Alder Mechanism Research Articles

Catalytic pyrolysis of municipal plastic waste over nano MIL-53 (Cu) derived @ zeolite Y for gasoline, jet fuel, and diesel range fuel production

In this study, municipal polymer wastes that were no longer recyclable and were previously buried underground according to the usual municipal waste management program were converted to liquid fuel by catalytic pyrolysis technique. In the first step, zeolite Y catalyst was used to improve the quality of liquid fuel. In the second step, MIL-53 (Cu) was incorporated onto zeolite and pyrolyzed in nitrogen in the atmosphere. The analysis shows that clusters of carbon nanopores with a copper core, and its oxides were deposited on the zeolite. For both types of catalysts, the crystallization time of zeolite was investigated, and it was found that this leads to the synthesis of samples with different percentages of crystallinity. For each test, the liquid fuel produced was divided into four cuts: gasoline, jet fuel, diesel, and wax. The test results in a fixed bed reactor for every twelve samples of catalyst and their effect on the efficiency of different sections of liquid fuel show a significant improvement in the desired product. The properties and morphology of the catalysts were investigated. It was found that at 400 °C and a crystallization time of 18 h for support with 76.62% crystallinity, gasoline production efficiency will be 37.00%. At 500 °C and low crystallinity, the tendency of reaction to produce jet fuel with a maximum efficiency of 48.64%. Furthermore, the physical properties of each cut of liquid fuel and their comparison with the reported values indicating the appropriate qualities of the produced fuel were evaluated. In the optimal state, the octane number of the produced gasoline is 93.5 and its pour point is 41 °C. Also, a jet fuel with an octane number of 43.2 and a flashpoint of 69 °C has been obtained. In the case of diesel, the octane number and its viscosity have reached 46 and 2.407 cp, respectively. Examining the results obtained from GC MS, it was found that the zeolite catalyst modified by Diels Alder mechanism and branching will improve the quality of liquid fuel and on the other hand, will cause the cracking of the wax compounds and reduce their percentage in product analysis.

From Biomass to Green Aromatics: Direct Upgrading of Furfural–Ethanol Mixtures

This work demonstrates that the production of aromatics by gas-phase Diels–Alder condensation of biomass platform molecules (furfural and ethanol) is feasible in the same terms as using chemicals from a petrochemical origin or more complex preparation procedures (as ethylene or furan). Thus, a double benefit for the environment is obtained since a waste biomass is proposed as the raw material to produce industrial high-value products by a renewable route. Experimental results with acid zeolites (ZSM-5) at 500 °C reveal total conversion and aromatic selectivities >42% (mono and bicyclic ones), with a similar catalytic stability to the most widely studied furan–ethylene system, a clear consequence that the furfural oligomerization is prevented by the prevalence of a Diels–Alder mechanism.

Efficient one-pot synthesis of the unexpected fused multicyclic iminosugars by an aza-Diels–Alder mechanism

A simple and efficient one-pot protocol has been developed by an aza-Diels–Alder mechanism for the stereoselective synthesis of novel fused multicyclic iminosugars with structural diversity.

Experimental Study of Pyrolytic Oils from Used Tires: Impact of Secondary Reactions on Liquid Composition

Thermal pyrolysis of scrap truck tires was carried out in a semi-batch fixed reactor at 500 °C. The pyrolysis mechanism and product yields were investigated in this study. We aimed to elucidate the effects of key parameters including the evolution of intern reactor temperature, volatile products residence time and reactor free volume on the quantity and quality of liquid products, which has been rarely discussed in the literature. Upon use of carrier gas, the pyrolysis liquid yield was improved considerably, showing a decreased extent for secondary cracking of primary volatiles however bigger empty volume and longer residence time promote its extending. High value-added products such as d-limonene, p-cymene, and BTX were identified in the pyrolysis liquid. Subsequently, the formation mechanisms of these compounds of interest via Diels–Alder mechanism involving cyclization, aromatization, and dehydrogenation reactions were characterized. However, the most abundant product was d-limonene, which had been competed with the p-cymene regardless of the degradation pathway and secondary reactions extent.

A thermoresponsive crosslinker for reversible micelle stabilization

Herein we report a thermoresponsive crosslinker that can be utilized to stabilize the surface of micelles through “click” reaction and to trigger the disassembly via retro Diels Alder (rDA) mechanism.

Synthesis of Coumarins via [4+2] Cyclization of Siloxy Alkynes and Salicylaldehydes

AbstractA new approach for the synthesis of coumarins from siloxy alkynes and salicylaldehydes is disclosed. Unlike the previous benzannulation reactions of siloxy alkynes that all proceed by electron-inversed Diels–Alder mechanism, this process represents a new [4+2] cyclization. In the presence of the superior HNTf2 catalyst, a wide range of coumarins were efficiently synthesized. This process was also extended to the synthesis of 2-quinolones. The polarized electron-rich triple bond might react sequentially with the aldehyde and hydroxy group by polarity switching in the stepwise formation of the C–C and C–O bonds. Control experiments provided insights into the mechanistic understanding.

