Absence Of Catalyst Research Articles

A green, catalyst-free synthesis of pyrazolopyranopyrimidines in polyethylene glycol as a biodegradable medium at ambient temperature.

A facile, efficient and environmentally safe strategy for the synthesis of pyrazolopyranopyrimidines via one-pot, four-component reaction of hydrazine hydrate, barbituric acid, ethyl acetoacetate, and aromatic aldehydes in polyethylene glycol (PEG) as a safe solvent in the absence of catalyst at ambient temperature has been described. The advantages of the present protocol, such as simplicity, mild conditions, high yields of products, straightforward workup procedure, a green and biodegradable reaction medium, make this new process an attractive to current methodologies.

Catalyst-Free Aromatic Radiofluorination via Oxidized Iodoarene Precursors.

Oxidized iodoarenes (OIAs), prepared via mCPBA-mediated oxidation, have been demonstrated as versatile precursors for the synthesis of [18F]fluoroarenes in the absence of catalysts. OIAs have been identified as intermediates in single-pot syntheses of iodonium salts and ylides but have never been recognized as radiofluorination precursors. Here, the isolated OIAs were used without any catalysts to produce functionalized [18F]fluoroarenes, regardless of the electronic nature of the arenes. This method was also applied to the production of radiolabeling synthons for use as aromatic 18F-labeled building blocks.

Cycloaliphatic epoxy resin cured with anhydride in the absence of catalyst

Understanding mechanisms of cycloaliphatic epoxy resin curing with anhydride is important for the preparation of new thermosetting polymer materials. In this paper, the curing of commercial epoxy monomer 4-epoxycyclohexylmethyl-3,4-epoxycyclohexane-carboxylate ERL-4221 with 4-methylhexahydrophthalic anhydride in the absence of catalyst was studied by two complementary methods: Fourier-transform infrared spectroscopy and differential scanning calorimetry. Different reaction pathways were examined, and the most probable curing mechanism was proposed. It was shown that the synthesized polymer network possesses glass transition temperature of 222 °C, which is among the highest values for cured epoxy resin obtained so far.

Thermally healable PTMG-based polyurethane elastomer with robust mechanical properties and high healing efficiency

Polymers can repair their own mechanical damage and prolong their service life by self-healing, so it has received extensive attention in recent years. But the self-healing polymers through the exchangeable dynamic covalent bonds have relatively poor mechanical performance. The polyurethanes were prepared with poly(tetramethylene ether) glycol (PTMG) as soft segments and 4,4′-diphenylmethane diisocyanate, 1,4-butanediol as hard segments, in the absence of catalyst. The change of carbamate and hydrogen bonding in polyurethane was studied by variable-temperature infrared spectroscopy. The results showed that there were exchangeable dynamic equilibria of above two. The effect of molecular weight of soft segments on the healing efficiency was also discussed. The results showed that the higher molecular weight of soft segments enhanced the microphase separation of polyurethane. It not only provided the high mechanical strength, but also facilitated the reversible exchange of carbamate and hydrogen bonding in the region of the fracture, thus promoting the self-healing effect. The study will provide a healing method for the PTMG-based polyurethane elastomer of scale production.

Preparation and properties of biobased autocatalytic polyols and their polyurethane foams

In the present work, we developed a green and more efficient method to prepare biobased polyurethane (PU) foams under catalyst-free condition. Firstly, novel organosilicon grafting cardanol-based autocatalytic polyols (SCAPs) with low viscosity were synthesized through the ring opening of cardanol glycidyl ether (CGE) and the hydrosilation of unsaturated alkyl chain with heptamethyltrisiloxane (HMTS). Subsequently, PU foams were synthesized by SCAPs in absence of catalyst. The structure and properties of the PU foams were evaluated and discussed. In addition, the thermal degradation mechanism of PU foams was investigated by using a thermogravimetric analysis instrument coupled with fourier transform infrared and mass spectrometer (TG-FTIR-MS). The results showed that the PU foams had high compression strength and thermo-stability.

Intrinsic reaction kinetics and mechanism for the reverse disproportionation reaction to methyl phenyl carbonate

The extensive researches about the thermodynamic and intrinsic kinetic of disproportionation reaction of methyl phenyl carbonate to diphenyl carbonate were investigated independently with dibutyltin oxide as a catalyst, at a temperature range of 433.15–473.15 K and different catalyst concentrations in a stirred batch reactor, for a deeper knowledge of reaction essence. This reaction was found endothermic and showed hardly any reaction in the absence of catalyst which indicate an inferior kinetic characteristics. The reaction rate increases with an increasing catalyst concentration until the concentration went to 8.08 × 10−4 mol mol−1. A possible mechanism involving an in-situ Sn-based species was proposed and finally verified by a good agreement between experimental and simulated data. The available Sn-based species was then demonstrated to play a real catalytic role by extra experiments. All results can also be further utilized to explore the essence of transesterification reaction network.

