substituent, such as a halogen atom, a nitro-, or a yields, as shown in runs 2 and 4, Table 1.
Table 1: Preparation of arylsulfur chlorotetrafluorides 2a–o.
runa
ArSSAr or ArSH (mmol)b
Cl2c
MFd
ArSF4Cle
conditionsf
yield (%)g
1
1a (150)
C6H5SH (91)
1b (500)
p-(t-Bu)C6H4SH (60)
1d (39)
≈8
KF (16)
KF (9)
2a (t)
ice bath, 9.5 h
88
83
73
84
67
80
88
77
86
60
97h
82
80
87
83
86
2
4.9
7.7
7.5
7.2
8
2a (t)
6–10 °C, 6.5 h
3
KF (16)
CsF (10)
KF (16)
KF (16)
KF (17)
KF (16)
KF (15.7)
KF (16)
KF (40)
CsF (18)
KF (22)
KF (24)
KF (19)
KF (22)
2b (t)
ice bath, 10.5 h
4
2c (t)
5–10 °C, 3.5 h to rt, 24 h
ice bath, 2.5 h to rt, o.n.
ice bath, 2.5 h to rt, o.n.
5–8 °C, 3.5 h
5
2d (t)
6
1e (39)
2e (t)
7
1f (87)
6.6
7.2
6.9
7.2
27
10
16
16
15
15
2f (t)
8
1g (100)
1h (127)
1i (100)
2g (t)
ice bath, 4.5 h to rt, o.n.
ice bath, 5.5 h to rt, o.n.
ice bath, 4.5 h to rt, o.n.
rt, 3 d
9
2h (t)
10
11
12
13
14
15
16
2i (t)
1j (26)
2j (t)
1k (100)
1l (130)
2k (t/c = 92/8)
2l (t/c = 89/11)
2m (t/c = 96/4)
2n (t/c = 86/14)
2o (t/c = 60/40)
ice bath, 5 h to rt, o.n.
ice bath, 6 h to rt, o.n.
ice bath, 6 h to rt, o.n.
ice bath, 7.5 h to rt, o.n.
ice bath, 5 h to rt, o.n.
1m (77)
1n (70)
1o (65)
aThe experimental procedure is described in the Supporting Information File 1. bThe number in parentheses is the amount (mmol) of ArSSAr or ArSH
used. cMolar ratio of Cl2 per mole of ArSSAr or ArSH. dThe number in parentheses is molar ratio of MF per mole of ArSSAr or ArSH. et = trans-
isomer, c = cis-isomer. The t/c ratio was determined by 19F NMR of the reaction mixture before post-treatment. frt = room temperature, o.n. =
overnight. gIsolated yields. hCrude product.
463

Beilstein J. Org. Chem. 2012, 8, 461–471.
The method using aryl thiols as starting materials was success- Scheme 3 shows a postulated reaction mechanism, which
fully applied to the preparation of aryl bis- and tris(sulfur consists of six steps including intermediates 4, 5, 6, 7 and 8.
chlorotetrafluorides) as shown in Scheme 2 and Table 2. The Treatment of p-nitrophenylsulfenyl chloride with Cl2/KF gave
method using the corresponding polymeric disulfides did not p-nitrophenylsulfur chlorotetrafluoride in 76% yield. Treatment
work well because of their extremely low solubility.
of phenylsulfur trifluoride with Cl2/KF gave phenylsulfur
chlorotetrafluoride in 84% yield. These results support the
hypothesis that arylsulfenyl chloride 4 and trifluoride 7 are
intermediates for the reaction of diaryl disulfide giving aryl-
sulfur chlorotetrafluoride.
