Kinetics and mechanisms of OH‐initiated oxidation of small unsaturated alcohols

Smog chamber relative rate techniques were used to measure rate coefficients of (5.00 ± 0.54) × 10^?11, (5.87 ± 0.63) × 10^?11, and (6.49 ± 0.82) × 10^?11 cm³ molecule^?1 s^?1 in 700 Torr air at 296 ± 1 K for reactions of OH radicals with allyl alcohol, 1‐buten‐3‐ol, and 2‐methyl‐3‐buten‐2‐ol, respectively; the quoted uncertainties encompass the extremes of determinations using two different reference compounds. The OH‐initiated oxidation of allyl alcohol in the presence of NO_x gives glycolaldehyde in a molar yield of 0.85 ± 0.08; the quoted uncertainty is two standard deviations. Oxidation of 2‐methyl‐3‐buten‐2‐ol gives acetone and glycolaldehyde in molar yields of 0.66 ± 0.06 and 0.56 ± 0.05, respectively. The reaction of OH radicals with allyl alcohol, 1‐buten‐3‐ol, and 2‐methyl‐3‐buten‐2‐ol proceeds predominately via addition to the >C?CH₂ double bond with most of the addition occurring to the terminal carbon. © 2010 Wiley Periodicals, Inc. Int J Chem Kinet 42: 151–158, 2010     

Pressure dependence in the methyl vinyl ketone + OH and methacrolein + OH oxidation reactions: an electronic structure study.

High-level electronic structure calculations were carried out for the study of the reaction pathways in the OH-initiated oxidations of methyl vinyl ketone (MVK) and methacrolein (MACR). For the two conformers of MVK (called synperiplanar and antiperiplanar), the addition channels of OH to the terminal and central carbon atom of the double bond dominate the overall rate constant, whereas the abstraction of the methyl hydrogen atoms has no significant kinetic role. In the case of MACR, only the antiperiplanar conformer is important in its reactivity. In addition, the lower Gibbs free energy barrier for MACR corresponds to the aldehydic hydrogen abstraction reaction, which will be somewhat more favorable than the addition processes. The subtle balance between the different pathways (additions versus abstractions) serves to give an understanding of the pressure dependence of the rate constants of these tropospheric oxidation processes.     

The fate of the hydroxyalkoxy radical in the OH‐initiated oxidation of isoprene

Rate constants for several intermediate steps in the OH‐initiated oxidation of isoprene were determined using laser‐photolysis/laser‐induced fluorescence of OH radicals at total pressures between 3 and 4 Torr at 295 K. The rate constant for decomposition of the hydroxyalkoxy radical was determined to be (3.0 ± 0.5) × 10⁴ s^?1 in this pressure range, which is in fair agreement with previous work. The presence of a prompt alkoxy decomposition pathway was also investigated and found to contribute less than 10% to the total hydroxyalkoxy radical decomposition. The rate constant for the reaction of the hydroxyperoxy radical with NO was determined to be (2.5 ± 0.5) × 10^?11 cm³ molecule^?1 s^?1, which is moderately higher than previously reported. © 2002 Wiley Periodicals, Inc. Int J Chem Kinet 34: 255–261, 2002     

Measurements of the kinetics of the OH‐initiated oxidation of isoprene: Radical propagation in the OH + isoprene + O2 + NO reaction system

The mechanism of the OH‐initiated oxidation of isoprene in the presence of NO and O₂ has been investigated using a discharge‐flow system at 298 K and 2 torr total pressure. OH radical concentration profiles were measured using laser‐induced fluorescence as a function of reaction time. The rate constant for the reaction of OH + isoprene was measured to be (1.10 ± 0.05) × 10⁻¹⁰ cm³ mol⁻¹ s⁻¹. In the presence of NO and O₂, regeneration of OH radicals by the reaction of isoprene‐based peroxy radicals with NO was measured and compared to simulations of the kinetics of this system. The results of these experiments are consistent with an overall rate constant of 9 × 10⁻¹² cm³ mol⁻¹ mol⁻¹ (with an uncertainty factor of 2) for the reaction of isoprene‐based hydroxyalkyl peroxy radicals with NO. © 1999 John Wiley & Sons, Inc. Int J Chem Kinet 31: 637–643, 1999     

