Allylic Double Bond Research Articles

Bio-based ester- and ester-imine resins for digital light processing 3D printing: The role of the chemical structure on reprocessability and susceptibility to biodegradation under simulated industrial composting conditions

Four biobased ester and ester-imine photocurable resins were formulated and evaluated for printability by digital light processing 3D printing. The resin formulations consisted of methacrylated eugenol alone or in combination with methacrylated poly(hydroxybutyrate)-oligomers and/or methacrylated vanillin-derived Schiff-base monomers. It was not possible to print methacrylated eugenol alone into coherent thermosets, likely due to the lower reactivity of the allyl-double bond. However, in combination with the other building blocks methacrylated eugenol improved the printability, although some over-curing phenomena were registered especially for the resins composed of methacrylated eugenol and methacrylated poly(hydroxybutyrate)-derived oligomers. The three formulations that were successfully printed to coherent thermosets were further evaluated for their solvent resistance, thermal and mechanical properties, reprocessability and biodegradability under simulated industrial composting conditions. The reprocessing experiments documented the synergic effect of ester and imine dynamic covalent bonds in favoring the preservation of the elastic modulus of the thermosets; while an evidently higher deterioration of the mechanical properties was registered for the ester-thermosets. The biodegradation studies highlighted a clear correlation between the biodegradation rate and the chemical structure of the thermosets, with the aliphatic components and ester and imine bonds increasing the thermosets’ susceptibility to the biodegradation under simulated industrial composting conditions.

Zinc/Bismuth-Mediated Allylation Reaction of Biomass Feedstocks: Synthesis of Furanic Diols

AbstractBiomass-based diols have been synthesized by a Zn/Bi-mediated Barbier-type of reaction from furanic aldehydes and allyl halides to access allylated diols. The allylated diols can be readily converted into alkylated diols by hydrogenation. These furanic diols could be potential replacements for fossil fuel based bisphenol A (BPA) which has an adverse endocrine-disrupting effect on humans. This mild and green protocol provides symmetric and nonsymmetric diols in high yields. A chemoselective reduction of allylic double bonds provides diols with unique substitution.

Quantum Chemical Insight into 1,2-Shift Rearrangement in Bromination of Allylaryls.

In this work, we have provided mechanistic insight into the addition of bromine to an allylic double bond of allylaryl derivatives using experimental and DFT-based electronic structure methods. The experimental yields indicate the influence of the functional group on the aryl ring on the ratio of 1,2-dibromo and 1,3-dibromo adducts formed in the reaction. The optimized geometry and the electron density maps of the allylaryls and their cationic intermediates from DFT simulations revealed that electron-rich aryl rings promoted formation of cationic spiro[2.5] intermediate II, whereas electron-poor aryl rings resulted in formation of bromonium intermediate I. It was observed that electron-rich allylaryls promoted the 1,2-shift of the aryl ring that resulted in bond formation between the carbon atom (C1) on the aryl ring and the central carbon atom (C3) in the allylic double bond and formed spiro[2.5] intermediate II, a trend which was confirmed by harmonic oscillator model of aromaticity index. Also, Wiberg bond order analysis is in good agreement with the experimental work. Thermochemical analysis indicates that smaller C1···C3 distance resulted in favorable values for the difference in free energy change (ΔΔG). The favorable ΔΔG values are a result of higher electron density on the aryl ring, making it more nucleophilic toward C3 carbon and promoting 1,2-shift that led to formation of the spiro[2.5] intermediate. Thus, the underlying mechanism indicates that the electron-rich allylaryls promote the formation of 1,3-dibromo compounds through formation and stabilization of the spiro[2.5] intermediate II.