Synthesis of acetyl-substituted tetrahydrobenzofuran and tetrahydronaphthalene via cascade Diels–Alder cycloadditions and dehydration of renewable furanics

A acetyl-substituted tetrahydrobenzofuran, 1-(4,5,6,7-tetrahydro-1-benzofuran-6-yl)ethenone (6-AcBZOF) and a acetyl-substituted tetrahydronaphthalene, 1-(1,2,3,4-tetrahydronaphthalen-2-yl)ethenone (2-AcTNAPH) were conveniently synthesized from renewable furanics by cascade Diels–Alder and dehydration reactions. The Diels-Alder cycloaddition of 4-(2-Furyl)-3-buten-2-one (4-FB) with ethylene followed by dehydration in presence of zeolites was studied. Sn grafted Beta zeolite exhibited high performance with 69% yield of 2-AcTNAPH starting from 4-FB. In this reaction, 6-AcBZOF was produced as intermediate. Further, it was found that this acetyl-substituted tetrahydrobenzofuran could be formed in high yield, 86%, in the absence of catalyst. For the first time in the literature, we report the synthesis of a renewable acetyl-substituted tetrahydronaphthalene in high yield from biomass-derived 4-FB in a tandem approach. While a acetyl-substituted tetrahydrobenzofuran could be prepared without a catalyst, catalyst was essential for the successful synthesis of the acetyl-substituted tetrahydronaphthalene.

A Convenient Method of Synthesis of 3-(4, 5-diphenyl-1H imidazole2-yl) From Benzil in Absence of Catalyst


 
 
 In this study new imidazoles derivatives were synthesized.The first stage involved preparation of 3-(4,5-diphenyl-1Himidazole-2-yl)phenol(AA1)by reacting Benzil with Substituted benzaldehyde in presence of sodium cyanide catalyst .The second stage involved the synthesis of Synthesis of 3-(4, 5 - diphenyl-1H imidazole-2-yl) sulfonamide(AA2) using TEA in glacial acetic acid. Finally the compound were synthesized using the three component system (Compound AA2), Substituted benzaldehyde and ammonium acetate. The structure of all compounds were confirmed by elemental analysis ,NMR and IR data and by melting point. In conclusion this method give some advantages such as good yield, simple procedure , low cost of chemicals and easy work up.
 
 

Synthesis of New 5-amino-7-(aryl)-1,2,3,7-tetrahydro-8-nitroimidazo[1,2-a]pyridine- 6-carboxamide and 6-amino-2,3,4,8-tetrahydro-9-nitro-8-(aryl)-1H-pyrido[1,2- a]pyrimidine-7-carboxamide Derivatives

Aim and Objectives: Development of simple synthetic routes for widely used organic compounds from readily available reagents is one of the major tasks in organic chemistry. Therefore, new approaches for increasing the molecular diversity of simple starting materials, are needed. Herein, an efficient synthesis of imidazo[1,2-a]pyridine, pyrido[1,2-a]pyrimidine and pyrido[1,2-a][1,3]diazepine derivatives is described. Materials and Methods: A one-pot, multi-component reaction of nitro ketene aminal derived from the addition of various 1,n-diamines to 1,1-bis(methylthio)-2-nitroethene with cyanoacetamide and aromatic aldehydes is described. The reactions are completed within 2-5 h, in ethanol at reflux, in good to high yields (70-93%). The structures of products were deduced from their IR, mass, 1H NMR, and 13C NMR spectra. Results: Optimal reaction conditions for the synthesis of products were obtained, when ethanol was used as the solvent at reflux. This protocol involves Michael reaction, imine–enamine tautomerization, and cyclization sequences. Conclusion: This work represents an efficient synthesis of imidazo[1,2-a]pyridine, pyrido[1,2-a]pyrimidine and pyrido[1,2-a][1,3]diazepine derivatives via a one-pot, multi-component reaction. The advantages of this protocol are mild conditions, easy accessibility of reactants, absence of catalyst, high atom economy, simple work-up and purification process with no chromatographic technique.

