Carbon-chain isomerization during the electrochemical fluorination in anhydrous hydrogen fluoride - A mechanistic study

Article abstract of DOI:10.1016/S0022-1139(03)00174-X

The compounds i-C₄H₉SO₂F, i-C₃H₇SO₂F and cyclo-C₃ H₇C(O)F have been subjected to electrochemical fluorination in anhydrous hydrogen fluoride. The resulting products were fully analyzed by NMR spectroscopy. From the reaction balances, literature data and quantum chemical calculations, a new mechanism for carbon-chain isomerization during the electrochemical fluorination (ECF) is proposed. The key step in the formation of isomeric products is believed to be a ring closure reaction involving carbo-cationic or biradical intermediates.

Full text of DOI:10.1016/S0022-1139(03)00174-X

Journal of Fluorine Chemistry 124 (2003) 21–37
Carbon-chain isomerization during the electrochemical fluorination
in anhydrous hydrogen fluoride—a mechanistic study
Nikolai V. Ignat’eva,*, Urs Welz-Biermanna, Udo Heidera, Andriy Kucherynab,
Stefan von Ahsenb, Wolfgang Habelb, Peter Sartorib, Helge Willnerb
aMerck KGaA, Frankfurter Str. 250, D-64271 Darmstadt, Germany
bInorganic Chemistry Department, Gerhard-Mercator-University of Duisburg, Lotharstrasse 1, D-47048 Duisburg, Germany
Received 28 October 2002; received in revised form 16 June 2003; accepted 18 June 2003
Dedicated to Professor Dr. Dieter Naumann on the occasion of his 60th birthday
Abstract
The compounds i-C4H9SO2F, i-C3H7SO2F and cyclo-C3H7C(O)F have been subjected to electrochemical fluorination in anhydrous
hydrogen fluoride. The resulting products were fully analyzed by NMR spectroscopy. From the reaction balances, literature data and quantum
chemical calculations, a new mechanism for carbon-chain isomerization during the electrochemical fluorination (ECF) is proposed. The key
step in the formation of isomeric products is believed to be a ring closure reaction involving carbo-cationic or biradical intermediates.
# 2003 Published by Elsevier B.V.
Keywords: Electrochemical fluorination; Simons process; Isomerization; Mechanism
1. Introduction
A carbo-cationic mechanism of the isomerization in the
Simons process was proposed by Gambaretto et al. [26] based
on the hypothetical four-step (ECbECN) route for the electro-
chemical fluorination in anhydrous HF. According to this
approach, the first step in the Simons process is the electro-
chemical oxidation (E—electrochemical step) of the organic
compounds on the nickel anode to a radical cation, which
eliminate a proton (Cb—chemical step) resulting in the
formation of the corresponding radical. The second (E)
electrochemical step leads to the oxidation of the radical into
a carbo-cation followed by fluorination (addition of fluoride
anion—CN step) or isomerization [26]. The key step in this
mechanism is the direct electrochemical oxidation of the
starting material on the surface of nickel anode (further possi-
blemechanismsoftheSimonsprocessarereviewedin[1,28]).
Recently, we have demonstrated that the Simons process
does not proceed via direct electrochemical oxidation [19].
According to the ECEC mechanism [1,26] the first step in
the Simons’ process cannot proceed in the absence of
electrical current flowing through the cell. We have shown
[19] that fluorination takes place (after pre-electrolysis in
pure HF) if the Simons’ cell is disconnected from the power
supply. We therefore proposed a NiF2/NiF3 (NiF4) mediated
process. [29,30].
Isomerization of the carbon frameworks via cyclization or
chain branching during electrochemical fluorination (ECF)
of the Simons type reduces the yields of target fluoro-
chemicals produced by this method [1–7]. Cyclic compounds
formed by ECF of carboxylic acid derivatives [8–11], pri-
mary aliphatic alcohols and aldehydes [12] or substituted
alkylamines [13,14] are sometimes the main products and
can be isolated in reasonable yield. To suppress the formation
of cyclic or other isomerized products, partially fluorinated
compounds [5,15–21] or those containing a nitrogen atom in
an appropriate position may be used as the starting material
for ECF [22–24].
Possible mechanisms of the isomerization process during
the ECF have been discussed in the literature. Plashkin et al.
[25] rationalized the isomerization of a branched alkyl chain
into the linear one by the migration of a methyl (alkyl) group
to the neighboring carbon atom. This simple approach does
not explain the isomerization of a linear alkyl group into an
i-alkyl group observed by the electrochemical fluorination of
different compounds [5,22,26,27].
* Corresponding author. Fax: þ49-203-3792231.
High oxidation state nickel fluorides have been synthesized
ˇ
by Zemva et al. [31]) and could mediate the electrochemical
E-mail address: nikolai.ignatiev@merck.de (N.V. Ignat’ev).
0022-1139/$ – see front matter # 2003 Published by Elsevier B.V.
doi:10.1016/S0022-1139(03)00174-X

Fig. 1. (a) Nickel electrodes immediately after opening of the cell. Black area on the surface of the anode coat of the high oxidation state nickel fluorides, protected from the air and moisture by the film of
perfluorinated material. (b) Nickel electrodes in 2–3 min after opening of the cell. Perfluorinated material is evaporated and high oxidation state nickel fluorides are partially destroyed. (c) Nickel electrodes in
30 min after opening of the cell. High oxidation state nickel fluorides are completely converted into NiF2.

N.V. Ignat’ev et al. / Journal of Fluorine Chemistry 124 (2003) 21–37
23
process in anhydrous HF. The key step in the Simons process
O
F
O
F
O
F
CH2
CH2
CH2
CH2
CH2
CH
CH
C
C
CH
C
is a chemical fluorination, similar to that demonstrated by
Bartlett et al. [32] in the fluorination of organic compounds
with NiF3 and NiF4.
According to our proposed [29,30] mechanism, fluorina-
tion takes place on the black nickel fluoride film (see Fig. 1)
of the nickel anode. The organic molecule is adsorbed and
orientated on the surface of the anode so that the carbon
atom bearing a hydrogen is in contact with two NiF3 formula
units which convert the C–H bond into a C–F bond. This
anode process is formulated in Eqs. (1) and (2) [29]:
CH2
Singlet state
Triplet state with
two orthogonal SOMO
.
U(rel) = - 256 kJ mol-1
(it is spontaneously cyclized
in accordance with calculations)
U(rel) = 0.0
Scheme 2.
surface of Ni anode, covered with NiF3 (see Scheme 1).
Quantum chemical calculations demonstrate that cyclization
of b-biradicals into cyclo-propane derivatives is thermody-
namically favored process, (Scheme 2).
1,3-Biradicals readily undergo cyclization [39,40], for
example ring closure to cyclo-propanes [40].
The formation of a cyclo-propane derivative (structure D)
is also possible by a two-electron oxidation of one methyl
group (one-site oxidation) via the intermediate formation of
a ‘‘non-classical’’ carbo-cation ion C (Scheme 3), of the
type, proposed by Olah [41]. C is a protonated cyclo-
propane which can be diverted to D via deprotonation with
fluoride, generated in the process (see Scheme 3).
(1)
2NiF2 þ 2HF ! 2NiF3 þ 2Hþ þ 2eÀ
(2)
Reaction (1) proceeds in two steps within the Ni coordi-
nation sphere with the formation of an intermediate radical
species [29]. In some cases these radicals are stable [33–35]
and leave the surface of the anode without picking up a
fluorine atom [36] or even can be detected by ESR in crude
products after ECF of trialkylamines [37,38].
Carbo-cation B can be stabilized also via hydrogen
migration giving E, which by addition of fluoride anion is
converted to the mono-fluorinated product (F) (Scheme 3).
That is probably the route to the formation of mono-fluori-
nated sulfonyl fluoride (CH3)2CFCH2SO2F, which is present
in a low but significant amount in the product after ECF of
i-butylsulfonyl fluoride (I) (see Table 1).
Both, the radical (Scheme 1) and carbo-cation (Scheme 3)
route to D, are reasonable but the radical route may be more
favorable due to the facile single-electron oxidation rather
than a two-electron oxidation (Scheme 3), assuming that
oxidation on each site (biradical formation) proceeds inde-
pendently. It is possible that during the early stages of
fluorination when the molecule is still hydrogen-rich the
carbo-cation route predominates but that after introduction
of more fluorine into the molecule, the radical path way
becomes more favorable.
2. Results and discussion
2.1. The proposed reaction mechanism
If the geometry of the organic molecule permits adsorp-
tion on the nickel anode at two sites, formation of a biradical
(A) is possible. In this case, the intramolecular interaction
of both radical centers may lead to the formation of cyclic
products, having for example a cyclo-propane structure (D)
(see Scheme 1).
ˇ
Zemva et al. [31] found the Ni–Ni distance in solid NiF3 to
˚
be about 3.5 A. Calculation shows the distances between the
different hydrogen atoms bonded to 1 and 3 carbons in the
˚
i-alkane structure are in the range 2.6–3.8 A. This distance
fits with the 1,3-coordination of i-alkane derivatives on the
Scheme 1.

