Mechanism of electrophilic fluorination of aromatic compounds with NF-reagents

Article abstract of DOI:10.1134/S1070428007100077

Kinetic isotope effects H/D in electrophilic fluorination of aromatic compounds with NF-reagents were investigated. The small values of k _H/k _D (0.86-1.00) are in agreement with the polar reaction mechanism where the Wheland complex

Full text of DOI:10.1134/S1070428007100077

ISSN 1070-4280, Russian Journal of Organic Chemistry, 2007, Vol. 43, No. 10, pp. 1451−1459. © Pleiades Publishing, Ltd., 2007.
Original Russian Text © G.I. Borodkin, P.A. Zaikin, M.M. Shakirov, V.G. Shubin, 2007, published in Zhurnal Organicheskoi Khimii,
2007, Vol. 43, No. 10, pp. 1460−1468.
Mechanism of Electrophilic Fluorination of Aromatic Compounds
with NF-Reagents*
G. I. Borodkina,b, P. A. Zaikina,b, M. M. Shakirova, and V. G. Shubina
aVorozhtsov Novosibirsk Institute of organic Chemistry, Siberian Division, Russian Academy of Sciences,
Novosibirsk, 630090 Russia
e-mail: gibor@nioch.nsc.ru
bNovosibirsk State University, Novosibirsk, Russia
Received November 30, 2006
Abstract—Kinetic isotope effects H/D in electrophilic fluorination of aromatic compounds with NF-reagents were
investigated. The small values of kH/kD (0.86–1.00) are in agreement with the polar reaction mechanism where the
Wheland complex decomposition is not the limiting stage. The fluorination of 1,3,5-trideuterobenzene was
established by 1H and 19F NMR spectroscopy to occur with a 1,2-migration of a hydrogen (deuterium) atom. The
analysis of Brown–Stock relationship demonstrated that the activity of NF-reagents exceeded that of many
known electrophilic systems including halogenation, but it was essentially less than the activity of elemental
fluorine.
DOI: 10.1134/S1070428007100077
The growing interest in fluorinated aromatic com-
pounds caused by their extensive application as drugs,
pesticides, dyes, liquid crystals, and polymers requires a
development of environmentally safe and economically
feasible fluorination procedures [2–18]. The majority of
known fluorinating reagents used for electrophilic arenes
fluorination are poisonous and unsafe for handling (F2,
FClO3, XeF2, CF3OF, AcOF etc.) [3, 4, 7, 12, 16, 19]. In
the last decade extensive application in fluorination of
aromatic and heteroaromatic compounds found a new
class of F+ “carriers”: NF-reagents like 1-fluoro-4-chloro-
methyl-1,4-diazoniabicyclo[2.2.2]octane bis(tetrafluoro-
borates) (F–TEDA–BF4) (I), 1,1-difluoro-2,2'-bipyr-
idinium bis(tetrafluoroborates) (II), N-fluorobenzene-
sulfonimide (III) etc. [3–16].
Although quite a number of publications reported on
properties and synthetic applications of NF-reagents the
mechanism of electrophilic aromatic fluorination at their
use remains free to discussion [5, 6, 9–11, 16, 19, 20].
The observed prevalence of ortho and para isomers with
respect to electron-donor substituent in the benzene ring
shows that the NF-reagents exhibit electrophilic properties
[9, 12, 20] (cf. [19]). Inasmuch as the formation of F+
cation is thermodynamically extremely unfavorable (its
enthalpy of formation in the gas phase ΔHf is 1760 kJ
mol−1 ) compared with Cl+, Br+, I+ (ΔHf 1370, 1260, and
1120 kJ mol−1 respectively) [6] the formation of the cation
in the course of electrophilic aromatic fluorination is hardly
expectable, and the NF-reagents are regarded as the
source of “pseudopositive” or “electrophilic” fluorine [9].
Therefore generally two routes are considered for fluorine
atom transfer to the arene: nucleophilic substitution at
the fluorine atom (polar SEAr mechanism) and one-
electron transfer involving into the process a cation radical
(SET mechanism) (Scheme 1).
