Unsaturated Carbonyl Species Research Articles

Enhanced uptake of methacrolein at the acidic nanoparticle interface: Adsorption, heterogeneous reaction and impact for the secondary organic aerosol formation

Considering the moderate acidity of aerosols, the formation of secondary organic aerosols (SOA) through acid-catalyzed heterogeneous reactions has become a recent concern. However, the detailed information on the multiphase chemistry of organic compounds adsorbed onto acidic aerosols remains uncertain. In this work, we investigated the multiphase chemical processes between methacrolein (MACR) and sulfuric acid (SA) and their relationship with SOA formation. Results show that the aqueous nanoparticle interface, especially when it is an acidic nanoparticle interface, is a perfect area to adsorb and accommodate MACR. The occurrence percentage of MACR on the interface is more than 70%. With the increase of SA concentration, the first solvation shell changed from only water to the mixture of SA and water, which facilitates the heterogeneous hydration reaction of MACR. Compared with the neutral nanoparticle interface, the acidic nanoparticle interface exhibits a better ability to uptake and accommodate gaseous carbonyl species. Moreover, SA can catalyze the hydration reaction of MACR inside the aqueous media, and the resulting oligomers contribute to the formation and growth of SOA. The hydration reaction indirectly promotes the continuous adsorption of MACR at the acidic nanoparticle interface. The rate constant shows a positive altitude dependence, and acid-catalyzed reactions have an important impact on environmental chemistry, such as cloud SOA formation, within the range of about 2–6 km. This study reports a complete description of the heterogeneous interactions between unsaturated carbonyl species and acidic nanoparticles by using molecular dynamics and quantum chemistry methods, aiming to provide some insights for the further study on heterogeneous chemistry and its role in the formation of tropospheric SOA.

Nickel‐ or Palladium‐Catalyzed Stereoselective Synthesis of Tetrasubstituted Olefinic Indolines‐Fused Triazoles: Extension to the Spiroindoline Core

AbstractA nickel‐ or palladium‐catalyzed cascade approach to afford indolines‐fused triazoles with tetrasubstituted olefins in good yields with excellent control of regio‐ and stereoselectivity is described. We have also discussed the synthesis of unsaturated carbonyl species when the alkyne was appended to an alkyl chain. The synthetic methodology has been extended to construct the biologically active spiroindoline core via a vinylcylopropane (VCP) intermediate. The synthesized tetrasubstituted scaffolds were investigated for their photophysical properties and all of the them exhibited good absorption and fluorescence emission in the UV‐visible region.magnified image

Thermal ageing behavior of styrene–butadiene random copolymer: A study on the ageing mechanism and relaxation properties

Thermal oxidative ageing process of commercial available styrene–butadiene random copolymer (SBR) has been studied by the combination use of in-situ collected dynamic FTIR spectrum and two dimensional correlation analysis. The modification on the viscoelastic properties were studied by dynamic mechanical analysis (DMA) and differential scanning calorimetry (DSC). It was found that the degradation took place predominantly in the aliphatic segment at the allylic position, giving rise to a maximum absorption at 1725 cm−1 in the carbonyl stretching region. The initiation process occurring in the aromatic parts produced acetophenone end groups as evidenced by the shoulder peak at 1679 cm−1. A series of oxygenated species were identified in the dynamic spectrum including anhydrides, lactones, peracids, aliphatic ketones and unsaturated carbonyl species. However, the band of unsaturated carbonyl species at 1695 cm−1 varied nonmonotonously, first increase sharply and then decreased. Concerning the concentration of double bonds, a detailed analysis revealed the different evolving trend between benzylic and aliphatic vinyls. The former showed an increment whereas the later were found to decrease, resulting in the broadening at 1638 cm−1. Furthermore, the relative generation rates of different carbonyls were ranked by two dimensional correlation analysis together with two shoulder peaks at 1713 and 1679 cm−1 identified subtly in the asynchronous spectrum. On the basis of the above spectroscopic results, the mechanisms of thermal degradation were proposed.The relaxation behavior of thermally degraded SBR was studied by DMA and DSC. Both of the two techniques evidenced an increasing and broadening Tg, suggesting the crosslinking reaction dominated thermal degradation. After checking the normalized spectra, it is found that all of the relaxation curves (irrespective of storage modulus, loss modulus or loss tangent) get widen over ageing. Two parameters, steepness (S) and wideness index (W) were defined in normalized storage modulus plot to make a quantitative discussion. The S reduced whereas the W rose up after degradation. The broader glass transition zone after ageing was attributed to the more heterogeneous relaxation environment and the wider size distribution of motion units participating in the transition.

