Methyl Ethyl Ketone Research Articles

Evaluation of isoprene nitrate chemistry in detailed chemical mechanisms

Abstract. Isoprene nitrates are important chemical species in the atmosphere which contribute to the chemical cycles that form ozone and secondary organic aerosol (SOA) with implications for climate and air quality. Accurate chemical mechanisms are important for the prediction of the atmospheric chemistry of species such as isoprene nitrates in chemical models. In recent years, studies into the chemistry of isoprene nitrates have resulted in the development of a range of mechanisms available for use in the simulation of atmospheric isoprene oxidation. This work uses a 0-D chemical box model to assess the ability of three chemically detailed mechanisms to predict the observed diurnal profiles of four groups of isoprene-derived nitrates in the summertime in the Chinese megacity of Beijing. An analysis of modelled C5H9NO5 isomers, including isoprene hydroperoxy nitrate (IPN) species, highlights the significant contribution of non-IPN species to the C5H9NO5 measurement, including the potentially large contribution of nitrooxy hydroxyepoxide (INHE). The changing isomer distribution of isoprene hydroxy nitrates (IHNs) derived from OH-initiated and NO3-initiated chemistry is discussed, as is the importance of up-to-date alkoxy radical chemistry for the accurate prediction of isoprene carbonyl nitrate (ICN) formation. All mechanisms under-predicted C4H7NO5 as predominately formed from the major isoprene oxidation products, methyl vinyl ketone (MVK) and methacrolein (MACR). This work explores the current capability of existing chemical mechanisms to accurately represent isoprene nitrate chemistry in urban areas significantly impacted by anthropogenic and biogenic chemical interactions. It suggests considerations to be taken when investigating isoprene nitrates in ambient scenarios, investigates the potential impact of varying isomer distributions on iodide chemical ionisation mass spectrometry (I−-CIMS) calibrations, and makes some proposals for the future development of isoprene mechanisms.

Homogeneous Gold Catalysis Using Complexes Recovered from Waste Electronic Equipment.

Despite the greater awareness of elemental sustainability and the benefits of the circular economy concept, much waste electrical and electronic equipment (WEEE) is still destined for landfill. Effective methods for valorizing this waste within our society are therefore imperative. In this contribution, two gold(III) complexes obtained as recovery products from WEEE and their anion metathesis products were investigated as homogenous catalysts. These four recovery products were successfully applied as catalysts for the cyclization of propargylic amides and the condensation of acetylacetone with o-iodoaniline. Impressive activity was also observed in the gold-catalyzed reaction between electron-rich arenes (2-methylfuran, 1,3-dimethoxybenzene, and azulene) and α,β-unsaturated carbonyl compounds (methyl vinyl ketone and cyclohexenone). These recovered compounds were also shown to be effective catalysts for the oxidative cross-coupling reaction of aryl silanes and arenes. When employed as Lewis acid catalysts for carbonyl-containing substrates, the WEEE-derived gold complexes could also be recovered at the end of the reaction and reused without loss in catalytic activity, enhancing still further the sustainability of the process. This is the first direct application in homogeneous catalysis of gold recovery products sourced from e-waste.

Investigation into the differences and relationships between gasSOA and aqSOA in winter haze pollution on Chongming Island, Shanghai, based on VOCs observation

To investigate the formation of secondary organic aerosol (SOA) under current atmospheric conditions, we conducted a field observation of SOA precursors in the downwind region of the Yangtze River Delta (YRD) in winter 2019 using a variety of offline and online instruments. During the entire observation period, the averaged fine particulate SOA was 7.9 ± 2.3 μg m−3, with precursor concentrations of 31 ± 11 ppbv for the measured volatile organic compounds (VOCs) and 16 ± 12 ppbv for NOx. Compared to those on the clean days, SOA on the haze days increased by a factor of 1.6, while the VOC and NOx increased by a factor of 1.3 and 2.0, respectively. Aerosol liquid water content (ALWC) and oxygenated VOCs (OVOCs, including acetaldehyde, formic acid, acetone, acetic acid, methyl ethyl ketone, and methylglyoxal) relationships suggested that the gasSOA and aqSOA occurred simultaneously on Chongming Island in winter. The gasSOA was primarily formed by the oxidation of aromatics and NOx at low RH (RH < 80%) conditions. In contrast, the aqSOA was formed under higher RH (RH > 80%) conditions via a combination of daytime photochemical aqueous phase processes of water-soluble OVOCs and nocturnal dark aqueous phase processes of primary emissions from biomass. The inversed higher mass ratio of NACs to (benzene + toluene) and nitrogen oxidation ratio (NOR) in the daytime during the gasSOA-dominated haze periods indicated that gasSOA could be transformed to aqSOA at high NOx levels. Our results also suggested the importance of NOx and VOC reduction measures in directly mitigating gasSOA and indirectly mitigating aqSOA during winter haze pollution.

