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4 Figuras.-- 2 Tablas, The reactions of different lipid-derived reactive carbonyls with ammonia-producing compounds were studied to investigate the formation of pyridines in foods. 2-Alkyl, 3-alkyl-, and 2,5-dialkylpyiridines were produced by oligomerization of short-chain aldehydes in the presence of ammonia. Thus, acetaldehyde/crotonaldehyde mixtures and 2,4-alkadienals were the main responsible for the formation of 2-alkylpyridines; acrolein or 2,4-alkadienals were needed for the formation of 3-alkylpyridines; and 2-alkenals were responsible for the formation of 2,5-dialkylpyridines. On the contrary, 2,6-dialkylpyridines were produced by cyclization of unsaturated ketones. Reactions pathways for formation of these pyridines are proposed, and confirmed by isotopic labelling experiments. Aldehydes and ketones required for their formation are produced in the course of lipid oxidation. Therefore, pyridine formation seems to be an additional consequence of the lipid oxidation pathway. This new knowledge can employed for the optimization of reactions to achieve the desired targeted flavor generation during food processing., We are indebted to José L. Navarro for technical assistance. This study was supported in part by the European Union (FEDER funds), the Plan Nacional de I + D of the Ministerio de Economía y Competitividad of Spain (project AGL2015-68186-R), and the Programa Estatal de I + D + I of the Ministerio de Ciencia, Innovación y Universidades of Spain (project RTI2018-096632-B-100).

A new example of the reactivity of enals with benzoylnitromethane was studied in a Michael-Michael-Aldol-Dehydration quadruple organocascade reaction. The reaction unexpectedly yielded a tetrasubstituted cyclohexene carbaldehyde with excellent enantiomeric excess when crotonaldehyde was used as the Michael-acceptor, whereas using (E)-Hex-2-enal as the Michael-acceptor formed a cyclic hemiacetal by steering the reaction into the intramolecular formation of the same intermediate via a Michael-Heterocyclization domino reaction.

10 Figuras, Food processing is responsible for the destruction of some health hazards, but it is responsible for the formation of new ones. Among them, the formation of heterocyclic aromatic amines (HAAs) has received a considerable attention because of their carcinogenicity. In spite of this, HAA formation is still poorly understood. This study was undertaken to identify precursors and formation pathways for 2-amino-3-methylimidazo(4,5-f)quinoline (IQ). IQ was produced by reaction of acrolein, crotonaldehyde, creatinine, and ammonia. Reaction conditions were studied, and its activation energy (Ea) was determined to be 77.0 ± 1.3 kJ/mol. IQ formation was always accompanied by the formation of the HAA 2-amino-3,4-dimethylimidazo(4,5-f)quinoline (MeIQ), which was produced with an Ea of 72.2 ± 0.4 kJ/mol. A reaction pathway for the competitive formation of IQ and MeIQ is proposed. Obtained results demonstrate the significant role of reactive carbonyls (the food carbonylome) in HAA formation and provide evidences for designing HAA mitigation strategies., This study was supported by the Ministerio de Ciencia, Innovación y Universidades (MCIU) from Spain, the Agencia Estatal de Investigación (AEI) from Spain, and the Fondo Europeo de Desarrollo Regional (FEDER) from the European Union (Project RTI2018-096632-B-100).

Small Pt and Pt-Co nanoparticles (NPs) stabilized on La2O2CO3 nanorods (LOC) were prepared by wet impregnation method, and probed in liquid-phase chemoselective hydrogenation of crotonaldehyde (CRAL) to crotyl alcohol (CROL). It is found that incorporation of Co atoms into Pt catalyst significantly improves the hydrogenation activity and desired selectivity to CROL as it destroys the Pt-lanthanum interfaces and results into the formation of Pt-Co particles. In addition, a close examination of catalyst surface and reactive performance suggests that the impregnation sequence of Pt and Co exerts great influence on the physicochemical property and the catalytic hydrogenation behavior of PtCo/LOC catalysts. As a result of the interaction between Pt and Co species, high alloying degree of Pt-Co NPs is obtained in the co-impregnated catalyst (Pt-Co/LOC), thus achieving the highest hydrogenation activity. The selective deposit of Co atoms onto the low-coordinated Pt sites leads to the smallest metal particle size and high dispersion of Pt-Co NPs over the Pt/Co/LOC, giving rise to the highest selectivity and yield to CROL.