24
N.V. Ignat’ev et al. / Journal of Fluorine Chemistry 124 (2003) 21–37
Scheme 3.
ECF of the cyclo-propane carboxylic acid fluoride (see
More experimental support for this mechanism
(Schemes 1 and 3) is now presented. Three compounds,
i-butylsulfonyl fluoride (I), i-propylsulfonyl fluoride (II) and
cyclo-propane carboxylic acid fluoride (III) were subjected
to electrochemical fluorination in anhydrous HF under
typical Simons conditions.
Section 2.4) resulted in cyclo-propane ring opening. Possibly,
it proceeds in a way similar to the addition of two fluorine
atoms in olefinic or aromatic systems during the Simons
process [28,42]. A possible mechanism involves attachment
of D to the electrochemically recovered NiF3 (or NiF4) layer
on the anode surface then addition of 2 F (Scheme 4).
The process represented by Scheme 4 can proceed over
several steps and electron transfer may not be concerted.
In some respects high oxidative state nickel fluorides are
stronger fluorinating agents than diluted F2 [29]. The mecha-
nism of isomerization based on intermediate cyclo-propane
ring formation has been briefly presented previously [7,43] to
rationalize the isomerization of i-butyl to n-butyl during the
electrochemical fluorination of tri-i-butylphosphine [7].
2.2. Electrochemical fluorination of i-butylsulfonyl
fluoride (I)
ECF of i-butylsulfonyl fluoride (I) resulted in the formation
of n-, i-, s- and t-perfluorobutylsulfonyl fluorides (IV–VII)
together with small quantities of perfluoroacyl fluorides,
perfluoroalkanes, SO2F2 and SOF2 (Scheme 5) and partially
fluorinated products (Tables 1 and 2). The yields of the
products were estimated by 19F NMR spectroscopy.
The total yield of all isolated products (see Table 1) was
59.3%, usually viewed as a good yield from the Simons
process. The remainder, 41%, were volatile perfluorinated
(or polyfluorinated) small molecules, such as CF4, C2F6,
SO2F2, etc. These molecules have low boiling points and
cannot be completely trapped at À78 8C. Trapping with
liquid nitrogen is dangerous due to the possible co-trapping
of OF2 which can cause a severe explosion.
Our main aim was to elucidate the distribution pattern
of per- and poly-fluorinated products originating from the
starting compound, the mass loss in balance deficiency due
to loss of small perfluorinated molecules has no great
influence on the origins of isomeric products. We assume
that carbon-chain isomerization takes place before the final
molecular degradation, because the C–H bonds are fluorina-
ted prior to C–C.
Extensive chain isomerization revealed by the ratio of
(IV)-to-(V) (Scheme 5) is proposed to arise through the
Scheme 4.

N.V. Ignat’ev et al. / Journal of Fluorine Chemistry 124 (2003) 21–37
25
e , Ni
HF
CF3
CF3
CH3
CH3
CF3CF2CF2CF2SO2F
CHCH2SO2F
( I )
CFCF2SO2F
( V ) 4.8 %
+
+
( IV )
Yield (NMR): 36.6 %
CF3
CF3CSO2F
CF3CF2CFSO2F
+
+
+
CF3
( VII )
CF3
( VI )
0.1 %
0.9 %
O
F
CF3
O
F
CF3CF2CF2C
+
CFC
+
+
+
CF3
( IX ) 1.1 %
CF2
( XXXVIII ) 0.3 %
+
CF3 CF
+
CF CF2
CF3 CF2
O
CF2
O
( XXXVII )
( XXXVII )
0.3 %
0.6 %
SO2F2 SOF
(CF ) CF
CF3CF2CF2CF3
+
+
+
+
2
3 3
0.5 %
0.1 %
( XLIII ) 0.4 % ( XLII ) 1.0 %
Scheme 5.
Table 1
Composition of the mixtures obtained after electrochemical fluorination of i-C4H9SO2F
Compound
bp (8C)
Contents (mol%)
Total in the mixture
(mol%, 152 g)
Product separated
from HF in the
cell (70 g)
Product dissolved
in HF from the
cell (58 g)
Product trapped
at À78 8C
(24 g)
(IV)
64 [44]
81.3
10.4
49.4
6.3
42.3
6.5
61.7
8.1
(V)
–
(VI)
–
1.8
1.0
1.9
1.5
(CF3)3C–SO2F (VII)
CF3–CF2–CF2–SO2F (VIII)
–
36 [44]
ꢀ0.1
<0.1
ꢀ0.2
0.3
2.3
ꢀ0.1
0.2
0.5
(IX)
0–2 [60]
0.2
ꢀ0.1
0.8
–
10.8
–
1.9
0.2
(X)
–
–
–
–
–
–
0.3
(XI)
0.8
–
0.6
(XII)
ꢀ0.1
ꢀ0.1
<0.1
ꢀ0.2
<0.1
0.8
–
<0.1
0.4
(XIII)
(XIV)
(XV)
–
ꢀ0.1
1.2
–
<0.1
0.6
–
CF3–CF2–CF2–CHF–SO2F (XVI)
CF3–CHF–CF2–CF2–SO2F (XVII)
CF3–CF2–CF2–CH2-SO2F (XVIII)
CF3–CH2–CF2–CF2–SO2F (XIX)
CF3–CH2–CF2–CHF–SO2F (XX)
CF3–CHF–CF2–CH2–SO2F (XXI)
CF3–CH2–CF2–CH2–SO2F (XXII)
51–55/150 mbar [61]
–
0.9
ꢀ0.1
1.4
1.3
–
–
–
–
–
–
–
–
0.9
<0.1
4.0
77–79/150 mbar [61]
8.5
0.7
0.7
2.3
4.6
–
–
–
–
0.4
0.4
ꢀ0.1
ꢀ0.1
0.4
0.3
1.0
2.0

26
N.V. Ignat’ev et al. / Journal of Fluorine Chemistry 124 (2003) 21–37
Table 1 (Continued )
Compound
bp (8C)
Contents (mol%)
Total in the mixture
(mol%, 152 g)
Product separated
from HF in the
cell (70 g)
Product dissolved
in HF from the
cell (58 g)
Product trapped
at À78 8C
(24 g)
–
–
0.4
–
0.2
(XXIII)
(XXIV)
(XXV)
–
–
–
–
0.5
–
–
0.2
ꢀ0.3
ꢀ0.1
(XXVI)
(XXVII)
(XXVIII)
(XXIX)
(XXX)
–
–
–
–
–
–
–
–
–
–
0.4
1.2
–
–
–
–
–
0.2
0.5
0.5
0.2
0.9
0.3
ꢀ0.3
ꢀ0.1
CHF2–CF2–CF2–CH2–SO2F (XXXI)
CHF2–CH2–CF2–CH2–SO2F (XXXII)
CH2F–CH2–CF2–CH2–SO2F (XXXIII)
–
–
–
–
–
–
0.6
0.9
0.4
–
–
–
0.2
0.3
0.2
(XXXIV)
–
–
4.3
–
1.7
CF3–CF2–SO2F (XXXV)
CF3–SO2F (XXXVI)
8 [44]
–
–
–
–
2.2
0.4
À21 [62]
ꢀ0.1
<0.1
(XXXVII)
CF3–CF2–CF2–COF (XXXVIII)
(XXXIX)
–
–
–
–
–
–
–
5.6
2.7
2.9
1.0
0.4
0.5
7–9 [63]
–
CF3–CF2–COF (XL)
CF3–COF (XLI)
À27 [64]
–
–
–
–
0.4
ꢀ0.2
<0.1
<0.1
À53—50 [65]
(I)
47/16 mbar [66]
–
7.9
–
3.2
starting material
CF3–CF2–CF2–CF3 (XLII)
(CF3)3CF (XLIII)
(CF3)3CH (XLIV)
CF3–CF2–CF3 (XLV)
CF3–CF3 (XLVI)
SO2F2
À1 [67]
<0.1
<0.1
<0.1
<0.1
–
–
9.7
3.5
1.7
0.7
À1 to 1 [68]
10–12 [69]
À38 [67]
À78 [67]
À55 [70]
À44 [70]
<0.1
<0.01
–
ꢀ0.2
2.3
<0.1
0.4
–
ꢀ0.1
0.4
<0.1
ꢀ0.1
0.9
<0.1
ꢀ0.2
ꢀ0.5
<0.1
–
OSF2
4.7
Others
ꢀ3.0
ꢀ1.0
ꢀ1.6
formation of a cyclo-propane intermediate (Id), ring-opening
fluorination of which preferentially gives a linear product
(Scheme 6).
According to Scheme 6 the linear compound should be
formed in double the quantity compared with the i-structure,
assumingthatineachringopeningprocessbothways(1and2)
are equally likely (that probably not a case if a bulky
fluorinated group is bonded directly to i-position, see Section
2.3). The cyclo-propane structure can be formed not only
initially but also, to some extent, later, from partially fluori-
nated compounds that are intermediates in perfluorination
(Scheme 7).
From Scheme 7 the upper limit of the product ratio linear-
to-branched structure is 26:1. As the probabilities of cycliza-
tion-opening process occurring during thesecond (stepB) and
third (step C) fluorinations run are low, although not zero, the

