Stability of 1-naphthalenediazonium ion in solution. Complexation and decomposition of 1-naphthalenediazonium tetrafluoroborate in the presence of crown ethers and acyclic polyethers in 1,2-dichloroethane and the gas phase under fast atom bombardment conditions

Article abstract of DOI:10.1002/1099-1395(200008)13:8<452::AID-POC254>3.0.CO;2-8

The effects of solvent, temperature and pH on the rate of decomposition of uncomplexed 1-naphthalenediazonium tetrafluoroborate were studied by UV spectrometry. The complexation of the 1-naphthalenediazonium ion with crown ethers containing 4-10 oxygen atoms and some acyclic polyethers was detected and characterized in the gas phase by fast atom bombardment mass spectrometry (FAB-MS). In addition, the host-guest complexation and the kinetics of the thermal dediazoniation of 1-naphthalenediazonium ion in the presence of four crown ethers and two acyclic polyethers were studied in 1,2-dichloroethane (DCE) solution at 40 °C by UV spectrometry. All hosts, except 12-crown-4, formed 1:1 complexes under FAB conditions. The values of the thermodynamic stability K and the stabilizing ability of the complexation (k₂/k₁) in DCE were calculated from the kinetic data. The thermodynamic and kinetic stabilities were observed to be greater for the inclusion complex of the 1-naphthalenediazonium ion formed with crown ethers containing at least six oxygen atoms than for the non-spesific adduct formation formed with 15-crown-5. This was also true for tetraglyme, whose chain is too short to be capable of being fully wrapped around the diazonium group as in the complex of PEG 1000. Crown ethers with seven oxygen atoms are the strongest complexing agents for all the aromatic diazonium ions studied, for the 1-naphthalenediazonium ion investigated here and for arenediazonium ions examined earlier. The values of the activation enthalpy ΔH^≠ for the thermal dediazoniation of the uncomplexed salt in both the acidic aqueous solution and DCE were observed to be high, and the corresponding values of activation entropy ΔS^≠ were clearly positive. The results are consistent with a heterolytic S_NI-like mechanism involving the decomposition of the uncomplexed and complexed 1-naphthalenediazonium ion into a highly reactive naphthyl cation, followed by fast product-determining reactions with nucleophiles to give the products. Copyright

Full text of DOI:10.1002/1099-1395(200008)13:8<452::AID-POC254>3.0.CO;2-8

JOURNAL OF PHYSICAL ORGANIC CHEMISTRY
J. Phys. Org. Chem. 2000; 13: 452–460
Stability of 1-naphthalenediazonium ion in solution.
Complexation and decomposition of 1-naphthalene-
diazonium tetra¯uoroborate in the presence of crown
ethers and acyclic polyethers in 1,2-dichloroethane and the
gas phase under fast atom bombardment conditions
Toivo Kuokkanen,1* Jarmo Palokangas2 and Merja Talvensaari1
1Department of Chemistry, University of Oulu, P.O. Box 3000, FIN-90401 Oulu, Finland
2Ekopine Oy, P.O. Box 171, FIN-90101 Oulu, Finland
Received 8 October 1999; revised 13 February 2000; accepted 21 February 2000
ABSTRACT: The effects of solvent, temperature and pH on the rate of decomposition of uncomplexed 1-
naphthalenediazonium tetrafluoroborate were studied by UV spectrometry. The complexation of the 1-
naphthalenediazonium ion with crown ethers containing 4–10 oxygen atoms and some acyclic polyethers was
detected and characterized in the gas phase by fast atom bombardment mass spectrometry (FAB-MS). In addition, the
host–guest complexation and the kinetics of the thermal dediazoniation of 1-naphthalenediazonium ion in the
presence of four crown ethers and two acyclic polyethers were studied in 1,2-dichloroethane (DCE) solution at 40°C
by UV spectrometry. All hosts, except 12-crown-4, formed 1:1 complexes under FAB conditions. The values of the
thermodynamic stability K and the stabilizing ability of the complexation (k2/k1) in DCE were calculated from the
kinetic data. The thermodynamic and kinetic stabilities were observed to be greater for the inclusion complex of the
1-naphthalenediazonium ion formed with crown ethers containing at least six oxygen atoms than for the non-spesific
adduct formation formed with 15-crown-5. This was also true for tetraglyme, whose chain is too short to be capable of
being fully wrapped around the diazonium group as in the complex of PEG 1000. Crown ethers with seven oxygen
atoms are the strongest complexing agents for all the aromatic diazonium ions studied, for the 1-naphthal-
enediazonium ion investigated here and for arenediazonium ions examined earlier. The values of the activation
enthalpy DH≠ for the thermal dediazoniation of the uncomplexed salt in both the acidic aqueous solution and DCE
were observed to be high, and the corresponding values of activation entropy DS≠ were clearly positive. The results
are consistent with a heterolytic SN1-like mechanism involving the decomposition of the uncomplexed and
complexed 1-naphthalenediazonium ion into a highly reactive naphthyl cation, followed by fast product-determining
reactions with nucleophiles to give the products. Copyright 2000 John Wiley & Sons, Ltd.
