Boronic acids aqueous solutions

Marken and coworkers examined Ti02 NPs in various types of interfadal assemblies [38, 40, 57, 58]. In their first study, commerdally available 6-nm diameter Ti02 NPs were directly adsorbed onto polished boron-doped diamond electrodes from acidic aqueous solutions containing the Ti02 sol [38]. Using field emission SEM and STM, they observed relatively uniform adsorption of the Ti02 NPs and small... 

The boron cation is stable in acidic aqueous solution, somewhat less stable in water, but decomposes in alkaline solution. The proton magnetic resonance spectrum in D20 relative to external TMS shows three bands —8.60 (broad), - —8.19 (doublet, J = 7 Hz.), and —2.85 (singlet), with the expected intensities corresponding to the a- and /6-ring hydrogen atoms and the methyl group, respectively. The bromide is very soluble in cold water and hot ethanol but insoluble in acetone. The hexafluorophosphate is slightly soluble in cold water but very insoluble in acetone. 

Figure 2.28 - Current-potential curve for a boron-doped diamond electrode In an acidic aqueous solution...

S. Iwatsuki, Y. Kanamitsu, H. Ohara, E. Watanabe and K. Ishihara, Higher reaetivity of 3-pyridinium boronic acid compared with 3-pyr-idinium boronate ion toward 4-isopropyltropolone in acidic aqueous solution fundamental reaction analyses for an effective organoboron-based chemosensor,/. Phys. Org. Chem., 2012,25(9), 760-768. 

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... 

Acetic anhydride adds to acetaldehyde in the presence of dilute acid to form ethyUdene diacetate [542-10-9], boron fluoride also catalyzes the reaction (78). Ethyfldene diacetate decomposes to the anhydride and aldehyde at temperatures of 220—268°C and initial pressures of 14.6—21.3 kPa (110—160 mm Hg) (79), or upon heating to 150°C in the presence of a zinc chloride catalyst (80). Acetone (qv) [67-64-1] has been prepared in 90% yield by heating an aqueous solution of acetaldehyde to 410°C in the presence of a catalyst (81). Active methylene groups condense acetaldehyde. The reaction of isobutfyene/715-11-7] and aqueous solutions of acetaldehyde in the presence of 1—2% sulfuric acid yields alkyl-y -dioxanes 2,4,4,6-tetramethyl-y -dioxane [5182-37-6] is produced in yields up to 90% (82). 

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 ... 

Vapor phases ia the B2O3 system iaclude water vapor and B(OH)3(g) at temperatures below 160°C. Appreciable losses of boric acid occur when aqueous solutions are concentrated by boiling (43). At high (600—1000°C) temperatures, HB02(g) is the principal boron species formed by equiUbration of water vapor and molten B2O3 (44). At stiU higher temperatures a trimer (HB02)3(g) (2) is formed. 

Orthoboric acid, B(OH)3, is the normal end product of hydrolysis of most boron compounds and is usually made ( 160 000 tonnes pa) by acidification of aqueous solutions of borax. Price depends on quality, being 805 per tonne for technical grade and about twice that for refined material (1990). It forms flaky, white, transparent crystals in which a planar array of BO3 units is joined by unsymmetrical H bonds as shown in Fig. 6.25. In contrast to the short O—H O distance of 272 pm within the plane, the distance between consecutive layers in the ciystal is 318 pm, thus accounting for the pronounced basal cleavage of the waxy, plate-like ciystals, and their low density (1.48 g cm ). B(OH)3 is a very weak monobasic acid and acts exclusively by hydroxyl-ion acceptance rather than proton donation ... 

Interesting developments in simple azetidine chemistry continue to be reported. The apparently general acetylative dealkylation of Af-tert-butyl-3-substituted azetidines 6 (R = Bu ) in the presence of boron trifluoride provides a two-step route to azabicyclobutane 7 from 6 (R = Bu, R = Cl). An aqueous solution of 7 reacts with ethyl chloroformate to give 8. Relatively unexplored 3-azetidinones 9 (R = Ac or NO2) are available from 3-acetoxya2Ktidine 6 (R = Ac, R = OAc) which is obtained by acetylative dealkyation of 6 (R = Bu , R = OAc) <96JOC5453>. 3-Substituted azetidines can be utilized in the synthesis of polyfunctional y- and S-aminophosphonic acid derivatives <95TL9201>. 

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. 

The B2O3 content of borax may be determined by extraction into HCl solution followed by complexation with mannitol and titration with dUute NaOH. The Na20 content of horax may he measured by titration of an aqueous solution with dUute HCl. Boron and sodium metals in the acid extract of horax may be analyzed by atomic absorption or emission spectroscopy after appropriate dUution of the extract. In the solid phase B2O3 and Na20 may he measured nondestructively by x-ray techniques. 

A reactor containing 10 ml of toluene and 10 ml of aqueous Na2C03 was treated with the step 2 product (1.0 mmol), 2,7-dipinacol boron-9,9-di-octyl-fluoiene (1.0 mmol), tetrakis triphenylphosphine palladium (0.01 mmol), and 0.16 ml of tricaprylmethyl-ammonium chloride. The mixture was then treated with a few drops of bromobenzene and then refluxed for 1 hour and treated with a few drop of phenyl boronic acid and then further refluxed 15 hours and cooled. The mixture was diluted with toluene and isolated toluene layer washed with water. The mixture was filtered after adding 40 mg of the palladium scavenger 3-mercaptopropyl modified silica gel. The solution was then poured into methanol and a yellow polymer isolated. The polymer was redissolved in toluene and then purified using a short column of silica gel. The solution was rewashed with water, reprecipitated in ethanol, and 0.80 g of polymer isolated having an Mn of 32,800 Da. 

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. 

The formation of polymeric boron ions in solution is well established. The significant increase in solubility in terms of B203 in aqueous mixtures of borax and boric acid relative to the individual components is explained by such polyborate formation. The comprehensive reviews by Nies (307) and Sprague (392) reveal that, despite the many investigations over the last 50 years, the identity of the borate ions involved has still not been completely resolved. 

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