N.V. Ignat’ev et al. / Journal of Fluorine Chemistry 124 (2003) 21–37
27
Table 2
NMR dataa of the compounds identified in the mixture after electrochemical fluorination of i-C4H9SO2F and i-C3H7SO2F
Compound
19F (d, ppm)
1H (d, ppm)
46.36 t, t, (SO2F); À81.01 t, t (3F1); À107.87 m (2F4);
(IV)
3
2
3
À120.57 m (2F ); À125.59 m (2F ); JF4;F5 ¼ 6:0 Hz;
4
5
4JF3;F5 ¼ 8:6 Hz; JF1;F3 ¼ 10:2 Hz; JF1;F4 ¼ 2:0 Hz
44.94 d, t, sep (SO2F); À71.90 d, t, d (6F1); À100.13 d, d,
3
2
3
sep (2F ); À182.88 d, sep, t (F ); JF3;F4 ¼ 4:1 Hz;
(V)
3
4
3JF1;F2 ¼ 6:6 Hz; JF2;F3 ¼ 5:8 Hz; JF2;F4 ¼ 9:2 Hz;
4JF1;F3 ¼ 10:6 Hz; JF1;F4 ¼ 2:6 Hz
5
57.57 m (SO2F); À70.59 d, d, d, q, d (3F4); À80.13 d, q, d (3F1);
À115.27 d, m (1F2A); À116.82 d, m (1F2B); À163.96 m (1F3);
(VI)
3
4
2JF
¼ 304 Hz; JF3;F4 ¼ 6:6 Hz; JF1;F3 ¼ 11:3 Hz;
2A;F2B
4JF4;F5 ¼ 6:9 Hz; JF4;F2A ¼ 13:4 Hz; JF4;F2B ¼ 13:2 Hz;
4 4
5
5JF1;F4 ¼ 6:7 Hz; JF1;F5 ¼ 2:7 Hz
4
(CF3)3C–SO2F (VII)
65.75 dec (SO2F); À62.95 d (3CF3); JF;F ¼ 10:6 Hz;
b
4
65.24 dec (SO2F); À62.82 d (3CF3); JF;F ¼ 10:2 Hz
32.60 d, sep (1F3); À74.51 d, d (6F1); À180.75 d, sep (1F2);
3
4
3JF2;F3 ¼ 21:8 Hz; JF1;F2 ¼ 7:5 Hz; JF1;F3 ¼ 6:6 Hz
(IX)
66.33 m (SO2F); À60.82 m (3F4); À83.03 d, q (3F1);
À109.35 d, m (1F2A); À114.64 d, m (1F2B);
(X)
(XI)
(XII)
5
5
2JF
¼ 293 Hz; JF1;F4 ¼ 6:2 Hz; JF1;F5 ¼ 2:3 Hz
2A;F2B
38.08 t, sep (SO2F); À61.57 t, d, d (6F1); À96.44 d,
4.23 t, sep (H ) JH;F3 ¼ 11:8 Hz
2
3
3
3
3
d, sep (2F ); JF3;F4 ¼ 6:3 Hz; JH2;F1 ¼ 7:0 Hz;
3JH;F1 ¼ 6:9 Hz
3JH2;F3 ¼ 11:3 Hz; JF1;F3 ¼ 10:8 Hz; JF1;F4 ¼ 4:0 Hz
4
5
44.72 m (SO2F); À67.00 d, d, d (6F1); À187.70 d,
4
2
3
m (1F ); JH3;F4 ¼ 43 Hz; JH2;F1 ¼ 11:6 Hz;
4JF1;F4 ¼ 11:6 Hz; JF1;F5 ¼ 2:6 Hz
5
1
3
3
58.68 sep (SO2F); À67.87 d, d (6F ); JH2;F1 ¼ 7:5 Hz;
3.70 d (CH2) JH2;H3 ¼ 4:7 Hz;
5JF1;F4 ¼ 4:3 Hz
signal of CH2 group is overlapped
with another signals
(XIII)
62.52 d, m (SO2F); À77.45 d, q, d, d (CF3); À183.59 m (1F3);
4
4
(XIV)
(XV)
3JF1;F3 ¼ 5:8 Hz; JF1;F2 ¼ 5:9 Hz; JF1;F4 ¼ 10:0 Hz;
5
4JF3;F5 ¼ 13:8 Hz; JF1;F5 ¼ 3:9 Hz; signal of CHF is
overlapped with another signals
66.59 d, sep (SO2F); À76.54 d, d (6F1) À183.70 d, t,
3.67 d, d (CH2) JH3;F2 ¼ 15:6 Hz
3
2
3
3
sep (F ); JH3;F2 ¼ 15:6 Hz; JF1;F2 ¼ 6:9 Hz;
3JH3;F4 ¼ 3:1 Hz
4JF2;F4 ¼ 11:9 Hz; JF1;F4 ¼ 3:2 Hz
5
55.60 d, d, d, d (SO2F); À80.88 d, d, d (3F1); À126.22 d, d,
5.96 d, d, d, d (H) JH;F4 ¼ 44:0 Hz
2
(XVI)
d (2F2); À119.12 d, m (1F3A); À125.20 d, m (1F3B); À189.50 d,
3JH;F3A ¼ 17:0 Hz JH;F3B ¼ 2:2 Hz
3
4
m (1F ); JH;F4 ¼ 44:0 Hz; 2JF
¼ 297 Hz; JH;F5 ¼ 2:3 Hz;
3JH;F5 ¼ 2:0 Hz
2
3
3A;F3B
3JF4;F5 ¼ 6:3 Hz; 3JF
¼ 2:6 Hz; JF2;F3B ¼ 4:5 Hz;
3
2;F3A
4JF1;F3A ¼ 11:1 Hz; JF1;F3B ¼ 8:7 Hz; JF2;F4 ¼ 13:4 Hz;
4
4
4JF ;F3A
5
¼ 6:3 Hz; JF5;F3B ¼ 12:0 Hz; JF1;F4 ¼ 2:4 Hz
4
5
46.75 m (SO2F); À74.20 d, t, d, t (3F1); À107.67 m (2F5);
(XVII)
3
2
3
À211.36 d, m (1F ); JH2;F3 ¼ 43 Hz; JH2;F1 ¼ 5:4 Hz;
3JF1;F3 ¼ 10:9 Hz; JF1;F4 ¼ 10:4 Hz; JF1;F5 ¼ 1:6 Hz; signals of
4
5
4
CF2 group (A, B system) are overlapped with another signals
66.47 t, t, t (SO2F); À80.46 t (3F1); À113.64 m (2F3);
4.13 t, d, t (CH2) JH;F4 ¼ 3:7 Hz
3
(XVIII)
(XIX)
2
3
4
4
À126.94 m (2F ); JH;F4 ¼ 3:5 Hz; JF3;F4 ¼ 12:4 Hz;
3JH;F3 ¼ 15:2 Hz JH;F2 ¼ 0:8 Hz
5
4JF1;F3 ¼ 9:9 Hz; JF2;F4 ¼ 1:1 Hz
45.79 t, t (SO2F); À61.26 t, t, t (3F1); À110.70 d, m (2F4);
3
3
3
À111.50 d, t, q (2F ); JF4;F5 ¼ 5:3 Hz; JH2;F1 ¼ 9:3 Hz;
4
4
3JH2;F3 ¼ 16:7 Hz; JF1;F3 ¼ 9:3 Hz; JF3;F5 ¼ 8:8 Hz;
5JF1;F4 ¼ 2:1 Hz

