Showing papers on "Methyl vinyl ketone published in 2021"

Catalysis by Bidentate Iodine(III)-Based Halogen Donors: Surpassing the Activity of Strong Lewis Acids.

Abstract: The poorly understood mode of activation and catalysis of bidentate iodine(III)-based halogen donors have been quantitatively explored in detail by means of state-of-the-art computational methods. To this end, the uncatalyzed Diels-Alder cycloaddition reaction between cyclohexadiene and methyl vinyl ketone is compared to the analogous process mediated by a bidentate iodine(III)-organocatalyst and by related, highly active iodine(I) species. It is found that the bidentate iodine(III)-catalyst accelerates the cycloaddition by lowering the reaction barrier up to 10 kcal mol-1 compared to the parent uncatalyzed reaction. Our quantitative analyses reveal that the origin of the catalysis is found in a significant reduction of the steric (Pauli) repulsion between the diene and dienophile, which originates from both a more asynchronous reaction mode and a significant polarization of the π-system of the dienophile away from the incoming diene. Notably, the activity of the iodine(III)-catalyst can be further enhanced by increasing the electrophilic nature of the system. Thus, novel systems are designed whose activity actually surpasses that of strong Lewis acids such as BF3.

Reactions of α,β-Unsaturated Carbonyls with Free Chlorine, Free Bromine, and Combined Chlorine.

Abstract: Chemical disinfectants employed in water and wastewater treatment can produce a variety of transformation products, including carbonyl compounds (eg, saturated and unsaturated aldehydes and ketones) Experiments conducted under conditions relevant to chlorination at drinking water treatment plants and residual chlorine application in distribution systems indicate that α,s-unsaturated carbonyl compounds readily react with free chlorine and free bromine over a wide pH range but react slowly with combined chlorine (ie, NH2Cl) For nearly all of the 11 α,s-unsaturated carbonyl compounds studied, the apparent second-order rate constants for the reaction with free chlorine increased in a linear manner with hypochlorite (OCl-) concentrations, yielding species-specific second-order rate constants for the reaction with OCl- ranging from 021 to 12 M-1 s-1 Predictions based on the second-order rate constants indicate that a substantial fraction (ie, >60%) of several of the more prominent α,s-unsaturated carbonyls (eg, acrolein, crotonaldehyde) will be transformed to an appreciable extent in distribution systems by free chlorine Products from the reaction of chlorine with acrolein, crotonaldehyde, and methyl vinyl ketone were tentatively identified using nuclear magnetic resonance (NMR) and gas chromatography coupled to high-resolution time-of-flight mass spectrometry (GC-HRT-MS) These products lacked unsaturated carbons and, in some cases, contained multiple halogens

Combining palladium and ammonium halide catalysts for Morita–Baylis–Hillman carbonates of methyl vinyl ketone: from 1,4-carbodipoles to ion pairs

Abstract: Here we report that Morita–Baylis–Hillman carbonates from diverse aldehydes and methyl vinyl ketones can be directly utilised as palladium-trimethylenemethane 1,4-carbodipole-type precursors, and both reactivity and enantioselectivity are finely regulated by adding a chiral ammonium halide as the ion-pair catalyst. The newly assembled intermediates, proposed to contain an electronically neutral π-allylpalladium halide complex and a reactive compact ion pair, efficiently undergo asymmetric [4 + 2] annulations with diverse activated alkenes or isatins, generally with high regio-, diastereo- and enantio-selectivity, and even switchable regiodivergent or diastereodivergent annulations can be well realised by tuning the substrate or catalyst assemblies. An array of control experiments, including UV/Vis absorption study and density functional theory calculations, are conducted to rationalise this new double activation mode combining a palladium complex and an ammonium halide as an ion-pair catalyst.

General Mechanism for Sulfate Radical Addition to Olefinic Volatile Organic Compounds in Secondary Organic Aerosol.

