Ammonium tetrafluoborate

Boron oxide obtained from pure crystallized boric acid by this procedure is a snow-white, porous, slightly sintered substance. It can be powdered easily, but atmospheric moisture must be excluded during this operation. The sintered material is highly reactive and, when wet with water, evolves heat and hisses, like phosphorus (V) oxide. 

Ammonium tetrafluoborate is frequently used for the preparation of boron trifluoride. The pure fluoborate is most readily obtained in the manner described below. Procedure A is satisfactory for small amounts. Procedure B is more suitable where larger quantities are desired. 

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Ammonium tetrafluoborate is a clear crystalline solid that sublimes when heated strongly. It is soluble in 100 ml. of water to the extent of 25 g. at 16" and 97 g. at 100°... 

FIGURE 3 Cyclic voltammogram of a polypyrrole film with fluoborate counterion. Medium tetra- -butyl ammonium tetrafluoborate (0.1 M) in ACN. Scan rate 100 mV/s. Potential referred to Ag/Ag" electrode. (Data from Ref. 38.)... 

Ionic liquids have also been used as reaction media (Box 9). The high polarity of quaternary ammonium salts is exploited to favour polar reaction steps. For example, with l- -butyl-3-methylimidazolium tetrafluoborate, 2,7-octadien-l-ol (Section 5.4.3) was obtained in good yield from butadiene and water and was readily separated as it was immiscible with the ionic liquid below 5°C [J. E. L. Dullius, P. A. Z. Suarez, S. Einloft, R. F. deSouza, J. Dupont, J. Fisher and A. DeCian, Organometallics 1998, 17, 815]. 

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