28
N.V. Ignat’ev et al. / Journal of Fluorine Chemistry 124 (2003) 21–37
Table 2 (Continued )
Compound
19F (d, ppm)
1H (d, ppm)
54.43 d, d, d (SO2F), À61.53 t, t, d (3F1); À106.52 d,
(XX)
m (1F3A); À109.33 d, m (1F3B); À187.60 d, m (1F5);
2
3
2JF
¼ 282 Hz; JH4;F5 ¼ 44 Hz; JH2;F1 ¼ 9:3 Hz;
3A;F3B
3JF5;F6 ¼ 7:2 Hz; 4JF
¼ 11:1 Hz; 4JF
¼ 7:3 Hz;
3A;F6
3B;F6
5
4JF1;F3 ¼ 9:3 Hz; JF1;F5 ¼ 2:4 Hz
64.95 d, d, d, t, (SO2F); À74.32 t, d, d (3F1); À106.56 d,
5.15 d, d, d, q (CHF) JH2;F3 ¼ 43:8 Hz
2
(XXI)
m (1F4A); À109.06 d, m (1F4B); À209.78 d, m (1F3);
3JH2;F4A ¼ 5:6 Hz JH2;F4B ¼ 14:3 Hz
3
2
3
2JF
¼ 280 Hz; JH2;F3 ¼ 44 Hz; JH2;F1 ¼ 5:6 Hz;
3JH2;F1 ¼ 5:6 Hz; signal of CH2 group
4A;F4B
3JH5;F6 ¼ 2:7 Hz; JH5;F3 ¼ 2:0 Hz; JF1;F3 ¼ 9:1 Hz;
is overlapped with another signals
4
3
4JF1;F4 ¼ 11:1 Hz; 4JF
¼ 13:9 Hz; 4JF
¼ 11:2 Hz;
4A;F6
4B;F6
5JF3;F6 ¼ 5:3 Hz
63.83 t, t (SO2F); À61.94 t, t (3F1); À92.72 m (2F3)c;
3.08 t, q (CH22) 4.04 t, d (CH2
)
4
(XXII)
3JH4;F5 ¼ 3:8 Hz; JF3;F5 ¼ 12:9 Hz;
3JH2;F3 ¼ 14:4 Hz JH2;F1 ¼ 9:6 Hz
4
3
3JH2;F1 ¼ 4JF1;F3 ¼ 9:5 Hz
3JH4;F5 ¼ 4:0 Hz JH4;F3 ¼ 13:0 Hz
3
66.08 t, m (SO2F); À80.06 t (3F1); À123.79 d, d, d, m (1F4A);
À124.24 d, d, d, m (1F4B); 2JF
¼ 295 Hz; JH4;F4 ¼ 54 Hz;
2
(XXIII)
4A;F4B
4
4
3JH3;F4 ¼ 15:5 Hz; JF2;F5 ¼ 11:6 Hz; JF4;F5 ¼ 3:4 Hz;
2
5JF1;F4 ¼ 7:9 Hz; signals of CF2 group (A, B system) are
overlapped with another signals
58.36 m (SO2F); À68.10 t, d, d (3F1); À122.4 d, d, d, q, d (1F2A);
(XXIV)
À125.5 d, d, d, q, d (1F2B); 2JF
¼ 298 Hz;
2A;F2B
3
3
2JH2;F2 ¼ 54 Hz; JH3;F1 ¼ 6:8 Hz; JH3;F2A ¼ 8:2 Hz;
3JH3;F2B ¼ 19:7 Hz; JF ;F2A
1
¼ 7:1 Hz; JF1;F2B ¼ 7:9 Hz;
4
4
5JF1;F5 ¼ 4:2 Hz; 5JF
¼ 7:0 Hz; 5JF
¼ 2:2 Hz
2A;F5
2B;F5
57.56 quin (SO2F); À124.10 d, d, m (4F1,2); JH;F ꢀ 53 Hz;
2
5
3JH3;F1 ꢀ 12 Hz JF1;F5 ¼ 4:0 Hz
(XXV)
57.29 m (SO2F); À225.82 t, d, t (2F1,2); JH;F ¼ 47 Hz;
2
3JH3;F1 ¼ 21:2 Hz; JF1;H2 ¼ 1:4 Hz
4
(XXVI)
65.2 d, m (SO2F); À76.31 d, d, d, d (3F1); À129.9 d, d, d, q,
d (1F2A); À131.6 d, d, d, q, d (1F2B); À184.2 m (F3);
3.86 d, d (CH2) 6.32 t, d, q (CHF2)
3
(XXVII)
2JH2;F2 ¼ 52:9 Hz JH2;F3 ¼ 4:0 Hz
2
3
3
2JF
3JF
¼ 309 Hz; JH2;F2 ¼ 53 Hz; JF1;F3 ¼ 9:1 Hz;
3JH4;F3 ¼ 8:5 Hz JH4;F5 ¼ 3:6 Hz
2A;F2B
4
¼ 7:6 Hz; 3JF
¼ 7:6 Hz; JF ;F2A
1
¼ 7:9 Hz;
4JH2;F1 ¼ 1:1 Hz
2A;F3
2B;F3
4
5
4JF1;F2B ¼ 7:5 Hz; JF3;F5 ¼ 15:3 Hz; JF1;F5 ¼ 2:6 Hz;
5JF
¼ 4:8 Hz; 5JF
¼ 3:6 Hz
2A;F5
2B;F5
65.94 d, m (SO2F); À132.62 d, d, d (4F1,2);
6.30 t, d, t (CHF2) JH;F ¼ 55:4 Hz
2
3
2
3
4
À184.73 m (1F ); JH;F ¼ 54 Hz; JF1;F3 ¼ 7:8 Hz;
3JH1;F3 ¼ 4:0 Hz JH1;F2 ¼ 1:8 Hz
(XXVIII)
(XXIX)
5
4JF3;F5 ¼ 14:3 Hz; JF1;F5 ¼ 3:5 Hz
À132.18 d, d, d, m (1F1A); À133.55 d, d, d, m (1F1B);
3
2
2
ꢀÀ184.8 m (1F ); À228.20 t, d, m (1F ); JH1;F1A ¼ 56 Hz;
2
3
2JH1;F1B ¼ 55 Hz; JH2;F2 ¼ 47 Hz; JF2;F3 ¼ 12:5 Hz;
3JF
¼ 7:6 Hz; 3JF
¼ 7:2 Hz; signal of SO2F group is
1A;F3
1B;F3
overlapped with another signal
ꢀÀ185 m (1F3); À238.78 t, d, m (2F1,2); JH;F ¼ 46 Hz;
3JF1;F3 ¼ 13:8 Hz; signal of SO2F group is overlapped with
another signal
2
(XXX)
65.48 t, t (SO2F); À114.20 m (2F4); À130.33 m (2F3);
(XXXI)
2
2
3
À137.22 d, t, t (2F ); JH1;F2 ¼ 52 Hz; JF2;F3 ¼ 5:2 Hz;
4
4
3JH5;F6 ¼ 3:8 Hz; JF2;F4 ¼ 7:9 Hz; JF4;F6 ¼ 11:4 Hz
63.76 t, t (SO2F); À92.60 m (2F4); À115.65 d, t, t (2F2);
3
3
2JH1;F2 ¼ 55 Hz; JH3;F2 ¼ 15:3 Hz; JH5;F6 ¼ 3:6 Hz;
4
4JF2;F4 ¼ 5:7 Hz; JF4;F6 ¼ 12:9 Hz
(XXXII)

