Quaternary Ammonium Hydroxide Research Articles

Acid-site control of ZSM-5 zeolites using quaternary ammonium hydroxides for shale gas dehydroaromatization

The direct non-oxidative shale gas dehydroaromatization is a promising route for BTX (benzene, toluene, and xylenes) production, offering an effective alternative to conventional crude-oil-based processes. However, it faces crucial challenges such as rapid catalytic deactivation in Mo/ZSM-5 catalysts and limited regenerability due to the formation of external hard coke, resulting from external Mo active sites. This study introduces a hydrothermal post-treatment approach that can selectively control the external Al sites in ZSM-5 zeolites using quaternary ammonium hydroxides, aimed at reducing external Mo anchoring sites. This method successfully reduced the external Al and Mo-site densities in Mo/ZSM-5 catalysts, concurrently introducing mesoporosity, eventually leading to improved catalytic stability, reduced hard coke formation, and enhanced regenerability of spent catalysts. We highlight the significance of the roles of quaternary ammonium cations in the hydrothermal post-treatment, contrasting their effects with the NaOH treatment and analogous processes conducted at lower temperatures.

Berberine protects against neomycin-induced ototoxicity by reducing ROS generation and activating the PI3K/AKT pathway

In mammals, aminoglycoside antibiotic-induced injury to hair cells (HCs) and associated spiral ganglion neurons (SGNs) is irreversible and eventually leads to permanent hearing loss. Efforts have been directed towards the advancement of efficacious therapeutic treatments to protect hearing loss, but the ideal substance for treating the damaged cochlear sensory epithelium has yet to be identified. Berberine (BBR), a quaternary ammonium hydroxide extracted from Coptis chinensis, has been found to display potential anti-oxidant and neuroprotective properties. However, its involvement in aminoglycoside antibiotic-induced ototoxicity has yet to be explored or assessed. In the present study, we explored the possible anti-oxidative properties of BBR in mitigating neomycin-triggered ototoxicity. An improved survival of HCs and SGN nerve fibers (NFs) in organ of Corti (OC) explants after neomycin with BBR co-treatment was observed, and BBR treatment attenuated reactive oxygen species (ROS) generation and reduced cleaved caspase-3 signaling by activating six phosphatidylinositol 3-kinase/protein kinase B (PI3K/AKT) signaling relative subtypes, and the addition of PI3K/AKT suppressor LY294002 resulted in a decrease in the protective effect. The protective effect of BBR against ototoxicity was also evident in a neomycin-injured animal model, as evidenced by the preservation of HC and SGN in mice administered subcutaneous BBR for 7 days. In summary, all results suggest that BBR has potential as a new and effective otoprotective agent, operating via the PI3K/AKT signaling pathway.

Approaching High-Performance TS-1 Zeolites in the Presence of Alkali Metal Ions via Combination of Adjusting pH Value and Modulating Crystal Size.

Lewis acid zeolites play an important role in industrially important green reactions closely related to fine chemical and biomass conversion. Titanium-doped TS-1 zeolite is a milestone Lewis acid zeolite widely used in industrially significant green oxidation processes with hydrogen peroxide as an oxidant under mild conditions. TS-1 zeolites are normally synthesized in basic conditions under hydrothermal treatment. Up to now, there has still been no success in synthesizing active TS-1 Lewis acid zeolites by using inorganic alkali, e.g., NaOH or KOH as base, which is cheaper and more stable compared to the quaternary ammonium hydroxide or organic amines used in traditional synthesis. Here, an inorganic base of NaOH was employed in synthesizing active TS-1 zeolites for the first time. The crucial factor was the control of adverse effects of sodium cations on the incorporation of active titanium cations. Higher catalytic activity was achieved by further reducing the size of the TS-1 crystal by using the seed-added strategy, which uses the catalytic activity of a commercial catalyst, the production cost being much lower than commercial TS-1 catalysts, indicating great commercial potential and the possibility of preparing other cheap Lewis acid catalysts by using inorganic alkali.