Mechanism of chloramine-T oxidation of methyl vinyl ketone and isopropyl methyl ketone in aqueous alkaline media

The oxidation kinetics of methyl vinyl ketone and isopropyl ketone by chloramine-T in aqueous alkaline solutions show first-order dependence on chloramine-T, both substrates and alkali. No effect of p-toluenesulphonamide was evident. Observed stoichiometry, negligible effect of ionic strength and a positive dielectric effect point to a mechanism involving interaction of enolate anions with chloramine-T in the rate determining step. Activation parameters and the isolation of the product formaldehyde are in agreement with the proposed mechanism.     

Organometal-initiated polymerization of vinyl ketones. III. Polymerization of methyl isopropenyl ketone initiated by the triethylaluminum–methyl isopropenyl ketone complex

The kinetics and mechanism of the triethylaluminum–methyl isopropenyl ketone complex-initiated polymerization of methyl isopropenyl ketone (3-methyl-3-butene-2-one) in toluene have been studied over a range of temperature. Equimolar quantities of monomer and triethylaluminum were premixed to form the initiator species prior to the addition of the excess monomer for polymerization. Initial and overall reaction rates indicate a first-order dependence on monomer and initiator concentrations. The overall activation energy for the polymerization is 52 ± 3 kJ/mole. Molecular weight distributions were bimodal, with peaks corresponding to the trimer and high molecular weight material. The kinetic data are consistent with a coordinate polymerization mechanism.     

Controlled nitroxide‐mediated radical polymerization of methyl and phenyl vinyl ketone

The article describes unprecedented nitroxide‐mediated radical polymerization of methyl and phenyl vinyl ketone (MVK and PVK) using a sterically highly hindered alkoxyamine as initiator/regulator. It is shown that controlled polymerization of PVK is far more difficult to achieve than controlled MVK polymerization. Whereas for MVK high conversion resulting in polyvinyl ketone with low polydispersity index is readily obtained, the PVK polymerization provides good results only in the presence of free nitroxide and styrene as additives. Vinyl ketone polymerizations are analyzed by ESI mass spectrometry. These MS studies provide insights into the problems associated with the controlled nitroxide‐mediated polymerization of PVK. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

Overall rate constant measurements of the reaction of hydroxy- and chloroalkylperoxy radicals derived from methacrolein and methyl vinyl ketone with nitric oxide

The overall rate constants of the reactions of NO with hydroxy- and chloroalkylperoxy radicals, derived from the OH- and Cl-initiated oxidation of methacrolein and methyl vinyl ketone, respectively, were directly determined for the first time using the turbulent-flow technique and pseudo-first-order kinetics conditions with high-pressure chemical ionization mass spectrometry for the direct detection of peroxy radical reactants. The individual 100 Torr, 298 K hydroxyalkylperoxy + NO rate constants for the methacrolein [(0.93 +/- 0.12) (2sigma) x 10(-11) cm3 molecule(-1) s(-1)] and methyl vinyl ketone [(0.84 +/- 0.10) x 10(-11) cm3 molecule(-1) s(-1)] systems were found to be identical within the 95% confidence interval associated with each separate measurement, as were the chloroalkylperoxy + NO rate constants for both methacrolein [(1.17 +/- 0.11) x 10(-11) cm3 molecule(-1) s(-1)] and methyl vinyl ketone [(1.14 +/- 0.14) x 10(-11) cm3 molecule(-1) s(-1)]. However, the difference in the rate constants between the hydroxyperoxy + NO and chloroalkylperoxy + NO systems was found to be statistically significant, with the chloroalkylperoxy + NO rate constants about 30% higher than the corresponding hydroxyalkylperoxy + NO rate constants. This substituent effect was rationalized via a frontier molecular orbital model approach.     

