Ketene Group Research Articles

Poly(ester amide)s from biomass‐based 3,4‐dihydrocoumarine through Meldrum's acid mediated ketene chemistry

AbstractMeldrum's acid mediated ketene chemistry (MAMKC) is applied to synthesis of poly(ester amide)s in this work. An MA‐functionalized phenolic amide compound (MA_PhOH‐Am) is synthesized from the reaction between a MA‐functionalized amine and 3,4‐dihydrocoumarine (DHC, a biomass‐based chemical) through amine‐lactone addition reaction. Polymerization of MA_PhOH‐Am results in the corresponding poly(ester amide) (P(Es‐Am)), through MA thermolysis reaction (generating the corresponding ketene groups) and ketene‐phenol addition reaction. Both MA_PhOH‐Am and P(Es‐Am) have been characterized with spectral methods and thermal analysis. P(Es‐Am) has an inherent viscosity of 0.49 dL g−1, a molecular weight of 76,500 Da, a glass transition temperature of 145°C (tanδ peak in dynamic mechanical analysis), a thermal stability of about 320°C, and a storage modulus at 50°C of 1.0 GPa. In the stress–strain measurement, P(Es‐Am) exhibits a Young's modulus, a tensile strength, and an elongation at break of 10.6 ± 0.7 GPa, 165 ± 40 MPa, and 1.83 ± 0.41%, respectively. An effective approach for the synthesis of high‐performance poly(ester amide)s has been demonstrated.

2,2-Dimethyl-1,3-dioxane-4,6‑dione functionalized poly(ethylene oxide)-based polyurethanes as multi-functional binders for silicon anodes of lithium ion batteries

Chemically reactive groups (2,2-dimethyl-1,3-dioxane-4,6‑dione (Meldrum's acid, MA) and poly(ethylene oxide) (PEO) segments are incorporated to polyurethanes as binders of silicon anode for lithium ion batteries, aiming to address the volume change issue of the silicon anode in lithiation/delithiation cycles. The polymeric binder builds up multiple interaction to silicon surfaces, including hydrogen bonding between the urethane linkages of the bonder and silanol groups of silicon surfaces and covalent linkages through the addition reaction between ketene groups (generated from MA thermolysis reaction) and silanol groups of silicon surfaces. Self-dimerization of ketene groups also results in crosslinked structure of the binder. Both of the above-mentioned interaction and crosslinked structure contribute to stabilize the silicon anode materials. Moreover, the PEO segments facilitate the transportation of lithium ions and increase the ion conductivity of the anode. Consequently, the corresponding silicon anode is workable at a high C rate (0.8C) to demonstrate a specific capacity of approximately 1,785 mAh g − 1 and a capacity retention of 58% after a 600-cycle charge/discharge test. Morphological observation on the anode materials after a 300-cycle test indicates that the reactive PU binder could effectively depress cracks and interphase separation of the anode materials caused by the lithiation/delithiation-induced volume changes. The prepared binder also exhibits stabilization on the solid electrolyte interphase (SEI) layer and prevent anode material delamination. The results demonstrate a successful example of designs and preparation of multi-functional binders for silicon anodes.

In situ crosslinking and micro-cavity generation in fabrication of polymeric membranes for pervaporation dehydration on methanol aqueous solutions

Crosslinked membranes exhibiting in situ crosslinking and micro-cavity generation in membrane fabrication processes have been reported for pervaporation dehydration on methanol aqueous solutions. Meldrum's acid (MA) modified poly(2,6-dimethyl-1,4-phenylene oxide) (PPO-MA) with various MA contents have been synthesized and well characterized with Fourier transform infrared spectroscopy and 1H nuclear magnetic resonance spectroscopy. PPO-MA polymers could perform thermally-induced self-crosslinking reaction through cycloaddition reaction between ketene groups generated from MA thermolysis reaction. Meanwhile, MA thermolysis reaction evolves CO2 and acetone molecules which contribute to generation of micro-cavities in the formed membranes. Consequently, compared to the pervaporative separation performance of pristine PPO membrane (permeation flux: 290 g m−2 h−1; separation factor: 57) on a 90 wt% methanol solution at 25 °C, the crosslinked PPO-MA membrane shows a separation factor of 809 with a slight decrease in permeation flux to about 226 g m−2 h−1. Based on the pervaporation separation index (PSI, the product of permeation flux and separation factor), an 11-times enhancement has been achieved.