Electromembrane separation coupled with urea electrolysis for energy-saving recovery of quaternary ammonium hydroxide from industrial wastewater

The electrolytic recovery of quaternary ammonium hydroxide (R4NOH) from the wastewater produced in the process of template-synthesizing molecular sieves has considerable economic benefits. The current practices are challenged by the anode corrosion and high operation costs due to harmful chlorine chemicals in wastewater and high energy consumption. This work proposes a promising energy-saving strategy by combining the recovery of quaternary ammonium hydroxides with urea electrolysis technology. This strategy reduces the anodic oxidation potential and achieves low-energy consumption while avoiding the formation of hypochlorite ions. Through the laboratory-scale closed membrane electrolysis system (CMES) cycle test, it was found that when the cathode output concentration of 0.5 M was reached at a current density of 50 mA cm−2, the energy consumption was saved by 64.7% compared with the traditional technology. Along with the achievement of the expected recovery rate, the high value-added R4NOH were recycled. More specifically, the ultra-low voltage of the electrolyze protected the ecosystem by avoiding the corrosion of harmful chlorine chemicals and demonstrated the potential for large-scale applications at the reduced process costs.

Reacting Mn3O4 powders with quaternary ammonium hydroxides to form two-dimensional birnessite flakes

There is a current interest in synthesis of two-dimensional (2D) materials that would be cost-efficient to scale to industry production. In this study, we report on a bottom-up approach to convert a manganese oxide (Mn3O4) powder into crystalline, 2D layered birnessite flakes. The Mn3O4 precursor powder, is reacted with aqueous solutions of, tetramethyl-, tetraethyl- or tetrabutylammonium hydroxide in a shaker oven at 80 °C for 4 days. X-ray diffraction confirmed that in all cases, upon filtration of colloidal suspensions, well-stacked, crystalline, 2D MnO2 birnessite layers formed, that upon characterization were found to be quite similar. The major differences were the spacings between the flakes that depended on cation size. Selected area diffraction patterns in a transmission electron microscope confirmed both the structure and the polycrystallinity of the flakes. Raman spectroscopy confirmed the structure. The zeta-potentials of the 2D flakes were measured to be ≈−35 ± 2 mV. When UV–Vis spectra were converted to Tauc plots, direct and indirect band gap energies of ≈2.15 and ≈2.60 eV were obtained, respectively. Additionally, the oxygen evolution reactivity of our birnessite flakes significantly are better than those found for Pt/C, demonstrating a high degree of catalytic reversibility. The facile conversion of a relatively inexpensive, earth-abundant oxide, Mn3O4, into a highly value-added 2D birnessite using a one-pot, simple hugely scalable, protocol at near ambient temperatures and pressures with various quats can be considered a breakthrough in the production of these nanomaterials.

Effect of Hydration on the Intermolecular Interaction of Various Quaternary Ammonium Based Head Groups with Hydroxide Ion of Anion Exchange Membrane Studied at the Molecular Level

Currently, the main limitation of Anion Exchange Membrane Fuel Cells is related to their low chemical stability under alkaline conditions due to the degradation of quaternary ammonium-based head groups, which lowers the transportation of hydroxide ions as well. The knowledge of the intermolecular interaction of various quaternary ammonium head groups with hydroxide ions is the key to improving hydroxide ion’s diffusivity and chemical stability of various quaternary ammonium-based head groups. Consequently, the intermolecular interaction of hydroxide ions with different quaternary ammonium head groups of anion exchange membranes is investigated at the different hydration levels via classical all-atom Molecular Dynamics and molecular well-tempered MetaDynamics simulation methods in this work. Several quaternary ammonium head groups (a) pyridinium, (b) 1,4-diazabicyclo [2.2.2] octane, (c) benzyltrimethylammonium, (d) n-methyl piperidinium, (e) guanidium, and (f) trimethylhexylammonium were investigated in detail. Classical all-atom molecular dynamic simulations illustrate that the results of radial distribution function between the nitrogen atoms of six different quaternary ammonium head groups and hydroxide ion are as follows: (a) > (c) ≥ (f) > (d) > (e) > (b). In addition, from the diffusion coefficient values it was found that the mobility of hydroxide ion by quaternary ammonium head group (f) was lower than (c) at the different hydration levels.

