Preparation of α, α-difluoroalkanesulfonic acids

Article abstract of DOI:10.1016/j.jfluchem.2003.11.031

Chlorodifluoromethanesulfonic acid (1) was prepared using a new procedure starting from perchloromercaptan, which is readily obtained from chlorination of CS₂. Modified Swarts reaction transformed N, N-diethyl trichloromethanesulfenamide into N, N-diethyl chlorodifluoromethanesulfenamide, and the latter species was further oxidized and hydrolyzed into chlorodifluoromethanesulfonic acid. The preparations of other two new α,α-difluoroalkanesulfonic acids, phenyl difluoromethanesulfonic acid (2) and 2-phenyl-1,1,2,2, -tetrafluoroethanesulfonic acid (3), are also disclosed. The acids 2 and 3 are stable in the forms of sodium (lithium) salts or in aqueous solutions; however, the pure forms of 2 and 3 can readily undergo defluorinations. 1-3 and their salts have potential applications as superacid catalysts and lithium battery electrolytes.

Full text of DOI:10.1016/j.jfluchem.2003.11.031

Journal of Fluorine Chemistry 125 (2004) 595–601
Preparation of a,a-difluoroalkanesulfonic acids
G.K. Surya Prakash*, Jinbo Hu, Jurgen Simon, Donald R. Bellew, George A. Olah1
Department of Chemistry, Donald P. and Katherine B. Loker Hydrocarbon Research Institute,
University of Southern California, 837 Bloom Walk, Los Angeles, CA 90089-1661, USA
Received 21 October 2003; accepted 17 November 2003
Abstract
Chlorodifluoromethanesulfonic acid (1) was prepared using a new procedure starting from perchloromercaptan, which is readily obtained
from chlorination of CS2. Modified Swarts reaction transformed N,N-diethyl trichloromethanesulfenamide into N,N-diethyl chlorodifluor-
omethanesulfenamide, and the latter species was further oxidized and hydrolyzed into chlorodifluoromethanesulfonic acid. The preparations
of other two new a,a-difluoroalkanesulfonic acids, phenyl difluoromethanesulfonic acid (2) and 2-phenyl-1,1,2,2,-tetrafluoroethanesulfonic
acid (3), are also disclosed. The acids 2 and 3 are stable in the forms of sodium (lithium) salts or in aqueous solutions; however, the pure forms
of 2 and 3 can readily undergo defluorinations. 1–3 and their salts have potential applications as superacid catalysts and lithium battery
electrolytes.
# 2004 Elsevier B.V. All rights reserved.
Keywords: Chlorodifluoromethanesulfonic acid; Phenyl difluoromethanesulfonic acid; 2-Phenyl-1,1,2,2-tetrafluoroethanesulfonic acid; Fluorinations
1. Introduction
dimerization of styrenes [10] and as lithium battery electro-
lyte [11]. The latter study claimed its advantage over con-
ventional CF3SO3ꢀLiþ by preventing passivation of the
anodes and improving the low-temperature discharge perfor-
mance of the batteries. More recently, Smertenko and cow-
orkers [12] claimed the preparation of 1 via electrochemical
oxidation of sulfodifluoroactetic acid (HOSO2CF2CO2H) in
the presence of chlorine (Cl2). But no specific synthetic
procedures were made available.
Other a,a-difluoroalkanesufonic acids of potential inter-
est such as phenyl difluoromethanesulfonic acid (PhCF2-
SO3H, 2), and 2-phenyl-1,1,2,2-tetrafluoroethanesulfonic
acid (PhCF2CF2SO3H, 3) are still unknown.
Hence, we wish to report our results on the new synthesis
of a,a-difluoroalkanesufonic acids, specifically of chlorodi-
fluoromethanesulfonic acid 1, phenyl difluoromethanesufo-
nic acid 2, and 2-phenyl-1,1,2,2,-tetrafluoroethanesulfonic
acid 3. These acids are potential superacidic catalysts and
lithium battery electrolytes.
Fluorinated alkanesulfonic acids are strong Bronsted
acids and they have found important applications as both
acid catalysts and surfactants [1]. The strong electron-with-
drawing effect of fluoroalkyl groups increase the stability of
the fluoroalkanesufonate anion (RfSO3ꢀ) and thus enhance
the acidity of these acids. Fluoroalkanesulfonic acid cata-
lysts include trifluoromethanesulfonic acid (triflic acid) [2],
pentafluoroethanesulfonic acid (pentflic acid) [3], perfluori-
nated resinsulfonic acid (Nafion-H1) [4], Nafion/silica
nanocomposites [5], etc. These perfluorinated sulfonic acids
are superacids and much stronger than such acid catalysts, as
sulfonated cross-linked polystyrene type resin (Dowex1 and
Amberlyst1) [6] and zeolites [7].
Although perfluoroalkanesufonic acids are known for dec-
ades, few selectively fluorinated a,a-difluoroalkanesufonic
acids have been reported. Chlorodifluoromethanesufonic acid
(ClCF2SO3H, 1) can be considered as a superacidic analog of
triflic acid. The first preparation of ClCF2SO3H was reported
by Yagupol’skii and co-workers [8] via a tedious pathway.