Probing O2 dependence of hydroperoxy-butyl reactions via isomer-resolved speciation

Degenerate chain-branching mechanisms of n-alkanes are centered on the formation of hydroperoxy-alkyl radicals (̇QOOH), formed via ̇R + O2 reactions, and the ensuing competition between unimolecular decomposition and second-O2-addition. Quantitative measurements of partially oxidized intermediates formed via reactions of ̇QOOH provide critical constraints that are required for accurate modeling of combustion chemistry. To examine the influence of temperature and oxygen concentration on intermediates from unimolecular decomposition of ̇QOOH, isomer-resolved speciation measurements were conducted on n-butane oxidation at 835 Torr in a jet-stirred reactor (JSR) from 500 – 900 K. Resulting from negative-temperature coefficient behavior, cyclic ether formation peaked at two temperatures, 650 K and 800 K, which were selected for separate experiments to quantify the O2-dependence of species profiles using O2 concentrations of 4.2 · 1017 – 1.1 · 1019 molecules cm–3.Utilizing vacuum-ultraviolet absorption spectroscopy and electron-impact mass spectrometry, cyclic ether isomers were quantified separately, including explicit resolution of cis- and trans- isomers of 2,3-dimethyloxirane. Stereoisomers of 2-butene were also quantified explicitly. For all cyclic ethers, a common trend in O2-dependence emerged: species concentrations reach a maximum near 3.0 · 1018 molecules cm–3 (equivalence ratio of 0.5). Although quantitative disparities are evident, chemical kinetics modeling qualitatively reproduces the O2 dependence of species at 650 K. However, at 800 K, weak dependence on O2 is predicted, which is in contrast with the measurements. Two carbonyls, diacetyl and methyl vinyl ketone, were also quantified and follow similar dependence on [O2] and temperature as the cyclic ethers, which indicates some fraction forms via ̇QOOH-mediated reactions. The discrepancies between the measured and model-predicted species profiles indicate that sub-mechanisms for important intermediates may require additional elementary reactions, including stereochemical-specific reactions, to improve the fidelity of n-alkane combustion modeling.

Machine Learning-Based Rapid Detection of Volatile Organic Compounds in a Graphene Electronic Nose.

Rapid detection of volatile organic compounds (VOCs) is growing in importance in many sectors. Noninvasive medical diagnoses may be based upon particular combinations of VOCs in human breath; detecting VOCs emitted from environmental hazards such as fungal growth could prevent illness; and waste could be reduced through monitoring of gases produced during food storage. Electronic noses have been applied to such problems, however, a common limitation is in improving selectivity. Graphene is an adaptable material that can be functionalized with many chemical receptors. Here, we use this versatility to demonstrate selective and rapid detection of multiple VOCs at varying concentrations with graphene-based variable capacitor (varactor) arrays. Each array contains 108 sensors functionalized with 36 chemical receptors for cross-selectivity. Multiplexer data acquisition from 108 sensors is accomplished in tens of seconds. While this rapid measurement reduces the signal magnitude, classification using supervised machine learning (Bootstrap Aggregated Random Forest) shows excellent results of 98% accuracy between 5 analytes (ethanol, hexanal, methyl ethyl ketone, toluene, and octane) at 4 concentrations each. With the addition of 1-octene, an analyte highly similar in structure to octane, an accuracy of 89% is achieved. These results demonstrate the important role of the choice of analysis method, particularly in the presence of noisy data. This is an important step toward fully utilizing graphene-based sensor arrays for rapid gas sensing applications from environmental monitoring to disease detection in human breath.

Kinetics and Mechanisms of Aqueous-Phase Reactions of Triplet-State Imidazole-2-carboxaldehyde and 3,4-Dimethoxybenzaldehyde with α,β-Unsaturated Carbonyl Compounds.

