A new method of the preparation of imido-bis(sulfuric acid) dihalogenide, (F,Cl), and the potassium salt of imido-bis(sulfuric acid) difluoride

Article abstract of DOI:10.1002/zaac.200400325

The article describes a new and effective synthesis of pure imido-bis(sulfuric acid) dihalogenides (halogenide = F, Cl) and the potassium salt of imido-bis(sulfuric acid) difluoride, KN(SO₂F)₂.

Full text of DOI:10.1002/zaac.200400325

A New Method of the Preparation of Imido-bis(sulfuric acid) Dihalogenide,
(F,Cl), and the Potassium Salt of Imido-bis(sulfuric acid) Difluoride
ˇ
ˇ
´
´
Martin Beran and Jirı Prıhoda*
Brno, Czech Republic, Masaryk University, Department of Inorganic Chemistry, Faculty of Science
Received July 28th, 2004.
Dedicated to Professor Manfred Meisel on the Occasion of his 65th Birthday
Abstract. The article describes a new and effective synthesis of pure
imido-bis(sulfuric acid) dihalogenides (halogenide ϭ F, Cl) and the
Keywords: Imido-sulfuric acid; Halogens
potassium salt of imido-bis(sulfuric acid) difluoride, KN(SO2F)2.
Eine neue Methode zur Darstellung von Imido-bis(schwefelsäure)dihalogeniden, (F,Cl),
und das Kaliumsalz von Imido-bis(schwefelsäure)difluorid
Inhaltsübersicht. Es wird eine neue und effektive Methode zur Dar-
stellung von reinem Imido-bis(schwefelsäure)dihalogeniden und
dem Kaliumsalz Imido-bis(schwefelsäure)difluorid, KN(SO2F)2,
beschrieben
Introduction
In recent years the interest in II was concentrated on the
preparation of its salts that are used in electrotechnics.
A number of preparation methods of II were published
but none of them is optimal with regards to possible indus-
trial application.
II was prepared by the reaction of fluorosulfuric acid
with urea [3]. The authors suggested the following reaction
mechanism (Scheme A):
Imido-bis(sulfuric acid) dichloride, Cl-SO2-NH-SO2-Cl, I, is
a colourless solid substance, forming needlelike crystals,
m.p. 37 °C [1]. It can be distilled under vacuum (95 °C/
1.3 kPa [2]) without decomposition. Cl-SO2-NH-SO2-Cl is
soluble in a number of organic solvents, such as benzene,
nitrobenzene, dichloromethane, etc. [1]. The reaction with
water is violent, hydrolysis in alcaline media yields imido-
bis(sulfate), while amidosulfate and sulfate are formed in
acid media. Ammonolysis leads to the formation of am-
monium imidosulfamide [1].
I can be prepared in two steps by the reaction of amido-
sulfuric acid with phosphorus (V) chloride in 80 % [1] or
88 % [2] yield, respectively. However, the reaction is not too
convenient because of problems with the separation of the
main product from the POCl3, by product. I can be ob-
tained also in the reaction of chlorosulfuric acid with urea
but only in a negligible yield (4%) [1].
Scheme A Suggested mechanism of the reaction between urea and
flurosulfuric acid
Imido-bis(sulfuric acid) difluoride, F-SO2-NH-SO2-F, II,
is a colourless liquid, m.p. 17 °C, b.p. 170 °C, density
1.892 g/cm3 [3, 4]. It is very well soluble in water and in a
number of organic solvents. Hydrolysis in water is relatively
slow and leads to the formation of HF, sulfuric acid, and
amidosulfuric acid [3]. Imido-bis(sulfuric acid) difluoride is
considered to be a strong acid, pKa ϭ 1,28 [5].
The main problem of this reaction is its difficult control
because of problems with local overheating of the reaction
system in the course of fluorosulfuric acid addition. Thor-
ough homogenization of the reaction mixture but with
greater quantities is practically impossible. This may be the
reason for very variable yields (61 % [3] or 14.5 % [6]. The
exploitation of expensive and highly corrosive fluorosul-
furic acid is also inconvenient because of problems with iso-
lation of single reaction products. (b.p. of II is 170 °C) [3],
b. p. of fluorosulfuric acid is 165.5 °C) [7].
