Cu(II) catalyzed reaction between phenyl hydrazine and toluidine blue - dual role of acid

Article abstract of DOI:10.1002/(SICI)1097-4601(1999)31:4<271::AID-KIN4>3.0.CO;2-V

The detailed kinetics of Cu(II) catalyzed reduction of toluidine blue (TB⁺) by phenyl hydrazine (Pz) in aqueous solution is studied. Toluidine white (TBH) and the diazonium ions are the main products of the reaction. The diazonium ion further decomposes to phenol (PhOH) and nitrogen. At low concentrations of acid, H⁺ ion autocatalyzes the uncatalyzed reaction and hampers the Cu(II) catalyzed reaction. At high concentrations, H⁺ hinders both the uncatalyzed and Cu(II) catalyzed reactions. Cu(II) catalyzed had stoichiometry similar to the uncatalyzed reaction, Pz+2 TB⁺+H₂O = PhOH+2 TBH+2 H⁺+N₂. Cu(II) catalyzed reaction occurs possibly through ternary complex formation between the unprotonated toluidine blue and phenyl hydrazine and catalyst. The rate coefficient for the Cu(II) catalyzed reaction is 2.1×10⁴ M^-2 s^-1. A detailed 13-step mechanistic scheme for the Cu(II) catalyzed reaction is proposed, which is supported by simulations.

Full text of DOI:10.1002/(SICI)1097-4601(1999)31:4<271::AID-KIN4>3.0.CO;2-V

Cu(II) Catalyzed Reaction
between Phenyl Hydrazine
and Toluidine Blue—Dual
Role of Acid
S. B. JONNALAGADDA, K. NATTAR
Department of Chemistry, University of Durban-Westville, P Bag X54001, Durban 4000, South Africa
Received 11 May 1998; accepted 10 November 1998
ABSTRACT: The detailed kinetics of Cu(II) catalyzed reduction of toluidine blue (TBϩ) by phenyl
hydrazine (Pz) in aqueous solution is studied. Toluidine white (TBH) and the diazonium ions
are the main products of the reaction. The diazonium ion further decomposes to phenol
(PhOH) and nitrogen. At low concentrations of acid, Hϩ ion autocatalyzes the uncatalyzed
reaction and hampers the Cu(II) catalyzed reaction. At high concentrations, Hϩ hinders both
the uncatalyzed and Cu(II) catalyzed reactions. Cu(II) catalyzed had stoichiometry similar to
the uncatalyzed reaction, Pz ϩ 2 TBϩ ϩ H2O ϭ PhOH ϩ 2 TBH ϩ 2 Hϩ ϩ N2. Cu(II) catalyzed
reaction occurs possibly through ternary complex formation between the unprotonated tolu-
idine blue and phenyl hydrazine and catalyst. The rate coefficient for the Cu(II) catalyzed
2
reaction is 2.1 ϫ 104 MϪ sϪ1. A detailed 13-step mechanistic scheme for the Cu(II) catalyzed
reaction is proposed, which is supported by simulations. ᭧ 1999 John Wiley & Sons, Inc., Int J
Chem Kinet 31: 271–276, 1999
INTRODUCTION
tion conditions motivated the further studies. Here, we
report the kinetics and mechanism of the Cu(II) cata-
lyzed reaction between TBϩ and Pz.
The phenothiazine class dyes have been studied ex-
haustively because of their useful insecticidal and an-
thelminite properties [1]. The uncatalyzed and Mo(VI)
catalyzed reactions between toluidine blue and Sn(II)
in acid were known to exhibit complex kinetics with
fractional orders with respect to the reactants [2]. In
an earlier communication, we reported the kinetic
study of the autocatalyzed reaction between toluidine
blue (TBϩ) and phenyl hydrazine (Pz) [3]. Based on
its selective catalytic efficiency, the suitability of the
Cu(II) catalyzed reaction as an indicator reaction for
kinetic-catalytic analysis of Cu(II) was explored. Due
to the reaction’s sensitivity to [Hϩ], it was found un-
suitable for the purpose. The autocatalytic and retard-
ing effects displayed by acid under varied concentra-
EXPERIMENTAL
Reagents
All the reagents used were of analytical reagent grade,
and double distilled water was used in all preparations.
