Concerted aminolysis of diaryl carbonates: Kinetic sensitivity on the basicity of the nucleophile, nonleaving group, and nucleofuge

Article abstract of DOI:10.1002/kin.20700

The kinetics of the reactions of 4-methylphenyl, phenyl, and 4-chlorophenyl 2,4,6-trinitrophenyl carbonates (1, 2, and 3, respectively) with a series of anilines and secondary alicyclic (SA) amines has been carried out spectrophotometrically in 44 wt% ethanol-water, at 25.0°C, ionic strength 0.2 M. The BrAnsted plots (statistically corrected) for the reactions of carbonates 1-3 with anilines and SA amines were linear with slopes (β_N) in the range of 0.69-0.78 and 0.45-0.48, respectively, attributed to a concerted mechanism. The negative values found for the sensitivity of log k_N to the basicity of the nonleaving (β_nlg) and leaving (β_lg) groups are discussed. Anilines are more reactive than isobasic SA amines, probably because of the greater steric hindrance offered by the latter.

Full text of DOI:10.1002/kin.20700

Concerted Aminolysis of
Diaryl Carbonates: Kinetic
Sensitivity on the Basicity
of the Nucleophile,
Nonleaving Group,
and Nucleofuge
ENRIQUE A. CASTRO, MARIA CUBILLOS, ROCIO IGLESIAS, JOSE G. SANTOS
Facultad de Qu´ımica. Pontificia Universidad Cato´lica de Chile. Casilla 306, Santiago 6094411, Chile
Received 28 September 2011; revised 17 November 2011; accepted 19 November 2011
´
´
´
DOI 10.1002/kin.20700
Published online in Wiley Online Library (wileyonlinelibrary.com).
ABSTRACT: The kinetics of the reactions of 4-methylphenyl, phenyl, and 4-chlorophenyl 2,4,6-
trinitrophenyl carbonates (1, 2, and 3, respectively) with a series of anilines and secondary
alicyclic (SA) amines has been carried out spectrophotometrically in 44 wt% ethanol–water, at
25.0◦C, ionic strength 0.2 M. The Brønsted plots (statistically corrected) for the reactions of
carbonates 1–3 with anilines and SA amines were linear with slopes (βN) in the range of 0.69–
0.78 and 0.45–0.48, respectively, attributed to a concerted mechanism. The negative values
found for the sensitivity of log kN to the basicity of the nonleaving (βnlg) and leaving (βlg)
groups are discussed. Anilines are more reactive than isobasic SA amines, probably because
of the greater steric hindrance offered by the latter. ꢀ 2012 Wiley Periodicals, Inc. Int J Chem
C
Kinet 1–8, 2012
of these reactions have been described as stepwise,
through a zwitterionic tetrahedral intermediate (T )
[3–11], whereas others have been found to be con-
certed, i.e., with no T intermediate in a single step
[12–16]. The mechanism of these aminolysis reactions
has been mainly assigned by the shape and slopes of the
corresponding Brønsted-type plots obtained. The lin-
ear plots with slopes (β) 0.8–1.1 have been attributed to
stepwise mechanisms, whereby decomposition of T
to products is the rate-determining step [3,7,10,11].
The curved Brønsted plots, with two linear portions at
low and high pKa values (biphasic plots), have been
INTRODUCTION
The kinetics and mechanisms of the aminolysis of di-
aryl carbonates are well documented [1–16]. Some
Correspondence to: Jose´ G. Santos; e-mail: jgsantos@uc.cl.
Contract grant sponsor: MECESUP of Chile.
Contract grant number: UCH-06011.
Contract grant sponsor: FONDECYT of Chile.
Contract grant number: 1060593.
Supporting Information is available in the online issue at
www.wileyonlinelibrary.com.
c
ꢀ
2012 Wiley Periodicals, Inc.

2
CASTRO ET AL.
EXPERIMENTAL
Materials
explained by the existence of the T intermediate
on the reaction pathway and a change in the rate-
limiting step, from T decomposition to its forma-
tion, as the amine basicity increases [4–6,8–10]. On
the other hand, the linear Brønsted plots with β values
0.4–0.7 have been assigned to concerted mechanisms
[10,12–18].