ˇ´
* Doc. RNDr. J. Prıhoda, CSc.
Department of Inorganic Chemistry, Faculty of Science
Masaryk University
´ˇ
´
Kotlarska 2
Another published preparation of II is based on the reac-
tion of sulfuryl diisocyanate with fluorosulfuric acid [8].
Brno / Czech Republic
E-mail: prihoda@chemi.muni.cz
Z. Anorg. Allg. Chem. 2005, 631, 55Ϫ59
DOI: 10.1002/zaac.200400325
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55

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M. Beran, J. Prıhoda
This reaction has also disadvantages, especially the reaction
time is too long (150 hours). II arises also in the reaction
of fluorosulfuric acid with some trichlorophosphazo group
(-NϭPCl3) containing compounds, e.g. Cl3PϭN-SO2-Cl [9],
Cl3PϭN-SO2-NϭPCl3 [10] or Cl3PϭN-SO2-POF2 [11]. One
of the II preparation methods consists of the replacement
of chlorine atoms in I molecule for fluorine atoms by using
AsF3 [4] in 85 % yield. However, this method is hardly ap-
plicable on an industrial scale because of the high toxicity
of AsF3.
Alkali metal bis(fluorosulfuryl)amides, MN(SO2F)2, M ϭ
alkali metal, are white and crystalline substances, very well
soluble in water and polar organic solvents [5]. Their
stability in aqueous solutions is relatively high and therefore
the degree of hydrolysis is low. Potassium salt melts at
100 °C, cesium salt at 116 °C [5].
The usual preparation of alkali metal bis(fluorosulfuryl)
amides consists of neutralization of II by corresponding al-
kali metal carbonate in cold aqueous media. The yields are:
45 % for K salt, 78 % for Rb salt, and 85 % for Cs salt [4,
5]. KN(SO2F)2 can be also prepared by the reaction of I
with an excess of anhydrous KF in nitromethane [12] in a
80 % yield.
Therefore the main aim of this work was to discover a
simple and cheap preparation method for potassium salt of
II with respect to the potential industrial exploitation.
Fig. 1 19F NMR spectra of reaction products:
Results and Discussion
Spectrum A: Reaction between fluorosulfuric acid and urea in
thionyl dichloride
Preparation of II and its potassium salt by the
reaction of urea and flurosulfuric acid
Spectrum B: Reaction between fluorosulfuric acid and amidosul-
furic acid in thionyl dichloride
Spectrum C: Conversion of imido-bis(sulfuric acid) difluoride
potassium salt into imido-bis(sulfuric acid) difluoride
First, we concentrated on optimizing the synthesis of II
based on the reaction between fluorosulfuric acid and urea.
However, some our attempts to prepare this substance by
various approaches (reaction with melted urea or in nitro-
methane, sulfuryl chloride, 100 % sulfuric acid) did not lead
to the optimal reaction because of negligible yields of II in
all cases.
On the contrary, the reaction carried out in thionyl di-
chloride media led to the substantial increase in the yield.
The 19F NMR spectrum proved the presence of three fluor-
ine containing substances in the reaction mixture: II : im-
ido-bis(sulfuric acid) fluoride-chloride : fluorosulfuric acid
in a molar ratio of 2.9 : 2.3 :1 in the reaction mixture
(Fig. 1, Spectrum A). As the separation of pure II from this
reaction mixture is very complicated and uneconomic (very
close boiling points of compounds present in the reaction
mixture), we converted all mixture components into potas-
sium salts by their reactions with anhydrous potassium flu-
oride. Chlorine atoms were replaced for fluor simul-
taneously. Suggested course of reactions is shown in
Scheme B.
