112
QUARTARONE ET AL.
Table III Kinetic Constants Calculated by Nonlinear Fitting of the Experimental Data
103 Initial Concentration
102 kD
(L mol−1 s−1
10−3 kDR
(s−1
10−2 kT
(L mol−1 s−1
10−3 kTR
(s−1
(mol L−1
)
)
)
)
)
ε kDa
104 ε kTa
108 σ2
1
1
1
3
4
3.0
5.0
6.3
1.01
0.94
2.65
2.59
2.26
3.09
1.71
1.79
1.75
1.53
2.08
1.15
9.11
9.72
8.63
8.41
8.63
9.26
9.87
8.75
8.55
8.75
1.1
1.6
1.5
1.0
4.3
9.8
12
19
6.6
9.1
2.8
3.2
8.5
0.36
0.6
aThe correlation matrix values of the regression variables (kD and kT) are comprised between 0.1 and 0.4.
activity coefficient factor is practically constant in the
range investigated.
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Except indole protonation, which is in stationary
state, the faster step is the formation of 3 that is the
direct consequence of the high reactivity of the carbo-
cation (2). The values of the kinetic constant (kD) are
comparable with those measured by other authors for
the additions of benzhydrylium ions to indoles [17]. As
expected, the nucleophilic attack of indole to the proto-
nated indole dimer (3) is much slower because the pos-
itive charge is mainly localized on the nitrogen atom,
which is, in this case, a secondary ammonium ion.
Furthermore, the protonated 2-alkyl-aniline (4) does
not react with (1), since the positive charge is on the
nitrogen atom and the anilinium ion is ineffective as
electrophile. Nevertheless, under different experimen-
tal conditions, Plancher rearrangement, additions and
aromatization reactions occur [3,4,10,18].
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The complete thermodynamic and kinetics analysis
of the reactions are in course of study.
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We thank Dr. Laura Sperni for mass spectra, Sig. Augusto
Tassan for NMR spectra and for elemental analysis, and
Dr. Marco Bortoluzzi for the helpful suggestions and dis-
cussions.
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International Journal of Chemical Kinetics DOI 10.1002/kin