Heterogeneous reactions of various atmospheric gaseous pollutants on particle surfaces are important pathways for the formation of secondary aerosols. However, these heterogeneous reactions are inevitable affected by each other in the real atmosphere. In this study, the impacts of the heterogeneous uptake of NO2 on the conversion of acetaldehyde on the particle surfaces in the absence and presence of simulated solar irradiation were investigated by using diffuse reflectance infrared spectroscopy (DRIFTS) at 298 K. It is found that in the absence of simulated solar irradiation the hydration reaction and subsequent polyoligomeric reaction as well as oligomeric reaction of CH3CHO are promoted by the pre-adsorption of NO2 for a short reaction time, but these reactions are significantly hindered, accompanied with the slightly enhanced formation of crotonaldehyde and adsorbed acetate by the pre-adsorption of NO2 for a longer time. In the presence of simulated solar irradiation, the occurrence of the aldol condensation and the oxidation of CH3CHO are promoted by the combined impacts of illumination, hydrogen bond (H-bond) catalysis, the enhanced surface acidity and the formed nitrite and nitrate, especially, the photolysis of the formed nitrite and nitrate, whereas the hydration reaction and subsequent polyoligomeric reaction as well as oligomeric reaction of CH3CHO molecules are suppressed. Meanwhile, the hydrogen bond catalysis for aldol condensation is significantly enhanced by light irradiation, showing a combined result of hydrogen bond catalysis and illumination. The heterogeneous reaction mechanism is proposed, and atmospheric implications based on these results are discussed in this study.

This study reports that the C2–C2 aldolization in ethanol conversion to C4 products, particularly butadiene, can be catalyzed by silica-supported LaMnO3 catalysts. The concentration and strength of Mn4+ was discovered to be related to the particle size of supported LaMnO3: the smaller the particle size is, the higher the concentration and acidity of Mn4+ are. The presence of high concentration and acidity of Mn4+ of small LaMnO3 particles concurrently increases the amount of weak basic nonstoichiometric oxygen, with which the surface concentration of Lewis acid–base adducts can be elevated. The Mn4+/nonstoichiometric oxygen pair is intrinsically active in C2–C2 aldolization, and the concentration of the paired site is positively correlated to the selectivity of C4 products. By coreacting ethanol with its evolved intermediates, that is, acetaldehyde and crotonaldehyde, we discovered the aldol condensation of acetaldehyde molecules to be rate-limiting. Accordingly, a plausible mechanism of aldolization of a...

α,β-Unsaturated alcohols are a group of important chemicals and have frequently been synthesized by catalytic hydrogenation method due to its low cost and environmental friendly nature. However, the synthesis of high reactivity and selectivity catalyst that favors C═O hydrogenation is very challenging. Many references have reported the results of selective hydrogenation of crotonaldehyde to crotonyl alcohol, which either have high conversion and low selectivity or high selectivity and low conversion. Herein, Au-supported ZnAl-layered double hydroxides (Au/ZnAl–LDHs) were synthesized and used on the hydrogenation reaction of crotonaldehyde (CDE) to crotonyl alcohol (COL) under the moderate reaction conditions supplied with light irradiation. The experimental results indicated that the reactivity of CDE hydrogenation and selectivity of COL both have been greatly improved under visible light irradiation, from 42% to 99% for conversion of CDE, from 59.5% to 96% for COL selectivity, and from 101 to 272 h–1 for...

A new four-step pathway for the synthesis of γ-halo-δ-lactones is described from simple, commercially available substrates: aryl bromides and 3-methyl crotonaldehyde. The halogenolactonization reaction of β,δ-substituted, γ,δ-unsaturated carboxylic acid 4 a-c is regio- and stereoselective and gives only the trans-isomers of lactones 5 a-c, 6 a-c, and 7 a-c. The structures of all synthesized compounds were confirmed by using spectroscopic methods. For bromolactone, containing a naphthyl moiety in the structure, crystallographic analysis was also performed. The lactones were tested for their cytotoxic activity against L929 cell lines (mouse fibroblasts) and antibacterial activity against Escherichia coli strains ATCC 8739 and Staphylococcus aureus ATCC 65389. Compounds 5 a, 5 c, 7 a, and 7 b statistically significantly inhibited the metabolic activity of mouse fibroblasts L929. Compounds 5 b and 6 a were not cytotoxic towards L929 cells, but showed moderate bactericidal properties.