In a typical reaction of diphenyl disulfide, an orange color
appears immediately as chlorine (Cl2) gas is introduced into a
mixture of Ar2S2 and KF in acetonitrile. Cl2 is absorbed as fast
as it is introduced until ArSF3 7 is formed, at which point the
solution becomes colorless. 19F NMR analysis of the reaction
mixture at this moment confirms the formation of 7. After that,
the absorption of Cl2 becomes slow. Thus, the sequence of steps
1 to 4 giving 7 is fast, while the sequence of steps 5 and 6
giving the final product 2 is slow. The slow reaction is prob-
ably due to an equilibrium reaction (step 5) between 7 and 8.
The reaction of aryl thiol as a starting material is similar to that
Scheme 2: Preparation of Ar(SF4Cl)n from Ar(SH)n (n = 2, 3).
The reaction of a diaryl disulfide with Cl2 and KF is given as of the disulfide 1 since aryl thiol reacts with Cl2 to form disul-
Equation 1. Per 1 mol of a diaryl disulfide, 5 mol of Cl2, and fide 1.
8 mol of KF are theoretically consumed.
The arylsulfur chlorotetrafluorides 2a–j and bis(sulfur chloro-
(1)
tetrafluorides) 2p′ and 2q′ obtained were trans-isomers, while
Table 2: Preparation of aryl bis- and tris(sulfur chlorotetrafluorides) 2p'–u'.
runa
Ar(SH)n (mmol)b
Cl2c
KFd
Ar(SF4Cl)ne
conditionsf
yield (%)g
1
2
3
4
5
6
1p (68.7)
1q (64)
1r (80)
1s (63)
1t (64)
18
20
23
20
20
40
25
47
38
20
27
60
2p′ (t)
ice bath, 6 h to rt, 2 d
ice bath, 6 h to rt, 2 d
rt, 2 d
56
2q′ (t)
74
2r′ (t/c = 89/11)
2s′ (t/c = 95/5)
2t′ (t/c = 58/42)
2u′ (t/c = 79/21)
96h
52
ice bath, 7 h to rt, o.n.
ice bath, 7 h to rt, o.n.
rt, 3 d
79
1u (57)
98h
aThe experimental procedure is described in the Supporting Information File 1. bThe number in parentheses is the amount (mmol) of Ar(SH)n used.
cMolar ratio of Cl2 per mole of Ar(SH)n. dMolar ratio of KF per mole of Ar(SH)n. et = trans-configuration, c = cis-configuration. The t/c ratio was deter-
mined by 19F NMR of the reaction mixture or crude product. frt = room temperature, o.n. = overnight. gIsolated yields. hCrude product.
Scheme 3: Reaction mechanism for the formation of ArSF4Cl.
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Beilstein J. Org. Chem. 2012, 8, 461–471.
the polyfluorinated 2k–o, bromo and polyfluoro bis(sulfur 2a decomposed in 1 h and the decomposition product was
chlorotetrafluorides) 2r′–t′, and tris(sulfur chlorotetrafluoride) phenylsulfonyl chloride. Phenylsulfonyl fluoride was detected
2u′ were a mixture of trans- and cis-configuration. Since we did in a trace amount (≤1%) by GC–mass analysis.
not observe any isomerization at room temperature or upon dis-
tillation, it is reasonable to conclude that each isomer was Arylsulfur chlorotetrafluorides 2 have relatively high thermal
formed through each isomeric salt of 8 as shown in Scheme 4. stability. Thus, 2a did not decompose during 134 hours at
The multifluoro derivatives 2o and 2t′ have the highest ratio of 100 °C or 48 h at 150 °C in a Teflon tube. The isomerization of
cis-configuration. This suggests that the relative stability of the the trans- to the cis-isomer occurred very slowly. A very small
cis-isomeric salts 8 increases particularly with increased fluo- amount (3–4%) of the cis-isomer was formed after heating of 2a
rine substitution. The high ratio of cis-configuration of 2u′ (trans-isomer) at 150 °C for 48 h. The real thermal decomposi-
suggests the ability of electron-withdrawing groups, such as tion temperatures of 2 could not be determined by a differential
–SF4Cl, to stabilize the cis-configuration salt form.
scanning calorimeter (DSC), because 2 reacted with the cell ma-
terials, i.e., stainless steel and gold, at elevated temperature due
to their strongly oxidizing effect on the hexavalent sulfur(VI)
element. Many arylsulfur chlorotetrafluorides were measured
with DSC and these are discussed in Supporting Information
File 1.
