Types Of Hydroxyl Groups Research Articles

Kinetics and Mechanism of Carbamate Reaction of 4-Hydroxybenzyl Alcohol with Phenyl Isocyanate

The reaction of 4-hydroxybenzyl alcohol with phenyl isocyanate in 1,4-dioxane was investigated, using in-situ FT-IR as the main tool. It was found that there was a remarkable induction phase in the reaction. Further, the reaction between isocyanate and the two types of hydroxyl groups in 4-hydroxybenzyl alcohol falls into two phases, with the phenolic hydroxyl being unexpectedly more reactive than the alcoholic hydroxyl. The reaction kinetics were also studied, and the activation energies were calculated to be 46.4 kJ mol−1, 35.2 kJ mol−1 and 41.5 kJ mol−1 for the induction, phenolic and alcoholic phases, respectively.

P-Toluenesulfonyl Chloride (p-TsCl)-Catalyzed Trimethylsilylation of Hydroxyl Groups Using Hexamethyldisilazane and Their Regeneration Under Mild Conditions: The First Example for Catalytic Application of p-Toluenesulfonyl Chloride

The first catalytic application of p-toluenesulfonyl chloride (p-TsCl) for the efficient and selective trimethylsilylation of various types of hydroxyl groups with hexamethyldisilazane (HMDS) in dichloromethane and desilylation of these compounds in water is reported. The reactions were carried out at room temperature and were found to proceed in good to excellent yields.

Access to Highly Fluorinated Silica by Direct F2 Fluorination: Chemical Compositions and FTIR Investigations

The direct F2 gas fluorination of a mesoporous silica gel has been shown to be a unique method leading to very high levels of fluorination (up to 13 wt % F in the bulk). The final powders are homogeneous with a controlled amount of grafted fluorine. In this study, various conditions of fluorination were tested, such as duration, temperature, F2 gas concentration of the fluorinating gas, or an annealing pretreatment. The content of grafted fluorine on silica was quantified by XPS and by the Seel method. Infrared spectroscopy measurements accounted for the consumption of different types of hydroxyl groups, that is, isolated (3740 cm−1), terminal (3715 cm−1), and bound (3520 cm−1), and also for the presence of unreacted internal hydroxyl groups inaccessible to D2O molecules and so to F2. Results showed that an F/OH substitution occurs during the fluorination process and that the grafted amount depends on the F2 concentration of the fluorinating gas and on the concentration of surface hydroxyl groups and phys...

Infrared Characterization of Hydroxyl Groups on MgO: A Periodic and Cluster Density Functional Theory Study

The infrared OH stretching frequencies of the various types of hydroxyl groups on MgO surfaces have been calculated by periodic (VASP) and cluster (Gaussian) DFT simulations. Surface irregularities (mono and diatomic steps, corners, step divacancies, and kinks) have been considered to model the IR spectra of hydroxylated MgO powders. A good correspondence between calculated and experimental frequencies is obtained with the B3LYP functional. Hydrogen-bonding is the parameter which influences most the IR frequency of OH groups, followed by location of OH groups in concave or convex areas of the surface and then oxygen coordination. The evolution of experimental IR spectra upon evacuation at increasing temperature can be rationalized on the basis of calculated thermal stabilities of each kind of OH groups. A new model is finally proposed to help assign the experimental bands, in terms of hydrogen-bonding, local topology of the hydroxylated sites, and coordination of oxygen.

Syntheses and Cation Extraction Properties of Polycalixarenes from p-Hydroxycalix[6]arene

A new polymer, polycalixarene, was prepared by the reaction of p-hydroxycalix[6]arene (HQ[6]) with paraformaldehyde under HCl acidic conditions. HQ[6] had two types of hydroxyl groups at the upper and lower rims and showed a conelike conformation. The conformation of the HQ[6] unit was maintained in the polymer chain. The extraction ability of poly(p-hydroxycalix[6]arene) (P-HQ[6]) for alkali metal cations was determined and compared with that of the monomeric HQ[6]. The extraction ability of P-HQ[6] was higher than that of HQ[6] due to new cation binding sites consisting of the aggregated HQ[6] units in the polymer. The affinity and selectivity of new binding sites depended on the aggregated state of HQ[6] units in the polymer chain. The aggregated state was controlled by the conformation of the polymer.