Oxide-catalyzed conversion of acetic acid into acetone: an FTIR spectroscopic investigation

Adsorptive and catalytic interactions of gas phase acetic acid with surfaces of alumina, titania and ceria were observed by in situ Fourier-transform infrared (FTIR) spectroscopy on heating from room temperature up to 400 °C. The results revealed that, on alumina the acid was irreversibly, non-dissociatively adsorbed in the form of hydrogen-bonded molecules, and dissociatively in the form of bidentate bound acetate species over the full range of temperature scanned. In the gas phase, no chemical change was observed. On titania, the gas phase remained unchanged on heating up to 300 °C, but at 400 °C the acetic acid was largely converted into acetone (as well as CO 2 and H 2O) and minor products of isobutene and methane. Similar changes to the gas phase were observed on ceria, however, at 300 °C. The acetic acid conversion on ceria was almost complete. The appearance of acetone molecules in the gas phase was pertained by the emergence of IR absorptions implying the formation on the surface of unsaturated carbonyl species. Thus, the formation of these surface species, together with isobutene and CH 4 molecules in the gas phase, was considered consequent to the occurrence of further surface reactions of acetone molecules. Observance of structural and chemical stability of the surface and bulk of TiO 2 and CeO 2 throughout the reaction was taken to emphasize the catalytic nature of the acetic acid conversion into acetone in the gas phase, a process that is evidently more simple and economic than the conventional pyrolytic synthesis of acetone from metal acetate compounds in the solid state. The catalytic sites were suggested to be Lewis acid–base pair sites, with the Lewis acid sites (Ti 4+ or Ce 4+) being reducible. Mechanistic pathways were proposed for the observed adsorptive and catalytic interactions of acetic acid molecules on the test oxides.

The photochemistry of poly(4 ′-ethoxyacrylophenone) in the solid state

The photolysis of poly(4 ′-ethoxyacrylophenone) was studied in the solid phase, thin films being exposed to long-wave (i.e. λ⩾300 nm) UV radiation under high vacuum at 298 K. The principal photo-induced reaction was random chain scission, which in turn, was the result of a Norrish type II decomposition involving the carbonyl triplet. However, the quantum yield for scission was more than an order of magnitude lower, than that for the corresponding reaction in dilute solution, and this was associated with conformational restrictions imposed upon the collapse of the biradical. Low molecular weight products were also formed, but in low quantum yields ( Φ≈10 −4 mol (Einstein) −1), and their presence indicates the formation of ethyl radical intermediates. This observation is consistent with O–Et bond fission, and it also confirms that long-wave UV irradiation of ring substituted poly(acrylophenone)s leads to fission of the O-alkyl bonds. The polymer also underwent colouration (yellow), and this was attributed to the formation of quinonoid entities, the precursors being the phenoxy radicals formed simultaneously with the ethyl radicals. Because of their stability and their long lifetimes in the solid polymer at sub- T G temperatures, phenoxy radicals may also participate in other reactions, such as cross-linking, which can be brought about by reaction of these with each other, and by their interaction with radicals formed on the polymer backbone by ethyl radical abstraction of H-atoms. Cross-linking, which manifests itself by insolubilization and gel formation, is more apparent after longer exposures. It does, however, reduce the effective rate of chain scission, as does self-quenching, the new terminally unsaturated carbonyl species acting as effective triplet quenchers. Quenching of the triplet, which also occurs when naphthalene and 1,3- cis-pentadiene are added, conforms to the Perrin relationship. However, the high volume of the quenching sphere for naphthalene indicates that the process is subject to steric inhibition, the adjacent polymer chain restricting access of the quenchers to the carbonyl triplet.