Modular photoinduced grafting onto approach by ketene chemistry

ABSTRACTA modular approach for the synthesis of graft copolymers by the combination of reversible addition–fragmentation chain‐transfer (RAFT) polymerization and photoinduced acylation processes is described. In the two‐step approach, first the copolymers of benzodioxinone containing monomer, namely, 4‐oxo‐2,2‐diphenyl‐4H‐benzo[d][1,3]dioxin‐7‐yl methacrylate (BDMA) and methyl methacrylate (MMA) in different feed ratios were prepared by RAFT polymerization. In the subsequent step, dichloromethane solutions of these copolymers (PMMA‐co‐PBDMA) were irradiated at λ = 300 nm in the presence of independently prepared hydroxyl functional polymers such as poly(ethylene glycol) (MeO‐PEG‐OH) and poly(ɛ‐caprolactone) (PCL‐OH). Side‐chain esterification reaction between photochemically generated ketene groups and hydroxyl functionalities resulted in the formation graft copolymers. The intermediates and final graft copolymers were characterized by 1H NMR, UV, IR, fluorescence, and GPC measurements. The success of the process was also confirmed by a model reaction using pyrene methanol. © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2019, 57, 274–280

Effective Synthesis Route for Linear and Cross-Linked Biodegradable Polyesters Using Aliphatic Meldrum's Acid Derivatives as Monomers.

On the basis of the reaction between ketene and alcohol groups to result in an ester linkage and Meldrum’s acid as an effective precursor of ketene group, a bifunctional aliphatic Meldrum’s acid compound (BisMA) is synthesized and used as a monomer to react with ethylene glycol and glycerol for the preparation of linear and cross-linked aliphatic polyesters, respectively. A 62 and 35 wt % of biodegradation fraction have been recorded on the linear and cross-linked aliphatic polyesters after an 8 week biodegradation test, respectively, to demonstrate the good biodegradability of the synthesized polyesters. In addition to conventional linear biodegradable polyesters, this synthetic route also provides a new and convenient method for preparation of cross-linked biodegradable polyesters. The types of the required monomers and reaction methods for preparation of the cross-linked biodegradable polyesters are similar to those used for conventional thermosetting resins. An integration of biodegradable polymers and thermosetting resins in polymer chemistry has been demonstrated.

A comparison for application time of electrical discharge onto 3-acetamidocoumarin molecule

A topic of great interest is discussed as the atmospheric-pressure non-equilibrium plasma jets and their applications. In this study, our plasma generated here can be described as the dielectric barrier discharge-like. It is known that these types of plasma can be used in various applications like surface modification, inactivation of microorganism etc. An interesting application of the atmospheric pressure plasma is decomposing of the long chemical chain molecules. We present a new decomposing method for the molecules. Investigation of molecular structure of coumarin is very important. We perform the structural analysis of molecules that interact with atmospheric pressure plasma jet. The 3-acetamidocoumarin molecule plays an important role in biology and medicine. It has physiological effects and it has been used to product of drug for many diseases such as treatment of burns, brucellosis-rheumatic diseases and cancer. The atmospheric-pressure non-equilibrium plasma jet of argon (Ar) has been formed by ac-power generator with frequency – 24 kHz and voltage-12 kV. FT-IR spectra of the molecule “3-acetamidocoumarin” (abbreviated as 3ADC) dissolved in ethanol and methanol have been analysed after applying (application times, 1 minute and 3 minutes) the plasma, for the first time. Also the changes of structure have been evaluated. 4C-O band is broken and the main photoreactions were observed the characteristic IR intense band due to the antisymmetric stretching vibration of the ketene (-3C4CO) group. New photoproduct is obtained in the E arrangement of the (O) 5C-10C11C-3C (4CO) fragment.

Revealing the Adsorption Mechanisms of Nitroxides on Ultrapure, Metallicity-Sorted Carbon Nanotubes

Carbon nanotubes are a natural choice as gas sensor components given their high surface to volume ratio, electronic properties, and capability to mediate chemical reactions. However, a realistic assessment of the interaction of the tube wall and the adsorption processes during gas phase reactions has always been elusive. Making use of ultraclean single-walled carbon nanotubes, we have followed the adsorption kinetics of NO2 and found a physisorption mechanism. Additionally, the adsorption reaction directly depends on the metallic character of the samples. Franck–Condon satellites, hitherto undetected in nanotube–NOx systems, were resolved in the N 1s X-ray absorption signal, revealing a weak chemisorption, which is intrinsically related to NO dimer molecules. This has allowed us to identify that an additional signal observed in the higher binding energy region of the core level C 1s photoemission signal is due to the C=O species of ketene groups formed as reaction byproducts . This has been supported by density functional theory calculations. These results pave the way toward the optimization of nanotube-based sensors with tailored sensitivity and selectivity to different species at room temperature.