N.V. Ignat’ev et al. / Journal of Fluorine Chemistry 124 (2003) 21–37
29
Table 2 (Continued )
Compound
19F (d, ppm)
1H (d, ppm)
63.05 t, t (SO2F); À94.50 m (2F4); À241.76 t, t, t (1F2);
3
3
2JH1;F2 ¼ 46 Hz; JH3;F2 ¼ 15:2 Hz; JH5;F6 ¼ 3:6 Hz;
(XXXIII)
4
4JF2;F4 ¼ 5:5 Hz; JF4;F6 ¼ 12:6 Hz
3
3
63.21 d, t (SO2F); À136.88 m (F ); JH4;F5 ¼ 3:1 Hz;
1.62 d (2CH3) 3.73 d, d (CH2)
3
3JH1;F3 ¼ 21:3 Hz; JH4;F3 ¼ 15:8 Hz; JF3;F5 ¼ 12:9 Hz
3JH1;F3 ¼ 21:3 Hz JH4;F3 ¼ 15:8 Hz
3
4
(XXXIV)
b
À75.98 d, d, t (3F1); À82.43 d, m (2F3,4); À82.94 d, m (2F5,6);
2
2
3
(XXXVII)
(mixture of two isomers)
À183.39 m (1F ) JF3;F4 ¼ 2JF5;F6 ¼ 102 Hz JF1;F2 ¼ 8:8 Hz;
4JF1;F3;5 ¼ 8:7 Hz JF1;F4;6 ¼ 4:2 Hz
4
b
À80.99 d, d, m (3F1); À79.83 d, d, t (1F4); À84.79 d, d, t (1F5);
(XXXIX)
À124.16 d, d, d, d, q (1F2A) À126.21 d, m (1F2B); À133.62 m (1F3);
2JF
¼ 217 Hz; JF4;F5 ¼ 91 Hz; JF1;F2A ¼ 1:0 Hz;
3 3
2
3
2A;F2B
3JF1;F2B ¼ 10:0 Hz; JF3;F4 ¼ 9:0 Hz; JF3;F5 ¼ 8:6 Hz;
3JF
¼ 6:0 Hz; 4JF
¼ 8:1 Hz; 4JF
¼ 14:1 Hz;
2A;F3
2A;F4
2A;F5
4JF1;F3 ¼ 3:0 Hz; 4JF
ꢀ JF
¼ 8:6 Hz
4
2B;F5
2B;F4
d55.82 d, d, d, q (SO2F); À82.14 d, m (CF3); À120.78 d, m;
(CF2, FA); À127.81 d, m;(CF2, FB); À190.85 d, m (CHF)
5.22 d, m
(L)
2
2
3
JFAFB ¼ 288 Hz; JH;F ¼ 44:0 Hz; JH;F4 ¼ 2:7 Hz;
3JF3;F4 ¼ 6:5 Hz; 4JF
¼ 12:3 Hz; 4JF
¼ 5:9 Hz
2A;F4
2B;F4
d66.28 m (SO2F); À84.91 m (CF3); À116.09 dt (CF2);
4.73 t, d, q
(LI)
3JH;F4 ¼ 4:3 Hz; JH;F2 ¼ 15:5 Hz; JH;F1 ¼ 0:6 Hz;
3
4
4JF2;F4 ¼ 11:9 Hz
d42.50 t, m (SO2F); À60.39 quin, d (CF3); À97.72 d, t, q
(LII)
(LIII)
3
3
(CF2); JH2;F1 ¼ 9:0 Hz; JH2;F3 ¼ 17:1 Hz;
3JF3;F4 ¼ 8:5 Hz; JF1;F3 ¼ 8:8 Hz; JF1;F4 ¼ 1:4 Hz
4
5
d65.75 t, t, t (SO2F); À115.89 d, t, d, t (CF2); À136.65 d,
2
3
m (CF2H); JH;F1 ¼ 52:5 Hz; JH3;F4 ¼ 4:3 Hz;
4JF2;F4 ¼ 11:8 Hz; JF1;F4 ¼ 1:0 Hz
5
d56.40 sex, d (SO2F); À73.25 d, d, d, m (CF3); À167.80 m (CF);
3
4
(LIV)
(LV)
3JF1;F3 ꢀ 7 Hz; JF3;F4 ¼ 3:9 Hz; JF1;F4 ¼ 10:1 Hz;
signals of CHF2 group (A, B system) are
overlapped with stronger signals
d56.20 quin, d, t (SO2F); À131.29 dt (CHF2);
2
3
À175.39 quin, t, d (CF); JH;F ¼ 52 Hz; JH1;F2 ¼ 6:2 Hz;
3
3
4JH1;F3 ¼ 2:1 Hz; JF2;F3 ¼ 4:1 Hz; JF1;F2 ¼ 10:2 Hz;
4JF1;F3 ¼ 10:5 Hz
d52.68 d, t, m (SO2F); À131.1 d, d, d, d, d, t (CHF2, FA);
À132.2 d, d, d, d, d, t (CHF2, FB); À171.67 m (CF);
(LVI)
À240.55 t, d, d, t, d (CH2F); 2JF
ꢀ 300 Hz;
A;FB
2
4
2JH1;F1 ¼ 52 Hz; JH2;F2 ¼ 46 Hz; JH1;F2 ¼ 1:6 Hz;
3
3
4JH2;F1 ¼ 1:2 Hz; JF1;F3 ¼ 9:9 Hz; JF2;F3 ¼ 14:9 Hz;
4
4
4JF1;F2 ¼ 2:6 Hz; JF1;F4 ¼ 9:9 Hz; JF2;F4 ¼ 13:5 Hz
d49.22 t, m (SO2F); À166.46 m (CF);
2
(LVII)
À236.78 t, d, d, m (CH2F); JH1;F1 ¼ 46 Hz;
3JF1;F2 ¼ 14:4 Hz; JF2;F3 ¼ 2:6 Hz; JF1;F3 ¼ 13:0 Hz
3
4
d40.68 d, m (SO2F); À158.83 q, d, d, d, d (CF);
2
À229.94 t, d, d, q (CH2F); JH1;F1 ¼ 46 Hz;
(LVIII)
3
3JF1;F3 ¼ 6:4 Hz; JH2;F3 ¼ 22:8 Hz; 3JH
¼ 10:8 Hz;
1A;F3
3
4
3JH
¼ 9:6 Hz; JF3;F4 ¼ 2:4 Hz; JF1;F4 ¼ 16:2 Hz
1B;F3
d66.26 sep, d (SO2F); À62.13 dd (2CF3);
6.08 sep, d
3
4
3JH2;F3 ¼ 1:9 Hz; JH2;F1 ¼ 7:0 Hz; JF1;F3 ¼ 10:9 Hz
(LIX)
(LX)
d
ꢀ66.3 m (SO2F); À61.84 d, d, d, d, d (CF3); À122.0 d,
m (CHF2, FA); À123.0 d, m (CHF2, FB);
2JF
ꢀ 300 Hz; JH2;F2 ¼ 52 Hz; JF1;H3 ¼ 8:3 Hz;
4 4
2
3
A;FB
4JF1;F4 ¼ 9:8 Hz; JF1;F2 ꢀ 9 Hz; JF1;H2 ꢀ 1:9 Hz

30
N.V. Ignat’ev et al. / Journal of Fluorine Chemistry 124 (2003) 21–37
Table 2 (Continued )
Compound
19F (d, ppm)
1H (d, ppm)
d
2
65.97 sep, d, t (SO2F); À121.60 d, m (2CHF2); JH1;F1 ¼ 53 Hz;
3JH3;F4 ¼ 3:5 Hz; 4JF
¼ 10:8 Hz; JH1;F4 ¼ 1:9 Hz
4
(LXI)
1;2;F4
d
2
À230.12 t, d, d, t (2CH2F); JH1;F1 ¼ 46 Hz;
4
(LXII)
3JF1;H3 ¼ 26:9 Hz; 4JF
¼ 11:6 Hz; JF1;H2 ¼ 4:2 Hz;
1;2;F4
signal of SO2F group is overlapped with another signal
d
2
49.00 d, m (SO2F); À225.91 t, d, d, q (CH2F); JH1;F1 ¼ 46:5 Hz;
3JF1;H3 ¼ 22:1 Hz; JF1;F4 ¼ 14:5 Hz; JF1;H2 ꢀ 1 Hz
4
4
(LXIII)
a Spectra were recorded for a neat liquid with CD3CN-film. CCl3F and TMS served as internal references.
b
19F and 1H NMR spectra were recorded at À30 8C for a neat liquid.
c Position of the signal depends on the concentration.
d Solvent: CD3CN, CCl3F internal.
2
NiF3
n-nonafluorobutylsulfonyl fluoride (IV)-to-i-nonafluorobu-
tylsulfonyl fluoride (V) was about 7.6:1 (see Scheme 5
and Table 1). Taking into consideration all partially fluori-
nated products present in the mixture (see Table 1) and
the products, which are formed from the i-structure by loss
of methyl groups or conversion to acyl fluorides and
s-butylsulfonyl fluorides, the corrected ratio is about 4.3:1.
This is in good agreement with the prediction of our model
(Schemes 1 and 3).
( linear-structure )
FSO2CH2CHFCH2CH2F
CH2F
1
CH2
2
NiF3
FSO2CH2CH
( iso-structure )
FSO2CH2CH
2
CH2F
CH2
1
( Id )
2
NiF3
( linear-structure )
FSO2CH2CHFCH2CH2F
Scheme 6.
real molar ratio linear-to-i-structure in the resulting mixture
should be substantially less than 26:1 but higher than 2:1.
Analysis of the reaction mixture obtained from ECF of
i-butylsulfonyl fluoride (I) indicated that the molar ratio,
Remarkably, all partially fluorinated compounds of the
n-butyl-type, XVI–XXII and XXXI–XXXIII bear a –CF2–
group in the b-position to the SO2F group (Tables 1 and 2).
At the same time fluorination in the g- and especially the
CH2F
CH3
NiF3
FSO2CH2CHFCH2CH2F
+
FSO2CH2CH
FSO2CH2CH
CH2F
CH3
(step A)
18 mol
27 mol
9 mol
NiF3
(step B)
CHF2
+
FSO2CH2CHFCHFCHF2
FSO2CH2CH
3 mol
CHF2
6 mol
NiF3
(step C)
CF3
+
FSO2CH2CHFCF2CF3
2 mol
FSO2CH2CH
CF3
1 mol
Scheme 7.
CH3
CH2
CH2
CH3
2 NiF3
2 HF
2 NiF3
HF
2 NiF3
FSO2CH2CF
FSO2CH2CH
( I )
FSO2CH2CF
CH3
CH3
( Id )
( XXXIV)
CH2F
FSO2CH2CF2CH2CH2F
( XXXIII )
+
FSO2CH2CF
( XXX )
CH2F
Scheme 8.