Liquid phase exfoliation of metal–organic frameworks in aqueous quaternary ammonium hydroxide solution enables highly efficient photocatalytic CO2 reduction

Metal−organic framework nanosheets (MONs) show promising applications in many fields, but the production of large amounts of high-quality MONs remains a challenge. Here, we report a general liquid-phase stripped approach to exfoliate a benzoic acid linked MOF (Al2(OH)2TCPP-Co) in water by using quaternary ammonium hydroxides as deprotonation reagent, intercalator and stabilizer simultaneously. It is shown that the stripped yield is high up to 27.5%, the thickness of MONs is mainly 1–3 nm, and the horizontalsize is less than one hundred nanometers. The molecular geometry and alkalinity of quaternary ammonium hydroxides play vital roles in the exfoliation of MONs. Moreover, the MONs have been applied as photocatalysts for the conversion of CO2 to CO in a gas–solid model under UV–visible light illumination without using anyphotosensitizer and sacrificialagents. The productivity rate of CO is 118.7 μmol g−1 h−1, which outperforms most of the photocatalysts reported previously. Thus, the liquid phase stripping method reported in this work has great potential in the large-scale production of MONs for efficient photocatalysis of CO2 reduction in the gaseous phase.

Design and introduction of quaternary ammonium hydroxide‐functionalized graphene oxide quantum dots as a pseudo-homogeneous catalyst for epoxidation of α,β-unsaturated ketones

In present work, design and synthesis of a novel pseudo-homogeneous catalyst is described. For this purpose, amine-functionalized graphene oxide quantum dots (N-GOQDs) were prepared from graphene oxide (GO) by a facile one-step oxidative fragmentation approach. The prepared N-GOQDs were then modified with quaternary ammonium hydroxide groups. Various characterization techniques clearly revealed that the quaternary ammonium hydroxide‐functionalized GOQDs (N-GOQDs/OH−) have been successfully synthesized. TEM image revealed that the GOQDs particles are almost regularly spherical in shape and mono-dispersed with particle sizes < 10 nm. The efficiency of the synthesized N-GOQDs/OH− as a pseudo-homogeneous catalyst in epoxidation of α,β-unsaturated ketones in the presence of aqueous H2O2 as an oxidant at room temperature was investigated. The corresponding epoxide products were obtained in good to high yields. This procedure has the advantages of a green oxidant, high yields, involvement of non-toxic reagents and reusability of the catalyst without discernible loss in activity.

An Evaluation of Bath Life Effects on Photoresist Removal for Wafer Level Packaging

With the emergence of 3D integration and wafer level packaging, the pillar bumping process has become a critical processing step. As the process has matured, significant efforts have been made for optimization in terms of both production and cost. This is especially true for photoresist stripping, since thick photoresists are needed to pattern high aspect ratios and must be removed in subsequent steps to expose underlying metal films. In this study, the removal of a thick negative tone photoresist with solder pillar plated wafers were investigated using a dimethyl sulfoxide blend with a quaternary ammonium hydroxide. Emphasis was placed on exploring the feasibility of an extended bath life beyond 7 days. Coupon level beaker tests were used to provide insight into the swelling and dissolution mechanisms with fresh and aged chemistry. Additionally, several chemistries were compared to examine the effect of the quaternary ammonium hydroxide. Based on these findings, chemical aging studies were performed on 300 mm wafers using a highly customizable single wafer processing tool that combined soaking and a high-pressure spray processing to potentially prolong the bath age even further. In addition to stripping efficiency at extended bath life, the compatibly with pillar structures and seed layers is investigated. Results from the study highlight potential methods to extend bath life while maintaining photoresist stripping efficiency.