We examined reaction conditions for the conversion of trans-
PhSF4Cl (2a) to PhSF5 (3a) with various reactive fluorides
using an approximately one-gram scale of 2a, as seen in
Table 3. Janzen et al. described in the experimental section that
bubbling an excess of BF3 into a mixture of cis- and trans-2a in
CD2Cl2 at 25 °C led to the gradual disappearance of 2a and the
formation of PhSF5 (3a) [52]. We conducted the reaction of
trans-2a (isolated) with BF3 in a sealed reactor and found that
Scheme 4: Reaction mechanism for the formation of trans and cis-
ArSF4Cl.
It is noticeable that, except for the polyfluorinated compounds all the starting material became a solid residue, probably a
and others discussed above, trans-isomeric ArSF4Cl was exclu- polymer (run 1, Table 3). The reaction in dichloromethane
sively formed by the reactions of Ar2S2 with Cl2/KF, while the solvent resulted in only a 28% yield of 3a (run 2). The use of
reactions of Ar2S2 with XeF2/Et4NCl gave a mixture of cis- and HBF4·OEt2 at room temperature provided a better yield (40%)
trans-isomers according to Janzen's report [52]. Janzen (run 3). A strong Lewis acid SbF5 led to polymeric product, but
proposed radical reactions with Cl· species [52]. The Cl2/KF SbF3 at 80 °C gave 33% (run 4). A combination of SbF3/
reactions are ionic in nature, in which trans-form salts 8 exclu- SbCl5(cat.) at room temperature provided a better yield (54%)
sively form and react with Cl2 to give the trans-isomers.
(run 5). At 80 °C, transition-metal fluorides TiF4 and CuF2
afforded 35 and 57%, respectively (runs 7, 8). Finally, we found
Arylsulfur chlorotetrafluorides are stable during long periods of that inexpensive and easily handled ZnF2 produced 3a in high
storage in a fluoropolymer vessel at room temperature. We did yield (runs 9, 10).
not observe any isomerization between trans- and cis-isomers
on standing. Whereas arylsulfur trifluorides are extremely sensi- A 19F NMR tracing experiment of the conversion reaction of
tive to moisture (water) [50,53], with the exception of the trans-PhSF4Cl (trans-2a) provided some information on the
Fluolead reagent [50], arylsulfur chlorotetrafluorides are rela- reaction mechanism. With HBF4·OEt2, it was observed that the
tively insensitive to moisture. The half life time of decomposi- molar ratio of trans-2a:cis-2a:PhSF5 was 156:172:100 in the
tion of phenylsulfur chlorotetrafluoride (2a) in a CDCl3 solu- reaction mixture after 7 h, and 3:6:100 after 21 h. With ZnF2,
tion (≈1.2 mol/L) on direct contact with water was 300 to the ratio observed was 22:117:100 during the reaction. A
500 min at room temperature. The tracing experiment was considerable amount of the cis-isomer was formed as an inter-
conducted with a NMR tube. The 19F NMR was measured by mediate. It may thus be suggested that there are two routes, a
using an internal standard (p-chlorobenzotrifluoride) and the direct route of the trans-isomers to the SF5 products and an
NMR tube was shaken between the measurements. Gas chroma- indirect route via cis-isomers. The experiment with HBF4·OEt2
tography (GC) could not be used because of decomposition of or ZnF2 may be considered to be thermal isomerization of
arylsulfur chlorotetrafluorides in the GC column. When a few trans-2a to cis-2a with an acid catalyst, suggesting that the cis-
drops of D2O were added to a solution of 2a in CD3CN (1 mL), isomer is more thermodynamically stable than the trans-isomer.
