KINETICS OF PHASE-TRANSFER FORMATION OF POTASSIUM CARBAZOLATE
75
As seen from data listed in Table 2, an increase in
the carbazole concentration in the solution by a factor
1
Vinit, mmol min
of 3 at a constant amount of KOH does not substan-
tially affect the initial rate of the process; this is
true for the state of the maximal catalysis efficiency
reached with the given catalyst ([18-C-6] = 7.5 mM).
Thus, as in the case of the noncatalyzed process,
under catalysis with crown ether the process rate is
limited by the transport of the reagent to the phase
boundary aqueous interphase organic phase; the reac-
tion proceeds not in the bulk of the organic phase but
at the phase boundary or in the vicinity of the phase
boundary. It is well known that aqueous interphase at
the surface of solid salts or alkalis ( -phase) efficient-
ly sorbs the phase-transfer catalyst from the organic
phase [3]. It is likely that the phase-transfer catalyst
dissolved in the -phase facilitates the reagent trans-
port in the bulk of this phase between the solid liquid
and liquid liquid phase boundaries. This mechanism
can easily explain the saturability of the catalytic ef-
fect of the phase-transfer catalyst.
C, mM
Fig. 1. Initial rate of formation of potassium carbazolate
V
as a function of concentration of 18-crown-6 C.
init
X, mmol
Since, as mentioned above, potassium carbazolate
is formed (and also hydrolyzed) at the liquid liquid
phase boundary, the process rate, if only in view of
mathematical formalism, should be described by mac-
rokinetic model (1). This suggestion was verified by
the mathematical simulation [1]. This procedure is
based on simultaneous solution of differential kinetic
equation (1) and algebraic equation corresponding to
equilibrium (2). The calculation was carried out by
numerical integration by the second-order Runge
Kutta procedure. As seen from Fig. 2, the dynamics of
accumulation of carbazolate during the experiment is
adequately described by this mathematical model with
t, min
Fig. 2. Calculated (curves) and experimental (points)
dynamics of accumulation of potassium carbazolate (X).
(t) Reaction time. 18-C-6 concentration (mM): (1) 3.0,
(2) 5.0, and (3) 7.5.
the toluene sample treated with water (spectropho-
tometrically, as described in [1]) and the amount of
potassium ions in the aqueous extract of this sample.
The content of potassium ions was determined using
a pH-673m device equipped with an EM-K-01 ion-
selective electrode. The potentiometric data were
processed using the calibration plots.
appropriate values of kinetic coefficients k, k , and K.
Experiments were repeated no less than three times.
The results of calculations given in this work are the
averages with their root-mean-square deviations.
2/3
The averages of k, k , and V
= k(m ) /w (from
init
b 0 0
3 4 similar runs) are listed in Table 1. It should be
noted that the numerical values of k and K = 0.02 are
almost the same as in the case of the noncatalyzed
process [1], which additionally suggests the identity
of the mechanisms of both processes.
The initial content of water in the reaction mixtures
was evaluated as the sum of the amounts of water
added with alkali ( 15%) and toluene ( 0.03%).
Table 2. Initial rates of formation of potassium carbazolate
Vinit at various concentrations of carbazole Cc*
EXPERIMENTAL
The experimental procedure differed from that
described in [1] only in the method of monitoring the
course of the reaction. Potassium carbazolate formed
in the catalyzed process occurs partially in the form of
the complex with crown ether, slowly crystallizing
from the filtered toluene solution. Therefore, the
amount of unchanged carbazole was determined as the
difference between the total content of carbazole in
Carbazole
amount, mmol
Cc,
mM
Vinit 102,
mmol min
Number
of runs
1
1.0
2.0
3.0
16.8
33.3
50.0
6.4 0.2
8.4 0.6
7.7 0.5
3
3
4
* Toluene volume 60 ml; KOH and H O amounts 1.50 and
2
1.69 mmol, respectively; [18-C-6] 7.5 mM; 110 C.
RUSSIAN JOURNAL OF APPLIED CHEMISTRY Vol. 74 No. 1 2001
Frolova
