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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.