465

Beilstein J. Org. Chem. 2012, 8, 461–471.
Table 3: Conversion of phenylsulfur chlorotetrafluoride (2a) to PhSF5 (3a).
runa
2a (mmol)b
fluoride (mmol)c
solvent (mL)d
temperature (°C) time
yield of 3a (%)e
1
4.5
6.4
4.5
4.5
4.5
4.5
4.5
4.5
4.5
4.5
13.6
BF3f
none
rt
3 d
0
2
BF3f
CH2Cl2 (6.4)
CH2Cl2 (4.5)
none
rt
5 h
28
40
33
54
34
35
57
85
88
53
3
HBF4·OEt2 (5.4)
SbF3 (2.2)
rt
21 h
5 h
4
80
rt
5
SbF3/SbCl5 (2.0/cat.)
SnF4 (1.4)
hexane (2)
none
3 d
6
80
80
80
80
120
rt
2 h
7
TiF4 (1.4)
none
16 h
22 h
20 h
4 h
8
CuF2 (2.8)
none
9
ZnF2 (2.7)
none
10
11
ZnF2 (2.7)
none
ZnF2/SbCl5 (8.2/1.4)
heptane (5)
17 h
aThe experimental procedure is described in Supporting Information File 1. bThe amount (mmol) of 2a used. cThe number in parentheses is the
amount (mmol) of fluoride used. dThe number in parentheses is the amount (mL) of solvent used. eDetermined by 19F NMR. fSee Supporting Informa-
tion File 1 for the amount of BF3 used.
With ZnF2/SbCl5 the cis-isomer was barely detected (run 11,
Table 3). The ratio of trans-2a:cis-2a:PhSF5 was 385:0:100
after 10 min; 63:trace:100 after 1.5 h; 34:trace:100 after 3 h;
and 18:2:100 after 17 h. Thus, the lack of detectable cis-isomer
may suggest that the addition of a strong Lewis acid such as
SbCl5 gives priority to the direct route. However, we cannot
rule out the possibility that the conditions could very quickly
convert the cis-isomer to the product.
The method with ZnF2 was applied to 10–50 gram scale reac-
tions of PhSF4Cl (2a) and its derivatives 2b,d,e–i,k (Scheme 5).
A fluoropolymer reactor charged with the reactants (ArSF4Cl
Scheme 5: Preparation of ArSF5 with ZnF2.
and ZnF2) was heated under the pressure of a balloon filled with
N2 gas (no flow of N2). The reaction conditions and yields are
shown in Table 4. Liquid 2a,b,d–f,h efficiently reacted with minor one, during the reaction. The complete removal of the
solid ZnF2 (powder) under stirring without solvent. The two byproducts from 3f was difficult due to similar boiling points.
fluorine atoms of ZnF2 were effectively consumed for the reac- We found that the byproducts were suppressed by the addition
tion. 2a and monohalogenated 2d–h were converted to the of a strong Lewis acid AlCl3 and that the addition of ZnCl2
corresponding products 3 in good to high yields at 120 °C (bath modified the exothermic reaction of 2f with ZnF2. The addition
temperature). It was observed that the start of the exothermic of AlCl3 decreased the reaction temperature and the addition of
reaction of halogenated 2f was significantly delayed compared ZnCl2 probably helped to form reactive “ZnFCl” species.
to that of unsubstituted 2a. p-Methyl-2b reacted with ZnF2 at Finally the byproduct was restricted to less than 1% with ZnF2/
90 °C (run 2). p-Nitro-2i and 2,6-difluoro-2k required a high ZnCl2/AlCl3 (molar ratio 100:10:5). The detailed experimental
temperature of 150 °C or more and their yields were fair to poor procedure is described in Supporting Information File 1.
