Alkoxy Research Articles

Remarkable enhancement of tracking resistance of addition-cure liquid silicone rubber by alkyl-disubstituted ureido siloxane immobilized on the silica filler surface

It is urgent and significant to prepare silicone rubber with excellent tracking resistance in a harsh environment. In this work, alkyl-disubstituted ureido siloxane immobilized on silica (U-SiO2) was prepared by the dehydration condensation of hydrolysates of alkoxy groups in alkyl-disubstituted ureido siloxanes (US) and hydroxyl groups on the silica surface. The effect of U-SiO2 on the tracking resistance of addition-cure liquid silicone rubber (ALSR) was investigated by inclined-plane test (IP test). It was found that U-SiO2 could effectively enhance the tracking resistance of ALSR. Especially, diisopropylureidopropyltriethoxysilane and diisobutylureidopropyltriethoxysilane with isomeric substitution immobilized on silica (DIPUPES-SiO2 and DIBUPES-SiO2) performed the best. With less than 1.00 phr content, ALSR samples could reach 1A4.5 level. The erosion mass was only 0.40 % and 0.62%, respectively. Moreover, ALSR / DIPUPES-SiO2 had excellent water resistance. It could still reach 1A4.5 level and the erosion mass was almost unchanged after ALSR / DIPUPES-SiO2 was immersed in the water for five days. The results of plasma irradiation and thermal treatment showed that U-SiO2 could effectively inhibit the aggregation of platinum in Karstedt's catalyst, which could promote the crosslinking of ALSR chains under the elevated temperature to form a compact ceramic protected layer. It could not only isolate the oxygen and heat and suppress the thermal degradation of ALSR, but also resist the plasma bombardment. Therefore, the tracking resistance of ALSR was remarkably enhanced.

New Nitro-Laterally Substituted Azomethine Derivatives; Synthesis, Mesomorphic and Computational Characterizations.

Two new homologues series, based on two rings of the azomethine central group bearing the terminal alkoxy group of various chain lengths, were prepared. The alkoxy chain length varied between 6 and 16 carbons. The other terminal wing in the first series was the F atom, and the compound is named N-4-florobenzylidene-4-(alkoxy)benzenamine (In). The second group of compounds included a lateral NO2 substituent in addition to the terminal F atom, named N-(4-fluoro-3-nitrobenzylidene)-4-(alkyloxy)aniline (IIn). Mesomorphic and optical properties were carried out via differential scanning calorimetry (DSC) and polarized optical microscopy (POM). Elemental analyses, FT-IR, and NMR spectroscopy were carried out to elucidate the molecular structures of the synthesized groups. Mesomorphic investigations indicated that all the synthesized homologues (In) were monomorphic, possessing the smectic A (SmA) phase monotropically, while the second group (IIn) members were non-mesomorphic. The experimental data indicated that the formation of the mesophase is affected by the protrusion of the lateral nitro group. The disruption of the mesophase in the second group was attributed to the increase of its molecular width, which affects its lateral intermolecular interactions. The computational simulations were in agreement with the experimental data. On the other hand, the location of NO2 group within the molecular geometry increased the melting temperature of the molecule, and thus, affected their thermal and physical properties. By discussing the estimated parameters, it was found that the molecular architecture, the dipole moment, and the polarizability of the investigated compounds are highly affected by the electronic nature and position of the terminal and lateral substituents as well as their volumes.

Synthesis and Antitrypanosomal Activity of 6-Substituted 7-Methyl-7-deazapurine Nucleosides.

Human African Trypanosomiasis caused by Trypanosoma brucei species is one of the most damaging neglected tropical diseases. While the number of newly diagnosed cases per year is record low, there is still high interest in the development of new antitrypanosomal agents in case of resistance to currently used drugs and their combinations, and to replace drugs with serious side effects. We report a series of 7-methyl-7-deazapurine (5-methyl-pyrrolo[2,3-d]pyrimidine) ribonucleosides bearing alkyl, methylsulfanyl, methylamino, or diverse alkoxy groups at position 6 that was prepared through glycosylation of 6-chloro-7-methyl-7-deazapurine followed by nucleophilic substitutions or cross-coupling reactions at position 6 and deprotection. Most of the title nucleosides displayed significant activity against Trypanosoma brucei brucei and T. b. gambiense at submicromolar or nanomolar concentrations and low cytotoxicity and thus represent promising candidates for further development.