Low Coordination State RhI‐Complex as High Performance Catalyst for Asymmetric Intramolecular Cyclopropanation: Construction of penta‐Substituted Cyclopropanes

AbstractA simple, broad‐scope rhodium(I)/chiral diene catalytic system for challenging asymmetric intramolecular cyclopropanation of various tri‐substituted allylic diazoacetates was successfully developed. The low coordination state RhI‐complex exhibits an extraordinarily high degree of tolerance to the variation in the extent of substitution of the allyl double bond, thus allowing the efficient construction of a wide range of penta‐substituted, fused‐ring cyclopropanes bearing three contiguous stereogenic centers, including two quaternary carbon stereocenters, in a highly enantioselective manner with ease at catalyst loading as low as 0.1 mol %. The stereoinduction mode of this RhI‐carbene‐directed asymmetric intramolecular cyclopropanation was investigated by DFT calculations, indicating that π‐π stacking interactions between the aromatic rings of chiral diene ligand and diazo substrate play a key role in the control of the reaction enantioselectivity.

Low Coordination State Rh(I)-Complex as High Performance Catalyst for Asymmetric Intramolecular Cyclopropanation: Construction of penta-Substituted Cyclopropanes.

A simple, broad-scope rhodium(I)/chiral diene catalytic system for challenging asymmetric intramolecular cyclopropanation of various tri-substituted allylic diazoacetates was successfully developed. The low coordination state Rh(I)-complex exhibits an extraordinarily high degree of tolerance to the variation in the extent of substitution of the allyl double bond, thus allowing the efficient construction of a wide range of penta-substituted, fused-ring cyclopropanes bearing three contiguous stereogenic centers, including two quaternary carbon stereocenters, in a highly enantioselective manner with ease at catalyst loading as low as 0.1 mol%. The stereoinduction mode of this Rh(I)-carbene-directed asymmetric intramolecular cyclopropanation was investigated by DFT calculations, indicating that π-π stacking interactions between the aromatic rings of chiral diene ligand and diazo substrate play a key role in the control of the reaction enantioselectivity.

Regio- and Chemoselective Access to Dihydrothiophenes and Thiophenes via Halogenation/Intramolecular C(sp2)-H Thienation of α-Allyl Dithioesters at Room Temperature.

An operationally simple, practical, and efficient cascade approach employing α-allyl dithioesters and NBS/NIS has been achieved to access a series of dihydrothiophenes and thiophenes containing diverse functional groups of different electronic and steric natures in good to excellent yields at room temperature in open air. The reaction proceeds via the electrophilic addition of a halogen source (NBS/NIS) to an allylic double bond, followed by intramolecular regio- and chemoselective S-cyclization. This protocol avoids potential toxicity and tedious work-up conditions, and features easy synthesis from readily available starting materials under catalyst-free conditions. Furthermore, 4,5-dihydrothiophenes were aromatized to thiophenes by treatment with KOH in DMF at room temperature. A probable mechanism for the formation of dihydrothiophenes and thiophenes from α-allyl dithioesters has been suggested. Notably, a large-scale experiment and the transformations of products indicated the potential utility of this reaction compared to competing processes for the synthesis of 4,5-dihydrothiophenes and thiophenes.

Advantages of tandem versus simultaneous operation: The case of isomerization/hydrogenation of terpinolene epoxide to Terpinen-4-ol using a Ni/TiO2-SiO2 bifunctional catalyst

The conversion of terpinolene epoxide to terpinen-4-ol is a desirable chemical transformation for the production of a valuable intermediate. This paper describes a one-pot, two-step system for the reaction that uses a bifunctional Ni/TiO2-SiO2 catalyst with isomerization and hydrogenation capabilities. The TiO2-SiO2 serves to isomerize the starting epoxide. The Ni component works to hydrogenate the allylic double bond. The tandem system achieves a high 64% yield of terpinen-4-ol. X-ray diffraction analysis showed that TiO2-SiO2 was a mixed binary oxide, and Fourier transform infrared spectroscopy of adsorbed pyridine suggested that acid sites were mainly Lewis acid sites. Electron microscopy showed that the Ni/TiO2-SiO2 catalyst consisted of spherical particles comprising a titanosilicate phase with highly dispersed zero-valent Ni or anatase on the surface. Additionally, there was strong interaction between Ni and the TiO2-SiO2 mixed oxides. Control kinetic experiments demonstrated that the tandem use of the catalysts was more effective than simultaneous operation.

