The reactions of the Criegee intermediate CH3 CHOO in the gas-phase ozonolysis of 2-butene isomers

Ozonolysis of cis- and trans-2-butene isomers were carried out in a 570 l spherical glass vessel in 730 torr synthetic air at 295 ± 3 K. The initial concentrations were 5 to 10 ppmv for the isomers and 2 to 5 ppmv for ozone. Quantitative yields were determined by FTIR spectroscopy for CH₃CHO, HCHO, CH₄, CH₃OH, CO, and CO₂. By means of computational subtraction of the spectral contribution of the identified products from the product spectra, residual spectra have been obtained. Formation of 2-butene ozonide, propene ozonide, and l-hydroperoxyethyl formate CH₃CH(OOH)(SINGLE BOND)O(SINGLE BOND)CH(O) have been identified in the residual spectra. These products have been shown to be formed in the reactions of the Criegee intermediate CH₃CHOO with CH₃CHO, HCHO, and HCOOH, respectively. Mechanistic implications and atmospheric relevance of these observations are discussed. © 1997 John Wiley & Sons, Inc. Int J Chem Kinet 29: 461–468, 1997.     

Linear-Reactor-IR.-Matrix and Microwave Spectroscopy of the System O3/NO2/(Z)-2-Butene

Investigation of the formation of complex reaction products in the gas-phase system O₃/NO₂/(Z)-2-butene by combination of linear reactors with IR. matrix and microwave Stark Spectroscopy is reported. Besides the polyatomic products observed earlier in the gas-phase ozonolysis of (Z)-2-butene, the following products were identified; N₂O₅, HNO₃, HNO₄, CH₃NO₂, CH₃ONO, CH₃COONO₂ and CH₃COO₂NO₂ (peroxyacetyl nitrate, PAN). Matrix IR. spectra of N₂O₅, HNO₃. CH₃COONO, CH₃COONO₂ required for reference purposes are presented. It is shown that PAN-formation occurs already in the absence of light. A reaction scheme is proposed for explanation of the observed complex NO_x-containing products, which assumes methyldioxirane as a central intermediate. Particular reaction steps of the scheme will be discussed, including thermochemical estimates of reaction enthalpies.     

Formation of organic peroxides in the photooxidation of CH4

The formation of organic peroxides in the Cl-atom-initiated photooxidation of CH₄ in O₂-N₂ mixtures at 101 325 Pa and 298 K was studied with HPLC and FT-IR methods. Four peroxidic products were detected, which were H₂O₂, hydroxymethyl hydroperoxide (HOCH₂OOH; HMHP), methyl peroxide (CH300H; MHP) and dimethyl peroxide (CH₃00CH₃). A chromatogram peak at retention time of 8.08 min was assigned tentatively to peroxyformic acid (HC(O)OOH). The identification of HMHP in the reaction system showed that one of the reaction paths for the self-reaction of CH₃00. led to producing Criegee intermediate CH₂OO. The formation mechanism of organic peroxide in the photooxidation of CH₄ is more complicated than it was assumed before. Photooxidation of CH₄ is probably an important source of organic peroxides in the troposphere. Project supported by the State Scientific and Technological Commission of China (Grant No. E96-05)     

Activation of Hydrogen by Cationic Cyclopentadienyl Molybdenum Dimers with Sulfido Ligands. 4. A Cationic Complex with an Allyl Thiolate Ligand

A mixture of cis,trans-1-bromo-2-butene was reacted with (CpMoS)₂S₂CH₂ (Cp=C₅H₅) to form the cationic sulfur-alkylated product [(CpMo)₂(S₂CH₂)(μ-S)(μ-SCH₂CH=C(H)Me]Br, (1), which was characterized by spectroscopic methods. The reactivity of the allyl thiolate complex was compared with that of [(CpMo)₂(S₂CH₂)(μ-S)(μ-SCMe=CHMe)]Br, (2), an isomer with a vinyl thiolate ligand. Complex 1 does not undergo detectable isomerization in chloroform solution while a complex rearrangement process was observed for 2. The reaction of 1–2 atm of hydrogen with 1 resulted in the formation of 2-bromobutane and a previously characterized molybdenum complex [CpMoS₂CH₂]₂. [(CpMo)₂(S₂CH₂)(μ-S)(μ-SCHMe( Et))]Br was an intermediate in this reaction with hydrogen. It was detected by NMR and synthesized by an independent route. The reaction of methyl lithium with 1 led to the formation of a neutral complex (CpMo)₂(S₂CH₂)(μ-SMe)(μ-SCH₂CH=CHMe), (3). Complex 3 reacted under 1–2 atm of hydrogen to form an isomeric mixture of butenes. The nature of the molybdenum products which were isolated from this reaction suggested that homolytic cleavage of the carbon sulfur bond in the allyl thiolate ligand had occurred. Possible reaction pathways for the transformations of 1 and 3 under hydrogen are discussed.     