Amination of Phenylketene Revisit. Substituent Effect on Reactivity

Abstract The asymmetric stretching frequencies of the ketene group of the m,p-substituted phenylketenes were found to be correlated with σ. The substituent effects for the second-order rate constants of phenylketenes with various amines were not correlated linearly with any single substituent constants. The curved σ°-correlations with a plateau at a high reactivity region were observed for meta-substituents and p-chloro. The substituent effects including para-π-acceptors were described in terms of the Yukawa–Tsuno equation modified by a quadratic term as an approximation. The resultant ρ value decreases significantly from 2.92 for 2,2,2-trifluoroethylamine to 0.83 for benzylamine while an r− value increases from 0.50 to 1.10. The opposite change of ρ and r− with amines was interpreted by the dual electronic interactions between substituents and positive/negative charges at the zwitterionic transition structure. According to this interpretation, benzylamine with small ρ value and large r− value attributes to early transition state and larger ρ value with smaller r− value for 2,2,2-trifluoroethylamine attributes to late transition state.

Determination of Mechanism for Soot Oxidation with NO on Potassium Supported Mg‐Al Hydrotalcite Mixed Oxides

AbstractSoot oxidation with NO (in the absence of gas phase O2) on potassium‐supported Mg‐Al hydrotalcite mixed oxides (K/MgAlO) was studied using a temperature‐programmed reaction and in situ FTIR techniques. Nitrite and the ketene group were identified as the reaction intermediates and thus a nitrite‐ketene mechanism was proposed in which surface active oxygen on K sites of K/MgAlO is transferred to soot by NO through nitrites. In the absence of gas phase O2, soot oxidation with NO at lower temperatures (below 450 °C) is limited by the amount of active oxygen on the K sites. This kind of active oxygen is not reusable but can be replenished in the presence of gas phase O2.

A non-adiabatic quantum-classical dynamics study of the intramolecular excited state hydrogen transfer in ortho-nitrobenzaldehyde

Ab initio surface-hopping dynamics calculations have been performed to simulate the intramolecular excited state hydrogen transfer dynamics of ortho-nitrobenzaldehyde (o-NBA) in the gas phase from the electronic S(1) excited state. Upon UV excitation, the hydrogen is transferred from the aldehyde substituent to the nitro group, generating o-nitrosobenzoic acid through a ketene intermediate. The semiclassical propagations show that the deactivation from the S(1) is ultrafast, in agreement with the experimental measurements, which detect the ketene in less than 400 fs. The trajectories show that the deactivation mechanism involves two different conical intersections. The first one, a planar configuration with the hydrogen partially transferred, is responsible for the branching between the formation of a biradical intermediate and the regeneration of the starting material. The conversion of the biradical to the ketene corresponds to the passage through a second intersection region in which the ketene group is formed.

Removal of copper (II) and phenol from aqueous solution using porous carbons derived from hydrothermal chars

The feasibility of hydrothermal char (HTC), a byproduct from biomass hydrothermal liquefaction for bio-oil production, as raw material for preparation of porous carbons was investigated in the present study. The resultant HTC-derived porous carbons were characterized and utilized as adsorbents for copper (II) and phenol removal from aqueous solution. Compared with porous carbons using pyrolytic char as precursor, the HTC-derived porous carbons exhibited unique textural features, e.g., narrow pore size distribution, high surface area and large pore size. In addition, FT-IR analysis confirmed that substantial amount of ketene groups existed on the surface of the HTC-derived porous carbons. As the adsorbents, the copper (II) adsorption onto HTC-derived carbons was strongly affected by the pH value of the solution in comparison with phenol adsorption. The carbons derived from pinewood and rice husk HTC exhibited high adsorption capacity of 83.88 and 39.30 mg/g for phenol and 25.18 and 22.62 mg/g for copper (II), respectively. The adsorption data for copper (II) and phenol onto the carbon adsorbents could be well described by Langmuir and Freundlich models. In comparison with pinewood sawdust HTC-derived carbon, the adsorption onto rice husk HTC-derived carbon preferentially followed Freundlich model due to the presence of silica on the surface.