Scheme B Conversion of the reaction products into their potas-
sium salts
methane was used only for easier homogenization of the
reaction system at the beginning. As the result of this ap-
proach we got an off-white pasty solid that turned hard on
cooling. To avoid treating this hard and compact solid we
added an inert solvent (n-butyl acetate) before the reaction
A similar approachϪconversion of I into potassium salt
ˇ
´
of II was carried out in nitromethane by Cernık and cowor-
kers [12]. We used method of the conversion by using anhy-
drous potassium fluoride in dichloromethane. Dichloro-
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Z. Anorg. Allg. Chem. 2005, 631, 55Ϫ59

A New Method of the Preparation of Imido-bis(sulfuric acid) Dihalogenide
The reaction was carried out in the same way as the reac-
Table 1 Yields of KN(SO2F)2
tion with urea. 19F NMR spectroscopy proved that the
product contained besides the expected imido-bis(sulfuric
acid) fluoride-chloride also II, and the unreacted fluorosul-
furic acid in a molar ratio of 10.5 : 4.8 : 1 (Fig. 1, Spec-
trum B).
The mixture of imido-bis(sulfuric acid) halogenides was
converted into potassium salt by the method mentioned in
the previous section.
Reaction
product
g /1 g of the
reaction product HSO3X
g /1 g starting % of the theory compared
with starting HSO3X
Product A
Product B
Product C
0.68
0.83
0.89
0.40
0.91
1.60
41.6
84.8
Product A:
Product B:
Product C:
HN(SO2F)2 : HN(SO2Cl)(SO2F) : HSO3F ϭ 2.9 : 2.3 : 1 a)
HN(SO2F)2 : HN(SO2Cl)(SO2F) : HSO3F ϭ 4.8 : 10.5 : 1 a)
HN(SO2Cl)2
a) molar ratio from 19F NMR spectra
Preparation of II and its potassium salt by the
reaction of amidosulfuric and chlorosulfuric acids
mixture solidified. It was possible to apply this approach
also in the case of carrying out the reaction on a larger
scale. II potassium salt was then extracted from this mixture
by tetrahydrofurane. The pure product was isolated after
addition of an excess of dichloromethane. A colourless crys-
talline substance was obtained. IR and 19F NMR spec-
troscopy (singlet at 51.37 ppm) proved that this substance
was II potassium salt of high purity. IR spectrum is shown
in Fig. 2 and corresponds to the data given in literature [5].
It is obvious from the above mentioned information that a
mere replacement of urea with amidosulfuric acid led to the
twofold increase of the yield of II. However, all preparative
reactions start from fluorosulfuric acid handling of which
is problematic. The acid itself is corrosive, not easily acces-
sible, and is relatively expensive. These were reasons why
fluorosulfuric acid is not too suitable for industrial pro-
duction of II and its salts. Therefore we tried to use com-
monly accessible chlorosulfuric acid instead of fluorosul-
furic acid. Its reaction with amidosulfuric acid in thionyl
dichloride was carried out analogously. Assumed mecha-
nism of the reaction follows from Scheme D:
Scheme D Mechanism of the reaction between amidosulfuric and
chlorosulfuric acids in thionyl dichloride
Fig 2 IR spectrum of imido-bis(sulfuric acid) difluoride potas-
sium salt
The product of this reaction was pure I (b.p. 95 °C/650
Pa). It was prepared in practically quantitative yield. Ra-
man spectrum of the solid product (Fig. 3) is identical with
Preparation of II and its potassium salt by the
reaction of amidosulfuric and fluorosulfuric acids
It can be supposed that the arising intermediate (OϭSϭN-
SO2Cl) reacts with fluorosulfuric acid under the formation
of imido-bis(sulfuric acid) fluoride-chloride. The possible
reaction mechanism follows from Scheme C:
Scheme C Suggested mechanism of the reaction between amido-
Fig. 3 Raman spectrum of solid imido-bis(sulfuric acid) dichlo-
sulfuric and fluorosulfuric acids in thionyl dichloride
ride
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M. Beran, J. Prıhoda
1
55/S spectrometer with FRA 106/S equipment. IR spectra were
measured in Nujol, Raman spectra were excited by using Nd:YAG
laser (λ ϭ 1064 nm), maximal output 500 mW. Samples were meas-
ured in glass ampoules.
data published in literature [14]. Also chemical shift in H
NMR spectrum (9.66 ppm) is very close to the data pub-
lished in literature (9.83 ppm [2] ).
The conversion of I into II potassium salt was done by
the above mentioned way whereas the yield was 86 % of the
theory [compared to I].