Abstract: Previous laboratory studies have suggested that sulfate radical addition to olefinic biogenic volatile organic compounds (BVOCs) is a potential formation mechanism for some organosulfates detected in ambient secondary organic aerosol (SOA). However, these studies propose conflicting reaction products, possibly because laboratory dissolved oxygen levels did not accurately reflect atmospheric conditions. Additionally, these studies used analytical methods that could not definitively identify and quantify the structurally specific products. Here, we describe a method that allows for the study of the reaction of sulfate radicals and several olefinic precursors, including allyl alcohol (AA), methyl vinyl ketone (MVK), 2-methyl-3-buten-2-ol (MBO), and methacrolein (MA), with careful control of dissolved oxygen levels and using the isomer-specific nuclear magnetic resonance (NMR) method to definitively identify and quantify the reaction products. Specific mechanisms for each olefinic precursor were developed, as well as a generalized mechanism that can be used to predict the sulfate radical reaction pathways for any olefin. The product yield results indicate that this mechanism is dominated by carbon backbone fragmentation pathways: 61, 83, 79, and 100% for AA, MVK, MBO, and MA, respectively. Several of the observed organosulfate products have also been detected in field observations of SOA, which indicates the potential relevance of this mechanism in the atmosphere.

Photodissociation dynamics of methyl vinyl ketone oxide: A four-carbon unsaturated Criegee intermediate from isoprene ozonolysis.

Abstract: The electronic spectrum of methyl vinyl ketone oxide (MVK-oxide), a four-carbon Criegee intermediate derived from isoprene ozonolysis, is examined on its second π* ← π transition, involving primarily the vinyl group, at UV wavelengths (λ) below 300 nm. A broad and unstructured spectrum is obtained by a UV-induced ground state depletion method with photoionization detection on the parent mass (m/z 86). Electronic excitation of MVK-oxide results in dissociation to O (1D) products that are characterized using velocity map imaging. Electronic excitation of MVK-oxide on the first π* ← π transition associated primarily with the carbonyl oxide group at λ > 300 nm results in a prompt dissociation and yields broad total kinetic energy release (TKER) and anisotropic angular distributions for the O (1D) + methyl vinyl ketone products. By contrast, electronic excitation at λ ≤ 300 nm results in bimodal TKER and angular distributions, indicating two distinct dissociation pathways to O (1D) products. One pathway is analogous to that at λ > 300 nm, while the second pathway results in very low TKER and isotropic angular distributions indicative of internal conversion to the ground electronic state and statistical unimolecular dissociation.

Towards a chemical mechanism of the oxidation of aqueous sulfur dioxide via isoprene hydroxyl hydroperoxides (ISOPOOH)

Abstract: . In-cloud chemistry has important ramifications for atmospheric particulate matter formation and gas-phase chemistry. Recent work has shown that, like hydrogen peroxide ( H2O2 ), the two main isomers of isoprene hydroxyl hydroperoxide (ISOPOOH) oxidize sulfur dioxide dissolved in cloud droplets ( SO2,aq ) to sulfate. The work revealed that the pathway of SO2,aq oxidation with ISOPOOH differs from that of H2O2 . We investigate the chemical mechanisms of oxidation of SO2,aq with ISOPOOH in the cloud-relevant pH range of 3–6 and compare them with the previously reported mechanisms of oxidation of SO2,aq with H2O2 , methyl hydroperoxide and peroxyacetic acid. The organic products of the reaction are identified, and two pathways are proposed. For 1,2-ISOPOOH, a higher yield pathway via proposed radical intermediates yields methyl vinyl ketone (MVK) and formaldehyde, which can react to hydroxymethanesulfonate (HMS) when SO2,aq is present. A lower yield non-fragmentation oxygen addition pathway is proposed that results in the formation of isoprene-derived diols (ISOPOH). Based on global simulations, this mechanism is not a significant pathway for formation of MVK and formaldehyde relative to their gas-phase formation but, as previously reported, it can be regionally important for sulfate production. The study adds to previous work that highlights similarities and differences between gas-phase and cloud-droplet processing of reactive organic carbon.