Catalytic performance and mechanism of potassium-promoted Mg–Al hydrotalcite mixed oxides for soot combustion with O2

Abstract Potassium-promoted Mg–Al hydrotalcite mixed oxides were studied for soot combustion with O2. The significant activity was elucidated by an oxygen spillover mechanism. First, the surface-activated oxygen on K sites might spill over to the free carbon sites on soot to form a carbon–oxygen complex, ketene group, which was identified as the reaction intermediate. Then the ketene group combined with another active oxygen species to give out CO2. Two kinds of K species, Mg(Al)–O–K (tightly bound to Mg or Al) and free (isolated) K, were determined to be catalytically active sites by kinetic investigations. They could increase the reactivity and amount of surface active oxygen responsible for formation of the ketene group. The stability of K was greatly improved through the interaction with Al, which is a contribution to soot combustion of Al addition into MgO to form a K-promoted composite oxide via the hydrotalcite route.

Facilitating functionality

Monomers that contain masked ketene groups provide new opportunities for facile crosslinking and post-synthetic modification of polymers in a wide variety of materials applications.

Catalytic performance and mechanism of potassium-promoted Mg–Al hydrotalcite mixed oxides for soot combustion with O 2

Potassium-promoted Mg–Al hydrotalcite mixed oxides were studied for soot combustion with O 2. The significant activity was elucidated by an oxygen spillover mechanism. First, the surface-activated oxygen on K sites might spill over to the free carbon sites on soot to form a carbon–oxygen complex, ketene group, which was identified as the reaction intermediate. Then the ketene group combined with another active oxygen species to give out CO 2. Two kinds of K species, Mg(Al)–O–K (tightly bound to Mg or Al) and free (isolated) K, were determined to be catalytically active sites by kinetic investigations. They could increase the reactivity and amount of surface active oxygen responsible for formation of the ketene group. The stability of K was greatly improved through the interaction with Al, which is a contribution to soot combustion of Al addition into MgO to form a K-promoted composite oxide via the hydrotalcite route.

Thermal degradation of star-shaped poly(ɛ-caprolactone)

Thermal degradation of a serials of star-shaped poly(ɛ-caprolactone) (PCL) with well-defined arm numbers and arm length was investigated. The weight loss of star-shaped PCL during heating process showed a two-stage character, and its dependence on molecular weight and multi-armed structure was well discussed. It was found that the thermal stability could be improved not only by increasing molecular weight but also by increasing arm numbers when the molecular weight is in a certain range. Based on the analyses of pyrolytic products by 1H NMR and TGA–FTIR, two mechanisms of thermal degradation for the random cleavage of ester bonds of PCL chains were proposed. Ester bonds were pyrolyzed into alkene and carboxyl functional groups in mechanism I while they were pyrolyzed into ketene and hydroxyl functional groups in mechanism II. The effects of multi-armed structure of star-shaped PCL on the cleavage of ester bonds of PCL chains were discussed in terms of the limitation of central “core” on mobility of each PCL arm. Combined the results of viscosity analysis with thermal analysis, it could be concluded that both thermal stability and processability of PCL materials can be improved by controlling the multi-armed structures.

In situ direct photoproduction of ketenes from substituted coumarins isolated in solid argon: The case of N-(2-oxo-2 H-chromen-3-yl)acetamide

In this study, the infrared spectrum of N-(2-oxo-2 H-chromen-3-yl)acetamide (3-acetamidocoumarin; 3AC) isolated in solid argon, at 10 K, was obtained and assigned. In consonance with the relative energies of the three conformers predicted theoretically, only the most stable form was observed experimentally. This conformer is stabilized by two intramolecular hydrogen bonds and is similar to the structural unit of 3AC found in crystalline phase. Upon in situ UV ( λ > 215 nm) irradiation of the matrix-isolated compound, the characteristic IR intense band due to the antisymmetric stretching vibration of the ketene ( C C O) group was observed, indicating occurrence of the ring-opening isomerization reaction to the open-ring ketene isomeric of 3AC. In consonance with the theoretical structural predictions for the most stable isomers of this photoproduct, the experimental data indicates that it is produced in the E arrangement of the (O )C C C C( C O) fragment. There were also experimental indications pointing to occurrence of a second photoreaction channel, corresponding to decarbonylation. On the other hand, contrarily to what is generally observed for α-pyrones derivatives, including unsubstituted coumarin, no photochemical production of Dewar isomer of 3AC was observed. This last result, follows the trend observed for 2-pyrone-3-carboxylate, and seems to be a quite general rule for matrix-isolated α-pyrones bearing relatively volumous substituents at the position 3, as a consequence of the unfavorable relaxation of the matrix around the guest molecule that would be required to accommodate the Dewar isomers of these compounds, whose structure deviates strongly from planarity, thus mismatching the primarily occupied matrix sites.