Effects of steric hindrance and electron density of ester prodrugs on controlling the metabolic activation by human carboxylesterase

Carboxylesterase (CES) plays an important role in the hydrolysis metabolism of ester–type drugs and prodrugs. In this study, we investigated the change in the hydrolysis rate of hCE1 by focusing on the steric hindrance of the ester structure and the electron density. For 26 kinds of synthesized indomethacin prodrugs, the hydrolytic rate was measured in the presence of human liver microsomes (HLM), human small intestine microsomes (HIM), hCE1 and hCE2. The synthesized prodrugs were classified into three types: an alkyl ester type that is specifically metabolized by hCE1, a phenyl ester type that is more easily metabolized by hCE1 than by hCE2, and a carbonate ester type that is easily metabolized by both hCE1 and hCE2. The hydrolytic rate of 1-methylpentyl (hexan–2–yl) ester was 10–times lower than that of 4–methylpentyl ester in hCE1 solution. hCE2 was susceptible to electron density of the substrate, and there was a difference in the hydrolysis rate of up to 3.5–times between p-bromophenyl ester and p-acetylphenyl ester. By changing the steric hindrance and electron density of the alkoxy group, the factors that change the hydrolysis rate by CES were elucidated.

Dynamic Activation of C1 Molecules Evoked by Zeolite Catalysis.

Direct observation of the activation and transformation of reactant molecules is extremely attractive but very challenging in the study of most chemical processes. Here is reported the first case of dynamic activation of C1 molecules in zeolite-catalyzed chemistry. During the methanol conversion over the HZSM-5 zeolite, a sequence of progressive activation states of dimethyl ether (DME) evoked by the special catalysis from CH3-Zeo, a hybrid supramolecular catalytic system formed by the organic methylic species growing on the inorganic silico-aluminate zeolite framework, has been directly observed by in situ ssNMR spectroscopy at programmed temperatures. Operando simulations visually display the variability of this hybrid supramolecular system of which the C–O bond property goes through a dynamic transition from covalent to ionic with the temperature increase, and thus the gradually enhanced electrophilicity of CH3δ+ and nucleophilicity of Zeoδ− lead to the dynamic activation of DME. This dynamic transition is generally reflected in the alkyl-Zeo system with other alkoxy groups, which linked the alkoxy species and carbocations in zeolite catalysis. Consequently, this work not only sheds light on the key issue of the first carbon–carbon (C–C) bond formation in the methanol to hydrocarbons (MTH) process but also brings a new awareness on the essence of acid catalysis in zeolite mediated chemical processes.

Nanocomposite film with antimicrobial activity based on gold nanoparticles, chitosan and aminopropylsilane

In the present work the role that 3-aminopropyltrimethoxysilane (APTMS) plays in the chitosan‑gold nanoparticles system was studied. For this purpose, gold nanoparticles (AuNP) (ca. 4.0 nm), were synthesized using chitosan as stabilizer and after, the APTMS, which presents both alkoxy and amine groups, was added to the system. No changes in both size and shape of the AuNP were observed. The addition of APTMS to chitosan produced a significant decrease in dynamic viscosity and this feature can contribute to the achievement of greater miscibility in the system. The AuNP dispersion containing APTMS was used to build a film on the surface of glass slide by using the drop-casting method. The gold amount on the resulting film was estimated as 17.5 μmol of gold atoms per cm2, in the nanoparticle form. The film was analyzed by UV–Vis, TEM, SEM, perfilometry and AFM. The film presented thickness of 36 μm, while the estimated roughness was lower than 1% of this value. The antimicrobial activity of the film based on chitosan, APTMS and gold nanoparticles was evaluated against Salmonella bacterium. The synergistic effect of the three components provided greater antimicrobial activity.

Selective Cross-Coupling of Unsaturated Substrates on AlI.

