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Phosphorus tribromide, like PCl 3 and PF 3, has both properties of a Lewis base and a Lewis acid. For example, with a Lewis acid such as boron tribromide it forms stable 1 :1 adducts such as Br 3 B · PBr 3. At the same time PBr 3 can react as an electrophile or Lewis acid in many of its reactions, for example with amines.
A Lewis base is also a Brønsted–Lowry base, but a Lewis acid does not need to be a Brønsted–Lowry acid. The classification into hard and soft acids and bases ( HSAB theory ) followed in 1963. The strength of Lewis acid-base interactions, as measured by the standard enthalpy of formation of an adduct can be predicted by the Drago–Wayland ...
Thiophosphoryl bromide can be prepared by heating phosphorus tribromide with phosphorus pentasulfide, or with elemental sulfur in an inert atmosphere at 130 °C. [4] Thiophosphoryl bromide is one product of the bromination of P 4 S 7 in cold carbon disulfide: [1] 3 P 4 S 7 + 12 Br 2 → 2 PBr 3 + 2 PSBr 3 + 2 P 2 S 6 Br 2 + 2 P 2 S 5 Br 4
Phase behavior Triple point? K (? °C), ? Pa Critical point? K (? °C), ? Pa Std enthalpy change of fusion, Δ fus H o? kJ/mol Std entropy change of fusion, Δ fus S oJ/(mol·K)
Since Lewis adducts are formed by dative bond between Lewis bases and Lewis acids, the orbital overlap between the Lewis base and σ*(Sb–X) orbital is the source of the acidity. According to Gabbaï et al., NBO analysis of the Sb(C 6 F 5) 3 P(O)Ph 3 adduct indicates a donor-acceptor interaction between lp(O) and σ*(Sb–C 6 F 5). [7] [8]
Phosphoryl bromide is prepared by the reaction between phosphorus pentabromide and phosphorus pentoxide: [4] [5]. 3 PBr 5 + P 2 O 5 → 5 POBr 3. It can also be prepared via the slow addition of liquid bromine to phosphorus tribromide at 0 °C, followed by the slow addition of water and vacuum distillation of the resulting slurry.
Tribromide is the anion with the chemical formula Br 3 −, or salts containing it: . Tetrabutylammonium tribromide; Tetrabromophosphonium tribromide; Pyridinium perbromide; Sodium and potassium tribromides can be prepared by reacting NaBr or KBr with aqueous bromine.
An example of the Hell–Volhard–Zelinsky reaction can be seen in the preparation of alanine from propionic acid.In the first step, a combination of bromine and phosphorus tribromide is used in the Hell–Volhard–Zelinsky reaction to prepare 2-bromopropionic acid, [3] which in the second step is converted to a racemic mixture of the amino acid product by ammonolysis.