Programming dynamic imine bond into elastomer/graphene composite toward mechanically strong, malleable, and multi-stimuli responsive vitrimer

A combination of malleability, supramechanical properties and multi-stimuli response into catalyst-free and commercially available polymer-based networks is particularly attractive to extend the realm of thermally malleable polymers. Toward this goal, herein we demonstrated a paradigm by introducing dynamic imine bonds into styrene-butadiene rubber (SBR)/graphene composites. SBR was firstly grafted with aldehyde groups and then cross-linked with p-phenylene diamine and it-modified graphene through imine condensation between aldehyde and amino groups. The crosslinked networks were able to alter their topologies via imine exchange reactions in both the bulk network and SBR-graphene interphase in the absence of catalyst, enabling them to be recycled and reshaped under heating or IR irradiation. The incorporation of graphene led to spectacular improvements on the mechanical properties of vitrimer composites, and the mechanical properties could be tuned through solid-state drawing. The relationships between morphological structure and dynamic properties as well as mechanical properties of the vitrimer composites were addressed.

Hydrothermal reaction of tryptophan over Ni-based bimetallic catalysts

The major products from hydrothermal reactions of tryptophan at 350 and 400 °C in the absence of catalyst were indole and methyl indoles, indicating simultaneous deoxygenation and deamination. In the presence of carbon-supported Ni and NiM catalysts (M = Ru, Cu, Pd, Pt) primary aromatic amines also appeared, via cleavage of the heterocyclic ring of the indoles. Ni and NiCu catalysts have the lowest selectivity for the formation of this family of compounds, while NiRu had the highest selectivity. Catalysts containing noble metals also produced monosubstituted alkylaromatics, due to the deamination of the aromatic amines, with the NiPt catalyst providing the highest molar yield (∼7%). We propose catalytic and non-catalytic hydrothermal reaction pathways for tryptophan based on the observed product distributions. The bimetallic particles were smaller than the pure Ni particles and the surfaces of NiRu and NiPd particles were enriched in Ni, relative to the nominal bulk composition.

Facile and rapid synthesis of piperidinium-6-amino-4-aryl-3, 5-dicyano-1,4-dihydropyridine-2-thiolate

ABSTRACTA fast and convenient protocol for the synthesis of a new class of piperidin-1-ium 6-amino-4-aryl-3,5-dicyano-1,4-dihydropyridine-2-thiolate (piperidinium salt) derivatives is developed by the one-pot, three-component reactions of cyanothioacetamide, aromatic aldehydes and piperidine in dichloromethane at room temperature. The features such as operational simplicity, mild conditions, absence of catalyst, high yields in short reaction times, simple purification process with no chromatographic technique make the protocol highly attractive.

Catalytic pyrolysis of waste polypropylene using Ahoko kaolin from Nigeria

The aim of this study is to convert polypropylene waste into usable liquid fuel via pyrolysis technique using kaolin as a low-cost catalyst. Waste polypropylene was thermally and catalytically degraded in a chemical vapour deposition (CVD) horizontal glass reactor at a temperature of 450 °C, residence time of 30 min, and heating rate of 30 °C/min. The kaolin clay was characterized by XRF analysis while the ultimate and proximate analysis of the polypropylene feed carried out gave combustible materials content of 93.77 wt%, fixed carbon of 1.62 wt%, calorific value of 45.20 MJ/kg and elemental composition with carbon (83.65%), hydrogen (14.27%), oxygen (0.15%), sulphur (0.1%), chlorine (1.16%), and nitrogen (0.67%). Thermal cracking was carried out in the absence of catalyst and the process gave a yield of liquid, gaseous, and solid products of 67.48, 8.85, and 23.67 wt%, respectively. Furthermore, kaolin clay was employed as a catalyst in catalytic pyrolysis of the same feedstock for catalyst-to-plastic ratio of 1:1, 1:2, 1:3, and 1:4 at the same operating parameters as in thermal cracking. Optimum yield was obtained at a catalyst-to-plastic ratio of 1:3 with a yield of 79.85, 1.48, and 18.67 wt% for liquid, gaseous, and solid products, respectively. The liquid products obtained for both thermal and catalytic cracking at optimum conditions were characterized for their suitability as fuel. The properties determined were density, viscosity, flash point, fire point, pour point, and calorific value. The results suggest that catalytic pyrolysis produced liquid products, whose properties are comparable to conventional fuels (gasoline and diesel oil) than that produced through thermal pyrolysis. FTIR analysis of the liquid product from catalytic pyrolysis also shows that it contains hydrocarbons with different functional groups such as aromatics, olefins, carbonyl, amines, sulphides, and hydroxyl.

Morphology Control Studies of MnTiO3 Nanostructures with Exposed {0001} Facets as a High-Performance Catalyst for Water Purification.

