Catalytic alkylation of phenol with methanol over zinc aluminate

Two samples (A and B) of zinc aluminate spinel were prepared and used as catalysts of phenol methylation. Both catalysts were synthesised at hydrothermal conditions from zinc acetate and from various aluminium precursors: aluminium isopropoxide (catalyst A) or basic aluminium nitrate (catalyst B). Catalyst A was pure ZnAl₂O₄ and B - besides ZnAl₂O4 contained traces of -Al₂O₃. Reactions of phenol alkylation with methanol were carried out in the gas phase under atmospheric pressure in a standard flow reactor with fixed bed. Catalysts indicated different properties in dependence on the aluminium precursor used during preparation. In the presence of catalyst A higher selectivity of ortho-methylation of phenol was obtained. Catalyst B was active both in O-alkylation and C-alkylation.     

Homolytic dissociation in hydrogen-bonding liquids: energetics of the phenol O–H bond in methanol and the water O–H bond in water

The energetics of the phenol O–H bond in methanol and the water O–H bond in liquid water were investigated by microsolvation modelling and statistical mechanics Monte Carlo simulations. The microsolvation approach was based on density functional theory calculations. Optimised structures for clusters of phenol and the phenoxy radical with one and two methanol molecules are reported. By analysing the differential solvation of phenol and the phenoxy radical in methanol, we predict that the phenol O–H homolytic bond dissociation enthalpy in solution is 24.3±11 kJ/mol above the gas-phase value. The analysis of the water O–H bond dissociation by microsolvation was based on optimised structures of OH–(H₂O)_1–6 and –(H₂O)_1–7 clusters. Microsolvation modelling and statistical mechanics simulations predict that the HO–H bond dissociation enthalpies in the gas phase and in liquid water are very similar. Our results stress the importance of estimating the differences between the solvation enthalpies of the radical species and the parent molecule and the limitations of local models based on microsolvation.Proceedings of the 11th International Congress of Quantum Chemistry satellite meeting in honor of Jean-Louis Rivail     

<Emphasis Type="Italic">O</Emphasis>-vinylacetoxime as a hydrogen bond acceptor

According to quantum chemical calculations (B3LYP/6-311G*) and IR spectroscopy the basicity of oxygen atom of O-vinylacetoxime is substantially lower than that of O-ethylacetoxime and is comparable to the basicity of phenyl vinyl and diphenyl ethers. In CCl₄ solution, O-vinylacetoxime gives H-complexes wit methanol by formation of N···HO bonds. With phenol and trifluoroacetic acid under these conditions it enters in the reaction of electrophilic addition. O-Ethylacetoxime in inert media forms with methanol and phenol two types of H-complexes with the N···HO or O···HO bonds.     

Acyl Iodides in Organic Synthesis: I. Reactions with Alcohols

Reaction of acyl iodides RC(O)I (R = Me, Ph) with alcohols R'OH (R' = Me, Et, i-Pr, t-Bu, CH₂ = CHCH₂, HCCCH₂) provides in the corresponding organyl iodides R'I. Unlike that 2-chloroethanol and phenol (R' = CH₂CH₂Cl, Ph) react with RC(O)I in the same way as with acyl chlorides yielding esters RCO₂R'. This reaction path occurs partially also with methanol and ethanol.     

A new mechanism for the addition of alcohols to disilenes revealed by DFT and ONIOM calculations

Density functional and ONIOM calculations of alcohol and phenol additions to two (tetramethyl and tetramesityl) disilenes were carried out. The dimer of MeOH adds to Me₂SiSiMe₂ more readily than the monomer. The trimer does not afford the adduct, but a zwitter-ionic intermediate. In the (CF₃OH)₂ addition to Me₂SiSiMe₂, H?Si bond formation is more advanced than O?Si bond formation in the transition state (TS). Addition of seven phenol derivatives to Me₂SiSiMe₂ was examined, and the dimer reactions were found to be superior to the monomer reaction regardless of the substituents on the benzene rings. (MeOH)₂ reacts also with Mes₂SiSiMes₂ favorably, and an isomer of the reactant-like complex (precursor) may afford an adduct of different stereochemistry via internal rotations. Generally, the dimer of the alcohol or phenol is the reactant toward the disilenes. Exceptionally, a monomer of p-(dimethylamino)phenol reacts with Mes₂SiSiMes₂ owing to steric congestion by the four mesityl groups.     

