acids and energy-carrying molecules
(e.g. ATP) and also involved in various
metabolic reactions. The element
was discovered by Hennig Brand
(c. 1630–92) in 1669.
A
- Information from the WebElements site
phosphorus(III) bromide (phos-
phorus tribromide) A colourless fum-
ing liquid, PBr 3 ; r.d. 2.85; m.p. –40°C;
b.p. 173°C. It is prepared by passing
bromine vapour over phosphorus but
avoiding an excess, which would lead
to the phosphorus(V) bromide. Like
the other phosphorus(III) halides,
PBr 3 is pyramidal in the gas phase. In
the liquid phase the P–Br bonds are
labile; for example, PBr 3 will react
with PCl 3 to give a mixture of prod-
ucts in which the halogen atoms
have been redistributed. Phospho-
rus(III) bromide is rapidly hydrolysed
by water to give phosphonic acid and
hydrogen bromide. It reacts readily
with many organic hydroxyl groups
and is used as a reagent for introduc-
ing bromine atoms into organic mol-
ecules.
phosphorus(V) bromide (phos-
phorus pentabromide) A yellow
readily sublimable solid, PBr 5 , which
decomposes below 100°C and is solu-
ble in benzene and carbon tetrachlo-
ride (tetrachloromethane). It may be
prepared by the reaction of phospho-
rus(III) bromide with bromine or the
direct reaction of phosphorus with
excess bromine. It is very readily hy-
drolysed to give hydrogen bromide
and phosphoric(V) acid. An interest-
ing feature of this material is that in
the solid state it has the structure
[PBr 4 ]+Br–. It is used in organic chem-
istry as a brominating agent.
phosphorus(III) chloride (phos-
phorus trichloride)A colourless fum-
ing liquid, PCl 3 ; r.d. 1.57; m.p.
–112°C; b.p. 75.5°C. It is soluble in
ether and in carbon tetrachloride but
reacts with water and with ethanol.
It may be prepared by passing chlo-
rine over excess phosphorus (excess
chlorine contaminates the product
with phosphorus(V) chloride). The
molecule is pyramidal in the gas
phase and possesses weak electron-
pair donor properties. It is hy-
drolysed violently by water to
phosphonic acid and hydrogen chlo-
ride. Phosphorus(III) chloride is an
important starting point for the syn-
thesis of a variety of inorganic and
organic derivatives of phosphorus.phosphorus(V) chloride (phos-
phorus pentachloride)A yellow-
white rhombic solid, PCl 5 , which
fumes in air; r.d. 4.65; m.p. 166.8°C
(under pressure); sublimes at
160–162°C. It is decomposed by
water to give hydrogen chloride and
phosphoric(V) acid. It is soluble in or-
ganic solvents. The compound may
be prepared by the reaction of chlo-
rine with phosphorus(III) chloride.
Phosphorus(V) chloride is structurally
interesting in that in the gas phase it
has the expected trigonal bipyrami-
dal form but in the solid phase it con-
sists of the ions [PCl 4 ]+[PCl 6 ]–. The
same ions are detected when phos-
phorus(V) chloride is dissolved in
polar solvents. It is used in organic
chemisty as a chlorinating agent.
phosphorus(III) chloride oxide
(phosphorus oxychloride; phosphoryl
chloride)A colourless fuming liquid,
POCl 3 ; r.d. 1.67; m.p. 2°C; b.p.
105.3°C. It may be prepared by the
reaction of phosphorus(III) chloride
with oxygen or by the reaction of
phosphorus(V) oxide with phospho-
rus(V) chloride. Its reactions are very
similar to those of phosphorus(III)
chloride. Hydrolysis with water gives
phosphoric(V) acid. Phosphorus(III)
chloride oxide has a distorted tetra-
hedral shape and can act as a donor413 phosphorus(III) chloride oxide
p