N.V. Ignat’ev et al. / Journal of Fluorine Chemistry 124 (2003) 21–37
31
a-positions has occurred later, in accordance with the pro-
CH2
CH3
CH3
CH3
NiF
2 HF
2
3
FSO2CHCH
( Ic )
FSO2CH2CH
( I )
_
posed mechanism (see Schemes 6 and 7). By opening of the
cyclo-propane- to the n-butyl-structure, the fluorine atoms
occupy positions b and o, but not positions a and g in respect
to the SO2F group (Scheme 8).
Both XXX and XXXIII are found among the other
products (see Table 1).
2
NiF3
FSO2CHFCH2CHFCH3
( linear-structure )
1
FSO2CH
CH CH3
2
NiF3
The concentrations of products CF3CH2CF2CH2SO2F
(XXII) and CF3CF2CF2CH2SO2F (XVIII) in the resulting
mixture is much higher than those of the corresponding com-
pounds, containing one additional fluorine atom (Table 1).
This observation indicates that by the opening of the cyclo-
propane structure into the linear n-butyl structure (Scheme 8)
the fluorine atoms are placed preferably on the b- and
o-positions but not into positions a and g with respect to
the SO2F group and the fluorination process on the positions
a and g is hindered by the presence of the bulky fluorinated
SO2F group and neighboring CF2 and CF3 groups.
In (CF3)2CHCF2SO2F (XI), replacement of the last hydro-
gen atom in the i-position is difficult and therefore the
content of this compound in the mixture is relatively high
(Table 1).
The presence of perfluoro-(1-methylpropane)sulfonyl
fluoride (VI) in the mixture indicates that during the ECF
process, i-butylsulfonyl fluoride (I) isomerizes, not only to
the linear n-butyl structure but also to the s-butyl structure,
possibly according to the mechanism (Scheme 9).
Formation of biradical (Ic) on the surface of Ni/NiFx
anode could be hindered by the bulky FSO2 group, possibly
explaining why perfluoro-s-butylsulfonyl fluoride (VI) is a
minor product in the mixture after ECF of i-butylsulfonyl
fluoride. Compound FSO2CH(CH2F)CHFCH3 (Scheme 9)
can undergo additional fluorination or participate in the next
step of cyclo-propane ring-contraction/ring-opening reac-
tions. The probability of the cyclo-propane ring contraction
described by Scheme 9 is low. Therefore, the concentration
of perfluoro-s-butylsulfonyl fluoride (VI) is low and is
extremely low for perfluoro-t-butylsulfonyl fluoride (VII)
(see Table 1 and Scheme 5).
2
FSO2CFCF2CF3
CH2
( Ie )
FSO2CHCHFCH3
3
CH2F
( secondary-structure )
CF3
( VI )
CH3
2
NiF3
FSO2CHFCH
( iso-structure )
Scheme 9.
CH2F
[45]. A similar process can take place in the electrochemical
cell.
At the early stage of fluorination, formation of carbo-
cations of type B (Scheme 3) is possible. For carbo-cation
(Ia) (Scheme 10) no optimized open-chain geometry was
found (no energy minimum) by quantum chemical cal-
culations [46]. Assuming a reasonable starting geometry
for cation (Ia) led directly to the cyclic structure (Ib)
(Scheme 10).
Possibly, cyclocations such as (Ib) could be intermediates
in the conversion of fluorinated sulfonyl fluorides into acyl
fluorides (Scheme 11).
Formation of cyclic cations like (Ib) is possible, not only
from carbo-cations generated directly from the starting
material (I) but also from the later stage of the fluorination
process. Sulfonium salts of type (Ib) are known in the
literature and the equilibrium between the sulfonium salt
(Ib) and the sulfurane (If) is well established [47,48].
Nucleophilic attack by fluoride ion on the activated a-carbon
atom in (Ib) should open irreversibly the cyclic into the
i-structure (Ig) (Scheme 11).
The mechanism of formation of perfluorooxetane
(XXXVII) and perfluorooxirane (XXXIX) is not clear.
Formation of perfluoroacyl fluorides during electro-
chemical fluorination of alkanesulfonyl fluorides is a phe-
nomenon which appears have been mentioned only once
previously in the literature [44] but was not investigated.
Recently, Behr and Cheburkov [45] have published the
conversion of perfluoroalkanesulfonyl fluorides into per-
fluoroacyl fluorides catalyzed by SbF5.
2.3. Electrochemical fluorination of
i-propylsulfonyl fluoride
ECF of i-propylsulfonyl fluoride (II) results in branched
and linear fluoropropylsulfonyl fluorides (see Scheme 12
and Table 3) together with partially fluorinated compounds
bearing one or two hydrogen atoms.
A possible mechanism of this process is based on the inter-
mediate formation of fluorosulfinic acid perfluoalkylesters
+
CH2
CH3
2 NiF3
HF
F
FSO2CH2CH
( I )
FSO2CH2CH
_
+
S
CH3
CH3
CH3
O
( Ib )
( Ia )
Scheme 10.

32
N.V. Ignat’ev et al. / Journal of Fluorine Chemistry 124 (2003) 21–37
CH3
CH3
e , Ni
HF
CF3
CF3
CHSO2F
( II )
CF3CF2CF2SO2F
( VIII )
CFSO2F
( IL )
+
9.7 %
Yield (NMR): 22.8 %
CF3
SO2F2
+
CF3CF2CF3
CF3CF2CHFSO2F
+
+
CHSO2F
+
CF3
0.5 %
1.1 %
( XLV )
( L )
( LIX ) 5.5 %
3.6%
Scheme 12.
The ratio of linear-to-branched molecules is about 1:3
(see Table 3). This ratio is not consistent with the prediction
of our cyclo-propane model (Schemes 1 and 3), probably due
to hindrance to cyclo-propane ring formation opening by the
neighboring FSO2 group (Scheme 13).
Electrochemical fluorination of i-propylsulfonyl fluoride
(II) is preferred over one-site (methyl group) fluorination,
which leads to the enrichment of compounds with the
i-structure. The presence of compounds (for example,
Scheme 11.
Table 3
Composition of the mixture obtained after electrochemical fluorination of i-C3H7SO2F
Compound
bp (8C)
Contents (mol%)
Total in the
mixture (mol%)
Product from the
cell (24.4 g)
Product from trapped
at À78 8C (23.2 g)
–
38.5
57.6
48.0
(IL)
CF3–CF2–CF2–SO2F (VIII)
CF3–CF2–CHF–SO2F (L)
CF3–CF2–CH2–SO2F (LI)
CF3–CH2–CF2–SO2F (LII)
CHF2–CF2–CH2–SO2F (LIII)
36 [44]
21.4
1.5
19.7
20.6
0.8
77 [71]
–
–
–
–
–
–
–
3.4
1.7
<0.1
0.3
<0.1
ꢀ0.1
(LIV)
(LV)
–
–
2.9
1.9
–
–
1.5
0.9
(LVI)
–
–
0.6
–
–
0.3
(LVII)
ꢀ0.1
<0.1
(LVIII)
(LIX)
–
–
–
–
ꢀ0.1
23.2
0.9
–
–
–
–
<0.1
11.7
0.5
(LX)
(LXI)
0.3
ꢀ0.1
(LXII)
–
0.2
–
ꢀ0.1
(LXIII)
–
ꢀ0.1
–
–
<0.1
(II, starting material)
32–33/13 mbar [72]
4.2
2.2
CF3–CF2–SO2F (XXXV)
CF3–SO2F (XXXVI)
8 [44]
–
–
2.7
1.3
À21 [62]
<0.1
<0.1

