Dual-parameter correlations on rate of an aromatic nucleophilic substitution reaction in aqueous solutions of methanol, ethanol, and propan-2-ol

Article abstract of DOI:10.1002/1097-4601(200102)33:2<118::AID-KIN1003>3.0.CO;2-U

Reaction kinetics of 1-chloro-2,4-dinitrobenzene with piperidine was studied spectrophotometrically in aqueous solutions of methanol, ethanol, and propan-2-ol at 25 °C. The reaction in these solutions is not catalyzed by piperidine. The plots of second-order rate constants of the reaction vs. mole fraction of water show maxima in the all-aqueous solutions. Single-parameter correlations of log k₂ vs. π* (dipolarity/polarizability), α (hydrogen-bond donor acidity), and E_T^N (normalized polarity parameter) are very poor in the all solutions (for example, in aqueous solutions of ethanol, regression coefficients are 0.814, 0.113, and 0.486, respectively). Dual-parameter correlations of log k₂ vs. π* and α in all cases represent significant improvement with regard to the single-parameter models (in aqueous solutions of ethanol: n = 11, r = 0.980, and s = 0.034). Dipolarity/polarizability and hydrogen-bond donor acidity (HBD) of media have opposite effects on the reaction rate. The activated complex leading to the zwitterionic intermediate is expected to be favored by increasing the solvent dipolarity/polarizability parameter. Increasing the hydrogen-bond donor acidity of solvent stabilizes piperidine and hence the reaction rate decreases. A dual-parameter equation of log k₂ vs. π* and α was obtained in the all-aqueous solutions (n = 31, r = 0.956, s = 0.055) in which π* and α have approximately equal and opposite effects on the reaction rate.

Full text of DOI:10.1002/1097-4601(200102)33:2<118::AID-KIN1003>3.0.CO;2-U

Dual-Parameter
Correlations on Rate of an
Aromatic Nucleophilic
Substitution Reaction in
Aqueous Solutions of
Methanol, Ethanol, and
Propan-2-ol
M. R. GHOLAMI,* A. HABIBI YANGJEH
Department of Chemistry, Sharif University of Technology, Tehran, Iran, P. O. Box 11365-9516
Received 30 March 2000; accepted 15 August 2000
ABSTRACT: Reaction kinetics of 1-chloro-2,4-dinitrobenzene with piperidine was studied spec-
trophotometrically in aqueous solutions of methanol, ethanol, and propan-2-ol at 25ꢀC. The
reaction in these solutions is not catalyzed by piperidine. The plots of second-order rate
constants of the reaction vs. mole fraction of water show maxima in the all-aqueous solutions.
Single-parameter correlations of log k2 vs. ␲* (dipolarity/polarizability), ␣ (hydrogen-bond
donor acidity), and ETN (normalized polarity parameter) are very poor in the all solutions (for
example, in aqueous solutions of ethanol, regression coefficients are 0.814, 0.113, and 0.486,
respectively). Dual-parameter correlations of log k2 vs. ␲* and ␣ in all cases represent signif-
icant improvement with regard to the single-parameter models (in aqueous solutions of eth-
anol: n ϭ 11, r ϭ 0.980, and s ϭ 0.034). Dipolarity/polarizability and hydrogen-bond donor
acidity (HBD) of media have opposite effects on the reaction rate. The activated complex
leading to the zwitterionic intermediate is expected to be favored by increasing the solvent
dipolarity/polarizability parameter. Increasing the hydrogen-bond donor acidity of solvent sta-
bilizes piperidine and hence the reaction rate decreases. A dual-parameter equation of log k2
vs. ␲* and ␣ was obtained in the all-aqueous solutions (n ϭ 31, r ϭ 0.956, s ϭ 0.055) in which
␲* and ␣ have approximately equal and opposite effects on the reaction rate. ꢁ 2001 John Wiley
& Sons, Inc. Int J Chem Kinet 33: 118–123, 2001
INTRODUCTION
chemical equilibria, position and intensity of spectral
absorption bands) has been well established [1]. Sol-
vent effects are closely related to the nature and extent
of solute–solvent interactions locally developed in the
immediate vicinity of the solutes. Solute–solvent in-
teractions are much more complex in mixed solvents
than in pure solvents due to the possibility of prefer-
That solvents have considerable influence on chemical
and physical processes (reaction rates, selectivity,
Correspondence to: M. R. Gholami (Gholami@Ch.Sharif.Ac.Ir)
ꢁ 2001 John Wiley & Sons, Inc.