Understanding the Photo- and Electro-Carboxylation of o-Methylbenzophenone with Carbon Dioxide

The lack of understanding of the radical reaction mechanism of Carbon dioxide (CO2) in photo- and electro-catalysis results in the development of such applications far behind the traditional synthesis methods. Using methylbenzophenone as the model, we clarify and compare the photo-enolization/Diels−Alder (PEDA) mechanism for photo-carboxylation and the two-step single-electron reduction pathway for electro-carboxylation with CO2 through careful control experiments. The regioselective carboxylation products, o-acylphenylacetic acid and α-hydroxycarboxylic acid are obtained, respectively, in photo- and electro-chemistry systems. On the basis of understanding the mechanism, a one-pot step-by-step dicarboxylation of o-methylbenzophenone is designed and conducted. Both the experimental results and related density functional theory (DFT) calculation verify the feasibility of the possible pathway in which electro-carboxylation is conducted right after photo-carboxylation in one vessel. This synthesis approach may provide a mild, eco-friendly strategy for the production of polycarboxylic acids in industry.

Thermal degradation of α-pinene using a Py–GC/MS

Mediterranean forest fires may be accelerated, partly due to biogenic volatile organic compounds produced by vegetation, mainly monoterpenes largely represented by α-pinene. To model the propagation of biomass combustion, it is necessary to study the flammability of the produced gas mixture, and thus, necessary to identify the emitted volatile compounds. However, thermal degradation of monoterpenes is rarely experimented above 300 °C, whereas forest fires reach higher temperatures. Thus, in this work, we experimented a 2-min pyrolysis of α-pinene at temperatures from 300 to 800 °C using a Py–GC/MS device. Less than 1% of pyrolysis products were detected at 300 and 400 °C. The pyrolysis products increased then from 14 compounds at 500 °C to 31 compounds at 800 °C. Degradation of α-pinene started with its isomerization at 500 °C. At 800 °C, alkenes detected increased as well as aromatics produced through the Diels–Alder mechanism. These results are consistent with the literature on thermal degradation of α- and β-pinene presented in our article.

Red-oils in ethylene plants: formation mechanisms, structure and emulsifying properties

In most ethylene plants, the caustic sections suffer from red-oils formation which results from the polyaldol condensation of some oxygenate species in basic media. These red-oils lead to solid material deposition which is generically referred to as fouling and which can cause severe energy losses or operational issues. This specific red-oil fouling can be successfully mitigated by regularly washing the caustic scrubber with a hydrocarbon washing stream which acts as a solvent. However, such washing streams can be further rerouted to the quench water system, increasing the risk of emulsion formation due to its amphiphilic components, i.e., red-oils, compromising the safe operation of the whole plant. The complexity of red-oil structures renders its analysis and characterization challenging. Consequently, there has been no study showing the effect of the type of hydrocarbon wash on the red-oils structure and its potential emulsifying properties. This study describes an in-house developed analytical technique based on UPLC-High resolution QTOF which allows characterizing hydrocarbon streams with complex mixtures of oxygenated species. This method has been successfully applied to monitor red-oil structures during a plant trial where Pyrolysis Gasoline and Toluene-Xylene hydrocarbon washes were successively applied. The data revealed that reactive compounds from the Pyrolysis Gasoline react with the polyaldol species, likely through a Diels–Alder mechanism, thus increasing the diene adduct concentration in the red-oil. It was further found that toluene-xylene washes hindered the emulsifying properties of the red-oils more effectively than Pyrolysis Gasoline washes, in that they could best inhibit the formation of polyaldols adducts.

Hyperjapones F–I, terpenoid polymethylated acylphloroglucinols from Hypericum japonicum

Hyperjapones F–I (1–4), novel terpenoid polymethylated acylphloroglucinols (TPAPs) with three unusual carbon skeletons, were characterized from Hypericum japonicum. Their structures were determined on the basis of comprehensive MS and NMR spectroscopic data. Compounds 1 and 2 could be formed by hybridization of a trimethylated acylphloroglucinol core with a sabinene-type monoterpenoid unit, while compounds 3 and 4 contained a pinene-type monoterpenoid unit in their molecules. Biosynthetically, a key hetero-Diels–Alder mechanism was proposed for the generation of compounds 1–4.