KEYWORDS: diazonium ion; crown ether; acyclic polyether; dediazoniation; host–guest complexation
INTRODUCTION
nium ions has versatile applications in synthetic chem-
istry in the preparation of many widely different
compounds.2,3,6 It has been shown that thermal dediazo-
niations of aromatic diazonium salts involve a variety of
mechanisms, heterolytic and homolytic, and small
modifications to the reaction conditions (solvent, sub-
stituent, pH, atmosphere, addition of other solvents or
substrates) may change the mechanism and products
drastically.2,3,5–8 Nevertheless, publications describing
thermal dediazoniation of naphthalenediazonium salts
are surprisingly very few.6,9
Host–guest complexation has been studied with great
interest in recent decades owing to its many possible
applications, e.g. synthetic chemistry, phase-transfer
reactions, ion-selective electrodes, enhancement of the
solubility and stability of compounds and studies of
Organic diazonium salts were first prepared as early as
18581 and their reactions were among the first to be
studied systematically by organic chemists. Arenediazo-
nium salts have been shown to be very important for
synthetic chemistry2,3 and the dyestuff industry.4 The use
of arenediazonium ions as chemical trapping reagents has
also increased notably in recent years.5 A great number of
publications, many wide reviews and even several books
concerned with arenediazonium compounds have been
published.2–8 The thermal dediazoniation of arenediazo-
*Correspondence to: T. Kuokkanen, Department of Chemistry,
University of Oulu, P.O. Box 3000, FIN-90401 Oulu, Finland.
E-mail: toivo.kuokkanen@oulu.fi
Copyright 2000 John Wiley & Sons, Ltd.
J. Phys. Org. Chem. 2000; 13: 452–460

STABILITY OF 1-NAPHTHALENEDIAZONIUM ION IN SOLUTION
453
the host–guest complexation of polyethers with naphtha-
lenediazonium ions has not been studied by any other
groups (T. Kuokkanen and J. Palokangas, 2-naphtalene-
diazonium ion under study).
Although it is generally assumed that the 1:1 inclusion
complex is the only type of complexation between
arenediazonium ions and crown ethers, we have demon-
strated, through several spectroscopic, kinetic and gas–
liquid chromatographic measurements, that organic
diazonium ions form weak non-specific adducts (also
called charge-transfer complexes3) with 15-crown-5,
whose cavity diameter12 is too small for inclusion-type
complexation (see Scheme 1).14,21 The peak of this
complex has also been detected in the FAB mass
spectrum.14
The strength of complexation is much more difficult to
predict for flexible organic molecules than for rigid metal
cations. We have used spectroscopic and kinetic methods
to investigate, in solution, the effects of ring size and
substituent of the crown ether, the length of the chain in
acyclic polyethylene glycol, the character and position
(ortho-effect) of the substituent of the benzenediazonium
ion, the temperature, the solvent and the pressure on the
host–guest complexation between crown ethers and
arenediazonium ions.13,18,20–23,25 Complexation in the
gas phase under FAB conditions has been detected and
characterized by mass spectrometry (FAB-MS).14,24
Continuing our studies on the interactions of cyclic and
acyclic polyethers with stable organic cations, we have
now investigated, by spectroscopic and kinetic methods,
the complexation of the 1-naphthalenediazonium ion
with some crown ethers and PEGs. In addition, effects of
solvent, temperature and pH on the thermal stability of
the uncomplexed ion have been explained. The resonance
formulae of the 1-naphthalenediazonium ion (1a–d) and
the structure of some of the crown ethers used in this
work (2–5) are shown in Scheme 1.
Scheme 1. Resonance formulae of the 1-naphthalenedia-
zonium ion (1a±d) and structures of some crown ethers (2±5)
naturally occurring compounds.10–12 Although acyclic
polyethylene glycols (PEGs) are weaker complexing
agents than crown ethers, they may have practical use in
the future: it has been shown that inexpensive, commer-
cially available PEGs can be used as effective phase
transfer agents instead of expensive crown ethers for
reactions of arenediazonium salts in solvents of low
polarity.13 The host–guest complexation in solution has
usually been studied by spectroscopic, thermodynamic
and kinetic methods.10–15 Modern mass spectrometry
with fast atom bombardment (FAB-MS), which is easily
implemented with various mass spectrometric systems,
and more recently electrospray ionization (ESI-MS), has
emerged as a viable method for studying the host–guest
complexation of large macro(poly)cycles with metal and
organic ions in the gas phase.16
EXPERIMENTAL
Gokel and Cram reported in 197317 that crown ethers
of suitable dimensions solubilize arenediazonium ions
through complexation in non-polar solvents in which
they otherwise are insoluble. Bartsch et al.18 reported 3
years later that the complexation of 18-membered crown
ethers with the p-tert-butylbenzenediazonium ion in 1,2-
dichloroethane markedly increases the stability of the
diazonium salt against thermal decomposition. Since
then, the host–guest complexation of crown ethers with
arenediazonium ions has been investigated inten-
sively.3,10–12,14–22 Publications describing both the ther-
modynamic and the kinetic stability of these complexes
are relatively few, however.14,15,19,21,22 Polyether–arene-
diazonium ion systems (polyether = crown ether or
acyclic polyether22–24) are the only host–guest systems
for which the thermodynamic stabilities have been
calculated from their kinetic data. As far as we know,
Materials. 1-Naphthalenediazonium tetrafluoroborate
was synthesized from 1-naphthalenamine (Merck) by
diazotization with sodium nitrite at 2–5°C in H2O–EtOH
(4:1) acidified with tetrafluoroboric acid, and was
recrystallized twice from acetic acid–tetrafluoroboric
acid (1:4). The melting temperature, 105–107°C, and
the UV spectral data for the 1-naphthalenediazonium salt
4
in acidic aqueous solution (1 Â 10 M HCl), ꢀmax
=
256 nm, ꢁ = 1.31 Â 104 l mol 1 cm 1 and ꢀmax = 365 nm
(broad), ꢁ = 6.44 Â 103 l mol 1 cm 1, are in accordance
with the corresponding values in the literature.7 The
diazonium salt was stored in the dark at a low
temperature to minimize its thermal decomposition.