N.V. Ignat’ev et al. / Journal of Fluorine Chemistry 124 (2003) 21–37
33
Table 3 (Continued )
Compound
bp (8C)
Contents (mol%)
Total in the
mixture (mol%)
Product from the
cell (24.4 g)
Product from trapped
at À78 8C (23.2 g)
CF3–CF2–COF (XL)
CF3–CF2–CF3 (XLV)
CF3–CHF–CF3 (LXIV)
CF3–CH2–CF3 (LXV)
CF3–CF2–CHF2 (LXVI)
CF3–CF3 (XLVI)
SO2F2
À27 [64]
À38 [67]
À16 [73]
À0.5 [74]
À17 [75]
À78 [67]
À55 [70]
À44 [70]
–
–
–
–
–
–
–
–
1.8
4.9
0.8
1.8
1.1
0.5
2.2
6.8
0.9
2.4
0.4
0.9
0.5
0.2
1.1
3.4
OSF2
Scheme 13.
CF3CH2CF2SO2F) in the reaction mixture (see Table 3)
confirms, that the process of cyclo-propane ring contrac-
tion–additional fluorination still takes place to an extent.
Gambaretto et al. (Scheme 14; [26]) have observed
the same phenomenon in electrochemical fluorination of
i-butyryl chloride.
Contrary to ECF of i-butyryl chloride [26] (see above),
n-heptafluorobutyryl fluoride (XXXVIII) and i-heptafluoro-
butyryl fluoride (IX) are formed in a molar ratio of 2.3:1.
This is in good agreement with the prediction of our model
(Schemes 1 and 3).
The ratio of the linear-to-i-structure of about 1:1.8 [26] is
at variance with the prediction of our model. We suggest that
a bulky fluorinated –C(O)F group a- to the reaction center,
as in the –SO2F group case, hinders isomerization via the
intermediate cyclo-propane ring contraction, ring-opening
process. Isomerization of i-butyryl chloride is higher (36%
[26]) than found for i-propylsulfonyl fluoride, as the –C(O)F
group is less bulky. In order to investigate this further we
carried out the electrochemical fluorination of a similar
compound, that has the cyclo-propane-ring, cyclo-propane
carboxylic acid fluoride (III).
2.5. Comparisons with other studies
The following is an attempt to determine the applicability
of our model to published data.
In 1974, Plashkin et al. reported the isomerization of
heterocyclic N-i-alkylamines during electrochemical fluori-
nation; the migration of the alkyl group was proposed [25].
The molar ratio of the perfluoro-N-(n-butyl)pyrrolidine
and perfluoro-N-(i-butyl)pyrrolidine resulting from ECF
of N-i-butylpyrrolidine is 2:1, in harmony with our model.
The analysis of the reaction mixture after electrochemical
fluorination of N-i-butylpiperidine [25] gives a similar
result. The molar ratio of the sum of the products per-
fluoro-N-(n-butyl)piperidine plus perfluoro-N-(n-butyl)-
3-(trifluoromethyl)pyrrolidine having an n-structure and
the sum of product perfluoro-N-(i-butyl)piperidine plus
2.4. Electrochemical fluorination of cyclo-propane
carboxylic acid fluoride (III)
The electrochemical fluorination of compound (III) leads
to the formation of a mixture of perfluorobutyryl fluorides
with linear (XXXVIII) (NMR yield 27.5%) and i-structures
(IX) (yield 11.9%). Other compounds formed include of
perfluoroethane (yield 4.8%), propane (yield 2.0%), and
cyclobutane (yield 3.5%). A rationalization is given in
Scheme 15.
Scheme 14.
Scheme 15.

34
N.V. Ignat’ev et al. / Journal of Fluorine Chemistry 124 (2003) 21–37
perfluoro-N-(n-propyl)piperidine is again 2:1. Perfluoro-N-
(n-propyl)piperidine is formed by splitting off the methyl
group in the position 2 of the i-butyl chain and should be
included into the sum of the products with a branched
structure.
isomerizations, but also the isomerization of n-alkyl into
i-alkyl groups.
The formation of cyclic products in the production of
perfluorooctanoic acid, C7F15COOH, with the Simons
method is well known. Approximately 60% of the starting
material, C7H15C(O)F, is converted into perfluorooxolanes
and perfluorooxanes [5] with perfluoro-n-alkyl and per-
fluoro-i-alkyl groups in position 2. This indicates that ring
closure is straight forward and that the isomerization of alkyl
groups in position 2 occurs after oxolane or oxane ring
formation. The content of perfluoro-2-alkyl-oxolanes in
the mixture after ECF is particularly high and corresponds
to 42 wt.% [5]. Product perfluoro-2-(n-butyl)oxolane
reflects the intramolecular cyclization during the Simons
process via attack of a carbon centered radical on oxygen
[5]. The products perfluoro-2-(s-butyl)oxolane and per-
fluoro-2-(i-butyl)oxolane are formed similarly but with
subsequent isomerization of a n-butyl into s-butyl or
i-butyl groups, probably involving intermediate formation
of cyclo-propane derivatives between the positions 1 and 3, 2
and 4 of the n-butyl chain. The formation of a t-butyl
structure is not possible and it was not found in the reaction
mixture [5].
The picture is different for the mixture obtained by the
electrochemical fluorination of N-i-propylpiperidine [25].
The ratio of the products perfluoro-N-(n-propyl)piperidine
plus perfluoro-N-(n-propyl)-3-(trifluoromethyl)pyrrolidine to
perfluoro-N-(i-propyl)piperidine plus perfluoro-N-(n-ethyl)-
piperidine is 1.17:1, less than predicted by our model. It
seems that nitrogen in the aliphatic chain hinders the ring
closing–ring opening reactions similar to the SO2F group
in FSO2CH(CH3)2. That leads to a larger content of the
i-product in the mixture. The influence of the nitrogen on the
efficiency of five and six-membered ring formation during
ECF is known [22–24]. Abe et al. [24] have proposed the
strategic incorporation of a nitrogen atom in the aliphatic
chain to prevent the intramolecular cyclization.
In the mixture from ECF of N-t-butylpyrrolidine [25] the
higher probability of cyclo-propane ring formation invol-
ving all three methyl groups in the starting compound should
be considered. The molar ratio between the sum of isomeric
products perfluoro-N-(s-butyl)pyrrolidine, perfluoro-N-(i-
butyl)pyrrolidine, perfluoro-N-(n-butyl)pyrrolidine and the
product perfluoro-N-(t-butyl)pyrrolidine with the structure
of the starting material is 5.25:1, in good agreement with our
prediction.
3. Conclusion
Our new model for the mechanism of ECF process
(Schemes 1 and 3) is able to explain or to predict:
ECF of N-(o-chloroalkyl)-hexahydroazepines yields the
mixture of corresponding fluoro-(N-alkyl-hexahydroaze-
pines) together with isomeric fluoro-(1-alkyl-methylpiperi-
dines) [49]. According to our model, the formation of
biradicals is possible by the simultaneous oxidation of two
C–H bonds with NiF3 on the surface of the anode at the
positions 2 and 4; 3 and 5; 4 and 6; 5 and 7 of the hexahy-
droazepine ring. Ring closure reactions at these positions
with subsequent C–C bond cleavage in the cyclo-propane
derivatives formed lead to the formation of the mixed
perfluoro-1-alkyl-methylpiperidines with predicted molar
ratio, 3-CF3:4-CF3:2-CF3 of 1:0.5:0.5, respectively. Due to
the influence of the nitrogen atom, the yield of the 2-CF3
compound may be lower. Consequently, the experimental
product distribution, 1:0.53:0.29 [49,50], is in good agree-
ment with our model.
(i) the isomerization of branched alkyl to linear chains;
(ii) the isomerization of linear to branched alkyl chain;
(iii) ring contraction isomerization.
The key step in the formation of isomeric products during
the Simons process is the ring closure reaction via carbo-
cationic or biradical intermediates. A quantitative estimation
of product distribution patterns is possible. The influence
of bulky groups (–SO2F, –C(O)F, etc.) or the nitrogen atom
on the isomerization can be rationalized.
4. Experimental
4.1. Apparatus
ECF of N-substituted piperidines, leads to the formation
of perfluoro-3-CF3-pyrrolidine derivatives [6,27,51].
Obviously, cyclo-propane ring closure reaction between
the positions 2 and 4, 4 and 6 of the piperidine ring is
hindered by nitrogen. The only possibility is ring formation
between the positions 3 and 5. In this case, subsequent
cyclo-propane ring opening reactions during ECF can give
either 3-CF3-pyrrolidine derivatives or compounds with the
structure of the starting material, in harmony with experi-
mental results [6,27,51]. Our proposed model (Schemes 1
and 3) is able to explain not only the isomerization of
branched alkyl chains into linear chains or ring contraction
A stainless steel Simons-type cylindrical cell (total
volume 390 cm3) with an array of nickel anodes (effective
anodic area: S ¼ 4:27 dm2) and cathodes with the same
effective area was used for ECF of i-butylsulfonyl fluoride
and cyclo-propane carbonic acid fluoride. The cell was
equipped with a stainless steel condenser and two FEP-traps
cooled to À78 8C. ECF of i-propylsulfonyl fluoride was
carried out in a cell with a total volume of 310 cm3, effective
anodic area, S ¼ 3:75 dm2. In all experiments the tempera-
ture of the cell body was maintained at 0 8C and the
temperature of the condenser was kept at À30 8C.

