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The thermal decomposition reaction of acetone cyclic triperoxide (3,3,6,6,9,9-hexamethyl-1,2,4,5,7,8-hexaoxacyclononane, ACTP) in the temperature range of 130.0-166.0 degrees C and an initial concentration of 0.021 M has been studied in toluene solution. The thermolysis follows first-order kinetic laws up to at least ca. 78% acetone triperoxide conversion. Under the experimental conditions, a radical-induced decomposition reaction as a competing mechanism may be dismissed, so the activation parameters correspond to the unimolecular thermal decomposition reaction of the ACTP molecule [delta H++ = 41.8 (+/- 1.6) kcal mol-1 and delta S++ = 18.5 (+/- 3.8) cal mol-1K-1]. Analysis of the reaction products are not enough to elucidate the real mechanism for the thermolysis of the acetone triperoxide in toluene solution.

Recebido em 5/1/01; aceito em 14/11/01 THERMAL DECOMPOSITION OF PINACOLONE DIPEROXIDE (3,6-ditertbutyl-3,6-dimethyl-1,2,4,5-tetraoxacyclohexane) IN 2-METHOXYETHANOL SOLUTION. The thermal decomposition reaction of pinacolone diperoxide (DPP; 0.02 mol kg -1 ) in 2-methoxyethanol solution studied in the temperature range of 110.0-150.0 °C, follows a first-order kinetic law up to at least 50% DPP conversion. The organic products observed were pinacolone, methane and tert-butane. A stepwise mechanism of decomposition was proposed where the first step is the homolytic unimolecular rupture of the O-O bond. The activation enthalpy and activation entropy for DPP in 2-methoxyethanol were calculated (DH # = 43.8 ± 1.0 kcal mol -1 and DS # = 31.9 ± 2.6 cal mol -1 K -1 ) and compared with those obtained in other solvents to evaluate the solvent effect.Keywords: cyclic peroxide; kinetic; solvent effect. INTRODUCCIONLos peróxidos orgánicos son compuestos que tienen gran importancia en numerosas reacciones de combustión e importantes aplicaciones industriales tales como iniciadores de polimerización, agentes de entrecruzamiento, blanqueadores, desinfectantes, etc.Los estudios cinéticos y mecanísticos correspondientes a la termólisis en solución de peróxidos orgánicos cíclicos y todas las comparaciones entre ellos que de allí surgen, han sido el objetivo inicial de este grupo de investigación. Sin embargo, en los últimos años ha resultado de gran interés la aplicación de este tipo de compuestos como iniciadores polifuncionales en los procesos de polimerización radicálica de estireno. Si bien el diperóxido de pinacolona (3,6-diterbutil-3,6-dimetil-1,2,4,5-tetraoxaciclohexano, DPP; Figura 1) fue utilizado hace varias décadas como iniciador en la obtención de poliestireno 1 , actualmente, a través de la introducción de algunas modificaciones en las condiciones de trabajo, se ha logrado su utilización a temperaturas relativamente altas y con mayores conversiones del monómero (ca. 99 %) 2 . Por lo tanto, el estudio del comportamiento de estos peróxidos en solución es complementario de los estudios relacionados con su aplicación en procesos industriales.Las técnicas de polimerización que se están desarrollando contemplan el agregado del peróxido cíclico polifuncional en estado sólido 2 o en solución 3 , dando en cada caso diferentes resultados. De todos los peróxidos orgánicos cíclicos estudiados hasta el momento, el DPP y el triperóxido cíclico de dietilcetona (TPDEC) son los que han manifestado el mejor comportamiento como iniciadores polifuncionales. Sin embargo, el efecto de solvente que presentan algunos peróxidos orgánicos en su descomposición térmica no siempre se transmite en el mismo sentido en relación a su función como iniciador cuando se lo agrega en solución, como se ha evidenciado para el TPDEC 3 .De acuerdo a los resultados obtenidos en estudios anteriores la constante de velocidad correspondiente a la descomposición térmica de DPP no es sensiblemente afectada cuando la reacción se lleva a cabo en benceno 4 , acetonitri...

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The kinetic data of the thermal decomposition reaction of acetone cyclic triperoxide (3,3,6,6,9,2,4,5,7, ACTP) are reported for a wide range of organic solvents (acetone, toluene, 2-propanol, 2-methoxyethanol, n-butylamine, diethylamine, triethylamine, and chlorobenzene) at 0.02 M initial concentration and in the temperature range of 135.0-172.0 8C. The thermolysis reaction follows pseudo firstorder kinetic laws up to at least ca. 70% ACTP conversion. The results indicate the importance of solvent polarity and specific solvent-peroxide interactions in governing the rates of the reactions. The activation enthalpy and entropy of the thermal decomposition reaction of this triperoxide in several organic solvents were correlated through ''isokinetic relationships'' to verify the existence of a genuine solvent effect on this reaction. Other cyclic organic di-and triperoxides and some cyclic trioxanes showed a similar behavior, in contrast to the pinacolone cyclic diperoxide (PDP), probably due to a relatively great steric hindrance of this molecule.

mL of dry ra-pentane-diethyl ether (3:2 by volume) containing 2.0 mmol of n-heptane as internal standard was cooled to -23 °C under a blanket of argon and 4.0 mmol of t-BuLi as a solution in pentane was added via syringe over a 5-min period. The reaction mixture was stirred for 30 min -23 °C, the cooling bath was removed, and 10 mL of water was cautiously added. After warming to room temperature, the organic phase was separated, dried (MgSOJ, and analyzed by GLC on column A at 35 °C. The results are presented in Scheme II. Methylcyclopentane and 1-hexene were identified by comparison of their retention times and mass spectra obtained by GC/MS with those of authentic samples.Acknowledgment. This investigation was supported by a grant from the Humphrey Chemical Company, North Haven, CT, and we are gratefiil for their continued interest in our work. We acknowledge with thanks the help of Marvin Thompson in obtaining numerous high-resolution mass spectra. WFB thanks Professor Jack Baldwin of the Dyson Perrins Laboratory, Oxford, for his kind hospitality during the period when this paper was written.