Reaction of fluorosulfuric acid with urea
Urea (9 g, 0.15 mol) was placed into 100 ml round-bottom flask.
The flask was immersed into a cold water bath and 45 ml (0.62
mol) thionyl dichloride was added under dry nitrogen. Then 33 ml
(0.61 mol) HSO3F was added dropwise. The mixture spontaneously
warmed up, bubbles of a gas were released, urea dissolved slowly,
and a intermediate white solid precipitated. At the end of the
HSO3F addition, the reaction mixture became again liquid and two
immiscible phases were formed. Immediately, after the addition of
the whole amount of HSO3F the flask was fitted with a reflux
condenser, connected to a CaCl2 drying tube, and the mixture was
heated on an oil bath at 110 °C for 42 hours. The reaction mixture
reached a viscous consistence and became light brown in colour.
Then the reaction mixture was fractionally distilled under vacuum.
The main fraction (product A) was collected in the range 45Ϫ65
°C/650 Pa as a colourless, clear liquid (36 g).
Role of thionyl dichloride in syntheses
Thionyl dichloride was used as the reaction media in all
above mentioned syntheses of imido-bis(sulfuric acid) di-
halogenides. Its exploitation was based on the fact [13] that
thionyl dichloride reacts with amino group to N-sulfinyl im-
ino group (-NϭSϭO) the formation of which is supposed
in the course of the imido-bis(sulfuric acid) dihalogenides
formation (Schemes C, D). The N-sulfinyl imino group
is analogous to isocyanate group (-NϭCϭO) anticipated
in the reaction of fluorosolfuric acid with urea (see
Scheme A).
Reaction of fluorosulfuric acid with amidosulfuric acid
Amidosulfuric acid (39 g, 0.40 mol) was placed into 250 ml round-
bottom flask and 80 ml (1.10 mol) thionyl dichloride was added
under dry argon. Then 24 ml (0.44 mol) HSO3F was added drop-
wise. At the end of the HSO3F addition the reaction mixture con-
tained two liquid and one solid phases. Then the flask was
equipped with a reflux condenser, connected to a CaCl2 drying
tube, and the mixture was heated on an oil bath at 120 °C for 38
hours. In the course of heating the reaction mixture became clear
and homogenous, coloured light brown. The reaction the mixture
was fractionally distilled under vacuum. The main fraction (pro-
duct B) was collected in the range 47Ϫ80 °C/650 Pa as a colourless,
clear liquid (48.5 g).
Conversion of imido-bis(sulfuric acid) difluoride
potassium salt into II
Possible way of conversion consists of exploitation of strong
acids for this purpose but preliminary experiments with e.g.
100 % H2SO4 or methanesulfonic acid led to a very con-
taminated product. Therefore we investigated to carry out
this conversion by using fluorosulfuric acid. The raw prod-
uct was isolated by vacuum distillation in a 62 % yield. The
process led to almost pure II. 19F NMR spectra proved that
the main product was obtained, the only impurity was
HSO3F (Fig. 1, Spectrum C).
Reaction of chlorosulfuric acid with amidosulfuric acid
Amidosulfuric acid (48.5 g, 0.50 mol) was placed into 250 ml
round-bottom flask and suspended in 100 ml (1.38 mol) thionyl
dichloride. All handling was done under dry nitrogen. Then 33 ml
(0.50 mol) HSO3Cl was added and the flask was equipped by a
reflux condenser, connected to a CaCl2 drying tube. Then this
heterogenous mixture was heated on an oil bath at 130 °C for
24 hours. After heating the reaction mixture became clear and
homogenous, coloured into pale brown. The reaction mixture was
then fractionally distilled under vacuum, oil bath (125 °C) was used
for heating. The main fraction (product C) was collected at 95 °C/
650 Pa as a colourless, clear liquid that forms long needle crystals
after cooling. The yield of I was 106 g (99 % of the theory).
Scheme
potassium salt into II
E
Conversion of imido-bis(sulfuric acid) difluoride
Experimental Section
All reactions were performed under nitrogen in anhydrous con-
ditions using conventional Schlenk techniques.
Conversion of imido-bis(sulfuric acid) halogenides into KN(SO2F)2
Fine pulverized anhydrous KF (100 g) was placed in 500 ml round-
bottom flask and dried under vacuum (190 °C/650 Pa) for 1 hour.
