Note: Descriptions are shown in the official language in which they were submitted.
11 h 8 7~9
HOE 79/H 041
The present invention relates to a process ~or
making magnesium phosphide of the ~ormula Mg~P2 from
magnesium and phosphorus under ~ommercially attractive
conditions. Magnesium phosphide is a suitable insecticide
for use~ e. g. in grain and food.
It has been described by G. Brauer~ Handbuch der
praparativen anorganischen Chemie, 3rd edition, 1978,
volume 2, page 1913, that small quantities of
magnesium phosphide can be made by a process, wherein
phosphorus in vapor form, which is produced by heating
red phosphorus, is reacted with magnesium turnings at
temperatures lower than the melting point of magnesium
and, a~ter completion of the reaction, phosphorus in
excess is expelled at about 700 C.
A further process has been disclosed in German
Patent Specification "Auslegeschrift" 1,567,520,
wherein heavily contaminated magnesium phosphide
is made by mixing pulverulent magnesium with ground
phosphorus and pulverulent magnesium oxide as an inert
diluent, and the resulting mi~ture is reacted by
electrically igniting it. The diluent is more speci~ically
used for desensitizing the strongly exothermal reaction
and temporariIy binding the reaction heat.
These known processes are beset with serious dis~
advantages which result from the use of fine particulate
magnesium and red phosphorus as feed materials. Magnesium
~.
powder or turnings ~ two to four times more costly
than compact magnesium as powder or turningsare inai-
dentally expensive and hazardous to prepare. Ana}ogously,
red phosphorus is considerably more costly than the
colorless modification of thls element. The use of an
excess of phosphorus in vapor form which means greater
expenditure of work and time is a further adverse effect
which is essociated with these prior processes inasmuch
as it is additionally necessary for the phosphorus in
excess to be removed by increasing the working temperature
at the end of the reaction~ Last but not least, it is
impossible to use the process described in the above
German Patent Specification "Auslegeschrift" 1,567,520
for the production of pure magnesium phosphide. The
compound invariably has diluent therein.
The present invention now provides a process which
avoids the adverse effects described hereinabove. To
this end, the invention provides for magnesium phos-
phide to be made from compact magnesium and colorless
phosphorus as feed materials. The invention also provides
for the reaction to be effected under conditions which
make it possible for the reactants to undergo a
reasonably rapid and stoichiometric conversion but make
it practically impossible ~or the reaction to occur
explosively even in the absence of desensitizing agent~
The present invention is based on the observation
that covering layers of solid Mg3P2 are being formed
on the magnesium during its reaction with phosphorus.
-- 3 --
As a result, the reactants move towards one another at
reduced velocity. This naturally has consequential e~ec-ts
on the velocity of the overall reaction which may e~en
come to a standstill. This is the reason why large-
surfaced solid magnesium powdsr reacts more rapidlyat 600 C with phosphorus in vapor form than liquid
magnesium at 700 C,
The present invention relates more particularly
to a process for making magnesium phosphide by reacting
10 magnesium and phosphorus at elevated temperature with
exclusion of air, which comprises: contacting and
thereby reacting liquid magnesium with stoichiometric
proportions o~ uid or gaseous phosphorus at a tempera-
ture higher than 650~C and with thorough agitation of the
reaction components to give magnesium phosphide~ the for-
mation of covering layers of solid magnesium phosphide on
the surface of the magnesium being i~libited by means of
continuously actuated mechanical aids.
A feature of the present invention provides for
the feed materials to be selected from colorless
phosphorus and compact magnesium, which may be in the
form of bars or ingots~ for example, and for the com-
pact magnesium to be fused. The reaction should pre-
ferably be effected at temperatures of about 700 to
900 C in the presence of an inert gas 9 e. g. argon.
In order effectively to inhibit the ~ormation of
covering layers of magnesium phosphide, it is good
practice to use milling balls~ which should be placed
-- 4 --
~ ~8'~
in the reaction batch and kept in motion therein in
accordance with the principle underl~ing a ball mlll,
The same effect can be produced by e~fecting the
reaction inslde a hea~able kneader, tubular mill,
pan mill or the like.
An exemplary apparatus for use in carrying out
the process of this invention will now be described
with reference to the accompanying drawing of which
: Figure 1 is a side-elevational view, partially
in section, of the apparatus used
in accordance with this invention, and
Figure 2 is a cross-sectional view of the
apparatus of Figure 1.