Self-healing polymers: evaluation of self-healing process via non-destructive techniques

The scope of this study is the real-time monitoring and evaluation of the healing process using novel testing procedures and non-destructive evaluation techniques. In this work, the healing approach that has been followed is that of the intrinsic Diels–Alder (DA) and retro-DA mechanism. Two polymers were used as adhesives in single lap-joint specimens that were subjected to static tensile loading. The healed specimens were subjected to the same testing procedure as the one before the first failure and the healing efficiency was assessed by the correlation of the experimental results prior and after healing. Acoustic emission and infrared thermography were employed with the destructive tests so as to monitor changes in the acoustic and the thermal profile between the virgin and the ‘healed’ specimen.

Reversible oligomerization of 3-aryl-2-cyanothioacrylamides via [2s + 4s] cycloaddition to substituted 3,4-dihydro-2H-thiopyrans

Novel difunctional monomers are synthesized which are able to dimerize as well as oligomerize via the hetero-Diels–Alder (HDA) mechanism. These monomers are based on 3-aryl-2-cyanothioacrylamides, which are used as functional units for the HDA reaction to form 3,4-dihydro-2H-thiopyrans. Different substituents of the aromatic ring are utilized to shift the equilibrium to the dimeric or oligomeric species. The HDA reaction is reversible and can be influenced by the temperature as well as the concentration. In contrast, the N,N-dimethylthioacrylamide analogues do not dimerize or the dimerization is not reversible. The most promising compound is furthermore investigated in detail by 1H NMR spectroscopy to elucidate the dimerization kinetics. In addition, a difunctional molecule is able to oligomerize reversibly, as confirmed by means of 1H NMR, size exclusion chromatography (SEC), and ESI MS measurements. A respective alcohol is employed as initiator for the ring-opening polymerization of l-lactide resulting in an end-functional polymer that undergoes reversible dimerization as confirmed by SEC measurements.

Density Functional Theory (DFT) study on the pyrolysis of cellulose: The pyran ring breaking mechanism

Pyran ring breaking is a key step for cellulose pyrolysis to produce small molecular products. Cellotriose was employed as the model compound of cellulose to explore the mechanism of pyran ring breaking based on Density Functional Theory (DFT). Four kinds of reaction mechanisms were studied: (1) directly breaking mechanism, (2) Retro–Diels–Alder mechanism, (3) C6OH assisted pinacol ring cleavage mechanism and (4) Retro–Aldol mechanism. The calculated results showed that pyran ring break via Retro–Aldol mechanism (with C3O formed) was kinetically favored over Retro–Diels–Alder mechanism (with C3C4 bond formed), followed by C6OH assisted pinacol ring cleavage mechanism, 2′+2′+2′ and 2+2+2 mechanism. Activation energies for both of the two-step mechanisms, Retro–Diels–Alder and Retro–Aldol, varied on the positions of CC bond and CO group formed. The results provided a better understanding on pyran ring breaking mechanism during cellulose pyrolysis.

The interaction of maleic anhydride and derivatives of long-chain olefins

The possibility of interaction between maleic anhydride and derivatives of long-chain olefins, where the double bond is in the depth of the hydrocarbon chain was considered in the paper. Available and cheap natural raw material - oleic acid is taken as such olefin. It was assumed that the nucleophilic addition of oleic acid to maleic anhydride by the double bond with retaining the molecular structures may proceed by the Alder mechanism under appropriate conditions: reaction temperature of more than 150ºC or in the presence of Lewis acid-type catalysts. Series of syntheses in melts and organic solvents: trihloretilene, perhloretilene and o-xylene were conducted. Reaction temperature modes were from 130ºC (boiling temperature of solvents) to 210ºC. As a result, three types of products were obtained: white crystal sediment, colorless plates and viscous filtrate from light brown to dark brown. The products were separated by different solvents, identified by the melting point and the acid number. The target reaction products were colorless plate crystals with the acid number of 369.6 mg KOH/g and the melting point of 140-142ºC. Additional analyses (IR and NMR spectroscopy) have shown that the plates are the product of addition of oleic acid residue to maleic anhydride by the double bond. The resulting substance possesses surfactant properties. Thus, during studies, it was proved that the addition of olefins with the double bond in the center of a hydrocarbon radical with structure retaining to maleic anhydride is impossible in conditions, specified in the literature.