High-pressure behaviour of serpentine minerals: a Raman spectroscopic study

Four main serpentine varieties can be distinguished on the basis of their microstructures, i.e. lizardite, antigorite, chrysotile and polygonal serpentine. Among these, antigorite is the variety stable under high pressure. In order to understand the structural response of these varieties to pressure, we studied well-characterized serpentine samples by in situ Raman spectroscopy up to 10 GPa, in a diamond-anvil cell. All serpentine varieties can be metastably compressed up to 10 GPa at room temperature without the occurrence of phase transition or amorphization. All spectroscopic pressure-induced changes are fully reversible upon decompression. The vibrational frequencies of antigorite have a slightly larger pressure dependence than those of the other varieties. The O–H-stretching modes of the four varieties have a positive pressure dependence, which indicates that there is no enhancement of hydrogen bonding in serpentine minerals at high pressure. Serpentine minerals display two types of hydroxyl groups in the structure: inner OH groups lie at the centre of each six-fold ring while outer OH groups are considered to link the octahedral sheet of a given 1:1 layer to the tetrahedral sheet of the adjacent 1:1 layer. On the basis of the contrasting behaviour of the Raman bands as a function of pressure, we propose a new assignment of the OH-stretching bands. The strongly pressure-dependent modes are assigned to the vibrations of the outer hydroxyl groups, the less pressure-sensitive peaks to the inner ones.

Photoinduced hydroxylation at ZnO surface

We observed UV-stimulated hydroxylation at the surface of ZnO crystals. Reactive defective sites were initially formed in the surface layer via photoreduction induced with energetic photons above the band gap of ZnO. Hydroxyl groups were produced by a chemical reaction of the photoinduced defective sites with water molecules in the atmosphere. Two types of hydroxyl groups were found at the irradiated surface because two kinds of defective sites were induced with the UV illumination.

1H and 29Si-MAS NMR characterization of silicate fiberglass supports

The structural properties of alumina–sodium–silicate fiberglass (S) and microporous silica–alumina fiberglass supports (CCB18 and CCB20) were investigated using solid state NMR. Structural changes of samples of S as a result of partial extraction of Na with acid treatment were explored. Strongly and weakly hydrogen-bonded hydroxyls with non-uniform distribution of hydrogen bond strengths were revealed. Decreasing of Na concentration is followed with partial polymerization of the glass framework and hydroxylation of the surface. Deuterium exchange and the thermal dependence of the dehydration of silica–alumina fiberglass (CCB18 and CCB20) were monitored using 1H and 29Si MAS technique in order to classify surface hydroxyl groups. These samples were prepared by full extraction of Na from alumina–sodium–silicate fiberglass materials similar to S. At least four types of hydroxyl groups were revealed for both samples: internal isolated accessible silanols (2.65 ppm), internal silanols (6.7 ppm and 3.7 ppm) with low accessibility, molecular water displaying broad resonance at 5 ± 1 ppm. Spin–spin relaxation times T2 were measured for these silanol groups using a standard echo sequence. The full content of water and silanol groups were determined.