It has been shown that the mechanism of the aminol-
ysis of carbonates and esters, and their thio derivatives,
depends on the stability of the T intermediate, which,
in turn, depends on the groups attached to its central
carbon atom [17,18].
With the aim to clarify the mechanisms of the
aminolysis reactions of diaryl carbonates and to de-
termine the effect of the amine nature and of the leav-
ing and nonleaving groups of the carbonate, in this
work we report a kinetic investigation of the reactions
of 4-methylphenyl, phenyl, and 4-chlorophenyl 2,4,6-
trinitrophenyl carbonates (1, 2, and 3, respectively)
with a series of anilines and secondary alicyclic (SA)
amines.
Anilines and SA amines were distilled or recrystal-
lized before use. Carbonates 1–3 were synthesized by
a modification [14] of a general procedure reported in
the literature [8].
Kinetic Measurements
The reactions were carried out at 25.0 0.1◦C, ionic
strength 0.2 M (KCl) in 44 wt% ethanol aqueous
solution. The kinetics was measured by monitoring the
appearance of 2,4,6-trinitrophenoxide anion at 360 nm,
by using a diode array spectrophotometer.
All the reactions were studied under excess amine
over the substrate. The initial substrate concentration
was about 5 × 10−5 M and, in most cases, the pH was
maintained constant by the use of an external buffer
(0.01 M phosphate or 0.01 M acetate buffer).
Pseudo–first-order rate coefficients (kobs) were
found throughout and determined by using the spec-
trophotometer kinetic softwarefor first-order reactions.
Errors in the kobs values were less than 3%. The exper-
imental conditions of the reactions and the values of
kobs are presented in Tables S1–S36 of the Supporting
Information.
Because the reactions of carbonates 1–3 with
pyridines are concerted [14] and the SA-aminolysis
and anilinolysis of 4-methylphenyl, phenyl, and 4-
chlorophenyl 2,4-dinitrophenyl carbonates (4, 5, and
6, respectively) proceed by concerted mechanisms
[15,16], it follows that the reactions of these studies
should also be concerted. The kinetic results obtained
in this work will be compared with those of the pyridi-
nolysis of 1–3 and will be systematized by comparison
with the same aminolysis of 4–6 and 4-nitrophenyl
2,4-dinitrophenyl carbonate (7) [14–16] and bis(2,4-
dinitrophenyl) carbonate (8) [14–16]. The main objec-
tive of this work is to determine the sensitivity of the
rate constants (kN) of these reactions to the basicity of
the nucleophile and the leaving and nonleaving groups
of the carbonates. This will be achieved by obtaining
the corresponding Brønsted-type plots (log kN against
the pKa of the corresponding groups).
Determination of pKa Values
The pKa values of the conjugate acids of anilines and
SA amines under the experimental conditions of the
kinetic measurements (44 wt% ethanol–water, 25.0
0.1◦C, ionic strength 0.2 M) were determined previ-
ously, as reported in [13]. The pKa of phenol under
the aforementioned conditions was taken from the lit-
erature [19]. The pKa values of 4-methylphenol and
2,4,6-trinitrophenol were obtained using Eq. (1) with
O2N
O
O2N
O
X
O C O
NO2
X
O C O
NO2
O2N
1: X = Me
2: X = H
3: X = Cl
4: X = Me
5: X = H
6: X = Cl
O2N
X
O
O2N
O C O
NO2
7: X = H
8: X = NO2
International Journal of Chemical Kinetics DOI 10.1002/kin

CONCERTED AMINOLYSIS OF DIARYL CARBONATES
3
pKa (water) 11.1 and 0.4, respectively. Equation (1) was
obtained from the linear relation between the pKa of
some phenols in water and 44 wt% ethanol–water, both
at 25.0◦C and ionic strength 0.2 M; this relationship
is shown in Fig. S1 in the Supporting Information
(n = 7, R2 = 0.9993). The values obtained for the pKa
of 4-methylphenol and 2,4,6-trinitrophenol in 44 wt%
ethanol–water are 11.33 and −0.58, respectively.
than those of kN[free amine] in Eq. (3).
d[P]
= kobs[S]
dt
(2)
(3)
kobs = k0 + kN[free amine]
The values of kN for all reactions were obtained as the
slopes of the linear plots of kobs versus [free amine] and
were found to be pH independent. The kN values for
the reactions of anilines and SA amines are presented
in Tables I and II, respectively, together with the pKa
values of the series of nucleophiles employed.