Eugenol, a Promising Building Block for Biobased Polymers with Cutting-Edge Properties.

Biobased materials, derived from biomass building blocks, are essential in the pursuit of sustainable materials. Eugenol, a natural phenol obtained from clove oil, but also from lignin depolymerization, possesses a chemical structure that allows its easy modification to obtain a broad and versatile platform of biobased monomers. In this Perspective, an overview of the variety of reactions that have been executed on the allylic double bond, phenol hydroxyl group, aromatic ring, and methoxy group is given, focusing our attention on those to obtain monomers suitable for different polymerization reactions. Furthermore, possible applications and perspectives on the eugenol-derived materials are provided.

Mechanistic Aspects of the Photophysics of UVA Filters Based on Meldrum Derivatives.

Skin photoprotection against UVA radiation is crucial, but it is hindered by the sparsity of approved commercial UVA filters. Sinapoyl malate (SM) derivatives are promising candidates for a new class of UVA filters. They have been previously identified as an efficient photoprotective sunscreen in plants due to their fast nonradiative energy dissipation. Combining experimental and computational results, in our previous letter (J. Phys. Chem. Lett. 2021, 12, 337-344) we showed that coumaryl Meldrum (CMe) and sinapoyl Meldrum (SMe) are outstanding candidates for UVA filters in sunscreen formulations. Here, we deliver a comprehensive computational characterization of the excited-state dynamics of these molecules. Using reaction pathways and excited-state dynamics simulations, we could elucidate the photodeactivation mechanism of these molecules. Upon photoexcitation, they follow a two-step logistic decay. First, an ultrafast and efficient relaxation stabilizes the excited state alongside a 90° twisting around the allylic double bond, giving rise to a minimum with a twisted intramolecular excited-state (TICT) character. From this minimum, internal conversion to the ground state occurs after overcoming a 0.2 eV barrier. Minor differences in the nonradiative decay and fluorescence of CMe and SMe are associated with an additional minimum present only in the latter.

Enantioselective Epoxidation by Flavoprotein Monooxygenases Supported by Organic Solvents

Styrene and indole monooxygenases (SMO and IMO) are two-component flavoprotein monooxygenases composed of a nicotinamide adenine dinucleotide (NADH)-dependent flavin adenine dinucleotide (FAD)-reductase (StyB or IndB) and a monooxygenase (StyA or IndA). The latter uses reduced FAD to activate oxygen and to oxygenate the substrate while releasing water. We circumvented the need for the reductase by direct FAD reduction in solution using the NAD(P)H-mimic 1-benzyl-1,4-dihydronicotinamide (BNAH) to fuel monooxygenases without NADH requirement. Herein, we report on the hitherto unknown solvent tolerance for the indole monooxygenase from Gemmobacter nectariphilus DSM15620 (GnIndA) and the styrene monooxygenase from Gordonia rubripertincta CWB2 (GrStyA). These enzymes were shown to convert bulky and rather hydrophobic styrene derivatives in the presence of organic cosolvents. Subsequently, BNAH-driven biotransformation was furthermore optimized with regard to the applied cosolvent and its concentration as well as FAD and BNAH concentration. We herein demonstrate that GnIndA and GrStyA enable selective epoxidations of allylic double bonds (up to 217 mU mg−1) in the presence of organic solvents such as tetrahydrofuran, acetonitrile, or several alcohols. Notably, GnIndA was found to resist methanol concentrations up to 25 vol.%. Furthermore, a diverse substrate preference was determined for both enzymes, making their distinct use very interesting. In general, our results seem representative for many IMOs as was corroborated by in silico mutagenetic studies.