N.V. Ignat’ev et al. / Journal of Fluorine Chemistry 124 (2003) 21–37
35
4.2. Analytical procedures
bifluoride in water (200 g, 2.56 mol of KHF2 in 200 cm3 of
H2O) in a 1 l polyethylene flask. The reaction mixture was
intensively stirred at room temperature during three days
(after 24 and 48 h 50 cm3 of H2O were added) and the
organic phase was separated and filtered off from the white
deposit. Two hundred and forty grams of the resulting clear
liquid (contained 70% of i-BuSO2F and 30% of i-BuSO2Cl)
were mixed again with 70 g (0.9 mol) of KHF2 in 150 cm3 of
H2O and stirred at room temperature additionally during 4
days. The organic phase was separated, washed with water,
filtered and dried with Na2SO4. One hundred ninety grams
of i-butylsulfonyl fluoride (purity of 98.6% by GC analysis)
were obtained (yield 71.4%). 19F NMR spectrum (solvent:
CDCl3; standard internal CCl3F) d (ppm): À57.50 t (SO2F).
1H NMR spectrum (solvent: CDCl3; standard: internal
TMS) d (ppm): 1.15 dd (CH3), 2.23 t, sep (CH), 3.43 dd
(CH2); JH;F ¼ 0:9 Hz, JH;H ¼ 6:7 Hz, JH;F ¼ 4:0 Hz.
i-Propylsulfonyl fluoride (purity 98.7% by GC analysis)
was synthesized in 91% yield from i-propylsulfonyl chloride
by halogen exchange with KF in water.
cyclo-Propane carboxylic acid fluoride was prepared in
situ from the corresponding chloride (Acros Organics)
by dissolving in anhydrous HF at À78 8C with following
warming up (slowly and carefully by the reason of HCl
evolution) to 5 8C. The formation of cyclo-propane car-
boxylic acid fluoride was confirmed by 19F NMR spectra
1
19F and H NMR spectra were measured on the Brucker
WP 80 SY (80.1 MHz for 1H NMR and 75.4 for 19F NMR),
Brucker Advance 300 (300.13 MHz for 1H NMR and 282.40
for 19F NMR) and Brucker DRX 500 (500.13 MHz for H
1
NMR and 470.59 for 19F NMR) spectrometers from neat
liquids obtained in the Simons cell and collected in the traps
at À78 8C. Spectra were recorded using FEP sample tubes
inside a 5 mm thin walled NMR tube with an acetonitrile-D3
film as an external lock and CCl3F as internal reference. For
the proton spectra the frequency of the TMS in acetonitrile-
D3 solution was used as a standard frequency. For complete
identification of all compounds, the product from the cell
and traps after washing with water and drying was separated
into several narrow fractions by distillation. High resolution
1
5
3
3
19F and H NMR spectra were measured for every fraction
in CDCl3 solution. NMR data are given in the Table 5.
Published 19F and 1H NMR data for different partially
fluorinated n- and i-butanes [52,53] were very useful for
complete identification of the substances in the ECF experi-
ment with i-butylsulfonyl fluoride.
The purity of the starting materials was checked with a
Perkin-Elmer gas chromotograph using a column (4% sili-
conoil DC 2000 on Chromosorb) of length 1.5 m and 2 mm
i.d. at 120 8C. The temperature of the injector was 130 8C
and the temperature of the FID detector was maintained at
250 8C. The carrier gas was He.
(solvent HF) at À20 8C: 29.03 ppm, d [C(O)F], JH;F
¼
8:2 Hz. The absence of other signals in the spectra con-
firms that the cyclo-propane ring remains untouched by the
treatment with HF.
4.3. Calculations
The solution of cyclo-propane carboxylic acid fluoride in
HF (two different concentrations: 31.9 and 45.7 wt.%), was
used for the electrochemical fluorination.
Caution! Anhydrous HF is an extremely hazardous
chemical. Good ventilation and proper protecting clothes
are required for the work with this substance. For details
see [1].
Quantum chemical calculations were performed with the
GAUSSIAN 98 software package [46] using the density
functional theory (DFT) [54]. All molecule geometries were
optimized to standard convergence criteria using a DFT
hybrid method with Becke’s [55,56] non-local three para-
meter exchange and the Lee et al. [57] correction (B3LYP)
and a 6–31G(d) basis set for the C4 species and 6–311G(d, p)
for the C3 compounds. The calculations were performed for
C4H8SO2F radicals (n-, i-, and s-structures), [C4H8SO2F]þ
cations (n-, i, and five-membered cyclic structures),
[C3H6C(O)F]þ cations (n-, i-, cyclopropyl structures), C2H4-
CHC(O)F biradicals (triplet and singlet state, the last one is
spontaneously cyclized into a cyclo-propane structure), and
the corresponding mono- and bifluorinated compounds as
isolated gaseous species.
4.5. Electrochemical fluorination of i-butylsulfonyl
fluoride
One hundred thirty grams of i-butylsulfonyl fluoride were
added in 10 equal portions (firstly at the beginning and
subsequently after 46.7; 89.4; 135.5; 180.2; 219.6; 264.3;
309.5; 356.5 and 400.9 A h, respectively) to 334 g of liquid
hydrogen fluoride previously electrolyzed in the cell for 28 h.
The gaseous products from the cell were passed through the
condenser at À30 8C and two FEP traps held at À78 8C. The
electrolysis, which proceeded at a cell voltage of 4.8–5.2 V
and a current density of 0.42–0.47 A/dm2, was completed
after consumption of 534.6 A h (119.3% of the theoretical
value calculated for a 18 electron process).
The resulting relative energies of different isomers and
reaction enthalpies do not include any influences from the
solvent HF nor the electric field near the anode.
4.4. Chemicals
i-Butylsulfonyl fluoride was synthesized from i-butylsul-
fonyl chloride (obtained by the method [58,59]) in the
following manner: 297.5 g (1.9 mol) of i-butylsulfonyl
chloride were mixed with a saturated solution of potassium
Seventy grams of a transparent liquid were drained from
the cell, washed with water and dried over MgSO4. Dilution
of the HF solution from the cell with ice-water gave in
addition, 58 g of a liquid, which was dried over MgSO4.

36
N.V. Ignat’ev et al. / Journal of Fluorine Chemistry 124 (2003) 21–37
Table 4
The gaseous products from the cell were passed through
the condenser at À30 8C and two FEP traps held at À78 8C.
The electrolysis, which proceeded at a cell voltage of 4.9–
5.2 V and a current density of 0.35–0.47 A/dm2, was com-
pleted after consumption of 312.7 A h (101.9% of the
theoretical value calculated for a 12 electron process).
97.8 g of a transparent liquid were obtained from the trap
after separation from the HF layer. Analyses of this sample
was carried out by means of 19F NMR spectroscopy.
Added mass of starting material (i-C3H7SO2F) vs. electricity consumed
Mass of i-C3H7SO2F (g)
Electricity consumed (A h)
15.00
12.05
11.04
10.97
5.43
0
44.80
84.72
122.68
160.98
Twenty-four grams of a transparent liquid were obtained
from the trap after separation from the HF layer. Analyses of
all those samples was carried out by means of 19F NMR
spectroscopy. Data are given in the Tables 1 and 2.
Acknowledgements
Donation of high quality hydrogen fluoride from the
company ‘‘Solvay Fluor & Derivate GmbH’’ (Germany)
is gratefully acknowledged.
4.6. Electrochemical fluorination of i-propylsulfonyl
fluoride
54.49 g (0.432 mol) of i-propylsulfonyl fluoride were
added in five portions, Table 4, to 229 g of liquid hydrogen
fluoride previously electrolyzed in the cell for 24 h. The
gaseous products from the cell were passed through the
condenser at À30 8C and two FEP traps held at À78 8C. The
electrolysis, which proceeded at a cell voltage of 5.0–5.2 V
and a current density of 0.44–0.45 A/dm2, was completed
after consumption of 195.0 A h (120.7% of the theoretical
value calculated for a 14 electron process).
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