Alkylation Of Phenol Research Articles

Computational studies of the mechanism of Pd-Catalyzed Intramolecular Friedel–Crafts allylic alkylation of phenols

We previously reported a synthetic method of spirocyclohexadienones using an Pd-catalyzed intramolecular ipso-Friedel–Crafts allylic alkylation of para-substituted phenol derivatives. However, the mechanism for the step leading to spirocyclization and driving force behind the remarkably easier formation of the five-membered spirocyclohexadienone as compared with the six-membered spirocyclohexadienone were unclear. Herein, detailed density functional theory (DFT) calculations for the spirocyclization were performed to obtain a plausible reason for the observed behavior. In addition, the mechanistic basis of the characteristic ortho-selectivity in the related Pd-catalyzed intramolecular Friedel–Crafts allylic alkylation of meta-substituted phenol derivatives was elucidated. DFT calculations and experimental studies revealed that the ortho-selective allylation proceeded via an unexpected eleven-membered oxapalladacycle-mediated intramolecular Friedel–Crafts type process.

Aromatics production from fast co-pyrolysis of lignin and waste cooking oil catalyzed by HZSM-5 zeolite

Lignin and waste cooking oil are wastes from paper and food industries, respectively. In this work, the catalytic fast co-pyrolysis of lignin and waste cooking oil for the production of aromatics in a pyroprobe was investigated with an aim to improve the utilization of lignin waste and waste cooking oil. Furthermore, lignin-derived monomers, including phenol, o-cresol, and guaiacol, were also used as model feedstock for the catalytic co-pyrolysis in order to study the mechanism underlying aromatic formation. The mechanistic study helped lay theoretical foundation for the industrial application of the co-pyrolysis process. The effects of catalyst and waste cooking oil addition on co-pyrolysis product fractional yield and selectivity were studied. High amount of waste cooking oil in the feedstock with appropriate catalyst-to-feedstock ratio (3:1) contributed to high peak-area yields of the total detected compounds and aromatics. The alkylation and demethoxylation of phenols were enhanced at high ratios of catalyst to feedstock and waste cooking oil to lignin. When the ratio of waste cooking oil to lignin was 1:1, the highest mono-aromatic selectivity (82.6%) and synergistic extent (52.1%) for mono-aromatic production were obtained. The catalytic co-pyrolysis of the lignin-derived monomers and waste cooking oil showed that guaiacol was the most active compound to be converted to aromatics, followed by o-cresol, and phenol. The reaction mechanism underlying the formation of aromatics from the synergistic conversion of aliphatics and phenolics was elaborated.

One-pot Synthesis of Hierarchical Mesoporous ZSM-5 from the Assembly of Nanocrystals Using Urea as Additive

A hierarchical mesoporous ZSM-5 catalyst with aggregated nanocrystals structure was one-pot hydrothermally synthesized by using urea as the additive. The crystalline phase, morphology and hierarchical architectures were characterized by the XRD, SEM, TEM and N2 adsorption/desorption analyses. The nano-aggregates showed MFI crystalline phase and were composed of connected nanoparticles. The samples had the high surface area and the pore volume from intercrystalline among the nanoparticles due to spontaneously stacking of nanocrystals. The pyridine-adsorbed FTIR and the catalytic performances in the alkylation of phenol and tert-butyl alcohol were applied to evaluate the accessibility of acid sites and the catalytic activities for the hierarchical mesoporous ZSM-5 samples. The samples possessed high accessibility of acid sites which resulted from their large amount of mesopores, and its catalytic activity was improved dramatically. The phenol conversion could reach up to 95.6%, and the corresponding selectivity of 4-TBP and 2,4-DTBP was 44% and 51.5%, respectively.

Single-Electron Transfer from Dimsyl Anion in the Alkylation of Phenols.

While attempting to synthesize biaryl ethers we discovered the inadvertent formation of a methylsulfoxylmethyl ether byproduct. Formation of this unexpected byproduct presented an opportunity to streamline the synthesis of methylsulfoxylmethyl ethers. Mechanistic studies suggest a radical pathway with dimsyl potassium as a reducing agent.