The unsubstituted crown ethers, 12-crown-4, 15-crown-
5 (2) and 18-crown-6 (3) from Fluka, and 21-crown-7 (4,
Pfaltz & Bauer), the dicyclohexane-substituted crown
Copyright 2000 John Wiley & Sons, Ltd.
J. Phys. Org. Chem. 2000; 13: 452–460

454
T. KUOKKANEN, J. PALOKANGAS AND M. TALVENSAARI
was monitored with a digital thermometer and was
constant to within Æ0.1°C. Because benzo-substituted
crown ethers are also UV absorbing, the same concentra-
tion of the host was used in both cells in the
measurements of the complexation between dibenzo-
21-crown-7 and 1-naphthalenediazonium ion in 1,2-
dichloroethane. In the other studies, only the solvent
was used in the reference cell. After thermostating, about
20 values of the absorbance At were recorded at suitable
time intervals up to about 2–3 half-lives. The observed
rate constant of the dediazoniation kobs was calculated
using the equation
lnꢁAt A † ˆ a1 t ‡ a0; kobs ˆ a1
ꢁ1†
Figure 1. Effect of solvent and temperature on the thermal
decomposition of uncomplexed 1-naphthalenediazonium
1
4
tetra¯uoroborate in (*) 1 Â 10 M HCl and (*) 1,2-
The absorbance at infinite time A?, was determined by
measuring the absorbance after about 10 half-lives. All
decomposition reactions in this work were found to obey
first-order kinetics within the intervals studied: the
correlation constant r for the straight line (1) was about
0.9998 and the standard deviation usually 0.5–2%.
Two different buffer systems were used in studies of
the effect of pH on thermal decomposition of the
uncomplexed 1-naphthalenediazonium ion in aqueous
solutions: HCl for pH 1.0 and 2.0 and citric acid–sodium
biphosphate in the pH range 3.0–8.0. The pH values of
the buffer solution were determined with a Radiometer
PHM63 digital pH-meter. For measurements of com-
plexation in solution, small amounts of the 1-naphthale-
nediazonium salt and polyether were accurately weighed
with a Perkin-Elmer AD-2 autobalance. A solution of 1-
naphthalenediazonium tetrafluoroborate was first pre-
pared by weighing. An aliquot of this solution was
transferred into a volumetric flask containing the desired
dichloroethane
ether dicyclohexano-24-crown-8 (5, Fluka), the benzene-
substituted crown ethers dibenzo-21-crown-7 (Fluka) and
dibenzo-30-crown-10 (Aldrich Chemie), and also acyclic
polyethers tetraethylene glycol (TeEG) (Fluka), penta-
glyme (pentaethylene glycol dimethylther, Riedel-de
Hae¨n) and PEG 1000 (polyethylene glycol 1000, Fluka),
were commercial chemicals and were used without
further purification. Dibenzo-24-crown-8 (Fluka) was
purified as described previously.13 1,2-Dichloroethane
(Fluka) was purified, dried and distilled by a common
procedure.26 3-Nitrobenzyl alcohol (NBA) from Aldrich
Chemie was used without further purification.
Apparatus and measurements. The complexes of cyclic
and acyclic polyethers with 1-naphthalenediazonium
tetrafluoroborate and their fragments in the gas phase
under FAB conditions were identified on a Kratos MS 80
autoconsole mass spectrometer operating with a DART
data system. The atom gun was operated at 8 keV and
argon was used as the bombarding gas with a pressure of
about 1 Â 10 6 Torr (1 Torr = 133.3 Pa) in the collision
region. NBA was shown earlier to be the best solvent for
our FAB experiments, owing to its electron-scavenging
nature. NBA was also used as the liquid matrix in this
study. The stainless-steel tip of the FAB probe was coated
with a thin layer of a mixture of polyether, 1-
amount of polyether. All other solutions, with constant
‡
[NapN2
]
but different concentrations of polyether,
total
were prepared by mixing the desired aliquots of these two
solutions. The melting point of the uncomplexed salt was
determined with a Thermopan microscope (Reichert,
Vienna, Austria).
RESULTS
Effects of temperature, solvent and pH on
thermal stability of the uncomplexed 1-naphtha-
lenediazonium ion
naphthalenediazonium tetrafluoroborate, and the liquid
‡
NBA matrix ([polyether]total ꢀ [1-NapN2
]
total ꢀ 2 Â
2
10 M). The spectrum was recorded immediately after
the sample had been inserted.