Insertion reactions of difluorocarbene generated by pyrolysis of hexafluoropropene oxide to OH bond

ROCHF₂-type fluorinated ethers were synthesized by the reaction of hexafluoropropene oxide (HFPO) with alcohol or phenol. In this reaction, although the insertion reaction of difluorocarbene to OH bond and the nucleophilic attack of alcohol or phenol to HFPO were competition, the insertion reaction proceeded predominantly to give fluorinated ether in the case of low nucleophilic alcohol or phenol. In addition, high reaction pressure is advantageous to the selectivity of the fluorinated ethers in the reaction of HFPO with (CF₃)₂CHOH or C₆F₅OH.     

Hydrogen bonding and molecular association in methylated 3-hydroxypyridines

Association in derivatives of 3-hydroxypyridine has been examined via the chemical shifts for OH in PMR for equimolar mixtures of the derivatives of pyridine and phenol in CCl₄ and CH₂Cl₂. It is found that spatial screening of the pyridine N and phenol OH by methyl groups has an anomalous effect on the strength of the complex. A possible explanation is that the ionic form NH . . . O is stabilized on account of increased basicity of the N and acidity of the H in the methyl derivatives of pyridine and phenol. Domination by the intermolecular hydrogen bond between OH and N is the distinctive feature of association in 3-hydroxypyridines relative to association in phenol. The temperature dependence of _OH gives the enthalpy and entropy of association for 2, 4, 6-trimethyl-3-hydroxypyridine and of complex formation for various model systems. IR measurements confirm the conclusions.See [1] for the previous communication.We are indebted to G. G. Dvoryantseva for making the IR measurements.     

Apparent molal volumes and heat capacities of some 1:1 electrolytes in anhydrous methanol at 25°C

A flow calorimeter and flow densimeter have been used to measure volume specific heats and densities of solutions of LiCl, LiBr, NaCl, NaBr, KF, KBr, Kl, CsF, and Bu₄NBr in anhydrous methanol at 25°C. The concentrations ranged from approximately 0.01m to close to saturation in some cases. Apparent molal heat capacities _cp and volumes _v have been evaluated and extrapolated to infinite dilution to obtain _cp ^o and _v ^o . Nearly all the heat capacities in methanol are negative. However, with the exception of the lithium halides and Bu₄NBr they are more positive than heat capacities of the corresponding salts in water. The dependence of the heat capacities on ionic radii is generally opposite in methanol solutions from that observed for aqueous solutions. In agreement with others, the _v ^o data indicate that electrostriction in methanol solutions is greater than in aqueous solutions.     

Effect of water on the ionic-molecular interaction in the acetone-phenol-H2SO4 system

Complexation in the acetone-phenol system and the effect of water on the ionic-molecular interaction in the acetone-phenol-H₂SO₄ system at 30C were investigated by MFTIR (multifrustrated total internal reflection) IR spectroscopy. Acetone and phenol form a 11 complex (PAC-l). In an excess of acetone, all of the phenol is bound with this complex, and a 21 complex (PAC-2) is formed in an excess of phenol. Relatively small amounts of H₂O virtually do not decompose PAC-1. A broad continuous absorption band due to the formation of complexes with a strong quasisymmetric H bond is observed in the IR spectra of solutions with H₂SO₄. Quasi-ion pairs HOSO₂O...H...OC-(CH₃)₂, are formed in an anhydrous system. The acid-solvent complexes decompose and (H₂O...H...OH₂)⁺ ions are formed on addition of water. The continuous absorption coefficients, ₂₀₀₀, of (H₂O...H...OH₂)⁺ ions and quasi-ion pairs were determined.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 5, pp. 1001–1006, May, 1991.     

Heterogeneous-Catalytic Dimerization of Methanol

Oxide systems supported by -Al₂O₃ and MgO were studied in oxidative dimerization of methanol. The highest selectivity is exhibited by tin oxide promoted with Na₂O and La₂O₃ supported by magnesium oxide. Reactions of partial oxidation and etherification of methanol and ethylene glycol proceed on this system to the same extent as dimerization of methanol to ethylene glycol.     

Comparative basicities of heterocyclic analogs of chalcone

Measurements are made of valence vibration frequency shifts of the hydroxyl group of phenol in carbon tetrachloride solution due to the effect of hydrogen bonding with the carbonyl group (u_OH) of chalcone, and its furan, thiophene, selenophene, and N-methylpyrrole analogs. All the compounds form rather stable hydrogen bonds with phenol; u_OH varies in the range 200–284 cm^–1. For propen-3-ones, where the carbonyl group is remote from the heterocyclic ring, a linear relationship is observed between u_OH and pK , previously determined in 100% sulfuric acid solution in glacial acetic acid. The absence of a linear relationship between these quantities for the other ketones is ascribed to steric factors. It is established that heterocyclic groups exhibit a positive conjugation effect as compared with phenol, decreasing in the order N -methyl-2-pyrryl > 2-furyl > 2-selenienyl > 2-thienyl.     

