Quantum-chemical study of isocyanate reactions with linear methanol associates: IX. Methyl isocyanate reaction with methanol-phenol complexes

Quantum-chemical method B3LYP/6-311++G(df,p) was applied to the study of complex formation between phenol and methanol. The complexes of molecules bound by the hydrogen bond possess enhanced donoracceptor and acid-base properties as compared to monomer molecules. The reactions of phenol and methanol complexes with methyl isocyanate proceed through a concerted late asymmetric transition state by the type of nucleophilic addition. The most kinetically and thermodynamically favorable transformation is the process involving the complex “phenol-acceptor, methanol-donor.” Phenol compounds are able to catalyze the addition of alcohols to isocyanates.     

Quantum-chemical investigation of isocyanate reactions with linear methanol associates: V. Aryl isocyanate reactions with linear methanol associates

The mechanism of addition of linear methanol associates (monomer, dimer, trimer) to aryl isocyanates at their C=N and C=O bonds was investigated applying the quantum-chemical method B3LYP/6-311++G(df,p). Notwithstanding the electronic character of substituents in the aromatic ring of the isocyanates all reactions proceed through concerted asymmetric late transition states. The addition to the C=N bond is considerably more preferable than to the C=O bond. In the transformations under consideration the intermolecular donor-acceptor interactions between the reagents result in the appearance of abnormal selectivity.     

Quantum-chemical study on the reaction of phenyl isocyanate with linear methanol associates. Addition at the C=N bond

Quantum-chemical calculations at the B3LYP/6-311++G(df,p) level of theory showed that reactions of phenyl isocyanate with methanol associates involve formation of pre-and post-reaction complexes. The reactions proceed through late asymmetric cyclic transition states. The height of the energy barrier decreases as the degree of association of the alcohol increases. The relative change in the Gibbs energy in the reaction of phenyl isocyanate with methanol also becomes smaller as the degree of alcohol association increases.     

Quantum-chemical study on reactions of isocyanates with linear methanol associates: VII. Effect of nonspecific solvation on the reaction of methyl isocyanate with linear methanol associates

The effect of nonspecific solvation on the reactivity of methyl isocyanate toward linear methanol associates and thermodynamic parameters of this reaction was studied at the B3LYP/6-311++G(df,p) level of theory in terms of the polarizable continuum model (PCM). Transformations in the liquid phase are more exothermic than in the gas phase. Change of the solvent nature leads to variation of the geometric parameters and intrinsic free energies of the reactants and transition states. Increase in solvent polarity is accompanied by increase in the degree of asymmetry and polarity of transition states. As the dielectric permittivity rises, the polar constituent of the Gibbs energy of solvation decreases, while its nonpolar constituent increases. Owing to the opposite variations of these constituents of the Gibbs energy of activation, the reaction is weakly sensitive to solvent polarity.     

Vibrational analysis of phenol/(methanol)1

Ab initio calculations at the Hartree-Fock 4-31G* level were performed in order to calculate binding energies and vibrational frequencies of the phenol/CH₃OH-cluster and two deuterated isotopomers (d-phenol/CH₃OD,d-phenol-CD₃OD). The minimum energy structure is trans-linear, as for the phenol/H₂O-cluster. The calculated frequencies of phenol and methanol as well as the intramolecular frequencies of the phenol/CH₃OH-cluster are assigned to experimental values. The calculated intermolecular frequencies of the phenol/CH₃OH-cluster are compared with the available experimental frequencies of theS ₀ (andS ₁)-state of the phenol/methanol-cluster and the similarp-cresol/methanol-cluster. Assignments are suggested for the σ andp ₁-mode. In order to clarify the assignment of the low frequency vibration at 22 cm^?1 anharmonic corrections for the β₂-mode of the phenol/CH₃OH-cluster are calculated. These calculations show only slight anharmonicity compared with the β₂-mode calculations carried out for the phenol/H₂O-cluster.     