Effect of Alternative Developer Solutions on EUVL Patterning

This work explores the application of alternative developer solutions (“developers”) with the aim of understanding their potential effectivity in the reduction of resist-based stochastic pattern defects (or “stochastic defects”) in extreme ultraviolet lithography (EUVL). Specifically, the application of a quaternary ammonium hydroxide type aqueous developer; ethyltrimethylammonium hydroxide (ETMAH) in comparison to the industry de facto standard aqueous alkali tetramethylammonium hydroxide (TMAH) developer was investigated. Focusing on EUV exposed contact hole (CH) patterns on a typical chemically amplified resist (CAR), the effect of these developers on stochastic defects were assessed. As a result, patterning investigations showed that the lithographic performance of the CAR developed in ETMAH is comparable to the those obtained with TMAH. In situ resist dissolution analysis using the high-speed atomic force microscope (HS-AFM) confirms this as it showed that the rate of CH formation during resist dissolution in both developers are relatively the same. Moreover, it was also understood that compared to the commonly used alkali developer concentration of 0.26N, a lower ETMAH developer concentration of 0.20N resulted in stochastic defect margin improvement, while maintaining lithographic performance. In situ resist dissolution analysis showed an obvious slowing down of CH pattern formation rate at 0.20N concentration, suggesting the possibility that of over-dissolution at the higher concentration condition, translating to an increase in merging CH defects. The results from this study show the advantages of further pursuing optimal developers for EUVL. This is especially significant as these findings indicate how optimal developers mitigate resist-based stochastic defects while maintaining lithographic performance.

On the structure of one-dimensional TiO2 lepidocrocite

•Scalable, cheap, one pot facile synthesis of titanium dioxide nanofilaments (NFs) •Raman HRTEM and XRD indicated the NF’s structure is 1D TiO2, lepidocrocite-based •TEM images suggest the smallest NFs may have cross sections of the order of 5 × 5 Å2 •NFs grow along [100] and self-align in two directions, viz. in- and out-of-plane We recently reported on the synthesis of one-dimensional (1D) TiO2-based nanofilaments, (NFs) by reacting water insoluble, earth abundant, and non-toxic Ti-containing precursors, such as TiC, TiB2, and TiSi2, among others, with quaternary ammonium hydroxides, mostly tetramethylammonium hydroxide at near-ambient conditions. From selected area diffraction, X-ray diffraction, and Raman spectroscopy, we previously concluded that the NF's structure was anatase-based. Herein, using high-resolution scanning transmission electron microscopy, Raman spectroscopy, obtained using low laser power, and density functional theory modeling, we conclude that the actual structure is 1D titania lepidocrocite-based structure with minimal cross sections of ≈ 5 × 5 Å2. The NFs grow along [100] with a and c lattice parameters of 3.78 ± 0.01 Å and 3.04 ± 0.06 Å. They tend to self-assemble/stack in two directions, viz. along the b and c axes. And while in-plane and out-of-plane interfilamentous distances are functions of the nature of the cations surrounding the NFs, the band gap, at ≈ 4 eV, is not. We recently reported on the synthesis of one-dimensional (1D) TiO2-based nanofilaments, (NFs) by reacting water insoluble, earth abundant, and non-toxic Ti-containing precursors, such as TiC, TiB2, and TiSi2, among others, with quaternary ammonium hydroxides, mostly tetramethylammonium hydroxide at near-ambient conditions. From selected area diffraction, X-ray diffraction, and Raman spectroscopy, we previously concluded that the NF's structure was anatase-based. Herein, using high-resolution scanning transmission electron microscopy, Raman spectroscopy, obtained using low laser power, and density functional theory modeling, we conclude that the actual structure is 1D titania lepidocrocite-based structure with minimal cross sections of ≈ 5 × 5 Å2. The NFs grow along [100] with a and c lattice parameters of 3.78 ± 0.01 Å and 3.04 ± 0.06 Å. They tend to self-assemble/stack in two directions, viz. along the b and c axes. And while in-plane and out-of-plane interfilamentous distances are functions of the nature of the cations surrounding the NFs, the band gap, at ≈ 4 eV, is not.