With reference to the drawing:
The apparatus comprises a cylindrical container (1)
which has milling balls (2) placed therein and is
surrounded by a heating jacket (3). The base and top
areas of the container (1) have the hollow shafts(4)
and (4a), respectively, concentrically connected
thereto~ which provide support for the container (1)
and enable it to be rotated. The hollow shaft (4) ;~
is used for the admission of inert gas and phosphorus
in vapor form, and the hollow shaft (4a) for the
removal of the inert gas from the container (1)~ In
the event of liquid phosphorus being used, it is
good practice for it to be delivered to the reaction
chamber through capillary tubes (5). Fur-ther con-
structional elements forming part of the present
,
apparatus comprise a flow breaker or interrupter (6) and
a sealing ~lap t7) through which reaction product
is taken from the container (1).
The process of this invention compares favorably
with the prior art methods inasmuch as it permits
pure magnesium phosphide to be produced in yields
of more than 90 % of the theoretical under commercially
attractive condition in the absence of diluents.
The following Examples illustrate the invention:
EXAMPLE 1:
Placed in cylindrical heat-resistant steel container
(1) with a capacity of 3 litres were 300 g (12.~4 mol)
rod-shaped magnesium and 3.2 kg (35) milling balls of
steel with a diameter of 28 mm. The air inside the con-
tainer ~1) was expelled by the introduction of argonthrough the hollow shaft (4), and the container (1) was
heated to 810 C by means of the heating jacket (3). Next,
the admission of argon was reduced down to 15 l/h and
255 g (8.23 mol) gaseous phosphorus was admitted within
90 minutes to the reaction chamber, through the hollow
shaft (4). For compensation of heat evolved during the
reaction, the heating power of the heating jacket ~3)
was reduced from 1.7 kw to 1.1 kw. The phosphorus
admitted was completely bound chemically by the
magnesiumso that just traces of phosphorus were found
to escape through the hollow shaft (4a). The formation
of solid covering layers of magnesium phosphide on
the surface of the magnesium was avoided by rotating
the container (1) around its longitudinal axis at 38 rpm.
10 minutes after the introduction of phosphorus in ~apor
form was complete, the heating jacket (3) was removed,
the container was water-sprayed and cooled rapidly~ Next,
the material was taken from the container through
sealing flap (7), the milling balls were separated
from magnesium phosphide which was weighed and analyzed,
541 g magnesium phosphide which was in the form of a
yellow-green powder 9 had an apparent density of 0068 g/ml
and contained 93.3 % Mg3P2 was obtained. This corresponded
to a yield of 95.9 % of the theoretical, based on
magnesium used.
EXAMPLE 2-
The procedure was as in Example 1, but 250 g
(10.2 mol) magnesium and 212 g (6,8 mol) liquid color-
less phosphorus which was admitted to the reaction
chamber through the capillary tubes~passed through
the hollow shaft (4)~ were reacted within 70 minutes
at 680 to 720 C. 440 g of reaction product, which con-
tained 95.1 % Mg~P2 was taken from the container (1).This corresponded to a yield of 90.5 % of the theoreticalO
EXAMPLE 3:
The procedure was as in Example 1, but 200 g
(8.2 mol) magnesium was reacted at 860 to 890 C
with 170 g (5.5 mol) gaseous phosphorus~ 349 g reaction
product which contained 97.0 % Mg3P2 was taken from
the container (1). This corresponded ~o a yield of
91.5 % of the theoretical.
EXAMPLE ~: tComparative Example)
The procedure was effected as in Example 1,but in
the absence of milling balls. At 250 C, the container (1)
was fed with 250 g (10.2 mol) magnesium. Next~ the con-
tainer was heated to 750 C and 170 g (5.5 mol) phosphorus
in vapor form was admitted to the container within 85
minutes. Argon wasSimultaneously passed through the con-
tainer. As a result, a good deal of phosphorus in vapor
form escaped unreacted from the container. After the
container was cool, it was impossible to remove product
therefrom. The magnesium was found to have regularly
fused onto the container's inside wall. It just had
a thin Mg3P2-layer thereon. To determine the con-
version, the Mg3P2 was hydrolyzed with water inside
the container and the quantity of hydrogen phosphide
which was evolved was identifieda 11.2 l PH3 was found
to have been formed at 23 C under a pressure of 1.014 bar.
This corresponded to a yield of 8.4 % of the theoretical,
based on magnesium used.