Determination of the isomerization rate constant HOCH2CH2CH2CH(OO·)CH3 →HOC·HCH2CH2CH(OOH)CH3. Importance of intramolecular hydroperoxy isomerization in tropospheric chemistry

The rate constant of the title reaction is determined during thermal decomposition of di-n-pentyl peroxide C₅H₁₁O( )OC₅H₁₁ in oxygen over the temperature range 463–523 K. The pyrolysis of di-n-pentyl peroxide in O₂/N₂ mixtures is studied at atmospheric pressure in passivated quartz vessels. The reaction products are sampled through a micro-probe, collected on a liquid-nitrogen trap and solubilized in liquid acetonitrile. Analysis of the main compound, peroxide C₅H₁₀O₃, was carried out by GC/MS, GC/MS/MS [electron impact EI and NH₃ chemical ionization CI conditions]. After micro-preparative GC separation of this peroxide, the structure of two cyclic isomers (3S*,6S*)3α-hydroxy-6-methyl-1,2-dioxane and (3R*,6S*)3α-hydroxy-6-methyl-1,2-dioxane was determined from ¹H NMR spectra. The hydroperoxy-pentanal OHC( )(CH₂)₂( )CH(OOH)( )CH₃ is formed in the gas phase and is in equilibrium with these two cyclic epimers, which are predominant in the liquid phase at room temperature. This peroxide is produced by successive reactions of the n-pentoxy radical: a first one generates the CH₃C·H(CH₂)₃OH radical which reacts with O₂ to form CH₃CH(OO·)(CH₂)₃OH; this hydroxyperoxy radical isomerizes and forms the hydroperoxy HOC·H(CH₂)₂CH(OOH)CH₃ radical. This last species leads to the pentanal-hydroperoxide (also called oxo-hydroperoxide, or carbonyl-hydroperoxide, or hydroperoxypentanal), by the reaction HOC·H(CH₂)₂CH(OOH)CH₃+O₂→O()CH(CH₂)₂CH(OOH)CH₃+HO₂. The isomerization rate constant HOCH₂CH₂CH₂CH(OO·)CH₃→HOC·HCH₂CH₂CH(OOH)CH₃ (k₃) has been determined by comparison to the competing well-known reaction RO₂+NO→RO+NO₂ (k₇). By adding small amounts of NO (0–1.6×10¹⁵ molecules cm⁻³) to the di-n-pentyl peroxide/O₂/N₂ mixtures, the pentanal-hydroperoxide concentration was decreased, due to the consumption of RO₂ radicals by reaction (7). The pentanal-hydroperoxide concentration was measured vs. NO concentration at ten temperatures (463–523 K). The isomerization rate constant involving the H atoms of the CH₂( )OH group was deduced: or per H atom: The comparison of this rate constant to thermokinetics estimations leads to the conclusion that the strain energy barrier of a seven-member ring transition state is low and near that of a six-member ring. Intramolecular hydroperoxy isomerization reactions produce carbonyl-hydroperoxides which (through atmospheric decomposition) increase concentration of radicals and consequently increase atmospheric pollution, especially tropospheric ozone, during summer anticyclonic periods. Therefore, hydrocarbons used in summer should contain only short chains (<C₄) hydrocarbons or totally branched hydrocarbons, for which isomerization reactions are unlikely. © 1998 John Wiley & Sons, Inc. Int J Chem Kinet 30: 875–887, 1998     

