Calcium phosphide

Structural formula
3 Ca 2+ 2
General
Surname	Calcium phosphide
other names	Phosphorus calcium Tricalcium diphosphide Calcium phosphide
Molecular formula	Ca 3 P 2
Brief description	malodorous ("after carbide"), flammable, brown-red amorphous mass
External identifiers / databases
CAS number 1305-99-3 EC number 215-142-0 ECHA InfoCard 100,013,766 PubChem 4337964 Wikidata Q421408
properties
Molar mass	182.18 g · mol -1
Physical state	firmly
density	2.51 g cm −3
Melting point	~ 1600 ° C
solubility	soluble with decomposition in water
safety instructions
GHS hazard labeling from  Regulation (EC) No. 1272/2008 (CLP) , expanded if necessary danger H and P phrases H: 260-300-311-330-318-400 EUH: 029-032 P: 231 + 232-280-233-301 + 310-405-501
As far as possible and customary, SI units are used. Unless otherwise noted, the data given apply to standard conditions .

Calcium phosphide (Ca ₃ P ₂ ) is a chemical compound from the group of phosphides . It is in the form of a brown-red, amorphous mass. Technical calcium phosphide always contains calcium phosphite and calcium phosphate impurities . Calcium monophosphide (CaP) is sometimes used with the same term .

Occurrence

Calcium phosphide occurs as an impurity in calcium carbide .

Extraction and presentation

Calcium phosphide can be produced by reacting quick lime with phosphorus in the form of vapor . Calcium phosphide is also formed when phosphorus and calcium melt together under petroleum or in a vacuum.

${\displaystyle \mathrm {3\ Ca+2\ P\longrightarrow Ca_{3}P_{2}} }$

In addition, the reduction of calcium phosphate with carbon to calcium phosphide at high temperatures is also possible (side reaction in calcium carbide production).

${\displaystyle \mathrm {Ca_{3}(PO_{4})_{2}+8\ C\longrightarrow Ca_{3}P_{2}+8\ CO} }$

It is also possible to replace carbon with aluminum during the reaction .

${\displaystyle \mathrm {3\ Ca_{3}(PO_{4})_{2}+16\ Al\longrightarrow 3\ Ca_{3}P_{2}+8\ Al_{2}O_{3}} }$

properties

Calcium phosphide is a red-brown solid. In moist air it slowly decomposes, with water briskly to form calcium hydroxide and monophosphane. In contrast to the diluted acids, concentrated acids hardly attack calcium phosphide at all, especially in the cold. Calcium phosphide reacts explosively with potassium permanganate . Anhydrous alcohol , ether and benzene do not react with calcium phosphide at ordinary temperature.

use

Calcium phosphide can be used to make phosphine :

${\displaystyle \mathrm {Ca_{3}P_{2}+6\ H_{2}O\longrightarrow 2\ PH_{3}+3\ Ca(OH)_{2}} }$

In this sense, it is also used as a fumigant ( rodenticide ) against voles .

Its main area of ​​application is pest control in grain stores and grain transports (e.g. on ships). Calcium phosphide tablets are added to the grain. The residual moisture in the grain is sufficient to gradually hydrolyze the calcium phosphide , releasing phosphine, which reliably kills grain beetles and other pests .

In the navy, this reaction (through the formation of diphosphine self-ignition) is used to operate beacons .

Rodenticides with calcium phosphide as an active ingredient (trade name Polytanol ) are approved in Germany, Austria and Switzerland .

safety instructions

Calcium phosphide forms extremely flammable gases in the form of the poisonous and foul-smelling phosphine PH ₃ and diphosphine (P ₂ H ₄ ) on contact with water or moist air . The gaseous mixture of phosphine PH ₃ / diphosphine can decompose explosively in the event of external ignition - similar to oxyhydrogen gas .

Explosive decomposition is possible on contact with acids. The hydrolysis produces a gas mixture that is also very toxic for humans (phosphine PH ₃ and diphosphine P ₂ H ₄ ). In mills and grain stores there have already been several deaths due to incorrect use of calcium phosphide and sealing or insufficient ventilation.

literature

• Zh. V. Dobrokhotova u. a .: Thermodynamic properties of calcium and barium phosphides. In: Journal of Thermal Analysis and Calorimetry . 38, No. 5, 1992, pp. 1113-1122, doi: 10.1007 / BF01979173 .

Individual evidence

1. ↑ ^{a b c d e} Entry on calcium phosphide in the GESTIS substance database of the IFA , accessed on February 1, 2016(JavaScript required) .
2. ↑ Entry on Tricalcium diphosphide in the Classification and Labeling Inventory of the European Chemicals Agency (ECHA), accessed on February 1, 2016. Manufacturers or distributors can expand the harmonized classification and labeling .
3. ↑ Data sheet calcium phosphide at AlfaAesar, accessed on May 5, 2016 ( PDF )(JavaScript required) .
4. ↑ ^{a b} Brockhaus ABC chemistry. VEB F. A. Brockhaus, Leipzig 1965, pages 635-636.
5. ↑ ^{a b} Georg Brauer: Handbook of Preparative Inorganic Chemistry . tape 2 , 1978, ISBN 3-432-87813-3 , pp. 931 .
6. ↑ Water voles and moles in gardens, plants and parks. (PDF; 588 kB) Berlin Plant Protection Office, February 2016, p. 5 , accessed on June 25, 2017 . 
7. ↑ General Directorate Health and Food Safety of the European Commission: Entry on calcium phosphide in the EU pesticide database ; Entry in the national registers of plant protection products in Switzerland , Austria and Germany ; accessed on March 11, 2016.