Hydroxyl in MgSiO3akimotoite: A polarized and high-pressure IR study

Hydrous MgSiO 3 akimotoite (ilmenite-type structure), containing 350 ppm wt H 2 O as hydroxyl, was synthesized at 19 GPa and 1300 °C in a multi-anvil apparatus. Polarized Fourier-transform infrared spectra show bands at 3300 and 3320 cm -1 due to hydroxyl groups oriented nearly perpendicular to the c axis as well as a strong band at 3390 cm -1 caused by OH molecules aligned nearly parallel to c. Unpolarized infrared measurements performed up to 13.8 GPa in a diamond anvil cell show that the bands shift to lower frequencies with increasing pressure, which is consistent with hydrogen bonding. At ~9 GPa, the bands initially at 3300 and 3320 cm -1 merge, suggesting that these two bands represent the same type of hydroxyl group. The compression behavior of the infrared bands shows that the pressure derivative of the frequency, dʋ/dP, decreases with increasing initial wavenumber, ʋ io , and this decrease is not linear. These observations are consistent with the compression mechanism of akimotoite, as previously published. The data indicate that the relative compressibility of the hydrogen bonds within a structure (i.e., the sign of dʋ/dP vs. ʋ io ) is governed by a combination of the directionality of the hydrogen bonds and the anisotropy of compression, whereas the rate of compression (i.e., the slope of dʋ/dP vs. ʋ io ) is a function of the bulk modulus.

Near-infrared spectroscopic study of nontronites and ferruginous smectite

The existence of life on planets such as Mars depend upon the presence of water. This water may not necessarily be as liquid or crystalline water but may be as interlayer water such as is found in smectitic clays. One group of smectites, relevant to the search for interplanetary life are those which have a high iron content, known as nontronites. Near-IR reflectance spectroscopy has been used to show the presence of water and hydroxyl units in these minerals. Three near-IR spectral regions are identified, (a) the high frequency region between 6400 and 7400 cm −1 attributed to the first overtone of the hydroxyl stretching mode; (b) the 4800–5400 cm −1 region attributed to water combination modes; and (c) the 4000–4800 cm −1 region attributed to the combination of the stretching and deformation modes of the FeFeOH units of nontronite. Two types of hydroxyl groups were identified using near-IR spectroscopy, hydroxyl units coordinated to the iron; and hydroxyl groups from water in the nontronite structure. The first hydroxyls are characterised by several bands, firstly in the 7055–7098 cm −1 region assigned to the first overtone of the AlFeOH stretching unit, secondly in the 6958–6878 cm −1 region attributed to the FeFeOH unit. The overtone of the hydroxyl stretching frequency of water was observed at around 6800 cm −1. These observations show that nontronites can be a source of water that may support life.

On the Temperature Dependence of Intrinsic Surface Protonation Equilibrium Constants: An Extension of the Revised MUSIC Model

The revised multisite complexation (MUSIC) model of T. Hiemstra et al. (J. Colloid Interface Sci.184, 680 (1996)) is the most thoroughly developed approach to date that explicitly considers the protonation behavior of the various types of hydroxyl groups known to exist on mineral surfaces. We have extended their revised MUSIC model to temperatures other than 25°C to help rationalize the adsorption data we have been collecting for various metal oxides, including rutile and magnetite to 300°C. Temperature-corrected MUSIC model A constants were calculated using a consistent set of solution protonation reactions with equilibrium constants that are reasonably well known as a function of temperature. A critical component of this approach was to incorporate an empirical correction factor that accounts for the observed decrease in cation hydration number with increasing temperature. This extension of the revised MUSIC model matches our experimentally determined pH of zero net proton charge pH values (pHznpc) for rutile to within 0.05 pH units between 25 and 250°C and for magnetite within 0.2 pH units between 50 and 290°C. Moreover, combining the MUSIC-model-derived surface protonation constants with the basic Stern description of electrical double-layer structure results in a good fit to our experimental rutile surface protonation data for all conditions investigated (25 to 250°C, and 0.03 to 1.0 m NaCl or tetramethylammonium chloride media). Consequently, this approach should be useful in other instances where it is necessary to describe and/or predict the adsorption behavior of metal oxide surfaces over a wide temperature range.