The effect of temperature on the thermal decomposition
of 1-naphthalenediazonium tetrafluoroborate was studied
by determining the first-order rate constant of dediazo-
Spectra were scanned and kinetic measurements were
carried out with a Shimadzu UV 160 A double-beam
spectrometer with two cell holders. The quartz cells of
10 mm pathlength were held at the desired temperature
by circulating water from an electrically thermostated
water-bath into the self-constructed temperature attach-
ment. The accuracy of the wavelength at the maximum
ꢀmax was within Æ1 nm. The temperature inside the cells
3
niation k1 in acidic aqueous solution (1 Â 10 M HCl)
and in 1,2-dichloroethane at four temperatures. The
corresponding Arrhenius plots are presented in Fig. 1.
The values of activation enthalpy DH≠ and activation
entropy DS≠ were calculated using the usual procedure by
comparing the constants Ea and A of the Arrhenius
Copyright 2000 John Wiley & Sons, Ltd.
J. Phys. Org. Chem. 2000; 13: 452–460

STABILITY OF 1-NAPHTHALENEDIAZONIUM ION IN SOLUTION
455
Table 1. Activation enthalpy, DH≠, activation entropy, DS≠, and rate constant k1 at 25°C for decomposition of the 1-
4
naphthalenediazonium ion in 1 Â 10 M HCl and 1,2-dichloroethane
Temperature range
1
1
1
Solvent
(°C)
Ea (kJ mol
)
DH≠ (kJ mol
)
DS≠ (JK 1 mol
)
k1 (s 1) (25°C)
5
1,2-Dichloroethane
Watera
22–41
22–46
115.0
112 Æ 4
116 Æ 3
43 Æ 12
50 Æ 10
2.30 Â 10
5
118.6 (118b)
1.28 Â 10
a
3
1.0 Â 10 M HCl.
b Taken from Ref. 7.
equation
Studies in the gas phase under FAB conditions
It has been shown repeatedly that FAB-MS is a viable and
rapid method for studying the host–guest complexation
of polyethers with stable organic cations such as
arenediazonium, tropylium and pyridium in the gas
phase.14,16,20,24,28,29 In the FAB-MS method the complex
is first formed in the liquid matrix and is then analysed in
the gas phase by mass spectrometry. Hence the complex
must exist both in solution and in the gas phase. In this
work we studied TeEG and pentaglyme with the 1-
naphthalenediazonium ion under FAB-MS conditions.
lnk1 ˆ lnA ꢁEa=R†ꢁ1=T†
with those in the equation
ꢁ2†
ꢁ3†
lnꢁk1=T† ˆ lnꢁkB=h† ‡ ÁSz=R ÁHz=ꢁRT†
derived from the activated state theory, where kB and h
are the Boltzmann and Planck constants, respectively.
Table 1 shows the values of the activation parameters,
and, to reveal the solvent effect, we have included the
calculated k1 values at constant temperature, T = 25°C.
The effect of pH on the thermal stability of the 1-
naphthalenediazonium ion in aqueous solution was
studied by determining the first-order rate constant k1 in
aqueous solution, in HCl (pH 1.0 and 2.0) and in
HOC(CH2COOH)2COOH–Na2HPO4 buffer solutions
(pH 3.0–7.5). The results are presented in Fig. 2. For
comparison, we have included the corresponding pH
dependence in the case of benzenediazonium ion27 in Fig.
2.
‡
The complexation between PEG 1000 and 1-NapN2 was
not studied in the gas phase because the molar mass of
‡
[PEG 1000-NapN2] is too large for our mass spectro-
meter. Fig. 3 shows the positive ion FAB mass spectrum
‡
of 1-NapN2 BF4 in the presence of 18-crown-6 in the
NBA matrix. The ions at m/z 155 (100%) and 265
‡
(28.4%) indicate the presence of the abundant NapN2
‡
ion and [18C6 ‡ H] cation. The peak of the complex
‡
‡
[18C6 Na] at m/z 287 shows that the Na ion competes
effectively in complex formation with 1-naphthalenedia-
zonium ion. The peak of the two cation–one anion cluster
‡
(PhN2 )2BF4 has always been observed in our FAB
spectra but never its Na adduct at m/z 297 ‡ 22. Hence
we believe that the signal at m/z 397 belongs to the two
‡
cation–one anion cluster (NaphN2 )2BF4 and the peak
‡
at m/z 419 (3.6%) only to the complex [18C6 NapN2] .
Furthermore, the fragmentation of 1-naphthalenediazo-
‡
nium ion gives naphthyl ion (Nap ) at m/z 127, phenyl
‡
cation (C6H5 ) at m/z 77, etc. Partial positive ion FAB
mass spectra for the investigated systems are presented in
Table 2. In agreement with earlier studies, the fragmenta-
tion pattern of the crown ether and PEG consists of a
series of losses of protonated C2H4O structural units, and
the mass spectra therefore consistently include m/z 45,
89, 133, 177, etc., depending on the size of the crown
ether or PEG, and in addition m/z 103, 147, etc. for
‡
glymes. The ion [PhOC2H4O] at m/z 136 is typical in the
mass spectra of benzene-substituted crown ethers, while
the peaks at m/z 154, 136 and 107 are due to the
fragmentation of the NBA matrix. Possible adducts of
NBA with crown ethers have not been observed in our
FAB spectra of the studied polyether–PhN2 systems.