Reactions of unsymmetrically substituted allyl radicals with methyl radicals

The Hg(6³P₁) photosensitized decompositions of 3-methyl-1-butene, 2-methyl-2-butene, 3,3-dimethyl-1-butene, and 2,3-dimethyl-1-butene have been used to generate 1-methylallyl, 1,2-dimethylallyl, 1,1-dimethylallyl, and 1,1,2-trimethylallyl radicals in the gas phase at 24 ± 1°C. From a study of the relative yields of the CH₃ combination products, the relative reactivities of the reaction centers in each of these unsymmetrically substituted ambident radicals have been determined. The more substituted centers are found to be the less reactive, and this is ascribed primarily to greater steric interaction at these centers during reaction. Measurement of the ratio of trans- to cis-2-pentene formed from the 1-methylallyl radical, combined with published values for this ratio at higher temperatures, enabled the differences in entropy and heat of formation of the trans- and cis-forms of this radical to be calculated as 0.62 ± 0.85 J mol^?1 K^?1 and - 0.63 ± 0.25 kJ mol^?1, respectively, at 298K. Approximate values of the disproportionation/combination ratios for reaction of CH₃ with 1,1-dimethylallyl and 1-methylallyl have been estimated and used to compute rate constants for the recombinations of tert-butyl and isopropyl radicals that are in agreement with recently published data.     

Reaction of 3,3,3-trifluoropropene-1 with bromoform and methylene bromide

The radical telomerization of 3,3,3-trifluoropropene with bromoform and methylens bromide has been studied. The nature of the products with bromoform depends substantially on the method of initiation. In the presence of Fe(CO)₅ + DMF, telomers of CHBr₂(CH₅₂CHCF₃)_nBr are formed, while with initiation with benzoyl peroxide other compounds are also formed that contain two, three, or four bromine atoms per molecule. To elucidate the formation of these products a reaction scheme is proposed that involves rearrangement of CHBr₂CH₂CH(CF₃)CH₃CHCF₃ radicals to CBr₂CH₂CH(CF₃)CH₂CH₂CF₃ radicals.Deceased.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 11, pp. 2558–2562, November, 1989.     

Products of the gas-phase reaction of the OH radical with 3-methyl-1-butene in the presence of NO

The products of the gas-phase reaction of the OH radical with 3-methyl-1-butene in the presence of NO have been investigated at room temperature and 740 torr total pressure of air by gas chromatography with flame ionization detection, in situ Fourier transform infrared absorption spectroscopy, and direct air sampling atmospheric pressure ionization tandem mass spectrometry. The products identified and quantified by GC-FID and in situ FT-IR absorption spectroscopy were HCHO, 2-methylpropanal, acetone, glycolaldehyde, and methacrolein, with formation yields of 0.70±0.06, 0.58±0.08, 0.17±0.02, 0.18±0.03, and 0.033±0.007, respectively. In addition, IR absorption bands due to organic nitrates were observed, consistent with API-MS observations of product ion peaks attributed to the β-hydroxynitrates (CH₃)₂CHCH(ONO₂)CH₂OH and/or (CH₃)₂CHCH(OH)CH₂ONO₂ formed from the reactions of the corresponding β-hydroxyalkyl peroxy radicals with NO. A formation yield of ca. 0.15 for these nitrates was estimated using IR absorption band intensities for known organic nitrates. These products account for essentially all of the reacted 3-methyl-1-butene. Analysis of the potential reaction pathways involved shows that H-atom abstraction from the allylic C(SINGLEBOND)H bond in 3-methyl-1-butene is a minor pathway which accounts for 5–10% of the overall OH radical reaction. © 1998 John Wiley & Sons, Inc. Int J Chem Kinet: 30: 577–587, 1998     

Ruthenium-Catalyzed Cross-Metathesis of Trisubstituted Vinylsilanes with Light Alkenes

In the cross-metathesis reaction of tri(methyl, ethoxy)vinylsilanes with propene and/or 1-butene catalyzed by RuCl₂(PPh₃)₃ activated in benzene at 115–130 °C, a series of l-alkenylsilanes of general formula CH₃(CH₂)_mCH = CHSiMe_3−n(OEt)_n, where m=0, 1, and n=0–3 (1-silyl-1-alkenes), as well as of formula CH₂=C(Me)SiMe_3−n(OEt)_n, where n=1, 2 (2-silyl-1-alkenes), were obtained. Additional products determined were allysilanes of general formula CH₂=CHCH₂SiMe_3−n(OEt)_n and CH₃CH= CHCH₂SiMe_3−n(OEt)_n, where n=1–3. © 1997 John Wiley & Sons, Ltd.     