Towards a single crystal Raman spectrum of kaolinite at 77 K

The Raman spectra at 77 K of the hydroxyl stretching of kaolinite were obtained along the three axes perpendicular to the crystal faces. Raman bands were observed at 3616, 3658 and 3677 cm −1 together with a distinct band observed at 3691 cm −1 and a broad profile between 3695 and 3715 cm −1. The band at 3616 cm −1 is assigned to the inner hydroxyl. The bands at 3658 and 3677 cm −1 are attributed to the out-of-phase vibrations of the inner surface hydroxyls. The Raman spectra of the in-phase vibrations of the inner-surface hydroxyl-stretching region are described in terms of transverse and longitudinal optic splitting. The band at 3691 cm −1 is assigned to the transverse optic and the broad profile to the longitudinal optic mode. This splitting remained even at liquid nitrogen temperature. The transverse optic vibration may be curve resolved into two or three bands, which are attributed to different types of hydroxyl groups in the kaolinite.

Proton NMR Investigations of Surface Hydroxyl Groups on Oxidic Mo–P/γ-Al2O3Catalysts

Proton MAS NMR spectroscopy has been used to investigate the influence of the impregnation procedure on the surface hydroxyl structure of dehydrated γ-Al2O3impregnated with varying amounts of molybdenum or phosphorus. Large differences were observed for catalysts prepared by coimpregnation, sequential impregnation, and sequential impregnation with intermediate calcination. A quantitative analysis of the spectra showed that molybdate ions preferentially reacted with basic OH groups at low molybdate loading, but also with acidic hydroxyl groups at higher. Phosphate ions adsorbed on both types of hydroxyl groups, even at low or moderate coverage, while at high surface coverage a nearly constant density of Al–OH and P–OH groups indicated AlPO4formation. Phosphorus and molybdenum were well dispersed after coimpregnation, whereas after sequential impregnation (phosphorus first) some pore-plugging occurred and Mo–O compounds adsorbed on underlying phosphates.

First-principles molecular dynamics simulation of water dissociation on TiO 2 (110)

We have performed first-principles molecular dynamics calculations of water adsorption on TiO 2 (110). We find that dissociative adsorption occurs at the fivefold-coordinated Ti site resulting in the formation of two types of hydroxyl group. The vibrational spectra calculated from this hydroxylated surface show that a clear stretch frequency is present for only one of these groups, with vibrations from the other hydroxyl broadened due to hydrogen bonding between the two hydroxyl groups.

The dipolar 1,3 cycloaddition of C,N‐dialkylnitrone to olefins with hydroxyl group and the derivatives

AbstractThe reaction rate and stereoselectivity of intermolecular dipolar 1,3 cycloaddition of the C,N‐dialkylnitrone to olefins with hydroxyl groups and their derivatives were found to depend upon the type of hydroxyl group. The rate is accelerated in the order: magnesium alkoxide (OMgBr); free hydroxyl group (OH); ether (OR). Selectivities are improved moderately when magnesium alkoxide is used.

Phase transition of capillary condensed liquids in porous silica: effect of surface hydroxyl groups

Phase transition temperatures of capillary condensed organic liquids in porous silica were measured using a 1020/DSC system (Perkin-Elmer Ltd.). The amounts and types of hydroxyl groups on the sample surfaces were precisely controlled to discuss the surface effect on the phase transition temperature. The melting point of the solid phase of benzene in the pores decreased with increasing concentration of the surface hydroxyl groups. On the other hand, in the case of n-hexane, such an effect was not observed. From these results, it is assumed that the liquid structure of capillary condensed benzene in the pores changes with the amounts and types of surface hydroxyl groups. This consideration is confirmed from IR spectroscopy.