Collision induced dissociation of deprotonated guanine: Fragmentation of pyrimidine ring and water adduct formation

This investigation of collision induced dissociation of deprotonated guanine was conducted by using sequential ion trap tandem mass spectrometry and isotopically labelled guanine analogs to clarify the complex dissociation reactions of pyrimidine ring of deprotonated guanine. The fragmentation patterns confirmed that the gas-phase dissociation processes are initiated from the pyrimidine ring through charge site controlled reactions involving charge redistribution, proton transfer and nucleophilic attack to generate the three primary fragment products by the elimination of ammonia, cyanamide and isocyanic acid. Our findings shed light on the process of pyrimidine ring opening and closure prior to the decomposition of deprotonated guanine and therefore the identity of N1 and exocyclic N 2 is lost in deprotonated guanine as a result of scrambling. Intriguing association products of water addition to fragment ions have been structurally characterized to establish the role of ketene group in the selective gas-phase reaction of water addition and the formation of water adducts. The elimination of CO 2 from negatively charged water adducts provides evidence for the covalent attachment of water to the ketene moiety. The established mechanisms of the dissociation reactions of pyrimidine ring should provide a basis for the structural elucidation of guanine relevant species modified on its active sites. To lend support for our proposals, collision induced dissociation study of 8-phenyl-2′-deoxyguanosine adduct was performed.

A computational study of the electrocyclization of o-divinylbenzene and derivatives

Electrocyclization reactions of o-divinylbenzene and several derivatives were studied by performing density functional theory (DFT) calculations together with the 6-31+G ∗ basis set. Reactants, products and transition states for each reaction were localized and the path connecting reactants and products was also obtained. Along the reaction path, magnetic properties were evaluated to elucidate the characteristics of the reactions studied. Considering the overall results obtained with different indexes, such as magnetic susceptibility, nucleus independent chemical shift (NICS) or anisotropy of the current-induced density (ACID), all the reactions were found to keep the main characteristics of pericyclic reactions, showing an enhanced aromaticity in the vicinity of the transition state. Only two cyclizations, involving an isocyanate or ketene group, arose some doubts about their behaviour, but both still showed characteristics of pericyclic reactions, though weakened with respect to prototypical electrocyclizations as that of o-divinylbenzene.

CO fixation to stable acyclic and cyclic alkyl amino carbenes: stable amino ketenes with a small HOMO-LUMO gap.

CO fixation to stable acyclic and cyclic alkyl amino carbenes: stable amino ketenes with a small HOMO-LUMO gap.

Density functional study of the chemisorption of O 2 on the armchair surface of graphite

The reaction between O 2 and the armchair surface of a model graphite molecule has been studied using density functional calculations at the B3LYP/6-31G( d) level of theory. Both equilibrium and transition state geometries were optimized to provide a fundamental understanding of the energetics and kinetics of the chemisorption, desorption, rearrangement, and migration reactions that contribute to carbon gasification. A small barrier of 18 kJ mol −1 was found for the chemisorption reaction, which is 578 kJ mol −1 exothermic overall, producing a stable quinone. A number of reaction pathways with barriers below 578 kJ mol −1 were characterized. Gasification of carbon occurs as CO, with barriers of 296 and 435 kJ mol −1 for the first and second CO loss, respectively. The stable quinone can also undergo a rearrangement reaction to form two ketene groups, with a barrier of 260 kJ mol −1. If the armchair edge is extended to include an adjacent aromatic ring, the oxide can migrate along the surface. This initially forms a furan-like bridge structure, with a barrier of just 89 kJ mol −1. A further barrier of 383 kJ mol −1 leads to CO desorption from the furan. The furan can also rearrange further with a barrier of 212 kJ mol −1 to form a five-membered lactone, the most stable structure identified on the potential energy surface. Rearrangement and migration reactions, which have not generally been incorporated into carbon gasification models, are shown to be potentially important pathways in carbon oxidation reactions.