Formation of secondary fullerene ozonides in the ozonolysis of C60 solutions and chemiluminescence upon their hydrolysis

The formation of secondary fullerene ozonides (SFOs) in the ozonolysis of C₆₀ solutions in CCl₄ has reliably been determined for the first time; SFOs are accumulated during the whole ozonolysis time as a suspension in CCl₄. Hydrolysis of the SFOs results in chemiluminescence (CL) (I _max = 2.65·10⁸ photon s⁻¹ mL⁻¹), whose spectra contain maxima at 558, 608, and 685 nm. The most probable CL emitters are excited fullerene polyketones. Hydrogen peroxide was identified as a stable hydrolysis product of the SFOs by the color reaction with diphenylcarbazide and CL arisen upon the addition of an aqueous solution of FeSO₄·9H₂O to the hydrolyzate of the SFO. Chemiluminescence upon hydrolysis is a selective test for SFOs and allows one to find them in a complex mixture of the ozonolysis products of C₆₀. The rate constant and activation energy of SFO hydrolysis were determined from the kinetic measurements of CL. For SFO hydrolysis several probable reactions were proposed, including the formation of the CL emitters, and their heat effects were estimated using the PM3/RHF and AM1/RHF semiempirical methods for one-and two-cage model structures of SFOs. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 8, pp. 1322–1329, August, 2006.     

Mechanisms for the formation of secondary organic aerosol components from the gas-phase ozonolysis of alpha-pinene

Gas-phase ozonolysis of alpha-pinene was studied in static chamber experiments under 'OH-free' conditions. A range of multifunctional products-in particular low-volatility carboxylic acids-were identified in the condensed phase using gas chromatography coupled to mass spectrometry after derivatisation. The dependence of product yields on reaction conditions (humidity, choice of OH radical scavengers, added Criegee intermediate scavengers, NO(2)etc.) was investigated to probe the mechanisms of formation of these products; additional information was obtained by studying the ozonolysis of an enal and an enone derived from alpha-pinene. On the basis of experimental findings, previously suggested mechanisms were evaluated and detailed gas-phase mechanisms were developed to explain the observed product formation. Atmospheric implications of this work are discussed.     

Pressure dependent mechanistic branching in the formation pathways of secondary organic aerosol from cyclic-alkene gas-phase ozonolysis

The gas-phase ozonolysis of cyclic-alkenes (1-methyl-cyclohexene, methylene-cyclohexane, α-pinene, β-pinene) is studied with respect to the pressure dependent formation of secondary organic aerosol (SOA). We find that SOA formation is substantially suppressed at lower pressures for all alkenes under study. The suppression coincides with the formation of ketene (α-pinene, 1-methyl-cyclohexene), ethene (1-methyl-cyclohexene) and the increased formation of CO (all alkenes) at lower reaction pressures. The formation of these products is independent of the presence of an OH scavenger and explained by an increased chemical activation of intermediate species in the hydroperoxide channel after the OH elimination. These findings underline the central role of the hydroperoxide pathway for SOA formation and give insight into the gas-phase ozonolysis mechanism after the stage of the Criegee intermediate chemistry.     

Organic acid formation in the gas-phase ozonolysis of alpha-pinene

The mechanism of formation of pinonic and norpinonic acids from alpha-pinene ozonolysis has been investigated by studying the products of the ozonolysis of an enone derived from alpha-pinene using gas chromatography coupled to mass spectrometry.     

On the use of CO as scavenger for OH radicals in the ozonolysis of simple alkenes and isoprene

The OH radical yields generated in the ozonolysis of ethene (ET), propene (PR), cis-2-butene (CB), trans-2-butene (TB), 2,3-dimethyl-2-butene (TME), and isoprene (ISP) in the presence of 20 Vol.% O₂ have been determined in a darkened glass reactor at 1 bar total pressure. The hydroxyl radicals formed were scavenged by an excess of CO added to the systems. The O₂ present converted H atoms formed in this reaction into HO₂. From measurements of the increase in CO₂ generation by FTIR the OH formation yields were determined to be 0.08 (ET), 0.18 (PR), 0.17 (CB), 0.24 (TB), 0.36 (TME), and 0.19 (ISP), respectively, per molecule of reacted ozone. The combined error in the OH determinations is estimated to be <10%. © 1997 John Wiley & Sons, Inc.     