Sweeney et al. [9] also reported the preparation of 1 by the
reaction of Cl2CHSH with HOFover CuCl2–KCl in low yield.
1 was reported to have been used as an acid catalyst in the
2. Results and discussion
2.1. Chlorodifluoromethanesulfonic acid (ClCF2SO3H) 1
Our first approach to prepare chlorodifluoromethane-
sulfonic acid 1 was to synthesize the intermediate chloro-
difluoromethanesulfenyl chloride (ClCF2SCl) from
* Corresponding author. Tel.: þ1-213-740-5984; fax: þ1-213-740-6270.
E-mail address: gprakash@usc.edu (G.K.S. Prakash).
1 Co-corresponding author.
0022-1139/$ – see front matter # 2004 Elsevier B.V. All rights reserved.
doi:10.1016/j.jfluchem.2003.11.031

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G.K.S. Prakash et al. / Journal of Fluorine Chemistry 125 (2004) 595–601
Swarts reaction
Cl3CSCl
CF2ClSCl
(Cl3CSO2Cl)
(CF2ClSO2Cl)
Scheme 1. Attempted Swarts reactions.
perchloromethyl mercaptan (Cl3CSCl) by Swarts reaction.
However, under reaction conditions of the Swarts (SbF3/
SbCl5, 70 8C; or SbF3/HF, RT) perchloromethyl mercaptan
or trichloromethanesulfonyl chloride did not give the fluori-
nated product chlorodifluormethylsufenyl(sulfonyl) chlor-
ide (Scheme 1).
Yarovenko et al. [13] found that C–S bond was cleaved
during the reaction between perchloromethyl mercaptan and
metal fluoride. It was also observed earlier that, in the
reaction of CS2 with HF/Cl2 or with SbF3/SbCl5, the C–S
bonds were broken and fluoromethanes were formed [14].
We successfully modified the approach developed by
Yarovenko et al. [13] to avoid the C–S bond cleavage under
Swarts reaction conditions, using the N,N-diethyl trichlor-
omethanesulfenamide 4 as the precursor (Scheme 2). This
reaction works well but is sensitive to close controls of
reaction temperature and heating time.
Needed N,N-diethyl trichloromethanesulfenamide 4 was
prepared from perchloromethyl mercaptan 6 and diethyla-
mine in 91% yield. The Swarts reaction was carried out
without solvent using SbF3 as the fluorinating agent in the
presence of catalytic amount of SbCl5. Temperature (67–
70 8C) and reaction time (1.5–2 h) were the optimized
conditions for the halogen-exchange reaction. After separ-
ating from some black tar-like byproduct, product 5 was
isolated via vacuum distillation in 44–51 % yields (in con-
trast to the results of Yarovenko et al.’s 21–24%). The
reaction is also dependent on the amount of SbCl5 added
to the reaction mixture to initiate the exothermic reaction. It
was found 5–10 mol% of SbCl5 was needed to efficiently
activate the halogen-exchange reaction. Without SbCl5 or
with trace amount of SbCl5 the yields were extremely poor.
The proposed role of SbCl5 in the reaction is shown in
Scheme 3.
Scheme 3. Mechanistic suggestion of the role of SbCl5 in halogen-
exchange reaction.
N,N-Diethyl chlorodifluoromethanesulfenamide 5 was
subsequently further oxidized by 30% aqueous hydrogen
peroxide (H2O2) in acetic acid at 90–100 8C, which pro-
duced N,N-diethyl chlorodifluoromethanesulfonamide 7. 7
was then hydrolyzed into chlorodifluoromethanesulfonic
acid 1 (Scheme 4). Neutralization of 1 by NaOH gave
sodium chlorodifluorosulfonate 8, which was dried under
vacuum at 120 8C. Dried salt 8 was mixed with 98% sulfuric
acid and then distilled under vacuum to produce pure
CF2ClSO3H as a colorless fuming liquid.
2.2. Phenyl difluoromethanesulfonic acid
(PhCF2SO3H) 2
The new phenyl difluoromethanesulfonic acid 2 was
prepared starting from a,a,a-trifluorotoluene 9. In the
first step, we prepared a-bromo-a,a-difluorotoluene 10 by
halogen-exchange reaction between PhCF3 and BBr3
(Scheme 5). This reaction can also produce a,a,a-bromodi-
fluoro-, dibromofluoro- and tribromotoluenes under differ-
ent reaction conditions. PhCF2Br 10 was isolated in 43%
yield by reacting 10 eq. of PhCF3 with 1 eq. of BBr3 under
reflux for 2 h.
Sulfinatodehalogenation [16,17] of a-bromo-a,a-difluor-
otoluene 10 using sodium dithionite (Na2S2O4) under basic
condition gave phenyl difluoromethanesulfinic acid sodium
salt (PhCF2SO2ꢀNaþ) 13 (Scheme 6). Oxidation of 13 by
Since antimony trifluoride (SbF3) has one non-bonded
electron pair, it repulses the lone-pair electrons of chlorine
atoms in chlorinated compounds resulting in sluggish fluor-
ination (Scheme 3 (I)). When the strong Lewis acid SbCl5 is
added, its coordination with SbF3 diminishes interaction of
the antimony’s lone-pair electron with chlorine atoms, and
thus increasing the fluorinating ability of SbF3 (Scheme 3
(II)). A similar explanation was offered by Yagupol’skii and
coworkers [15] for the fluorination of benzylic C–Cl bonds
into the corresponding C–F bonds.