Chitosan grafted crotonaldehyde (CGC) by nucleophilic addition reaction of the amine group with α,β-unsaturated aldehyde was achieved by simple method using Lewis acid FeCl3.6H2O or ZrOCl2.8H2O as a catalyst. The product has been extensively characterized using FTIR, TGA, SEM, and EDX. The CGC was used for removal of hexavalent chromium from its aqueous solution. Batch experiment was tested using different contact times and initial Cr6+ ion concentrations under acidic condition (pH 1.5). Isotherm studies were achieved using variable models (Langmuir, Freundlich, and Tempkin) which showed a 10-fold greater uptake (434.78 mg/g) for modified chitosan over non-modified chitosan. The kinetics of Cr6+ adsorption by CGC followed the pseudo-second order model. This study proved that the CGC is a promising material for the treatment of wastewater containing Cr6+ ions.

This study investigated the performance of a biofilter to remove crotonaldehyde from air. Total average of removal efficiency (RE) and elimination capacity (EC) were 88% and 0.73 g m−3 h−1, respectively. Nearly 57% of the RE was occurred in the first 20 cm of the biofilter, where the bacterial population (7.42 log10CFU g−1) and fungi population (5.25 log10CFU g−1) were significantly more than the other sections. Predominant species of bacteria in the biofilter bed were Pseudomonas, Acinetobacter, and Proteus spp. Finally, it can be inferable that the biofilter can be a suitable method to remove crotonaldehyde from air.

Valuable polyester monomers and plasticizers-1,4-cyclohexanedimethanol (CHDM), 1,4-cyclohexanedicarboxylic acid (CHDA), and 1,2-cyclohexanedicarboxylates-have been prepared by a new strategy. The synthetic processes involve a proline-catalyzed formal [3+1+2] cycloaddition of formaldehyde, crotonaldehyde, and acrylate (or fumarate). CHDM is produced after a subsequent hydrogenation step over a commercially available Cu/Zn/Al catalyst and a one-pot hydrogenation/oxidation/hydrolysis process yields CHDA, whereas 1,2-cyclohexanedicarboxylate is obtained by a Pd/C-catalyzed tandem decarbonylation/hydrogenation step.

The critical node (CN) is an important stage during seed aging, which is related to effective genebank conservation. Previous studies have demonstrated that proteins undergo carbonylated modification at the CN in rice, indicating oxidative damage. However, the levels of reactive carbonyl species (RCS) and the associated scavenging system at the CN are largely unknown. In this study, we optimized methods for the extraction and analysis of RCS from dry rice embryos. In order to acquire seeds at the CN, rice seeds were subjected to natural conditions for 7, 9, 11 and 13 months, and the seed germination rates were reduced to 90%, 82%, 71% and 57%, respectively. We chose the stage with seed germination rate of 82% as the CN according to the rice seed vigor loss curve. The levels of crotonaldehyde and 4-hydroxy-(E)-2-nonenal (HNE) were significantly increased at the CN. In addition, genes encoding carbonyl-scavenging enzyme, including OsALDHs and OsAKRs, were significantly down-regulated at the CN, and reductions in the expression of OsALDH2-2, OsALDH2-5, OsALDH3-4, OsALDH7, OsAKR1 and OsAKR2 in particular could be responsible for RCS accumulation. Thus, the accumulations of crotonaldehyde and HNE and down-regulation of genes encoding carbonyl-scavenging enzyme might be related to an accelerating loss of seed viability at the CN. Key words: carbonyl-scavenging system, reactive carbonyl species, seed aging, crotonaldehyde, critical node, rice storage

The aza-Michael reaction of (S)-(–)- and (R)-(+)-α-methylbenzylamines with trans-cinnamaldehyde and other α,β-unsaturated carbonyl compounds occurs with 52–98% diastereoselectivity (de); however, in the reaction with crotonaldehyde, the de is lower (20–38%). In the products obtained from the reaction with α,β-unsaturated aldehydes, the de could be determined on the basis of the relative intensities of the aldehydic protons of the two diastereomers. Theoretical investigations of the reaction of (S)-(–)-α-methylbenzylamine with trans-cinnamaldehyde at the DFT (B3LYP/6-31+G*) level reveal that the diastereomer formed from the attack of the amine on the Re face is thermodynamically more stable. The calculations also show that the aldehydic proton of this diastereomer is expected to be more deshielded, which on the basis of the 1H NMR spectrum is the major product.