Efficient isolation of keratin from protein-rich waste biomass: a practical approach to minimize environmental impact and valorize waste biomass

Among various protein-containing biomass wastes, waste animal wool, poultry feather, and human hair are considered one of the most important renewable sources of keratin. Animal wool and human hair are utilized for the production of several products. However, the substantial quantity of short fibers that are inappropriate for spinning and being unusable is thrown away as waste resulting in significant environmental issues in terms of their accumulation in water bodies resulting in obstruction of waterways and other related problems. Similarly, poultry wastes, especially waste chicken feathers (WCF) are dumped or burnt or used as low-value fertilizer in certain applications. The purpose of this research is to develop an efficient method that can extract the recoverable keratin from various wastes and effectively utilize the spent solvent in the extraction process. Herein suitability of an aqueous solution of quaternary ammonium hydroxide known as tetramethyl ammonium hydroxide (TMAOH, 25% w/w in water) to solubilize these protein wastes and extract keratin from them was investigated. The solvent could solubilize ca. 39–44% w/w of waste animal wool (WAW), 19–25% of waste human hair (WHH), and 55–60% of WCF. Crude keratin with ca. 19–20%, 35–37%, and 69–74% were isolated from WAW, WHH, and WCF, respectively. The chemical and structural stability of keratin thus isolated was established. The recovered TMAOH, insoluble WAW, and WCF were found to be nontoxic to soil microbes. The recovered TMAOH thus generated after isolation of keratin was used for green gram (Vigna radiata) seed treatment, and a substantial increase in the height (4–12%) and weight (9–58%) of the plants was observed. Treating biomass waste as a source of high-value compounds may minimize environmental impact by reducing the waste load.

Synthesis of Al-BEC zeolite as an efficient catalyst for the alkylation of benzene with 1-dodecene

A novel quaternary ammonium hydroxide, p-Xylylene-bis(N-methylpiperidinium hydroxide) (XBMPOH), was prepared and used as an organic structure-directing agent (OSDA) for the syntheses of BEC zeolites. Both Si,Ge-BEC and Al incorporated BEC (Al-BEC) zeolites were successfully synthesized. In comparison with commonly used OSDA (tetraethylammonium hydroxide (TEAOH)), XBMPOH was more suitable for the crystallization of BEC structure, especially in the Al containing system. Al-BEC zeolites were directly synthesized at lower germanium and OSDA content, in a wider (Si + Ge)/Al ratio range (20 to ∞ vs. 50 to ∞) and shorter time (6 h vs. 12 h). For the first time, Al-BEC zeolites were used as a solid acid to catalyze the alkylation of benzene with 1-dodecene, and showed significant catalytic performance. After an acidic treatment procedure, the catalytic performance was further improved due to the removal of non-framework Al with accompanied exposure of framework Al.

