Kinetic Study and Reaction Mechanism of the Gas-Phase Thermolysis Reaction of Methyl Derivatives of 1,2,4,5-Tetroxane

Tetroxane derivatives are interesting drugs for antileishmaniasis and antimalaric treatments. The gas-phase thermal decomposition of 3,6,-dimethyl-1,2,4,5-tetroxane (DMT) and 3,3,6,6,-tetramethyl-1,2,4,5-tetroxane (acetone diperoxide (ACDP)) was studied at 493-543 K by direct gas chromatography by means of a flow reactor. The reaction is produced in the injector chamber at different temperatures. The resulting kinetics Arrhenius equations were calculated for both tetroxanes. Including the parent compound of the series 1,2,4,5-tetroxane (formaldehyde diperoxide (FDP)), the activation energy and frequency factors decrease linearly with the number of methyl groups. The reaction mechanisms of ACDP and 3,6,6-trimethyl-1,2,4,5-tetroxane (TMT) decomposition have been studied by means of the DFT method with the BHANDHLYP functional. Our calculations confirm that the concerted mechanism should be discarded and that only the stepwise mechanism occurs. The critical points of the singlet and triplet state potential energy surfaces (S- and T-PES) of the thermolysis reaction of both compounds have been determined. The calculated activation energies of the different steps vary linearly with the number of methyl groups of the methyl-tetroxanes series. The mechanism for the S-PES leads to a diradical O···O open structure, which leads to a C···O dissociation in the second step and the production of the first acetaldehyde/acetone molecule. This last one yields a second C···O dissociation, producing O2 and another acetone/acetaldehyde molecule. The O2 molecule is in the singlet state. A quasi-parallel mechanism for the T-PES from the open diradical to products is also found. Most of the critical points of both PES are linear with the number of methyl groups. Reaction in the triplet state is much more exothermic than the singlet state mechanism. Transitions from the singlet ground state, S0 and low-lying singlet states S1-3, to the low-lying triplet excited states, T1-4, (chemical excitation) in the family of methyl tetroxanes are also studied at the CASSCF/CASPT2 level. Two possible mechanisms are possible here: (i) from S0 to T3 by strong spin orbit coupling (SOC) and subsequent fast internal conversion to the excited T1 state and (ii) from S0 to S2 from internal conversion and subsequent S2 to T1 by SOC. From these experimental and theoretical results, the additivity effect of the methyl groups in the thermolysis reaction of the methyl tetroxane derivatives is clearly highlighted. This information will have a great impact for controlling these processes in the laboratory and chemical industries.

Theoretical study of the gas-phase thermolysis reaction of 3,6-dimethyl-1,2,4,5-tetroxane. Methyl and axial-equatorial substitution effects

Organic peroxides are interesting compounds with a broad range of properties from antimalarial and antimicrobial activities to explosive character. In this work the gas-phase thermolysis reaction mechanism of the 3,6-dimethyl-1,2,4,5-tetroxane (DMT) is studied by DFT calculations, considering axial-axial, axial-equatorial, and equatorial-equatorial position isomers. The critical points of the singlet (S) and triplet (T) potential energy surfaces (PES) are calculated. Three mechanisms are considered: i) S-concerted, ii) S-stepwise, and iii) T-stepwise. The first intermediate of the reaction through S-stepwise-PES is a diradical open structure, o, yielding, as products, two molecules of acetaldehyde and one of O₂ in the S state. The S-stepwise-mechanism gives exothermic reaction energies (Er) in the three position isomers. The S-concerted mechanism yields very high activation energies (Ea) in comparison with those of the S-stepwise mechanism. In the T-stepwise mechanism, a triplet open structure (T-o) is first considered, yielding an Er 12 kcal mol^-1 more exothermic than that of the S-mechanisms. The S-o and T-o are similar in structure and energies; therefore, a crossing from the S- to T-PES is produced at the o intermediate as a consequence of a spin-orbit coupling. The highest Ea is the first step after o intermediate, and thus it is considered the rate limiting step. Therefore, the Er at the T-PES is more in agreement with the Er of the exothermic experimental diperoxide products. Ea, Er, and O···O distances are studied as a function of the number of methyl groups and the position isomerization.

Chemiluminescence in the reaction of 1,2,4,5-tetraoxanes with ferrous ions in the presence of xanthene dyes: fundamentals and perspectives of analytical applications

The reaction of biologically active bridged 1,2,4,5-tetraoxanes and diperoxide of trifluoroacetone with Fe²⁺ ions in the presence of xanthenes, methylene blue and methylene green is accompanied by bright chemiluminescence.

Bulk Polymerization of Styrene using Multifunctional Initiators in a Batch Reactor: A Comprehensive Mathematical Model

A detailed, comprehensive mathematical model for bulk polymerization of styrene using multifunctional initiators – both linear and cyclic – in a batch reactor was developed. The model is based on a kinetic mechanism that considers thermal initiation and chemical initiation by sequential decomposition of labile groups, propagation, transfer to monomer, termination by combination and re-initiation reactions due to undecomposed labile groups. The model predicts the evolution of global reaction variables (e.g, concentration of reagents, products, radical species and labile groups) as well as the evolution of the detailed complete polymer molecular weight distributions, with polymer species characterized by chain length and number of undecomposed labile groups. The mathematical model was adjusted and validated using experimental data for various peroxide-type multifunctional initiators: diethyl ketone triperoxide (DEKTP, cyclic trifunctional), pinacolone diperoxide (PDP, cyclic bifunctional) and 1,1-bis(tert-butylperoxy)cyclohexane (L331, linear bifunctional). The model very adequately predicts polymerization rates and complete molecular weight distributions. The model is used to theoretically evaluate the influence of initiator structure and functionality as well as reaction conditions.

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.