The effect of methanol on the self reaction of HO2 radicals

The rate constant for the HO₂ self reaction has been determined as a function of methanol vapor concentration at 278 K and 299 K. A molecular modulation technique was used in which HO₂ radicals were photochemically produced in flowing gas mixtures comprised of Cl₂, CH₃OH, N₂ and O₂ with HO₂ monitored in the UV at 220 nm. A positive linear dependence of the second order rate constant on methanol concentration was found and this effect increased with decreasing temperature. The rate constant for the HO₂ self reaction can be described by in nitrogen at atmospheric pressure and in the methanol concentration range 1 · 10¹⁶ to 3 · 10¹⁷ molecules cm^?3.     

Intramolecular cyclization of phenol derivatives with CC double bond in a side chain

Intramolecular cyclization of phenol derivatives with CC double bond on a side chain was examined using copper and silver catalyst. For example, 2-allylphenol (1a) was converted to 2,3-dihydro-2-methylbenzofuran (2a) in 70% yield using Cu(OTf)₂ or in 90% yield using AgClO₄. This catalysis was applied to cyclization of 2-allylphenol derivatives, 2-(3-butenyl)phenol, benzoic acids with CC double bond, 2-allyl-N-tosylaniline, and 2-(3-butenyloxy)phenol. Furthermore, allyl phenyl ether was converted to 2a via Claisen rearrangement and cyclization.     

Determination of Phenol in Surface Waters by High-Performance Liquid Chromatography with Sorption Preconcentration

The retention of phenol and its derivatives on Silasorb C₈ and PepRPC ^TMHR 5/5 was studied. Both columns are suitable for the separation of pyrocatechol–phenol–o-cresol(p-cresol)–2,6-xylenol mixtures using mobile phases containing 10–20 vol % of isopropanol and 1% glacial acetic acid in water. A procedure was developed for determining phenol with a detection limit of 4 mg/L (acetonitrile; signal-to-noise ratio, 2; loop volume, 25 L). With preconcentration from 1-L samples in a Diapak-phenol/P cartridge, the procedure allows phenol to be determined in water samples with a detection limit of 4 g/L. The procedure was used in analyses of samples of river and tap water.     

Hydroxylation of phenol over MeAPO molecular sieves synthesized by vapor phase transport

In this study, MeAPO-25 (Me = Fe, Cu, Mn) molecular sieves were first synthesized by a vapor phase transport method using tetramethyl guanidine as the template and applied to hydroxylation of phenol. The zeolites were characterized by XRD, SEM, FT-IR, and DR UV–Vis. As a result, MeAPO-21 and MeAPO-15 were synthesized by changing the Me/Al ratio. UV–Visible diffuse reflectance study suggested incorporation of heteroatoms into the framework and FT-IR study also supported these data. Effects of heteroatoms, contents of Me in MeAPO-25, reaction temperature, phenol/H₂O₂ mole ratios, reaction time and concentration of catalyst on the conversion of phenol, as well as on the selectivity were studied. FeAPO-25 exhibited a high catalytic activity at the mole ratio of FeO and Al₂O₃ equal to 0.1 in the synthesis gel, giving the phenol conversion of 88.75% and diphenols selectivity of 66.23% at 60°C within 3 h [n(phenol)/n(H₂O₂) = 0.75, m(FeAPO-25)/m(phenol) = 7.5%]. Experimental results indicated that the FeAPO-25 molecular sieve was a fairly promising candidate for the application in hydroxylation of phenol.     

Hydrogen peroxide yields in methanol-water mixtures gamma-irradiated at room temperature and 77 K

Hydrogen peroxide yields in air-saturated methanol-water mixtures with methanol: water volume ratios varying from 199 to 1000, produced by⁶⁰Co gamma-irradiation boith at room temperature and at 77 K have been determined. At room temperature, G(H₂O₂) values are almost constant over the entire range of methanol: water ratios. However, for irradiations at 77 K, G(H₂O₂) values increase with increasing methanol concentration up to the volume ratio of 982.     

