Molecule of National Chemistry Week!
October 22, 2018
I’m nasty on Earth, but perhaps valuable in space.
What molecule am I?

Phosphine, the simplest phosphorus hydride, is a colorless and extremely toxic gas. Some people think it smells like rotting fish; it reminds others of the odor of garlic. In any case, pure phosphine is actually odorless; an impurity, diphosphane (P2H4), is responsible for its foul scent.

Phosphine is formed naturally via the anaerobic decay of phosphorus-containing organic matter. The earliest reported preparation was made by Antoine Lavoisier’s student Philippe Gengembre in the late 18th century.

Phosphine is made industrially from white phosphorus by hydrolysis with an alkali metal hydroxide or an aqueous acid–catalyzed disproportionation reaction. The industrial product is normally shipped as liquefied gas.

Although phosphine’s molecular structure is analogous to that of ammonia, the 3d orbital of its phosphorus atom interacts with its hydrogen atoms to reduce its ability to hydrogen bond. Thus, whereas ammonia is completely miscible in water, the aqueous solubility of phosphine is very low.

The hazard information box shows that phosphine is dangerous in several ways on Earth. But recent findings indicate that its presence in outer space may have had a key role in the beginnings of life.

Ralf I. Kaiser at the University of Hawaii at Manoa (Honolulu) and his colleagues there and in Taiwan and France simulated ices found in space by combining phosphine, carbon dioxide, water, and oxygen at near–absolute zero temperatures. They then bombarded the ices with high-energy electrons (typical of those found in space) to produce several phosphorus oxyacids, including some with the same phosphorus oxidation state that exists in DNA, ATP, and other important biomolecules.

The theme of this year’s National Chemistry Week (which begins today) is “Chemistry Is Out of This World”. Celebrate it by recognizing extraterrestrial phosphine’s potential contribution to life.

Phosphine fast facts

CAS Reg. No. 7803-51-2
Empirical formula H3P
Molar mass 34.00 g/mol
Appearance Colorless gas
Boiling point –87.7 ºC
Water solubility ≈300 mg/L

Phosphine hazard information

GHS classification*: flammable gases, category 1
H220—Extremely flammable gas Chemical Safety Warning
GHS classification: gases under pressure, compressed gas 
H280—Contains gas under pressure; may explode if heated Chemical Safety Warning
GHS classification: skin corrosion, category 1B
H314—Causes severe skin burns and eye damage Chemical Safety Warning
GHS classification: serious eye damage, category 1
H318—Causes serious eye damage Chemical Safety Warning
GHS classification: acute toxicity, inhalation, category 1
H330—Fatal if inhaled Chemical Safety Warning
GHS classification: hazardous to the aquatic environment, acute hazard, category 1
H400—Very toxic to aquatic life Chemical Safety Warning

*Globally Harmonized System of Classification and Labeling of Chemicals. Explanation of pictograms.

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Learn more about this molecule from CAS, the most authoritative and comprehensive source for chemical information.

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