Of boric acid

Boron III) oxide, B2O3, is obtained by ignition of boric acid. Combines with water to reform B(0H)3. The fused oxide dissolves metal oxides to give borates. 

Prepared by condensing p-chlorophenol with phlhalic anhydride in sulphuric acid solution in the presence of boric acid. The chlorine atom is replaced by hydroxyl during the condensation. It can also be prepared by oxidation of anthraquinone or 1-hydroxyanthraquinone by means of sulphuric acid in the presence of mercury(ll) sulphate and boric acid. 

Boron trioxide, B2O3 is the anhydride of boric acid, H3BO3 and can be prepared by heating the acid ... 

With sodium hydroxide as the base boron of the alkylborane is converted to the water soluble and easily removed sodium salt of boric acid... 

Although not commonly used, thermometric titrations have one distinct advantage over methods based on the direct or indirect monitoring of plT. As discussed earlier, visual indicators and potentiometric titration curves are limited by the magnitude of the relevant equilibrium constants. For example, the titration of boric acid, ITaBOa, for which is 5.8 X 10 °, yields a poorly defined equivalence point (Figure 9.15a). The enthalpy of neutralization for boric acid with NaOlT, however, is only 23% less than that for a strong acid (-42.7 kj/mol... 

Secondary alcohols (C q—for surfactant iatermediates are produced by hydrolysis of secondary alkyl borate or boroxiae esters formed when paraffin hydrocarbons are air-oxidized ia the presence of boric acid [10043-35-3] (19,20). Union Carbide Corporation operated a plant ia the United States from 1964 until 1977. A plant built by Nippon Shokubai (Japan Catalytic Chemical) ia 1972 ia Kawasaki, Japan was expanded to 30,000 t/yr capacity ia 1980 (20). The process has been operated iadustriaHy ia the USSR siace 1959 (21). Also, predominantiy primary alcohols are produced ia large volumes ia the USSR by reduction of fatty acids, or their methyl esters, from permanganate-catalyzed air oxidation of paraffin hydrocarbons (22). The paraffin oxidation is carried out ia the temperature range 150—180°C at a paraffin conversion generally below 20% to a mixture of trialkyl borate, (RO)2B, and trialkyl boroxiae, (ROBO). Unconverted paraffin is separated from the product mixture by flash distillation. After hydrolysis of residual borate esters, the boric acid is recovered for recycle and the alcohols are purified by washing and distillation (19,20). 

Borolane products of mixed composition can be synthesized by direct addition of boric acid to pentaerythritol (23). 

An aqueous PVA solution containing a small amount of boric acid may be extmded into an aqueous alkaline salt solution to form a gel-like fiber (15,16). In this process, sodium hydroxide penetrates rapidly into the aqueous PVA solution extmded through orifices to make it alkaline, whereby boric acid cross-links PVA molecules with each other. The resulting fiber is provided with sufficient strength to withstand transportation to the next process step and its cross section does not show a distinct skin/core stmcture. 

Boron trifluoride [7637-07-2] (trifluoroborane), BF, was first reported in 1809 by Gay-Lussac and Thenard (1) who prepared it by the reaction of boric acid and fluorspar at duU red heat. It is a colorless gas when dry, but fumes in the presence of moisture yielding a dense white smoke of irritating, pungent odor. It is widely used as an acid catalyst (2) for many types of organic reactions, especially for the production of polymer and petroleum (qv) products. The gas was first produced commercially in 1936 by the Harshaw Chemical Co. (see also Boron COMPOUNDS). 

The hydrolysis of BF occurs stepwise to BF OH, BF2 (OH)2, and BF(OH)3. By conductivity measurements the reaction of boric acid and HF was found to form H[BF2(OH)] [15433-40-6] rapidly subsequentiy HBF formed much more slowly from HBF OH. These studies demonstrate that BF is... 

Manufacture. Fluoroborate salts are prepared commercially by several different combinations of boric acid and 70% hydrofluoric acid with oxides, hydroxides, carbonates, bicarbonates, fluorides, and bifluorides. Fluoroborate salts are substantially less corrosive than fluoroboric acid but the possible presence of HF or free fluorides cannot be overlooked. Glass vessels and equipment should not be used. 

Mixtures of glycerol with other substances are often named as if they were derivatives of glycerol eg, boroglycetides (also called glyceryl borates) are mixtures of boric acid and glycerol. Derivatives, such as acetals, ketals, chlorohydrins, and ethers, can be prepared but are not made commercially, with the exception of polyglycerols. 