H3O+
O
CF2ClSNEt2
H2O2 / HOAc
CF2ClSNEt2
CF2ClSO3H
90 oC
O
5
7
1
98 % H2SO4
distill
(a) NaOH
(b) Dry
CF2ClSO3H
CF2ClSO3Na
HNEt2
SbF3/SbCl5 (cat.)
67oC, 90 min
51 %
CCl3SCl
CCl3SNEt2
CF2ClSNEt2
8
1
Et2O, 0oC~r.t.
91 %
5
6
4
overall yield from 5: 45%
Scheme 2. Preparation of CF2ClSNEt2.
Scheme 4. Preparation of CF2ClSO3H.

G.K.S. Prakash et al. / Journal of Fluorine Chemistry 125 (2004) 595–601
597
CFBr2
CBr3
CF3
CF2Br
BBr3
+
+
condition a,b,c
11
12
10
9
conditon a:
43%
14%
-
trace(0.3%)
24%
48%
92%
b:
c:
trace
-
Condition a: neat, PhCF3 / BBr = 10/1, reflux for 2 hr followed by standing overnight at r.t.
3
b: CH Cl as solvent, PhCF3 / BBr = 3/1, the reaction was run for 5 days at r.t.
2
2
3
c: CCl as solvent, PhCF3 / BBr = 1/1.1, at r.t. for 32 h.
4
3
Scheme 5. F/Br exchange reaction of PhCF3 using BBr3.
30% aqueous H2O2 yielded sodium phenyldifluorometha-
2.3. 2-Phenyl-1,1,2,2-tetrafluoroethanesulfonic acid
(PhCF2CF2SO3H) 3
nesufonate (PhCF2SO3ꢀNaþ) 14. The crude stable salt 14
was dried under vacuum. An aqueous solution of 14 was ion-
exchanged over an acid resin Amberlyst1 column, giving
the acid form PhCF2SO3H 2. Acid 2 is stable in aqueous
solution. However, attempted to remove water to obtain its
pure dry form at 60–70 8C/0.1 mmHg led to decomposition.
The product isolated from its decomposition residue was
benzoic acid. Other attempts to isolate pure PhCF2SO3H by
vacuum distillation of the salt 14 and 98% sulfuric acid gave
similar decomposition.
Due to the unsuccessful isolation of pure PhCF2SO3H, we
considered an alternative, 2-phenyl-1,1,2,2-tetrafluoroetha-
nesulfonic acid 3 and carried out its preparation. Since there
is one additional –CF2– group intervening the –CF2SO3H
moiety, it was presumed that the benzylic C–F bonds in this
acid would be more stable. The retro synthetic route is
shown in Scheme 7.
The attempted synthesis of 16 with fluoride induced
bromodifluoromethylation of methyl benzoate using
Me3SiCF2Br reagent [18], however, failed. The magnesium
metal mediated defluorination [19,20] of 2,2,2,-trifluoroa-
cetophenone provided an efficient way to prepare compound
16 from inexpensive PhCOCF3 in high yield (Scheme 8).
The difluorosilyl enol ether 17 was conveniently prepared,
followed by bromination with bromine. The bromination
reaction was facile even at ꢀ78 8C, and the reaction pro-
ceeded smoothly with high selectivity (Scheme 8).
Deoxofluorination of 2-Bromo-2,2-difluoroacetophenone
16 readily gave 2-bromo-1,1,2,2-tetrafluoroethylbenzene 19
(Scheme 9). Diethylaminosulfur trifluoride (DAST) was
used as deoxofluorinating agent.
This decomposition is most probably an acid-catalyzed
hydrolysis process. The stability of PhCF2SO3H in water
solution indicates that the hydrolysis reaction is dependent
on the acidity rather than the amount of water. Due to the
leveling effect of water, the acidity of PhCF2SO3H is
decreased in water solution making the hydrolysis ineffi-
cient. When the bulk of water was removed, the super-
acidity of PhCF2SO3H self-catalyzes its decomposition.
Another reason is the lability of benzylic C–F bonds in
this acid 2, which was confirmed by the fact that, PhCF3
also readily hydrolyzes into benzoic acid in triflic acid
medium.
By similar approach as the preparation of PhCF2SO3H, 19
was transformed into the new acid PhCF2CF2SO3H 3
(Scheme 10). However, although acid 3 was stable in
aqueous solution, it readily decomposed upon attempted
removal of water by vacumm distillation. Similarly, when
the stable salt PhCF2CF2SO3Na was mixed in 98% sulfuric
acid followed by vacuum distillation, rapid decomposition
-
CF2SO3 Na+
-
CF2Br
CF2SO2 Na+
Na2S2O4
2 NaHCO3
H2O2
H2O / CH3CN
800C
14
10
13
Amberlyst
O
CF2CF2SO3H
CF2CF2Br
CF2SO3H
CF2Br
2
3
15
16
Scheme 6. Preparation of PhCF2SO3H.