It is interesting to observe that 15-crown-5 and the 1-
naphthalenediazonium ion also form a 1:1 complex under
Figure 2. Effect of pH on the thermal stability of
uncomplexed 1-naphthalenediazonium ion (*) and benze-
nediazonium ion (*) in acidic and neutral aqueous solution
at 40°C
‡
Copyright 2000 John Wiley & Sons, Ltd.
J. Phys. Org. Chem. 2000; 13: 452–460

456
T. KUOKKANEN, J. PALOKANGAS AND M. TALVENSAARI
Figure 3. Mass spectrum of 1-naphthalenediazonium tetra¯uoroborate in the presence of 18-crown-6 ([crown
‡
ether]tot ꢀ [NapN2
]tot) recorded by the FAB technique in NBA as the matrix
FAB conditions, m/z 375 (0.8% in Table 2), although they
cannot form an inclusion complex since the diazonium
group has a cylindrical diameter2 of about 0.25 nm and
the cavity diameter12 of 15-crown-5 is only 0.17–0.22
nm.14–16 The complex peak at m/z 331 was not detected in
the presence of 12-crown-4, which means that complexa-
tion of this small and rigid host with the 1-naphthalene-
diazonium ion is, at most, very weak even in the gas
phase, where there are no complicating effects of
counterion and solvation.
fast compared with dediazoniation, the complexation
process being in effect diffusion-controlled.10,15 When
the decomposition of the complex cannot be ignored, the
values of K and k1 k2 can be calculated from the kinetic
data by an iteration method using the linear Eqn. (5) and
Eqns. (6)–(9);
1
1
1
1
ˆ
Â
‡
ꢁ5†
ꢁ6†
ꢁ7†
ꢁ8†
k1 kobs ꢁk1 k2†K ‰polyetherŠ k1 k2
‡
K ˆ ‰complexŠ=ꢁ‰NapN2 Š  ‰polyetherŠ†
‰polyetherŠ ˆ ‰polyetherŠ
‰complexŠ
‰complexŠ
total
Calculation of kinetic and thermodynamic
stability in solution
‡
‡
‰NapN2 Š ˆ ‰NapN2
Š
total
‰complexŠ ˆ
The reactions of 1-naphthalenediazonium salt in the
presence of polyether in solution can be represented by
the equation
q
‡
fsum
ꢁsum2 4‰NapN2 Š‰polyetherŠ†g=2 ꢁ9†
‡
where sum = [NapN2
]
‡ [polyether]total ‡ 1/K; kobs
total
K
„
‡
NapN2 BF4 ‡ polyether
complex
# k2
is the dediazoniation constant measured in the presence
of the free polyether, [polyether]. If the complex is
unreactive, or k2 ꢂ k1, the value of K can be calculated
more easily for every data pair (kobs, [polyether]) by the
equation
ꢁ4†
# k1
products
products
in which ‘complex’ denotes a 1:1 complex (inclusion
complex or non-specific adduct formation), k1 and k2 are
the rate constants for the thermal decomposition of the
uncomplexed and complexed benzenediazonium ion,
respectively, and K is the complexation equilibrium
constant.3,13–15,19,21–24
K ˆ ꢁk1 kobs†=kobs  ꢁ1=‰polyetherŠ†
ꢁ10†
We studied the host–guest complexation in solution
using as model crown compounds 15-crown-5, 18-
crown-6, dibenzo-21-crown-7 and dicyclohexano-24-
crown-8, and as model acyclic hosts we used tetraglyme
Complexation and decomplexation reactions in the
presence of crown ethers have been observed to be very
Copyright 2000 John Wiley & Sons, Ltd.
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STABILITY OF 1-NAPHTHALENEDIAZONIUM ION IN SOLUTION
457
Table 2. Partial positive ion FAB mass spectra of 1-naphthalenediazonium tetra¯uoroborate in the presence
‡
of crown ethers and acyclic polyethers,a [host]tot ꢀ [NapN2
]
tot
Crown ether
Ion (m/z) with relative abundance (%) in parentheses
‡
‡
‡
‡
‡
12-C-4
15-C-5
18-C-6
21-C-7
155 (10) [1-NapN2] ; 177 (100) [12C4] ; 331 (0.0) [1-NapN2:12C4]
‡
‡
155 (42) [1-NapN2] ; 221 (100) [15C5] ; 375 (0.8) [1-NapN2:15C5]
‡
‡
‡
155 (100) [1-NapN2] ; 265 (16) [18C6] ; 419 (3.6) [1-NapN2:18C6]
‡
‡c
155 (100) [1-NapN2] ; 309 (1.1) [21C7] ; 464 (2.2) [1-NapN2:21C7]
‡
‡
‡
‡
‡
DB-21-C-7b
DC-24-C-8b
DB-24-C-8
DB-30-C-10
TeEG
155 (100) [1-NapN2] ; 404 (5.1) [DB21C7] ; 559 (1.5) [1-NapN2:DB21C7]
‡
‡
155 (100) [1-NapN2] ; 461 (3.0) [DC24C8] ; 615 (1.1) [1-NapN2:DC24C8]
‡
‡
155 (100) [1-NapN2] ; 448 (3.9) [DB24C8] ; 603 (1.4) [1-NapN2:DB24C8]
‡
‡
‡
155 (100) [1-NapN2] ; 536 (5.8) [DB30C10] ; 691 (1.9) [1-NapN2:DB30C10]
‡
‡
‡
155 (10) [1-NapN2] ; 195 (100) [TeEG] ; 349 (0.1) [1-NapN2:TeEG]
‡
‡
‡
‡
‡
Tetraglyme
Pentaglyme
155 (31) [1-NapN2] ; 223 (100) [Tetraglyme] ; 349 (2.8) [1-NapN2:Tetraglyme]
‡
155 (44) [1-NapN2] ; 267 (100) [pentaglyme] ; 421 (2.2) [1-NapN2:pentaglyme]
a
Fragmentations of polyethers and 1-naphthalenediazonium ions are omitted; see Results.