Detection of the keto-enol tautomerization in acetaldehyde, acetone, cyclohexanone, and methyl vinyl ketone with a novel VUV light source

Abstract: The discovery of enols in combustion environments and our atmosphere has garnered increasing attention to the many unanswered questions surrounding enol chemistry. The scarcity of experimental data concerning these enols renders combustion and atmospheric models with a lack of constraining parameters, leading to varying computational predictions. Experimental detection is difficult because mass spectrometry, a powerful tool for probing a wide variety of species, cannot distinguish between enols and their thermodynamically favorable ketone isomers. A solution to this ambiguity is to use tunable vacuum ultraviolet (VUV) light from a synchrotron to identify the presence of the enol by its lower ionization energy compared to the isomer. We present a tabletop-scale VUV light source that implements highly cascaded harmonic generation, a new regime of cascaded nonlinear optics, to provide a set of spectral lines spaced by 1.2 eV. We demonstrate that the variety of photon energies available allows us to detect the keto-enol tautomerization of four aldehydes and ketones. By combining this novel VUV light source with an established microreactor, we first revisit the formation of vinyl alcohol from acetaldehyde and confirm that the observed isomerization is indeed unimolecular. Secondly, we observe the thermal tautomerization of acetone to propen-2-ol for the first time. Finally, we observe the thermal tautomerization of cyclohexanone to 1-cyclohexenol and methyl vinyl ketone to 2-hydroxybutadiene, where the results are in good agreement with those reported at a synchrotron. Our measurements can be used to constrain models, inform future experimental studies of enol reactivity, and potentially enhance current understanding of combustion and environmental chemistry.

Infrared characterization of formation and resonance stabilization of the Criegee intermediate methyl vinyl ketone oxide

Abstract: Methyl vinyl ketone oxide (MVKO) is an important Criegee intermediate in the ozonolysis of isoprene. MVKO is resonance stabilized by its allyl moiety, but no spectral characterization of this stabilization was reported to date. In this study, we photolyzed a mixture of 1,3-diiodo-but-2-ene and O2 to produce MVKO and characterized the syn-trans-MVKO, and tentatively syn-cis-MVKO, with transient infrared spectra recorded using a step-scan Fourier-transform spectrometer. The O‒O stretching band at 948 cm−1 of syn-trans-MVKO is much greater than the corresponding bands of syn-CH3CHOO and (CH3)2COO Criegee intermediates at 871 and 887 cm−1, respectively, confirming a stronger O‒O bond due to resonance stabilization. We observed also iodoalkenyl radical C2H3C(CH3)I upon photolysis of the precursor to confirm the fission of the terminal allylic C‒I bond rather than the central vinylic C‒I bond of the precursor upon photolysis. At high pressure, the adduct C2H3C(CH3)IOO was also observed. The reaction mechanism is characterized. Methyl vinyl ketone oxide is an important Criegee intermediate formed during the ozonolysis of isoprene, but its formation and resonance stabilization remain poorly characterized. Here, transient infrared spectroscopy of the syn-trans-conformer shows a stronger O‒O stretching band at 948 cm-1 that confirms the stabilization.

Synthesis of vinyl polymers substituted with 2-propanol and acetone and investigation of their reversible hydrogen storage capabilities

Abstract: Developing a safe hydrogen carrier without the risks of high pressures and toxicities is an issue of significant urgency. In this study, we prepared a polymeric hydrogen carrier with high thermal stability by incorporating 2-propanol and acetone units into polymers. Poly(methyl vinyl ketone) with a high molecular weight (~105) was synthesized via bulk polymerization of methyl vinyl ketone and then dehydrogenated in one step to give poly(3-buten-2-ol) in high yield. Reversible hydrogen fixation and release by these polymers were achieved with full conversion under mild conditions (80–180 °C, ≦3 atm hydrogen pressure). A simple temperature-dependent hydrogenation/dehydrogenation cycle that operated at temperatures higher than the boiling points of 2-propanol and acetone in the presence of an iridium complex catalyst was established by virtue of having these groups as pendants of the vinyl chain, with a compact repeating unit to maximize the mass hydrogen storage density of 2.8 wt%. Polymeric hydrogen carrier with high thermal stability was prepared by incorporating isopropanol and acetone units into polymers via a facile reaction process. Reversible hydrogen fixing and releasing were achieved with full conversion under mild conditions. Temperature-dependent facile hydrogenation and dehydrogenation cycle that operated at temperatures higher than the boiling points of isopropanol and acetone, in the presence of an iridium complex catalyst, was established by virtue of having these groups as pendants of the vinyl chain, with a compact repeating unit to maximize the mass hydrogen storage density of 2.8 wt%.