DUAL-PARAMETER CORRELATIONS IN VARIOUS AQUEOUS SOLUTIONS
119
B
ential solvation by any of the solvents present in the
mixtures. Moreover, the solvent–solvent interactions
produced in solvent mixtures can affect the solute–
solvent interactions and therefore they can also affect
preferential solvations [2].
Modeling of solvent effects is one of the most use-
ful methods used to obtain information about the
mechanism of organic reactions [1]. Also, the com-
plexity of the chemistry of life in vivo, which occurs
primarily in an aqueous environment, should be en-
couraging chemists to investigate further the reactions
in aqueous solutions. Water is considered an unusual
and poorly understood liquid. The complexity of even
the simplest reactions in aqueous solutions is signifi-
cantly greater than that of reactions in organic solvents
[3–7].
In addition to the nonspecific, columbic inductive
and dispersion interactions, others such as specific hy-
drogen-bond, electron-pair donor–acceptor, and sol-
vophobic interactions may play a part in the solvent
effects. The problemis to identify and to assess the
relative importance of these various factors on the sol-
vent effects. The purpose of our work is to identify the
medium effects in aromatic nucleophilic substitution
reactions in aqueous solutions. Therefore, the kinetics
of the reaction of 1-chloro-2,4-dinitrobenzene with pi-
peridine was studied in aqueous solutions of methanol,
ethanol, and propan-2-ol at 25ꢀC.
b. k2 ϩ k3 [B] ϽϽ kϪ1 . This situation corresponds
to rapid formation of the intermediate followed
by its rate-determining decomposition to prod-
ucts. In this case, Eq. (1) reduces to Eq. (2),
which predicts base catalysis with a linear de-
pendence of kA on [B]:
B
kA ϭ k1k2/kϪ ϩ (k1k3 /kϪ )[B]
(2)
1
1
B
c. k2 ϩ k3 [B] ϳ kϪ1 . In this intermediate situa-
tion, Eq. (1) indicates that base catalysis should
be observed with a curvilinear dependence of kA
on [B].
The reaction of 1-chloro-2,4-dinitrobenzene with
piperidine is not catalyzed by base (situation (a)) [9–
11] in aprotic and protic solvents. The second-order
rate constants of the reaction, kA , are well correlated
by the Dimroth-Reichardt solvent polarity scale ET(30)
in several aprotic solvents. In some alcohols, the val-
ues of rate constants of the reaction are not well cor-
related by ET(30) parameters, but the reactivity is in-
versely proportional to the hydrogen-bond donor
acidity (HBD) of the solvents [9–11].
EXPERIMENTAL
The gross mechanism of aromatic nucleophilic sub-
stitution reactions is now well established when pri-
mary or secondary amines are the nucleophiles
(Scheme I) [8].
Reagents and Solvents
1-chloro-2,4-dinitrobenzene was prepared from4-ni-
tro-1-chlorobenzene as follow: 16 g nitric acid (65%)
was added gradually into a solution of 4-nitrochloro-
benzene (16 g) in 70 ml sulphuric acid (98%). The
reaction mixture was heated on the water-bath, then
cooled to roomtemperature and poured on ice, and the
precipitate was washed with water. Recrystallization
was carried out in aqueous solution of ethanol. All
solvents were of the highest quality available and were
purified as usual. Water was redistilled in a quartz dis-
tillation unit.
Application of the steady-state approximation derives
Eq. (1), in which kA is the observed second-order rate
constant and B can be either a second molecule of the
nucleophile or an added base:
Kinetic Procedures
The kinetics of the reaction was studied spectropho-
tometrically. The spectrophotometer was coupled to a
PC with an interface that allows absorbance measure-
ments vs. time (four readings per second). Absorbance
was recorded at wavelengths from370 (in propan-2-
ol) to 400 nm(in water) at 25 ꢀC. Pseudo-first-order
(kobs) conditions were used in all cases. Infinity values
of absorbance (Aϱ) were experimentally determined
for each run. All the kinetic runs were carried out at
least in triplicate. Concentration of 1-chloro-2,4-dini-
B
B
kA ϭ {k1(k2 ϩ k3 [B])}/{kϪ ϩ k2 ϩ k3 [B])} (1)
1
The main situations of interest with respect to the re-
action shown in Scheme I are as follows:
B
a. k2 ϩ k3 [B] ϾϾ kϪ1 . In this case, base catalysis
is not possible and Eq. (1) simplifies to kA ϭ
k1 , and formation of the intermediate is the rate-
determining step of the reaction.