A zinc salt of toluidine blue was used in all the studies.
A fresh solution of 0.01 M phenyl hydrazine was pre-
pared daily.
Kinetic Measurements
The reagents were kept in a thermostatted water bath
at 25ЊC. The total volume of the reaction mixture was
kept at 10 ml. Reagents were mixed in the order to-
Correspondence to: S. B. Jonnalagadda
᭧ 1999 John Wiley & Sons, Inc.
CCC 0538-8066/99/040271-06

272
JONNALAGADDA AND NATTAR
luidine blue, water, and other reagents. The reaction
was initiated by the addition of phenyl hydrazine and
the homogeneous reaction mixture was then trans-
ferred to the cell. Reaction dynamics were monitored
at 630 nm using the Cary UV-Visible spectrophotom-
eter thermostatted to (25.0 Ϯ 0.1)ЊC. For all the ki-
netic runs, the instrument was set to monitor the re-
action 20 s after initiation of the reaction.
Reaction Dynamics
In the earlier communication, the first-order depen-
dence of the reaction rate on both TBϩ and Pz, and the
autocatalytic role of Hϩ ion, was established [3]. In
further investigations, it was observed that depending
on its relative concentration to Pz, acid acted either as
an autocatalyst or an inhibitor for the uncatalyzed re-
action. Figure 1 illustrates the dual role played by acid
in the uncatalyzed reaction depending on its concen-
tration conditions. Curve a shows a typical kinetic
curve in absence of added acid, featuring the initial
slow reaction, followed by an increasing rate, due to
the autocatalytic effect of Hϩ ion. Curve b shows a
swift drop in the [TBϩ] confirming the catalyzing ef-
fect of Hϩ at 0.002 M. Curves c and d demonstrate
the inhibition by acid, at 0.003 and 0.04 M concentra-
tions, respectively.
The effect of variation of [Cu(II)] on the reaction
rate was studied, with [TBϩ] (5.5 ϫ 10Ϫ5 M), excess
of Pz (9.0 ϫ 10Ϫ3 M), and low concentrations of
Cu(II). Figure 2 shows the typical kinetic curves due
to variation of the catalyst concentration. The curves
e, f, and g show that at low [Cu], the reaction starts
slowly and the rate of reaction increases with time.
With increased catalyst concentration (curves h, i, and
j), the curves change from the autocatalyzed to the
exponential decay characteristics. In the preliminary
studies, both the initial rates (from the absorbance ver-
sus time data) and the rate constants (log absorbance
Determination of Formation Constants
The alkalimetric titrations were carried out at (25 Ϯ
0.1)ЊC, using a pH/ISE meter (model EC40, Hach
company, USA), with data acquisition facility. Titra-
tions in duplicate were performed for each system in
the ranges: Sodium chloride (0.02–0.04 M), phenyl
hydrazine (0.01–0.02 M), cupric chloride (0.004 M),
and sodium hydroxide (0.2 M). The protonation con-
stants of toluidine blue and phenyl hydrazine and their
stability constants with copper were calculated from
the alkalimetric data using a nonlinear least-square’s
program SUPERQUAD [4].
RESULTS AND DISCUSSION
Product Identification and Stoichiometry
Toluidine blue (500 mg in 100 ml water), phenyl hy-
drazine (5.0 g in 10 ml alcohol), and 0.01 M HCl (10
ml) were mixed and diluted to 200 ml with water.