Biodegradable PCL-b-PLA Microspheres with Nanopores Prepared via RAFT Polymerization and UV Photodegradation of Poly(Methyl Vinyl Ketone) Blocks.

Abstract: Biodegradable triblock copolymers based on poly(e-caprolactone) (PCL) and poly(lactic acid) (PLA) were synthesized via ring-opening polymerization of L-lactide followed by reversible addition–fragmentation chain-transfer (RAFT) polymerization of poly(methyl vinyl ketone) (PMVK) as a photodegradable block, and characterized by FT-IR and 1H NMR spectroscopy for structural analyses, and by differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA) for their thermal properties. Porous, biodegradable PCL-b-PLA microspheres were fabricated via the oil/water (O/W) emulsion evaporation method, followed by photodegradation of PMVK blocks by UV irradiation. The macro-chain transfer agent (CTA) synthesized by reacting a carboxylic-acid-terminated CTA—S-1-dodecyl-S′-(a,a′-dimethyl-a′′-acetic acid)trithiocarbonate (DDMAT)—with a hydroxyl-terminated PCL-b-PLA block copolymer was used to synthesize well-defined triblock copolymers with methyl vinyl ketone via RAFT polymerization with controlled molecular weights and narrow polydispersity. Gel permeation chromatography traces indicated that the molecular weight of the triblock copolymer decreased with UV irradiation time because of the photodegradation of the PMVK blocks. The morphology of the microspheres before and after UV irradiation was investigated using SEM and videos of three-dimensional confocal laser microscopy, showing a change in their surface texture from smooth to rough, with high porosity owing to the photodegradation of the PMVK blocks to become porous templates.

Dissociative Photoionization of Methyl Vinyl Ketone-Thermochemical Anchors and a Drifting Methyl Group.

Abstract: The dissociative photoionization of methyl vinyl ketone (MVK), an important intermediate in the atmospheric oxidation of isoprene, has been studied by photoelectron photoion coincidence spectroscopy. In the photon energy range of 9.5-13.8 eV, four main fragment ions were detected at m/z 55, 43, 42, and 27 aside from the parent ion at m/z 70. The m/z 55 fragment ion (C2H3CO+) is formed from ionized MVK by direct methyl loss, while breaking the C-C bond on the other side of the carbonyl group results in the acetyl cation (CH3CO+, m/z 43) and the vinyl radical. The m/z 42 fragment ion is formed via a CO-loss from the molecular ion after a methyl shift. The lightest fragment ion, the vinyl cation (C2H3+ at m/z 27), is produced in two different reactions: acetyl radical loss from the molecular ion and CO-loss from C2H3CO+. Their contributions to the m/z 27 signal are quantified based on the acetyl and vinyl fragment thermochemical anchors and quantum chemical calculations. Based on the experimentally derived appearance energy of the m/z 43 fragment ion, a new, experimentally derived heat of formation is proposed herein for gaseous methyl vinyl ketone (ΔfH0K = -94.3 ± 4.8 kJ mol-1; ΔfH298K = -110.5 ± 4.8 kJ mol-1), together with cationic heats of formation and bond dissociation energies.

Substituent Effect in the Reactions between Criegee Intermediates and 3-Aminopropanol.