F
Cl
2BF4_
N+
N+
2BF4_
N
+
N+
F
F
I
II
NF-Reagents are either neutral (R2NF) or salts with
a positively charged cation (R3NF+), and these facts
should be taken into account in the treatment of the
mechanism of arenas electrophilic fluorination. The nature
of the aromatic compound is also essential, especially its
(PhSO2)2NF
III
* For preliminary communication, see [1].
1451

BORODKIN et al.
1452
capability of oxidation. In a general case various fluorina-
tion mechanisms might operate depending on the char-
acter of the NF-reagent, aromatic compound, and the
reaction conditions. In [20, 21] the comparison of experi-
mental fluorination rate constants of naphthyllithium,
potassium 2-methyl-3,4-dihydro-1-naphtholate and a series
of other compounds in reaction with 2-fluoro-3,3-dimethyl-
2,3-dihydro-1,2-benzisothiasole 1,1-dioxide with the values
As fluorination objects we selected monocyclic and
bicyclic arenas: benzene, toluene, mesitylene, and
naphthalene. As already mentioned, the fluorination of
mesitylene and durene with reagent I occurred presumab-
ly by the polar mechanism [23]. Whereas the ionization
potential of benzene (9.24384 eV), toluene (8.8276 eV),
and naphthalene (8.1442 eV) is higher than that of durene
(8.025 eV) [33] the SET mechanism for these compounds
is also hardly probable.
O
calculated from the standard redox potentials Ε in
keeping with Marcus theory led to the conclusion that
the preferable mechanism was the polar one, SEAr (cf.
[22]). The high substrate selectivity in the fluorination of
mesity-lene (MesH) and durene (Dur) with the reagent
F–TEDA–BF4 (kMesH : kDur = 6–10) also testifies to the
reaction proceeding by the polar mechanism [23]. In
contrast in several studies on the fluorination of aromatic
compounds and olefins arguments were advanced sup-
porting the SET mechanism [24–31], and therewith the
lifetime of the pair cation radical– fluorine atom was very
short (10–13–10–15 s) [16]. In this event according to [32]
the arguments “pro” and “contra” SET mechanism
become senseless [16]. Both considered mechanisms,
SET and SEAr, involve a formation of σ-complex, or
Wheland complex, which through proton elimination
transformes into fluorinated aromatic derivative.
The kinetics of mesitylene reaction with fluorinat-
ing reagent I in MeCN fits to the polar mechanism
(Scheme 2).
The dependence of rate constant k on time t in the
approximation of a quasistationary concentration of the
σ-complex is described by the following expression:
ln ([MesH]/[I]) = k([MesH]0 – [I]0)t + ln([MesH]0/[I]0),
(1)
where k = k1k2/(k–1)(k–1 + k2).
A good linear correlation exists between the values
ln([MesH]/[I]) and current time t with r 0.9999. From
the obtained values of second order rate constants [k273.2K
(1.41 0.02)×10–5, k303.8K (5.67 0.04)×10–4, k312.0K
(1.85 0.01)× ×
10–3, k323.0K (5.54 0.08) 10–3 l/(mol s)]
the following activation parameters were evaluated:
Ea 88 3 kJ mol−1, logA12.0 0.5, ΔH≠ 86 3 kJ mol−1,
ΔS ≠ –24 9 J/mol K. The large ΔH≠ and small absolute
value of ΔS≠ correspond to the enthalpy control of the
fluorination where the C–F bond formation occurs in the
rate-limiting stage.
The target of this study was investigation of the
mechanism of electrophilic fluorination of arenes with
NF-reagents applying kinetic isotope effects and the
estimation of activity of the reagents as compared with
other electrophiles using Brown–Stock relationship.
Scheme 1.
−
R2Nδ
F
H
SEAr
δ+
F
_R2N_
H
F
X
R2NF +
+
_H+
X
X
X
_R2N_
R2N-F_
.
.
SET
Ar+
Scheme 2.