pKa (44 wt% ethanol−water) = 1.2287pKa (water) − 1.0713
(1)
Product Studies
Figures 1 and 2 show the Brønsted plots (statisti-
cally corrected) for the reactions of carbonates 1–3 with
anilines and SA amines, respectively. In these plots, the
kN values, as well as the values of the pKa of the con-
jugate acids of these amines (presented in Tables I and
II), are statistically corrected,with q = 2 for phenylen-
diamine and piperazine (q = 1 for the other amines), p
= 3 for all the conjugate acids of the studied anilines,
and p = 4 and p = 2 for the conjugate acids of piper-
azinium ion and the other SA amines, respectively [20].
The parameter q is the number of equivalent basic sites
in the free amine, and p is the number of equivalent
dissociable protons in the conjugate acid of the amine
[21]. As seen in Figs. 1 and 2, the Brønsted plots for
the studied reactions are linear; their slopes (β) are
summarized in Table III.
One of the products of the reactions under scrutiny was
identified as 2,4,6-trinitrophenoxide ion, as shown by
a comparison of the UV–vis spectra after completion
of the reactions with that of an authentic sample un-
der the same experimental conditions. A quantitative
analysis (by UV–vis) shows that 98
trinitrophenoxide is obtained.
2% of 2,4,6-
RESULTS AND DISCUSSION
For all the reactions, pseudo–first-order coefficients
(kobs) were obtained (under amine excess). The exper-
imental conditions of the reactions and the values of
kobs are presented in Tables S1–S36 of the Supporting
Information.
The rate law obtained for all the reactions studied
is given by Eqs. (2) and (3), where P, S, and [free
amine] represent the product (2,4,6-trinitrophenoxide
anion), the substrate (carbonates 1–3), and the free
amine concentration, respectively; k0 and kN are the
rate coefficients for solvolysis and aminolysis of the
substrate, respectively. The values of k0 are much lower
Mechanism
The Brønsted slope (β) values for the SA aminoly-
sis of the aryl 2,4,6-trinitrophenyl carbonates 1–3 are
in the range β = 0.4–0.5, in accordance with a con-
certed mechanism [17,18]. In fact, the concerted reac-
tions of SA amines, quinuclidines, anilines, and other
Table I Values of pKa for the Conjugate Acids of Anilines and kN Values for the Reactions of Anilines with
4-Methylphenyl (2,4,6-trinitrophenyl) Carbonate (1), Phenyl (2,4,6-trinitrophenyl) Carbonate (2), and 4-Chlorophenyl
(2,4,6-trinitrophenyl) Carbonate (3)a
kN(s−1M−1
)
Aniline Substituent
pK
1
2
3
a
4-Amine
4-Methoxy
4-Methyl
None
3-Methoxy
3-Acetyl
4-Acetyl
6.45
5.31
4.90
4.46
4.26
3.1
265 12
340 40
264 12
33
1
33
1
38
1
16.8 0.2
4.9 0.1
2.9 0.1
0.58 0.01
0.046 0.002
14.9 0.5
22.2 0.5
6.8 0.1
6.4 0.1
1.07 0.06
0.124 0.006
2.6 0.1
0.57 0.02
0.078 0.002
1.73
aBoth the pKa and kN values were determined in 44 wt% ethanol–water, at 25.0◦C, ionic strength 0.2 M (KCl).
International Journal of Chemical Kinetics DOI 10.1002/kin

4
CASTRO ET AL.
Table II Values of pKa for the Conjugate Acids of SA Amines and kN Values for the Reactions of SA Amines with
4-Methylphenyl (2,4,6-trinitrophenyl) Carbonate (1), Phenyl (2,4,6-trinitrophenyl) Carbonate (2), and 4-Chlorophenyl
(2,4,6-trinitrophenyl) Carbonate (3)a
kN(s−1M−1
)
SA Amine
pK
1
2
3
a
Piperidine
Piperazine
Morpholine
1-Formylpiperazine
Piperazinium ion
10.82
9.71
8.48
7.63
5.37
640 10
690 10
310 20
1500 30
430 20
237
38
9
1
68
20
2
1
124
33
4
5
15.8 0.6
2.2 0.1
2.9 0.1
5.9 0.2
aBoth the pKa and kN values were determined in 44 wt% ethanol–water, at 25.0◦C, ionic strength 0.2 M (KCl).