The uptake of methyl vinyl ketone, methacrolein, and 2-methyl-3-butene-2-ol onto sulfuric acid solutions

To investigate the link between molecular structure, reactivity, and partitioning of oxygenated organic compounds in acidic aerosols, the uptake of three compounds found in the atmosphere, methyl vinyl ketone (MVK), methacrolein (MACR), and 2-methyl-3-butene-2-ol (MBO), by sulfuric acid solutions has been measured using a rotated wetted-wall reactor (RWW) coupled to a chemical ionization mass spectrometer (CIMS). MVK was found to partition reversibly into 20-75 wt % H(2)SO(4) solutions, and we report Henry's law coefficients between 20 and 7000 M atm(-1) over this range. A chemical reaction for MVK was likely responsible for the uptake observed for 80-96 wt % H(2)SO(4) solutions. We derive an upper limit to the aldol self-reaction rate coefficient for MVK in 80 wt % solution of approximately 3 M(-1) s(-1). MACR partitioned reversibly over most of the acidity range, and in contrast to that for MVK, the Henry's law coefficient was relatively independent of H(2)SO(4) content. These differences indicate that the increase of the coefficient with acidity is likely due to the ability of the carbonyl molecule to form an enol. These results indicate that aldol condensation can be facile in concentrated sulfuric acid solutions, but it should be negligibly slow in dilute acid solutions such as tropospheric aerosols. MBO uptake could be explained by a Henry's law coefficient that decreases slightly as acid content varies from 20 to 55 wt % H(2)SO(4); we also measured the value in water, 70 M atm(-1) at 298 K. A steady-state uptake of MBO was observed onto 40-80 wt % H(2)SO(4) solutions, a reaction product was observed, and the reaction was tentatively identified as Pinacol rearrangement. Similar rearrangements could be at the origin of some substituted oxygenated species found in atmospheric aerosols.     

Photodegradation in solution of copolymers of methyl vinyl ketone and methyl isopropenyl ketone with methyl methacrylate

Copolymers of methyl vinyl ketone (MVK) and methyl isopropenyl ketone (MIK) with methyl methacrylate (MMA), have been prepared covering the whole composition range. Reactivity ratios have been estimated as follows: MMA/MVK, r_MMA = 0·63 ± 0·2, r_MVK = 0·53 ± 0·2; MMA/MIK, r_MMA = 0·98 ± 0·2, r_MIK = 0·69 ± 0·2. Number average molecular weights have been measured during the course of photodegradation under 253·7 nm radiation in methyl acetate solution and rates of chain scission calculated. In each system the copolymers are less stable than the corresponding homopolymers, the rate passing through a maximum at 20–30% ketone content. These results have been discussed from a mechanistic point of view.     

Laboratory studies of the OH‐initiated photooxidation of Di‐n‐propyl ether

The OH‐initiated photooxidation of di‐n‐propyl ether was investigated in this study. Di‐n‐propyl ether was mixed with nitric oxide and a hydroxyl radical precursor and irradiated using UV black lamps in a glass environmental chamber. Mass spectrometry was used as the primary analytical technique to monitor the reactants and products. FTIR spectroscopy was used to monitor formaldehyde. The products observed were propyl formate, acetaldehyde, propionaldehyde, and propyl propionate, with molar yields relative to di‐n‐propyl ether concentration loss of 0.61 ± 0.044, 0.60 ± 0.057, 0.15 ± 0.062, and 0.043 ± 0.015, respectively. Errors represent ±2σ. Nitrates could not be quantified because of a lack of commercially available standards. However, evidence exists for nitrate formation from the photooxidation of di‐n‐propyl ether. Formaldehyde concentrations were negligible. Mechanism predictions were performed on the di‐n‐propyl ether/OH system using the Carter kinetic software. Propyl formate and acetaldehyde yields were reasonably predicted (under 11.7% error). However, propionaldehyde and propyl propionate yields were vastly underpredicted, and examination of the experimental data suggested secondary production of both propionaldehyde and propyl propionate. Reactions were proposed for the photolysis and OH‐initiated photooxidation of a primary nitrate product (1‐propoxy propyl nitrate) that resulted in the formation of propionaldehyde and propyl propionate. Basic semiempirical computational chemistry calculations at the UHF/PM3 level of theory were performed using Hyperchem® to investigate pathways for the secondary formation of propionaldehyde in particular. © 2000 John Wiley & Sons, Inc. Int J Chem Kinet 32: 703–711, 2000     