Zinc maleate and calcium stearate as a complex thermal stabilizer for poly(vinyl chloride)

Zinc maleate (ZnMA) and calcium maleate (CaMA) were synthesized by reaction of maleic acid with the corresponding metal oxides and were characterized by X‐ray diffraction, thermal analysis, and Fourier‐transform infrared (FTIR) spectroscopy. The thermal stabilizing effects of ZnMA and CaMA on poly(vinyl chloride) (PVC) were investigated at 180°C in air by a static stability test. The stabilization mechanism of ZnMA and the synergism of ZnMA/CaSt2 (St = stearate) were also studied by UV‐visible and FTIR spectroscopies, as well as a thermal stability test. The PVC with the ZnMA stabilizer exhibited good thermal and color stability caused by the ability of ZnMA to replace the labile chlorine atoms in PVC chains, absorb hydrogen chloride, and react with the polyene intermediates via a Diels–Alder mechanism. The gel content of the PVC/ZnMA samples reached 31% after 2 min of heating and 44% after 10 min, thereby indicating that crosslinking could easily occur with ZnMA, probably owing to catalysis by Zn species. The static and dynamic stability results showed that the synergistic effect of the ZnMA/CaSt2 stabilizer was greater than that of ZnSt2/CaSt2. J. VINYL ADDIT. TECHNOL., 20:1–9, 2014. © 2014 Society of Plastics Engineers

ChemInform Abstract: An Efficient Method for the Synthesis of Indolo[3,2‐c]quinoline Derivatives Catalyzed by Iodine.

AbstractThe reaction proceeds presumably through an imino Diels—Alder mechanism.

On the Way to Biofuels from Furan: Discriminating Diels–Alder and Ring-Opening Mechanisms

We performed kinetics experiments and quantum calculations to investigate the reaction of furan to benzofuran catalyzed by the acidic zeolite HZSM-5, which is a key step in the conversion of biomass to biofuels through catalytic fast pyrolysis. The reaction was studied experimentally by placing the zeolite in contact with solution-phase furan and detecting the benzofuran product over the temperature range 270–300 °C, yielding an apparent activation energy of 72 ± 3 kJ/mol. The reaction was modeled in gas and zeolite phases to determine the energetics of the following two competing pathways: a Diels–Alder mechanism often assumed in interpretations of experimental data and a ring-opening pathway predicted by the chemoinformatic software RING. Quantum calculations on the zeolite/guest system were performed using the ONIOM embedded cluster approach. We computed the energetics of reactants, products, and all intermediate steps. Locating relevant transition states fell beyond our computational resources because...

Quantitative and qualitative analysis of high molecular compounds in vegetable oils formed under high temperatures in the absence of oxygen

Conditions of deodorization/physical refining of sunflower oil were simulated by high temperature heating in laboratory at 240, 250, and 260 °C. Oxygen atmosphere was excluded by argon atmosphere. Influence of temperature, initial oxidation of incoming oil (peroxide value 2–30 mmol ½ O2/kg) on geometrical, positional isomerization, and polymerization was measured. The level of initial oxidation of the oil has a significant influence on rate of isomerization, polymerization, and duration of induction period of polymerization reactions. Induction period of polymerization is dependent linearly on temperature at constant hydroperoxide content and is extended with decreasing temperature and lower peroxide value of oil. Significant conjugation took place with geometrical isomerization and resulted in all-trans diene formation. All-trans dienes are incoming reactants for polymerization according to the Diels–Alder mechanism. Suggested “propagation” phase of polymerization took place later. Induction period was observed only in the case of polymerization reactions of triacylglycerols. This is the confirmation of the hypothesis that the cis/trans isomerization, positional isomerization, and polymerization are consecutive reactions in ascending order. Identification of molecular peaks and confirmation of fragments were possible by connecting HPSEC with APCI-MS. Dimers of triacylglycerols (TAG) dominated in studied system. Remaining compounds may have been formed from di-, monoacylglycerols, and other minor constituents of sunflower oil.

Decomposition mechanisms and dynamics of N6: Bond orders and partial charges along classical trajectories

Ab initio molecular dynamics (AIMD) simulations using B3LYP combined with Natural Bond Orbitals (NBO) analysis of partial charges and bond orders along trajectories are used to study the decomposition dynamics of three theoretically known isomers of N6. The results show that significant changes in bonding and in charge distribution occur in intervals of about 10fs during the process. The decomposition of one isomer proceeds in two steps through a retro Diels Alder (RDA) mechanism while the other isomers decompose to 3N2 directly. It is suggested that this approach may provide useful insights into reactions in general.

Evidence Contrary to the Accepted Diels–Alder Mechanism in the Thermal Modification of Vegetable Oil

AbstractA fatty methyl ester product has been made using two routes. Soybean oil was thermally polymerized anaerobically without a catalyst at 330 °C and the material was then transesterified using base catalyst and methanol. Alternatively, a similar product can be obtained by heating methyl linoleate to the same temperature in a pressure reactor. The product structure was studied by NMR spectroscopy, gel permeation chromatography and mass spectrometry. It is a dimeric product which does not contain substituted cyclohexane structures. This evidence shows that the Diels–Alder reaction has not occurred under these conditions. This is in contradiction to many literature reports, but in agreement with a neglected paper from 1971. This correction has implications in both biodiesel and industrial oil products.