Silylation of water glass. II. Synthesis and copolymerization of carbon-functional silylated silicic acid

Carbon-functional silylates were prepared by reacting trialkoxysilanes and trimethylchlorosilane with silicic acid which had been derived from aqueous sodium silicate solution. The trialkoxysilanes used here were polymerizable silanes, i.e., vinyltriethoxysilane, (γ-methacryloyloxypropyl)trimethoxysilane, and (p-vinylphenyl)triethoxysilane. Molecular weights of these silylates containing more than one mole of the functional group ranged from 4000 to 9000. These silylates were found to serve as effective crosslinking agents for vinyl polymerization. However, soluble copolymers could be obtained under appropriate conditions, such as high dilution and low conversion in copolymerization. Glass transition temperatures (T_g) of the soluble copolymers were measured by differential scanning calorimetry to determine the effect of the silylates on the thermal properties of the copolymers. A slight variation of the T_g of these copolymers was observed when small amounts of the silylates were incorporated. It was also noticed that the water repellency of these copolymers was influenced by their composition.     

Solvent extraction of metals with macrocyclic compounds. I

Summary The extractants studied in this work are 5,6; 14,15-dibenzo-l,4-dioxa-8,12-diazacyclopentadeca-7,12-diene (I) and 5,6; 14,15-dibenzo-1,4-dioxa-8,12-diazacyclopentadecane (II). Radioactive nuclides were used to investigate the extraction of Ag(I), Hg(II), Cu(II), Cd, Co(II), Zn, Fe(III), Mn(II), and Pd with chloroform solutions of I and II. It is shown that compound I extracts only silver. The composition of the extracted compound has been established: silver is extracted as an AgLX complexe (L being macrocycle I and X being the counterion). The counterions involved in the experiment were perchlorate, picrate (Pi), and dipicrylaminate (DPA); the extraction of silver is intensified in the series: ClO₄ ^–––. The solvents used include nitrobenzene, 1,2-dichloroethane, chloroform, ando-xylene, the best being nitrobenzene and dichloroethane. Macrocycle II was found to exhibit poorer selectivity; in addition to Ag(I), it also extracts Hg(II), Cu(II) and Pd. The lower selectivity of macrocycle II, as compared to that of I, must be due to the graeter comformational mobility of molecule II.

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Metallextraktion durch makrocykliscbe Verbindungen. I

Zusammenfassung 5,6; 14,15-Dibenzo-1,4-dioxa-8,12-diazacyklopentadeka-7,12-dien (i) und 5,6; 14,15-Dibenzo-1,4-dioxa-8,12-diazacyklopentadekan (II) wurden als Extraktionsmittel verwendet. Radioaktive Nuklide dienten zur Untersuchung der Extraktion von Ag(I), Hg(II), Cu(II), Cd, Co(II), Zn, Fe(III), Mn(II) und Pd durch Chloroformlösungen von I und II. Die Verbindung I extrahiert nur Silber. Die Zusammensetzung der extrahierten Verbindungen wurde ermittelt: Silber wird als AgLX (L=Makrocyklus I, X=Gegenion) extrahiert. Als Gegenionen wurden Perchlorat, Pikrat (Pi) und Dipikrylaminat (DPA) verwendet. Die Extraktion von Silber wächst in der Reihenfolge ClO₄     

Solvent extraction behaviour of thiocyanic acid

The solvent extraction behaviour of thiocyanic acid with isobutyl methyl ketone and xylene as solvents is described. In the ketone system the thiocyanic acid is solvated in the organic phase to give a complex with a proposed composition of HSCN. 2IBMK. Deviations from ideal behaviour, which can be attributed to variations in the activity coefficient of the acid in the aqueous phase, are shown.     

Preparation of polysiloxanes from silicic acid. IX. Partially silylated silicic acid and its spinnability

The reaction in different molar ratios of trimethylchlorosilane to silicic acid offered partially silylated silicic acids PSSX (X = OH) with various degrees of silylation. Esterification and acetylation of PSSX (X = OH) with 1-butanol or acetylchloride gave polysiloxanes PSSX (X = OBuⁿ and OCOCH₃). Some of them showed an excellent spinnability and provided a fine fiber with a length of about 250 cm. A fiber drawing test from concentrated PSSX solutions of various solvents revealed that spinnability markedly depended on the DS, functional group X of PSSX, and solvent. Spinnability may also be correlated to solubility parameter of PSSX and solvent.     

Influence of water molecules on dimerization of silicic acid

By means of the quantum-chemical MO LCAO SCF method in the valence approximation of MNDO, it has been shown that effective interaction of two molecules of Si(OH)₄ is possible with the participation of a water molecule that plays the role of a bridge in forming a six-center complex.Institute of Surface Chemistry, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 27, No. 4, pp. 485–487, July–August, 1991. Original article submitted February 14, 1991.     

Silylation of porous glass supported platinum catalysts

Effect of silylation with hexamethyldisilazane on adsorption and catalytic properties of porous glass-supported platinum catalysts has been studied. Catalytic activity decreases markedly with an increase in surface coverage by trimethylsilyl groups for all the following reactions examined: hydrogenation of benzene, dehydrogenation of cyclohexane and dehydrocyclization of n-hexane.