Reaction kinetics of melt post‐polycondensation process for polycarbonate in film state

AbstractMelt post‐polycondensation (MPP) process is one of manufactures industrially that can efficiently increase the molecular weight of polycarbonate (PC). Herein, the MPP experiments of several PC materials using quaternary ammonium hydroxides and alkali metal compounds as the catalyst in the film state are studied. The reaction products are characterized by Ubbelohde viscometer, DSC, 1H‐NMR, ultraviolet spectrophotometry, advanced polymer chromatography and rotational rheometer. It is found that MPP can effectively improve the intrinsic viscosity of PC. After a certain reaction time at a specific temperature, the number average molecular weight (Mn) of PC is raised from 19,000 to 54,600 g/mol. Furthermore, the 1H‐NMR results reveal that Fries rearrangement products are produced during the MPP process. Based on the functional group model, a reaction kinetic model, combining the effects of the main melt polycondensation reaction and the Fries rearrangement reaction, is established for the first time. The reaction rate constants at different temperatures and the reaction activation energies of the two PC materials are obtained. This work provides a new reaction kinetics model to guide the MPP process of PC, which contains Fries rearrangement reaction.

Protective desilication of β zeolite: A mechanism study and its application in ethanol-acetaldehyde to 1,3-butadiene

The conversion of bioethanol to 1,3-butadiene (ETB) is expected to be one of the most promising routes to alternate the petroleum route. However, the preparation of hierarchical β zeolite to serve as the catalyst support is still challenging. In this work, hierarchical β zeolite was prepared through protective desilication by quaternary ammonium hydroxide (TAAOH), and Zr-β zeolite was prepared using the hierarchical β zeolite by dealumination-metallization strategy for ETB reaction. The mechanism of protective desilication was clarified by some control experiments. The protection of TAA+ coexists with OH- attacking and they act in different treating stage, and there lies the best treatment concentration regarding to the mesoporous formation in β zeolite. By adjusting the length of TAAOH alkyl chain, the mesoporosity of β zeolite was tuned successfully. The catalytic activity of Zr-β zeolite was enhanced by the generation of mesoporosity and better capability of coke was achieved which mitigated the deactivation.

Effective carbon dioxide sorption by using phyllosilicate anchored poly(quaternary-ammoniumhydroxidemethyl styrene) nanocomposites

ABSTRACT Polymers are highly promising materials for capturing carbon dioxide (CO2), a greenhouse gas. Hence in this work, we prepared phyllosilicate supported mesoporous polymer via reversible addition–fragmentation chain transfer (RAFT) polymerisation, which is the one among the controlled radical polymerisation. The mesoporous material anchored on dodecanethiol trithiocarbonate acts as a chain transfer agent (CTA) for the polymerisation of chloromethyl styrene and further conversion to quaternary ammonium compound which is effective to trap CO2 using tertiary amine. The synthesised porous phyllosilicate/polymer nanocomposites have been characterised by using various analytical tools. The CO2 sorption experiments were carried out by passing CO2 onto the synthesised porous phyllosilicate/polymer nanocomposites. The sorption kinetics was monitored by X-Ray photoelectron spectroscopy (XPS) and Fourier-transform infrared spectroscopy (FT-IR) spectra in the presence of carbonate were obtained by reaction of quaternary ammonium hydroxide and CO2. The phyllosilicate anchored macromolecular CTA (macro-CTA) and the surface-initiated polymer nanocomposites encompassed apparent surface areas of 94.5 and 26.8 m2 g−1, respectively. In addition, the total pore volumes calculated for the macro-CTA and polymer were found to be 0.27 and 0.095 cm3g−1, while the average pore sizes were 14.24 and 11.46 nm, respectively. The CO2 sorption capacity of the phyllosilicate/polymer nanocomposites, monitored at different temperatures, is the fastest for 25°C but slower for the sample treated at 50°C which may due to the dipole and quadrupole interaction.

Kinetic Behavior of Quaternary Ammonium Hydroxides in Mixed Methane and Carbon Dioxide Hydrates.