Intramolecular Oxygen Transfer on the Ozonolysis of a Diphenylcyclopentene Derivative

The ozonolysis of cis-3,4a,7,7a-tetrahydro-3,3-dimethyl-6,7a-diphenylcyclopenta[1,2,4]trioxine ( 1 ) in CH₂Cl₂ at ?78° gave the secondary endo ozonide 2 (43% yield) and an acetal 3 (27% yield) derived from O-insertion at the ortho position of the C(7a) phenyl substituent. Both structures were elucidated by X-ray. Repetition of the ozonolysis in MeOH/CH₂Cl₂20:3 at ?78° also gave the same two products in 12 and 15% yields, repectively, together with the hemiperacetal 4 (54% yield) formally derived from the secondary ozonide by addition of MeOH.     

Theoretical study on the mechanism and kinetics for the ozonolysis of vinyl propionate

The O₃-initiated oxidation of vinyl propionate is studied using quantum chemistry calculations. Detailed and complete reaction mechanisms are presented which involve the formation of the primary ozonide (POZ), the subsequent decomposition of POZ, the secondary reactions of CH₃CH₂C(O)OCHO₂ (IM4) in the presence of H₂O or NO as well as the generation of the secondary ozonide (IM6). Based on the above PESs calculations, the Multichannel Rice–Ramsperger–Kassel–Marcus theory is employed to calculate the total and individual rate constants for major product channels. The rate constants and branching ratios of main products are obtained. The total rate constants are temperature dependent over the whole study temperature range (200–2,000 K), but pressure independent over the range of 0.01–10,000 Torr. In addition, the atmospheric lifetime is estimated in accordance with rate constants.     

A Peculiar Reaction of Aminoallenes with Aromatic and Heteroaromatic Aldehydes

Addition of the Allenic amine H₂C═C═CHNMe₂ and the corresponding N-morpholinoallene to a solution of an aromatic or heteroaromatic aldehyde, RCH═O, and lithium bromide in tetrahydrofuran followed by treatment of the reaction mixture with a small amount of acetic acid at elevated temperatures affords the aldehydes RCH═C(CH₂NR'₂)CH═O (NR'₂=NMe₂ or morpholino) in reasonable yields.     

Organic peroxide production in the Cl2-ethane-air photoreaction system

HPLC along with FT-IR technique was used to study the formation of organic peroxides in the Cl₂-ethane-air photoreaction system. Ethyl hydroperoxide (CH₃CH₂₁OOH, EHP) and peroxyacetic acid ( CH₃C(O)OOH, PAA) were conformed to be the peroxide product in the reaction system. In addition, methyl hydroperoxide (CH₃OOH, hydroxymethyl hydroperoxide (HOCH₂OOH, HMHP) and two unidentified organic peroxides were detected for the first time. EHP and were the dominant peroxide products. The identification of HMHP showed that Criegee biradical CH₂OO may be formed as an intermediate in the oxidation of ethane. Simulation results showed that photooxidation of ethane may make substantial contribution to source of organic peroxides in the atmosphere.     

Organic peroxide production in the Cl2-ethane-air photoreaction system

HPLC along with FT-IR technique was used to study the formation of organic peroxides in the Cl₂-ethane-air photoreaction system. Ethyl hydroperoxide (CH₃CH₂₁OOH, EHP) and peroxyacetic acid ( CH₃C(O)OOH, PAA) were conformed to be the peroxide product in the reaction system. In addition, methyl hydroperoxide (CH₃OOH, hydroxymethyl hydroperoxide (HOCH₂OOH, HMHP) and two unidentified organic peroxides were detected for the first time. EHP and were the dominant peroxide products. The identification of HMHP showed that Criegee biradical CH₂OO may be formed as an intermediate in the oxidation of ethane. Simulation results showed that photooxidation of ethane may make substantial contribution to source of organic peroxides in the atmosphere.     

