1
2892 J. Phys. Chem. A, Vol. 114, No. 49, 2010
Cervellati et al.
form, otherwise [I
life of I
2
] could not oscillate. It appears that the half-
MA is rather short. Another potential short-term
2
reservoir for iodine could be iodotartronic acid (ITTA). This
compound has not been detected directly in solutions, but
simulations of oxidation of tartaric acid by I
2
, where ITTA is
an intermediate, indicate a half-life for ITTA of approximately
3
1
00 s. ITTA is expected to decompose to mesoxalic acid.
+
-
Figure 6. Simulated vs experimental extent of reaction, [H
2
SO
4
]
0
)
)
H O + ICOH(COOH) f (HO) C(COOH) + H + I
2
2
2
2
0
.10 M, [K
2
IMA]
0
) 0.033 M, [Re]
0
) 0.039 M, and [acetic acid]
0
0
.020 M reference, 22 °C.
In regards to the IMA-based BR oscillator perturbed by
resorcinol, even though more experiments will be needed to
obtain a precise value of k , the obtained experimental estimate
cannot be too far off. This value is certainly
rate equations, kIN values are of several orders of magnitude
higher than kDEG values, so it was concluded that the scavenging
action by diphenols against HOO radicals is the main source
9
-
1
-1
•
of 0.043 M
s
•
much lower than that of the reaction C
6
H
4
(OH)
in the IMA-based oscillator. (In the MA-
based oscillator the calculated rate constant for this reaction
2
+ HOO f
of the inhibition of oscillations.
•
C
6
H
4
2 2
(OH)O + H O
The similarity between the inhibitory effects by resorcinol
on MA-based and IMA-based oscillators suggests that the above
interpretation can be also reasonable for the IMA-based oscil-
lator perturbed by resorcinol.
7
-1 -1 11
was 1.2 × 10 M s ). The facts indicate that the anti-
inhibitory effect of IMA is due to its iodination to I MA and
2
-
2
subsequent decomposition to form I
2
and I .
Lawson et al. claimed that the “anti-inhibitory” effect of IMA
In conclusion, degradation pathways for both IMA and I
2
MA
on the MA-based oscillator is due to the iodination of resorcinol
by IMA:
must be elucidated and included in the mechanism for BR
oscillators. For resorcinol-perturbed oscillators, that degradation
pathway will also affect the step DEG in the mechanistic model
of both MA-based and IMA-based oscillators, step IN remaining
the main step responsible for the inhibitory effects.
+
+
C H (OH) + IMA + (H ) f C H I(OH) + MA + (H )
6
4
2
6
3
2
(9)
References and Notes
We then decided to obtain an experimental estimate of the rate
constant for this reaction.
(
1) Briggs, T. S.; Rauscher, W. C. J. Chem. Educ. 1973, 50, 496.
+
Kinetics of the System IMA+Re+H . The kinetics of this
(2) Lawson, T.; F u¨ l o¨ p, J.; Wittmann, M.; Nosztizcius, Z.; Muntean,
1
N.; Szab o´ , G. J. Phys. Chem. A 2009, 113, 14095.
system was followed by H NMR spectrometry in a mixture of
(
(
3) Furrow, S. D.; Aurentz, D. J. J. Phys. Chem. A; 2010, 114, 2526.
4) Vanag, V. K. J. Chem. Biochem. Kinet. 1992, 2, 75.
initial formal composition [H
.033 M, [resorcinol] ) 0.039 M, and [acetic acid]
M at 22 °C.
2
SO
4
]
0
) 0.10 M, [K
2
IMA]
0
)
0
0
0
) 0.020
(5) Noyes, R. M.; Furrow, S. D. J. Am. Chem. Soc. 1982, 104, 45.
(
(
6) De Kepper, P.; Epstein, I. R. J. Am. Chem. Soc. 1982, 104, 49.