After approximately 24 h, the reaction mixture was
extracted in diethyl ether. The ether extract was sub-
sequently dried and the products were analyzed. Thin-
layer chromatography and infrared spectroscopy were
used to identify the products. A comparison of the in-
frared spectrum of the product with standard samples
showed the presence of phenol (PhOH). A minor prod-
uct of the reaction was a green solid, thus confirming
the presumption of diazonium ion formation and de-
composition to phenol in acidic solutions. Toluidine
blue was reduced to toluidine white (TBH), a colorless
compound [2]. The diazonium ion has been reported
as the product of oxidation phenyl hydrazines with
lead tetraacetate, chlorine, bromine, and by acidic bro-
mate [5,6]. Based on the stoichiometric ratios and the
products identified, the reaction in the presence of the
copper ion is the same as the uncatalyzed reaction [3].
Figure 1 Effect of acid on the uncatalyzed reaction
Pz ϩ 2 TBϩ ϩ H2O ϭ PhOH
ϩ 2 TBH ϩ 2 Hϩ ϩ N2
ϩ
Ϫ
Ϫ
ϩ
[TB ] ϭ 5.5 ϫ 10 5 M, [Pz] ϭ 3.0 ϫ 10 2 M. [H ]/M ϭ
Curve a, Uncatalyzed; b, 0.002; c, 0.003; and d, 0.04.

REACTION BETWEEN PHENYL HYDRAZINE AND TOLUIDINE BLUE
273
Table I Pseudo First-Order Rate Coefficients (kЈ) for
Cu(II) Catalyzed Reaction between Toluidine Blue and
Phenyl Hydrazine
[TBϩ] ϭ 5.5 ϫ 10Ϫ5 M and [Pz] ϭ 9.0 ϫ 10Ϫ3 M
Ϫ6
Ϫ
Ϫ1
[Cu]/10
M
kЈ/10 3 s
*
0.5
0.6
0.7
1.0
2.0
3.0
5.0
7.0
10.0
0.23
0.25
0.27
0.35
0.53
0.76
1.14
1.57
2.19
* Mean of duplicate experiments with less than 5% deviation.
talyzed reaction. For typical mixtures, initial pH val-
ues for uncatalyzed and Cu catalyzed reactions were
7.527 and 7.561, respectively. By the completion of
the reaction, the values decreased to 7.379 and 7.433,
respectively. The marginal change in the pH of the
reactions points towards the formation Hϩ ions and
swift protonation of organic moieties in the system.
To explain the dual role of acid in the reaction, the
equilibrium chemistry of toluidine blue and phenyl hy-
drazine was further investigated. The protonation con-
stants of Pz and TBϩ, their stability constants with
Cu(II), and stability of ternary complex of TBϩ,
Figure 2 Toluidine blue–phenyl hydrazine reaction—
ϩ
Ϫ
Variation of [Cu(II)]. [TB ] ϭ 5.5 ϫ 10 5 M and [Pz] ϭ
Ϫ
Ϫ7
9.0 ϫ 10 3 M; Cu(II)/10 M ϭ Curve e, 2.0; f, 4.0; g, 6.0;
h, 10.0; i, 30.0; and j, 50.0.
versus time data) were investigated. Table I summa-
rizes the pseudo first-order rate coefficients, kЈ for dif-
ferent [Cu(II)]. A plot of kЈ versus [Cu(II)] gave a
linear curve with gradient 206 Ϯ 2 (Corr. Coeff.
1
0.988) and an intercept of (1.29 Ϯ 0.15) ϫ 10Ϫ4 sϪ .
The ratio of the intercept to [Pz] was in agreement with
the experimentally determined second-order rate con-
stant for the uncatalyzed reaction [3]. Further, the
mean value of the gradient to the [Pz] gave the rate
coefficient for the Cu(II) catalyzed reaction as
2
1
(2.1 Ϯ 0.1) ϫ 104 MϪ sϪ . Considering that acid ex-
hibits both autocatalytic and inhibiting effects on the
uncatalyzed reaction, the influence of Hϩ on the cop-
per catalyzed reaction was investigated.