3
1,5
2
0,0
1
–1,5
0
6
8
10
12
2
4
6
pKa + log p/q
pKa + log p/q
Figure 2 Brønsted-type plots (statistically corrected) for
Figure 1 Brønsted-type plots (statistically corrected) for
the aminolysis (SA amines) of 1 (ꢀ), 2 ( ), and 3 ( ) in
ꢀ
the anilinolysis of 1 (ꢀ), 2 ( ), and 3 ( ) in 44 wt% ethanol–
◦
ꢀ
◦
44 wt% ethanol–water, 25.0 0.1◦C, ionic strength 0.2 M
(KCl).
water, 25.0 0.1◦C, ionic strength 0.2 M (KCl)
primary amines with alkyl aryl and diaryl carbonates
and their thio derivatives in aqueous solutions show lin-
ear Brønsted plots with slopes in the range of 0.4–0.7
[10–18].
Williams has argued that the β value alone is not
sufficient to decide whether a mechanism is concerted
[22–24]. It is also needed that the expected pKa value
at the center of the Brønsted curvature (pKa0) for a
hypothetical stepwise mechanism is within the pKa
range used [22,24]. Although it is difficult to esti-
mate the pKa0 for these reactions, this can be attempted
by the following arguments: For stepwise reactions,
there is an increase in the pKa0 value, of ca. 1 unit, by
changing pyridines to SA amines [25,26]. On the other
hand, the substitution of 2,4-dinitrophenoxy by 2,4,6-
trinitrophenoxy as the leaving group lowers the pKa0
value by ca. 1.3 units [27,28]. Taking into account these
variations and the fact that the pKa0 for the pyridinol-
ysis of phenyl 2,4-dinitrophenyl carbonate in 44 wt%
ethanol–water is 8.0 [29], a pKa0 value of ca. 7.7 (8.0 +
1 − 1.3) can be estimated for the SA aminolysis of
Table III Values of β for the Anilinolysis and SA Aminolysis of Carbonates 1–3 in 44 wt% Ethanol–Water, 25.0
0.1◦C, Ionic Strength 0.2 M (KCl)
Anilinolysis
SA Aminolysis
Carbonate
1
2
3
1
2
3
β
0.78
0.75
0.69
0.45
0.48
0.45
International Journal of Chemical Kinetics DOI 10.1002/kin

CONCERTED AMINOLYSIS OF DIARYL CARBONATES
5
carbonate 2 in the above solvent mixture. For the
pyridinolysis of 4-methylphenyl and 4-chlorophenyl
2,4-dinitrophenyl carbonates in 44 wt% ethanol–water,
the pKa0 values are 8.3 in both cases [25], so the esti-
mated pKa0 for the hypothetical stepwise mechanisms
of the SA aminolysis of carbonates 1 and 3 in the
aforementioned aqueous ethanol solvent would be 8.0.
As shown in Fig. 2, there are no breaks around pKa
7.7–8 in the Brønsted plots for the SA aminolysis,
which rules out a stepwise mechanism for the reac-
tions of these amines with carbonates 1–3 in aqueous
ethanol.
There are two more reasons in favor of the con-
certed mechanism for the SA aminolysis of carbon-
ates 1–3: (i) The pyridinolysis reactions of carbonates
1–3 in 44 wt% ethanol–water have been described as
concerted [14]. This means that the zwitterionic tetra-
hedral intermediate (T ) in these reactions does not ex-
ist or is highly unstable [29–31]. On the other hand, SA
amines are known to destabilize the T intermediate
compared with isobasic pyridines [17,18].Therefore,
it is reasonable that the T intermediate in the SA
aminolysis would be even more unstable than that
formed with pyridines and that the former reactions
of carbonates 1–3 would be concerted. (ii) The
SA aminolysis of 4-methylphenyl, phenyl, and 4-
chlorophenyl 2,4-dinitrophenyl carbonates (4, 5, and
6, respectively) in 44 wt% ethanol–water has been de-
scribed as concerted [10,13,32]. Taking into account
that 2,4,6-trinitrophenoxide ion is a better nucleofuge
than 2,4-dinitrophenoxide ion, the hypothetical T in-
termediate would be more unstable with the former
group and, therefore, it is more likely that the SA
aminolysis of the title carbonates would be concerted.