120
GHOLAMI AND YANGJEH
Table I Search for Piperidine Catalysis. Second-Order Rate Constants in Reaction of 1-Chloro-2,4-Dinitrobenzene
with Piperidine in Aqueous Solutions of Methanol, Ethanol, and Propan-2-ol at 25ꢀC.a
[Piperidine]
Methanol
Ethanol
Propan-2-ol
Ϫ
Ϫ
Ϫ1
Ϫ
Ϫ1
Ϫ
Ϫ1
(mol dm) 3
k2*102/dm3mol s1ec
k2*102/dm3mol s1ec
k2*102/dm3mol s1ec
0.00462
0.00712
0.01245
0.02790
0.05650
0.07480
3.52 Ϯ 0.04
3.48 Ϯ 0.04
3.50 Ϯ 0.05
3.49 Ϯ 0.03
3.49 Ϯ 0.04
3.50 Ϯ 0.05
5.10 Ϯ 0.06
5.13 Ϯ 0.04
5.06 Ϯ 0.04
5.02 Ϯ 0.05
5.14 Ϯ 0.07
5.15 Ϯ 0.06
7.19 Ϯ 0.08
7.26 Ϯ 0.06
7.25 Ϯ 0.06
7.29 Ϯ 0.09
7.20 Ϯ 0.10
7.25 Ϯ 0.10
a Mole fractions of water in aqueous solutions of methanol, ethanol, and propan-2-ol are 0.839, 0.884, and 0.908, respectively.
trobenzene was 10Ϫ4 M, and those of piperidine were
dicates that rate of the reaction was not catalyzed by
bases in the all-aqueous solutions. Hence, it can be
concluded that the formation of zwitterionic interme-
diate is the rate-determining step of the reaction [5].
Similar results have been reported for this reaction in
aprotic and protic solutions. The second-order rate
constants of the reaction, kA , in aqueous solutions of
methanol, ethanol, and propan-2-ol were obtained at
25ꢀC (Tables II, III, and IV). In all cases, the rate con-
stants of the reaction increase with the increasing mole
fraction of water (approximately up to XW ϭ 0.85),
then it starts to decrease. In fact, in these aqueous so-
lutions, rate constants of the reaction vs. XW show
maxima (Fig. 1). The results show that this increase
of the reaction rate in aqueous solutions of propan-2-
ol is higher than those of ethanol and methanol.
between 5 ϫ 10Ϫ M to 10Ϫ M. Regression coeffi-
cients of plots of ln(Aϱ Ϫ At) vs. time were at least
0.9900. Thermostated water was circulated around the
cell of the spectrophotometer, and the temperature was
maintained at 25 Ϯ 0.1ꢀC.
3
1
RESULTS AND DISCUSSION
Although no base catalysis is expected for the reaction
of 1-chloro-2,4-dinitrobenzene with piperidine, to
confirmthis the influence of piperidine concentration
on the reaction rate with different mole fractions of
water was studied in aqueous solutions of methanol,
ethanol, and propan-2-ol. For instance, three experi-
mental data are shown in Table I. As can be observed,
no significant acceleration in the reaction rate occurs
with increasing concentration of piperidine. This in-
N
The normalized polarity parameter (ET ) of media
increases with the mole fraction of water in aqueous
solutions of the alcohols. In the same mole fraction of
N
water, ET of aqueous solutions of methanol Ͼ
N
ethanol Ͼ propan-2-ol. If the ET of media was the
Table II Second-Order Rate Constants of the
Reaction in Aqueous Solutions of Methanol at 25ꢀC.
