Ammonium metal borate

Many borates are known that contain non-metal cations. Examples include the ammonium borates [39], such as the commercial products ammonium pentaborate, NH4[B506(0H)4] 2 H2O, and ammonium tetraborate, (NH4)2 [6405(011)4] 2 H2O, both of which contain isolated borate anions shown above (Figs. 5a and 6a, respectively) [40]. Isolated borate anions containing more than six boron atoms are rare. However, the mineral ammonioborite [(NH4)3[Bi502o(OH)g] 4 H20 = (NH4)20 5 B2O3 2 2/3 H2O), which may be prepared synthetically by prolonged reflux of a saturated solution of ammonium pentaborate, contains the unusual isolated anion [Bi502o(OH)g] , shown in Fig. 10 [41]. This anion is not known to occur in any metal borate, its formation is apparently directed exclusively by the ammonium cations which can donate H-bonds to interstitial water and the borate structural unit. 

Boron compounds such as borax and boric acid are well-known fire retardants in cellulosic products and coatings.12 However, the use of boron compounds such as zinc borate, ammonium pent-aborate (APB), melamine borate, boric oxide, boron phosphate, and other metal borates in polymers has become prominent only since early 1980s.3 6 This chapter will review the chemical and physical properties, the end-use applications, as well as the mode of actions of major boron compounds as fire retardants in different applications. Since boron-based flame retardants are extensively used and quoted in literature, only those formulations of commercial importance and representative literature examples will be discussed and/or cited in this chapter. 

Fire Retardants with emphasis on metal hydroxides but also inclusion of antimony oxide, ammonium polyphosphate, borate salts and low melting temperature glasses. Chapter 17. 

Supporting electrolyte is the mixture of quaternary ammonium salts and inorganic salt. Quaternary ammonium salts such as ethyltributy-lammoniumsalt are effective not only for increasing the selectivity of adiponitrile generation but also for protection of cathode from corrosion. Inorganic salts such as potassium phosphate and alkali metal borate increases conductivity of electrolyte and prevent corrosion of the anode. 

Alkali metal and ammonium borates are considered to be reasonably soluble in water. Table 17.2 provides solubility data for several alkali metal and other metal borates at different temperatures [8]. 

The element boron forms strong bonds with oxygen. The resultant borates include boric acid, boric oxide, alkali, ammonium, and alkaline earth metal borates. All except for the alkaline earth borates are reasonably water soluble. When dissolved borates release boric acid, a Lewis acid, and its conjugate base, the tetrahydroxyborate anion. Borax, a form of di-sodium tetraborate, releases equimolar amounts of these species and consequently is an excellent mildly alkaline pH buffer. Borates exhibit several important behaviors in solution, including the sequestration of water hardness ions, the ability to form borate esters with polyols, and to deliver the oxidant hydrogen peroxide into solution from the dissolution of sodium perborate. 

Table 9. Aqueous Solubilities of Alkali Metal and Ammonium Borates at Various Temperatures...

On the other hand, metals such as Ta, Nb, Ti, Zr, Al, etc. (the valve metals ) do not exhibit transpassive behaviour, and in appropriate electrolyte solutions film growth at high fields rather than corrosion and/or oxygen evolution is the predominant reaction thus aluminium can be anodised to 500 V or more in an ammonium borate buffer titanium can be anodised to about 400 V in formic acid and tantalum can be anodised to high voltages in most acids, including hydrochloric acid. 

The use of other crosslinking metals developed simultaneously with the use of antimony, chromium, and boron(borate). Tiner, et al.(242) introduced titanium (IV) crosslinkers in 1975 as ammonium tetralactonate or bis(triethanolamine)bis(isopropyl)titanium(IV). Upon contact with water soluble titanium (IV) derivatives ordinarily form orthotitanic acid, Ti(0H)4, which rapidly forms oligimeric metatitanic acid, [Ti(0H)2] and titanium dioxide. Electron donors such as the hydroxyl groupsxof polysaccharides, if properly oriented, can participate in the sequence of titania reactions and a crosslinked gel network results. Various titanium metal crosslinkers remain in common use today. More will be said about titanium crosslinked gels later. 

Borazine originally was obtained by the reaction of ammonia with diborane.1 Mixtures of lithium or sodium tetrahydro-borate with ammonium chloride also have been pyrolyzed to yield this product.2 More recently, the reduction of B,B, B"-trichloroborazine with alkali metal hydroborates has proved to be a convenient laboratory-scale method for the preparation of this compound.3-7 The procedure described herein is a variation of the last method as reported by Dahl and Schaeffer.7 This method is effective for the synthesis of iV-substituted alkyl- and arylborazines, i.e., compounds of the formula (HBNR)3 where R is CH3, C2H6, C6H , C6H5, p-C6H4CH3, or p-C6H4OCH3.5... 

NMR (CeDg, 125.7 MHz, 25°C) 139.8, 132.5, 128.8-129.1 (overlapping resonances), 124.6, 17.0 (br). B NMR (CgDg, 128.3 MHz, 25°C) -10.96 ppm. The compound is a versatile precursor to a wide range of transition metal complexes supported by the tris(phosphino)borate ligand. It is air- and water-stable for extended periods, and, unlike the lithium and ammonium salts of [PhB(CH2PPh2)3] , it is both soluble and stable in chloroform and dichloromethane for days, making these useful solvents available for subsequent trans-metallation chemistry. 

Biocidal applications. The use of quaternary ammonium salts in disinfecting systems for household and industrial cleaners has been known for many years [95, 96]. Alkyl-benzyldimethyl quaternaries, alkyltrimethyl quaternaries, and dialkyldimethyl quaternaries are the more commonly used biocidal quaternary ammonium salts [16]. Recently, dialkyldimethyl quaternary ammonium salts have received renewed attention as potential wood preservatives to replace the heavy metal types [97]. Metal-free wood preservative formulations containing dialkyldimethyl ammonium salts with non-halide anions, such as carboxylates, borates, and carbonates, have been developed [98, 99]. 

The borates of the other metals are, in general, sparingly soluble in water, but fairly soluble in acids and in ammonium chloride solution. 

It is important to note that a large number of perfluorinated tetraorganoborates that are for the most part directly related to the tricoordinate species shown above have been prepared and proven highly useful as activators in olefin polymerization. Usually either trityl, ammonium, or oxonium borates are reacted with a suitable transition-metal complex as shown in Scheme 28. Borate salts may serve as highly active cocatalysts since counterions BAi " such as B(C6Fs)4 typically show a very low tendency for ion pairing with the cation Cp2ZrR+. 

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