Alpha vinylation of haloquinoline‐5,8‐diones with methyl acrylate and methyl vinyl ketone under baylis‐hillman reaction conditions

A synthesis of mono‐ and di‐vinylquinolinediones based on substitution of the halogens in 6,7‐dihaloquinoline‐5,8‐diones by DABCO‐assisted enolate ion is described. Divinylquinolines undergo 6π‐electrocyclization by thermally to give the benzo[g]quinoline derivatives.     

Aza-Baylis-Hillman reaction of salicyl N-tosylimines with methyl vinyl ketone, ethyl vinyl ketone or phenyl vinyl ketone

Reactions of salicyl N-tosylimines with methyl vinyl ketone, ethyl vinyl ketone or phenyl vinyl ketone proceeded smoothly under mild conditions to give the corresponding chromanes or aza-Baylis-Hillman adducts in moderate to excellent yields in the presence of phosphine or nitrogen Lewis base.     

Formation pathways of DMSO2 in the addition channel of the OH‐initiated DMS oxidation: A theoretical study

The production of dimethyl sulfoxide (DMSO) and dimethyl sulfone (DMSO₂) in the dimethyl sulfide (DMS) degradation scheme initiated by the hydroxyl (OH) radical has been shown to be very sensitive to nitrogen oxides (NO_x) levels. In the present work we have explored the potential energy surfaces corresponding to several reaction pathways which yield DMSO₂ from the CH₃S(O)(OH)CH₃ adduct [including the formation of CH₃S(O)(OH)CH₃ from the reaction of DMSO with OH] and the reaction channels that yield DMSO or/and DMSO₂ from the CH₃S(O₂)(OH)CH₃ adduct are also studied. The formation of the CH₃S(O₂)(OH)CH₃ adduct from CH₃S(OH)CH₃ (DMS‐OH) and O₂ was analyzed in our previous work. All these pathways due to the presence of NO_x (NO and NO₂) and also due to the reactions with O₂, OH and HO₂ are compared with the objective of inferring their kinetic relevance in the laboratory experiments that measure DMSO₂ (and DMSO) formation yields. In particular, our theoretical results clearly show the existence of NO_x‐dependent pathways leading to the formation of DMSO₂, which could explain some of these experimental results in comparison with experimental measurements carried out in NO_x‐free conditions. Our results indicate that the relative importance of the addition channel in the DMS oxidation process can be dependent on the NO_x content of chamber experiments and of atmospheric conditions. © 2008 Wiley Periodicals, Inc. J Comput Chem, 2009     

Electroinduced oxidative copolymerization of N‐vinyl carbazole with methyl ethyl ketone formaldehyde resin

In this study, a novel procedure to obtain the non‐crosslinked, photoconductive, white form of the linear copolymer of N‐vinyl carbazole (NVCz) and methyl ethyl ketone formaldehyde resin (MEKF‐R) is reported. A possible mechanism of copolymerization is suggested. The yield of the copolymer is increased almost 10 times by the addition of catalytic amounts of ceric ammonium nitrate as an oxidant during the electrochemical polymerization of NVCz in the presence of MEKF‐R in a divided electrochemical cell. Since cerium(III) is readily oxidized to cerium(IV) at the anode, the concentration of cerium(IV) remained constant and the deposition of green poly(NVCz) can be prevented. Copyright © 2004 John Wiley & Sons, Ltd.     