Reaction of propionitrile with methylidyne: A theoretical study

The results of a CCSD(T)-F12/cc-pVTZ-f12//ωB97XD/cc-pVTZ quantum-chemical study of the potential energy surface (PES) for the reaction of propionitrile with methylidyne are combined with Rice-Ramsperger-Kassel-Marcus (RRKM) calculations of the reaction rate constants and product branching ratios in the deep space conditions corresponding to the zero-pressure limit at various collision energies. The most energetically favorable reaction pathways have been identified. The reaction outcome has been shown to strongly depend on the branching in the entrance reaction channel, between CH additions and insertions into various C-H and C-C bonds. For instance, CH addition to the N atom predominantly leads to 3H-pyrrole + H (p9), with CH₂NC + C₂H₄ (p2) also being a significant product. CH addition to the triple C≡N bond mostly results in 2-methylene-2H-azirine + CH₃ (p13), whereas CH insertions into C-H bonds in the CH₃ and CH₂ groups of propionitrile form CH₂CN + C₂H₄ (p1) and CH₂CHCN + CH₃ (p7) respectively. Less likely CH insertions into single C-C bonds yield CH₃CHCHCN + H (p5) and CH₂CHCH₂CN + H (p8). The results indicate that the methylidyne + propionitrile reaction may represent a critical step toward the formation of heterocyclic N-containing molecules in the interstellar medium and in planetary atmospheres.     

The hydroxyl radical reaction rate constant and products of 3,5‐dimethyl‐1‐hexyn‐3‐ol

A bimolecular rate constant,k_DHO, of (29 ± 9) × 10^?12 cm³ molecule^?1 s^?1 was measured using the relative rate technique for the reaction of the hydroxyl radical (OH) with 3,5‐dimethyl‐1‐hexyn‐3‐ol (DHO, HC?CC(OH)(CH₃)CH₂CH(CH₃)₂) at (297 ± 3) K and 1 atm total pressure. To more clearly define DHO's indoor environment degradation mechanism, the products of the DHO + OH reaction were also investigated. The positively identified DHO/OH reaction products were acetone ((CH₃)₂C?O), 3‐butyne‐2‐one (3B2O, HC?CC(?O)(CH₃)), 2‐methyl‐propanal (2MP, H(O?)CCH(CH₃)₂), 4‐methyl‐2‐pentanone (MIBK, CH₃C(?O)CH₂CH(CH₃)₂), ethanedial (GLY, HC(?O)C(?O)H), 2‐oxopropanal (MGLY, CH₃C(?O)C(?O)H), and 2,3‐butanedione (23BD, CH₃C(?O)C(?O)CH₃). The yields of 3B2O and MIBK from the DHO/OH reaction were (8.4 ± 0.3) and (26 ± 2)%, respectively. The use of derivatizing agents O‐(2,3,4,5,6‐pentalfluorobenzyl)hydroxylamine (PFBHA) and N,O‐bis(trimethylsilyl)trifluoroacetamide (BSTFA) clearly indicated that several other reaction products were formed. The elucidation of these other reaction products was facilitated by mass spectrometry of the derivatized reaction products coupled with plausible DHO/OH reaction mechanisms based on previously published volatile organic compound/OH gas‐phase reaction mechanisms. © 2004 Wiley Periodicals, Inc. Int J Chem Kinet 36: 534–544, 2004     

Conformational isomerism of 1-butene secondary ozonide as studied by means of matrix isolation infrared absorption spectroscopy

Theoretical calculations of structures, stability and vibrational spectra of 1-butene secondary ozonide (SOZ) conformers were performed using DFT method B3LYP with a 6-311++G(3df, 3pd) basis set. The calculations predict six staggered structures of 1-butene SOZ. The FTIR spectra of 1-butene SOZ isolated in Ar, N₂ and Xe matrices were recorded. It was found that nitrogen is the best suited for the matrix isolation of 1-butene SOZ. The bandwidth of the spectral bands of the ozonide isolated in nitrogen was as narrow as 2 cm⁻¹. For the first time the existence of five conformers of 1-butene SOZ were confirmed experimentally by means of matrix isolation infrared absorption spectroscopy. The equatorial gauche (∠OCCC=−66.1°) conformer was proved theoretically and experimentally to be the most stable. It was found that due to high potential barriers of the conformational transitions annealing of the matrix is useless for the assignment of spectral bands to various conformers of 1-butene SOZ. Using the hot nozzle technique the van’t Hoff experimental plots were made for three additional conformers of 1-butene SOZ and experimental ΔH values for these additional conformers were established. The crystallization problems of 1-butene SOZ are discussed which accounts for the rich conformational diversity of the ozonide as well as high conformational barriers for axial-equatorial transitions.      