B = benzo; DB = dibenzo; DC = dicyclo.
In addition, 463 (0.5%) [1-NapN2:21C7] .
b
c
‡
and PEG 1000 (Table 3). We used the iteration
thermodynamic stability) and k2/k1, a measure of the
effect of complexation on the kinetic stability of the 1-
naphthalenediazonium ion in solution, are presented in
Table 4.
procedure, or Eqns. (4)–(9), for all systems studied.
The systems studied obeyed Eqn. (5) with a correlation
coefficient r ꢀ 0.996. The calculated values of K (the
Table 3. Effect of complexation on the thermal decomposition of 1-naphthalenediazonium tetra¯uoroborate in the presence of
crown ethers and acyclic polyethers in 1,2-dichloroethane at 40°C
1
Crown ether
15-Crown-5
[Crown] (M)
0
kobs (s
)
ꢀmax (nm)
4
4
4
4
4
4
4
4
5
5
5
5
6
6
5
6
4
4
4
5
5
4
4
4
4
4
4
4
4
4
3
3
2.71 Â 10
2.49 Â 10
2.45 Â 10
2.38 Â 10
2.30 Â 10
2.28 Â 10
1.30 Â 10
1.09 Â 10
9.82 Â 10
6.60 Â 10
5.06 Â 10
4.76 Â 10
3.48 Â 10
2.11 Â 10
1.36 Â 10
8.40 Â 10
1.54 Â 10
1.32 Â 10
1.08 Â 10
8.80 Â 10
7.10 Â 10
2.38 Â 10
1.89 Â 10
1.78 Â 10
1.53 Â 10
1.46 Â 10
1.41 Â 10
1.44 Â 10
1.16 Â 10
1.04 Â 10
7.94 Â 10
7.68 Â 10
262
261
260
260
260
260
258
258
257
257
256
4
1.55 Â 10
4
2.03 Â 10
4
2.64 Â 10
4
3.75 Â 10
4
4.51 Â 10
4
18-Crown-6
1.30 Â 10
4
1.76 Â 10
4
2.36 Â 10
4
3.47 Â 10
4
4.24 Â 10
4
a
Dibenzo-21-crown-7
Dicyclohexano-24-crown-8
Tetraglymeb
1.00 Â 10
—
4
a
1.47 Â 10
—
4
a
2.10 Â 10
—
—
—
4
a
3.27 Â 10
4
a
4.05 Â 10
4
1.40 Â 10
258
258
257
256
254
262
262
261
261
261
259
261
259
258
258
258
4
1.87 Â 10
4
2.46 Â 10
4
3.57 Â 10
4
4.33 Â 10
0
4
7.03 Â 10
3
1.02 Â 10
3
2.00 Â 10
3
2.80 Â 10
3
3.71 Â 10
PEG 1000b
1.50 Â 10
4
4
3.00 Â 10
4
4.98 Â 10
4
9.96 Â 10
3
2.00 Â 10
a
Not determined owing to the absorption of the host.
b At 39.8°C.
Copyright 2000 John Wiley & Sons, Ltd.
J. Phys. Org. Chem. 2000; 13: 452–460

458
T. KUOKKANEN, J. PALOKANGAS AND M. TALVENSAARI
Table 4. Thermodynamic and kinetic stability of 1-naphthalenediazonium tetra¯uoroborate in the presence of crown ethers and
acyclic polyethers, and the maximum hypsochromic shift due to the complexation in 1,2-dichloroethane at 40°C
1 a
Crown ether
K (l mol
)
k2/k1 (%)a,b
Dꢀmax (nm)c
15-Crown-5
18-Crown-6
Dibenzo-21-crown-7
Dicyclohexano-24-crown-8
Tetraglyme
(2.15 Æ 0.32) Â 103
(7.62 Æ 0.83) Â 103
(4.05 Æ 0.22) Â 104
(4.64 Æ 0.31) Â 103
(9.40 Æ 0.61) Â 102
(1.37 Æ 0.14) Â 104
67
4.0
2.5
10
46
31
6
6
—
8
4
6
d
PEG1000
a
Calculated by Eqn. (5).
b k1 = 2.71 Â 10
s .
4
1
c
The maximum hypsochromic shift due to the complexation.
d Not determined owing to the absorption of the host.
here for the dediazoniation of benzenediazonium salt in
DISCUSSION
3
1,2-dichloroethane and in 1 Â 10 M HCl at 25°C are
5
5
It has been shown earlier that three different stability
regions for every arenediazonium ion in aqueous solution
can be identified: (i) the arenediazonium ion is more or
less stable in clearly acidic solutions with the formation
of a corresponding substituted phenol via an SN1-like
heterolytic reaction mechanism; (ii) above a certain
specific pH the stability decreases abruptly {d[log(k1/
3.8 Â 10 and 4.6 Â 10
s
1, respectively, and also
show similarity to each other. The insensitivities of the k1
values to the solvent observed for the 1-naphthalenedia-
zonium and benzenediazonium ions indicate, according
to the Hughes–Ingold rules,32,33 that heterolytic dedia-
zoniation reactions involve only small changes in the
charge density during the activation step, which agrees
well with the proposed SN1-like reaction mechanism.