(runs 8 and 9). Thus, the electron-donating substituents increase
the reactivity of –SF4Cl, while the electron-withdrawing ones The reaction of PhSF4Cl (2a) with ZnF2 in Table 4 was
decrease it.
conducted under nonflowing N2 gas (under the pressure of a N2
balloon). When the reaction of 2a was conducted under a flow
It was found that the product p-chloro-3f obtained after distilla- of N2 gas, the reaction rate became low. We then examined the
tion (run 5, Table 4) was contaminated (3%) with reaction conditions for 2a in more detail and found that the
p-dichlorobenzene (major) and trichlorobenzene (minor), which reaction was dependent upon the atmosphere of the reaction
were formed by cleavage of the C–S bond, in the case of the mixture. While the reaction conducted under a N2 balloon (no
major byproduct, and further chlorination, in the case of the flow of N2) was completed in 4 h in 88% yield, the reaction
466

Beilstein J. Org. Chem. 2012, 8, 461–471.
Table 4: Preparation of various arylsulfur pentafluorides 3 with ZnF2.
runa
2 (mmol)b
solvent
temp (°C)
time (h)
product 3
yield (%)c
1
2
3
4
5
6
7
8
9
2a (200)
2b (137)
2d (42)
2e (42)
none
120
20
3ad
3be
3df
3e
75
71
62
59
73
79
78
36
52
none
90
overnight
16
none
120
none
120
15
2f (175)
2g (100)
2h (33)
2i (100)
2k (160)
none
120
16
3fd,g
3gd
3hd
3id
heptane (20 mL)
none
reflux
120
17
15
none
150
72
none
130→180
4→6
3k
aThe amount of ZnF2 used was 0.6 mol per 1 mol of 2 in runs 1–4 and 6–8, 0.53 mol in run 5, and 1.06 mol in run 9. The experimental procedure is
described in Supporting Information File 1. bThe number in parentheses is the amount (mmol) of 2 used. cIsolated yields. dSee [2]. eSee [52]. fSee
[54]. gProduct 3f (purity 97%) obtained after distillation was contaminated with 3% of p-dichlorobenzene (major) and trichlorobenzene (minor). Purity
was determined by GC.
conducted under a flow of N2 (through a reactor) was not method was adopted and a small amount of product 3a was
completed in 5 h and its yield was down to 67%. With a faster used as the reaction solvent. This procedure is described in
flow of N2, it became slower and the yield decreased. Appar- Supporting Information File 1.
ently, a small amount of gas was generated at the beginning of
the reaction. The gas was not analyzed because of experimental In contrast, anhydrous hydrogen fluoride (HF) is not easy to
difficulty. Therefore, it was most likely that removal of the gas handle under normal laboratory conditions due to its high toxi-
by the flow of N2 gas made the reaction slow. Surprisingly, city. However, in industry, in addition to its availability as a
when the reactor was filled with Cl2 gas, the reaction was cheap fluorine source, the gaseous or liquid nature of HF (bp
completed in a short time (1.7 h) and its yield was very high 19 °C) is quite suitable for large-scale industrial processes due
(92%). Thus, the presence of Cl2 significantly accelerated the to its ease in transfer, recovery and recycling.
reaction rate and increased the yield. We assumed that one of
the effects of the Cl2 atmosphere may be to inhibit a possible 2a satisfactorily reacted with HF at less than its boiling point to
disproportionation reaction [2PhSF4Cl (2a) → PhSF5 + PhSF3 produce 3a along with the evolution of hydrogen chloride
+ Cl2 ↑], as the disproportionation leads to the formation of Cl2. (Scheme 6). As seen in Table 5, this method has successfully
Although it remains unclear as to why Cl2 accelerated the reac- been applied to various substituted arylsulfur chlorotetra-
tion, Cl2 may also activate ZnF2 or intermediate “ZnFCl” fluorides. The products obtained by the method were of high
species.