Solid-state 13C high-power proton decoupling (HPDEC), cross-polarization (CP), and 2-dimensional (2D) 13C-13C homonuclear correlation NMR techniques were used to study the adsorption of acetaldehyde on the flame-made fluorinated TiO2 (F-TiO2) catalyst, subsequent photocatalytic oxidation, and complete photo-decomposition at the presence of oxygen under UV light irradiation. Crotonaldehyde is formed via the acid-catalyzed aldol condensation through the adsorption of acetaldehyde on the F-TiO2 catalyst at room temperature without light illumination. At the presence of molecular oxygen as an electron acceptor, surface bonded acetaldehyde and crotonaldehyde are completely oxidized by the transient holes in the oxygen framework generated by UV light irradiation. This work provides clear evidence for the formation of crotonaldehyde, acetic acid, and formic acid, along with acetate and formate complexes. The identified surfaces complexes participate actively in the photocatalytic oxidation and do not play a significant role in the poisoning of the active sites, at least in such concentrations. The reaction pathways are therefore established.

A high-flux molecular beam setup has been used to characterize the kinetics of the steady-state catalytic hydrogenation of unsaturated aldehydes, specifically of crotonaldehyde, promoted by platinum surfaces under single-collision conditions. Surprisingly, in addition to the hydrogenation of the individual single bonds, to yield the saturated aldehyde and the unsaturated alcohol, the formation of the saturated alcohol, the product of the hydrogenation of both C═C and C═O bonds, was detected as well. This indicates that the dual hydrogenation reaction is a primary pathway and not the result of secondary hydrogenation of the other products as commonly assumed. Moreover, an increase in the partial pressure of the reactant was found to shift the reaction selectivity from the saturated alcohol to the saturated aldehyde without significantly affecting the selectivity toward the production of the unsaturated alcohol. We explain these observations by proposing a mechanism involving the parallel formation of several monohydrogenated intermediates on the surface.

Bifunctional Zn–Y/Beta catalyst was applied in the reaction mechanism study of the ethanol to butadiene conversion to clarify the roles of Zn and Y functional sites in each individual reaction step. According to the results of several complementary methods, i.e., ethanol temperature-programmed desorption (TPD), temperature-programmed surface reaction (TPSR), and in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS), the reaction network consisting of several key steps, i.e., ethanol dehydrogenation, acetaldehyde aldol condensation, and crotonaldehyde reduction, was elucidated. An enolization mechanism was verified to involve in the coupling step. During this reaction, the Lewis acidic Zn and Y species in [Si]Beta zeolite were both active in the ethanol dehydrogenation, aldol condensation, and Meerwein–Ponndorf–Verley reduction. In this cycle, Zn species exhibited the higher dehydrogenation activity but lower coupling activity than that of Y species. Through the combination of the tw...

The vapor–liquid equilibrium (VLE) for the system acetic acid, acetaldehyde, and crotonaldehyde was investigated by combining the Gibbs ensemble Monte Carlo (GEMC) method and activity coefficient models prediction. The VLE of above pure components and their binary systems were first studied using GEMC method. Based on the strong association characteristics of acetic acid, the revised TraPPE-UA-D force field was developed with quantum chemistry methods for the VLE calculation of the acetic acid system. The original and mixed TraPPE-UA force field was introduced for the VLE calculation of the acetaldehyde and crotonaldehyde system, respectively. The results showed that the predictions agreed fairly well with the average relative deviations of the saturated densities smaller than 4.60%. Moreover, the binary VLE diagram was calculated using the above force fields. The simulation results of the mole composition were in good agreement with the experimental values, which verified the high simulation accuracy of ...