Aspects of the thermal oxidation of ethylene vinyl acetate copolymer

The thermal oxidation of ethylene-vinyl acetate copolymer [EVA-17 and 28% w/w VA (vinyl acetate) units] has been examined by thermo-gravimetric and hydroperoxide analysis, FTIR (Fourier transform infra-red) fluorescence spectroscopy and yellowness index. Thermal analysis indicates the initial loss of acetic acid followed by oxidation and breakdown of the main chain. The degradation rate is greater in an oxygen atmosphere as is the formation of coloured products. FTIR spectroscopic analysis of the oxidised EVA shows evidence for de-acetylation followed by the concurrent formation of hydroxyl/hydroperoxide species, ketone groups, α,β-unsaturated carbonyl groups, conjugated dienes, lactones and various substituted vinyl types. Hydroperoxide evolution follows typical autooxidation kinetics forming ketonic species. In severely oxidised EVA evidence is given for the subsequent formation of anhydride groups. The initial fluorescence excitation and emission spectra of EVA is not unlike that reported for polyolefins confirming the presence of low levels of unsaturated carbonyl species. There are however, significant differences in a long wavelength component in the fluorescence emission indicating the presence of other active chromophores. These long wavelength emitting components grow in intensity and shift to longer wavelengths with ageing time. However, unlike studies on PVC these emission spectra are limited due to the vinyl polyconjugation lengths and tend to be consistent with the formation of specific degraded units, possibly polyunsaturated carbonyl species of a limited length confined to the EVA blocks. During oxidation of EVA the original unsaturated carbonyl species remain as distinct emitting chromophores. This suggests that the growth and decay of these chromphores is virtually constant indicating that they could be an integral part of the EVA polymer that are responsible for inducing degradation. Degradation is limited to the vinyl acetate moieties where hydroperoxides can lead to the formation of polyconjugated carbonyl groups. The EVA degradation is therefore, different from that of PVC where in the latter case polyconjugated vinyl groups are evident through conjugated absorption bands in the UV spectrum. In the case of degraded EVA no such bands are observed. Also, degraded coloured EVA is not bleached by treatment with bromine, maleic anhydride or peracetic acid. Primary phenolic antioxidants exhibit variable activity in inhibiting the yellowing of EVA while combinations with phosphites generally display powerful synergism.

Aspects of the thermal oxidation, yellowing and stabilisation of ethylene vinyl acetate copolymer

The thermal oxidation of ethylene-vinyl acetate copolymer [EVA-17 and 28% w/w VA (vinyl acetate) units] has been examined by thermo-gravimetric and hydroperoxide analysis, FTIR (Fourier transform infra-red), fluorescence spectroscopy and yellowness index. Thermal analysis indicates the initial loss of acetic acid followed by oxidation and breakdown of the main chain. The degradation rate is greater in an oxygen atmosphere as is the formation of coloured products. FTIR spectroscopic analysis of the oxidised EVA shows evidence for de-acetylation followed by the concurrent formation of hydroxyl/hydroperoxide species, ketone groups, α, β-unsaturated carbonyl groups, conjugated dienes, lactones and various substituted vinyl types. Hydroperoxide evolution follows typical auto-oxidation kinetics forming ketonic species. In severely oxidised EVA, evidence is given for the subsequent formation of anhydride groups. The initial fluorescence excitation and emission spectra of EVA is not unlike that reported for polyolefins confirming the presence of low levels of unsaturated carbonyl species. There are, however, significant differences in a long wavelength component in the fluorescence emission indicating the presence of other active chromophores. These long wavelength emitting components grow in intensity and shift to longer wavelengths with ageing time. However, unlike studies on PVC these emission spectra are limited due to the vinyl polyconjugation lengths and tend to be consistent with the formation of specific degraded units, possibly polyunsaturated carbonyl species of a limited length confined to the EVA blocks. During oxidation of EVA the original unsaturated carbonyl species remain as distinct emitting chromophores. This suggests that the growth and decay of these chromphores is virtually constant indicating that they could be an integral part of the EVA polymer that are responsible for inducing degradation. Degradation is limited to the vinyl acetate moieties where hydroperoxides can lead to the formation of polyconjugated carbonyl groups. The EVA degradation is therefore, different from that of PVC where in the latter case polyconjugated vinyl groups are evident through conjugated absorption bands in the UV spectrum. In the case of degraded EVA no such bands are observed. Also, degraded coloured EVA is not bleached by treatment with bromine, maleic anhydride or peracetic acid. Primary phenolic antioxidants exhibit variable activity in inhibiting the yellowing of EVA while combinations with phosphites and hindered piperidine stabilisers display powerful synergism confirming the importance of hydroperoxides as precursors. Thermal oxidation was also was displayed through the inhibition of lactone, carboxylic acid and alkene groups illustrating the fact that oxidation and yellowing are synonymous reactions.