F
H F
CH2Cl
N+
N
CH2Cl
N+
N+
CH2Cl
k1
N +
k2
_
BF4_
2BF4_
BF4_
2BF4
+
+
+
+
_
N+
F
k
1
H
RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 43 No. 10 2007

MECHANISM OF ELECTROPHILIC FLUORINATION
1453
Scheme 3.
=
CH2Cl
N+
F
N
H F
CH2Cl
N+
N+
+δF
H+δ
+
+
_H+
CH2Cl
N+
N
_
F
δ
+
Kinetic isotope effects are extensively used for
establishing the mechanisms of electrophilic aromatic
substitution [34]. We estimated the values of kH/kD for
the electrophilic fluorination of arenas with reagents I–
III by means of GC-MS and NMR methods (Table 1).
As seen from Table 1, no primary kinetic isotope effect
was found (kH/kD ≤ 1). This fact disagrees with the
stepwise mechanism where the limiting stage is the proton
abstraction from the σ-complex (Scheme 1) (cf. [34–
37]). Besides the concerted mechanism with a con-
siderable loosening of the C–H bond in the transition state
is also excluded (Scheme 3).
effectively involved in hyperconjugation with the partially
vacant p-orbital in the arising σ-complex, and then the
value kH/kD > 1, whereas the rehybridization of the carbon
atom sp2 → sp3 should provide the opposite effect (kH/
kD < 1) [37]. The higher electron-donor effect of
deuterium compared with protium is especially important
when the deuterium is located in the positions 1, 3, and 5
+
of the σ-complex (cf. σ n−D –0.001) [38]. The observed
in the most cases kH/kD < 1 may be ascribed to the
prevalence of the sp2 → sp3 rehybridization effect and
also to the large electron-donor effect of deuterium. The
most active among the NF-reagents used is F–TEDA–
BF4 [39, 40].According to Hammond rule in the event of
an active agent the transition state should be early and
therefore the hyperconjugation effect leading to enhanced
ratio kH/kD should be less significant. In this connection
becomes understandable some reduction in the kH/kD
ratio at the use of the reagent F–TEDA–BF4 as compared
with the ratio for neutral reagent III (Table 1).
The ratio kH/kD is practically unchanged at solvent
variation and evidently is governed by the structural factors
of substrate and the character of the fluorinating reagent.
The observed variations in the secondary kinetic isotope
effects in the fluorination reaction at the change of the
structure of the aromatic substrate may originate from
several factors superimposed. The C–H bond is more
Table 1. Kinetic isotope effects in electrophilic fluorination of arenas estimated by GC-MS method
Number of NF-reagent
ArH
Solvent
MeCN
Temperature, °C
110
kH/kD
I
C6H6/C6D6
C6H6/C6D6
C6H6/C6D6
0.92 0.06
MeCN
[bmim][BF4]b
110
110
60
1.00 0.04a
0.89 0.02
0.89 0.02
Mesitylene/mesitylene-1,3,5-d3
Naphthalene/naphthalene-d8
MeCN
MeCN
MeCN
60
0.86 0.01
0.86 0.03
II
C6H6/C6D6
110
Naphthalene/naphthalene-d8
Mesitylene/mesitylene-1,3,5-d3
Naphthalene/naphthalene-d8
Naphthalene/naphthalene-d8
MeCN
60
110
110
110
0.91 0.05
0.99 0.03
III
MeCN
MeCN
0.895 0.007
0.889 0.007
ClCH2CH2Cl
a
Data reported were obtained by two measurements of 19F NMR spectra.
[bmim] is 1-butyl-3-methylimidazolium.
b
RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 43 No. 10 2007

BORODKIN et al.
1454
Additional proofs of σ-complexes formation in the
with the experimental one permitted the estimation of
isotopomers ratio A:B:C:D (1.0:0.5:0.8:1.1). To our
knowledge this is the first example of detecting
rearrangement of σ-complexes involved in electrophilic
fluorination of aromatic compounds.
course of electrophilic fluorination were obtained from
the analysis of the products of reaction between 1,3,5-
trideuterobenzene and reagent I. The ratio of isotopomers
fluorobenzene-d3/fluorobenzene-d2 estimated by GC-MS
method was too high (1.28). The reason of the fact is
presumably the interconversion of the arising σ-complexes
by 1,2-shift of a hydrogen or a deuterium atom
(Scheme 4). Such 1,2-shifts in “long-lived” arenonium
ions are known to occur with very high rates [41–43].