Reactions in the atmospheric aqueous phase are an important source of secondary organic aerosols (SOA). Within the present study, the reactions of triplet-state imidazole-2-carboxaldehyde (32-IC*) with methyl vinyl ketone (MVK, R1), methacrolein (MACR, R2), and methacrylic acid (MAA, R3), as well as the reaction of triplet-state 3,4-dimethoxybenzaldehyde (3DMB*) with the unsaturated compounds (MVK, R4), (MACR, R5), and (MAA, R6), in the aqueous phase were investigated using laser flash excitation-laser long path absorption and ultraperformance liquid chromatography coupled with high definition electrospray ionization spectrometry. The second-order reaction constants for 32-IC* were determined to be k1 = (1.0 ± 0.1) × 109 L mol-1 s-1 at pH 4-5 and 9, k2 = (1.4 ± 0.4) × 109 L mol-1 s-1 and (1.5 ± 0.1) × 109 L mol-1 s-1 at pH 4-5 and 9, and k3 = (1.4 ± 0.4) × 109 L mol-1 s-1 and (1.1 ± 0.4) × 108 L mol-1 s-1 at pH 4-5 and 9, respectively. The main products of the [2 + 2] photocycloaddition reactions of 32-IC* with both monomer and dimer of MVK as well as MACR were characterized. Similarly, the [2 + 2] photocycloaddition of the carbonyl of the excited triplet state of 3,4-dimethoxybenzaldehyde (3DMB*) with MVK was observed. The second order rate constants for the reactions of 3DMB* were determined: k4 = (1.5 ± 0.2) × 108 L mol-1 s-1, k5 = (2.8 ± 0.5) × 108 L mol-1 s-1, and k6 = (5.2 ± 1.2) × 106 L mol-1 s-1 at pH 9. The studied reactions show that different triplet photosensitizers react with strongly varying rate constants. Advanced CAPRAM process model studies show that active photosensitizers such as 3DMB* can quickly react with unsaturated organic compounds under deliquesced aerosol conditions modifying SOA, while the quenching with oxygen dominates the excited photosensitizer loss under cloud conditions.

Direct Organocatalytic Reductive Alkylation of Syncarpic Acid: Scope and Applications.

Biologically important 4-alkylsyncarpic acids, which resemble the core structure of many natural products, were synthesized in one-pot through the organocatalytic three-component reductive alkylation with excellent yields and C-selectivity. Synthetic applications of 4-alkylsyncarpic acids were demonstrated by converting into the functionally rich molecules through different reactions like Michael, retro-Michael, reduction, and oxidation reactions. In a continuation, formal total synthesis of (±)-triumphalone, (±)-isotriumphalone, and monomeric phloroglucinol derivatives was reported in a few steps starting from 4-alkylsyncarpic acids in overall very good yields. Further showcasing the importance of C-alkylated products, 4-benzylsyncarpic acid and its Michael adduct with methyl vinyl ketone were synthesized in a gram scale without compromising rate/yields.

The co-adsorption potential of metal–organic framework/activated carbon composites against both polar and non-polar volatile organic compounds in air

Adsorbents with high surface area and diverse functional groups are regarded as an effective option to deal with volatile organic compounds with different polarities. Herein, a metal–organic framework-199 (MOF-199 (prototypical Cu-MOF))/powdered activated carbon (PAC) composite (MOF-199@PAC) was fabricated and utilized to simultaneously treat multiple VOC system consisting of both non-polar (i.e., benzene) and polar VOCs (i.e., methyl ethyl ketone (MEK)). Kinetic and isotherm models combined with density functional theory simulations were also employed to address the adsorption mechanism of different VOCs onto the MOF-199@PAC composite (e.g., relative to pristine PAC and MOF-199). The overall results suggest that the MOF-199@PAC composite should be used efficiently for the adsorptive removal of polar (e.g., MEK) and non-polar VOCs (e.g., benzene) on its surface with the aid of abundant π-π conjugated sites and polar groups, respectively.