Functionalization of Metal Surface via Thiol-Ene Click Chemistry: Synthesis, Adsorption Behavior, and Postfunctionalization of a Catechol- and Allyl-Containing Copolymer.

Surface functionalization tailors the interfacial properties without impacts on the mechanical strength, which is beneficial for industry and daily applications of various metallic materials. Herein, a two-step surface functionalization strategy, (1) catechol-mediated immobilization of clickable agent and (2) postfunctionalization based on thiol–ene click reaction, is achieved using a copolymer, namely poly[2-(methacryloyloxy)ethylundec-10-enoate]-co-(N-(3,4-dihydroxyphenethyl) methacrylamide) [P(MEUE-co-DPMAm)]. To reduce the potential side reactions of allylic double bonds in allyl methacrylate during the polymerization, the MEUE are designed and synthesized with better control over the polymer chain growth. The surface functionalization via the two-step method is demonstrated using various thiols, e.g., hydrophobic, hydrophilic, and polymeric thiols under room conditions. Additionally, the hydrophobic-thiol-functionalized anodic aluminum oxide is found to be a candidate for the oil/water separation with a separation efficiency of ∼99.2%. This surface modifier provides practical insights into the further design of functional materials.

Radical 1,3-Difunctionalization of Allylboronic Esters with Concomitant 1,2-Boron Shift

Summary Radical 1,3-trifluoromethylation/alkynylation of various allylboronic esters with concomitant 1,2-boron shift with alkynyl triflones is reported. These chain reactions proceed via CF3-radical addition to the allylic double bond, and the adduct radical undergoes 1,2-boron migration to give a translocated C-radical that is trapped by the alkynyl triflone. As products, 1,2,3-trisubstituted alkanes with the trifluoromethyl group at position 1 and the alkynyl functionality at position 3 are formed. The valuable boron moiety is retained in the product and is rearranged to position 2. By using trifluoromethanesulfonyl azide as the radical trapping reagent, the cascade provides a 1-trifluoromethyl-3-azidyl-alk-2-ylboronic ester as the product and Michael acceptors as trapping reagents in combination with the Langlois reagent as the CF3-radical precursor applying photoredox catalysis afford the corresponding 3-alkylated congeners in a three-component process. Further, the stereochemical course of the 1,2-boron migration and the trapping reaction are investigated.

Synthetically Induced 1→4‐C Branching Motif ‐ An Access Towards Dense Urethane Connecting Dendritic Scaffolds and Application in Nuclear Track Detection

AbstractA series of dumbbell‐shaped urethane connecting polyoleifinic dendrimers, are synthesized from commercial AB2 monomer through the concept of post‐generative synthetic induction of novel 1→4‐C branching motif in divergent and convergent growth methodology using carbamoyl chloride reactivity. A synthetic protocol is conducted through the iterative process of O‐carbamoyl‐allylation of hydroxyls followed by Upjohn dihydroxylation of the allylic double bonds, leading to protection/deprotection free divergent pathway. In parallel, convergent growth route gains dendrimers in relatively good yields. Also, the process of O‐carbonyloxy‐allylation of [G‐1] polyol affords urethane‐carbonate framework providing access to 1→2‐C branching further. Incorporation of current branching motif results in dendritic scaffold with dense periphery at lower generations itself. Free radical cast polymerization of [G‐0.5] dendrimer with allyl diglycol carbonate (ADC) produces thermoset polymer films, showing good sensitivity and ability to permanently record nuclear tracks.