Phosphorous Acid-Catalyzed Alkylation of Phenols with Alkenes.

A H3PO3-catalyzed alkylation of phenols with alkenes is achieved in a facile, efficient, and selective manner. The reaction shows a unique selectivity, i.e., excellent regioselectivity, thorough suppression of overalkylation, without alkylation of a simple phenyl ring, and can selectively provide ortho-, meta-, or para-alkylated phenol derivatives in good to excellent yields. This feature along with mild reaction conditions, sensitive functional group tolerance, and scale-up synthesis and late modification of phenolic bioactive compounds make it an ideal and practical alternative for the modification of phenols.

Mesoporous aromatic frameworks modified by metal chlorides in phenol alkylation with oct-1-ene

Mesoporous polyaromatic frameworks (PAF) based on tetraphenylmethane were synthesized. The PAF/AlCl3 and PAF/FeCl3 catalysts were prepared by impregnating the synthesized products with aluminum and iron chlorides, respectively. The resulting materials were characterized by low-temperature adsorption—desorption of nitrogen, IR spectroscopy, and transmission electron microscopy. The catalytic activity of PAF/AlCl3 and PAF/FeCl3 was tested in the phenol alkylation with oct-1-ene. The tests showed that the use of these catalysts gave both alkylphenols (C-alkylates) and alkyl phenyl ethers (O-alkylates) in the total yields up to 78 and 65% for PAF/AlCl3 and PAF/FeCl3, respectively. The fraction of alkylphenols depends on both the catalyst amount and reaction temperature.

Mechanistic Insights into the Chemo- and Regio-Selective B(C6F5)3 Catalyzed C-H Functionalization of Phenols with Diazoesters.

The Lewis acidic B(C6F5)3 was recently demonstrated to be effective for the C-H alkylation of phenols with diazoesters. The method avoids the general hydroxyl activation in transition-metal catalysis. Ortho-selective C-H alkylation occurs regardless of potential para-selective C-H alkylation and O-H alkylation. In the present study, a theoretical calculation was carried out to elucidate the reaction mechanism and the origin of chemo- and regio-selectivity. It is found that the previously proposed B(C6F5)3/N or B(C6F5)3/C bonding-involved mechanisms are not favorable, and a more favored one involves the B(C6F5)3/C═O bonding, rate-determining N2 elimination, selectivity-determining electrophilic attack, and proton transfer steps. Meanwhile, the new mechanism is consistent with KIE and competition experiments. The facility of the mechanism is attributed to two factors. First, the B(C6F5)3/C═O bonding reduces the steric hindrance during electrophilic attack. Second, the bonding forms the conjugated system by which the LUMO energy is reduced via the electron-withdrawing B(C6F5)3. The ortho-selectivity resulted from the greater ortho-C-C (than para-C-C) interaction and the O-H···O and O-H···F hydrogen-bond interaction during electrophilic attack. The greater C-C (than C-O) interaction and the π-π stacking between the benzene rings of phenol and diazoester concerted contribute to the chemo-selective C-H alkylation.

Detosylative (Deutero)alkylation of Indoles and Phenols with (Deutero)alkoxides.

An efficient strategy for N/O-(deutero)alkylation of indoles and phenols with alkoxides/alcohols as the alkylation reagents is described. The consecutive detosylation/alkylation transformations feature mild reaction conditions, high ipso-selectivity, and good functional group tolerance (>50 examples). A one-pot selective N-alkylation of unprotected indoles with alcohols and TsCl is also realized. The application of this method is demonstrated by the introduction of isotope-labeled (CD3 and 13CH3) groups using the readily accessible labeled alcohols and the synthesis of pharmaceuticals.

Alkylation of Phenols with tert-Butanol Catalyzed by H-Form of Y Zeolites with a Hierarchical Porous Structure

tert-Butyl-substituted phenols have been synthesized via the reaction of phenol, o-, m-, and p-cresols with tert-butanol under the action of CBr4-promoted Y-zeolites in the H-form with a hierarchical porous structure.