ENT , ␲*, and ␣ are Normalized Polarity Parameter,
Dipolarity/Polarizability and Hydrogen-Bond Donocity
of Solvent.a
ETN
␲*
␣
Ϫ
Ϫ1
XW
k2*102/dm3mol s1ec
0.000
0.200
0.360
0.491
0.599
0.692
0.771
0.839
0.900
0.953
1.00
1.17 Ϯ 0.01
1.54 Ϯ 0.02
1.88 Ϯ 0.02
2.27 Ϯ 0.04
2.90 Ϯ 0.05
3.20 Ϯ 0.04
3.44 Ϯ 0.03
3.49 Ϯ 0.04
3.24 Ϯ 0.04
3.26 Ϯ 0.03
3.46 Ϯ 0.05
0.762
0.779
0.791
0.794
0.823
0.838
0.870
0.896
0.925
0.964
1.00
0.58
0.70
0.79
0.88
0.95
1.01
1.05
1.09
1.11
1.12
1.14
1.14
1.09
1.04
1.03
1.01
1.01
1.04
1.08
1.13
1.19
1.26
Figure 1 Plot of second-order rate constants of the reaction
vs. mole fraction of water in aqueous solutions of methanol
(᭺), ethanol (ϩ), and propan-2-ol(*) at 25ꢀC.
a At least three runs were averaged.

DUAL-PARAMETER CORRELATIONS IN VARIOUS AQUEOUS SOLUTIONS
121
Table III Second-Order Rate Constants of the
Table IV Second-Order Rate Constants of the
Reaction in Aqueous Solutions of Ethanol at 25ꢀC. ENT ,
␲*, and ␣ are Normalized Polarity Parameter,
Dipolarity/Polarizability, and Hydrogen-Bond Donocity
of Solvent.a
Reaction in Aqueous Solutions of Propan-2-ol at 25ꢀC.
ENT , ␲*, and ␣ are Normalized Polarity Parameter,
Dipolarity/Polarizability, and Hydrogen-Bond Donocity
of Solvent.a
k2*102/dm3mol s1ec
ETN
␲*
␣
XW
k2*102/dm3mol s1ec
ETN
␲*
␣
Ϫ
Ϫ1
Ϫ
Ϫ1
XW
0.000
0.266
0.449
0.583
0.685
0.765
0.830
0.884
0.929
0.967
1.00
1.76 Ϯ 0.04
2.26 Ϯ 0.04
2.75 Ϯ 0.05
2.87 Ϯ 0.06
3.96 Ϯ 0.04
4.88 Ϯ 0.12
5.25 Ϯ 0.09
5.10 Ϯ 0.08
4.24 Ϯ 0.06
3.43 Ϯ 0.06
3.46 Ϯ 0.05
0.648
0.673
0.702
0.717
0.731
0.761
0.784
0.842
0.907
0.959
1.00
0.51
0.66
0.75
0.81
0.88
0.96
1.03
1.10
1.12
1.13
1.14
0.98
0.93
0.89
0.89
0.88
0.86
0.87
0.92
1.05
1.17
1.26
0.000
0.320
0.514
0.645
0.738
0.809
0.864
0.908
0.944
0.974
1.000
2.53 Ϯ 0.03
2.62 Ϯ 0.04
3.14 Ϯ 0.03
3.50 Ϯ 0.04
4.18 Ϯ 0.04
5.42 Ϯ 0.04
6.25 Ϯ 0.11
7.24 Ϯ 0.09
6.65 Ϯ 0.10
3.91 Ϯ 0.07
3.46 Ϯ 0.05
0.552
0.583
0.639
0.667
0.685
0.714
0.740
0.790
0.901
0.957
1.00
0.49
0.65
0.72
0.77
0.81
0.87
0.95
1.06
1.14
1.15
1.14
0.76
0.78
0.81
0.80
0.82
0.82
0.82
0.85
0.96
1.12
1.26
a At least three runs were averaged.
a At least three runs were averaged.
only factor for the solvent effects on the reaction rate,
it may be expected that the reaction rate in water
should be higher than those of all the aqueous solu-
tions of methanol, ethanol, and propan-2-ol.
anol and ethanol. This quantity increases continuously
with XW in aqueous solutions of propan-2-ol. If HBD
of media were the only factor for solvent effects on
the reaction rate, one would expect that the second-
order rate constant of the reaction in water similar to
protic solvents should be less than those of methanol,
ethanol, and propan-2-ol [9–11]. Single-parameter
correlations of log k2 vs. ␣ do not give good results in
the three types of the aqueous solutions (Table V).