This mechanism is shown in Scheme 1.
The Brønsted slopes found for the reactions of ani-
lines with carbonates 1–3 (β = 0.69–0.78; Fig. 1) are in
the borderline between stepwise and concerted mecha-
nisms. It is difficult to estimate the value for the center
of the Brønsted curvature (pKa0) for the stepwise anili-
nolysis of carbonates because, to our knowledge, no
biphasic Brønsted plots have been reported for these
reactions. Nevertheless, we are more inclined toward
a concerted mechanism for the following two reasons:
(i) The pyridinolysis reactions of carbonates 1–3 have
been found to be concerted [14], and it is known that
anilines destabilizethe putative zwitterionic tetrahedral
intermediate (T ) relative to pyridines [33]. Therefore,
the anilinolysis of these carbonates should also be con-
certed. (ii) The anilinolysis of carbonates 4, 5, and 6 has
been described as concerted [13,15]. As was mentioned
above, 2,4,6-trinitrophenoxide is a better leaving group
than 2,4-dinitrophenoxide; therefore, the putative T
intermediate formed with the former group would
O2N
O
X
O C O
NO2
+
HN
O2N
1: X = Me
2: X = H
3: X = Cl
kN
NH = SA amine
O2N
−O
O2N
O
O C
NH+
+
X
NO2
–H+
Fast
O
O C
N
X
Scheme 1
be even more unstable and the mechanism for the
anilinolysis of carbonates 1–3 should be concerted.
This mechanism is illustrated in Scheme 2.
Effect of the Amine Nature
Figure 3 shows the Brønsted-type plots for the reac-
tions of carbonate 2 with pyridines [14], SA amines,
and anilines (this study), all in 44 wt% ethanol–water. It
can be observed that for isobasic amines, pyridines are
more reactive than anilines, and these are more reac-
tive than SA amines. These results can be explained
considering steric effects: Pyridines being aromatic
heterocyclic amines are planar and show less steric
hindrance toward nucleophilic attack than anilines and
SA amines. Anilines are also planar, but because of
rotation of the N Ar bond they show greater steric
hindrance than pyridines. SA amines show the great-
est steric hindrance to nucleophilic attack, relative to
anilines and pyridines, as a result of their chair–boat
conformation.
Sensitivity of Rate Constants to the Basicity
of the Nucleofuge and Nonleaving Group
For diaryl carbonates, two multiparametric equations
can be obtained to determine the sensitivity of the rate
coefficient (kN) to the basicity of the nucleofuge and
International Journal of Chemical Kinetics DOI 10.1002/kin

6
CASTRO ET AL.
values in this equation are those in 44 wt% ethanol–
water, at 25◦C, and ionic strength 0.2. The pKa in these
media for the leaving and nonleaving groups is phe-
nol = 11.16, 4-methylphenol = 11.33, 4-chlorophenol
= 10.47, 4-nitrophenol = 7.5, 2,4-dinitrophenol = 4.0,
and 2,4,6-trinitrophenol = −0.58. Figure 4 shows a
dual plot of experimental log kN against that calculated
with Eq. (4); the slope and intercept values are 1 and
0, respectively.
O2N
O
X
O C O
O2N
NO2
+ ArNH2
1: X = Me
2: X = H
3: X = Cl
kN
O2N
O
O
log(kN/q) = (0.27 0.26) + (0.69 0.03)pKNcorr
–
+
NO2
X
O C
+NH2Ar
− (0.27 0.02)pKnlg − (0.38 0.02)pKlg
(4)
O2N
With the kN values obtained for the reactions of SA
amines with carbonates 1–3 (this study), 4 [32], 5 [10],
6 [13], 7 [16], and 8 [16], and the corrected pKa of the
conjugate acids of SA amines (pKNcorr) and those of
the leaving (pKlg) and nonleaving groups (pKnlg), Eq.