Abstract: Via intramolecular H atom transfer, 3-aminopropanol is more reactive toward Criegee intermediates, in comparison with amines or alcohols. Here we accessed the substituent effect of Criegee intermediates in their reactions with 3-aminopropanol. Through real-time monitoring the concentrations of two Criegee intermediates with their strong UV absorption at 340 nm, the experimental rate coefficients at 298 K (100-300 Torr) were determined to be (1.52 ± 0.08) × 10-11 and (1.44 ± 0.22) × 10-13 cm3 s-1 for the reactions of 3-aminopropanol with (CH3)2COO (acetone oxide) and CH2CHC(CH3)OO (methyl vinyl ketone oxide), respectively. Compared to our previous experimental value for the reaction with syn-CH3CHOO, (1.24 ± 0.13) × 10-11 cm3 s-1, we can see that the methyl substitution at the anti position has little effect on the reactivity while the vinyl substitution causes a drastic decrease in the reactivity. Our theoretical calculations based on CCSD(T)-F12 energies reproduce this 2-order-of-magnitude decrease in the rate coefficient caused by the vinyl substitution. Using the activation strain model, we found that the interaction of Criegee intermediates with 3-aminopropanol is weaker for the case of vinyl substitution. This effect can be further rationalized by the delocalization of the lowest unoccupied molecular orbital for the vinyl-substituted Criegee intermediates. These results would help us better estimate the impact of similar reactions like the reactions of Criegee intermediates with water vapor, some of which could be difficult to measure experimentally but can be important in the atmosphere. We also found that the B2PLYP-D3BJ/aug-cc-pVTZ calculation can reproduce the CCSD(T)-F12 reaction barrier energies within ca. 1 kcal mol-1, indicating that the use of the B2PLYP-D3BJ method is promising for future predictions of the reactions of larger Criegee intermediates.

The Kinetics of 1,3-Dipolar Cycloaddition of Vinyl Monomers to 2,2,5,5-Tetramethyl-3-imidazoline-3-oxides.

Abstract: In our previous work [Edeleva et al. Chem. Commun. 2019, 55, 190-193], we proposed a versatile approach to the activation of the homolysis of an aldonitrone group-containing alkoxyamine by 1,3-dipolar cycloaddition to a vinyl monomer. Both nitroxide- and alkoxyamine-containing aldonitrones were found to be capable of reacting with the activated alkenes. In the present study, the kinetics of these reactions with 11 different vinyl monomers were investigated using EPR and NMR spectroscopy, and apparent activation energies as well as pre-exponential factors were determined. The influence of monomer structure on the rate of the 1,3-dipolar cycloaddition is discussed. For the vinyl monomers typically used in nitroxide mediated polymerization (styrene, methyl methacrylate) the rate coefficient of cycloaddition to the nitroxide is around k(353 K) ∼4 ⋅ 10-4 L mol-1 s-1 , whereas for n-butyl acrylate and methyl vinyl ketone we observed the fastest cycloaddition reaction with k(353 K)=8 ⋅ 10-3 and 4 ⋅ 10-2 L mol-1 s-1 respectively.

“Exhaustive” Baeyer-Villiger Oxidation of Poly(Methyl Vinyl Ketone) and Its Copolymers

Abstract: Poly(vinyl acetate) and its copolymers represent an important class of commodity polymers. However, the preparation of copolymers of vinyl acetate (VAc) and more activated monomers (MAMs) via copolymerization is greatly restricted due to their disparate reactivities. Issues relating to reactivity ratios remain a fundamental challenge in copolymerization. Herein, we describe a post-polymerization modification approach using poly(methyl vinyl ketone-co-MAM)s as substrates to access synthetically challenging poly(VAc-co-MAM)s. Although the direct translations of existing small-molecule Baeyer-Villiger (BV) protocols into a post-polymerization modification method failed, a mechanism-guided multi-parameter optimization on polymer substrates disclosed a set of unique “exhaustive” BV protocols which enabled a nearly quantitative functionalization without obvious chain scission or cross-linking. Furthermore, a one-pot copolymerization/“exhaustive” BV post-modification procedure was developed to produce such copolymers in a convenient and scalable manner. This user-friendly methodology is able to access diverse poly(VAc-co-MAM)s including both statistical and narrow-dispersed block copolymers and could greatly facilitate the exploration of applications with such materials.