Boronates in aqueous solutions

The calibration graph was linear in the range 0.5-5pg of boron in aqueous solution (20-200pg L 1 of boron in the final solution to be measured). The detection limit and precision were lpg L 1 of boron and 3% for ten replicate determinations of 1.2pg of boron, respectively. Interference by foreign ions is minimal (see Table 12.1). 

W.D. Basson, P.P. Pille, L. du Preez, Automated in situ preparation of Azomethine-H and the subsequent determination of boron in aqueous solution, Analyst 99 (1974) 168. 

Zeebe 1999 Zeebe 2QQ5b) and less so for boron. In the following, the inorganic chemistry and stable isotope fractionation of dissolved boron in aqueous solution is used as an example to illustrate the steps taken in the process of understanding the... 

So far only the isotopic fractionation between a standard and the carbonates as a function of pH has been discussed. Now let us look at the dissolved species of boron in aqueous solution. The upper black solid, the dotted, and the dashed black lines in Figure 4 represent the 8 B of B(0H)4 (8 Bb(oh>4) as a function of pH calculated using a(B3-B4) = 1 019, 1.027, and 1.030 (Kakihana Kotaka 1977 Liu Tossell 2005 Zeebe 2005a). The dot-dashed black line represents the experimental a(B3-B4) = 1 0285 of Byrne et al. (2006). It is obvious that no matter what the true value of a(B3-B4) is, the assumption that B(OH)J is exclusively... 

The small boron (III) atom forms no simple cations in solution [10]. The least hydrolyzed form of boron in aqueous solution is boric acid, B(OH)3 [10]. The principal hydrolysis reaction involving boric acid is the rapid and... 

It forms an ion BCI4 only under special circumstances, and never in aqueous solutions (cf. BF3). Like the trifluoride, it is an electron pair acceptor, but the adducts formed tend to decompose more readily. Unlike the corresponding aluminium chloride, boron trichloride exists only as the monomer. 

Properties. Fluoroboric acid is stable in concentrated solutions, and hydroly2es slowly in aqueous solution to hydroxyduoroborates. For the stabihty of the duoroborate species, see Reference 3. The equiUbrium quotients (4,5) in 1 molal NaCl at 25°C show the strong affinity of boron for duo ride ... 

Anionic complexes of boron (boronates, borinates, etc.) have been introduced as convenient reagents in cross-coupling reactions of broad scope, particularly interesting for the transfer of alkynyl and primary alkyl residues, which cannot be accomplished using the standard protocols of the Suzuki-Miyaura reaction. Readily available Ph4BNa can be used as a convenient reagent for phenylation in place of the much more expensive PhB(OH)2, and all four phenyl groups can be utilized when the reaction is carried out with a phosphine-free catalyst in aqueous solutions.244... 

Al, Ga, In and T1 differ sharply from boron. They have greater chemical reactivity at lower temperatures, well-defined cationic chemistry in aqueous solutions they do not form numerous volatile hydrides and cluster compounds as boron. Aluminium readily oxidizes in air, but bulk samples of the metal form a coherent protective oxide film preventing appreciable reaction aluminium dissolves in dilute mineral acids, but it is passivated by concentrated HN03. It reacts with aqueous NaOH, while gallium, indium and thallium dissolve in most acids. 

Alkoxides are usually more difficult to hydrolyze than halides, although hydrolysis can be rapid in activated systems. Pyrimidinethiones can sometimes be hydrolyzed directly to pyrimidinones, but it is often better to convert the thiones into alkylsulfenyl, alkylsulfmyl, or alkylsulfonyl derivatives before hydrolysis <1994HC(52)1, 1996CHEC-II(6)93>. The formation of 5-hydroxypyrimidines is not normally performed using hydrolytic procedures, although it can be achieved by the oxidation of boronate species in aqueous solution <1996CC2719, 2006TL7363>. 

Within either of the polymer-rich phases, borate esters and diesters of the functional groups are assumed to form with the same association constants as observed for the independent functional groups in aqueous solution. The resulting equations simply describe the borate ester association constants as well as mass balances on boron and polymer-bound functional groups. Wise and Weber used the model to estimate association constants for the borate esters formed with the diols in PVA and to predict the gelation of PVA-borate solutions. As we have independently measured the association constants for the borate esters formed in this work, we have used the model to estimate the radius of gyration of the GP3 dendrimer and to predict both the boron speciation in borate/GP3 solutions and the efficacy of PAUF using these functional dendrimers. 

A number of biological studies have been conducted with the pinacol or pinanediol esters of boronic acid. At physiological pH these esters have biological activity equivalent to the free boronic acid. 6 This is due to the equilibrium of the ester with water as shown in Scheme 6. The pinanediol esters of boronic acids 16 are rapidly hydrolyzed in aqueous solution while the pinacol esters, though less stable, are hydrolyzed more slowly. In general, it is sufficient to incubate pinacol esters for 30 minutes in phosphate buffer, pH 7.5, prior to running biological reactions.16 ... 

AH0 is estimated to be about -370 kJ mol-1, i.e. B3+(aq)-written above as [B(H20)4]3+ - is a very strong acid, too strong to exist in aqueous solution. [B(0H)3(H20)] is a very weak base the OH oxygens have no measurable tendency to accept protons, presumably because of the withdrawal of electron density towards the boron atom. 

Sulphides of boron, aluminium, chromium, and silicon are at once decomposed by water, and cannot, therefore, be produced in aqueous solution. They are white substances formed by heating the elements to a high temperature in a current of sulphur vapour. 

Boron, aluminum and gallium are all highly hydrolysed trivalent elements, but the extent of their hydrolysis in seawater is distinctly different. While all three elements exist as M(OH) and M(OH)4 in seawater, Al is much more weakly hydrolysed than either B or Ga. The free-to-total metal ratio for Al3+ is in the order of 10 9A at 25°C and pH 8.2, while for Ga the free-to-total metal ratio is in the order of 10 15 7. Owing to its high charge and small radius, boron does not form a simple cation (M3+) in aqueous solution and, in fact, forms of boron less... 

The mode of dissolution of metal borates in aqueous solution is complex. Hydrolysis of the borate anion can result in completely different boron species that are stable only under particular conditions of pH, temperature, and concentration. 

Until recently, very little had been reported on the important area of metal borate complexation in aqueous solution. The effect of salts on the ionization of boric acid (358, 375) has been mentioned above, and subsequent research suggests that complexation of borate with, for example, calcium ions can account for the enhanced acidity of H O Literature on cationic complexes of boron was reviewed in 1970 (376). 

The relationship between the composition and structure of borates and their decomposition in aqueous solution has been reviewed (78, 226,414,417). Borates of the alkali and alkaline-earth metals give an alkaline reaction in solution, as the borates formed by hydrolysis possess a lower boron-to-metal ratio than in the initial material (414). 

Shinkai s group applied another method for the chiral spatial fixation of two porphyrins via peripheral substitution at the corresponding meso-position with boronic acid residue [67,68]. Thus, anionic 25 and cationic 26 formed an optically active 1 1 complex only in the presence of glucose and xylose in aqueous solution as a result of the boronic acid binding to the sac-... 

---