(5) was obtained (n = 34, R2 = 0.977). Both the kN and
pKa values used are those in 44 wt% ethanol–water,
25◦C and ionic strength 0.2 M. Figure 5 shows a dual
plot of experimental log kN versus log kN calculated
with Eq. (5); the slope and intercept values are 1 and
0, respectively.
–H+
fast
O
X
O C
NHAr
Scheme 2
log(kN/q) = (0.44 0.19) + (0.49 0.02)pKNcorr
− (0.18 0.01)pKnlg − (0.05 0.02)pKlg
(5)
4
2
0
The log kN sensitivity to amine basicity (βN) of 0.69
(Eq. (4)) and 0.49 (Eq. (5)) for the anilinolysis and SA
2
0
–2
0
3
6
9
12
pKa + log p/q
Figure 3 Brønsted-type plots (statistically corrected) for
the reactions of 2 with pyridines ( , [14]), anilines ( , this
•
◦
work), and SA amines ( , this work) in 44 wt% ethanol-
ꢀ
–2
water, 25.0 0.1 ◦C, ionic strength 0.2 M (KCl).
-2
0
2
nonleaving group: one for anilines and another for
SA amines. With the kN values for the reactions of
anilines with 1–3 (this work), 4 [13], 5 [15], 6 [13],
7 [15], and 8 [15], and with the corrected pKa of the
conjugate acids of anilines (pKNcorr), the nucleofuge
(pKlg) and nonleaving group (pKnlg), Eq. (4) was ob-
tained (n = 59 and R2 = 0.960). The kN and pKa
log (kN (s–1 M–1)calc.
Figure 4 Experimental log kN versus that calculated,
through Eq. (4), for the anilinolysis of carbonates 1 (ꢁ, this
work), 2 (ꢀ, this work), 3 ( , this work), 4 ( , [13]), 5 (ꢃ,
ꢀ
ꢂ
[15]), 6 ( , [13]), 7 ( , [15]), and 8 (∇, [15]), in 44 wt%
•
◦
ethanol–water, 25◦C, ionic strength 0.2.
International Journal of Chemical Kinetics DOI 10.1002/kin

CONCERTED AMINOLYSIS OF DIARYL CARBONATES
7
The reactivity sequence 3 > 2 > 1 is in accor-
dance with the electron-withdrawal sequence of
the nonleaving groups.
4
2
0
3. Anilines are more reactive than isobasic SA
amines, probably as a result of the greater steric
hindrance offered by the latter.
BIBLIOGRAPHY
1. Fife, T. H.; Hutchins, J. E. C. J Am Chem Soc 1981,
103, 4194–4199.
2. Brunelle, D. J. Tetrahedron Lett 1982, 23, 1739–1742.
3. Um, I.-H.; Park, H-R.; Kim, E.-Y. Bull Korean Chem
Soc 2003, 24, 1251–1255.
0
2
4
log (k N(s–1 M–1)calc.
4. Um, I.-H.; Kim, E.-Y.; Park, H.-R.; Jeon, S.-E. J Org
Chem 2006, 71, 2302–2306.
5. Um, I.-H.; Yoon, S.; Park, H.-R.; Han, H.-J. Org Biomol
Chem 2008, 6, 1618–1624.
6. Um, I.-H.; Son, M. J.; Kim, S.-I.; Akhtar, K. Bull Korean
Chem Soc 2010, 31, 1915–1919.
Figure 5 Experimental log kN versus that calculated,
through Eq. (5), for the SA aminolysis of carbonates 1 (ꢁ,
this work), 2 (ꢀ, this work), 3 ( , this work), 6 ( , [13]), 7
ꢀ
•
( , [15]), and 8 (∇, [15]), in 44 wt% ethanol–water, 25 ◦C,
◦
ionic strength 0.2 M.
7. Bond, P. M.; Moodie, R. B. J Chem Soc, Perkin Trans 2
1976, 679–682.
8. Gresser, M. J.; Jencks, W. P. J Am Chem Soc 1977, 99,
6963–6970.
9. Gresser, M. J.; Jencks, W. P. J Am Chem Soc 1977, 99,
6970–6980.
10. Castro, E. A.; Aliaga, M.; Campodo´nico, P.; Santos, J.
G. J Org Chem 2002, 67, 8911–8916.
11. Castro, E. A.; Gazitua, M.; Santos, J. G. J Org Chem
2005, 70, 8088–8092.