Ageing and spectroscopic properties of polyethylenes: comparison with metallocene polymer

The thermal and photooxidative stabilities of high, linear low and metallocene grade polyethylenes are compared using FTIR and hydroperoxide concentration analysis and thermal methods (DSC, TGA). The thermal ageing of solid films follow the order LLDPE > metallocene > HDPE while for light stability the order is LLDPE > HDPE > Metallocene. Derivative UV and FTIR spectroscopic analysis of the three polyethylene types show that the vinyl types and concentrations are different and that they reflect the thermal stability of the polymer materials. Hydroperoxide levels also appear to be important and correlate with the carbonyl index oxidation rates. Differences in catalyst residues play a less prominent role although the effect of the Ti levels may be important. The fluorescence and phosphorescence excitation and emission spectra of the three types of polyethylene are similar confirming earlier identities on the role and presence of unsaturated carbonyl species. There are however, significant differences in a long wavelength component in the fluorescence emission indicating the presence of other active chromophores. These were found to be significant in the case of the metallocene polymer. These chromophores may contribute to the differences in the light stability of the polymers with the metallocene exhibiting the greatest intensity and least stability followed by HDPE and LLDPE.

Adaptation of photoacoustic fourier transform infrared spectroscopy for studying the thermal oxidation of nylon 66 at 150°c correlated to mechanical properties

AbstractOven aged tensile bars of heat stabilized, glass reinforced nylon 66 material were studied by Fourier transform infrared (FTIR) spectroscopy using a photoacoustic detector. Flat weighed scrapings were removed from tensile bars whose tensile strength, elongation, impact, molecular weight, and thermal properties had previously been measured. Using the amide I band of nylon 66 as an internal standard, the thermal oxidation of nylon was followed using a commercially available photoacoustic detector. The infrared absorbance spectra demonstrate the formation of carbonyl stretching vibrations due to the thermal oxidation of nylon with a band center at 1713 cm−1 whose width at half height is 40 cm−1. The difference infrared spectra support reaction mechanisms dealing with an Initial increase in the degree of polymerization followed by transamidation reactions with subsequent formation of an α, β unsaturated carbonyl species and chain scissioning. By using data related to the percent retention of certain physical properties which had also been measured on these tensile bars, subtractive infrared spectroscopy yielded additional fundamental information regarding nylon 66 degradation. Consequently, nylon products being used in underhood automotive applications are currently being investigated for thermal oxidative degradation using this rapid and relatively non‐destructive photoacoustic FTIR technique for durability considerations.

Olefin metathesis with zerovalent precursor complexes of tungsten (W(CO) 5L) supported on η alumina. An infrared investigation

Interaction of zerovalent precursor complexes of tungsten (W(CO) 5L) with the surface of η alumina results in a highly active metathesis catalyst. However, in order to reach this high level of activity it is necessary that the support is highly dehydrated and exhibits a Lewis acidity. Infrared spectro- scopy indicates that the precursor complex is interacting with the surface through WCO → Al complexation. This complexation gives rise to a strong decrease in electron density on tungsten which results in the departure of the ligand, L. A coordinatively unsaturated carbonyl species seems to be stabilised on the surface.