Novel single-crystal hexagonal MnTiO3 nanosheets with exposed {0001} facets have been synthesized via a simple one-pot hydrothermal method using NaOH as a mineralizer and tetraethylammonium hydroxide (TEAH) as a morphology controller. The intermediate morphologies of MnTiO3 nanostructures such as nanoparticles, nanowires, nanorods, and nanodiscs are trapped kinetically by adjusting the synthesis conditions. This approach enables us to elucidate the growth mechanisms of MnTiO3 nanosheets based on the tetraethylammonium cation adsorption abilities on different MnTiO3 crystal facets combined with density functional theory calculations. Dissolution and recrystallization processes are involved during the MnTiO3 crystallization. The surface-controlled MnTiO3 has been found to be effective as a catalyst for ozonation in the degradation of 4-chlorophenol (4-CP). Within typical experimental conditions (catalyst dosage = 0.3 g L-1, [4-CP]0 = 50 mg L-1, [O3] = 20 mg L-1, gas flow = 0.1 L min-1, pH 6.8, and T = 293 K), the total organic carbon (TOC) removal efficiency of 4-CP in catalytic ozonation with well-structured MnTiO3 (MnTiO3-180-10 sample) was 76.3% after 60 min, compared with only 22.1 and 38.5% TOC removal in the absence of catalyst and with uncontrolled MnTiO3 (MnTiO3-no TEAH sample), respectively. Benefiting from the high exposure percentage of {0001} facet, mixed-valences of manganese, surface hydroxyl groups, and the enrichment Lewis acid sites provided by Mn and Ti, the morphology-controlled MnTiO3 nanosheets can be applied as heterogeneous catalytic ozonation catalysts which exhibit excellent pollutant degradation. We anticipate that MnTiO3 can be a promising candidate material for the application in remediation of organic pollutants in water.

Influence of Alkyne and Azide Substituents on the Choice of the Reaction Mechanism of the Cu+-Catalyzed Addition of Azides to Iodoalkynes.

The cycloaddition of azides to iodoalkynes is strongly enhanced by some Cu+-complexes. We have studied computationally six reaction pathways for the cycloaddition of 24 combinations of azide and iodoalkyne to identify the dominant pathways and the influence of reactant structure on the evolution of the reaction. Two pathways were found to be operating for distinct sets of reactants. In the first pathway, initial complexation of iodoalkyne by Cu+ is followed by the binding of the azide to the metal through its substituted nitrogen atom, followed by attack of the nonhalogenated alkyne carbon by the terminal nitrogen atom. This pathway is generally followed by aromatic or electron-deficient azides, unless the iodoalkyne bears an electron-withdrawing group. The second pathway is a single-step mechanism similar (apart from the alkyne bond weakening caused by complexation) to that observed in the absence of catalyst. Electron-deficient iodoalkynes and methyl azides strongly prefer this mechanism, regardless of the identity of the reaction partners. The catalytic gain obtained through the use of Cu+ depends only partially on its direct effect on the energy of the transition state (relative to that of the infinitely separated reactants) and may be lost if the iodoalkyne itself strongly interacts with the catalyst through the formation of too strong a π-complex.

Fabrication of Sb2O3/PbO photocatalyst for the UV/PMS assisted degradation of carbamazepine from synthetic wastewater

Photocatalytic degradation of carbamazepine (CBZ) was investigated by hydrothermally synthesized antimony trioxide (Sb2O3)/lead oxide (PbO) photocatalyst. The photocatalyst synthesized with different ratio of Sb2O3 and PbO viz. 1:1, 2:1, 3:1, 1:2, and 1:3. Photocatalyst with 3:1 ratio of Sb2O3 and PbO showed the best photocatalytic activity towards CBZ. Transmission electron microscopy (TEM) analysis suggested that the particle size increased by increasing PbO ratio in the catalyst. It was observed that Sb2O3 synthesis with PbO showed less band gap energy in comparison to Sb2O3. The Brunauer–Emmer–Teller (BET) surface area of the Sb2O3/PbO (3:1) was determined to be 4.78 m2 g−1. In absence of catalyst, very low degradation of CBZ was achieved, while significant enhancement in CBZ degradation was observed in presence of the synthesized catalyst. CBZ degradation followed the pseudo first-order kinetics with rate constant of 0.016 min−1. Increased degradation rate was recorded when peroxymonosulfate (PMS) was used with UV/Sb2O3/PbO. Active species trapping experiment revealed that in CBZ degradation, O2– radical produced by synthesized catalysts played a major role. In presence of PMS, generation of SO4-∙ radical enhanced the catalytic activity of synthesized catalyst.