Lignin nanoparticles modified with tall oil fatty acid for cellulose functionalization

In this study, tall oil fatty acid ester of softwood kraft lignin (TOFA-L) was used to prepare TOFA lignin nanoparticles (TLNP) in water. The average diameters for two prepared TLNPs in 0.1 mg/ml concentration were 140 nm and 160 nm. TLNPs were attached covalently onto modified and unmodified cellulose fibres to form an antimicrobial composite material. The modified cellulose fibres contained reactive allylic double bonds with a degree of substitution of 0.05. The antimicrobial properties of both TLNPs and TLNP coated fibres (TLNP-C) were studied against Escherichia coli, Staphylococcus aureus and Pseudomonas aeruginosa using silver nanospheres (average size 10 nm) and Lignoboost lignin particles with 300 and 400 nm sizes as references. Antimicrobial activity of the samples was stronger against Gram-positive S. aureus cells than against Gram-negative target microbes E. coli and P. aeruginosa.

Effect of acrylonitrile content of acrylonitrile butadiene rubber on mechanical and thermal properties of dynamically vulcanized poly(lactic acid) blends

AbstractWe report here the morphology, thermal and tensile properties of poly(lactic acid) (PLA) blends composed of acrylonitrile butadiene rubber (NBR) with different acrylonitrile contents with/without dynamic vulcanization by dicumyl peroxide (DCP). The interfacial tension of PLA and NBR measured by contact angle measurement decreased as the acrylonitrile content of NBR decreased. Likewise, SEM images showed that the rubber particle size reduced with decreasing acrylonitrile content owing to the stronger interfacial adhesion between the PLA matrix and NBR domains. Incorporation of DCP at 1.0 phr for dynamic vulcanization led to higher crosslink density and, in turn, optimal tensile strength and tensile toughness as a result of the action of PLA‐NBR copolymer as a reactive compatibilizer. The dynamic vulcanization of the blends containing low acrylonitrile NBR gave the most improved tensile properties because the free radicals from DCP decomposition preferentially attacked the allylic hydrogen atoms or double bonds of the butadiene backbone. Accordingly, more NBR macroradicals were generated and probably more PLA‐NBR copolymers were produced. Moreover, further addition of DCP at 2.0 phr provided a large amount of crosslinked NBR gel, which significantly degraded the tensile properties. From the DSC results, dynamic vulcanization lowered the cold crystallization temperature, implying an improvement of cold crystallization. Finally, TGA results showed a higher degradation temperature as a function of DCP content, which suggested that thermal stability increased due to stronger interfacial adhesion as well as higher gel content. © 2019 Society of Chemical Industry

Eugenol: A Promising Building Block for Synthesis of Radically Polymerizable Monomers

AbstractEugenol, a natural phenol currently mainly obtained from clove oil, is an interesting aromatic building block for the synthesis of novel biobased monomers. It can also be obtained from lignin depolymerization, becoming a promising building block due to lignin availability as biomass feedstock. The synthesis of eight monomers derived from eugenol containing polymerizable functional groups is achieved. The (meth)acrylation of eugenol, isoeugenol, and dihydroeugenol is performed and the solution homopolymerization of these biobased monomers is studied. Moreover, aiming to prepare functional polymers, the introduction of epoxy and cyclic carbonate groups is executed via modification of the allylic double bond present in eugenol derived methacrylate. Thus, a novel platform of versatile biobased monomers derived from eugenol is presented, opening the opportunity to use them in a wide range of polymerization processes and applications