The effect of temperature on the rate of dediazoniation
of the 1-naphthalenediazonium ion is relatively large, but
similar in 1,2-dichloroethane and acidic aqueous solu-
tions (Fig. 1 and Table 1). The values of activation
enthalpy DH≠ are high, as high as those for the
dediazoniation of uncomplexed and complexed arene-
diazonium ions,5,7,19,21 and for many unimolecular
reactions of acyclic and aliphatic compounds.33 The high
DH≠ values can be explained with a transition state that
has undergone bond breaking with little compensating
bond making. Our DS≠ values in Table 1 are clearly
positive, like those calculated earlier for the dediazonia-
tion of uncomplexed and complexed arenediazonium
salts5,7,19,21 and for some other unimolecular reactions
with an SN1 mechanism, but contrast with the negative
DS≠ values for bimolecular reactions with an SN2
mechanism.34
s
1)]/d(pH) <1}, and reactions become increasingly
complex; (iii) in clearly basic solutions the arenediazo-
nium ion is very unstable as evidenced by a rapid change
to syn-diazotate in two steps, followed by slower
isomeration to the stable anti-diazotate ion.2,3,27,30 Figure
2 shows that the pH dependence of the stability of the 1-
naphtalenediazonium ion in acidic and neutral aqueous
solution is similar to that of the benzenediazonium ion,
but its region of decreasing stability, region ii, begins
already above pH ꢀ 3, whereas the same region for
benzenediazonium ion does not begin until the pH is
above ca 6. In region ii, the value of log(k1/s 1) increases
linearly with pH for both 1-naphtalenediazonium ion (pH
range 3.0–6.1 in Fig. 2) and the arenediazonium ions. The
dependence of stability on pH is less for the 1-
naphthalenediazonium ion, however, than it is for the
benzenediazonium ion: the values of d[log(k1/s 1)]/
d(pH) are 0.11 (n = 4) and 0.4027 (pH range 7–8, n = 4),
respectively. Above a certain pH, all dediazoniation
reactions lost the behaviour of first-order kinetics [Eqn.
(1)]. The main reaction in the lower part of region ii can
be assumed to be the coupling reaction of the formed
phenol or naphthol with an unreacted diazonium
ion.3,27,30
Although it is generally assumed and reported10 that
the inclusion 1:1 complex (called the insertion-type
complex by Zollinger and co-workers3,15) is the only type
of complexation between crown ether and arenediazo-
nium ions, we have demonstrated by kinetic and
spectroscopic measurements and product analyses that
the benzenediazonium ion, whose diazonium group has a
cylindrical diameter3 of about 0.25 nm, can form a non-
specific adduct with 15-crown-514,21 whose cavity
diameter12 is only 0.17–0.22 nm, both in the gas phase
and in solution. The results of earlier work and this study
suggest that in the presence of a crown ether containing at
least an 18-membered ring, the complex between crown
ether and naphthalenediazonium or arenediazonium ion
Our measurements in 1,2-dichloroethane and acidic
aqueous solution (Fig. 1 and Table 1) show that the rate
of the heterolytic dediazoniation of the 1-naphthalene-
diazonium ion is more or less independent of the polarity
of the solvent. This coincides with earlier observations31
that the rate constants k1 for the heterolytic dediazonia-
tion of benzenediazonium ion, measured in 19 solvents,
differ only by a factor of about 9. The k1 values measured
Copyright 2000 John Wiley & Sons, Ltd.
J. Phys. Org. Chem. 2000; 13: 452–460

STABILITY OF 1-NAPHTHALENEDIAZONIUM ION IN SOLUTION
459
of the acyclic host molecule. The results of this study
parallel the earlier conclusions3,14,15,21–24 that the K
values of the inclusion complexes of organic arenedia-
zonium ions with polyethers containing six or more
oxygen atoms are clearly larger than those of non-specific
adduct formation in the presence of 15-crown-5.
Correspondingly, the small K value for the tetraglyme-
1-naphthalenediazonium ion in Table 4 shows that the
chain of tetraglyme with five oxygen atoms is too short to
be fully wrapped around the diazonium group, thus
forming a pseudocyclic complex. It has been observed
recently14 that a cyclohexano or benzo substituent(s) in
the host molecule has only a small effect on the
equilibrium constant K for the crown ether–benzenedia-
zonium ion complex. The greater ring flexibility of 21-
crown-7 and its derivatives (f ꢀ 0.34–0.43nm) com-
pared with 18-crown-6 (f ꢀ 0.26–0.32nm) may allow for
the relief of steric interaction between the macrocyclic
ring and 2-substituents of naphthalene- and benzenedia-
zonium ions. 18-Crown-6 is planar (D3d configuration) in
its complexes,10,35 but it seems reasonable to assume that
one of the CH2—O—CH2 units in 21-crown-7 or its
derivatives will turn upwards and away from the mean
plane of the other oxygen atoms, or else inwards over the
naphthalene or benzene ring of organic diazonium ion in
the modified inclusion-type complex structure with s-
base–p-acid interactions.14,20,35 The modified structure
would present a cavity of similar size to that found in 18-
crown-6 to the diazonium group, but the extra oxygen
atom of 21-crown-7 and its derivative can now interact
with other electrophilic centres to provide additional
stabilization to the overall complex. Correspondingly, in
solution the larger crown ethers, e.g. dicyclohexano-24-
crown-8, can also be assumed to be capable of wrapping
around the cation in order to form a stabilizing three-
dimensional cavity11,14 with all oxygen atoms coordi-
nated to the guest.
