Phase fluoroborate

Ammonium fluoroborate is both a condensed and vapor-phase flame retardant. It is available from M T Hatshaw, General Chemical Cotp., and Spectmm Chemical Cotp. 

Boron may be prepared by several methods, such as chemical reduction of boron compounds, electrolytic reduction in nonaqueous phase, or by thermal decomposition. Many boron compounds including boron oxides, borates, boron halides, borohydrides, and fluoroborates can be reduced to boron by a reactive metal or hydrogen at high temperatures ... 

Figure 5.3 Chromatograms of amines with mobile phases containing (a) water adjusted to pH 3 with HCl and (b) 30 mmol/L l-ethyl-3-methylimidazolium tetra-fluoroborate. Chromatographic conditions C18 column (5 pm, 150 X 4.6 mm ID) rate flow 1.0 mL/min detection at 254 nm. Peaks (1) benzylamine (2) benzidine (3) N,N-dimethylaniline and (4) N-ethylaniline. (Adapted from Xiaohua, X., Liang, Z., Xia, L., and Shengxiang, Anal. Chim. Acta, 519, 207-211, 2004.)...

One additional term occurs ui this Bom-Haber cycle the formation of the tetra-fluoroborate ion in the gas phase ... 

In the example (Expt 6.79) the reaction of the diazonium salt from o-chloroaniline with benzene to yield 2-chlorobiphenyl is illustrative. It should be noted, however, that when the liquid aromatic compound in which substitution is to occur is of the type ArZ, the directive influences which are used to explain electrophilic substitution processes are not operative. Thus irrespective of the nature of the substituent Z, ortho-para substitution predominates this result supports the assumption that the substitution process is radical in type. Although the classical reaction occurs in a two-phase system, the use of the more stable diazonium fluoroborates together with the phase-transfer catalyst 18-crown-6 can sometimes be more convenient. The literature method for the preparation of 4-chlorobiphenyl in this way is given as a cognate preparation in Expt 6.19 ... 

Effective catalysts for preparing the polyformals were p-toluenesulfonic acid, camphorsulfonic acid, methanedisulfonic acid, and perchloric acid. Various other acidic compounds were evaluated as catalysts with tetramethylcyclobutanediol. In these experiments, 0.5 to 1.0 gram of acidic compound per mole of tetramethylcyclobutanediol was normally added. If insufficient water was obtained, more catalyst was added. If the prepolymer was obtained but an appreciable amount of brown color was present, less catalyst was then used. Compounds which did not catalyze the reaction (no water obtained) were phosphoric acid, zinc chloride, trifluoroacetic acid, and heptafluorobutyric acid. Incomplete reactions (insufficient water) took place with concentrated hydrochloric acid, concentrated nitric acid, zinc fluoroborate, or Amberlite IRC-50 ion exchange resin as catalyst. A prepolymer was obtained when boron trifluoride etherate was used, but buildup did not take place in the solid phase (catalyst probably too volatile). Brown or speckled-brown polymers (after solid-phase buildup) were obtained with catalysts containing sulfonic acid groups (benzenesulfonic, dodecylbenzenesulfonic, sulfo-acetic, methanetrisulfonic, sulfuric, p-toluenesulfonic, camphorsulfonic, and methanedisulfonic acids). To obtain white polymers from tetramethylcyclobutanediol it was necessary to treat the solvent and prepolymer reaction mixture as previously described. (White polyformals were obtained from the other diols without this treatment.)... 

To a dichloromethane solution (5 ml) containing triphenylbismuth difluoride (239 mg, 0.50 mmol) and 4-methylphenylboronic acid (68 mg, 0.50 mmol) was added boron trifluoride diethyl etherate (65 p.1, 0.50 mmol) at 0°C, and the resulting mixture was stirred at room temperature for 2 h. An aqueous solution (20 M) of sodium fluoroborate (500 mg, 4.55 mmol) was then added and the two-phase mixture was vigorously stirred for 30 min. The water phase was extracted with dichloromethane (5 ml X 2), and the combined extracts were dried over MgS04, and passed through a short silica gel column. Evaporation of the solvent under reduced pressure left an oily residue, which was crystallized from ether-dichloromethane (10 1) to yield (4-methylphenyl)triphenylbismuthonium tetrafluoroborate (300 mg, 97%) as a colorless solid [980M4332]. 

Chromatography.2 Reverse phase chromatography on glass fibre paper using silver fluoroborate solutions as eluants has proved useful for separation of sesquiterpenes, even of mixtures that appear homogeneous on alumina and by gas-liquid chromatography. Silver nitrate is too insoluble to be used. 

Relatively fewer studies have been made on solid-phase olefin complexes. Quinn et al. s°) investigated the variation of dissociation pressure with temperature of several silver fluoroborate complexes and they were able to calculate the thermodynamic data, listed in Table 8, for the following reaction... 

Completely different monomers were called for. Before long, three of today s workhorses had been identified pyrrole, aniline and thiophene. In Japan, Yamamoto [38] and in Germany, Kossmehl [39] synthesized polythiophene doped with pentafluoroarsenate. At the same time, the possibilities of electrochemical polymerization were recognized. At the IBM Lab in San Jose, Diaz used oxidative electrochemical polymerization to prepare polypyrrole [40] and polyaniline. [41] Electrochemical synthesis forms the polymer in its doped state, with the counter-ion (usually an anion) incorporated from the electrolyte. This mechanism permits the selection of a wider range of anions, including those which are not amenable to vapor-phase processes, such as perchlorate and tetra-fluoroborate. Electrochemical doping also overcomes an issue associated with dopants... 

Thiophenes are generally obtained by sulfuration of 1,4-dicarbonyl compounds (Paal s)mthesis). The preparation of the highly substituted 2-(4-bromophenyl)-5-(3,4-dimethoxyphenyl)-3,4-dimethylthiophene from the respective 1,4-diketone represents a recent example. This type of reaction can be performed as a solid-phase synthesis with polymer-bound diketones (132) and LR (eq 44). Trifluoroacetic acid releases the thiophene (133) from the solid support. Bismuth triflate in 1,3-dialkylimida-zolium fluoroborate has been utilized as a catalytic ionic liquid system for the synthesis of thiophenes from 1,4-diketones and LR with significantly improved yields. 

The phase behaviour of many (ionic liquid + CO2) systems was subsequently studied, including CO2 solubility in imidazolium-based ionic liquids with tetra-fluoroborate anions, hexafluorophosphate anions, bis(trifluoro-methylsulfonyl)amide anions,and other ionic liquids. All these systems show similar phase behaviour as depicted in Figure 11.2. 

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