Scheme 7. Retro synthetic preparation of PhCF2CF2SO3H.

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G.K.S. Prakash et al. / Journal of Fluorine Chemistry 125 (2004) 595–601
O
O
OSiMe3
CF2
CF2Br
Mg / TMSCl
THF, 0 o
Br2
CF3
C
CH2Cl2
-78 oC~r.t.
16
(77 % for 2 steps)
18
17
Scheme 8. Preparation of PhCOCF2Br.
used as an internal standard for 1H and 13C NMR, CFCl3 was
used as internal standard for 19F NMR. For some cases,
CDCl3 was used as the internal standard for 1H NMR
(7.26 ppm) and 13C NMR (77 ppm). IR spectra were
obtained on a Perkin-Elmer FTIR Spectrometer 2000. Mass
spectra were obtained on a Hewlett-Packard 5890 Gas
Chromatograph equipped with a Hewlett Packard 5971
Mass Selective Detector at 70 eV.
O
CF2CF2Br
DAST
CF2Br
CHCl3, reflux
58 %
16
19
Scheme 9. Preparation of PhCF2CF2Br using DAST.
happened. Superacid catalyzed hydrolysis is fast and similar
to that of PhCF2SO3H (vide infra).
Both acids 2 and 3 when treated with LiOH gave the
corresponding lithium salts. These lithium sulfonates can be
dried. They can serve as lithium battery electrolytes.
4.2. Synthesis of chlorodifluoromethanesulfonic acid (1)
4.2.1. Perchloromethyl mercaptan (6)
Into a 1 l three-neck round bottom flask equipped with a
magnetic stirrer, a condenser and two septa, was added
440 ml CS2, 280 ml of water, and 200 ml of 37% HCl.
The flask was cooled to 0 8C, and chlorine gas was bubbled
into the reaction mixture slowly. The chlorine bubbling rate
was controlled carefully to avoid chlorine to permeate out-
side. The reaction was processed for 2 days, and totally
438 g (6.16 mol) chlorine gas was consumed. The organic
phase was isolated, washed three times with brine and dried
over MgSO4. The CS2 solvent was removed under vacuum
and 144 g crude product 6 was collected, yield 63%. After
fractional distillation, 131.9 g (57%) pure product 6 was
obtained as a colorless liquid, bp 144–145 8C. 13C NMR
(62 MHz, CDCl3): d 97.49 [21].
3. Conclusions
We developed a new route for the synthesis of chlorodi-
fluoromethanesulfonic acid 1, a useful superacid. Syntheses
of phenyl difluoromethanesulfonic acid (PhCF2SO3H) 2
and 2-phenyl-1,1,2,2-tetrafluoroethanesulfonic acid (PhCF2-
CF2SO3H) 3 were also carried out. It was found that the
sodium salts of latter two acids are quite stable, but the acids
themselves are only stable in aqueous solution. In isolated
form, both acids readily undergo self-catalyzed acid hydro-
lysis. The synthesized acids 1–3 have useful potential appli-
cations as acid catalysts and lithium battery electrolytes.
4.2.2. N,N-Diethyl trichloromethanesulfenamide (4)
4. Experimental
At 0 8C, into a mixture of 50 ml of ether and 56.5 ml
(546 mmol) of diethylamine, was slowly added 50.74 g
(273 mmol) of perchloromethyl mercaptan 6 in 35 ml of
ether through a dropping funnel. After addition was com-
pleted, the reaction mixture was stirred for another 1 h at
room temperature. Then 50 ml of 10% HCl was added, and
the organic phase was separated. The aqueous phase was
further extracted with 20 ml of ether. Combined ether phase
was washed with 10% NaHCO3 solution, and then with
30 ml of water. After drying over CaCl2, the solvent was
removed under vacuum. The crude product was distilled to
afford 55.12 g (91% yield) of product 4 as a colorless liquid,
4.1. General
Unless otherwise mentioned, all reagents were purchased
from commercial sources. Diethyl ether and THF were all
distilled under nitrogen over sodium/benzophenone ketyl
prior to use. Toluene was distilled over sodium. Column
chromatography was carried out using silca gel (60–
200 mesh).
1H, 13C, 19F NMR spectra were recorded on Bruker AMX
500 and AM 360 NMR spectrometers. (CH3)4Si (TMS) was
-
CF2CF2SO2 Na+
-
CF2CF2Br
CF2CF2SO3 Na+
CF2CF2SO3H
Na2S2O4
2 NaHCO3
H2O2
Amberlyst
H2O / CH3CN
800C
20
21
19
3
Scheme 10. Synthesis of PhCF2CF2SO3H.