Lead borate moaohydrate [14720-53-7] (lead metaborate), Pb(B02)2 H20, mol wt 310.82, d = 5.6g/cm (anhydrous) is a white crystalline powder. The metaborate loses water of crystallization at 160°C and melts at 500°C. It is iasoluble ia water and alkaHes, but readily soluble ia nitric and hot acetic acid. Lead metaborate may be produced by a fusion of boric acid with lead carbonate or litharge. It also may be formed as a precipitate when a concentrated solution of lead nitrate is mixed with an excess of borax. The oxides of lead and boron are miscible and form clear lead-borate glasses in the range of 21 to 73 mol % PbO. 

Boron, in the form of boric acid, is used in the PWR primary system water to compensate for fuel consumption and to control reactor power (3). The concentration is varied over the fuel cycle. Small amounts of the isotope lithium-7 are added in the form of lithium hydroxide to increase pH and to reduce corrosion rates of primary system materials (4). Primary-side corrosion problems are much less than those encountered on the secondary side of the steam generators. 

The quantity of boric acid maintained in the reactor coolant is usually plant specific. In general, it ranges from ca 2000 ppm boron or less at the start of a fuel cycle to ca 0 ppm boron at the end. Most plants initially used 12-month fuel cycles, but have been extended to 18- and 24-month fuel cycles, exposing the materials of constmction of the fuel elements to longer operating times. Consequendy concern over corrosion problems has increased. 

The reactor coolant pH is controlled using lithium-7 hydroxide [72255-97-17, LiOH. Reactor coolant pH at 300°C, as a function of boric acid and lithium hydroxide concentrations, is shown in Figure 3 (4). A pure boric acid solution is only slightly more acidic than pure water, 5.6 at 300°C, because of the relatively low ionisation of boric acid at operating primary temperatures (see Boron COMPOUNDS). Thus the presence of lithium hydroxide, which has a much higher ionisation, increases the pH ca 1—2 units above that of pure water at operating temperatures. This leads to a reduction in corrosion rates of system materials (see Hydrogen-ION activity). 

Chemical shim control is effected by adjusting the concentration of boric acid dissolved ia the coolant water to compensate for slowly changing reactivity caused by slow temperature changes and fuel depletion. Eixed burnable poison rods are placed ia the core to compensate for fuel depletion. 

The tertiary metal phosphates are of the general formula MPO where M is B, Al, Ga, Fe, Mn, etc. The metal—oxygen bonds of these materials have considerable covalent character. The anhydrous salts are continuous three-dimensional networks analogous to the various polymorphic forms of siHca. Of limited commercial interest are the alurninum, boron, and iron phosphates. Boron phosphate [13308-51 -5] BPO, is produced by heating the reaction product of boric acid and phosphoric acid or by a dding H BO to H PO at room temperature, foUowed by crystallization from a solution containing >48% P205- Boron phosphate has limited use as a catalyst support, in ceramics, and in refractories. 

Monobasic aluminum acetate is dispensed as a 7% aqueous solution for the topical treatment of certain dermatological conditions, where a combination of detergent, antiseptic, astringent, and heat-dispersant effects are needed (12). The solution, diluted with 20—40 parts water, is appHed topically to the skin and mucous membranes as a wet dressing (13). Burrow s solution, prepared from aluminum subacetate solution by the addition of a specific amount of acetic acid, is also used as a topical wet dressing. Standards of purity and concentration have been estabHshed for both pharmaceutical aluminum acetate solutions (13). Each 100 mL of aluminum subacetate solution yields 2.30—2.60 g of aluminum oxide and 5.43—6.13 g of acetic acid upon hydrolysis. For the Burow s solution, each 100 mL yields 1.20—1.45 g of aluminum oxide and 4.25—5.12 g of acetic acid. Both solutions may be stabilized to hydrolysis by the addition of boric acid in amounts not to exceed 0.9% and 0.6% for the subacetate and Burow s solutions, respectively (13). 

Ammonia and ammonium ions in industrial water streams, including waste-water streams, can be determined by either of two methods (ASTM Procedure D1426). In the first, the sample is buffered to a pH of 7.4 and distilled into a solution of boric acid where the ammonia nitrogen is deterrnined colorimetricaHy with Nessler reagents or titrated using standard sulfuric acid. 

Succinic anhydride is stabilized against the deteriorative effects of heat by the addition of small amounts (0.5 wt %) of boric acid (27), the presence of which also decreases the formation of the dilactone of gamma ketopimelic acid (28). Compared with argon, CO2 has an inhibiting effect on the thermal decomposition of succinic acid, whereas air has an accelerating effect (29,30). 