purity (≥99%) except for the cases of methyl derivative 2b (runs
4–6). When the reaction of 2a was conducted with the addition
Interestingly, this Cl2 atmosphere was effective for the reaction of KHF2 (KF:HF = 1:1), the yield improved (run 3). KF
of the p-methyl derivative 2b with ZnF2, but not for the suppressed the formation of impurities, such as polymeric
p-chloro derivative 2f. The reaction of 2f with ZnF2 was not residue and chlorinated byproducts, because basic KF neutral-
affected by N2 flow. As it is known that sulfur-related dispro- izes the strong acid HCl formed in the reaction.
portionation, for instance arylsulfinic acid giving arylsulfonic
acid and S-aryl arylthiosulfonate ester, is retarded by an elec-
tron-withdrawing group [55], it may thus be suggested that an
electron-withdrawing substituent limits the disproportionation.
Possibly the electron-withdrawing substituent lowers the dispro-
Scheme 6: Preparation of PhSF5 with anhydrous HF.
portionation rate or increases the temperature necessary for
disproportionation such that it is greater than that required for
the replacement reaction of –SF4Cl to –SF5.
In run 4, the purity of product 3b was 91%, which was contami-
nated with 8% of 3-chloro-4-methylphenylsulfur pentafluoride
The method with easily handled and inexpensive ZnF2 under a (3b·Cl) as the main byproduct. Compound 3b·Cl was tenta-
Cl2 atmosphere was successfully applied to a large-scale tively assigned by GC–mass analysis. When the reaction was
production (≈0.5 kg) of 3a from 2a, in which the addition conducted with the addition of KHF2, the purity greatly
467

Beilstein J. Org. Chem. 2012, 8, 461–471.
Table 5: Preparation of arylsulfur pentafluorides 3 with anhydrous hydrogen fluoride.
runa
ArSF4Cl 2 (mmol)b molar ratio 2/HF/additive
additivec
temperature (°C) time (h)
ArSF5 3
yield (%)d
1
2a (87.1)
2a (152)
2a (96.2)
2b (144)
2b (89.8)
2b (80.8)
2b (91.8)
2d (90.2)
2ej (292)
2f (146)
1/29/–
none
15
−10
15
15
15
15
15
15
19
15
20
20
20
18
19
20
79
17
21
22
20
2 d
3a
3a
3a
3b
3b
3b
3b
3d
3e
3f
62
2
1/24/–
none
66
3
1/25/1.1
1/22/–
KHF2
none
73
4
73e
79f
57g
56h
67
5
1/22/1.2
1/30/0.37
1/23/1.2/0.33i
1/28/-
KHF2
PhH
6
7
KHF2, PhH
none
8
9
1/23/-
none
76h
71
10
11
1/23/-
none
2g (250)
1/32/-
none
3g
77
aThe experimental procedure is described in Supporting Information File 1. bThe number in parentheses is the amount (mmol) of 2 used. cKHF2 =
potassium hydrogen difluoride. PhH = benzene. dIsolated yields after distillation. Purities of the products were >99% except for the cases labeled with
superscripts e, f, g, h. Purity was determined by GC. ePurity was 91%. fPurity was 97%. gPurity was 90%. hPurity was 99%. iMolar ratio: 1/23/1.2/0.33
= 2b/HF/KHF2/PhH. j2e (71 wt %) in CH3CN was used, which was obtained by concentration (with a vacuum pump) of the filtrate of the reaction mix-
ture after completion of reaction of Scheme 1.
increased to 97% (run 5). The occurrence of an intermolecular
side chlorination reaction was clearly demonstrated by the
experiment of run 6 in which benzene was used as an additive.
