downstream (Van Wazer 1958). Rayleigh (Mellor
(1) DISSOLUTION
1928) observed that P4 is slightly volatile at room
Suspended P4
Dissolved P4
temperature and that the increased luminosity
(up to 100 mg/L)
(up to 2.4 mg/L)
when the atmosphere is rarefied is due to the in-
creased volatilization of the P4. Thorpe (Mellor
(2) OXIDATION OF P 4
1928) concluded that P4 reacts with oxygen only
P4+ O 2
P4 O2
under conditions where the P4 volatilizes and
P4+ 3O2
2P2 O 3
that
the glow itself is nothing but a slowly burning
(3) HYDROLYSIS TO OXYACIDS
flame, having an extremely low temperature,
P4 O2+ 6H2O
4H3PO2
caused by the chemical union of oxygen with
the vapours of phosphorus and phosphorus ox-
2P 2O 3+ 6H2O
4H3PO3
ide. By suitable means this glow can be gradual-
ly augmented until it passes by regular grada-
(4) OXIDATION TO ORTHOPHOSPHORIC ACID
tion into the active vigorous combustion which
H 3PO 4
H 3PO 2 + O 2
we ordinarily associate with flame.
2H3PO 3 + O2
2H3PO4
The transition to burning with a bright yellow
flame occurs when the temperature is raised to
Figure 3. Oxidation pathway for white phosphorus in
the ignition point or the pressure lowered below
water. (After Sullivan et al. 1979.)
a definite limit (Fig. 2). Autoignition may also
occur at room temperature if white phosphorus
acids (e.g. nitric and sulfuric). The surface of sol-
is covered by cotton (Mellor 1928). Since the oxi-
id P4 is oxidized by aqueous solutions of metal
dation of P4 occurs by a reaction that occurs in
salts such as copper sulfate, reducing salts of
the vapor phase immediately adjacent to the sol-
copper to the metal via copper phosphide. In the
id phase, activities that result in higher concen-
past, first aid for P4 burns included bathing the
trations of P4 vapor lead to autoignition. Dainton
P4 in aqueous copper sulfate (Konjoyan 1983),
and Bevington (1946) observed surface melting
which coated the P4 particles with black copper
as a solid piece of P4 underwent transition from
phosphide (Mellor 1928) and prevented the P4
glow to flame. They speculated that not all the
from reigniting. White phosphorus stored under
heat of reaction is dissipated as light and that the
tap water will blacken due to reaction with cop-
glow reaction is slightly exothermic. The heat
per cations dissolved in the water from copper
causing the melting came from the oxidation re-
pipes (Rae 1916).
action in the spatially adjacent vapor phase,
Studies of the oxidation of P4 in water are
which in turn raised the surface temperature of
summarized by Sullivan et al. (1979). Dissolved
the solid P4, leading to increased vapor pressure,
P4 reacts with dissolved oxygen to form phos-
more heat and finally ignition.
phinic (H3PO2) and phosphonic (H3PO3) acids,
Dainton and Bevington (1946) described the
which in turn oxidize to orthophosphoric acid
greenish glow in terms of "width, intensity, and
(H3PO4) (Fig. 3). Phosphine is also produced,
distance from the phosphorus." They concluded
probably by hydrolysis (Spanggord et al. 1985).
that the rate of consumption of P4 vapor and oxy-
When solid P4 is introduced into water contain-
gen was limited by the rate of diffusion of either
ing dissolved oxygen, a film of oxidation product
reactant into the reaction zone. The conclusion of
forms on the surface. This film, the formation of
later work by Dainton and Kimberley (1950) was
which is accompanied by hydrogen evolution,
that "the glow reaction is only limited in velocity
was identified by Nikandrov and Smirnov (1983)
by the supply of phosphorus molecules to the re-
as (P4OH)2, an intermediate to the formation of
action zone." White phosphorus exposed to dry
phosphorus pentoxide.
air may form a layer of oxides that greatly reduc-
es or stops the rate of oxidation (Russell 1903,
Factors that affect the environmental fate of
Dainton and Bevington 1946). White phosphorus
white phosphorus
exposed to moist air forms a film of moisture that
may stop oxidation (Russell 1903). The develop-
ed aqueous or soil media. The thermodynamic
ment of the film is due to the formation of the
instability of P4 is illustrated in the potential-pH
hygroscopic phosphorus pentoxide (P4O10).
equilibrium diagram for phosphorus in water at
White phosphorus will react with other oxi-
25C (Fig. 4). The domain of stability for P4 is
dizing agents such as the halogens, sulfur and
4
Previous Page