On the Mechanism of the Reactivity of 1,3-Dialkylimidazolium Salts under Basic to Acidic Conditions: A Combined Kinetic and Computational Study.

Comprehensive spectroscopic kinetic studies illustrate an alternative mechanism for the traditional free-carbene intermediated H/D exchange reaction of 1,3-dialkylimidazolium salts under neutral (D2 O) and acidic conditions (DCl/D2 O 35 wt % solution). The deuteration of high purity [bmim]Cl in D2 O is studied at different temperatures, in absence of catalyst or impurities, to yield an activation energy. DFT transition-state modelling, of a small water cluster and [bmim] cation, also yields an activation energy which strongly supports the proposed mechanism. The presence of basic impurities are shown to significantly enhance the exchange reaction, which brings into question the need for further analysis of technical purities of ionic liquids and the implications for a wide range of chemical reactions in such media.

On the Mechanism of the Reactivity of 1,3‐Dialkylimidazolium Salts under Basic to Acidic Conditions: A Combined Kinetic and Computational Study

AbstractComprehensive spectroscopic kinetic studies illustrate an alternative mechanism for the traditional free‐carbene intermediated H/D exchange reaction of 1,3‐dialkylimidazolium salts under neutral (D2O) and acidic conditions (DCl/D2O 35 wt % solution). The deuteration of high purity [bmim]Cl in D2O is studied at different temperatures, in absence of catalyst or impurities, to yield an activation energy. DFT transition‐state modelling, of a small water cluster and [bmim] cation, also yields an activation energy which strongly supports the proposed mechanism. The presence of basic impurities are shown to significantly enhance the exchange reaction, which brings into question the need for further analysis of technical purities of ionic liquids and the implications for a wide range of chemical reactions in such media.

Modelling tool for solving manufactoring system dysfunction in rubber seed oil based alkyd resin preparation

Variability in production output, low quality, wastes, and downtimes are serious production problems which manufacturers of alkyd resin product are facing and it invariably affect manufacturers’ economic performance and the nation economic growth which are often caused by differences in process temperatures and length of the resin. There is a strong incentive in controlling the end of the batch product property values so as to minimize the variability in product quality. This study seeks to investigate the relationship among variables capable of affecting the production process output of rubber seed oil based alkyd resin. A random survey of relevant literature was conducted to gather relevant information required that are capable of causing a dysfunction in the manufacturing process of rubber seed oil based alkyd resin for use in anti-corrosion paint application. The sensitivity and versatile applicability of opinion discrimination analysis as an off-line tool for dealing with these types of problems was apt. Our result showed that there is a strong relationship between temperature, catalyst, absence of catalyst, length of resin, acidic content, water resistance which can be manipulated to appreciably reduce product degradation and control process variability. Moreover, we showed that opinion discrimination analysis modelling tool can be used to determine the need to understand production process approach for alkyd resin. The study has ably demonstrated that opinion discrimination analytical modelling tool is very effective in fault diagnosis. http://dx.doi.org/10.4314/njt.v37i3.19

Renewable Energy Integration: Economic Assessment of Solar Energy to Produce Biodiesel at Supercritical Conditions

In recent years, research on noncatalytic methods for biodiesel production has increased, mainly processes under supercritical conditions that allow the processing of waste vegetable oils (WVO) without the need to use catalysts, where the absence of catalyst simplifies the processes of purification of biodiesel. The high consumption of alcohol and energy to maintain the appropriate conditions of pressure and temperature of the reaction has turned the processes of supercritical conditions into an unfeasible method. However, the stages of biodiesel purification and methanol recovery are more straightforward, allowing the reduction of the total energy consumption by 25% compared to alkaline methods. Therefore, the present work describes a study through Aspen Plus® of the production of biodiesel by a process in supercritical conditions with WVO as raw material. Also, a solar collector arrangement was structured using the TRNSYS® simulator to supply energy to the process. To evaluate the economic feasibility of the proposed process, the installation of a pilot plant in Mexicali, Baja California, was considered. The internal rate of return (IRR) and the net present value (NPV) were determined for ten-year period. The planned system allows supplying solar energy, 69.5% of the energy required by the process, thus reducing the burning of fossil fuels and the operation cost. Despite the additional investment cost, for the solar collectors, the process manages to maintain a competitive production cost of USD 0.778/l of biodiesel. With an IRR of 31.7%, the investment is recovered before the fifth year of operation. The integration and implementation of clean technologies are vital in the development of the biofuels.