For instance, the rate constant of 1,2-shift in a benzenon-
ium ion at 110°C calculated by Arrhenius equation [43]
amounted to 4×109 s–1 and was evidently comparable
with the diffusion-controlled pseudofirst order rate
constant of proton elimination from the σ-complexa
(~1010 s–1) (cf. [44]).
It is of interest to consider the place by activity of
fluorinating reagents among the other electrophilic agents.
One of the ways of this estimation is the evaluation of
correlation between the substrate and position selectivity
in the framework of the Brown–Stock relationship [45–
47]. The comparison of substrate and position selectivity
was carried out in [46] for 108 reactions of electrophilic
substitution of a hydrogen atom in toluene, and the
following correlation equation was obtained:
(2)
log fp = –0.17 + 1.38 Sf , r 0.91,
To detect the isotopomers whose appearance may be
ascribed to 1,2-shifts of hydrogen and deuterium in the
where fp is the factor of a partial substitution rate of the
hydrogen atom in the para-position of toluene, Sf is the
selectivity factor [log (fp/fm)] for toluene. The correla-
tion was improved by excluding the data on toluene
nitration with the salt NO2+BF–4 in polar aprotic solvents
and also of some other findings (8 points in total were
excluded) since at the use of nitronium salts the limiting
stage of the reaction was likely the formation of
a π-complex [46]:
1
formed σ-complexes we registered H and 19F NMR
spectra of the fluorination products (Fig. 1 and 2). As
1
expected in the H NMR spectrum the resolution of
similar signals of isotopomers was not observed, and the
most informative was 19F NMR spectrum. Analysis of
the spectrum revealed the presence of isotopomers B
and C whose formation was evidently due to the
isomerization of σ-complexes with the rate of hydrogen
(deuterium) 1,2-shift comparable to the rate of their
elimination. The comparison of the calculated spectrum
log fp = –0.08 + 1.37 Sf , r 0.95.
(3)
Scheme 4.
F
D
D
D
_H+
_H+
F
F
H
D
F
F
D
D
H
D
D
D
D
~1,2-H
H
+
+
_D+
D
D
D
F
D
F
D
+
I
D
D
D
D
~1,2-D
F
H
+
+
_H+
D
D
_D+
D
D
_D+
D
D
RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 43 No. 10 2007

MECHANISM OF ELECTROPHILIC FLUORINATION
1455
Fig. 1. 1H NMR spectra of deuterofluorobenzenes (500 MHz, CD3CN) formed in reaction of 1,3,5-trideuterobenzene with reagent I
13
in CD3CN at 110°C. Satellites due to coupling H− C and H-D in 1,3,5-trideuterobenzene are marked with asterisks.
The calculation of log fp values by equation (3) for
toluene fluorination with reagents I–III at 110°C gives
the estimates 1.37, 1.30, and 1.18 respectively in a fair
agreement with the experimental findings (Table 2). The
low lgfp and Sf values indicate that the fluorinating agents
under investigation are fairly active. The comparison of
logfp and Sf for the fluorination with the published data on
other reactions of electrophilic aromatic substitution
showed that the activity of NF-reagents exceeded that
of many known electrophilic systems used for halo-
genation, deuteroexchange, acylation, and chloromethyla-
tion, but it was considerably lower than fluorine activity
(Table 2).* The studied NF-reagents possess similar
activities (cf. [49]).
fits to the laws characteristic of the most aromatic electro-
philic substitutions. Presumable the stage of π-complex
formation between the aromatic substrate and the
fluorinating reagent is not limiting, and the structure of
the transition stage is close to σ-complex.