Quantum-chemical study on reactions of isocyanates with methanol associates: VI. Quantum-chemical characterization of the relative reactivity of linear and cyclic methanol trimers in the addition to methyl isocyanate

Quantum-chemical study on the reaction of methyl isocyanate with cyclic methanol trimer at the B3LYP/6-311++G(df,p) level of theory showed that the process involves concerted asymmetric transition state in which the formation of new N-H bond outstrips the formation of new C-O bond. The reaction of methyl isocyanate with linear methanol trimer was found to be both kinetically and thermodynamically more favorable than with cyclic trimer.     

Phytochemical investigation and antioxidant activities of methanol extract,methanol fractions and essential oil of Dillenia suffruticosa leaves

Oxidative stress has been known as a key factor of many disorders affecting human beings. Reactive oxygen species (ROS) attack vital biomolecules, weakening their functioning, thus exacerbating diseases. To attenuate oxidative stress-associated diseases a novel approaches of antioxidant therapies have been anticipated. Antioxidants have the potential to inhibit the propagation and formation of ROS. Dillenia suffruticosa is a medicinal plant, used by the local people for the treatment of various ailments. The study aimed to evaluate the phytochemical screening, antioxidative activity, total phenolic and flavonoid contents of methanol extract, fractions and essential oil of D. suffruticosa. Furthermore, the analysis of phytochemicals was done using gas chromatography and mass spectrometry (GCMS). The result showed the existence of alkaloids, anthraquinones, flavonoids, phytosterol, saponins, tannins, triterpenoids and steroids in the methanol extract and fractions of D. suffruticosa. The butanol fraction and methanol extract showed high phenolic (379.00 ± 9.25 and 277.00 ± 3.50 mg/g) and flavonoid values (74.44 ± 2.18 and 34.83 ± 0.71 mg/g) as compared to ethyl acetate, n-hexane and chloroform fractions. The scavenging capacity of butanol fraction and methanol extract was also higher than other fractions. GCMS analysis indicated the presences of various compounds in methanol extract, fractions and essential oil including methyl glycolate, lauryl acetate, phenol, 2,4-bis (1,1-dimethylethyl), 9,12-octadecadienoic acid, hexadecanoic acid, methyl ester, methyl stearate, phenol, benzyl alcohol, 3-hexen-1-ol, acetate and phytol. Thus, methanol extract, fractions and essential oil of D. suffruticosa leaves mainly contain vital phytochemical and shows good antioxidant activity.     

The thermodynamic parameters of reactions of phenyl isocyanate with methanol associates

The thermodynamic parameters of reactions of phenyl isocyanate with methanol monomer, dimer, and trimer were calculated by the B3LYP and MP2 quantum-chemical methods. The enthalpies and entropies of transformations were found to increase as the degree of methanol association grew. An isokinetic dependence was observed for the transformations under consideration. The influence of the polarity of solvents on the Gibbs energies of these reactions was estimated.     

Alkylation of aromatics. Kinetics of phenol alkylation with methanol

A kinetic study of phenol alkylation with methanol in the presence of -Al₂O₃ has been carried out. A mechanism involving the reaction of phenol and methanol adsorbed on acid-base pair sites is proposed.     

Chemical oscillation in electrochemical oxidation of methanol on Pt surface

Based on dual path reaction mechanism, a nonlinear dynamics model reflecting the potential oscilla- tion in electrooxidation of methanol on Pt surface was established. The model involves three variables, the electrode potential (e), the surface coverage of carbon monoxide (x), and adsorbed water (y). The chemical reactions and electrode potential were coupled together through the rate constant ki = exp(ai(e ? ei)). The analysis to the established model discloses the following: there are different kinetics be- haviors in different ranges of current densities. The chemical oscillation in methanol electrooxidation is assigned to two aspects, one from poison mediate CO of methanol electrooxidation, which is the in- duced factor of the chemical oscillation, and the other from the oxygen-containing species, such as H2Oa. The formation and disappearance of H2Oa deeply depend on the electrode potential, and directly cause the chemical oscillation. The established model makes clear that the potential oscillation in methanol electrooxidation is the result of the feedback of electrode potential e on the reactions in- volving poison mediates CO and oxygen-containing species H2Oa. The numerical analysis of the estab- lished model successfully explains why the potential oscillation in methanol galvanostatic oxidation on a Pt electrode only happens in a certain range of current densities but not at any current density.     