The AlI compound NacNacAl (1, NacNac = [ArNC(Me)CHC(Me)NAr]- , Ar = 2,6-iPr2 C6 H3 ) serves as a template for the chemoselective coupling between carbonyls (benzophenone, fenchone, isophorone, p-tolyl benzoate, N,N-dimethylbenzamide, (1-phenylethylidene)aniline) and pyridine. With the CH-acidic ketone (1R)-(+) camphor, the reaction affords a hydrido alkoxide compound of Al, formed as the result of enolization, whereas an enolizable imine, (1-phenylethylidene)aniline, and the bulky ketone isophorone, still chemoselectively couple with pyridine. In contrast, reaction with the ester p-tolyl benzoate results in cleavage of the ester bond together with replacement of the alkoxy group by a hydrogen atom of the pyridine moiety. This study demonstrates that for carbonyl substrates featuring phenyl substituents, the reaction proceeds via intermediate formation of η2 (C,X)-coordinated (X = O, N) carbonyl adducts, whereas the reaction of 1 with (R)-(-)-fenchone in the absence of pyridine leads to CH activation in the pendant isopropyl group of the Ar substituent of the NacNac ligand.

Ir-Porphyrin-Based Metal-Organic Framework as a Dual Metallo- and Photocatalyst for Inert Alkyl C(sp3)-H Bond Activation and Direct Functionalization.

The activation and transformation of inert alkyl C(sp3)-H bonds to obtain high-value fine chemicals by sustainable solar energy are of great significance. Herein, by incorporating IrIII-porphyrin into metal-organic frameworks (MOFs) to stabilize the highly active carbene, we reported a new approach to combining metallo- and photocatalysis to efficiently accelerate carbene migratory insertion and C-H bond activation via the radical coupling pathway for inert alkane functionalization. The in situ-formed carbene was restricted into the pores of MOFs to produce IrIII-carbene, allowing the first-time isolation and structural characterization of the IrIII-carbene intermediate which are not stabilized by a heteroatom. The product of the reaction, especially the cyclic ethers as substrates, suggested that the functionalization of the α position of the alkoxy group was favored. Additionally, the new approach could be extended to stabilize the metal carbene intermediates to realize C(sp3)-H bond alkylation and arylation.

Electrophilic Etherification of α-Heteroaryl Carbanions with Monoperoxyacetals as a Route to Ketene O,O- and N,O-Acetals.

Alkyl ketene acetals are useful reactants in a variety of synthetic processes, and yet, there are limited routes to their formation as isolable products. We now report the successful synthesis and isolation of heteroaryl ketene acetals through intermolecular transfer of alkoxyl (δ+OR) from electrophilic peroxides to lithiated benzofurans, indoles, and pyridines. Primary and secondary peroxyacetals enable selective transfer of the nonanomeric alkoxy group in moderate to high yield; substrates bearing an electron-donating substituent show enhanced reactivity toward electrophilic oxygen. Heteroaryl ketene acetals are remarkably stable throughout traditional purification techniques; the superior stability of ketene N,O-acetals compared to ketene O,O-acetals is presumably due to increased aromaticity of the indole and pyridine structures. The presented method overcomes typical problems associated with alkyl ketene acetal synthesis as reported products withstood workup and flash column chromatography procedures.

Covalent modification of black phosphorus with alkoxy groups to improve the solubility and ambient stability.

Black phosphorus (BP), a new 2D material as a layered allotrope of phosphorus, has regained attention due to its outstanding semiconductor characteristics. However, the major hurdles of using few-layer BP for applications are its poor solution processability and low ambient stability. Here, we report a covalent modification of BP nanosheets by a chemical reaction with sodium alkoxide. Fourier transform infrared spectra, Raman spectra, X-ray photoemission spectra and thermogravimetric analyses all confirmed the successful introduction of alkoxy groups on the BP surface with P-O-C bonds, which increased the solubility and ambient stability of BP. The introduced alkoxy groups as soluble side chains on the BP surface not only increase the solubility of BP nanosheets by almost 3 times, but also decrease the degradation ratio of the modified BP by about 2 times because of the encapsulation. In this work we developed a facile synthetic strategy to covalently modify BP by introducing soluble side chains, suggesting an effective way to realize its full potential application in electronics.

A versatile iodo(III)etherification of terminal ethynylsilanes using BF3-OiPr2 and alkyl benzyl ethers.