Investigation of kinetics and mechanistic insights of the reaction of criegee intermediate (CH2OO) with methyl-ethyl ketone (MEK) under tropospherically relevant conditions

The temperature-dependent kinetics was investigated for the reaction of the simplest Criegee intermediate (CH2OO) with Methyl-ethyl ketone (CH3COC2H5, MEK). A direct method was employed to measure the rate of change of the concentration of CH2OO using a highly sensitive Pulsed Laser Photolysis-Cavity Ring-down Spectroscopy (PLP-CRDS) technique. The temperature dependent rate coefficient obtained for the CH2OO + MEK reaction was k4(T = 258–318 K) = (1.26 ± 0.16) × 10−14 × exp{(1179.1 ± 71.8)/T} cm3 molecule−1 s−1 and the rate coefficient at room temperature was k4(298 K) = (6.39 ± 0.20) × 10−13 cm3 molecule−1 s−1 at 50 Torr/N2. Theoretical calculations were performed to predict the reaction mechanism and probable end products. The secondary ozonide (SOZ) formation pathway was found to be the rate determining step, which gets decomposed into HCOOH and MEK as the major products. Both experimental and theoretical results show a negative T-dependency in the studied range.

Development of Self-Healing Carbon/Epoxy Composites with Optimized PAN/PVDF Core-Shell Nanofibers as Healing Carriers.

Two-component self-healing carbon/epoxy composites were fabricated by incorporating healing agents between to carbon fiber laminates via the vacuum bagging method. Vinyl ester (VE), cobalt naphthalene (CN), and methyl ethyl ketone peroxide (MEKP) were encapsulated in a polyacrylonitrile (PAN)/Poly(vinylidene fluoride) (PVDF) shell via co-axial electrospinning. Varying nanofiber compositions were fabricated, namely, 10, 20, 30, and 40% PAN in PVDF nanofibers. The 20% PAN fibers were finalized as the shell material owing to their superior tensile properties and surface morphology. The behavior of the PAN/PVDF nanofibers encapsulating the healing agents was studied via Fourier-transform infrared spectroscopy (FTIR), field emission scanning electron microscopy (FESEM), and thermogravimetric analysis (TGA) to affirm the presence of the healing agents. Mechanical analysis in the presence of core-shell nanofibers indicated an enhancement of 7 and 5% in flexural strength and Izod impact strength, respectively. Three-point bending tests confirmed the autonomous healing characteristics of these nanofibers, which retained 62% of their initial strength after 24 h. FESEM and energy dispersive X-ray (EDX) analyses of the fracture surface confirmed that the resin was released from the nanofibers, restoring the initial properties of the composites.

Solution and Solid-State Behavior of Amphiphilic ABA Triblock Copolymers of Poly(acrylic acid-stat-styrene)-block-poly(butyl acrylate)-block-poly(acrylic acid-stat-styrene)

A combination of statistical and triblock copolymer properties is explored to produce stable aqueous polymer dispersions suitable for the film formation. In order to perform an extensive structural characterization of the products in the dissolved, dispersed, and solid states, a wide range of symmetrical poly(acrylic acid-stat-styrene) x -block-poly(butyl acrylate) y -block-poly(acrylic acid-stat-styrene) x , poly(AA-st-St) x -b-PBA y -b-poly(AA-st-St) x , (x = 56, 108 and 140, y = 100-750; the AA:St molar ratio is 42:58) triblock copolymers were synthesized by reversible addition-fragmentation chain transfer (RAFT) solution polymerization using a bifunctional symmetrical RAFT agent. It is demonstrated that the amphiphilic statistical outer blocks can provide sufficient stabilization to largely hydrophobic particles in aqueous dispersions. Such a molecular design provides an advantage over copolymers composed only of homoblocks, as a simple variation of the statistical block component ratio provides an efficient way to control the hydrophilicity of the stabilizer block, which ultimately affects the copolymer morphology in solutions and solid films. It was found by small-angle X-ray scattering (SAXS) that the copolymers behaved as dissolved chains in methylethylketone (MEK) but self-assembled in water into stable and well-defined spherical particles that increased in size with the length of the hydrophobic PBA block. These particles possessed an additional particulate surface structure formed by the statistical copolymer stabilizer block, which self-folded through the hydrophobic interactions between the styrene units. SAXS and atomic force microscopy showed that the copolymer films cast from the MEK solutions formed structures predicted by self-consistent field theory for symmetrical triblock copolymers, while the aqueous dispersions formed structural morphologies similar to a close-packed spheres, as would be expected for copolymer particles trapped kinetically due to the restricted movement of the blocks in the initial aqueous dispersion. A strong correlation between the structural morphology and mechanical properties of the films was observed. It was found that the properties of the solvent cast films were highly dependent on the ratios of the hard [poly(AA-st-St)] and soft (PBA) blocks, while the aqueous cast films did not show such a dependence. The continuous phase of hard blocks, always formed in the case of the aqueous cast films, produced films with a higher elastic modulus and a lower extension-to-break in a comparison with the solvent-cast films.