High reactivity of hexafluoro acetone toward criegee intermediates in the gas‐phase ozonolysis of simple alkenes

Hexafluoro acetone CF₃COCF₃ has been shown to react rapidly with the CH₂OO, CH₃CHOO, and (CH₃)₂COO intermediates that are formed in the ozonolysis of C₂H₄, trans‐2‐C₄H₈, and 2,3‐dimethyl‐2‐butene, respectively, and to form products tentatively assigned to the corresponding secondary ozonides. Relative rate method applied to the C₂H₄ ozonolysis has indicated that CF₃COCF₃ reacts ∼13 times faster than CH₃CHO. © 1999 John Wiley & Sons, Inc., Int J Chem Kinet 31: 261–269, 1999     

Multifunctional acid formation from the gas-phase ozonolysis of beta-pinene

The gas-phase ozonolysis of beta-pinene was studied in static chamber experiments, using gas chromatography coupled to mass spectrometric and flame ionisation detection to separate and detect products. A range of multifunctional organic acids-including pinic acid, norpinic acid, pinalic-3-acid, pinalic-4-acid, norpinalic acid and OH-pinalic acid-were identified in the condensed phase after derivatisation. Formation yields for these products under systematically varying reaction conditions (by adding different OH radical scavengers and Criegee intermediate scavengers) were investigated and compared with those observed from alpha-pinene ozonolysis, allowing detailed information on product formation mechanisms to be elucidated. In addition, branching ratios for the initial steps of the reaction were inferred from quantitative measurements of primary carbonyl formation. Atmospheric implications of this work are discussed.     

Reactions of alkenes with ozone in the gas phase: a matrix-isolation study of secondary ozonides and carbonyl-containing reaction products

Gas phase ozonolysis reactions of the alkenes ethene, cis- and trans-but-2-ene, isoprene and the monoterpenes alpha-pinene, beta-pinene, beta-carene, limonene and beta-myrcene have been carried out and the reaction products have been trapped in O2-doped-argon matrices onto a Csl window held at 12 K. Products have been identified by IR spectroscopy. Comparison with previous matrix spectra, where secondary ozonides have been generated either in situ by annealing or in solution reactions allows a positive identification of the secondary ozonides of ethene and of cis- and trans-but-2-ene to be made. These observations are backed up by experiments utilising the isotopes 13C and 2H (D). It appears that secondary ozonides have also been formed from isoprene and the range of monoterpenes studied; this hypothesis is based upon the similarity of spectral features seen in the products of these reactions within those of the simpler alkenes. A number of other primary and secondary products are also identified from these reactions. Ethene gives formaldehyde as a primary product and acetaldehyde as a secondary product; it is found that the yield of acetaldehyde compared to formaldehyde increases as the reaction times are increased. Formaldehyde, one of the expected primary products, is formed by ozonolysis of beta-pinene, although the other expected primary product, nopinone, is not seen. A range of secondary reaction products have been identified from the ozonolysis of the monoterpenes studied.     

The gas-phase ozonolysis of unsaturated volatile organic compounds in the troposphere

The gas-phase reactions of ozone with unsaturated hydrocarbons are significant sources of free radical species (including *OH) and particulate material in the Earth's atmosphere. In this tutorial review, the kinetics, products and mechanisms of these reactions are examined, starting with a discussion of the original mechanism proposed by Criegee and following with a summary presentation of the complex, free radical-mediated reactions of carbonyl oxide (Criegee) intermediates. The contribution of ozone-terpene reactions to the atmospheric burden of secondary organic aerosol material is also discussed from the viewpoint of the formation of non-volatile organic acid products from the complex chemistry of ozone with alpha-pinene. Throughout the article, currently accepted understanding is supported through the presentation of key experimental results, and areas of persistent or new uncertainty are highlighted.     