7) Vukojevic, V.; Sørensen, P. Graae; Hynne, F. J. Phys. Chem. 1996,
Acetic acid was used as an internal standard. At the times
shown in Figure 6, a spectrum was acquired and five peaks were
integrated: one for acetic acid, one for malonic acid product,
one for iodoresorcinol product (4-iodo-1,3dihydrobenzene), and
two for resorcinol. Each peak was normalized to the acetic acid
reference. The extent of reaction was calculated as a fraction
between 0 and 1, comparing the normalized peak integral with
the total change from beginning to end (0-322.2 min). Those
fractions were averaged, giving the values shown in Figure 6.
1
00, 17175.
(8) Furrow, S. D.; Cervellati, R.; Amadori, G. J. Phys. Chem. A. 2002,
106, 5841.
(
9) Furrow, S. D. J. Phys. Chem. 1995, 99, 11131.
(
10) Cervellati, R,; H o¨ ner, K.; Furrow, S. D.; Neddens, C.; Costa, S.
HelV. Chim. Acta 2001, 84, 3533.
(11) Cervellati, R,; H o¨ ner, K.; Furrow, S. D.; Mazzanti, F.; Costa, S.
HelV. Chim. Acta 2004, 87, 133.
(
12) Cervellati, R.; Crespi-Perellino, N.; Furrow, S. D.; Minghetti, A.
HelV. Chim. Acta 2000, 83, 3179.
(13) Conrad, M.; Reinbach, M. Berichte 1907, 35, 1816.
22
The COPASI simulation program was used to calculate one
(14) Mahon, M. J.; Smith, A. L. J. Phys. Chem. 1985, 89, 1215.
(15) Leopold, K. R.; Haim, A. Int. J. Chem. Kinet. 1977, 9, 83.
(16) Onel, L.; Bourceaneau, G.; Wittmann, M.; Noszticzius, Z.; Szab o´ ,
parameter, the constant in the rate law d[IMA]/dt ) k[IMA]-
[
0
resorcinol]. The fit is shown in Figure 6, giving a value of k )
G. J. Phys. Chem A. 2008, 1121, 11649.
.043 M- s .
1
-1
(17) Noyes, R. M.; Furrow, S. D. J. Am. Chem. Soc. 1982, 104, 45.
(
18) Turner, D. H.; Flynn, G. W.; Sutin, N.; Beitz, J. V. J. Am. Chem.
Soc. 1972, 94, 1554.
Conclusion
(
(
(
(
19) Schmitz, G. Int. J. Chem. Kin. 2004, 36, 480.
20) Schmitz, G. Phys. Chem. Chem. Phys. 2000, 2, 2129.
21) Furrow, S. D. J. Phys. Chem. 1987, 91, 1215.
22) Hoops, S.; Sahle, S.; Gauges, R.; Lee, C.; Pahle, J.; Simus, N.;
IMA-based BR oscillators have many features in common
with MA-based BR oscillators. One difference is the formation
of I
oscillators, I
MA remains unreacted. When the [MA]
than 2:1, IMA is the major product, and the system ends
oscillations in state (I). With IMA-based oscillators, I MA is
formed, but begins to decompose and return I immediately to
the solution. There must be some hold-up of iodine in some
2
MA immediately in the IMA oscillators. In MA-based
Singhal, M.; Xu, L.; Mendes, P.; Kummer, U. Bioinformatics 2006, 22,
067–74.
23) Sirimungkala, A.; F o¨ rsterling, H.-D.; Dlask, V.; Field, R. J. J. Phys.
3
2
MA is a minor product initially so long as some
(
-
0 3 0
/[ IO ] ratio is greater
Chem. 1999, 103, 1038.
(24) Eberlin, A. R.; Williams, D. L. H. J. Chem. Soc., Perkin Trans.
1
996, 2, 883.
25) Awtrey, A. D.; Connick, R. E. J. Am. Chem. Soc. 1951, 73, 1842.
2
(
2
JP108684D