Production and Characterization of Waste Corncob Reinforced Polyester Composite

In this study, waste corncobs are ground and used in the polyester composite. Homogeneous distribution is provided by mixing it into unsaturated polyester (UP) as a filler under laboratory conditions. Then, methyl ethyl ketone peroxide (MEKP) and cobalt octoate (Co Oc) catalysts are added to the mixture. After mixing the additives and fillers used in certain amounts for a short time, the polyester composites are poured into standard molds and waited for curing. The density, Shore D hardness, and thermal decomposition behavior of the composite obtained after curing have been investigated. As the amount of corncob in the mixture increases, the density of the polyester composite decreases. Besides, the rise in the ratio of this filler in the mixture also increases the porosity of the polyester composite. In the thermal conductivity measurements, it is seen that the thermal conductivity coefficient of the polyester composite increases, albeit slightly, according to the increasing amount of filler. Also, corncob reinforcement reduces both Shore D hardness and activation energy of the polyester composite. According to the results obtained, it was observed that the use of corncob reinforcement above 3 wt.% negatively affected the surface morphology and mechanical properties of the composite. While obtaining an economical and light polyester composite, attention should be paid to the amount of filler so that both thermal and mechanical properties are not weakened.

Spatially Resolved Source Apportionment of Industrial VOCs Using a Mobile Monitoring Platform

Industrial emissions of volatile organic compounds (VOCs) directly impact air quality downwind of facilities and contribute to regional ozone and secondary organic aerosol production. Positive matrix factorization (PMF) is often used to apportion VOCs to their respective sources using measurement data collected at fixed sites, for example air quality monitoring stations. Here, we apply PMF analysis to high time-resolution VOC measurement data collected both while stationary and while moving using a mobile monitoring platform. The stationary monitoring periods facilitated the extraction of representative industrial VOC source profiles while the mobile monitoring periods were critical for the spatial identification of VOC hotspots. Data were collected over five days in a heavily industrialized region of southwestern Ontario containing several refineries, petrochemical production facilities and a chemical waste disposal facility. Factors associated with petroleum, chemical waste and rubber production were identified and ambient mixing ratios of selected aromatic, unsaturated and oxygenated VOCs were apportioned to local and background sources. Fugitive emissions of benzene, highly localized and predominantly associated with storage, were found to be the dominant local contributor to ambient benzene mixing ratios measured while mobile. Toluene and substituted aromatics were predominantly associated with refining and traffic, while methyl ethyl ketone was linked to chemical waste handling. The approach described here facilitates the apportionment of VOCs to their respective local industrial sources at high spatial and temporal resolution. This information can be used to identify problematic source locations and to inform VOC emission abatement strategies.

Production and catalytic upgrading of 2,3-butanediol fermentation broth into sustainable aviation fuel blendstock and fuel properties measurement

With the increasing demand for sustainable supplies of aviation fuel and need to address climate change, new conversion technologies are needed to efficiently process biomass, produce high quality jet fuel blendstock, and meet carbon emission targets. This study demonstrates the synthesis, conditioning, and catalytic upgrading of 2,3-butanediol (BDO) fermentation broth into a jet fuel blendstock candidate. A high-titer 2,3-BDO fermentation broth (i.e., ∼90 g/L) was produced at a 100-L scale and pretreated via nanofiltration to decrease the impurities level in the broth from 4.6 to 0.6 wt%. A novel process for catalytic upgrading of aqueous 2,3-BDO into a jet fuel blendstock candidate was developed, and each step was efficiently demonstrated. The catalytic steps include 1) 2,3-BDO dehydration into methyl ethyl ketone (MEK) over AlPO4, 2)MEK conversion into olefins over Zn1Zr10Ox, 3)oligomerization of olefins over a zeolite beta, and 4) hydrogenation over platinum/carbon. Both the model feed and real 2,3-BDO fermentation broth were tested for upgrading 2,3-BDO to MEK. With the real feed, a continuous loss of conversion (i.e., >50 % loss over ∼140 h time-on-stream [TOS]) was partly attributed to reversible deactivation from coking species. However, the conversion remained stable with the model feed, which demonstrates the efficiency of the first step for converting aqueous 2,3-BDO (10 wt% in water). For upgrading MEK to olefins, high selectivity to olefins (i.e., 82.5 %) was obtained at high conversion levels (i.e., 93–98 %) with stable conditions being achieved for > 70–hours TOS. Oligomerization of light olefins, which was demonstrated for > 270 h TOS, mainly led to the formation of dimers (C8-10) and trimers (C13–14). The oligomerized product was hydrogenated and distilled to recover the jet fraction (35mass% or 40.9 % carbon based yield), which consists mostly of desired isoalkanes (31.7 wt%), n-alkanes (24.5 wt%), and cycloalkanes (29.6 wt%). While some improvement is still needed to meet ASTM D7566 specifications for viscosity and final boiling point temperature, freezing point, density, aromatics content, and sulfur content of the jet blendstock candidate were within acceptable ranges, thus highlighting the potential of this process for production of jet fuel blendstock.