Results of quantum-chemical calculations by PΜ3
method [50] for the system mesitylene–reagent I are
consistent with the polar mechanism (Scheme 1). The
calculations show that the reaction of mesitylene with
the NF-reagent lead to the formation of a pair σ-complex-
1-chloromethyl-4-aza-1-azoniabicyclo[2.2.2]octane E
(Fig. 3) where occurs a practically complete transfer of
the fluorine atom to the mesitylene molecule. The distance
between N and F atoms in this pair (3.68 Å) exceeds the
sum of van der Waals radii of N and F atoms (2.85 Å)
[44] indicating that no significant interaction exists
between the atoms. This pair formation in the gas phase
A correspondance of the electrophilic fluorination with
the Brown–Stock relationship indicates that the reaction
* Evidently the difference in temperatures may be neglected.
RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 43 No. 10 2007

BORODKIN et al.
1456
Fig. 2. 19F NMR spectra of deuterofluorobenzenes (470 MHz, CD3CN) formed in reaction of 1,3,5-trideuterobenzene with reagent I
in CD3CN at 110°C (1), and the calculated spectrum (2). Chemical shifts are measured from CFCl3 and recalculated to the scale of the
external reference C6F6 (–162.9 ppm).
Fig. 3. Structures of mesitylene complexes with reagent I calculated by PΜ3 method.
RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 43 No. 10 2007

MECHANISM OF ELECTROPHILIC FLUORINATION
1457
is highly exothermal (ΔHf –387.0 kJ mol–1). On the PES
Table 2.
of this system one more minimum is present correspond-
ing to a structure where the hydrogen atom is transferred
to the nitrogen of the fluorinating reagent (complex F)
(Fig. 3), and the energy of this complex is higher by
79.0 kJ mol–1 than that of pair E. A significant feature of
this complex is the close position of C1 and the hydrogen
of the NH fragment; therewith the distance between them
is less than the value corresponding to the short contact
of C and H atoms (2.52 Å) [51]. If it is considered that the
transition state leading to this complex includes a four-
membered fragment with a significant loosening of C1–
H bond (Scheme 3), a notable kinetic isotope effect should
be observed, and consequently our experimental data rule
out this alternative mechanism.
Reagents and reaction conditions
Log fp
Sf
Reagent I, ArH, MeCN, 110°Ca
Reagent I, ArH, MeCN, 80°Ca
Reagent II, ArH, MeCN, 110°Ca
Reagent III, ArH, 110°Ca
F2, C6F5CF3, 40°Cb
Br2, 85% AcOH, 25°C
Cl2, AcOH, 25°C
Br2, AcOH, 25°C
1.35
1.38
1.40
1.36
1.06
1.16
1.01
0.92
0.62
0.53
3.384
2.914
2.728
1.771
1.914
3.778
2.624
2.920
2.644
2.219
2.053
1.373
1.311
3.000
2.044
2.221
2.192
1.160
1.366
1.229
1.226
1.297
0.842
1.993
1.014
0.819
1.165
1.041
HOBr, HClO4, 50% dioxane, 25°C
HOCl, HClO4, H2O, 25°C
DBr, 25°C
D2O, CF3CO2H, 70°C
PhCOCl, AlCl3, PhNO2, 25°C
CH3COCl, AlCl3, ClCH2CH2Cl, 25°C 2.874
PhSO2Cl, AlCl3, 25°C
HNO3, 90% AcOH, 45°C
AcONO2, Ac2O, 0°C
Thus the data obtained correspond to the stepwise
mechanism of electrophilic fluorination of arenes by NF-
reagents with the formation of σ-complex, and the stage
of proton elimination from the complex is not limiting.
