towards metal ions, thus giving rise
to a series of complexes.phosphorus cycleThe cycling of
phosphorus between the biotic and
abiotic components of the environ-
ment. Inorganic phosphates (PO 4 3–,
HPO 4 2–, or H 2 PO 4 – ) are absorbed by
plants from the soil and bodies of
water and eventually pass into ani-
mals through food chains. Within liv-
ing organisms phosphates are built
up into nucleic acids and other or-
ganic molecules. When plants and
animals die, phosphates are released
and returned to the abiotic environ-
ment through the action of bacteria.
On a geological time scale, phos-
phates in aquatic environments even-
tually become incorporated into and
form part of rocks; through a gradual
process of erosion, these phosphates
are returned to the soil, seas, rivers,
and lakes. Phosphorus-containing
rocks are mined for the manufacture
of fertilizers, which provide an addi-
tional supply of inorganic phosphate
to the abiotic environment.
phosphorus(III) oxide (phospho-
rus trioxide)A white or colourless
waxy solid, P 4 O 6 ; r.d. 2.13; m.p.
23.8°C; b.p. 173.8°C. It is soluble in
ether, chloroform, and benzene but
reacts with cold water to give phos-
phonic acid, H 3 PO 3 , and with hot
water to give phosphine and phos-
phoric(V) acid. The compound is
formed when phosphorus is burned
in an oxygen-deÜcient atmosphere
(about 50% yield). As it is difÜcult to
separate from white phosphorus by
distillation, the mixture is irradiated
with ultraviolet radiation to convert
excess white phosphorus into the red
form, after which the oxide can be
separated by dissolution in organic
solvents. Although called a trioxide
for historical reasons, phosphorus(III)
oxide consists of P 4 O 6 molecules of
tetrahedral symmetry in which eachphosphorus atom is linked to the
three others by an oxygen bridge.
The chemistry is very complex.
Above 210°C it decomposes into red
phosphorus and polymeric oxides. It
reacts with chlorine and bromine to
give oxo-halides and with alkalis to
give phosphonates (see phosphonic
acid).phosphorus(V) oxide (phosphorus
pentoxide; phosphoric anhydride)A
white powdery and extremely deli-
quescent solid, P 4 O 10 ; r.d. 2.39; m.p.
580 °C (under pressure); sublimes at
300 °C. It reacts violently with water
to give phosphoric(V) acid. It is pre-
pared by burning elemental phos-
phorus in a plentiful supply of
oxygen, then puriÜed by sublimation.
The hexagonal crystalline form con-
sists of P 4 O 10 molecular units; these
have the phosphorus atoms arranged
tetrahedrally, each P atom linked to
three others by oxygen bridges and
having in addition one terminal oxy-
gen atom. The compound is used as a
drying agent and as a dehydrating
agent; for example, amides are con-
verted into nitrites and sulphuric
acid is converted to sulphur trioxide.
phosphorus oxychlorideSee
phosphorus(iii) chloride oxide.
phosphorus pentabromide See
phosphorus(v) bromide.
phosphorus pentachlorideSee
phosphorus(v) chloride.phosphorus tribromide See phos-
phorus(iii) bromide.phosphorus trichlorideSee phos-
phorus(iii) chloride.phosphorus trioxideSee phos-
phorus(iii) oxide.phosphoryl chlorideSee phospho-
rus(iii) chloride oxide.
photoacoustic spectroscopy A
spectroscopic technique in whichphosphorus cycle 414p