Thereafter dried KF was suspended in 125 ml of dry dichlorometh-
ane. The flask was equipped with a descending condenser and the
solution of imido-bis(sulfuric acid) halogenides (73 g of product A,
or 66 g of product B, or 66 g of product C) in 60 ml dichlorometh-
ane was added in small portions. The content of the flask was oc-
casionally agitated by shaking. The mixture warmed spon-
taneously, at the end the mixture even boiled. After all halogenide
solution was completely added the reaction mixture underwent the
distillation at atmospheric pressure (oil bath at 80 °C). The remain-
ing solid was thoroughly agitated with glass stick. The content of
Solvents were dried by conventional methods prior to use [15].
Urea was supplied by Lachema in analytical purity, amidosulfuric
acid, p.a., by MT Chemica and chlorosulfuric acid 98 % by Fluka.
Thionyl dichloride was supplied by Web Laborchemie Apolda and
distilled with quinoline and linen oil before use [15].
Fluorosulfuric acid was prepared by the reaction of oleum and pot-
assium fluoride [16].
Potassium fluoride dihydrate was supplied by Lachema and con-
verted to anhydrous salt by heating under vacuum.
19F NMR spectra were recorded in THF, nitromethane or without
solvent using a Bruker AVANCE DRX 300 instrument. IR and
Raman spectra were recorded on a FT-IR Bruker EQUINOX IFS
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Z. Anorg. Allg. Chem. 2005, 631, 55Ϫ59

A New Method of the Preparation of Imido-bis(sulfuric acid) Dihalogenide
the flask was evacuated (650 Pa) and the temperature of the oil
bath was then increased up to 120 °C. The rest of dichloromethane
and HF were thus removed. Then the bath temperature was in-
creased to 170Ϫ180 °C and the mixture was heated under vacuum
for another 3 hours. Then n-butylacetate (90 ml) was added to a
warm pasty reaction mixture. The arising suspension was thor-
oughly stirred with a glass stick and 90 ml tetrahydrofurane was
added after cooling. The liquid phase was filtered off on a Schlenk
frit and the remaining solid phase was three times extracted with
60 ml tetrahydrofurane. The filtrate and extracts were combined
and the excess of solvents was evaporated in vacuum (water pump).
The crystallization was supported by an dropwise addition of 300
ml dichloromethane. A colourless crystalline product was filtered
off, washed with dichloromethane and dried in vacuum heated on
hot water bath.
Acknowledgement: The authors wish to acknowledge helpful
ˇ
´
suggestions made by Prof. Zdirad Zak. This work was done under
financial support of Grant No. 575/2003, Ministry of Education of
the Czech Republic.
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´
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Conversion of KN(SO2F)2 into HN(SO2F)2
KN(SO2F)2 (20 g, 91 mmol) was placed in dry 50 ml Schlenk vessel
and HSO3F (5 ml) was added under stream of dry nitrogen. The
mixture was stirred with a glass stick and was allowed to stay for
one hour. When the conversion was finished HN(SO2F)2 was dis-
tilled off under vacuum (b.p. 48Ϫ50 °C/650 Pa). The distillate con-
tained 93 % of HN(SO2F)2. The remaining HSO3F is possible to
remove by the method published in literature [17].
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Conclusion
A new and effective way of the synthesis of potassium salt
of imido-bis(sulfuric acid) difluoride was found. The yields
of reactions are very high, reactions are easily practicable
and can be done also on a greater scale. Potassium salt of
imido-bis(sulfuric acid) difluoride can be exploited as a
component of solid electrolytes in lithium batteries [18].
´
[14] S. P. Narula, M. L. Dele, Indian J. Chem. 1979, 17A, 397Ϫ399
[15] D. D. Perrin, Purification of Laboratory Chemicals, 3rd Edi-
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[16] K. Wiechert, Z. Anorg. Chem. 1950, 261, 310Ϫ323
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ˇ
[17] A. Ruzˇcka, A. Kotasova, Z. Chem. 1987, 27, 180Ϫ180
[18] Ch. Michot, University of Montreal, personal communication
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