A series of (E)-α-silyl-β-alkoxyvinyl-λ3-iodanes was synthesized from iodosylbenzene, BF3-ether complexes, and terminal ethynylsilanes. The combined use of BF3-OiPr2 and benzyl ethers of primary alcohols (ROBn) allows the chemoselective transfer of primary alkoxy groups (RO) onto the β-position of the terminal ethynylsilanes.

Copper(II) mediated ortho C-H alkoxylation of aromatic amines using organic peroxides: efficient synthesis of hindered ethers.

Synthesis of hindered alkyl aryl ether derivatives (R-O-Ar) remains a huge challenge and highly desirable in organic and medicinal chemistry because extensive substitution on the ether bond prevents the undesired metabolic process and thus avoids rapid degradation in vivo. Herein, we report an unprecedented hindered alkoxylation of picolinamide attached aromatic amines using economic copper salt and organic peroxide to get highly desirable α-tertiary alkyl aryl ethers.

Thermally stable polyfluorinated monoalkoxysilanetriols and dialkoxydisiloxanetetrols.

The reaction of the polyfluorinated lithium triarylmethanolates Ar3COLi (Ar = C6F5, 3,5-(CF3)2C6H3) with SiCl4 provided the monosubstituted products Ar3COSiCl3 (1a, Ar = C6F5; 1b, Ar = 3,5-(CF3)2C6H3). The hydrolysis of 1a and 1b produced the silanetriols Ar3COSi(OH)3 (2a, Ar = C6F5; 2b, Ar = 3,5-(CF3)2C6H3) without the aid of an HCl scavenger. The reaction of two equivalents of Ar3COLi (Ar = C6F5, 3,5-(CF3)2C6H3) with (Cl3Si)2O afforded the disubstituted products [(C6F5)3COSiCl2]2O (3a) and {[(3,5-(CF3)2C6H3)3CO]SiCl2}2O (3b), the hydrolysis of which gave the corresponding disiloxanetetraols [(C6F5)3COSi(OH)2]2O (4a) and [(3,5-(CF3)2C6H3)3COSi(OH)2]2O (4b). At high concentrations in the presence of HCl, 2b undergoes controlled condensation to yield 4b. In the solid-state, 2a, 4a and 4b are mainly associated by hydrogen bonds of the type SiO-H⋯O(H)Si whereas the competing SiO-H⋯O(C)Si type was not observed.

Boundary Friction of ZDDP Tribofilms

The frictional properties of ZDDP tribofilms at low entrainment speeds in boundary lubrication conditions have been studied in both rolling/sliding and pure sliding contacts. It has been found that the boundary friction coefficients of these tribofilms depend on the alkyl structure of the ZDDPs. For primary ZDDPs, those with linear alkyl chains give lower friction those with branched alkyl chain ZDDPs, and a cyclohexylmethyl-based ZDDP gives markedly higher friction than non-cyclic ones. Depending on alkyl structure, boundary friction coefficient in rolling-sliding conditions can range from 0.09 to 0.14. These differences persist over long duration tests lasting up to 120 h. For secondary ZDDPs, boundary friction appears to depend less strongly on alkyl structure and in rolling-sliding conditions stabilises at ca 0.115 for the three ZDDPs studied. Experiments in which the ZDDP-containing lubricant is changed after tribofilm formation by a different ZDDP solution or a base oil indicate that the characteristic friction of the initial ZDDP tribofilm is lost almost as soon as rubbing commences in the new lubricant. The boundary friction rapidly stabilises at the characteristic boundary friction of the replacement ZDDP, or in the case of base oil, a value of ca 0.115 which is believed to represent the shear strength of the bare polyphosphate surface. The single exception is when a solution containing a cyclohexylethyl-based ZDDP is replaced by base oil, where the boundary friction coefficient remains at the high value characteristic of this ZDDP despite the fact that rubbing in base oil removes about 20 nm of the tribofilm. XPS analysis of the residual tribofilm reveals that this originates from presence of a considerable proportion of C-O bonds at the exposed tribofilm surface, indicating that not all of the alkoxy groups are lost from the polyphosphate during tribofilm formation. Very slow speed rubbing tests at low temperature show that the ZDDP solutions give boundary friction values that vary with alkyl group structure in a similar fashion to rolling-sliding MTM tests. These variations in friction occur immediately on rubbing, before any measurable tribofilm can develop. This study suggest that ZDDPs control boundary friction by adsorbing on rubbing steel or tribofilm surfaces in a fashion similar to organic friction modifiers. However it is believed that, for primary ZDDPs, residual alkoxy groups still chemically bonded to the phosphorus atoms of newly-formed polyphosphate/phosphate tribofilm may also contribute to boundary friction. This understanding will contribute to the design of low friction, fuel efficient crankcase engine oils.Graphical

