Showing papers on "Silanol published in 1977"

Behaviour of chemically bonded alkylmethyldichlorosilanes to silica gel in reversed-phase high-performance liquid chromatography

Abstract: Bonded hydrocarbon phases were prepared by the reaction of alkylmethyldichlorosilanes to silica (Lichrosorb Si 100, 10 μm Merck). Alkyl phases, CH3 (CH2)n (CH3)Si= with n=7, 10, 14 and 17 were investigated and compared with materials obtained by the reaction of alkyltrichlorosilanes. In reversed phase chromatography using water-methanol as mobile phase a linear relationship between the capacity ratios k′ and the amount of carbon was found in all cases. All alkylmethyl phases proved to be superior to the alkyl phases. Capacity ratios and selectivities are increased and the efficiencies, with one exception, are higher. The improved properties are discussed in relation to residual silanol groups on the adsorbent surface.

Surface reactivity of zeolites type H-Y and Na-Y with methanol

Abstract: The surface reactions of methanol with zeolites type H-Y and Na-Y, between 20 and 350°C, were studied by infrared spectroscopy, gas liquid chromatography, adsorption isotherms and thermo-gravimetric techniques.At room temperature methanol is physically adsorbed on both zeolites. In the case of zeolite H-Y the adsorption occurs via hydrogen bonds between the OH-groups of the methanol molecules and the surface hydroxyl groups and the structural oxygen atoms of the zeolite. At 20°C, a part of the surface hydroxyl groups reacts with the methanol molecules, initiating the methoxylation of the surface, according to the scheme Si—OH + CH3OH →SiOCH3+ H2O. This esterification of the silanol groups is enhanced as the temperature increases, and reaches a maximum at ∼130°C. Above 120°C a new reaction of the surface methoxyl groups with methanol occurs, with formation of dimethylether. The production of dimethylether reaches its maximum at 210°C. Around 250°C, secondary reactions forming gaseous cracking products, predominantly butane and propene, were detected. In the temperature range studied no chemical reaction of methanol with the surface of the dehydrated Na-Y was observed. Therefore, it is concluded that the surface activity of the zeolite H-Y in dehydration of methanol is mainly due to the high Bronsted acidic character of its surface. The analysis of the methoxylation reaction in terms of surface diffusion of the methanol molecules, and of the proton exchange frequency between adsorbed methanol molecules and the zeolite surface, shows that the lifetime of the protonated CH3OH+2 molecule is the rate controlling factor of the methoxylation process.

Autoxidation of fatty acid monolayers adsorbed on silica gel: I. Nature of adsorption sites.

Abstract: An unsaturated fatty acid monolayer deposited on a silica gel surface has been chosen as a model for studying nonenzymatic autoxidation of membrane lipids. Studies to determine the suitability of this system as a model for biomembranes were conducted to define the nature of the monolayers, particularly with respect to the factors determining the concentration of the fatty acid molecule on unit area of the surface. The results from adsorption isotherm, high temperature dehydroxylation, and infrared spectra studies show that adsorption of a monomolecular layer of fatty acids occurs and that the number of molecules absorbed corresponds to the number of isolated, non-hydrogen-bonded silanol groups. it is presumed the binding is by hydrogen bonding of the carboxyl groups to silanol groups. The packing density of the fatty acid molecules is 1.25 molecule/100 A2 which is similar to the density of the isolated silanol sites on the surface.

Silane triols of high stability in aqueous solution

Abstract: ORGANO-SILICON compounds containing silanol groups are highly reactive, undergoing acid- or base-catalysed condensation to form siloxanes even in the presence of surface acid or base, the condensation being more facile in the order ≡SiOH < = Si(OH)2 < −Si(OH)3 By the use of plastic, quartz or washed borosilicate glass apparatus, several alkyl and aryl silanols and silane diols have been isolated1–3. But only aromatic silane triols (R.Si(OH)3) have been isolated3, the corresponding alkyl derivatives being known only as transient species in solution. We report here that certain organo-silane triols display outstanding stability in aqueous solution.

Cobalt lon exchange of crystalline quartz

Abstract: Fully hydrated pure crystalline quartz suspended in 10 −3 M Co 2+ solution does not exchange Co 2+ ions up to pH 7.00. An exchange under these conditions is observed only after heat treatments which allow the formation of isolated silanol groups or after implantation of other cations such as Al 3+ into the surface. The fraction of equimolar exchange is always higher than that of equivalent exchange.

Infrared spectra of the surface of silica immersed in a three-component liquid mixture

Abstract: I.r. spectra have been measured of silica immersed in heptane–toluene–acetone liquid mixtures and three i.r. bands which could be distinguished were assigned to surface silanol groups perturbed by interactions with heptane, toluene, or acetone molecules; the proportion of silanol groups perturbed by the adsorption of each component of the liquid mixture could be deduced from absorbance data and the method provides a novel technique for the study of adsorption from three-component liquid mixtures.