RESUMO

The pressure and temperature dependence of the thermal decomposition of 1-bromo-3-chloropropane has been theoretically investigated. The reaction takes place majorly through the elimination of HBr. Molecular properties of 1-bromo-3-chloropropane and transition states were derived from MN15/6-311++G(3df,3pd) and G4 quantum-chemical calculations. The resulting rate constants obtained from the unimolecular reaction rate theory for the high- and low-pressure limits of reaction BrCH2CH2CH2Cl → CH2CHCH2Cl + HBr at 400-1000 K were k∞ = 6.1 × 1013 exp(-57.2 kcal mol-1/RT) s-1 and k0 = [BrCH2CH2CH2Cl] 1.45 × 10-1 (T/1000 K)-7.9 exp(-55.9 kcal mol-1/RT) cm3 molecule-1 s-1. A value of -26.3 ± 1.0 kcal mol-1 for the standard enthalpy of formation of 1-bromo-3-chloropropane at 298 K was derived.

RESUMO

This work reports the experimental study of the ozonolysis of indene in the presence of SO2 and the reaction conditions leading to the formation of secondary aerosols. The reactions have been carried out in a Teflon chamber filled with synthetic air mixtures at atmospheric pressure and room temperature. As in the case of styrene, SO2 plays a key role in the oxidation of the Criegee intermediates and enhances the formation of particulate matter. Thus, for the ozonolysis of indene, nucleation was observed for reacted indene concentrations above (4.5 ± 0.8) × 1011 molecule cm-3 in the absence of SO2 while new particle formation was observed for concentrations one order of magnitude lower, (3 ± 1) × 1010 molecule cm-3, in the presence of SO2. Within the detection limit of the system, SO2 concentrations remained constant during the experiments. The formation of secondary aerosols in the smog chamber was inhibited by H2O and so the potential formation of secondary aerosols under atmospheric conditions depends on the concentration of SO2 and relative humidity. Computational calculations have been performed for the ozonolysis of both indene and styrene in the presence of SO2 and water to identify the reaction channels and species responsible for new particle formation. The release of SO3 and its subsequent conversion into H2SO4 from the reaction of the Criegee intermediate H2COO in the ozonolysis of styrene makes this aromatic have a high potential of aerosol formation in the atmosphere. On the other hand, quantitative conversion of SO2 into SO3 does not occur following the ozonolysis of indene.

RESUMO

Flusilazole is an organosilane fungicide used for treatments in agriculture and horticulture for control of diseases. The reaction kinetics and mechanism of flusilazole with sulfate and hydroxyl radicals were studied. The rate constant of the radicals with the fungicide were determined by laser flash photolysis of peroxodisulfate and hydrogen peroxide. The results were 2.0 × 109 s-1M-1 for the reaction of the fungicide with HO and 4.6 × 108 s-1 M-1 for the same reaction with SO4- radicals. The absorption spectra of organic intermediates detected by laser flash photolysis of S2O82- with flusilazole, were identified as α-aminoalkyl and siloxyl radicals and agree very well with those estimated employing the time-dependent density functional theory with explicit account for bulk solvent effects. In the continuous photolysis experiments, performed by photo-Fenton reaction of the fungicide, the main degradation products were: (bis(4-fluorophenyl)-hydroxy-methylsilane) and the non-toxic silicic acid, diethyl bis(trimethylsilyl) ester, in ten and twenty minutes of reaction, respectively.

Assuntos

Radical Hidroxila/química , Silanos/química , Sulfatos/química , Triazóis/química , Radicais Livres/química , Fungicidas Industriais/química , Peróxido de Hidrogênio/química , Cinética , Fotólise

RESUMO

A detailed kinetic study of the gas-phase thermal decomposition of 3-bromopropene over wide temperature and pressure ranges was performed. Quantum chemical calculations employing the density functional theory methods B3LYP, BMK, and M06-2X and the CBS-QB3 and G4 ab initio composite models provide the relevant part of the potential energy surfaces and the molecular properties of the species involved in the CH2═CH-CH2Br → CH2═C═CH2 + HBr (1) and CH2═CH-CH2Br → CH2═CH-CH2 + Br (2) reaction channels. Transition-state theory and unimolecular reaction rate theory calculations show that the simple bond fission reaction ( 2 ) is the predominant decomposition channel and that all reported experimental studies are very close to the high-pressure limit of this process. Over the 500-1400 K range a rate constant for the primary dissociation of k2,∞ = 4.8 × 10(14) exp(-55.0 kcal mol(-1)/RT) s(-1) is predicted at the G4 level. The calculated k1,∞ values lie between 50 to 260 times smaller. A value of 10.6 ± 1.5 kcal mol(-1) for the standard enthalpy of formation of 3-bromopropene at 298 K was estimated from G4 thermochemical calculations.

RESUMO

The results of a theoretical study of the molecular structure and conformational mobilities of the peroxynitrate CF(2)BrCFBrOONO(2) and its radical decomposition product CF(2)BrCFBrOO are reported in this paper. The most stable structures were calculated from ab initio G3(MP2)B3 and G4(MP2) methods and from density functional theory at the B3LYP/6-311+G(d) and B3LYP/6-311+G(3df) levels of theory. The equilibrium conformation of CF(2)BrCFBrOONO(2) indicates that the bromine atoms lie in position anti to each other and possess a COON dihedral angle of 114°. A quantum statistical analysis shows that about 40% of the internal rotors can freely rotate at room temperature. Our best values for the standard enthalpies of formation of CF(2)BrCFBrOONO(2) and CF(2)BrCFBrOO at 298 K obtained from isodesmic reactions at the G3(MP2)//B3LYP/6-311+G(3df) level of theory are -144.7 and -127.0 kcal mol(-1). From these values and the enthalpy of formation of the NO(2) radical, a CF(2)BrCFBrOO-NO(2) bond dissociation enthalpy of 26.0 ± 2 kcal mol(-1) was estimated.