ALTERNATIVE SYNTHESIS OF N-ALKENYLARYLAMINES WITH ALLYL DOUBLE BONDS

ALTERNATIVE SYNTHESIS OF N-ALKENYLARYLAMINES WITH ALLYL DOUBLE BONDS

Improvement of liquid crystal alignment using photo-fragment reactions

ABSTRACTTwo photo-activators, AAP and CAP, were synthesized with cyclohexanone oxime with methyl and cronic anhydrides. They were used to improve the liquid crystal (LC) alignment properties by increasing the surface azimuthal anchoring energy, that has been an image-sticking problems. These photo-activators were respectively mixed with twisted nematic (TN) planar alignment agent (TN-PAA) or photo-polyamic acid (P-PAA), respectively. It is remarkable that a photo-activator using crotonic anhydride (CAP) what has allyl double bond showed very high anchoring energy, 6.92 × 10−5 J/m2, which is comparable or better than that obtained with rubbing, 1.65 × 10−5 J/m2. The anchoring and the alignment properties were observed with the P-PAA were the lower than the TN-PAA. The photochemical reactions and the surface properties of the photo-polyimide (P-PI) were more complex due to more than double photochemical reactions. The fourier transform infrared spectroscopy (FT-IR), contact angle, atomic force microscope (AFM) and differential thermal analysis and thermogravimetic analysis (DTA-TGA) measurements indicated that the surface of polyimide (PI) became more hydrophobic due to the photoreactions of alkyl radicals. These radicals were generated by the photo-irradiation and the reduction of hydrophilic functional groups. The high anchoring energy was assisted by the rough and robust surface induced by carbon dioxide generation. These properties contribute to prevent the image-sticking and shorten the irradiation time with energy.

Organomercury complexes bearing (thioxothiazolidin-5-yl)methyl moiety by intramolecular heteromercuration reaction of diallyldithiocarbamate

Reaction of diallyldithiocarbamate and mercury chloride in different mole ratios afforded two different organomercury complexes: ((3-allyl-2-thioxothiazolidin-5-yl)methyl)mercury(II) chloride and N,N-diallyl-dithiocarbamat(3-allyl-2-thioxothiazolidin-5-yl)methyl)mercury(II) represented as complex 1 and 2 respectively. The complexes were characterized by microanalysis, spectroscopic (IR, 1H and 13C NMR) techniques and their structures were elucidated by X-ray crystallography. Formation of both complexes occurred by intramolecular solvomercuration reactions via the allylic double bond. This reaction pathway was favoured by the properties of the reactants used: mercury chloride and an alkenamine derivative. The dithiocarbamate moeiety acted as a highly nucleophilic neighbouring group, and induced heterocyclization process by anchimeric assistance leading to formation of thiazol, a five-membered ring in both complexes. The structure of complex 1 presents a mercury compound in which the positive charge of the Hg2+ atom is balanced by dithiocarbamato and chloride anions acting as monodentate ligands, while in complex 2 the Hg atom is coordinated to three dithiocarbamate ligands and a ring closure occurred with one of the S atoms forming a thiazole ring.

Dynamic DSC curing kinetics and thermogravimetric study of epoxy resin of 9,9′-bis(4-hydroxyphenyl)anthrone-10

Dynamic DSC curing kinetics of epoxy resin of 9,9′-bis(4-hydroxyphenyl) anthrone-10 (EAN) was carried out at 5, 10, 15 and 20 °C min−1 heating rates in nitrogen atmosphere using 4,4′-diaminodiphenylsulfone (DDS), 4,4′-diaminodiphenylmethane (DDM) and tetrahydrophthalicanhydride (THPA) hardeners. Peak exotherms shifted toward higher temperature range with increasing heating rate. DSC data were analyzed by Ozawa, Kissinger and Flynn–Wall–Ozawa methods to derive activation energy (E a) and frequency factor (A). Observed trend in E a and A is EAN-DDS > EAN > EAN-THPA > EAN-DDM. For EAN-amine systems, both E a and A decreased with increasing conversion and for EAN-THPA they increased up to 30% conversion and then decreased slowly with increasing conversion. Friedman plots showed autocatalytic nature of the EAN-hardener systems. Autocatalytic nature is due to dehydration of secondary alcohol groups with simultaneous formation of allylic double bonds. EAN-THPA showed 1.34 and 0.34, respectively, for n and m orders of kinetics. The validity of kinetic model was performed by simulation analysis using obtained kinetic constants for EAN-THPA. Experimental and calculated curves are in agreement between α = 0.2–0.6. Thermogravimetric study at 10 °C min−1 heating rate in nitrogen atmosphere revealed that cured resins (310–337 °C) are more thermally stable than thermally cured EAN (279 °C) and followed either one- or two-step degradation kinetics.