Acidity functions—IX : The preparation of buffered solutions of defined basicity in absolute methanol

Ionisation data for a series of phenol indicators are used to define H_m values for non buffered (H_m 16·4-13·9), phosphate buffered (14·0-12·2) and borate buffered (13·5-11·2) solutions of tetramethylammonium hydroxide and methoxide mixture in methanol. The dissociation constants of the phenols in methanol are also reported.     

Hydroxylation of selected hydrocarbon ions on reaction with methanol in the gas phase

The ion-molecule reactions of selected hydrocarbon cations with methanol which lead to the production of hydroxylated odd-electron molecular ions in the high-pressure ion source of a mass spectrometer or in the central quadrupole of a tandem quadrupole mass spectrometer are described. A wide variety of hydrocarbon cations were investigated, including aliphatic and aromatic cations; of these, only those having a vacant site on an aromatic system appear to undergo the hydroxylation reaction in high yield. A mechanism is proposed for the formation of the molecular ion of phenol from the ion-molecule reaction involving the phenyl cation with methanol. In addition, thermochemical data are provided which support the formation of the postulated species.     

Theoretical Van 't Hoff plots of gas-phase ion equilibria of chloride ion in water,methanol and acetonitrile

The gas-phase clustering reactions of chloride ion with water, methanol and acetonitrile molecules were investigated using a pulsed e-beam high-pressure mass spectrometer. Thermochemical data, −ΔH⁰ and −ΔS⁰, for these reactions agree with those reported previously. Theoretical van 't Hoff plots based on an ab initio MO calculation are compared with experimental ones.     

Zirconium meta-sulfonphenyl phosphonic acid-incorporated Nafion membranes for reduction of methanol permeability

Zirconium meta-sulfonphenyl phosphonic acid (Zr-msPPA)/Nafion^® composite membranes were prepared to reduce methanol permeability of the Nafion^® 117 membrane in direct methanol fuel cell (DMFC) applications. Zr-msPPA crystalline nano proton conductors were synthesized inside the membranes via the reaction of zirconium chloride octahydrate and meta-sulfonphenyl phosphonic acid that had been soaked prior. Synthesis of the Zr-msPPA in the membranes was identified from a series of chemical and physical structure characterizations using FTIR, NMR, EDS, and XRD spectroscopy. The thermal stability of the composite membranes was enhanced by addition of the Zr-msPPA, with considerable reduction in methanol permeability with increasing Zr-msPPA content, as the Zr-msPPA nano conductors acted as crystalline barriers to methanol permeation. The ion conductivity also decreased with increasing Zr-msPPA content, but its effect was not as strong as with methanol permeation given the innate, high conductivity of Zr-msPPA.     

Ring-methylation of pyrrole and indole using supercritical methanol

The ring-methylation of pyrrole or indole using supercritical methanol proceeded at 623 K without the further addition of catalysts. Pyrrole produced a mixture of unreacted pyrrole and mono-, di-, tri-, and tetra-methylpyrroles at the reaction time of 8 h. On the other hand, indole was selectively methylated at the C3 position to afford 3-methylindole in 79% yield at the reaction time of 5 h. The ring-methylation of indole using supercritical methanol was claimed to proceed via (1H-indol-3-yl)methanol. The conversion of indole to (1H-indol-3-yl)methanol would be achieved by the electrophilic aromatic substitution between the indol-1-ide (indole anion) and H₂C⁺–OH. The (1H-indol-3-yl)methanol must be reduced to 3-methylindole in the presence of supercritical methanol.     