Synthesis of Ethyl Phenol over Modified HZSM-5 Catalyst in a Fixed Bed Reactor

Abstract The selective synthesis of p-ethyl phenol in vapor phase alkylation of phenol with ethanol was investigated in a fixed bed flow reactor on cerium modified zeolite CeZSM5 at temperature 693 K. A series of cerium modified zeolite such as Ce4ZSM54, Ce6ZSM56, Ce8ZSM58, Ce10ZSM5 were prepared by modifying with 4 %, 6 %, 8 % and 10 % ceric ammonium nitrate solution respectively. HZSM-5 zeolite exchanged with 10 % cerium nitrate solution was proved to be the best of all the catalyst used. The modified catalyst was further characterized by SEM, XRD and EDS. Phenol reacted with ethanol to form ethylphenyl ether by O-alkylation, and p-ethylphenol- and o-ethylphenol isomers by C-alkylation; secondary products were m-ethylphenol and dialkylated compounds. Reactions were carried out in the temperature 623 K–693 K, reactant mole ratio 0.2–0.5 over modified HZSM-5 zeolite. The optimum operating condition for maximum selectivity of p-ethyl phenol were EtOH to phenol mole ratio, 4:1; temperature, 623 K; space-time, 10.2 kg h/kmol and 1 atm pressure. A detailed kinetic study was carried out for the ethyl phenol synthesis reaction. From the product distribution pattern, a kinetic model for the reactions was proposed following the Langmuir–Hinshelwood approach. The kinetic and adsorption parameters of the rate equation were determined by non-linear regression analysis. From the kinetic analysis of the experimental data, the apparent activation energy for the reaction was determined as 43.27 kJ/mol.

Kinetic analysis and reaction mechanism for anisole conversion over zirconia-supported molybdenum oxide

Gas-phase catalytic conversion of anisole and its reaction intermediates was studied over a 10 wt% MoO3/ZrO2 catalyst at temperatures between 553 and 633 K and H2 partial pressures (PH2) ≤ 1 bar. Benzene, phenol, cresol and methyl anisole were identified as the primary products from the hydrodeoxygenation (HDO), hydrogenolysis, intra- and intermolecular alkylation of anisole, respectively. The anisole to benzene conversion featured a first-order dependence with respect to PH2, while the conversion of phenol to benzene and m-cresol to toluene, showed PH2 and Poxygenate reaction orders of 1/2 and zero, respectively. A kinetic model showed that although the secondary pathway of phenol HDO to benzene has a rate constant ∼3 times higher than that for the HDO of anisole to benzene, the anisole HDO pathway is dominant at low anisole conversions. Apparent orders of ∼½ with Poxygenate for anisole hydrogenolysis and alkylation to form phenol, cresol, and methyl anisole implied the existence of different active sites than those responsible for HDO. Co-feed studies with H2O, pyridine, and di-tert butyl pyridine (DTBP) indicated that the active-sites responsible for HDO have a Lewis acid character that is associated with oxygen vacancies and that is distinct from the nature of sites responsible for hydrogenolysis and alkylation. Accordingly, co-feeding CH3OH resulted in increased phenol alkylation rates to form alkylated cresols along with inhibition of phenol to benzene HDO rates. A three-site model was proposed to unify the HDO, hydrogenolysis, and alkylation reactivity data obtained from the kinetic and co-feed studies.

Screening microwave susceptors for microwave-assisted pyrolysis of lignin: Comparison of product yield and chemical profile

Lignin was pyrolyzed with microwave heating in the presence of different microwave susceptors including silicon carbide (SiC), activated carbon (AC), and biochar (BC). The heating profiles of microwave heating with different susceptors were characterized. With SiC as the susceptor, three distinct heating stages were observed, which were believed to correspond to the three main stages of lignin decomposition. The effects of temperature, susceptor loading weight, and susceptor type on product yield and composition were investigated. Higher pyrolysis temperatures favored char reduction, demethoxylation and alkylation of phenols, and H2 formation. Higher SiC loading weight promoted the formation of alkyl phenols and syngas (CO and H2). Compared with SiC, both AC and BC enhanced the production of syngas, accounting for 74.5% and 70.1% in volume percentage, respectively. AC contributed to the highest bio-oil and gas production while BC showed highest selectivity to phenol and alkyl phenols, up to 58.2% and 37.7%, respectively.