In Figure 3, curves k, l, m, and n illustrate the ham-
pering effect of added acid. With a raise in [Hϩ] to
4.0 ϫ 10Ϫ3 M (curve j) the reaction slowed down sig-
nificantly. To further establish the role of acid, the
dynamics of Cu(II) catalyzed reactions were studied
with TBϩ (5.5 ϫ 10Ϫ5 M) and higher Pz (3.0 ϫ
10Ϫ2 M). Figure 4 compares the uncatalyzed (curve a)
and Cu catalyzed (curve o) kinetic runs. Curves p and
q demonstrate the effect of added acid on the Cu cat-
alyzed reaction. This confirms that Hϩ ions at all con-
centrations interfere and hinder the copper catalyzed
pathway. Although added acid hampers the Cu cata-
lyzed reaction, at high [Pz] it is interesting to note that
the reaction rate is still faster than that for the unca-
Figure 3 Effect of acid on the Cu(II) catalyzed reaction.
ϩ
Ϫ
Ϫ
[TB ] ϭ 5.5 ϫ 10 5 M, [Pz] ϭ 9.0 ϫ 10 3 M, and Cu(II)
Ϫ
ϩ
ϭ 5.0 ϫ 10 7 M. [H ]/M ϭ Curve k, 0.001; l, 0.002; m,
0.003; and n, 0.004.

274
JONNALAGADDA AND NATTAR
Table II Protonation and Stability Constants of
Toluidine Blue, Phenyl Hydrazine, and Their Complexes
with Copper
T ϭ 25ЊC; Computer program ϭ SUPERQUAD
Number of
System
log K
points
ϩ
TB *
Pz
7.20 Ϯ 0.01
5.18 Ϯ 0.03
7.17 Ϯ 0.01
4.85 Ϯ 0.07
13.02 Ϯ 0.03
89
75
94
90
104
ϩ
TB 9Cu(II)*
Pz9Cu(II)
ϩ
TB 9Cu(II)9Pz
* (Ref. 7)
involving the gain of two electrons [8]. The present
experimental results suggest that in the rate limiting
step, toluidine blue is also involved in a two-electron
reduction step, as one-electron step for toluidine blue
would have resulted in fractional order [4,9–11]. Con-
sistent with the reaction orders and products, the fol-
lowing mechanistic steps may be proposed for the re-
action sequence in presence of copper cations. The
proposed mechanism involves the oxidation of phenyl
hydrazine to its corresponding imide and to diazonium
ion as the reaction intermediate species and the for-
mation of toluidine white (TBH) and phenol as the
major products.
Figure 4 Effect of acid on the Cu(II) catalyzed reaction at
ϩ
Ϫ
Ϫ
high [Pz]. [TB ] ϭ 5.5 ϫ 10 5 M, [Pz] ϭ 3.0 ϫ 10 2 M,
Ϫ
Cu(II) ϭ 5.0 ϫ 10 6 M. Curve a, Uncatalyzed; o, Cu only
ϩ
ϩ
and no acid; p, Cu plus [H ] 0.002 M; q, Cu plus [H ] 0.04
M.
Cu(II), and Pz [4,7] were calculated from the alkali-
metric titration data (Table II). Based on the magni-
tudes of protonation and stability constants, dual be-
havior exhibited by acid can be explained. In absence
of the catalyst, the observed autocatalytic effect of Hϩ
ϩ
implies that protonated toluidine blue (TBH2 ) reacts
Mechanistic Scheme
faster than TBϩ with Pz [2,3]. Autocatalytic effect of
acid at low concentrations is explainable in terms of
favored protonation of TBϩ over Pz. Protonated tolu-
ϩ
1. TBϩ ϩ Pz : TBH2 ϩ I1
2
2. TBϩ ϩ Hϩ L TBHϩ
idine blue (TBH2 ) undergoes reduction faster, while
3. Pz ϩ Hϩ L PzHϩ
ϩ
ϩ
the protonated phenyl hydrazine (PzHϩ) is oxidized
slowly. With excess [Pz] as in the present case and at
low [Hϩ], the TBH2ϩ to Pz reaction will dominate over
4. TBH ϩ Hϩ L TBH2
5. TBHϩ ϩ Pz : TBH ϩ I1 ϩ 2 Hϩ
2
6. PzHϩ ϩ TBHϩ2 L TBH2 ϩ I1 ϩ 2 Hϩ
ϩ
ϩ
2
ϩ
ϩ
the slower TBH2 to PzHϩ reaction, hence the auto-
7. TBHϩ ϩ I1 L TBH2 ϩ I2
catalytic effect of Hϩ is observed. At high [Hϩ], due
to the increased [PzHϩ], the slow reaction becomes
increasingly significant and the overall reaction is
hampered. In the Cu(II) catalyzed reaction, at very low
[Hϩ], the {TBϩ 9Cu(II)} complex accelerates the ox-
idation of Pz, by the formation of the ternary complex,
{TBϩ 9Cu(II)9Pz}. At higher [Hϩ], considering the
higher protonation constants of TBϩ Pz relative to
their stability constants with Cu(II), TBϩ and Pz get
readily protonated. These phenomena interfere in the
formation of ternary complex between TBϩ, Cu(II),
and Pz, resulting in lower catalytic efficiency by
Cu(II).