Aza-Morita-Baylis-Hillman reaction of ethyl (arylimino)acetate with methyl vinyl ketone and ethyl vinyl ketone

Aza-Morita-Baylis-Hillman (aza-MBH) reaction of ethyl (arylimino)acetate with methyl vinyl ketone and ethyl vinyl ketone has been investigated. We found that aza-MBH adducts 1 could be formed in the presence of DABCO (30 mol %) and the corresponding adducts 2 could be obtained in the presence of PPh₃ (30 mol %) in moderate to good yields in acetonitrile under mild conditions, respectively.     

Methyl vinyl ketone+OH and methacrolein+OH oxidation reactions: a master equation analysis of the pressure- and temperature-dependent rate constants

High-level electronic structure calculations and master equation analyses were carried out to obtain the pressure- and temperature-dependent rate constants of the methyl vinyl ketone+OH and methacrolein+OH reactions. The balance between the OH addition reactions at the high-pressure limit, the OH addition reactions in the fall-off region, and the pressure-independent hydrogen abstractions involved in these multiwell and multichannel systems, has been shown to be crucial to understand the pressure and temperature dependence of each global reaction. In particular, the fall-off region of the OH addition reactions contributes to the inverse temperature dependence of the rate constants in the Arrhenius plots, leading to pressure-dependent negative activation energies. The pressure dependence of the methyl vinyl ketone+OH reaction is clearly more important than in the case of the methacrolein+OH reaction owing to the weight of the hydrogen abstraction process in this second system. Comparison of the theoretical rate constants and the experimental measurements shows quite good agreement.     

Triethylborane and methyl vinyl ketone as a bicom‐ponent transfer agent for the polymerisation of styrene

The polymerisation of styrene in the presence of methyl vinyl ketone (MVK) and triethylborane (BEt₃)was studied. The mixture of these two compounds was found to form a bicomponent complex that functions as a transfer agent for growing polystyryl radicals (C_T = 0.7; benzene, 60 °C). The analysis of the polymer chains formed by MALDI‐TOF‐MS showed that they were fitted with CH₂—CH₃ and CH₂—CH₂—C(O)—CH₃ as end groups which obviously emanated from MVK and BEt₃. In contrast, no such transfer occurred on using each of them as single compound.     

Theoretical investigation on the detailed mechanism of the OH‐initiated atmospheric photooxidation of o‐xylene

The reaction mechanism for o‐xylene with OH radical and O₂ was studied by density functional theory (DFT) method. The geometries of the reactants, intermediates, transition states, and products were optimized at B3LYP/6‐31G(d,p) level. The corresponding vibration frequencies were calculated at the same level. The single‐point calculations for all the stationary points were carried out at the B3LYP/6‐311++G(2df,2pd) level using the B3LYP/6‐31G(d,p) optimized geometries. Reaction energies for the formation of the aromatic intermediate radicals have been obtained to determine their relative stability and reversibility, and their activation barriers have been analyzed to assess the energetically favorable pathways to propagate the o‐xylene oxidation. The results of the theoretical study indicate that OH addition to o‐xylene forms ipso, meta, and para isomers of o‐xylene‐OH adducts, and the ipso o‐xylene adduct is the most stable among these isomers. Oxygen is expected to add to the o‐xylene‐OH adducts forming o‐xylene peroxy radicals. And subsequent ring closure of the peroxyl radicals to form bicyclic radicals. With relatively low barriers, isomerization of the o‐xylene bicyclic radicals to more stable epoxide radicals likely occurs, competing with O₂ addition to form bicyclic peroxy radicals. The study provides thermochemical data for assessment of the photochemical production potential of ozone and formation of toxic products and secondary organic aerosol from o‐xylene photooxidation. © 2007 Wiley Periodicals, Inc. Int J Quantum Chem, 2008