The normalized polarity parameter is a blend of di-
polarity/polarizability and HBD of media. Linear cor-
relations of log k2 vs. ␲* do not give good results in
N
Single-parameter correlations of log k2 vs. ET do
not give good results in three type of the aqueous so-
lutions (Table V). The rate of the reaction in some
protic solvents decreases with hydrogen-bond donor
acidity of solvent. HBD of water is higher than those
of methanol, ethanol, and propan-2-ol. HBD of media
first decreases and then increases with the increasing
mole fraction of water in aqueous solutions of meth-
Table V Regression Coefficients and Slopes of Solvent Parameters in Aqueous Solutions of Methanol, Ethanol,
Propan-2-ol and the All-Aqueous Solutions at 25ꢀC
Aqueous Solutions
of Methanol
ETN
␲*
␣
Intercept
r
1.612
—
—
—
0.624
—
—
—
0.474
—
—
—
0.384
—
—
—
—
0.856
—
0.897
—
0.580
—
0.778
—
0.482
—
1.061
—
0.596
—
0.918
—
—
0.152
Ϫ0.381
—
Ϫ2.975
Ϫ2.402
Ϫ1.758
Ϫ2.025
Ϫ1.958
Ϫ1.994
Ϫ1.336
Ϫ1.497
Ϫ1.734
Ϫ1.807
Ϫ1.432
Ϫ1.374
Ϫ1.782
Ϫ2.017
Ϫ1.055
Ϫ1.293
0.779
0.979
0.074
0.995
0.486
0.814
0.113
0.980
0.438
0.665
0.058
0.955
0.244
0.654
0.327
0.956
of Ethanol
—
0.130
Ϫ0.698
—
of Propan-2-ol
—
0.056
Ϫ1.061
—
—
0.438
Ϫ1.048
the All-Aqueous Solutions

122
GHOLAMI AND YANGJEH
all three types of solutions (Table V) [12,13]. So, we
decided to correlate log k2 vs. both ␲* and ␣ in aque-
ous solutions of methanol, ethanol, and propan-2-ol.
Dual-parameter correlations of log k2 vs. ␲* and ␣ in
the three all types of solutions give interesting results:
• In aqueous solutions of methanol:
log kA ϭ Ϫ2.025(Ϯ0.080)
ϩ 0.897(Ϯ0.032) ␲* Ϫ 0.381(Ϯ0.075) ␣
(n ϭ 11, r ϭ 0.995, s ϭ 0.018, F2,8 ϭ 396.30) (3)
• In aqueous solutions of ethanol:
Figure 2 Plot of experimental values of log k2 vs. the cal-
culated values of it fromEq. (6) in the all-aqueous solutions
at 25ꢀC.
log kA ϭ Ϫ1.497(Ϯ0.080)
ϩ 0.778(Ϯ0.057) ␲* Ϫ 0.698(Ϯ0.091) ␣
(n ϭ 11, r ϭ 0.980, s ϭ 0.034, F2,8 ϭ 95.21) (4)
In Eq. (6), dipolarity/polarizability and hydrogen bond
donor ability of the media have approximately equal
but opposite effects on the reaction rate. In order to
show the efficiency of suggested dual-parameter cor-
relations, experimental values of log k2 vs. its calcu-
lated values fromEq. (6) were plotted for different
aqueous solutions of alcohols. As can be seen, the ex-
perimental and calculated values of log k2 are in good
agreement in the all-aqueous solutions (Fig. 2).
The rates of some organic reactions in water and
several aqueous solutions are higher than those of or-
ganic solvents, and the reaction rate increases dramat-
ically with the increasing mole fraction of water
[16,17]. Hydrophobic interactions have important role
in these conditions [18–21]. In these reactions, the
rate of reaction in aqueous solutions of methanol is
higher than that of ethanol, while in the reaction re-
ported in this article, opposite observations were ob-
tained. Also in this reaction, the increase of the reac-
tion rate with XW is very low. In fact, because of
complete solubility of piperidine in water, hydropho-
bic interactions would not exist. This idea is estab-
lished by dual-parameter correlations of log kA vs. ␲*
and ␣ in the all-aqueous solutions.
• In aqueous solutions of propan-2-ol:
log kA ϭ Ϫ1.374(Ϯ0.096)
ϩ 1.061(Ϯ0.117) ␲* Ϫ 1.061(Ϯ0.162) ␣
(n ϭ 11, r ϭ 0.955, s ϭ 0.053, F2,8 ϭ 41.47) (5)
Regression coefficients and standard deviations of the
equations are good. As can be seen, the dipolarity/
polarizability and HBD of the media have opposite
effects on the reaction rate. The intermediate of the
reaction has zwitterionic character; the activated com-
plex of the reaction therefore, has higher polarity rel-
ative to those of the reactants of the reaction. The ac-
tivated complex leading to the zwitterionic
intermediate is expected to be favored by the increas-
ing dipolarity/polarizability of media and hence the
reaction rate increases. In the presence of piperidine,
alcohols are known to act as HBD, and there is abun-
dant evidence of strong hydrogen-bonding interactions
between piperidine and alcohols [14,15]. Therefore,
piperidine will be stabilized via hydrogen-bonding in-
teractions with hydrogen-bond donors. Hence, the re-
action rate decreases with the increasing HBD of the
media. Because of the opposite effects of dipolarity/
polarizability and HBD of the media, maxima appear
in plots of second-order rate constants of the reaction
vs. mole fraction of water.