8. TBϩ ϩ Cu(II) L [TBϩ Ϫ Cu(II)]
9. [TBϩ 9Cu(II)] ϩ Pz L [TBϩ 9Cu(II)9Pz]
10. [TBϩ 9Cu(II)9Pz] : TBH2 ϩ I1 ϩ
ϩ
Cu(II)
11. [TBϩ 9Cu(II)] ϩ PzHϩ L [TBϩ
9Cu(II)9PzHϩ]
ϩ
12. [TBϩ 9Cu(II)9PzHϩ] : TBH2 ϩ I1 ϩ
Hϩ ϩ Cu(II)
ϩ
13. TBH2 ϩ Cu(II) L [TBH2ϩ 9Cu(II)]
14. [TBH2ϩ 9Cu(II)] ϩ Pz L [TBH2
ϩ
9Cu(II)9Pz]
ϩ
15. [TBH2ϩ 9Cu(II)9Pz] : TBH2 ϩ I1 ϩ Hϩ
ϩ Cu(II)
ϩ
The reduction of toluidine blue to leuco-toluidine
blue (toluidine white, TBH) is a reversible reaction
16. [TBH2ϩ 9Cu(II)] ϩ PzHϩ L [TBH2
9Cu(II)9PzHϩ]

REACTION BETWEEN PHENYL HYDRAZINE AND TOLUIDINE BLUE
275
ϩ
17. [TBH2ϩ 9Cu(II)9PzHϩ] : TBH2 ϩ I1 ϩ
solves autonomous ordinary differential equation sys-
tems, was implemented [12]. Based on the responses
using the 24-step mechanism and after assessing the
significance of each step, the 24-step scheme with 40
parameters was simplified and reduced to a 13-step
scheme with 18 parameters. Basic features of the re-
action mechanism were maintained. The two sets of
two steps involving the formation of ternary complex
and their decompositions were reduced to two single
steps. All reactions involving the reaction of toluidine
blue copper complexes with protonated Pz (PzHϩ)
were excluded. The two steps involving diazonium ion
giving final products were combined to one. Table III
summarizes the simplified reaction scheme and the
rate parameters used for the simulations.
2 Hϩ ϩ Cu(II)
18. Pz ϩ Cu(II) L [Pz9Cu(II)]
19. [Pz9Cu(II)] ϩ TBϩ L [TBϩ 9Cu(II)9Pz]
ϩ
20. TBϩ ϩ I1 : TBH ϩ I2
21. PzHϩ ϩ TBϩ L TBH2 ϩ I1 ϩ Hϩ
ϩ
22. I1 ϩ Hϩ L I1Hϩ
ϩ
23. I2 ϩ Pz : Azo ϩ Hϩ
ϩ
24. I2 ϩ H2O : PhOH ϩ N2 ϩ Hϩ
ϩ
I1 ϭ imide, I2 ϭ diazonium ion, and Azo ϭ azo
compound.