The carbonyl emissions from a non-road machinery diesel engine running on diesel fuel (DF) or methanol-diesel blend fuel (M/DF) were investigated under a series of steady-state operating conditions. Carbonyl compounds (CBCs) were collected from the diluted exhaust, employing 2,4-dinitrophenylhydrazine-coated silica gel cartridges, and analyzed using a high-performance liquid chromatography system with a photodiode array detector. The results indicate that formaldehyde and acetaldehyde are the most abundant carbonyls, followed by acrolein, acetone, propionaldehyde and crotonaldehyde. Each of these compounds exhibit a consistent reduction with increases in the engine load. The M/DF produces much more formaldehyde, acetaldehyde, acrolein, acetone and crotonaldehyde than the DF at low loads, while there are marginal differences in the emission levels of these carbonyls between M/DF and DF at medium and high loads. The use of M/DF decreases propionaldehyde emissions at all test conditions. Compared with the results obtained using DF, the total CBC emissions increase by 45.3% and the ozone formation potential (OFP) increases by 57.0% when burning M/DF at low engine loads. In general, M/DF increases both OFP and total CBC emissions to a greater extent than biodiesel-blend fuel but to a lesser degree than ethanol- or butanol-containing blends.

In this paper, Au–Co/Ni bimetal supported layered double hydroxides (Au–Co,Ni/LDHs) were synthesized for the hydrogenation reaction of crotonaldehyde (CDE) to crotonyl alcohol (COL) with both high conversion and selectivity under light irradiation. The hydrogenation experimental results indicated that both the hydrogenation conversion of CDE and the selectivity of COL have been greatly improved by Au–Co,Ni/LDHs under visible light irradiation, with the best turnover frequency performance of 189 h−1, 100% conversion and 99.1% selectivity (using Au–Ni/LDHs). Such high properties are attributed to a synergistic effect of localized surface plasmon resonance (LSPR) of Au nanoparticles, and the additional Co or Ni species would further enhance this effect. The DFT calculation of CDE hydrogenation at Au–Co,Ni/LDHs showed that the hydrogenation happens at C2O1 first to produce COL by following mechanism A2. Au–Ni/LDHs with lower activation energy had higher catalytic activity than Au–Co/LDHs. Further calculation showed that the COL hydration reaction can be hindered on Au–Co,Ni/LDHs compared to the unmodified Au/LDHs, which indicates that the introduction of second metal Ni or Co besides Au could further increase the COL productivity. The DFT calculations well explained and supported the experimental results.

Crotonaldehyde is a ubiquitous air pollutant in the environment. It is reported to be harmful to the biosystems in vivo and in vitro. The exposure to crotonaldehyde irritates the mucous membranes and induces edema, hyperemia, cell necrosis, inflammation, and acute respiratory distress syndrome in the lungs. However, the effects of crotonaldehyde on the immune system have not been reported. In the present study, 6-8 weeks old male Wistar rats were exposed to crotonaldehyde by intratracheal instillation at doses of 4, 8, and 16 μL/kg body weight (b.w.). The general damage in the animals was investigated; the cell counting and the biochemical analysis in the peripheral blood were tested. Furthermore, we investigated the functions of alveolar macrophages (AMs), the alterations of the T-lymphocyte subsets, and the cell composition in the bronchoalveolar lavage fluid (BALF). We found that the activities of the animals were changed after exposure to crotonaldehyde, the cellular ratios and the biochemical components in the peripheral blood were altered, the ratio of mononuclear phagocytes decreased, and the ratios of lymphocytes and granulocytes elevated significantly in BALF. Meanwhile, crotonaldehyde altered the ratio of the T-lymphocyte subsets, and the phagocytic rates and indices of AMs increased obviously. In conclusion, crotonaldehyde induces dysfunction of immune system in male Wistar rats.

The hydrothermal reactions of acetaldehyde using cubic CeO2 nanoparticles were performed on the assumption that repolymerisation of monolignin by aldehydes can be suppressed by catalytic oxidation in the presence of CeO2 during depolymerisation of lignin. The catalytic potential of cubic CeO2 nanoparticles was evaluated by comparing them with octahedral CeO2 via their structural, morphological, catalytic characterisation and in terms of catalytic reactivity. In the cubic CeO2 system, the conversion of acetaldehyde and the selectivity of acetic acid (oxidation of acetaldehyde) were higher than those in octahedral CeO2, while the selectivity of crotonaldehyde produced by aldol condensation was lower than that in octahedral CeO2. The overall reaction mechanism was also developed based on a kinetic study on the primary products of acetaldehyde using the first-rank Delplot method. According to its catalytic oxidation rate constant, cubic CeO2 has 3–5 times higher oxidative catalytic potential than octahedral CeO2, suggesting that the repolymerisation of monolignin by aldehydes can be effectively suppressed by cubic CeO2 nanocatalysts.