BIBLIOGRAPHY
A dual-parameter correlation of log k2 vs. ␲* and
␣ was obtained in the all-aqueous solutions of the al-
cohols:
1. Reichardt, C. Solvents and Solvent Effects in Organic
Chemistry, 2nd ed; Verlag Chemie: Wainheim, 1988.
2. Marcus, Y. J ChemSoc, Perkin Trans 2 1994, 1015.
3. Engberts, J. B. F. N.; Blandamer, M. J. J Phys Org Chem
1998, 11, 841.
log kA ϭ Ϫ1.293(Ϯ0.074)
ϩ 0.918(Ϯ0.056) ␲* Ϫ 1.048(Ϯ0.083) ␣
(n ϭ 31, r ϭ 0.956, s ϭ 0.055, F2,28 ϭ 150.67) (6)
4. Streefland, L.; Blandamer, M. J.; Engberts, J. B. F. N.
J ChemSoc, Perkin Trans 2 1997, 769.

DUAL-PARAMETER CORRELATIONS IN VARIOUS AQUEOUS SOLUTIONS
123
5. Cativiela, C.; Garcia, J. I.; Gil, J.; Martinez, R. M.; May-
oral, J. A.; Salvatella, L.; Urieta, J. S.; Mainer, A. M.;
Abraham, M. H. J Chem Soc, Perkin Trans 2 1997,
653.
13. Roses, M.; Buhvestov, U.; Rafols, C.; Rived, F.; Bosch,
E. J ChemSoc, Perkin Trans 2 1997, 1341.
14. Sinsheimer, J. E.; Kecehneliam, A. N. Anal Chem 1974,
46, 89.
6. Blake, J. F.; Jorgensen, W. L. J AmChemSoc 1991,
113, 7430.
15. Prahan, S. D.; Mathews, H. B. Proc Indian Acad Sci,
Sect A 1978, 87, 23.
7. Repasky, M. P.; Jorgensen, W. L.; Faraday Discuss
ChemSoc 1998, 110, 379.
8. Nudelman, N. S. The Chemistry of Amino, Nitroso, Ni-
tro and Related Groups; Patai, S., Ed.; Wiley: Chich-
ester, 1996; Chapter 26.
9. Mancini, P. M. E.; Martinez, R. D. Vottero, L. R.; Nu-
delman, N. S. J Chem Soc, Perkin Trans 2 1984, 1133.
10. Martinez, R. D.; Mancini, P. M. E.; Vottero, L. R.; Nu-
delman, N. S. J Chem Soc, Perkin Trans 2 1986, 1427.
11. Mancini, P. M. E.; Terenzani, A.; Adam, C.; Vottero,
L. R. J Phys Org Chem1997, 10, 849.
16. Engberts, J. B. F. N. Pure & Appl Chem1995, 67, 823.
17. Gholami, M. R.; Habibi Y. A. J Chem Res(S) 1999, 226.
18. Gholami, M. R.; Habibi Y. A. Int J Chem Kinet 2000,
32, 431.
19. Gholami, M. R.; Habibi Y. A. J Phys Org Chem 2000,
13, 468.
20. Cativiela, C.; Garcia, J. I.; Mayoral, J. A.; Salvatella, L.
J ChemSoc, Perkin Trans 2 1994, 847.
21. Cativiela, C.; Garcia, J. I.; Mayoral, J. A.; Royo, A. J.;
Salvatella, L.; Assfeld, X.; Ruiz-Lopez, M. F. J Phys
Org Chem1992, 5, 230.
12. Buhvestov, U.; Rived, F.; Rafols, C.; Bosch, E.; Roses,
M. J Phys Org Chem1998, 11, 185.
22. Cativiela, C.; Mayoral, J. A.; Avenoza, A.; Peregrina,
J. M.; Roy, M. A. J Phys Org Chem1990, 3, 414.