12. Castro, E. A.; Cubillos, M.; Santos, J. G. J Org Chem
2001, 66, 6000–6003.
13. Castro, E. A.; Campodonico, P.; Toro, A.; Santos, J. G.
J Org Chem 2003, 68, 5930–5935.
aminolysis, respectively, is in accordance with those
values summarized in Table III. The negative values
found for the sensitivity of log kN to the nonleaving
group basicity (βnlg) of −0.27 (Eq. (4)) and −0.18
(Eq. (5)) are the result of the fact that as more basic
is the nonleaving group less positive is the carbonyl
carbon atom and less prone is to the amine attack.
The kN values of Tables I and II show the reactivity
sequence 3 > 2 > 1, which is in accordance with
the electron-withdrawal sequence of the nonleaving
groups [34].
14. Castro, E. A.; Ramos, M.; Santos, J. G. J Org Chem
2009, 74, 6374–6377.
15. Castro, E. A.; Domecq, C.; Santos, J. G. Int J Chem
Kinet 2011, 43, 191–197.
16. Castro, E. A.; Soto, C.; Vasquez, B.; Santos, J. G.
Arkivoc 2008, X, 151–160.
17. Castro, E. A. Chem Rev 1999, 99, 3505–3524.
18. Castro, E. A. J Sulfur Chem 2007, 28, 401–429.
19. Castro, E. A.; Aliaga, M.; Campodo´nico, P.; Cepeda,
M.; Contreras, R.; Santos, J. G. J Org Chem 2009, 74,
9173–9179.
20. Castro, E. A.; Ureta, C. J Org Chem 1989, 54, 2153–
2159.
21. Bell, R. P. The Proton in Chemistry; Methuen: London,
1959; p 159.
The negative values obtained for the sensitivity of
log kN to the leaving group basicity, βlg = −0.38 for
anilinolysis, Eq. (4), and −0.05 for SA aminolysis,
Eq. (5), are reasonable considering that a stronger
basicity of the nucleofuge means a less positive car-
bonyl and thus a smaller nucleophilic rate constant (kN)
value.
CONCLUSIONS
1. The anilinolysis and SA aminolysis of diaryl car-
bonates 1–3 are driven by a concerted mecha-
nism.
2. The negative values of βlg and βnlg can be ex-
plained by the fact that as the electron withdrawal
of the leaving and nonleaving groups is greater
(smaller basicity), the more positive becomes the
carbonyl carbon and more prone to amine attack.
22. Chrystiuk, E.; Williams, A. J Am Chem Soc 1987, 109,
3040.
23. Williams, A. Acc Chem Res 1989, 22, 387.
24. Williams, A. Free Energy Relationships in Organic and
Bio-Organic Chemistry; The Royal Society of Chem-
istry: Cambridge, UK, 2003; p 171.
International Journal of Chemical Kinetics DOI 10.1002/kin

8
CASTRO ET AL.
25. Castro, E. A.; Acun˜a, M.; Soto, C.; Trujillo, C.; Va´squez,
B.; Santos, J. G. J Phys Org Chem 2008, 21, 816–
822.
26. Castro, E. A.; Andujar, M.; Toro, A.; Santos, J. G. J Org
Chem 2003, 68, 3608–3613.
29. Jencks, W. P. Acc Chem Res 1980, 13, 161.
30. Jencks, W. P. Chem Soc Rev 1981, 10, 345.
31. Williams, A. Chem Soc Rev 1994, 23, 93.
32. Castro, E. A.; Andujar, M.; Campodo´nico, P.; Santos, J.
G. Int J Chem Kinet 2002, 34, 309–315.
33. Castro, E. A.; Mun˜oz, P.; Santos, J. G. J Org Chem 1999,
64, 8298–8301.
27. Castro, E. A.; Gil, F. J. J Am Chem Soc 1977, 99, 7611–
7612.
28. Castro, E. A.; Iban˜ez, F.; Lagos, S.; Schick, M.; Santos,
J. G. J Org Chem 1992, 57, 2691–2694.
34. Hansch, C.; Leo, A.; Taft, R. W. Chem Rev 1991, 91,
165–195.
International Journal of Chemical Kinetics DOI 10.1002/kin