Pyridine is an organocatalyst for the reductive ozonolysis of alkenes

Whereas the cleavage of alkenes by ozone typically generates peroxide intermediates that must be decomposed in an accompanying step, ozonolysis in the presence of pyridine directly generates ketones or aldehydes through a process that neither consumes pyridine nor generates any detectable peroxides. The reaction is hypothesized to involve nucleophile-promoted fragmentation of carbonyl oxides via formation of zwitterionic peroxyacetals.     

Determination of gas-phase ozonolysis rate coefficients of C(8-14) terminal alkenes at elevated temperatures using the relative rate method

The rates of ozonolysis of a suite of terminal alkenes ranging from C(8-14) are determined in the gas phase at an elevated temperature of 395.9 ± 1.2 K and a pressure of ～650 Torr using the EXTreme RAnge chamber (EXTRA). Rates are found to be invariant with carbon number, whilst literature measurements conducted under ambient conditions exhibited an increase in rate coefficient after 10 carbon atoms. These earlier findings appear to contradict the intuitive notion that the inductive effect is a short-range process operating over a maximum distance of a few carbon atoms. These new measurements support the hypothesis that operating under ambient conditions, kinetic measurements of condensable species can be influenced adversely by heterogeneous processes and should therefore be treated with caution.     

Linear-reactor-infrared-matrix and microwave spectroscopy of the cis-2-butene gas-phase ozonolysis

Investigation of the formation of complex products in the gas-phase ozonolysis of cis,-2-butene by linear-reactor-infrared-matrix and linear-reactor-microwave spectroscopy is reported. The following species have been unequivocally detected: secondary 2-butene ozonide, acetic acid, peracetic acid, glycolaldehyde, dimethyl ketene, the simple and mixed anhydrides of formic and acetic acid, 2,3-epoxybutane and 2-butanone, besides polyatomic products already known. In contrast, the primary ozonide has been detectable neither by LR.-MW. nor by LR.-IR. Observation of both stereoisomeric epoxides and kinetic modelling are used to support the intermediate formation of the O'Neal-Blumstein radical CH₃CH(O₂)CH(O)CH₃ and the existence of a reaction channel in which the two carbon atoms of the C, C double bond of the olefin remain connected. As the dominant reaction path a mechanism with a Criegee type split into methyldioxirane (ethylidene peroxide) and acetaldehyde is considered and subsequently proposed to explain formation of many complex products by either unimolecular or bimolecular processes of the peroxide. For the reactions considered, thermochemical estimates of reaction enthalpies and activation data are included. Kinetic modelling for a partial reaction mechanism involving at least two different paths of decay of the O'Neal-Blumstein biradical into Criegee-type intermediates and the 2, 3-epoxybutanes is discussed.     

The gas-phase ozonolysis reaction of methylbutenol: A mechanistic study

The gas-phase ozonolysis reaction of methylbutenol through the Criegee mechanism is investigated. The initial reaction leads to a primary ozonide (POZ) formation with barriers in the range of 10–28 kJ mol⁻¹. The formation of 2-hydroxy-2-methyl-propanal (HMP) and formaldehyde-oxide is more favorable, by 10 kJ mol⁻¹, than the syn-CI and formaldehyde. The unimolecular dissociation of the more stable syn-CI via 1,5-H transfer into an epoxide is more favored than the epoxide and ³O₂ formation. The ester channel led to the formation of the acetone and formic acid favorably from the anti-CI. The hydration of the anti-CI with H₂O and (H₂O)₂ is significantly barrierless with a higher plausibility to the latter, and thus they may lead to the formation of peroxides and ultimately OH radicals, as well as airborne particulate matter. Reaction of anti-CI with water dimers enhances its atmospheric reactivity by a factor of 28 in reference to water monomers.     

