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10.5: Bromine Trifluoride as a Solvent

  • Page ID
    212676
  • WARNING

    Bromine trifluoride is a toxic, colorless, and corrosive liquid with a pungent choking smell that is soluble in sulfuric acid but explodes on contact with water and organic compounds. Vapors severely irritate and may burn the eyes, skin, and respiratory system. The liquid burns all human tissue and causes severe damage.

    Bromine trifluoride (BrF3) has a liquid range similar to water (Mp = 8.8 °C and Bp = 127 °C), and like water it auto ionizes, (10.5.1).

    \[ \rm BrF_3 \rightarrow BrF_2^+ + BrF_4^-\]

    The products, like those of water’s self-ionization, are an acid (BrF2+) and a base (BrF4-). However, unlike water, BrF3 reacts with fluoride acids and bases not proton acids and bases. Thus, in BrF3 a base is a salt that provides F-, i.e., potassium fluoride (KF) is a base in BrF3 solution in the same manner as potassium hydroxide (KOH) is a base in water. The product from the reaction of a fluoride donor salt with BrF3 is the formation of the conjugate base, BrF4-, (10.5.2).

    \[ \rm AgF + BrF_3 \rightarrow Ag^+ + BrF_4^-\]

    Other examples of this type of reaction include:

    \[ \rm KF + BrF_3 \rightarrow K^+ + BrF_4^-\]

    \[ \rm NOF + BrF_3 \rightarrow NO^+ + BrF_4^-\]

    0By analogy, an acid in BrF3 solution is a compound that acts as a fluoride (F-) acceptor, i.e., a Lewis acid, (10.5.5).

    \[ \rm SbF_5 + BrF_3 \rightarrow SbF_6^- + BrF_2^+\]

    Exercise \(\PageIndex{1}\)

    What are the products from the reaction of HF with BrF3?

    Answer

    \[ \rm HF + BrF_3 \rightarrow HF_2^- + BrF_2^+\]

    Bromine trifluoride as a fluorinating agent

    Bromine trifluoride is a strong fluorinating agent that is able to convert a metal (e.g., vanadium) to its associated fluoride compound, (i.e., VF5). A wide range of salts and oxides may be converted to fluorides with the metal in a high oxidation state. However, it should be noted that BeO, MgO, and Al2O3 form oxo fluorides rather than the fluoride.

    The reaction of silver with BrF3 yields the monofluoride, while the same reaction with gold yields the trifluoride, Eq. If the reactions are combined in BrF3 solution a mixed metal fluoride salt is formed.

    A similar reaction occurs with NOCl and V2O5.

    Exercise \(\PageIndex{2}\)

    What are the products from the reaction of BrF3 with (a) Sb2O5, (b) KCl, and (c) a mixture of Sb2O5 and KCl?

    Answer

    (a) SbF5, (b) KF, and (c) K[SbF6].

    Bibliography

    • J. H. Simons, Inorg. Synth., 1950, 3, 184.
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