Catalytic tertiary butylation of phenol over sulfonated mesoporous polymer catalyst (MP-SO3H): Exceptional selectivity towards 2,4-di-t-Butylphenol

Abstract The alkylation of phenol with alcohols/olefins is an important reaction to transform lignin based phenolics to useful chemicals. In the present study, the sulfonated mesoporous polymers exemplified the exceptional selectivity towards 2,4-DTBP. This remarkable activity of the material is well correlated with its textural properties. The characterization data reveals that the presence of intrinsic mesoporosity, high acid strength, uniform distribution of acidic sites over high surface area are the prerequisites to facilitate this unusual selectivity to 2,4-DTBP. The various micro and mesoporous catalysts have been screened to compare the catalytic activity of MP-SO3H. The MP–SO3H–8 surpassed the catalytic activity of all the catalysts screened. The MP–SO3H–8 exhibits 99.5% phenol conversion and 78% selectivity to 2,4-DTBP. To the best of our knowledge, this is the highest yield ever achieved to 2,4-DTBP till date. In addition, leaching & recyclability studies prove that the material is stable to retain its catalytic activity up to three recycles.

Higher conversion rate of phenol alkylation with diethylcarbonate by using synthetic fly ash-based zeolites

Abstract In this study, zeolites prepared from fly ash pretreated with hydrochloric acid were used for catalysis. The synthesis was performed by a pre-fusion hydrothermal activation with low crystallization temperature (60 °C) and using both seawater and distilled water. The synthetic zeolites were tested via the base-catalyzed gas-phase alkylation of phenol using diethyl carbonate as an innovative alkylating agent, thus obtaining phenol conversions up to 95% with a selectivity of more than 85% in phenetole. These data indicate that the newly-formed zeolites are very selective for the O-ethylation of phenol also at high temperatures. Moreover, the results show that the zeolites formed from fly ash have a greater catalytic activity than that shown by commercial NaY and synthetic MgO, which were chosen as basic reference catalysts.

Production of High-Density Fuel Precursor from Biomass-Derived Aromatic Oxygenates: Effect of N2 Pressure on the Alkylation

The alkylation of biomass-derived aromatic oxygenates (anisole, phenol, guaiacol, and m-cresol) with furfural alcohol and 5-hydroxymethylfurfural is a step toward high-density biofuel. Conversion and selectivity trends toward monoalkylated products were evaluated in the presence of different operational conditions in batch process. It was observed that FeCl3 was the best catalytic system for phenol alkylation and produced 84.7% monoalkylated product at 80 °C, for 30 min in a continuous nitrogen flow. Guaiacol, anisole, and m-cresol gave 100%, 79.6%, and 85.5% monoalkylated product, respectively. The effect of nitrogen pressure on alkylation was reported for the first time; the monoalkylated product selectivity of phenol, anisole, m-cresol reached 95.5%, 88.7%, and 100% at 4, 8, and 10 bar of N2 pressure, respectively. The alkylation of 5-hydroxymethylfurfural (5-HMF) with aromatic oxygenates was also studied by replacing furfuryl alcohol with 5-HMF. The selectivity of the monoalkylated product reached alm...

Hierarchical ZSM-5 Zeolite with Enhanced Catalytic Activity for Alkylation of Phenol with Tert-Butanol

Using polyethylene glycol as a mesoporous soft template, a series of hierarchically porous ZSM-5 zeolites were prepared. X-ray diffraction, infrared spectroscopy, N2 adsorption–desorption, and transmission electron microscopy results demonstrated that the resultant materials contained a micro–mesoporous structure. Since the existence of mesoporous structure favors the diffusion of large molecular reactants and products, the phenol conversion and selectivity to 2,4-Di-TBP on the hierarchical ZSM-5 zeolite can be improved for the alkylation of phenol with tert-butanol.