Near-Infrared Spectroscopic Investigation of Inclusion Complex Formation of Cyclodextrins in Room-Temperature Ionic Liquid

Near-infrared spectrometry has been successfully used to determine association binding constants between phenol and -, - and -cyclodextrin (CD) in [butylmethylimidazolium][chloride] room-temperature ionic liquid (RTIL). It was found that adding CD into the RTIL solution of phenol resulted in an enhancement in the absorption coefficient of the stretching overtone of the aromatic C–H groups. However, the enhancement induced by CDs in RTIL is much lower (order of magnitude) than those corresponding in D₂O. The binding constants in RTIL are also much lower than those in D₂O ((11 ± 2) M^-1, (16 ± 2) M^-1and(40 ± 6) M^-1forphenol and -, - and -CD, respectively. compared to 87 M^-1and 214 M^-1for - and -CD in D₂O). The results obtained seem to suggest that in ionic liquid, the main interaction between phenol and CDs may not be inclusion complex formation but rather external adsorption. A variety of reasons may be responsible for relatively weaker interactions and lower binding constants in ionic liquid including differences in the polarity and viscosity of RTIL and D₂O. However, the main reason may be due to the fact that the cation of the ionic liquid (i.e., butylmethylimidazolium ion) may form inclusion complexes with the cyclodextrin, thereby preventing phenol from being included in cavity of CDs.     

Synthesis of polysubstituted pyridines under combined microwave and ultrasound irradiation: K2CO3-promoted tandem addition/cyclization/hydrogen shift process

A convenient and efficient K₂CO₃-promoted tandem reaction of chalcone, malononitrile, and methanol for the synthesis of highly functionalized pyridines has been developed. This multi-component reaction employing the weak nucleophilic agent methanol proceeded smoothly under combined microwave and ultrasound irradiation (CMUI). The reaction mechanism was proposed to consist of a Michael addition, a methoxylation of CN bond, a cyclization to a 1,4-dihydropyridine and an intermolecular hydrogen shift between 1,4-dihydropyridine and initial chalcone.     

Bimetallic Pt-Pd nanostructures supported on MoS<Subscript>2</Subscript> as an ultra-high performance electrocatalyst for methanol oxidation and nonenzymatic determination of hydrogen peroxide

The authors report on a composite based electrocatalyst for methanol oxidation and H₂O₂ sensing. The composite consists of Pt nanoparticles (NPs), Pd nanoflakes, and MoS₂. It was synthesized by chemical reduction followed by template-free electro-deposition of Pt NPs. FESEM images of the Pd nanoflakes on the MoS₂ reveal nanorod-like morphology of the Pd NPs on the MoS₂ support, whilst FESEM images of the Pt-Pd/MoS₂ composite show Pt NPs in high density and with the average size of ~15 nm, all homogeneously electrodeposited on the Pd-MoS₂ composite. A glassy carbon electrode (GCE) was modified with the composite to obtain an electrode for methanol oxidation and H₂O₂ detection. The modified GCE exhibits excellent durability with good catalytic efficiency (the ratio of forward and backward peak current density, I_f/I_b, is 3.23) for methanol oxidation in acidic medium. It was also used to sense H₂O₂ at an applied potential of ?0.35 V vs. Ag|AgCl which can be detected with a 3.4 μM lower limit of detection. The sensitivity is 7.64 μA μM^?1 cm^?2 and the dynamic range extends from 10 to 80 μM. This enhanced performance can be explained in terms of the presence of higher percentage of metallic 1T phase rather than a semiconducting 2H phase in MoS₂. In addition, this is a result of the high surface area of MoS₂ with interwoven nanosheets, the uniform distribution of the Pt NPs without any agglomeration on MoS₂ support, and the synergistic effect of Pt NPs, Pd nanoflakes and MoS₂ nanosheets. In our perception, this binder-free nano-composite has promising applications in next generation energy conversion and in chemical sensing.

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Graphical abstract A composite consisting of palladium nanoflakes and molybdenum disulfide was decorated with platinum nanoparticles and then placed on a glassy carbon electrode which is shown to be a viable electrocatalyst for both methanol oxidation and detection of hydrogen peroxide.

     

The application of the ion-interaction model to multicomponent 1-1 type electrolytes in mixed solvents

The ion-interaction model has been applied to published measurements for the multicomponent electrolytes HCl+MCl (M means Na or K) in mixed solvents (urea + water or methanol + water). The Pitzer parameters _HCl ⁽⁰⁾ , _HCl ⁽¹⁾ , C _HCl , ( _NaCl ⁽⁰⁾ + _NaH), _NaCl ⁽¹⁾ , _NaHCl in the HCl+NaCl + urea + water system were obtained by the method of least squares. A temperature and molality dependent equation for _HCl in this system was obtained. In the HCl+MCl + methanol + water system, the mixing parameter _HCl was obtained in terms of the Harned Rule. The relationship between Pitzer parameters and the composition of the mixed solvent was discussed.on leave from Department of Chemistry, Liaoning University Shenyang, China.