RATE LAW
For the three kinetically controlled steps, uncata-
lyzed (k1), Hϩ ion catalyzed (k5) [3], and Cu(II) cata-
lyzed (k10) reactions, the experimental rate constants
were used. For the equations 2, 3, and 9, experimen-
tally determined protonation and stability constants
were used as the ratios for the forward to reverse rate
constants (Table II). For these reactions, the ratios
were kept identical to their protonation or stability
constants, and the magnitudes of rate coefficients were
then estimated. Simulations were very sensitive to the
values of the experimentally determined parameters,
k1, k5, and k10. The values of k7 and k8 were kept larger
than k5 and k10. Other rate constants and other esti-
mated coefficients were adjusted until the theoretical
curves matched with the experimental curves. With a
fixed set of experimental and estimated rate coeffi-
cients, simulations were repeated for varied concen-
trations Cu(II) of reactants. Each simulated curve rep-
resents toluidine blue as the sum of [TBϩ] and
Ϫd[TB]/dt ϭ Uncatalyzed reaction rate
ϩ Acid catalyzed rate ϩ Cu(II) catalyzed rate
Ϫd[TB]/dt ϭ k1[TBϩ][Pz] ϩ k5[TBϩ]
[Hϩ][Pz] ϩ k10[TBϩ][Pz][Cu2 ]
ϩ
Ϫd[TB]/dt ϭ {k1[Pz] ϩ k10[Pz][Cu2 ]
ϩ
ϩ k5[Hϩ][Pz]}[TBϩ]
where k1, k5, and k10, are respectively the rate coeffi-
cients for the uncatalyzed, Hϩ catalyzed, and Cu(II)
catalyzed reactions. Under excess [Pz] conditions, re-
action initially exhibits pseudo first-order behavior
with respect to toluidine blue.
SIMULATIONS
Computer simulations using the proposed mechanistic
scheme were carried out. The semi-implicate Runge-
Kutta method in PASCAL language (TURBO PAS-
CAL 7.0 version) devised by Kaps and Rentrop, which
ϩ
[TBH2 ], as protonated toluidine blue has no phase
shift. Figure 5 shows the simulated curves (e؅, h؅, and
i؅) for the variation of Cu(II) superimposed on the cor-
Table III Simulations: Rate Equations and Rate Coefficients
ϩ
1. TB ϩ Pz : TBH2ϩ ϩ I1
k1 ϭ 1.4e Ϫ 2;
ϩ
ϩ2
2. TB ϩ Hϩ L TBH
;
k2 ϭ 9.6; kϪ ϭ 6e Ϫ 7
2
3. Pz ϩ Hϩ L PzH ;
k3 ϭ 4.8e1; kϪ ϭ 4e Ϫ 4;
ϩ
3
4. TBH ϩ Hϩ L TBH2
;
k4 ϭ 1.5e Ϫ 3;
ϩ
kϪ ϭ 1e Ϫ 8;
4
ϩ
2
ϩ
ϩ
5. TBH ϩ Pz : TBH2 ϩ I1 ϩ H ;
k5 ϭ 2e2;
k6 ϭ 1e Ϫ 2;
k7 ϭ 2e4;
k8 ϭ 1e5;
ϩ
2
ϩ
ϩ
6. TBH ϩ PzH : TBH2ϩ ϩ I1 ϩ 2 H ;
ϩ
2
ϩ
7. TBH ϩ I1 : TBH2ϩ ϩ I2
;
ϩ
ϩ
8. I2 : Products ϩ H ;
ϩ
ϩ
9. TB ϩ Cu(II) L [TB 9Cu(II)];
k9 ϭ 1.3e4; kϪ ϭ 1e Ϫ 3;
9
ϩ
10. [TB 9Cu(II)] ϩ Pz : TBH2ϩ ϩ I1 ϩ Cu(II);
k10 ϭ 2.1e4;
k11 ϭ 2.1e91; k11 ϭ 1e1;
k12 ϭ 20;
ϩ
11. TBH2 ϩ Cu(II) L [TBH2ϩ 9Cu(II)];
12. [TBH2ϩ 9Cu(II)] ϩ Pz : TBH2ϩ ϩ I1 ϩ Cu(II) ϩ H ;
ϩ
13. [TBH2ϩ 9Cu(II)] ϩ PzHϩ : TBH2ϩ ϩ I1 ϩ Cu(II) ϩ 2 H ;
k13 ϭ 1e Ϫ 1;
ϩ

276
JONNALAGADDA AND NATTAR
results with [TBϩ] ϭ 5.5 ϫ 10Ϫ5 M and [Pz] ϭ
3.0 ϫ 10Ϫ2 M. Curves d؅, o؅, and q؅ were produced
under identical concentration conditions to the respec-