G.K.S. Prakash et al. / Journal of Fluorine Chemistry 125 (2004) 595–601
599
bp 78 8C/12.9 mmHg. 1H NMR (360 MHz, CDCl3): d 1.24
added 146.1 g (1 mol) of PhCF3 and then slowly was added
25.05 g (0.1 mol) of BBr3 at room temperature. Slowly the
reaction mixture became warm and gaseous BF3 started
bubbling out. The color of the mixture turned to yellow
initially and amber-like. After 1 h, the effervescence ceased
and the mixture started to cool down. The mixture was
refluxed for another 2 h, followed by stirring at room
temperature overnight. Then the reaction mixture was
poured into 100 ml of ice water, and extracted with CH2Cl2
(50 ml  3). The combined organic phase was washed with
30 ml of water, and then was dried over CaCl2. After
evaporating solvents, 48.44 g of amber color liquid was
collected as the crude product, which was distilled to give
26.71 g (43% yield) of product 10 as a colorless liquid, bp
54 8C/20 Torr. 1H NMR (360 MHz, CDCl3): d 7.45 (m, 3H);
7.59 (m, 2H). 13C NMR (62 MHz, CDCl3): d 118.41
3
3
(t, JHꢀH ¼ 7 Hz, 6H); 3.34 (m, JHꢀH ¼ 7 Hz, 2H); 3.59
3
(m, JHꢀH ¼ 7 Hz, 2H). 13C NMR (62 MHz, CDCl3): d
14.37; 51.92; 104.46. MS (70þeV): 223 [Mꢀþ (36Cl)]; 223
[Mþ (35Cl)]; 188 [(Mꢀ35Cl) ]; 186 [(M 36Cl)þ]; 104
[(SNEt2)þ].
4.2.3. N,N-Diethyl chlorodifluoromethanesulfenamide (5)
Under an argon atmosphere, into a 500 ml three neck
round bottom flask equipped with a condenser and two septa,
was added 54.5 g (245 mmol) of 4 and 32.85 g (184 mmol)
of SbF3. The reaction mixture was heated up to 67 8C with
stirring, and 2 g (6.7 mmol) of SbCl5 was added in via
syringe. The exothermic reaction ensued immediately, and
the color of reaction mixture turned brown. The reaction
mixture was stirred for another 1.5 h, and then was cooled
down to room temperature. The upper liquid layer was
decanted out, and black tar at the bottom of flask was
washed with ether (25 ml  4). The combined organic phase
was vacuum distilled to give 23.85 g (51%) of product 5 as a
colorless liquid, bp 57–59 8C/50 mmHg. (Caution: the com-
pound 5 must be distilled under vacuum; one attempt to
1
3
(t, JCꢀF¼ 303:9 Hz); 124.29 (t, JCꢀF¼ 5:5 Hz); 128.62;
2
131.24; 138.15 (t, JCꢀF¼ 23:3 Hz). 19F NMR (338 MHz,
CDCl3): d ꢀ44.01. MS (70 eV): 189 [(PhCFBr)þ]; 127
[(PhCF2)þ]; 108 [(PhCF)þ]; 77 (Phþ).
4.3.2. a,a-Dibromo-a-fluorotoluene (11)
(0.12 g, 0.3% yield) was also obtained as a high boiling
1
distill under atmospheric pressure caused explosion!) H
3
1
NMR (360 MHz, CDCl3): d 1.16 (t, JHꢀH ¼ 7 Hz, 6H);
liquid. H NMR (360 MHz, CDCl3): 7.46 (m, 3H); 7.72
1
3.15 (b, 4H). 13C NMR (62 MHz, CDCl3): d 13.74; 52.48;
133.76 (t, 1JCꢀF¼ 336:7 Hz). 19F NMR (338 MHz, CDCl3):
d ꢀ35.57. MS (70 eV): 191 [Mþ (37Cl)]; 189 [Mþ (35Cl)];
104 [(SNEt2)þ]; 85 [(CF235Cl)þ].
(m, 2H). 13C NMR (62 MHz, CDCl3): d 90.65 (d, JCꢀF
316:0 Hz); 124.05 (d, JCꢀF¼ 7:3 Hz); 128.35; 130.37 (d,
2JCꢀF¼ 33:5 Hz); 144.71. 19F NMR (338 MHz, CDCl3):
ꢀ53.82.
¼
3
4.2.4. Chlorodifluoromethanesulfonic acid (1)
4.3.3. a,a,a–Tribromotoluene (12)
(7.76 g, 24% yield) was obtained as a white solid. H
1
Into a solution of 20.79 g (110 mmol) of 5 in glacial acetic
acid (100 ml) at 75–85 8C, was added dropwise 100 ml of
30% H2O2. Then the reaction mixture was heated at 90 8C
NMR (360 MHz, CDCl3): d 7.34 (m, 3H); 8.02 (d, 2H). 13
C
NMR (62 MHz, CDCl3): d 36.32; 126.45; 128.03; 130.09;
146.90.