Elucidation of biochemical formation of C1/C2-(bromo-/chloro)-hydrocarbons

Summary To elucidate possible biochemical pathways of the formation of halogenated C₁/C₂-hydrocarbons we investigated the product pattern of the reaction of chloroperoxidase (CPO) with natural substances including the haloform reaction as a second step. The analysis of the reaction products was performed by HRGC-ECD. We report here first results. As substrates we used acetic acid and acetone while KBr and NaCl served as halogen sources. The system acetic acid/KBr/CPO formed tribromomethane as the main product, with dibromochloromethane (CHBr₂Cl) and 1,1,2,2-tetrachloroethane as by-products. Incubation with acetone resulted in the formation of CHBr₃ as the main product, with CHBr₂Cl, CH₂Br-CH₂Br, CHCl₂-CHCl₂, CHCl₂-CCl₃ and trichloroethene as side products, while the reaction of acetone with NaCl and CPO yielded chloroform as a main product.Results partly presented at the ANAKON '91 in Baden-Baden, April 22–24, 1991     

The atmospheric oxidation of hydroxyacetone: Chemistry of activated and stabilized CH3C(O)CH(OH)OO• radicals between 252 and 298 K

The products of the Cl-atom-initiated oxidation of hydroxyacetone (HYAC, CH₃C(O)CH₂OH) have been examined under conditions relevant to the earth's lower atmosphere. Over the range of temperatures studied (252-298 K), in the absence of NO_x, methylglyoxal (CH₃C(=O)CH=O, MGLY) was formed with a primary yield >84% (96 ± 9% at 298 K), while in the presence of elevated NO_x, MGLY and formic acid were both formed as major primary products. In contrast to a previous study, acetic acid was not identified as a major primary product under the conditions studied. The results are quantitatively interpreted from a consideration of the formation of a stabilized CH₃C(O)CH(OH)OO• radical, either in a ≈50% yield from the addition of O₂ to CH₃C(O)CH•(OH) or in 100% yield from the addition of HO₂ to MGLY. At high temperature and low NO_x, decomposition of the stabilized CH₃C(O)CH(OH)OO• radical to MGLY is favored, while lower temperatures and conditions of high NO_x favor bimolecular reactions of the stabilized radical, with subsequent production of formic acid. Analysis of the data allows for a semiquantitative determination of K₃ = (2.9 ± 0.4) × 10⁻¹⁶ cm³ molecule⁻¹, for the HO₂ + MGLY ↔ CH₃C(O)CH(OH)OO• equilibrium process at 298 K and a roughly order of magnitude increase in K₃ at 252 K.     

Uncommon oxidative transformations of acetic and propionic acids

The oxidative decarbonylation of acetic and propionic acids with the formation of the corresponding alcohol and alkyl carboxylate is observed in the Rh^III/Cu^I,II/Cl⁻ catalytic system in the presence of O₂ and CO. The decarbonylation of propionic acid in a deuterated solvent results in the substitution of hydrogen atoms by deuterium in the alkyl part of the products to form CH₂DCOOD (CHD₂COOH) and CHD₂COOD (CD₃COOH). The subsequent decarbonylation of deuterated acetic acids affords the corresponding deuteromethanols detected as esters with propionic and deuteroacetic acids. The substitution of the hydrogen atom by deuterium in the alkyl part of molecules of the products of oxidative decarbonylation of propionic acid, when the reaction is carried out in a deuterated solvent, indicates that propionic acid behaves as saturated hydrocarbon and blocks the oxidation of poorly soluble methane. Unlike propionic acid, acetic acid enters only the oxidative decarbonylation reaction and does not block methane oxidation.