tive experimental curves, d, o, and q in Figures 1 and
4. Curve d؅ illustrates the effect of the addition of Hϩ
(0.04 M). Curve o؅ shows the effect of the addition of
Cu(II) (5 ϫ 10Ϫ6 M). Curve q؅ indicates the effect of
the addition of both Cu(II) and acid. The computations
are based on the fact that the proposed mechanism
could generate the catalytic effect of Cu(II), the au-
tocatalytic effect of Hϩ at low concentrations on the
uncatalyzed reaction, and the retarding effect of acid
on the Cu catalyzed reaction. These simulations also
demonstrate the retarding effect of acid on the unca-
talyzed reaction at high [Hϩ] ϭ 0.10 M (curve r؅).
Consistency in the characteristics of the experimental
and simulated curves for varied concentrations of the
reactants, catalyst and acid, support the proposed
mechanism as a plausible scheme for the reaction be-
tween toluidine blue and phenyl hydrazine.
Figure 5 Simulated curves. For curves e, h, and i—Con-
ditions are same as in Figure 2. Curves e؅, h؅, and i؅ are the
respective simulated curves by varying [Cu(II)].
The authors thank the University of Durban-Westville and
the Foundation for Research Development, South Africa for
their financial assistance. The authors also thank Dr. N. R.
Gollapalli for his help in estimating the protonation and sta-
bility coefficients.
responding experimental curves (e, h, and i). A perusal
of the curves show that the computed curves are in
good agreement with the experimental runs. Further,
the effect of acid on the simulations in the presence
and absence of the copper ion was investigated under
different reactant conditions. Figure 6 illustrates the
BIBLIOGRAPHY
1. Elderfield, R. C. Heterocyclic Compounds; John Wiley
& Sons: New York, 1957; Vol. 6.
2. Jonnalagadda, S. B.; Dumba, M; Fresenius J. Anal
Chem 1993, 345, 673–678.
3. Jonnalagadda, S. B.; Nattar, K. Int J Chem Kinet 1999,
31, 83–88.
4. Gans, P.; Sabartini, A.; Vacca, A. Inorg Chim Acta
1976, 18, 237.
5. Coffey, S., Ed. Rodd’s Chemistry of Carbon com-
pounds, 2nd ed.; Elsevier: Amsterdam, 1973; Vol. III,
pp 224–225.
6. Jonnalagadda, S. B.; Muthakia, G. K. J Chem Soc Per-
kin Trans II 1987, 1539–1541.
7. Jonnalagadda, S. B.; Gollapalli, N. R. Int J Chem Kinet
1998, (communicated).
8. Mahadevan, J.; Guha, S. N.; Kishore, K.; Murthy, P. N.
Proc Ind Acad Sci 1987, 101, 43–46.
9. Resch, P.; Field, R. J.; Schneider, F. W.; Burger, M. J
Phys Chem 1989, 93, 8181–8187.
10. Jonnalagadda, S. B.; Tshabalala, D. Int J Chem Kinet
1992, 24, 999–1007.
11. Jonnalagadda, S. B.; Dumba, M. Int J Chem Kinet 1993,
25, 745–753.
Figure 6 Simulated curves. Curves d؅, o؅, and q؅ and are
simulated curves under identical conditions as experimental
curves d, o, and q in Figure 4. Curve r؅: Simulated curve
under excess acid (0.01 M) with no Cu(II).
12. Kaps, P.; Rentrop, P. Numer Math 1979, 23, 25–33.