CA1128729A

CA1128729A - Production of magnesium phosphide

Info

Publication number: CA1128729A
Application number: CA362,600A
Authority: CA
Inventors: Friedrich W. Dorn; Gero Heymer
Original assignee: Hoechst AG
Current assignee: Hoechst AG
Priority date: 1979-10-31
Filing date: 1980-10-16
Publication date: 1982-08-03
Also published as: JPS6363483B2; DD153802A5; DE3064299D1; EP0028315A1; EP0028315B1; DE2943905A1; JPS5673607A; IN149449B

Abstract

PRODUCTION OF MAGNESIUM PHOSPHIDE
ABSTRACT OF THE DISCLOSURE:
The invention relates to an improved process for making magnesium phosphide by reacting magnesium and phosphorus at elevated temperature with exclusion of air. To this end, liquid magnesium is contacted and thereby reacted with stoichiometric proportions of liquid or gaseous phosphorus at a temperature higher than 650° C and with thorough agitation of the reaction components to give magnesium phosphide. The formation of covering layers of solid magnesium phosphide on the surface of the magnesium is inhibited by means of continuously actuated mechanical aids.

Description

11 h 8 7~9 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.

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 ~ ~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.

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.

Claims

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:
THE CLAIMS:

1) In a process for making magnesium phosphide by reacting magnesium and phosphorus at elevated temperature with exclusion of air, the improve-ment which comprises: contacting and thereby reacting liquid magnesium with stoichiometric proportions of liquid or gaseous phosphorus at a temperature higher than 650° C and with thorough agitation of the reaction components to give magnesium phosphide, the formation of covering layers of solid magnesium phosphide on the surface of the magnesium being inhibited by means of continuously actuated mechanical aids.

2) A process as claimed in claim 1, wherein colorless phosphorus is used.

3) A process as claimed in claim 1, wherein the reaction is effected at a temperature within the range about 700 to 900° C.

4) A process as claimed in claim 1, wherein the reaction is effected in the presence of an inert gas.

5) A process as claimed in claim 4, wherein the reaction is effected in the presence of argon.

6) A process as claimed in claim 1, wherein the formation of covering layers of magnesium phosphide is inhibited by placing milling balls in the reaction batch, the balls being kept in continuous motion.

7) A process as claimed in claim 1, wherein the reaction is effected in a kneader.