1.480
1.763
1.780
1.709
1.664
1.072
2.633
1.362
1.049
1.517
1.389
AcONO2, Ac2O, 30°C
HNO3, CH3NO2, 30°C
EXPERIMENTAL
CH3Br, GaBr3, ArH, 25°C
CH2O, HCl, ZnCl2, AcOH, 60°C
Hg(OAc)2, AcOH, 25°C
Hg(OAc)2, AcOH, 90°C
Hg(OAc)2, HClO4, AcOH, 25°C
Hg(OAc)2, HClO4, AcOH, 70°C
NMR spectra were registered on spectrometers
Bruker AC-200, AV-300, and DRX-500. As internal
1
references in recording H NMR spectra served the
residual proton signals of deuterochloroform (δ 7.24 ppm)
and deutero-acetonitrile (δ 1.96 ppm), and for 19F NMR
spectra, C6F6 (δ –162.9 ppm). GC-MS measurements
were carried out on a Hewlett Packard G1800 instrument
composed of a gas chromatograph HP5890 series II and
mass-selective detector HP5971. Ionizing electrons
energy 70 eV; oven temperature programmed as follows:
2 min at 50°C, further 10 deg/min till 280°C; vaporizer
tempera-ture 280°C; ion source temperature 173°C;
column 30 m × 0.25 mm, stationary phase HP-5ΜΒ (5%
of diphenylsiloxane, 95% of dimethylsiloxane); carrier gas
helium (1 ml/min).
Following reagents were used in the study: 1-fluoro-
4-chloromethyl-1,4-diazoniabicyclo[2.2.2]octane bis-
(tetrafluoroborate) purchased from Aldrich (95%),
N-fluorobenzenesulfonimide purchased from Lancaster
(95%), N,N'-difluoro-2,2'-bipyridinium bis(tetrafluoro-
borate) purchased from Acros, KI of “chemically pure”
grade, Na2S2O3 of “pure for analysis” grade, K2Cr2O7
of “chemically pure” grade, benzene-d6, 1,3,5-tri-
deuterobenzene, and CF3CO2D purchased from NPO
GIPKh with deuterium content 99.6, 99.4, and 98.5 at%
respectively, naphthalene-d8 (Aldrich, 99%). Mesitylene
was distilled in a vacuum and was stored over molecular
a Data of this study.
b Data from [48].
sieves 4 Å. Acetonitrile was purified as in [44], stored
over molecular sieves 4 Å, and was distilled over P2O5
under argon just before use.
1,3,5-Trideuteromesitylene was prepared similarly to
procedure [52]. Mesitylene was kept with 25-fold molar
excess of CF3CO2D for 3 h at 60°C, excess acid was
distilled off new portion of acid was added, and the
procedure was repeated thrice. The residue was diluted
with distilled Et2O, washed with a saturated solution of
NaHCO3 and with water. The ether solution was dried
with magnesium sulfate, the ether was distilled off.
According to the mass spectrum the compound obtained
contained 98.3 at% of deuterium.
Kinetics of mesitylene reaction with reagent I.
The prepared solutions of mesitylene (0.35 mol l–1) and
of reagent I (0.07 mol l–1) in acetonitrile were stored at
the required temperature for 30 min, the they were mixed
in such amounts that the concentration of reagent I was
0.05 mol l–1, and mesitylene, 0.1 mol l–1. The reaction
RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 43 No. 10 2007

BORODKIN et al.
1458
Applications, Berlin: Springer, 2000.
4. Kirsch, P., Modern Fluoroorganic Chemistry. Synthesis
Reactivity Applications, Weinheim: Wiley-VCH, 2004, p. 1.
5. Lal, G.S., Pez, G.P., and Syvret, R.G., Chem. Rev., 1996,
vol. 96, p. 1737.
6. Banks, R.E., J. Fluor. Chem., 1998, vol. 87, p. 1.
7. Hart, J.J. and Syvret, R.G., J. Fluor. Chem., 1999, vol. 100,
p. 157.
8. Taylor, S.D., Kotoris, C.C., and Hum, G., Tetrahedron, 1999
vol., 55, p. 12431.
9. Furin, G.G. and Fainzil’berg,A.A., Usp. Khim., 1999, vol. 68,
p. 725.
10. Salvatore, R., Chem. Today, 2004, vol. 22, p. 57.
11. Ibrahim, H. and Togni, A., Chem. Commun., 2004, p. 1147.
12. Singh, R.P. and Shreeve, J.M., Acc. Chem. Res., 2004,
vol. 37, p. 31.
13. Gouverneur, V. and Greedy, B., Chem. Eur. J., 2002, vol. 8,
p. 767.
progress was monitored by the consumption of the
fluorinating reagents measured in samples taken
intermittently. The concentration of residual reagent I was
evaluated iodometrically [28].