Figure 4. Effect of the number of oxygen atoms in the host
molecules on the thermodynamic stability of the crown
ether±1-naphthalenediazonium ion (*) and crown ether±
benzenediazonium ion (*) systems in 1,2-dichloroethane at
40°C
is of the inclusion type, whereas with 15-crown-5 it is a
weaker non-specific adduct (see hole diameters in
Scheme 1). Rigid and small polyether 12-crown-4 is
such a weak complexing agent for organic diazonium
ions, that no complexation has been detected either in
solution or in the gas phase. Acyclic polyethers form
pseudo-cyclic complexes with organic diazonium ions
when the chain of a acyclic polyether, PEG or glyme, is
long enough to wrap fully around the diazonium
group.14,23,24 The complexation caused a slight hypso-
chromic shift in the UV spectrum, which indicates a more
localized p-electron system in the complexed 1-naphtha-
lenediazonium ion than in the uncomplexed ion. This has
been explained by the electrostatic interactions in the
complexes between the oxygen atoms of the polyether
and the diazonium group carrying a positive charge.
Zollinger and co-workers15 have argued that, in the
charge-transfer complex, the acceptor centre of the
arenediazonium ion is either the b-N atom and/or the
combined p-electron system of the aryl part and the
diazonio group, while the donor centre is one or several
of the oxygen atoms in the crown ether.
Figure 4 shows that the effect of the ring size on the
thermodynamic stability of the 1-naphthalenediazonium
ion complexed with crown ethers is less than it is on the
crown ether–benzenediazonium ion system. The K value
for the non-specific adduct formation in the presence of
15-crown-5 is slightly larger for the 1-naphthalenedia-
zonium ion than for the benzenediazonium ion, whereas
all K values of inclusion complexes of the 1-naphtha-
lenediazonium ion are lower than those for the corre-
sponding crown ether–benzenediazonium ion system.
Owing to the flexibility of acyclic polyethers, the equi-
librium constant K for tetraglyme (five oxygen atoms) in
Table 4 is only slightly less than it is in the presence of
15-crown-5. For the same reason the thermodynamic
In accordance with earlier observations for crown
ether–arenenediazonium ion14,16,20 and acyclic poly-
ether–arenenediazonium ion24 systems, but in contrast
to crown ether–metal systems,10–12 the peaks of sandwich
‡
complexes [(polyether)2NapN2] were not detected in
the FAB spectra in this study. Omitting the results for
short tetraethylene glycol, the values of the relative
abundance of the 1:1 complex peak in Table 2 are 0.8–
3.6%.
The calculated K values in Table 4 and Fig. 4 show that
in solution the thermodynamic stability of the 1-
naphthalenediazonium ion complexed with four crown
ethers and two acyclic polyethers studied varies markedly
with the ring size of the crown ether and the chain length
‡
macrocyclic effect K(15-crown-5/PhN2 )/K(tetraglyme/
‡
PhN2 ) in DCE was earlier24 observed to be even less
than 1.
Of the studied polyethers (Table 4), only 18-crown-6
and dibenzo-21-crown-7 are relatively strong stabilizing
agents for the 1-naphthalenediazonium ion in solution.
Copyright 2000 John Wiley & Sons, Ltd.
J. Phys. Org. Chem. 2000; 13: 452–460

460
T. KUOKKANEN, J. PALOKANGAS AND M. TALVENSAARI
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Also, the value of k2/k1 for PEG1000, which can form
pseudocyclic complexes with diazonium compounds (the
number of oxygen atoms is 22.3), is large. The effect of
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In accordance with earlier work concerning crown ether–
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decomposition of 1-naphthalenediazonium salt in the
absence or presence of polyethers occurs by an SN1-like23
reaction mechanism, with the formation of a highly
reactive 1-naphthyl cation in the slow rate-determining
step of the heterolytic decomposition of the uncomplexed
ion or the complex. Subsequent fast product-determining
reactions with nucleophiles (counterion, solvent, crown
ether, etc.) give the products. The results support
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naphtalenediazonium ions complexed with crown ether
occur via non-specific adduct formation, called a charge-
transfer complex by Zollinger and co-workers (k2'), not
directly from the unreactive inclusion complex (k2@), or
k2' ꢃ k2@, and that there is a fast equilibrium between
these two types of complexes and the uncomplexed
arenediazonium ion, as presented in Scheme 2, where
R = arene or 1-naphtalene and, AF and IC = non-specific
adduct formation and inclusion complex, respectively.
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We thank Professor Jouni Pursiainen and Dr Jorma
Jalonen for helpful discussions and Mrs Pa¨ivi Joensuu for
the FAB mass spectra.
Copyright 2000 John Wiley & Sons, Ltd.
J. Phys. Org. Chem. 2000; 13: 452–460