The distilled product 3b (purity 90%) was contaminated with
Scheme 7: Preparation of 3a with HF–pyridine.
p-dichlorobenzene (6%) and o-dichlorobenzene (3%) in addi-
tion to the byproduct 3b·Cl (1%). The dichlorobenzenes were
formed by chlorination of the added benzene. Chlorobenzene
formed in this reaction was contained in an initial distillation
fraction, which was separated. The method of run 7 using both
KHF2 and benzene as additives provided product 3b with 99%
purity, as the formation of impurity 3b·Cl was completely
suppressed. It is likely that the SF4Cl part of 2b acts as a chlori-
nating agent toward 3b, or another 2b and benzene, under the
strong acidic conditions that are formed from the HCl gener-
ated in the anhydrous HF.
As seen in runs 8–11, halogenated arylsulfur pentafluorides
Scheme 8: Preparation of polyfluorinated ArSF5.
3d–g of high purity (≥99%) were obtained in good isolated
yields without any additive. The side reactions such as polymer-
ization and chlorination are restrained, as the aromatic nuclei and a strong Lewis acid, such as SbF5 or SbCl5, as shown in
are deactivated by the electron-withdrawing effect of the Scheme 8 and Table 6.
halogen atoms.
While treatment of 2,4,6-trifluoro-2m with a mixture of SbF3/
It was also found that when PhSF4Cl (2a) was treated with a SbF5 (4.5/1) gave 77% of product 3m (run 3, Table 6), treat-
70:30 w/w mixture of HF–pyridine at 55 °C, it gave PhSF5 (3a) ment of 2m with SbF5 alone gave a byproduct (20%) in addi-
in 63% isolated yield (Scheme 7). The HF–pyridine reagent is a tion to 3m (60%). The byproduct was tentatively assigned as
nonvolatile and easily handled chemical in the laboratory.
3-chloro-2,4,6-trifluorophenylsulfur pentafluoride by 1H and
19F NMR and GC–mass analysis. The chlorination as a side
Polyfluorinated arylsulfur chlorotetrafluorides 2k–o were reaction may occur from the action of a strong Lewis acid SbF5
smoothly converted to the corresponding sulfur pentafluorides on the fluorine atoms of the SF4Cl group of ArSF4Cl 2m,
3k–o in good yields by treatment with a combination of SbF3 forming a [ArSF3Cl]+ [SbF6]− species (Ar = 2,4,6-trifluoro-
468

Beilstein J. Org. Chem. 2012, 8, 461–471.
Table 6: Preparation of polyfluorinated arylsulfur pentafluorides with Sb(III)/(V) fluorides.
runa 2 (mmol)b
Sb(III)
(mmol)c
Sb(V)
(mmol)c
molar ratio
Sb(III)/Sb(V)
solvent (mL)d temperature (°C) time (h)
3
yield
(%)e
1
2
3
4
5
2k (3.9)
2l (36)
SbF3 (5.7)
SbF3 (39)
SbF3 (121)
SbF3 (145)
SbF3 (32)
SbCl5 (0.4)
SbF5 (9)
14/1
FC-72 (8)
rt
1
3k
3l
71
70
77
61
71
4.3/1
4.5/1
6.5/1
1.05/1
FC-72 (40)
FC-72 (110)
FC-72 (200)
FC-72 (40)
−60 → rt
5
2m (106)
2n (118)
2o (30.3)
SbF5 (26.7)
SbF5 (22.3)
SbF5 (30.4)
−60 → rt
≈5
4.5
1
3m
3n
3o
rt
rt
aThe experimental procedure is described in Supporting Information File 1. bThe number in parentheses is the amount (mmol) of 2 used. cThe
number in parentheses is the amount (mmol) of the Sb halide used. dThe number of parentheses is the amount (mL) of the solvent used. FC-72 is a
perfluorocarbon with bp 56 °C (3M Fluorinert™ Electronic Liquid FC-72, 3M Specialty Materials, St. Paul, MN, USA). eIsolated yields.
phenyl), which may act as a strong chlorinating agent (Cl+)
toward 3m or another molecule of 2m. Pentafluoro-2o was
converted to 3o in good yield with a high molar ratio of SbF5
(run 5) as the reactivity of 2o was considerably decreased by the
five fluorine atoms.