Estimation of kinetic isotope effects. The isotope
effects were measured by the method of competative
kinetics using GC-MS procedure (cf. [52]). The
fluorinating reagent, deuterated and undeuterated
substrates taken in equimolar amounts were dissolved in
anhydrous MeCN (c 0.05 mol l–1). After keeping the
mixture at the required temperature it was diluted with a
double volume of Et2O, the salt precipitate was filtered
off, and the ether was distilled off. Kinetic isotope effects
were calculated by equation
kH/kD = [ArH]/[ArD],
where kH, kD are the rate constants of fluorination, [ArH],
[ArD] are the running concentrations of undeuterated and
deuterated product ArF respectively. The concentrations
were evaluated from the integral intensity of the
respective molecular ion peaks in the mass spectra.
14. Stavber, S., Zupan, M., Acta Chim. Slov., 2005, vol. 52,
p. 13, .
15. Kiselyov, A.S., Chem. Soc. Rev., 2005, vol. 34, p. 1031.
16. Nyffeler, P.T., Duron, S.G., Burkart, M.D., Vincent, S.P.,
Wong, C.-H., Angew Chem. Int. Ed., 2005, vol. 44, p. 192.
17. Dawood, K.M., Tetrahedron, 2004, vol. 60, p. 1435.
18. Shimizu, M. and Hiyama, T., Angew. Chem. Int. Ed., 2005,
vol. 44, p. 214.
19. Shamma, T., Buchholz, H., Prakash, G.K.S., and Olah, G.A.,
Israel J. Chem., 1999, vol. 39, p. 207.
20. Laali, K.K. and Borodkin, G.I., J. Chem. Soc., Perkin Trans.
2, 2002, p. 953.
21. Differding, E. and Wehrli, M., Tetrahedron Lett., 1991,
vol. 32, p. 3819.
22. Andrieux, C.P., Differding, E., Robert, M., and Save-
ant, J.-M., J. Am. Chem. Soc., 1993, vol. 115, p. 6592.
23. Differding, E. and Ruegg, G.M., Tetrahedron Lett., 1991,
vol. 32, p. 3815.
Factors of partial rates of substitution in the meta and
para positions of toluene were measured by the method
of competitive kinetics. Reagents I or II, toluene and
benzene were dissolved in acetonitrile, and reagent III,
in excess of benzene and toluene mixture at the ratio of
concentrations III:benzene:toluene = 1:10:10. The reac-
tions were performed in sealed ampules at 80 or 110°C.
After the completion of the reaction the ampule was
opened, the analysis of the reaction mixtures was per-
formed by 19F NMR. The values fp and fm were evaluated
by the relative intensity of signals from fluorobenzene,
m- and p-fluorotoluenes in the 19F NMR spectra.
The study was carried out under a financial support
of the Russian Foundation for Basic Research (grant
no. 06-03-32406) and of the Division of Chemistry and
Material Science of the Russian Academy of Sciences
(program 5.1.9).
24. Umemoto, T., Fukami, S., Tomizawa, G., Harasawa, K.,
Kawada, K., and Tomita, K., J. Am. Chem. Soc., 1990,
vol. 112, p. 8563.
25. Umemoto, T. and Nagayoshi, M., Bull. Chem. Soc. Jpn.,
1996, vol. 69, p. 2287.
26. Bockman, T.M., Lee, K.Y., and Kochi, J.K., J. Chem. Soc.,
Perkin Trans. 2, 1992, p. 1581.
27. Stavber, S., Jereb, M., and Zupan, M., J. Phys. Org. Chem.,
2002, vol. 15, p. 56.
REFERENCES
1. Borodkin, G.I., Zaikin, P.A., and Shubin, V.G., Tetrahedron
Lett., 2006, vol. 47, p. 2639.
28. Iskra, J., Zupan, M., and Stavber, S., Org. Biomol. Chem.,
2003, vol. 1, p. 1528.
2. Organofluorine Chemistry. Principles and Commercial
Applications, Banks, R.E., Smart, B.E., and Tatlow, J.C.,
Eds., New York: Plenum Press, 1994.