for another 2 h. The reaction progress was monitored by 19
F
NMR: at beginning 5 was transformed into N,N-diethyl
chlorodifluoromethanesulfonamide 7 and then 7 was further
hydrolyzed into chlorodifluoromethanesulfonic acid 1 (19F
NMR: ꢀ63 ppm). Subsequently, most of the water and
acetic acid were distilled out from reaction mixture using
a 17 cm column, and to the residue 16 ml 50% aqueous
NaOH solution was added to neutralize the acids (using pH
paper). After water was removed, the sodium salt 8 was
dried at 120 8C/0.1 mmHg. To the dried salt 8, 50 ml of 98%
H2SO4 was added, and the mixture was stirred vigorously at
100 8C for 2 h, followed by careful fractional distillation to
afford 8.19 g (45% yield) acid 1 as a colorless fuming liquid,
bp 104–107 8C/7 mmHg. 13C NMR (62 MHz, DMSO-d6): d
4.3.4. Phenyl difluoromethanesulfonic acid (2)
Into a mixture of 135 ml of water, 90 ml of CH3CN,
25.66 g (305 mmol) of NaHCO3 and 31.61 g (153 mmol)
of PhCF2Br at room temperature, was added 53.2 g
(305 mmol) of Na2S2O4 under argon atmosphere. The reac-
tion mixture was heated to 80 8C for 12 h. After cooling
down, the reaction mixture was filtered, and the solid residue
was washed with hot CH3CN/H2O (9:1). The combined
filtrate was vacuum distilled to remove water and organic
solvents to give off-white solid product, which was further
washed with 10 ml of hexane and 10 ml petroleum ether.
Then the solid was dried at 80 8C under high vacuum to
afford 75 g of crude sodium 1-phenyl-1,1-difluoromethane-
sulfinate 13. 19F NMR (D2O): d ꢀ112.75.
1
125.96 (t, JCꢀF¼ 330 Hz). 19F NMR (338 MHz, DMSO-
d6): d ꢀ62.36.
Then the salt 13 was dissolved in 100 ml of water,
and 30 ml of 50% H2O2 was added dropwise at 0 8C.
After the exothermic reaction faded, the mixture was stirred
at room temperature for another 2 h. After removal of
water and excess H2O2 under vacuum, the residue salt
was washed by CH2Cl2 and pet ether. The resulting solid
was dried at 80 8C/0.1 mmHg to give 84 g of product sodium
4.3. Synthesis of phenyl difluoromethanesulfonic acid
(PhCF2SO3H) 2
4.3.1. a-Bromo-a,a-difluorotoluene (10)
Under an argon atmosphere, into a 1 l three-neck round
bottom flask equipped with a condenser and two septa, was

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G.K.S. Prakash et al. / Journal of Fluorine Chemistry 125 (2004) 595–601
1-phenyl-1,1-difluoromethanesufonate 14, 1H NMR (D2O):
d 7.44 (t, J ¼ 7:9 Hz, 2H); 7.51 (t, J ¼ 7:9 Hz, 1H); 7.59 (d,
J ¼ 7:9 Hz, 2H). 19F NMR (D2O): d ꢀ102.52.
afford 20.03 g product 16 as a colorless liquid, bp 99–
101 8C/15 mmHg, yield 77% based on PhCOCF3 used.
1H NMR (CDCl3): d 7.53 (t, J ¼ 7:8 Hz, 2H); 7.68 (t,
J ¼ 7:8 Hz, 1H); 8.15 (d, J ¼ 8:0 Hz, 2H). 13C NMR
Solid 14 was dissolved in 100 ml of H2O, and then was
Amberlyst1 acid resin column
(CDCl3): d 113.56 (t, JCꢀF¼ 319:1 Hz); 128.87; 129.05;
1
passed through
a
3
2
(15 mm  410 mm). The free water (ꢁ80 ml) was evapo-
rated from resulting solution to give a condensed aqueous
solution of phenyl difluoromethanesulfonic acid 2. 1H NMR
(D2O): d 7.58 (t, J ¼ 7:9 Hz, 2H); 7.66 (t, J ¼ 7:9 Hz, 1H);
7.73 (d, J ¼ 7:9 Hz, 2H). 13C NMR (D2O): d 117.05
130.61 (t, JCꢀF¼ 2:6 Hz); 135.09; 181.32 (t, JCꢀF ¼
26:0 Hz). 19F NMR (CDCl3): d ꢀ58.29. MS (70 eV): 234
(Mþ); 105 (PhCOþ); 77 (Phþ).
4.4.2. 2-Bromo-1,1,2,2-tetrafluoroethylbenzene (19)
1
3
(t, JCꢀF¼ 274:7 Hz); 123.43 (t, JCꢀF¼ 6:0 Hz); 125.41;
Under an argon atmosphere, into 9.40 g (40 mmol) 16 in
60 ml of dry chloroform was added 9.76 g (60 mmol) of
DAST. The reaction mixture was then refluxed for 34 h.
After cooling down to room temperature, the mixture was
poured into ice water, and then the organic phase was further
washed with NaHCO3, brine and water successively. After
drying over MgSO4 and solvent removal, 8.84 g crude
product 19 was obtained as a yellow liquid. Further pur-
ification by silica gel chromatography using hexane as the
eluent gave 5.84 g pure compound 19 as a colorless liquid,
127.00 (t, JCꢀF¼ 23:0 Hz); 128.50. 19F NMR (D2O):
2
ꢀ102.55.