Kinetics of oxidation of methanol and mono-deutero-methanol by chromium(VI) in perchloric acid medium

Kinetics of the oxidation of methanol and mono-deutero-methanol by Cr(VI) over a wide range of temperature (25–40°) have been studied in perchloric acid medium at constant ionic strength (μ = 1.0 M) adjusted with sodium perchlorate. Each reaction is first order with respect to the substrate and dichromate concentrations but the order with respect to [H⁺] is nearly 3 in each case. Both these reactions take place at almost the same rate under identical experimental conditions. The activation parameters of the reactions are not widely different and the values of ΔH3 and ΔS3 for the oxidation of methanol are 79.5 kJ mole ^-1 and - 38.1 J deg^-1 mole^-1 respectively, whereas the corresponding values for the deuterated compound are 83.8 kJ mole^-1 and -23.9 J deg^-1 mole^-1. The probable mechanism of the reactions is discussed.     

Synthesis and reactivity of 5-methylenehydantoins

5-Methylenehydantoin, as well as the N-mono- and N,N-di-protected derivatives, can be obtained by different synthetic routes. These compounds can undergo a large variety of reactions, such as Diels-Alder, epoxidation, methanol addition and conjugate addition reactions of different types of nucleophiles, including carbon (cyanide), nitrogen (piperidine) and sulfur (thiols, thioacetate) nucleophiles. The reactivity with electrophilic reagents, such as m-CPBA or methanol in acidic medium, and the need for Lewis acids to promote the conjugate addition reactions indicate that hydantoin is a poor electron-withdrawing group.     

Quantum-chemical investigation of isocyanate reactions with linear methanol associates: IV. Mechanism of autocatalytic reaction of methyl isocyanate with linear methanol associates

It was shown by quantum-chemical method B3LYP/6-311++G(df,p) that in the autocatalytic reaction the molecules of methyl carbamate formed prereaction complexes with the monomer and dimer of methanol. The complexes possess higher electron-donor properties than free alcohol molecules thus increasing the activity of complexes in the reaction with isocyanates. The products of the autocatalytic reaction are new molecules of carbamate and azomethinenol. The conversions occur through concerted asymmetric late transition states. The isomerization of azomethinenols into carbamates is catalyzed by molecules of alcohols and their associates. The autocatalytic reaction of isocyanates with alcohols becomes possible owing to the ability of alcohols to catalyze the mentioned isomerization.     

Electrostatic MO-O (methanol) bond in benzyltriphenylphosphonium trans-tetrachloro(methanol)oxomolybdate(V)

Benzyltriphenylphosphonium trans-tetrachloro(methanol)oxomolybdate(V) has been obtained from methanol suspension of benzyltriphenylphosphonium molybdate(VI) saturated with hydrogen chloride. The crystal structure comprises discrete trans-tetrachloro(methanol)oxomolybdate(V) anions and benzyltriphenylphosphonium cations. The anion has distorted octahedral geometry of central atom with visible trans influence imposed by short Mo-O bond (1.659(2) Å). The methanol O atom is bonded to the Mo atom, the bond being mostly electrostatic in character. A comparison with previously reported structures indicates that the methanol methyl moiety can switch between different positions with respect to the chloride ligands.     

Determination of kinetic parameters for the reaction between phenol and formaldehyde by differential scanning calorimetry

The kinetic parameters of the complex reaction between phenol and formaldehyde in the presence of sodium hydroxide (NaOH) have been obtained by differential scanning calorimetry (DSC). The two dominant reactions appear to be addition of formaldehyde to phenol with formation of o-hydroxymethyl-phenol and subsequent condensation of the latter. For both reactions, the activation energy (E_a), reaction order and rate constants at different temperatures have been determined. E_a for addition changes from 23·7 to 19·3 kcal mole^?1 and for condensation from 22·9 to 19·1 kcal mole^?1 when the amount of NaOH is increased from 0·25 to 1·00 per cent. The reaction order for addition is 2 and for condensation 1. Thus DSC appears useful for studying the kinetics of more complex polymerization reactions.