Various supported Ir/TiO2 catalysts were prepared using different Ir precursors (i.e., H2IrCl6, (NH4)2IrCl6 and Ir(acac)3) and tested for vapor phase selective hydrogenation of crotonaldehyde. The choice of Ir precursor significantly altered the Ir-TiOx interaction in the catalyst, which thus had essential influences on the geometric and electronic properties of the Ir species, reducibility, and surface acidity, and, consequently, their reaction behaviors. The Ir/TiO2-N catalyst using (NH4)2IrCl6 as the precursor gave the highest initial reaction rates and turnover frequencies of crotyl alcohol formation. Such high performance was ascribed to the high Ir dispersion and high surface concentration of Ir0 species, as well as a higher surface acidity, in the Ir/TiO2-N catalyst compared to its counterparts, indicating the synergistic roles of the Ir-TiOx interface in the reaction, as the interfacial sites were responsible for the adsorption/activation of H2 and the C=O bond in the crotonaldehyde molecule.

The authors studied Meerwein–Ponndorf–Verley (MPV) reduction of crotonaldehyde using batch and tubular flow reactors. Various ZrO2/SiO2 catalysts prepared from commercially available carriers and precursors were subjected to activity testing using autoclave batch reactors. To determine the degree of Zr dispersion in the ZrO2/SiO2 catalysts, X-ray photoelectron spectroscopy (XPS) measurements and the benzaldehyde-ammonia titration (BAT) method were carried out. The results suggested a positive correlation between Zr dispersion and crotonaldehyde conversion. Durability tests using tubular flow reactors were performed with the most suitable catalyst, which was selected through batch reactions and catalyst characterizations. Almost no degradation of the catalytic activity was observed over 2,200 h in a liquid-phase reaction, while catalyst durability was short in a gas-phase reaction. It was surmised that in the liquid-phase, 2-propanol (hydrogen donor) in the feed had dissolved the reaction byproducts to pur...

Size and shape selected anatase TiO2 (A-TiO2) nanocrystals that had either a truncated bipyramidal morphology exposing predominantly (101) facets, or a platelet morphology exposing a high fraction of (001) facets and ranging in size from 10 to 25 nm were used to study the influence of crystallite shape and size on the thermal and photocatalytic reactions of acetaldehyde on TiO2 using temperature-programmed desorption in ultra-high vacuum. The primary thermal reaction pathways on the bipyramidal and platelet nanocrystals were aldol condensation to produce crotonaldehyde and reductive coupling to butene. The platelet morphology, however, exhibited higher thermal activity, which was attributed to the higher fraction of exposed (001) facets. For both morphologies crystallite size was found to be important with smaller nanocrystals favoring butene and larger ones favoring crotonaldehyde. The dependence of the selectivity on crystallite size can be attributed to the populations of planar and edge sites exposed by the nanocrystals. The photocatalytic activity of the nanocrystals was also found to vary with size and shape with the platelets having higher activity for acetaldehyde photo-oxidation than the bipyramidal morphology. For both morphologies, photoactivity also increased as the size of the nanocrystals increased.

Acidic Cs salt of tungstophosphoric heteropoly acid, Cs2.5H0.5PW12O40 (CsPW), is excellent solid acid catalyst for liquid-phase cycloaddition reactions of biomass-based and easily available from essential oils monoterpenic compounds, such as limonene, α-terpineol, α-pinene, β-pinene and nerol, with aldehydes, including benzaldehyde, crotonaldehyde as well as biomass-derived cuminaldehyde and trans-cinnamaldehyde. The reactions give oxabicyclo[3.3.1]nonene compounds potentially useful for the fragrance and pharmaceutical industries in good to excellent yields. The process is environmentally benign and can be performed in biomass-derived solvent 2-methyltetrahydrofuran and eco-friendly “green” organic solvents such as dimethylcarbonate and diethylcarbonate under mild conditions at low catalyst loadings without leaching problems. The solid CsPW catalyst can be easily separated from the reaction media and low-boiling solvents can be removed by distillation. Silica-supported H3PW12O40 also demonstrated good performance in these reactions.