Enhancement of the response time in organic photorefractive composites using alkoxy-substituted PDCST as a nonlinear optical chromophore.

The ease of the molecular orientation of a chromophore has an important effect on the electro-optical (EO) properties of polymeric photorefractive (PR) composites. A derivative of 4-piperidinobenzylidene-malononitrile (PDCST) with an alkoxy group added as a side branch was synthesized to improve the molecular orientation characteristics. Electrophoresis was performed on the polymeric PR composite to which the improved PDCST had been added. The optical properties and response times were examined to evaluate the effects of the substitution of the alkoxy group. PDCST substituted with the alkoxy group showed enhanced EO properties and a PR grating formation rate.

Effect of replacing the terminal phenyl ring with 3-pyridyl and inversion of imine linkage on the mesophase behaviour of four-ring azo/ester/Schiff base compounds

ABSTRACT In the present work two homologue series of four-ring azo/ester/imine compounds; namely, 4-(4′–alkoxy–phenylazo) phenyl–4′′–(benzylidene–amino) benzoate, I n, and 4–(4′–alkoxy–phenylazo) phenyl–4′′–[(pyridin-3–ylmethylene)–amino] benzoate, II n, were prepared and investigated for their mesophase behaviour. In these two types of homologue series, the length of the terminal alkoxy group (n) varies between 6 and 16 carbons. Compounds prepared in both series were structurally characterised via thermogravimetric and elemental analyses, FTIR, 1H-NMR, and mass spectroscopy. Their mesophase transition temperatures were determined by differential scanning calorimetry (DSC), whereas, the type of the mesophase was identified by polarised light microscopy (PLM). The molecular structure–property relationship was conducted aiming to investigate the effect of replacing the terminal phenyl group in I n with a pyridyl one in II n, in addition to the effect of variation of the alkoxy chain length. Aiming to investigate the effect of inversion of the methineazo group on the mesophase behaviour of the compounds, a comparison was made between the prepared series of compounds (I n) with previously prepared four rings 4-(4′-alkoxyphenylazo)–phenyl 4′′–phenyliminomethyl–benzoate phenyl-4ʹ-(4′′-alkoxyphenylazo) benzoate, III n. Finally, the mesophases of series II n were compared with their corresponding three-ring analogues, 4-(4′-alkoxy phenyl −4′′-[(pyridin-4-ylmethylene)–amino] benzoate analogues (IV n).

Metal‐Free, Multicomponent Anti‐Markovnikov Hydroarylsulfonylation and Alkoxyarylsulfonylation of Vinyl Arenes

AbstractA unified strategy for the hydro‐arylsulfonylation of vinyl arenes has been developed under catalyst, additive‐free conditions at room temperature from the corresponding aryldiazonium salts, DABSO (DABCO ⋅ 2SO2), and thiophenol as hydrogen atom transfer (HAT) reagent. Mechanistically, an incipient arylsulfonyl radical is generated from the corresponding aryl diazonium salts and DABSO which undergoes anti‐Markovnikov addition to styrenes followed by hydrogen atom transfer from thiophenol. Interestingly, this multi‐component reaction is highly chemoselective suppressing deleterious thiosulfonylation and thiol‐ene reactions. Tuning the reaction conditions, a four‐component difunctionalization with alkoxy group has been achieved using 1,4‐dicyanobenzene as an oxidant. Furthermore, base‐promoted elimination to form vinyl sulfone has been also examined. The practicability of this present reaction has been demonstrated by the ex situ generation of sulfur dioxide in an H‐type reaction vessel and subsequent hydro‐ and alkoxyarylsulfonylation in good to moderate yields. The hydroarylsulfonylation reaction is scalable and applied to a metal‐free synthesis of the key intermediate for an anti‐migraine drug Eletriptan.magnified image

