306
LEIVA ET AL.
initial thermolysis. This means that the corresponding
activation enthalpies of the reaction (ꢀH , Table II)
ing the diradical generation, facilitating further C O
cleavages.
#
are almost compensated by the entropies of activation.
All these findings suggest that the ACDP thermoly-
sis conforms a genuine reaction series [6,18] where
the solvent affects the tetroxacyclohexane ring O O
bond rupture of their molecule. Therefore, these val-
ues are in agreement with a stepwise reaction mecha-
nism with homolytic rupture of one peroxidic bond of
ACDP molecule given a diradical, as it is observed in
other analogous ACDP reactions [6,8,9].
However a large variation in the enthalpies and en-
tropies of activation and the rate constant values can be
observedincomparingACDPthermolysisinMTBEre-
spect to other oxygenated solvents already investigated
CONCLUSIONS
1
2
3
. The thermolysis of ACDP in MTBE solution fol-
lows first-order kinetic law up to at least 60%
diperoxide conversion.
. Under the experimental conditions, the activation
parameters correspond to the unimolecular ther-
mal decomposition reaction of ACDP molecule.
. Analysis of the reaction products and the acti-
vation parameter values contributes to postulate
the mechanism for the thermolysis of the ACDP
in MTBE solution. The thermolyses would occur
through a common mechanism of decomposition
already advanced for the tetroxanes, which be-
gins with the homolytic rupture of the peroxydic
bond leading to the formation of an intermediate
diradical and further C O bond ruptures giving
acetone and oxygen as final products.
(methanol, THF, and 2-propanol), while small varia-
tion can be observed in the hydrocarbons (n-octane,
benzene). All of these findings suggest that the low po-
larity of MTBE determines the low rate found in the
ACDP thermolysis reaction.
Quantitative analysis of the acetone produced in the
thermolysis (Fig. 2) shows a molar yield practically
of 2 moles of carbonylic product for mole of ACDP
decomposed, which is not dependent on the temper-
ature and initial concentration of the tetroxane. Since
the concerted type decomposition could be discarded,
these results suggests that the formation of the prod-
ucts of the thermolysis can be interpreted in terms of an
initial O O homolysis to give the diradical [Eq. (1)],
which can rebuild the ACDP molecules undergoing
C O cleavages to give exclusively acetone plus oxy-
gen [Eq. (1)]. Thus, this suggests thatsolventmolecules
participate in the “reaction cage solvent” formed dur-
4
. ThekineticsofACDPthermolysisissignificantly
affected by the physicochemical characteristics
of the reaction media. Probably, the low polar-
ity of the MTBE solvent determinates the low
decomposition rates observed.
BIBLIOGRAPHY
1. Jorge, N. L. Theoretical conformationals studies, elec-
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4
59, 29.
3
4
. Jorge, N. L.; Peruchena, N.; Castro, E. A.; Cafferata, L.
F. R. J Mol Struct (Theochem) 1988, 433, 311.
. Cafferata, L. F. R.; Furlong, J. J. In Advances in Oxy-
genated Processes; Baumstark, A. L. (Ed.); JAI Press:
Greenwich, CT, 1995; Vol. 4, p. 81.
5
6
7
8
. Cafferata, L. F. R.; Eyler, G. N.; Mir ´ı fico, M. V. J Org
Chem 1984, 49, 2107.
. Cafferata, L. F. R.; Eyler, G. N.; Svartman, E. L.; Ca n˜ izo,
A. I.; Alvarez, E. E. J Org Chem 1991, 56, 411.
. Ca n˜ izo, A. I.; Cafferata, L. F. R. An Asoc Quim Ar-
gentina 1992, 80(4), 345.
. Leiva, L. C.; Castellanos, M. G.; Jorge, N. L.; Cafferata,
L. F. R.; G o´ mez Vara, M. E. Revista de la Sociedad
Qu ´ı mica de M e´ xico 1998, 42, 223.
Figure 2 Acetone molar yields (moles of acetone per mole
9. Leiva, L. C.; Cafferata, L. F. R.; G o´ mez Vara, M. E. An
Asoc Qu ´ı m Argentina 2000, 88(1/2), 9.
10. Reichardt, C. Solvent Effects in Organic Chemistry; Ver-
lag Chemie: New York, 1979.
of ACDP decomposed) of acetone diperoxide in MTBE solu-
◦
◦
◦
tion at different temperatures. 130 C (◦), 140 C (ꢀ), 150 C
◦
(
ꢁ), and 166 C (×).