PuUy hydroly2ed poly(vinyl alcohol) and iodine form a complex that exhibits a characteristic blue color similar to that formed by iodine and starch (171—173). The color of the complex can be enhanced by the addition of boric acid to the solution consisting of iodine and potassium iodide. This affords a good calorimetric method for the deterrnination of poly(vinyl alcohol). Color intensity of the complex is effected by molecular weight, degree of... 

Adhesives for paper tubes, paperboard, cormgated paperboard, and laminated fiber board are made from dispersions of clays suspended with fully hydrolyzed poly(vinyl alcohol). Addition of boric acid improves wet tack and reduces penetration into porous surfaces (312,313). The tackified grades have higher solution viscosity than unmodified PVA and must be maintained at pH 4.6—4.9 for optimum wet adhesion. 

The name boric acid is usually associated with orthoboric acid, which is the only commercially important form of boric acid and is found ia nature as the mineral sassoflte. Three crystalline modifications of metaboric acid also exist. AH these forms of boric acid can be regarded as hydrates of boric oxide and formulated as B2O3 3H20 for orthoboric acid and B2O3 H20 for metaboric acid. 

Forms of Boric Acid. Orthoboric acid, B(OH)3, formula wt, 61.83, crystaUi2es from aqueous solutions as white, waxy plates that are triclinic ia nature sp gi 4, 1.5172. Its normal melting poiat is 170.9°C, however, when heated slowly it loses water to form metaboric acid, HBO2, formula wt, 43.82, which may exist ia one of three crystal modifications. Orthorhombic HBO2-III or a-form d = 1.784 g/mL, mp = 176° C) forms first around 130°C and gradually changes to monoclinic HBO2-II or P-form (d = 2.045 g/mL, mp = 200.9° C). Water-vapor pressures associated with these decompositions foUow. To convert kPa to mm Hg, multiply by 7.5. 

At temperatures above 150°C, dehydration continues to yield viscous Hquid phases beyond the metaboric acid composition (39). The most stable form of metaboric acid, cubic HBO2-I or y-form (d = 2.49 g/mL, mp = 236° C) crystaUi2es slowly when mixtures of boric acid and HBO2-III are melted ia an evacuated, sealed ampul and held at 180°C for several weeks (41). 

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. 

The solubility of boric acid in water (Table 6) increases rapidly with temperature. The heat of solution is somewhat concentration dependent. For solutions having molalities in the range 0.03—0.9 the molar heats of solution fit the empirical relation (49) ... 

The presence of inorganic salts may enhance or depress the aqueous solubiUty of boric acid it is increased by potassium chloride as well as by potassium or sodium sulfate but decreased by lithium and sodium chlorides. Basic anions and other nucleophiles, notably borates and fluoride, greatly increase boric acid solubihty by forrning polyions (44). 

Table 7. Solubility of Boric Acid, Borax Decahydrate, and Borax Pentahydrate in Organic Solvents...

Dilute aqueous solutions of boric acid contain predorninantly monomeric, undissociated B(OH)3 molecules. The acidic properties of boric acid ... 

The apparent acid strength of boric acid is increased both by strong electrolytes that modify the stmcture and activity of the solvent water and by reagents that form complexes with B(OH) 4 and/or polyborate anions. More than one mechanism may be operative when salts of metal ions are involved. In the presence of excess calcium chloride the strength of boric acid becomes comparable to that of carboxyUc acids, and such solutions maybe titrated using strong base to a sharp phenolphthalein end point. Normally titrations of boric acid are carried out following addition of mannitol or sorbitol, which form stable chelate complexes with B(OH) 4 in a manner typical of polyhydroxy compounds. EquiUbria of the type ... 

Alcohols react with boric acid with elimination of water to form borate esters, B(OR)3. A wide variety of borate salts and complexes have been prepared by the reaction of boric acid and inorganic bases, amines, and heavy-metal cations or oxyanions (44,45). Fusion with metal oxides yields... 

Manufacture. The majority of boric acid is produced by the reaction of inorganic borates with sulfuric acid in an aqueous medium. Sodium borates are the principal raw material in the United States. European manufacturers have generally used partially refined calcium borates, mainly colemanite from Turkey. Turkey uses both colemanite and tincal to make boric acid. 

The handling of boric acid and borax is generally not considered dangerous. There are no fire risks associated with the storage or use of inorganic borates, and they are not explosive. 

Ammonium tetraborate tetrahydrate is prepared by crystallization from an aqueous solution of boric acid and ammonia having a B202 (NH4)20 ratio of 1.8 2.1. Ammonium pentaborate is similarly produced from an aqueous solution of boric acid and ammonia having a B202 (NH4)20 ratio of 5. Supersaturated solutions are easily formed and the rate of crystallization is proportional to the extent of supersaturation (130). A process for the production... 

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