Borate equilibrium

Two further reactions to be considered are the ionization of water and the borate equilibrium ... 

On the other hand, the kinetics of the boric acid-borate equilibrium are less well known. Yet in order to calculate fluxes, pH gradient and boron isotope distribution in the vicinity of a foraminifer, the kinetics (i.e. the speed of the conversion between the two dissolved boron species) is crucial. At the time when we developed the numerical models of the chemical microenvironment of foraminifera there was, to the best of our knowledge, no measured value for this rate constant available in the literature. The problem was eventually solved by considering sound absorption data in seawater, which is described in Zeebe et al. (2001). 

Zeebe, R. E., Sanyal, a., Ortiz, J. D. Wole-Gladrow, D. a. 2001. A theoretical, study of the kinetics of the boric acid - borate equilibrium in seawater. Marine Chemistry, 74, 113-124. 

Here A and X represent a highly hydrophilic and hydrophobic anion, respectively, equilibrium concentrations of which in the other phase are practically zero. Typical examples are chloride and tetrakis (4-chlorophenyl)borate anions, respectively. 

Borate-crosslinked fracturing fluids have been successfully used in fracturing operations. These fluids provide excellent rheologic, fluid loss, and fracture conductivity properties over fluid temperatures up to 105° C. The mechanism of borate crosslinking is an equilibrium process that can produce very high fluid viscosities under conditions of low shear [336]. 

Locust bean gum forms an interesting and unusual crosslinked complex by association of cis-dihydroxy groups in the mannose chains with borate ions, diagrammatically represented in structure 10.116. This complex forms a gel, which has been made use of in printing with vat dyes in a two-stage fixation process. The crosslinks are relatively weak, being in a state of dynamic equilibrium, and are ruptured in the presence of hydrotropes such as glycerol. 

In liquid detergents, the boric acid is generally added as Borax, Na2B4O7-10 H20. Borax is dissolved in the liquid detergents and a pH-dependent equilibrium between boric acid and the borate ion is thereby obtained. 

CZE-ELD, with a An microelectrode at —0.6 V vs. SCSE and a Pt wire as auxiliary electrode, using sodium borate buffer and dodecyltrimethylammonium bromide for dynamic coating of the capillary internal surface, can be applied for separation and determination of hydroperoxides in ultra-trace amounts. Thus, various hydroperoxides derived from linoleic acid undergo total dissociation to carboxylates in borate buffer however, due to their similar molecular masses, in order to resolve the ELD signals, it is necessary to add /3 -cyclodextrin (83) to form complexes with the analytes and reduce their mobility, in accordance with the value of the complexation equilibrium constants . 

The rate of the esterification reaction is very fast, with the B—O bonds breaking in this process, not the C—0 bond. The equilibrium of Eq. (4) does not lie far to the right, since water competes as a nucleophile in the reverse reaction, and rapid equilibration occurs unless water is removed to drive the reaction to the right. Hence most simple borate esters are readily hydrolyzed, displaying pseudo-first order hydrolysis kinetics. In most cases esterification... 

Fig. 6. Equilibrium water uptake of P(DEAEA-co-HEMA) samples with 30% (O) and 60% ( ) DEAEA with a crosslinking ratio of 0.003 mol EGDMA/mol monomers in a citrate-borate buffer solution as a function of pH...

Although electrical measurements have confirmed the ionic nature of borate melts, viscous flow and volumetric studies clearly indicated their difference from liquid silicates. Shartsia and co-workers (4 ) have suggested that an equilibrium exists in the melt between BOj triangles and B04 Letrahedra, this being both temperature and composition dependent. The only ionic model for the borates is that of Bockris and Mellors (8) which... 

Another important use of a-pinene is the hydrogenation to ttf-pinane (21). One use of the oy-pinane is based on oxidation to as- and /tt .f-pinane hydroperoxide and their subsequent catalytic reduction to as- and // J/w-pinanol (22 and 23) in about an 80 20 ratio (53,54). Pyrolysis of the r/r-pinanol is an important route to linalool overall the yield of linalool (3) from a-pinene is about 30%. Linalool can be readily isomerized to nerol and geraniol using an orthovanadate catalyst (55). Because the isomerization is an equilibrium process, use of borate esters in the process improves the yield of nerol and geraniol... 

A number of reviews have appeared covering the various aspects of borate glasses. The structure, physical properties, thermochemistry, reactions, phase equilibria, and electrical properties of alkali borate melts and glasses have been presented (73). The application of x-ray diffraction, nmr, Raman scattering, ir spectroscopy, and esr to structural analysis is available (26). Phase-equilibrium diagrams for a large number of anhydrous borate systems are included in a compilation (145), and thermochemical data on the anhydrous alkali metal borates have been compiled (17). 

The equilibrium shown in equation 3 normally lies far to the left. Usually the water formed is removed by azeotropic distillation with excess alcohol or a suitable azeotroping solvent such as benzene, toluene, or various petroleum distillate fractions. The procedure used depends on the specific ester desired. Preparation of methyl borate and ethyl borate is complicated by the formation of low boiling azeotropes (Table 1) which are the lowest boiling constituents in these systems. Consequendy, the ester—alcohol azeotrope must be prepared and then separated in another step. Some of the methods that have been used to separate methyl borate from the azeotrope are extraction with sulfuric acid and distillation of the enriched phase (18), treatment with calcium chloride or lithium chloride (19,20), washing with a hydrocarbon and distillation (21), fractional distillation at 709 kPa (7 atmospheres) (22), and addition of a third component that will form a low boiling methanol azeotrope (23). 

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