A cascade mechanism for a simple reaction: The gas-phase methylation of phenol with methanol

The gas-phase alkylation of phenol with methanol, a reaction triggered for the production of o-cresol and 2,6-xylenol, is catalysed by MgO-based catalysts. Despite the industrial use of this process, the mechanism of the reaction – which is commonly believed to be based on a classical electrophilic attack of activated methanol onto the aromatic ring – is far from being fully understood. In some previous studies we reported that the reaction intermediate is salicylic alcohol, which is formed by the reaction between the adsorbed phenolate and formaldehyde, the latter being formed in-situ by methanol dehydrogenation. Here we elucidate the following steps of the reaction mechanism, by combining reactivity experiments and DFT calculation, with MgO as a model catalyst. It was found that salicylic alcohol dehydrates into quinone methide, which is then reduced via H-transfer by methanol to o-cresol. Moreover, a dehydrogenation/hydrogenation equilibrium is established between salicylic alcohol and salicylic aldehyde. The methide can also react with methanol to form 2-methoxymethylphenol, which may decompose into o-cresol, thus providing an alternative pathway for the formation of the alkylated compound.

Synthesis of 3,3-Diarylazetidines by Calcium(II)-Catalyzed Friedel-Crafts Reaction of Azetidinols with Unexpected Cbz Enhanced Reactivity.

Azetidines are valuable motifs that readily access under explored chemical space for drug discovery. 3,3-Diarylazetidines are prepared in high yield from N-Cbz azetidinols in a calcium(II)-catalyzed Friedel-Crafts alkylation of (hetero)aromatics and phenols, including complex phenols such as β-estradiol. Electron poor phenols undergo O-alkylation. The product azetidines can be derivatized to drug-like compounds through the azetidine nitrogen and the aromatic groups. The N-Cbz group is crucial to reactivity by providing stabilization of an intermediate carbocation on the four-membered ring.

Nanocrystalline Hierarchical ZSM-5: An Efficient Catalyst for the Alkylation of Phenol with Cyclohexene.

In this paper, authors report the synthesis of nanocrystalline hierarchical zeolite ZSM-5 and its application as a heterogeneous catalyst in the alkylation of phenol with cyclohexene. The catalyst was synthesized by vacuum-concentration coupled hydrothermal technique in the presence of two templates. This synthetic route could successfully introduce pores of higher hierarchy in the zeolite ZSM-5 structure. Hierarchical ZSM-5 could catalyse effectively the industrially important reaction of cyclohexene with phenol. We ascribe the high efficiency of the catalyst to its conducive structural features such as nanoscale size, high surface area, presence of hierarchy of pores and existence of Lewis sites along with Brønsted acid sites. The effect of various reaction parameters like duration, catalyst amount, reactant mole ratio and temperature were assessed. Under optimum reaction conditions, the catalyst showed up to 65% selectivity towards the major product, cyclohexyl phenyl ether. There was no discernible decline in percent conversion or selectivity even when the catalyst was re-used for up to four runs. Kinetic studies were done through regression analysis and a mechanistic route based on LHHW model was suggested.

Propylphenol to Phenol and Propylene over Acidic Zeolites: Role of Shape Selectivity and Presence of Steam

This contribution studies the steam-assisted dealkylation of 4-n-propylphenol (4-n-PP), one of the major products derived from lignin, into phenol and propylene over several micro- and mesoporous acidic aluminosilicates in gas phase. A series of acidic zeolites with different topology (e.g., FER, TON, MFI, BEA, and FAU) are studied, of which ZSM-5 outperforms the others. The catalytic results, including zeolite topology and water stability effects, are rationalized in terms of thermodynamics and kinetics. A reaction mechanism is proposed by (i) analyzing products distribution under varying temperature and contact time conditions, (ii) investigating the dealkylation of different regio- and geometric isomers of propylphenol, and (iii) studying the reverse alkylation of phenol and propylene. The mechanism accords to the classic carbenium chemistry including isomerization, disproportionation, transalkylation, and dealkylation, as the most important reactions. The exceptional selectivity of ZSM-5 is attributed...