Theoretical study of the side reactions of ethanol-to-butadiene conversion on MgO catalyst: formation of diethyl ether, ethyl acetal, 1,3-butanediol, methyl ethyl ketone, n-butanol, butanal, and acetone

Theoretical study of the side reactions of ethanol-to-butadiene conversion on MgO catalyst: formation of diethyl ether, ethyl acetal, 1,3-butanediol, methyl ethyl ketone, n-butanol, butanal, and acetone

An Approach for Modeling, Simulation, and Optimization of Catalytic Production of Methyl Ethyl Ketone

The current exploration manifests the progress of a one-dimensional reactor for the production of methyl ethyl ketone (MEK) as a commercial-industrial solvent with a relatively rapid evaporation rate and high solvation ability. MEK has been extensively utilized in colorings, printing, artificial leather, and base oils. One of the methods for the production of MEK is catalytic dehydrogenation of 2-butyl alcohol in the temperature range of 650–750 K utilizing spherical ZnO catalyst. Considering the high cost of fossil fuels to achieve optimal energy consumption, thermal coupling with the Fischer–Tropsch reaction was employed. Eventually, an evolutionary genetic algorithm was adopted to optimize the reactor to maximize MEK production. MATLAB software was utilized for the modeling and optimization. The modeling results were verified by industrial data. Moreover, they indicated a 37 and 55.4% increase in the production rate of thermal coupling and optimal thermal coupling reactors, respectively.

Designer Gelators for the Crystallization of a Salt Active Pharmaceutical Ingredient-Mexiletine Hydrochloride.

We report an approach to obtain drug-mimetic supramolecular gelators, which are capable of stabilizing metastable polymorphs of the pharmaceutical salt mexiletine hydrochloride, a highly polymorphic antiarrhythmic drug. Solution-phase screening led to the discovery of two new solvated solid forms of mexiletine, a type C 1,2,4-trichlorobenzene tetarto-solvate and a type D nitrobenzene solvate. Various metastable forms were crystallized within the gels under conditions which would not have been possible in solution. Despite typically crystallizing concomitantly with form 1, a pure sample of form 3 was crystallized within a gel of ethyl methyl ketone. Various type A channel solvates were crystallized from gels of toluene and ethyl acetate, in which the contents of the channels varied from those of solution-phase forms. Most strikingly, the high-temperature-stable form 2 was crystallized from a gel in 1,2-dibromoethane: the only known route to access this form at room temperature. These results exemplify the powerful stabilizing effect of drug-mimetic supramolecular gels, which can be exploited in pharmaceutical polymorph screens to access highly metastable or difficult-to-nucleate solid forms.

Syntheses of 7‐, 8‐ and 9‐Bromobenzotropolone, Cross‐Couplings of Their Methyl Ethers, and Deprotection to 7‐, 8‐ or 9‐Substituted Benzotropolones

