The Synthesis and Properties of Monophosphane – Part of The Chemistry of Breaking Bad

Author: Falk Harnisch, Tunga Salthammer

The Synthesis and Properties of Monophosphane

Monophosphane (PH3) is a very strong nerve toxin. Walter explains to Jesse how it is produced as follows: “red phosphorus in the presence of moisture and accelerated by heat yields phosphorus hydride … phosphine gas”. This explanation is certainly sufficient for Jesse, but it is not technically accurate. When heated, phosphorus disproportionates in the presence of water to PH3 and hypophosphoric acid. The latter can, forming PH3 at each stage, continue its reaction to phosphoric acid and then to phosphorus acid.

2 P4 + 12 H2O → 2 PH3 + 6 H3PO2 → 4 PH3 + 4 H3PO4 → 5 PH3 + 3 H3PO4

When heated in sodium hydroxide solution, the reaction can be directed toward the products by the formation of sodium hypophosphite.

P4 + 3 NaOH + 3 H2O → PH3 + 3 NaH2PO2

In the Hollemann–Wiberg textbook [12], both reactions are described for white phosphorus instead of red phosphorus.

Walter’s plan to eliminate Emilio and Krazy-8 with PH3 is completely feasible in the given circumstances. The gas irritates the eyes, skin, and respiratory organs. A fatal oedema of the lungs is possible after a time [13]. The LD50 level for rats is 10 ppm after 4 hours of inhalation. There is however the risk of an explosion because PH3 is self-combusting at more than 1.6 vol % in the air. There would have been enough potential sources of ignition in the RV, so Walter would have to be quick in fleeing.


References

[12] N. Wiberg, Hollemann–Wiberg: Lehrbuch der Anorganischen Chemie, 102 Ed., Walter de Gruyter, Berlin, 2007.
[13] Air Liquide Deutschland GmbH, Sicherheitsdatenblatt Phosphin (gemäß RL 1907/2006EG). Rev.-Ausgabe Nr. 3-01 vom 7.2.2011, Sicherheitsdatenblatt-Nr.: 100-ALD, Düsseldorf.

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