4.3.5. Attempted purification of acid (2)
The condensed solution of 2 prepared above (3.0 g) was
vacuum distilled over a 70 8C in an oil bath under 0.1 mmHg
vacuum. After all the water distilled out, the gummy solid
residue immediately decomposed to give some white crys-
talline solid with a melting point 122–123 8C. The solid
1
1
turns out to be benzoic acid. H NMR (CDCl3): d 7.50
yield 58%. H NMR (CDCl3): d 7.47 (t, J ¼ 7:7 Hz, 2H);
(t, 2H); 7.64 (t, 1H); 8.17 (d, 2H). 13C NMR (CDCl3):
7.55 (t, J ¼ 7:5 Hz, 1H); 7.60 (d, J ¼ 7:6 Hz, 2H). 13C NMR
d 128.42; 129.25; 130.15; 133.74; 172.19. MS: 122 (Mþ).
(CDCl3): d 114.93 (tt, JCꢀF¼ 255:0 Hz, JCꢀF¼ 31:3 Hz);
1
2
1
2
117.66 (tt, JCꢀF¼ 312:8 Hz, JCꢀF¼ 44:7 Hz); 127.06 (t,
4.4. Synthesis of 2-phenyl-1,1,2,2-
tetrafluoromethanesulfonic acid (PhCF2CF2SO3H) 3
3JCꢀF¼ 6:2 Hz); 128.51; 128.71, 131.72. 19F NMR
3
(CDCl3): d ꢀ65.34 (t, JFꢀF¼ 4:8 Hz); ꢀ108.60 (t,
3JFꢀF¼ 4:8 Hz). MS (70 eV): 256 (Mþ); 177 (PhCF2CF2þ);
4.4.1. 2-Bromo-2,2-difluoroacetophenone (16)
127 (PhCF2þ); 77 (Phþ).
Into the mixture of magnesium turnings (5.31 g,
0.22 mol) and TMSCl (47.58 g, 0.44 mol) in 150 ml of
THF at 0 8C, was slowly added under argon atmosphere
PhCOCF3 (20.00 g, 0.11 mol). The reaction mixture was
stirred at 0 8C for 4 h. After removal of the solvent and
excess TMSCl under vacuum, 50 ml of hexane was added.
Solid species was removed via vacuum filtration, and the
filtrate was concentrated to give 25.18 g crude difluoro silyl
enol ether 17. 1H NMR (CDCl3): d 0.60 (s, 9H), 7.38
(t, J ¼ 7:5 Hz, 1H), 7.47 (t, J ¼ 7:5 Hz, 2H), 7.61
(d, J ¼ 8:8 Hz, 2H); 13C NMR (CDCl3): d ¼ 0:02, 114.09
4.4.3. 2-Phenyl-1,1,2,2-tetrafluoroethanesulfonic acid (3)
Under an argon atmosphere, 4.0 g (15.5 mmol) of 19 was
mixed with 3.9 g (46 mmol) of NaHCO3, 8.1 g (46 mmol)
Na2S2O4 in 12 ml of CH3CN and 20 ml of H2O, and the
reaction mixture was refluxed for 20 h. After cooling down,
the reaction mixture was filtered and the filtrate was con-
densed under vacuum to give 17.38 g of crude product
sodium 2-phenyl-1,1,2,2-tetrafluoroethanesulfinate 20.
Solid compound was further washed with 5 ml CH2Cl2
and then dried at 80 8C/0.1 Torr to give 10.75 g dry salt
20. 1H NMR (D2O): d 7.43 (t, 2H); 7.49 (t, 1H); 7.52 (d, 2H).
19F NMR (D2O): d ꢀ109.85; ꢀ129.68.
2
(q, JðC;FÞ¼ 18:0 Hz), 125.84, 127.72, 128.25, 132.71,
1
154.87 (t, JðC;FÞ¼ 286:8 Hz); 19F NMR (CDCl3):
2
2
d ¼ ꢀ100:39 (d, JðF;FÞ¼ 68:0 Hz), ꢀ112.16 (d, JðF;FÞ
¼
The above prepared solid 20 was dissolved in 15 ml of
H2O, cooled down to 0 8C and 5.3 ml 30% H2O2 was added
dropwise. The reaction mixture was stirred for another 4 h.
After filtration of reaction mixture, the resultant filtrate was
concentrated to give 8.23 g solid, which was dried at 80 8C
under high vacuum to give 8.04 g of dry crude sodium
2-phenyl-1,1,2,2-tetrafluoroethanesulfonate 21. 1H NMR
(D2O): d 7.39 (t, J ¼ 7:9 Hz, 2H); 7.46 (t, J ¼ 7:9 Hz,
1H); 7.51 (d, J ¼ 7:9 Hz, 2H). 19F NMR (D2O): d
ꢀ107.85; ꢀ114.05.
68:0 Hz). MS (70 eV) m/z (relative intensity): 228 (Mþ,
79), 213 (2), 197 (1), 186 (5), 177 (60), 165 (1), 149 (1),
143 (1), 131 (5), 115 (9), 105 (36), 89 (45), 81 (29), 77 (75),
73 (100).