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Solvent extraction studies using phosphonic acid monoesters

The extraction of radioactive^152–154Eu by ethyl hydrogen benzyl phosphonate (HEBP) and ethyl hydrogen benzoyl phosphonate (HEBOP) in n-hexane from an aqueous solution of ionic strength 0.1M (Na⁺, HClO₄) has been investigated at different temperatures and the thermodynamic functions evaluated. HEBOP was found to be more efficient than HEBP as extractant. In addition, the stability constant of the extracted complexes were determined.     

Solvent extraction studies using phosphonic acid monoesters

The extraction of radioactive⁶⁰Co by ethyl hydrogen benzoyl phosphonate (HEBOP) has been investigated. Different parameters that may effect this extraction such as the change in pH and [HEBOP] were studied. Extraction was carried out in three organic solvents. In addition, the equilibrium constants were determined at different temperatures and the thermodynamic parameters for such extraction process were calculated.     

Preparation of polysiloxanes from silicic acid. X. Preparation and properties of allyldimethylsilylated silicic acids

In order to obtain polysiloxanes capable of forming a film, the preparation and properties of allyldimethylsilylated silicic acid was investigated. The reaction in variable molar ratios of allyldimethylchlorosilane to silicic acid gave partially silylated silicic acids with different degrees of silylation. They provided not only fibrous polysiloxanes but also films from concentrated polymer solutions. Spinnability and film formation depended on the solvent, degree of silylation, molecular weight, and allyl group.     

Solvent extraction of reduced technetium from mineral acid solutions

The extraction of reduced^99mTc with 5,7-dichloroxine, tributyl phosphate (TBP) and 1-phenyl-3-methyl-4-benzoyl-pyrazolone-5 (PMBP) from HCl−LiCl mixtures has been studied. A mechanism of extraction is proposed and the stability of the chlorocomplexes of technetium (V) in a hydrochloric and—lithium chlorid—perchloric acid mixture has been established using extraction data of^99mTc and spectrophotometric measurements with⁹⁹Tc.     

Polymerization and polymers of silicic acid

Linear relationships among molecular weight, polymerization time, and gelation for the condensation of any monomer, including those of unknown size and functionality, are developed and applied to data on soluble silicic acids generated from tetraethyl silicate and from sodium silicate. The results suggest the formation of monomers containing ca. 12–15 ? OSi units with functionality of ca. 2.05 that condense with a rate constant of ca. 10^?4 liter/mole sec and an activation energy of 40–70 kJ/mole. One model compatible with these characteristics and the stoichiometry involved is a ladder polymer ca. 3 ? SiO units wide. Polymer isolation was achieved by replacing residual ? OH with (CH₃)₃Sio? , as well as by freezing of of aqueous solutions, which yielded fibers under special conditions. Solutions of the uncapped and capped polymers and melts of the latter had low viscosity even for fractions with M?_n ～100,000. This implies a coiled or globular nature for the polymers, which is supported by their limited propensity for film and fiber formation. Attemps to improve this situation by copolymerization, the use of other capping agents, and by the polymerization of precapped monomers were unsuccessful.     

Solvent extraction for cleaning phosphoric acid in fertilizer production

Phosphorites of sedimentary origin utilized in manufacturing of fertilizer contain uranium, thorium and products of their radioactive decay, as well as health-endangering compounds of cadmium, arsenic and fluorides. Some of them may transit into the phosphoric acid, when breaking down the phosphorites with sulphuric, acid, and then into the fertilizer. The purpose of the phosphoric acid cleaning is its decontamination from uranium and thorium as well as the removal of toxic cadmium. The above task can be achieved by solvent extraction. The paper presents the results of the extraction of uranium and cadmium from phosphoric acid using polyalkyl phosphasene and trioctyl amine, respectively. The extraction kinetics, equilibrium distribution of uranium and cadmium within the phases, the effect of extractant concentrations and temperature of the process is also discussed. The technological schemes for cleaning phosphoric acid from uranium and cadmium are given.     

Solvent extraction of pertechnetate with TBP from perchloric acid solution

Solvent extraction mechanism of pertechnetic acid with TBP from perchloric acid solutions is discussed. When cyclohexane is used as a diluent of TBP, perchloric acid can be extracted in the form of HClO₄(TBP)₂ into the organic phase. The TBP extraction of pertechnetic acid competes with perchloric acid and its equilibria are expressed as follows: HTcO₄+3TBPHTcO₄(TBP)₃ and HTcO₄(TBP)₃+TBPHTcO₄(TBP)₄.     

Solvent extraction of copper(II) with chlorendic acid

The solvent extraction of Cu(II) with chlorendic acid has been studied The composition of the extracted species appears to be a function of pH. In the pH range 3.2-4.6, a monomeric species exists [Cu(II)(L(2-)], while at pH values greater than 4.5, a dimer in the form of [Cu(II)(L(2-)). H(2)L](2) and/or [Cu(II)(HL(-))(2)](2) is extracted.     

Preparation of polysiloxanes from silicic acid. V. Condensation of silicic acid butyl esters and formation of silica fiber from the ester solutions

The condensation of silicic acid butyl esters was investigated by gel permeation chromatographic (GPC) analysis. The results revealed that the condensation was greatly dependent on a degree of esterification of the esters. The ester with the lowest degree of esterification underwent condensation to form a highly polymerized ester. It was found that fibers could be drawn from the ester solution before gelation.