Solid-State 1H MAS NMR Characterization of γ-Alumina and Modified γ-Aluminas

1H single pulse MAS and CPMG T2/CSA-filter NMR experiments have been performed in order to characterize the hydroxyl structure of γ-alumina, as well as fluoride- and phosphate-modified γ-alumina materials. We have shown that problems associated with the strong homonuclear dipole-dipole interactions between protons of neighboring OH groups can be overcome by isotopic dilution of the alumina surface protons by deuterium exchange. Partially deuterated γ-alumina yields resonances at around −0.3, 0.3, 1.5, 2.4, 4.0, 5.0, 6.5, 7.1, and 7.8 ppm. CPMG T2/CSA-filter NMR experiments performed on alumina calcined at 700°C show that five different types of hydroxyl groups are present. CPMG T2/CSA-filter NMR of deuterated F/Al2O3 produces a resonance at 11.5 ppm in addition to a range of resonances between −0.2 and 7 ppm. NMR data for calcined P/Al2O3 and P-Mo(12)/Al2O3 (Wt% P = 0.0-10.0) show that polymeric orthophosphates produce a resonance at 3.4 ppm, while the monomeric orthophosphate species gives rise to a resonance at 1.2 ppm.

1H and 51V high-resolution solid state nuclear magnetic resonance studies of supported V 2O 5/TiO 2 catalysts

1H solid state NMR data show the existence of several types of hydroxyl groups on TiO 2 surface, depending on the surface impurities. VOCl 3 selectively interacts with these groups. According to 51V NMR data, the structure of the surface vanadium complexes, independently of the preparation method, is determined by the type of surface hydroxyls. On clean TiO 2 surface at low vanadium concentration two types of surface complexes with vanadium in the distorted tetrahedral environment of oxygen atoms are formed, one of them containing OH groups in the coordination sphere. At high V content associated species, with V in octahedral coordination, are formed. nuclear magnetic resonance studies; solid state; titania; vanadia

Iron-substituted Beta molecular sieve: Synthesis and characterization

A synthesis of crystalline ferrisilicate having zeolite BEA topology (Fe-Beta) and containing significant quantities of iron in the framework (22 Fe atoms per unit cell based on 192 T-atoms per unit cell) has been reported. The synthesis of Fe-Beta was carried out using tetraethylammonium hydroxide (TEAOH), 25% methanolic instead of an aqueous solution, as a source of organic template. X-Ray powder diffraction (XRD) and scanning electron micrography (SEM) were used to check the structural identity and phase purity of the Fe-Beta samples. A thermogravimetric analysis (TGA) study showed that the amount of TEAOH ions interacting with Fe-Beta framework increases with increase in the iron content of the sample. The Fe ions in Fe-Beta were in the trivalent oxidation state which was confirmed by an X-ray photoelectron spectroscopy (XPS) study. A comparison of Si/Fe ratios determined by chemical analysis and XPS method allowed us to conclude that Fe 3+ species are distributed homogeneously from the bulk to the surface of Fe-Beta crystallites. However, the O 1s XP spectra indicated the presence of small amounts of extraframework iron oxidic impurities in as-synthesized as well as calcined samples. The infrared (IR) spectra showed three types of hydroxyl groups in Fe-Beta located at 3740, 3670 and a very broad band at ∼ 3540 cm −1. The band at 3680 cm −1 was found to be affected by pyridine adsorption and therefore was assigned to structural bridging hydroxyl groups (SiOHFe) formed by substitution of iron in the zeolite framework. The shift in the IR OH stretching frequency towards higher wave number and the desorption of NH 3 at lower temperature for Fe-Beta samples as compared to Al-Beta zeolite allowed us to conclude that the strength of Brönsted acid sites in Fe-Beta materials is lower than those Brönsted acids sites in Al-Beta zeolites.

Vibrational lifetime of surface species of zeolites by picosecond IR pulses

The dynamic behaviors of hydroxyl groups in zeolites, mordenite and Y-type, are studied by FT-IR and picosecond IR pulses. N 2 adsorption to form hydrogen bonding at low temperature revealed the existence of several different types of hydroxyl groups in both zeolites. The vibrational relaxation times of the OH(v=1) groups in these zeolites are compared.