This study evaluates the kinetic hydrate inhibition (KHI) performance of four quaternary ammonium hydroxides (QAH) on mixed CH4 + CO2 hydrate systems. The studied QAHs are; tetraethylammonium hydroxide (TEAOH), tetrabutylammonium hydroxide (TBAOH), tetramethylammonium hydroxide (TMAOH), and tetrapropylammonium hydroxide (TPrAOH). The test was performed in a high-pressure hydrate reactor at temperatures of 274.0 K and 277.0 K, and a concentration of 1 wt.% using the isochoric cooling method. The kinetics results suggest that all the QAHs potentially delayed mixed CH4 + CO2 hydrates formation due to their steric hindrance abilities. The presence of QAHs reduced hydrate formation risk than the conventional hydrate inhibitor, PVP, at higher subcooling conditions. The findings indicate that increasing QAHs alkyl chain lengths increase their kinetic hydrate inhibition efficacies due to better surface adsorption abilities. QAHs with longer chain lengths have lesser amounts of solute particles to prevent hydrate formation. The outcomes of this study contribute significantly to current efforts to control gas hydrate formation in offshore petroleum pipelines.

Synthesis and characterization of bio-based quaternary ammonium salts with gibberellate or l-tryptophanate anion

Numerous biologically active acids can be transformed into an ionic form in a facile way and combined with appropriate quaternary ammonium cation to improve their application properties or biological activity. This study describes the synthesis of new quaternary ammonium salts with anions of gibberellic acid, a common plant growth regulator from the gibberellin group, or l-tryptophan, an important precursor of auxin biosynthesis. The surface-active tetrapentylammonium ion and natural substances such as acetylcholine, choline, and quinine were the sources of cations. Novel salts of gibberellic acid and l-tryptophan were obtained with high yields exceeding 97% as a result of the metathesis reaction or the neutralization of quaternary ammonium hydroxides. Phase transition temperatures, thermal and chemical stability, and solubility in solvents with different polarities were determined for all obtained salts. On the basis of studies regarding the influence of synthesized salts on the post-harvest longevity and quality of leaves of Convallaria majalis, it was established that the biological activity of the natural plant regulators in most cases was maintained. Therefore, it can be concluded that the conversion of the active substance into the form of a quaternary ammonium salt results in obtaining novel forms of plant growth regulators with favourable physicochemical properties while maintaining the efficacy of the biological active ingredients.Graphic abstract

Cover: Journal of the Chinese Chemical Society 8/2020

In this figure, functional group engineering of abundant surface –NH2 and –NH groups present in the graphitic g–C3N4 to the corresponding quaternary ammonium hydroxide (g– C3N4–OH), serves as efficient heterogeneous metal‐free recyclable catalysts for hydroxylation of arylboronic acids to the corresponding substituted phenols with high selectivity and yield under mild conditions using air as oxidant in aqueous medium. More details about this figure will be discussed by Prof. S. Mannathan and his co–workers on page 1470–1476 in this issue. image

Quaternary ammonium hydroxide‐functionalized g‐C3N4 catalyst for aerobic hydroxylation of arylboronic acids to phenols

AbstractA new and efficient metal‐free approach toward the synthesis of phenols via an aerobic hydroxylation of arylboronic acids by using a novel quaternary ammonium hydroxide g‐C3N4 catalyst has been described. The functionalized quaternary ammonium hydroxide (g‐C3N4‐OH) has been prepared from graphitic carbon nitride (g‐C3N4) scaffold by converting the residual –NH2 and –NH groups to quaternary methyl ammonium iodide by performing a methylation reaction with methyl iodide followed by ion‐exchange with 0.1 N KOH or anion exchange resin Amberlyst A26 (OH‐ form) by post‐synthetic modification. The resultant g‐C3N4‐OH was characterized by XRD, FTIR, field‐emission scanning electron microscope (FESEM), high‐resolution transmission electron microscope (HRTEM), N2 adsorption/desorption isotherms, and acid–base titration. Tested as solid‐base catalysts, the g‐C3N4‐OH showed excellent catalytic activity in the aerobic hydroxylation reaction by converting a variety of arylboronic acids to the corresponding phenols in high yields. More importantly, the g‐C3N4‐OH solid‐base has been successfully reused four times with the minor loss of initial catalytic activity (10.5%).