Phenyl bis(sulfur chlorotetrafluorides) 2p′ and 2q′, bromo
derivative 2r′, and fluoro derivatives 2s′ and 2t′ were smoothly
converted to the corresponding bis(sulfur pentafluorides)
3p″–t″ in fair to good yields with SbF5 alone, as shown in
Scheme 9 and Table 7 (runs 1–5). Phenyl tris(sulfur chlorotetra-
fluoride) 2u′ was converted to phenyl tris(sulfur pentafluoride)
Scheme 9: Preparation of aryl bis- and tris(sulfur pentafluorides),
Ar(SF5)n (n = 2,3).
3u″ in 55% yield under similar conditions (run 6, Table 7).
Conclusion
We have developed the first practical and economical method yields. Since these methods are superior to the previous
for the production of various arylsulfur pentafluorides and their methods using AgF2, F2, or XeF2, or multiple-step methods
higher homologues, which consists of the treatment of diaryl starting from SF5Br or SF5Cl, in terms of cost, applicability,
disulfides or aryl thiols with chlorine in the presence of potas- and scalability of production, the processes developed here can
sium or cesium fluoride, followed by treatment of the resulting be used as the first practical and economical methods for the
arylsulfur chlorotetrafluorides with a fluoride, such as ZnF2, production of many kinds of arylsulfur pentafluorides. Thus, it
HF, and Sb(III/V) fluorides. The important characteristics of is expected that this will lead to new and rapid advances in
these new reactions were revealed and some reactions were “super-trifluoromethyl” arene chemistry and associated indus-
modified to provide the products in high purity and in high tries in many areas.
Table 7: Preparation of aryl bis- and tris(sulfur pentafluorides) with SbF5.
runa
2 (mmol)b
SbF5 (mmol)c solvent (mL)d
temperature (°C)
time (h)e
product 3
yield (%)f
1
2
3
4
5
6
2p′ (10.8)
2q′ (11)
2r′ (77)
21.4
24
CH2Cl2 (45)
CH2Cl2 (80)
CH2Cl2 (450)
FC-72 (390)
FC-72 (70)
−85 → −25
−85 → −15
ca. −85 → −15
−80 → rt, then rt
rt
2.5
3p″
3q″
3r″
3s″
3t″
57
71
66
52
67
55
1.5
130
30.7
14.4
99
5
2s′ (27.8)
2t′ (12.4)
2u′ (32)
8, then o.n.
o.n.
6
CH2Cl2/FC-72 (160/68) −95 → +7
3u″
aThe experimental procedure is described in Supporting Information File 1. bThe number in parentheses is the amount (mmol) of 2 used. cThe
number is the amount (mmol) of SbF5 used. dThe number in parentheses is the amount (mL) of the solvent used. FC-72 is a perfluorocarbon having
bp 56 °C (3M Fluorinert™ Electronic Liquid FC-72, 3M Specialty Materials, St. Paul, MN, USA). eo.n. = overnight. fIsolated yields.
469

Beilstein J. Org. Chem. 2012, 8, 461–471.
13.Kleeman, H.-W. Pentafluorosulfanylphenyl-substituted
Supporting Information
benzoylguanidines, method for the production thereof, their use as a
medicament or diagnostic agent, and a medicament containing these
compounds. U.S. Patent 7,446,225, Nov 4, 2008.
Supporting Information File 1
Experimental details and copies of 1H-, 19F-, and 13C NMR
spectra of new products.
14.Stamford, A. W.; Cumming, J. N. Pentafluorosulfurimino heterocyclic
compounds as BACE-1 inhibitors, compositions and their use. WO
Patent WO/2011/044184, April 11, 2011.
[http://www.beilstein-journals.org/bjoc/content/
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We thank Ube Industries, Ltd. in Japan for research funding for
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Rajendra P. Singh, and Junichi Chika for some technical contri-
butions.
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