Fluoroboric acid HBF

The Schiemann reaction is a means of preparing aryl fluorides. The process is similar to the Sandmeyer reaction. The source of the fluoride is fluoroboric acid, HBF,. Figure 13-29 illustrates the Schiemann reaction. 

Fluorine oxide, 1 109 Fluoroboric acid, HBF(, 1 25 Fluoropentamminecobalt(III) nitrate, 4 172... 

An electrolytic technology for the preparation of ozone was based on glassy carbon as the anode material in concentrated fluoroboric acid (HBF ) [22-24]. The cells also employed a Pt-catalyzed, oxygen reduction cathode (gas diffusion electrode (GDE)) to lower the cell voltage (and hence the energy consumption) and to avoid the need to handle H2 off-gas from the cathode. It was necessary to operate with cooling, and the preferred temperature was 268 K. 

For very strong acids, it is usually possible to use a solvent of a more conventional kind thus, for example, the acid HBF, tetra fluoroboric acid, is extremely strong, because attachment of the hydrogen to the tetrafluoroborate group BF is essentially ionic, H BF and hence dissociation to an acid is very easy. Hence HBF behaves as a strong acid in, for example, an organic solvent, in which it can be used. 

The boric and sulfuric acids are recycled to a HBF solution by reaction with CaF2. As a strong acid, fluoroboric acid is frequently used as an acid catalyst, eg, in synthesizing mixed polyol esters (29). This process provides an inexpensive route to confectioner s hard-butter compositions which are substitutes for cocoa butter in chocolate candies (see Chocolate and cocoa). Epichlorohydrin is polymerized in the presence of HBF for eventual conversion to polyglycidyl ethers (30) (see Chlorohydrins). A more concentrated solution, 61—71% HBF, catalyzes the addition of CO and water to olefins under pressure to form neo acids (31) (see Carboxylic acids). 

Potassium Fluoroborate. Potassium fluoroborate is produced as a gelatinous precipitate by mixing fluoroboric acid and KOH or K CO. Alternatively, fluorosihcic acid is treated with H BO in a 2 1 molar ratio to give HBF OH, which reacts with HF and KCl to yield 98% of KBF in 98.5% purity (52). Commercial KBF normally contains less than 1% KBF OH. 

Fluoroboric (or Fluoboric) Acid, HBF , mw 87.83 colorless clear, strongly acid liq bp 130° (dec) miscible with w ale. Can be prepd by action of boric + sulfuric acid on fluorspar. Used for prepn of fluoboraces and stabilized diazo sales. Its specially purified so In used in patented process for electrolytic brightening of Al... 

---