The kinetics of the gas-phase reaction between ozone and alkenes

The rate law ? d[O₃]/ dt = k₁[A][O₃] + k₃[A][O₃]²/ (k₄ + k₅[O₂]) has been found to obtain for the reaction of ozone with allene and with 1,2-butadiene. We now find that this rate law also applies to the reaction of ozone with ethylene and presumably with all lower alkenes. This generalizes the inhibiting effect of oxygen and accounts for the simplifed rate law found in the presence of excess oxygen. Oxygen itself is a product of the ozone–ethylene reaction, and we find that as [O₃]₀ increases, the (O₂ formed)/(O₃ used) ratio approaches 1.5. Values of k₁, k₃/k₅ for ethylene are compared with those for allene, 1,3-butadiene, and propene. A generalized mechanism is postulated for the reaction of ozone with alkenes involving a chain sequence that produces oxygen and which accounts for the observed rate law. A specific mechanism is postulated for the reaction of O₃ with ethylene, and the thermochemistry of the chain sequence is examined in detail.     

Gas-phase ozonolysis of alkenes: formation of OH from anti carbonyl oxides

Gas-phase ozone-alkene reactions are known to produce the hydroxyl radical (OH) in high yields. Most mechanistic studies to date have focused on the role of syn carbonyl oxides; however, OH production from ethene ozonolysis indicates a second, poorly understood OH-forming channel, which may contribute to OH production in the ozonolysis of substituted alkenes as well. Using laser-induced fluorescence, we have measured OH and OD yields from the ozonolysis of two partially deuterated alkenes, cis- and trans-3-hexene-3,4-d2. OD is formed from both alkenes, indicating a pathway of hydroxyl-radical formation involving vinylic hydrogens, accounting for one-third of total OH formation from cis-3-hexene. The lack of a significant kinetic isotope effect suggests this pathway is the "hot acid" channel, arising from rearrangement of anti carbonyl oxides. Measured yields also allow for the estimation of syn:anti carbonyl oxide ratios, approximately 50:50 for trans-3-hexene and approximately 20:80 for cis-3-hexene, qualitatively consistent with our understanding of ozonide decomposition pathways.     

Thermodynamic properties of simple alkenes

Employing low temperature thermal measurements, heat capacities (C_s) in the crystal and liquid states, and phase transition data, T_m and ΔH_m, the condensed phase thermodynamic properties, (G_s -H°₀)/T, H_s -H°₀, S_s and C_s, in the temperature range 0–360 K were evaluated for the following eleven alkenes: ethylene, propylene, 1-butene, cis-2-butene, trans-2-butene, 1-pentene, cis-2-pentene, trans-2-pentene, 2-methyl-1-butene, 3-methyl-1-butene and 2-methyl-2-butene. The sources of experimental data, methods of evaluation, and the calculated results are described in detail.     

Temperature‐dependent kinetics for the ozonolysis of selected chlorinated alkenes in the gas phase

The ozonolysis of olefinic species is an important tropospheric process impacting on climate and human health. However, few studies have investigated these reactions as a function of temperature and even less information is available upon the effects of alkene heteroatomic substitution on the Arrhenius parameters. The electron‐withdrawing capacity of substituents about the olefinic bond strongly influences the rate of alkene ozonolysis. To understand better the effect of these substitutions, the temperature‐dependence of a series of ozone–chloroalkene reactions is investigated. Experiments were conducted in the EXTreme RAnge (EXTRA) chamber, over the range of 292–409 K and 760 Torr. The experimentally determined rate coefficients were fitted using an Arrhenius‐type analysis to yield the following activation energies: 30.80 ± 0.79, 23.18 ± 0.59, 65.2 ± 2.8, 116.9 ± 5.6, 29.5 ± 1.8, and 18.67 ± 0.96 kJ mol^?1 and preexponential A‐factors 1.22^+0.39_?0.29×10^?15, 9.3^+6.7_?5.4×10^?16, 1.6^+2.5_?1.0×10^?10, 6⁺²²_?3.9×10^?4, 1.7^+1.6_?0.8×10^?14, and 4.2^+1.9_?1.3×10^?15 cm³ molecule^?1 s^?1 for cis‐1,2‐dichloroethene, trans‐1,2‐dichloroethene, trichloroethene, tetrachloroethene, 2‐chloropropene, and 3‐chloro‐1‐butene, respectively. © 2010 Wiley Periodicals, Inc. Int J Chem Kinet 43: 120–129, 2011