The above prepared 17 was dissolved in 100 ml of dry
CH2Cl2, and at ꢀ78 8C bromine was added via a syringe
until the brown color no longer disappeared. After stirring
for another 30 min, the solvent was evaporated under
vacuum, and the residue was washed and extracted with
CH2Cl2. The organic phase was further washed with
NaHCO3, brine and water sequentially. After drying over
MgSO4, the solvent was removed to give 21.40 g crude
product 16, yield 83% calculated from PhCOCF3. The crude
product was further purified by fractional distillation to
Above prepared solid 21 (2 g) was dissolved in 20 ml of
water, and was passed through a Amberlyst1 acid resin
column (10 mm  150 mm). The resulting amber colored
solution was concentrated by evaporating water under high
vacuum at room temperature to give 2.28 g concentrated

G.K.S. Prakash et al. / Journal of Fluorine Chemistry 125 (2004) 595–601
601
acid 3. 1H NMR (D2O): d 7.48 (t, J ¼ 7:9 Hz, 2H); 7.56 (t,
J ¼ 7:9 Hz, 1H); 7.61 (d, J ¼ 7:9 Hz, 2H). 13C NMR
[4] G.A. Olah, G.K.S. Prakash, P.S. Iyer, Synthesis (1986) 513.
[5] Q. Sun, M.A. Harmer, W.E. Farneth, Chem. Commun. (1996) 1201.
[6] S.-K. Ihm, M.-J. Chung, K.-Y. Park, Ind. Eng. Chem. Res. 27 (1988)
41.
1
2
(DMSO-d6): d 115.61 (tt, JCꢀF¼ 287:2 Hz, JCꢀF
¼
1
2
37 Hz); 117.62 (tt, JCꢀF¼ 253 Hz, JCꢀF¼ 31 Hz);
[7] M.L. Poutsma, in: J.A. Rabo (Ed.), Zeolite Chemistry and Catalysis,
ACS Monographs 171, American Chemical Society, Washington,
DC, 1976 (Chapter 8).
3
2
127.88 (t, JCꢀF¼ 6:4 Hz); 129.63; 132.07 (t, JCꢀF
¼
25 Hz); 132.55. 19F NMR (DMSO-d6): d ꢀ106.54;
ꢀ113.98.
[8] N.D. Volkov, V.P. Nazaretian, L.M. Yagupol’skii, Synthesis (1979)
972.
[9] R.F. Sweeney, J.O. Peterson, B. Sukornick, M.B. Berenbaum, H.R.
Nychka, R.E. Eibeck, Can. Patent CA 1,093,581 (1981).
[10] I. Shimizu, O. Tsuji, E. Matsuzaka, A. Sato, Jpn. Kokai. Tokkyo.
Koho. JP 55,057,524 (1980).
4.4.4. Attempted purification of acid (3)
The condensed solution of 3 prepared above (1.0 g) was
vacuum distilled over a 55–60 8C oil bath under 0.1 mmHg
vacuum. After most water distilled out, the gummy solid
residue was immediately decomposed to evolve gaseous
compounds (possibly HF and SO3). 19F NMR of the dark
liquid residue showed only one peak at ꢀ110.0 ppm.
[11] S. Furukawa, S. Yoshimura, M. Takahashi, Jpn. Kokai Tokkyo Koho
JP 02306544 (1990).
[12] E.A. Smertenko, N.D. Volkov, S.D. Datsenko, N.V. Ignat’ev, Theor.
Exp. Chem. 35 (2000) 231. Chemical Abstract: CAN 132: 129
167.
[13] N.N. Yarovenko, S.P. Motornyl, A.S. Vasil’eva, T.P. Gershzon, Zh.
Obshch. Khim. 29 (1959) 2163 (J. Gen. Chem. 29 (1959) 2129).
[14] O.B. Helfrich, E.E. Reid, J. Am. Chem. Soc. 43 (1921) 591, and the
references therein.
Acknowledgements
[15] L.M. Yagupol’skii, N.V. Kondratenko, V.I. Popov, Zh. Org. Khim. 13
(1977) 613 (English Transl.: J. Org. Chem. USSR 13 (1977) 561).
[16] B.N. Huang, W.Y. Huang, C.M. Hu, Acta Chim. Sinica 39 (1981)
481.
Support of our work by Loker Hydrocarbon Research
Institute is gratefully acknowledged.
[17] J.T. Liu, H.J. Liu, Chin. Chem. Lett. 11 (2000) 189.
[18] A.K. Yudin, G.K.S. Prakash, D. Deffieux, M. Bradley, R. Bau, G.A.
Olah, J. Am. Chem. Soc. 119 (1997) 1572.
References
[19] G.K.S. Prakash, J. Hu, G.A. Olah, J. Fluorine Chem. 112 (2001) 357,
and the references therein.
[1] G.A. Olah, G.K.S. Prakash, J. Sommer (Eds.), Superacids, Wiley-
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[20] G.K.S. Prakash, M.M. Alauddin, J. Hu, P.S. Conti, G.A. Olah, J.
Fluorine Chem. 121 (2003) 239.
[21] J.I. Grayson, Org. Process Res. Dev. 1 (1997) 240.
[2] R.D. Howells, J.D. McCown, Chem. Rev. 77 (1977) 69.
[3] G.A. Olah, T. Weber, D.R. Bellew, O. Farooq, Synthesis (1989) 463.