The process of lipid oxidation generates a diverse array of small aldehydes and carbonyl-containing compounds, which may occur in free form or esterified within phospholipids and cholesterol esters. These aldehydes mostly result from fragmentation of fatty acyl chains following radical oxidation, and the products can be subdivided into alkanals, alkenals (usually a,β-unsaturated), γ-substituted alkenals and bis-aldehydes. Isolevuglandins are non-fragmented di-carbonyl compounds derived from H2-isoprostanes, and oxidation of the ω-3-fatty acid docosahexenoic acid yield analogous 22 carbon neuroketals. Non-radical oxidation by hypochlorous acid can generate a-chlorofatty aldehydes from plasmenyl phospholipids. Most of these compounds are reactive and have generally been considered as toxic products of a deleterious process. The reactivity is especially high for the a,β-unsaturated alkenals, such as acrolein and crotonaldehyde, and for γ-substituted alkenals, of which 4-hydroxy-2-nonenal and 4-oxo-2-nonenal are best known. Nevertheless, in recent years several previously neglected aldehydes have been investigated and also found to have significant reactivity and biological effects; notable examples are 4-hydroxy-2-hexenal and 4-hydroxy-dodecadienal. This has led to substantial interest in the biological effects of all of these lipid oxidation products and their roles in disease, including proposals that HNE is a second messenger or signalling molecule. However, it is becoming clear that many of the effects elicited by these compounds relate to their propensity for forming adducts with nucleophilic groups on proteins, DNA and specific phospholipids. This emphasizes the need for good analytical methods, not just for free lipid oxidation products but also for the resulting adducts with biomolecules. The most informative methods are those utilizing HPLC separations and mass spectrometry, although analysis of the wide variety of possible adducts is very challenging. Nevertheless, evidence for the occurrence of lipid-derived aldehyde adducts in biological and clinical samples is building, and offers an exciting area of future research. [Review Article]

Combined application of kinetic measurements, SSITKA and deuterium tracing techniques allowed to elucidate the mechanism of the key steps of butadiene synthesis over silver promoted zirconia catalysts, including ethanol dehydrogenation, acetaldehyde aldol condensation, and crotonaldehyde reduction with ethanol, and to determine the rate-limiting step of the process. We show for the first time that butadiene synthesis involves two independent catalytic cycles: i) dehydrogenation of ethanol into acetaldehyde over metal sites, and ii) acetaldehyde/ethanol transformation into butadiene over Lewis acidic sites. The first cycle implies ethanol dehydrogenation into acetaldehyde via concerted cleavage of CH 2 and OH groups, followed by the fast desorption of the products formed into the gaseous phase. The second cycle starts with the activation of acetaldehyde over Lewis acid sites through enolization and its interaction with another acetaldehyde molecule from the gaseous phase via Eley-Rideal mechanism. The formed 3-hydroxybutanal further dehydrates into crotonaldehyde. The aldol condensation step was proposed to be rate-determining. Further transformation of crotonaldehyde proceeds through Langmuir-Hinshelwood mechanism, involving the interaction of crotonaldehyde with ethanol over a Lewis site via a six-member ring transition state. Subsequently, crotyl alcohol dehydrates into butadiene, and acetaldehyde adsorbed over Lewis sites initiates the next catalytic cycle. The proposed molecular-level mechanism gives insights into rational design of efficient catalysts for the ethanol conversion into butadiene.

A series of MoOx-promoted Ir/BN catalysts were tested for liquid phase selective hydrogenation of crotonaldehyde. The MoOx-promotion could significantly improve the reactivity up to 5-fold. Such improvement was mainly due to the formation of Ir-MoOx interfacial sites in the promoted catalyst, which accelerated the adsorption and activation of crotonaldehyde molecule as evidenced by a much lower activation energy (18.9 kJ mol−1 on the 0.3Mo-3Ir/BN versus 38.4 kJ mol−1 on the 3Ir/BN). The kinetic results revealed negative reaction order of crotonaldehyde (up to -1.1) and high reaction order of H2 (up to 2.2), indicating the high coverage of crotonaldehyde on the catalyst surface suppressed the adsorption of H2 due to its low solubility in the liquid phase. Therefore, the adsorption and activation of H2 on the catalyst might be the rate determining step. However, the preferred adsorption of crotonaldehyde on the Ir-MoOx interface alleviated the suppression of H2 adsorption, which was another reason for the higher activity.