Adriana I. Cañizo

Kinetics of the Thermal Decomposition of Substituted Cyclic Organic Peroxides in Toluene Solution: Substituent Effects on the Reaction Rates and the Activation Parameters of the Unimolecular Reactions

Thermal decomposition reactions of substituted cyclic organic di- and triperoxides have been carried out in toluene solution in order to investigate substituent effects on homolytic scission of the O-O bond in those compounds. A comparative analysis of the reactivities at 145 °C and the activation parameters for unimolecular reactions of molecules of this type were interpreted in terms of substituent effects and ring size. An isokinetic relationship was established to validate the existence of a genuine substituent effect for the unimolecular homolysis reaction of the substances considered. Cyclic organic peroxides of very high reactivity and sterically hindered deviated from correlations. It appears to be possible to determine whether a peroxy group is part of a six or nine membered ring on the basis of the activation parameters values.

Descomposicion termica del diperoxido de pinacolona (3,6-diterbutil-3,6-dimetil-1,2,4,5-tetraoxaciclohexano) en solución de 2-metoxietanol

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-1K-1) and compared with those obtained in other solvents to evaluate the solvent effect.

Heterogeneous Photocatalytic Discoloration/Degradation of Rhodamine B with H2O2 and Spinel Copper Ferrite Magnetic Nanoparticles

The discoloration/degradation of the artificial dye Rhodamine B (RhB) was investigated using advanced oxidation technologies. Aqueous solutions of RhB containing spinel copper ferrites (CuFe2O4) as a heterogeneous catalyst were exposed to UV irradiation/hydrogen peroxide. Under these experimental conditions the discoloration/degradation of RhB is strongly promoted by copper ferrites, reaching 95 % discoloration of the dye in 10 min and 97 % degradation in 200 min. The influence of the catalyst amount, H2O2 concentration, light source, and UV light intensity were studied. Optimum concentrations of H2O2 and catalyst dosage were found for the RhB degradation reaction. The catalyst had high magnetic sensitivity under an external magnetic field, which allowed its magnetic separation from water avoiding secondary pollution processes, and its recycling. A markedly synergetic effect of spinel copper ferrite and UV light irradiation was observed for the RhB discoloration/degradation with H2O2 as a green oxidant.

Use of Cyclic Di- and Triperoxides as Initiators of Styrene Polymerization at High Temperature with a View to Their Use in Industrial Applications

In industry, the bulk free radical polymerization of styrene takes place with the aid of peroxide initiators such as benzoyl peroxide. In this work di- and trimeric cyclic peroxides were used as initiators of the styrene polymerization in order to increase the rate of polymerization and molecular weights simultaneously.

Preparation and Thermal Decomposition Reaction of p-Chloro Benzaldehyde Diperoxide in Tetrahydrofuran Solution

Preparation and thermal decomposition studies of the title molecule (3,6-di-p-chlorophenyl-1,2,4,5-tetraoxacyclohexane) were carried out in tetrahydrofuran solution in the 52–130°C temperature range. The overall reaction follows a first-order kinetic law up to at least 60% diperoxide conversion. The activation parameters (ΔH# = 15.1±0.7 kcal mol−1 and ΔS# = − 35.5±1.9 cal mol−1 K−1) for the unimolecular rupture of the O–O bond in the diperoxide molecule were obtained by measuring the undecomposed diperoxide at different reaction times by the HPLC technique. P-chlorobenzaldehyde, p-chlorobenzoic acid, and chlorobenzene were detected by GC as the major organic products of the reaction.

Efecto de solvente sobre la descomposición térmica de trans-3,6-dimetil-3,6-difenil-1,2,4,5-tetraoxaciclohexano en solución

The thermal decomposition reaction of trans-3,6-dimethyl-3,6-diphenyl-1,2,4,5-tetraoxacyclohexane (acetophenone cyclic diperoxide, DPAF), in different solvents (methanol, 1,4-dioxane, acetonitrile and 2-propanol/benzene mixtures) in the initial concentration and temperature ranges of (4.2-10.5) x 10-3 M and 140.0 to 185.0 oC, respectively, follows a pseudo first order kinetic law up to at least 70% DPAF conversion. An important solvent effect on the rate constant values, activation parameters (DH# and DS#) and reaction products obtained in different solvents is detected, showing that the reaction is accelerated in alcohols.

Thermal Decomposition of Diethylketone Cyclic Triperoxide in Polar Solvents

The thermolysis of diethylketone cyclic triperoxide (3,3,6,6,9,9-hexaethyl-1,2,4,5,7,8-hexaoxacyclononane, DEKTP) was studied in different polar solvents (ethanol, 2-propanol, 1-butanol, 2-butanol, 2-methyl-2-propanol, and acetonitrile). The rate constant values (kd) are higher for reactions performed in secondary alcohols probably because of the possibility to form a cyclic adduct with the participation of the hydrogen atom bonded to the secondary carbon. The kinetic parameters were correlated with the physicochemical properties of the selected solvents. The products of the DEKTP thermal decomposition in different polar solvents support a radical-based decomposition mechanism.

Mono, Di and Trifunctional Cyclic Organic Peroxides: The Effect of Substituents and Ring Size on their Thermolysis in 1,4-dioxan

The thermal decomposition reaction of cyclic organic peroxides was studied in 1,4-dioxan at initial concentrations between ~10–4 and 10–2 mol L–1 and at a temperature interval between 100 and 170°C, according to the thermal stability of each compound. The kinetic behaviour observed in all systems studied follows a pseudo first order kinetic law up to at least ~86 % of peroxide conversion. An important substituent effect is operative on the rate constant values and consequently on the activation parameters of the thermal decomposition reaction. The application of different treatments (compensation affect or a statistical treatment) on the kinetic data shows the existence of two sets of cyclic peroxides with comparable kinetic behaviour. Different peroxide–solvent interaction mechanisms can be considered within each series.

3,3,6,6,9,9-Hexaethyl-1,2,4,5,7,8-hexaoxacyclononane at 296 K.

The title molecule (diethyl ketone triperoxide, DEKTP), C(15)H(30)O(6), is a cyclic triperoxide closely related to triacetone triperoxide (TATP), one of the most unstable explosives known. However, the stability of DEKTP is ca 20-50 times greater than that of TATP. DEKTP crystallizes with two molecules in the asymmetric unit, with virtually identical geometry. The cyclononane core is stabilized in a twisted boat-chair conformation (approximate D(3) symmetry), very close to that previously described for TATP. The explanation for the safe thermal behaviour of DEKTP compared with TATP should thus not be sought in the molecular dimensions, but rather in the thermal decomposition kinetics.

Effect of Substituents on the O-O Bond Rupture of Different Organic Peroxides in Toluene Solution

The thermal decomposition reaction of cyclic organic peroxides was studied in toluene solution in a wide temperature range. The kinetic data show an important substituent effect on the unimolecular homolysis of the O-O bond of these molecules.