Copper redox mediators with alkoxy groups suppressing recombination for dye-sensitized solar cells

Two copper complexes ([Cu(moby)2]2+/+ (moby=6,6′-bis(methoxymethyl)-2,2′-bipyridine) and [Cu(eoby)2]2+/+, (eoby=6,6′-bis(ethoxymethyl)-2,2′-bipyridine)) with bipyridine ligands were synthesized and used as redox mediators in dye-sensitized solar cells (DSSCs). The DSSCs exhibited high power conversion efficiencies of over 10% under simulated one sun irradiation (100 mW cm−2, AM 1.5G). The introduction of alkoxy groups onto the ligands effectively suppress charge recombination and increased the solubility of the copper complexes in acetonitrile, which led to the high photocurrent and stability of the DSSCs. The redox potentials of [Cu(moby)2]2+/+and [Cu(eoby)2]2+/+ were 0.65 and 0.70 V, respectively, whereas the open-circuit voltages of their DSSCs were still above 1.0 V. The relatively low redox potentials of the copper complexes enable them to match with more sensitizers to realize DSSCs with high photocurrent and photovoltage, providing an opportunity to further improve DSSCs by optimizing the copper redox mediator.

9,10-Anthraquinones Disubstituted with Linear Alkoxy Groups: Spectroscopy, Electrochemistry, and Peculiarities of Their 2D and 3D Supramolecular Organizations.

Spectroscopic, electrochemical, and structural properties of 2,6-dialkoxy-9,10-anthraquinones (Anth-OCn, n = 4, 6, 8, 10, and 12) of increasing alkoxy substituents length were investigated. UV–vis spectroscopy showed a substitution-induced bathochromic shift of the least energetic band from 325 nm in the case of unsubstituted anthraquinone to ca. 350 nm for the studied derivatives. Similarly as unsubstituted anthraquinone, the studied compound showed two reversible one electron reductions to a radical anion and spinless anions, respectively. The first reduction was affected by electron-donating properties of the substituents, its potential being shifted to ca. −1.5 V (vs Fc/Fc+), i.e., by 80 to 95 mV as compared to the case of unsubstituted anthraquinone. This corresponded to a decrease of |EA| from 3.27 to 3.19–3.17 eV. The experimental spectroscopic and electrochemical data were in full agreement with the DFT calculations. The introduction of the alkoxy substituent improved solution processibility of the studied compounds and facilitated the formation of their ordered supramolecular 2D aggregation on HOPG as well as single crystal growth from solutions. Comparative structural investigations carried out on single crystals and monolayers deposited on HOPG revealed two, mutually related, effects of the substituent length on the resulting supramolecular organization. The first one concerns both the 2D organization in the monolayers and 3D molecular arrangement in crystals: increasing substituent length evolution of the structure occurs from herringbone-type to lamellar. The second effect, observed in monolayers of the derivatives with longer substituents, concerns gradual evolution of their lamellar structures with increasing substituent length. This evolution is induced by the structure of the graphite substrate and involves increasing correlation of the molecules orientation (anthraquinone cores as well as alkoxy substituents) with the symmetry of the graphite substrate. As a result, their 2D and 3D structures become dissimilar.

Synthesis of 2‐O‐Functionalized‐5‐salicyloyl Pyridine Derivatives Catalyzed by 2‐Mercaptobenzimidazole

AbstractA concise and efficient one‐pot sequential approach for the synthesis of 5‐salicyloyl pyridine frameworks was developed from a reaction of 3‐formylchromones, malononitrile, various alcohols, and 2‐mercaptobenzimidazole as a catalyst. Malononitrile is the nitrogen source in this reaction. In this method, the variety of 2‐alkoxypyridines derivatives containing alkoxy, allyloxy, and acetylene functional groups can increase the bathochromic effect of the λmax of pyridine to the longer wavelengths. According to experimental and theoretical investigations by the DFT method, long‐wavelength bands of 5‐salicyloyl pyridine derivatives related to the HOMO→LUMO and HOMO→LUMO+1 transitions have the π→π* nature and are caused by intramolecular charge transfer from the phenol fragment to the pyridine ring.