29. Kralj, P., Zupan, M., and Stavber, S., J. Org. Chem., 2006,
vol. 71, p. 3880.
30. Zhang, X., Liao, Y., Qian, R., Wang, H., and Guo, Y., Org.
Lett., 2005, vol. 7, p. 3877.
3. Hiyama, T., Organofluorine Compounds: Chemistry and
RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 43 No. 10 2007

MECHANISM OF ELECTROPHILIC FLUORINATION
1459
pin, M.E., Ed., HarwoodAcad. Press, 1999, vol. 24, part 2,
p. 1.
31. Piana, S., Devillers, I., Togni, A., and Rothlisberger, U.,
Angew Chem. Int. Ed., 2002, vol. 41, p. 979.
43. Olah, G.A., Schlosberg, R.H., Porter, R.D., Mo, Y.K., Kel-
ly, D.P., and Mateescu, G.D., J. Am. Chem. Soc., 1972, vol. 94,
p. 2034.
44. Gordon, A.J. and Ford, R.A., The Chemist's Companion,
NewYork: Wiley, 1972.
45. Adv. Phys. Org. Chem., Ed. Gold, V., Ed., New York:
Academic, Press, 1963, vol. 1, p. 35.
46. Santiago, C., Houk, K.N., and Perrin, C.L., J. Am. Chem.
Soc., 1979, vol. 101, p. 1337.
32. Jencks, W.P., Acc. Chem. Res., 1980, vol. 13, p. 161.
33. NIST Chemistry WebBook (http://webbook.nist.gov/).
34. Taylor, R., Electrophilic Aromatic Substitution, New York:
J. Wiley and Sons, 1990, p. 25.
35. Olah, G.A., Narang, S.C., Malhotra, R., and Olah, J.A.,
J. Am. Chem. Soc., 1979, vol. 101, p. 1805; Dix, L.R. and
Moodie, R.B., J. Chem. Soc., Perkin Trans. 2, 1986, p. 1097.
36. Kresge, A.J. and Chiang, Y., J. Am. Chem. Soc., 1967,
vol. 89, p. 4411.
47. Stock, L.M. and Brown, H.C., J. Am. Chem. Soc., 1959,
vol. 81, p. 3323.
48. Cacace, F., Wolf, A.P., J. Am. Chem. Soc., 1978, vol. 100,
p. 3639; Cacace, F., Giacomello, P., and Wolf, A.P., J. Am.
Chem. Soc., 1980, vol. 102, p. 3511.
49. Toullec, P.Y., Devillers, I., Frantz, R., Togni,A., Helv. Chim.
Acta, 2004, vol. 87, p. 2706.
50. Stewart, J.P., J. Comput. Chem., 1989, vol. 10, p. 209.
51. Zefirov, Yu.V. and Zorkii, P.M., Zh. Strut. Khim., 1976,
vol. 17, p. 994.
37. Szele, I., Helv. Chim. Acta, 1981, vol. 64, p. 2733.
38. Correlation Analysis in Chemistry. Recent Advances, N.B.,
Chapman J.Shorter, NewYork: Plenum, Press, 1978 p. 439.
39. Tishchenko, O.V., Serguchev, Yu.A., Lur’e, L.F., and
Ponomareneko, M.V., TEKh., 2000, vol. 36, p. 281.
40. Fainzil’berg,A.A., and Faustov, V.I., Zh. Org. Khim., 2001,
vol. 37, p. 790; Fainzilberg, A.A. and Solkan, V.N., J. Fluor.
Chem., 1999, vol. 96, p. 43.
41. Koptyug, V.A., Areneonievye iony. Stroenie i reaktsion-
naya sposobnost’. Novosibirsk: Nauka, 1983, p. 164.
42. Borodkin, G.I. and Shubin, V.G., Molecular Rearrangements
of Cationic Organic Complexes. Chemistry Reviews, Vol’-
52. Lau, W. and Kochi, J.K., J. Am. Chem. Soc., 1984, vol. 106,
p. 7100.
RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 43 No. 10 2007