AbstractUnprotected6,7‐benzotropolone and bromine were known to undergo an electrophilic substitution delivering the 7‐bromo derivative; it was carried on as its methyl ether.O‐Acetyl‐6,7‐benzotropolone added bromine at the C8=C9bond whereupon an amine‐induced E1cbelimination led to the 8‐brominated benzotropolone acetate; ester cleavage with aqueous acetic acid and etherification with diazomethane delivered the corresponding methyl ether.O‐Methylbenzotropolone was brominated withN‐bromosuccinimide giving the 9‐brominated methyl ether. The mentioned bromobenzotropolone methyl ethers underwent Pd‐catalyzed C−C and C−B couplings. They comprised Suzuki‐Miyaura couplings (with R−BF3K, R=Me, Bu, vinyl, Ph), Negishi couplings (with BuZnCl), Sonogashira couplings (with HC≡C−R, R=SiMe3, CH2OH, Ph, Bu), Mizoroki‐Heck reactions (with methyl acrylate, methyl vinyl ketone, styrene, 3‐buten‐2‐ol), a carbonylative coupling, and Suzuki‐Miyaura borylations (with B2Pin2). SubsequentO‐demethylations with BCl3succeeded in most cases; they furnished a library of 34O‐unprotected Br‐free benzotropolones, 31 of which were unknown before.

Characterization of odorous industrial plumes by coupling fast and slow mass spectrometry techniques for volatile organic compounds.

This study aimed to develop a technique to chemically characterize odor issues in neighborhoods of designated industrial zones with pronounced emissions of volatile organic compounds (VOCs). Due to the elusive nature of odor plumes, speedy detection with sufficient sensitivity is required to capture the plumes. In this demonstration, proton-transfer-reaction mass spectrometry (PTR-MS) was used as the front-line detection tool in an industrial zone to guide sampling canisters for in-laboratory analysis of 106 VOCs by gas chromatography-mass spectrometry/flame ionization detector (GC-MS/FID). The fast but less accurate PTR-MS coupled with the slow but accurate GC-MS/FID method effectively eliminates the drawbacks of each instrument and fortifies the strength of both when combined. A 10-day PTR-MS field screening period was conducted to determine suitable trigger VOC species with exceedingly high mixing ratios that were likely the culprits of foul odors. Twenty canister samples were then collected, triggered by m/z 43, 61 (ethyl acetate, fragments, EA), m/z 73 (methyl ethyl ketone, MEK), or m/z 88 (morpholine) in all cases. Internal consistency was confirmed by the high correlation of critical species in the PTR-MS and trigger samples. Several long-lived halocarbons were exploited as the intrinsic internal reference for quality assurance. Oxygenated VOCs (OVOCs) accounted for 15%-75% of the total VOC mixing ratios in the triggered samples. However, EA and MEK, the most prominent OVOC species, did not appear to have common sources with morpholine, which presented with PTR-MS peaks incoherent with the other OVOCs. Nevertheless, these distinctive OVOC plumes were consistent with the multiple types of odor reported by the local residents. In contrast with the triggered sampling, random samples in the same industrial zone and roadside samples in a major metropolitan area were collected. The pronounced OVOC content in the triggered samples highlighted the advantage over random grab sampling to address odor issues.

Theoretical Spectroscopic Study of Two Ketones of Atmospheric Interest: Methyl Glyoxal (CH3COCHO) and Methyl Vinyl Ketone (CH3COCH═CH2).

Two ketones of atmospheric interest, methyl glyoxal and methyl vinyl ketone, are studied using explicitly correlated coupled cluster theory and core–valence correlation-consistent basis sets. The work focuses on the far-infrared region. At the employed level of theory, the rotational constants can be determined to within a few megahertz of the experimental data. Both molecules present two conformers, trans/cis and antiperiplanar (Ap)/synperiplanar (Sp), respectively. trans-Methyl glyoxal and Ap-methyl vinyl ketone are the preferred structures. cis-Methyl glyoxal is a secondary minimum of very low stability, which justifies the unavailability of experimental data in this form. In methyl vinyl ketone, the two conformers are almost isoenergetic, but the interconversion implies a relatively high torsional barrier of 1798 cm–1. A very low methyl torsional barrier was estimated for trans-methyl glyoxal (V3 = 273.6 cm–1). Barriers of 429.6 and 380.7 cm–1 were computed for Ap- and Sp-methyl vinyl ketone. Vibrational second-order perturbation theory was applied to determine the rovibrational parameters. The far-infrared region was explored using a variational procedure of reduced dimensionality. For trans-methyl glyoxal, the ground vibrational state was estimated to split by 0.067 cm–1, and the two low excited energy levels (1 0) and (0 1) were found to lie at 89.588 cm–1/88.683 cm–1 (A2/E) and 124.636 cm–1/123.785 cm–1 (A2/E). For Ap- and Sp-methyl vinyl ketone, the ground vibrational state splittings were estimated to be 0.008 and 0.017 cm–1, respectively.