Chemists discover a safe, green method to process red phosphorus | Chemical & Engineering News
Volume 94 Issue 12 | p. 11 | Concentrates
Issue Date: March 21, 2016

Chemists discover a safe, green method to process red phosphorus

Simple solution-based approach provides access to polyphosphides as starting materials for phosphorus chemistry
Department: Science & Technology
News Channels: Materials SCENE, Organic SCENE
Keywords: reagents, white phosphorus, red phosphorus, polyphosphide, flow reactor

When it comes to making phosphorus compounds, chemists have traditionally relied on white phosphorus, P4, a tetrahedral-shaped allotrope of the element. The downside with white phosphorus is that it’s toxic and flammable. Red phosphorus, an air-stable amorphous oligomeric allotrope, is a safer alternative. But chemists have had difficulty processing the relatively inert material in large quantities without resorting to high temperature and strong reducing agents. Florida State University chemists have now solved that problem by discovering an easy way to convert red phosphorus to soluble polyphosphides (Angew. Chem. Int. Ed. 2016, DOI: 10.1002/anie.201511186). Alina Dragulescu-Andrasi, a postdoctoral researcher in Michael Shatruk’s group, explained in San Diego how the team simply passes a solution of inexpensive potassium ethoxide in an organic solvent through red phosphorus under mild heating to produce P5, P162–, and P213–. These variously sized clusters, which the researchers isolate as potassium or tetrabutylammonium salts, could be used to synthesize phosphorus compounds or to make two-dimensional semiconductors and lithium-ion battery anodes. Taking the process a step further, the researchers adapted it to run as a continuous-flow reaction by passing potassium ethoxide through a stainless steel column packed with red phosphorus, generating multigram amounts of the soluble polyphosphides. “This appears to be a relatively safe and convenient methodology for generating soluble salts of polyphosphide anions,” commented MIT’s Christopher C. Cummins, who builds new compounds from elemental phosphorus. “It should open the door to more widespread study and application of these interesting little bits of reduced phosphorus.”

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By passing potassium ethoxide solution (flask at left) through a column packed with red phosphorus (top), chemists created a continuous process for making polyphosphide salts (flask at right).
Credit: Courtesy of Shatruk group
A flow reactor system shows production of polyphosphides from red phosphorus
 
By passing potassium ethoxide solution (flask at left) through a column packed with red phosphorus (top), chemists created a continuous process for making polyphosphide salts (flask at right).
Credit: Courtesy of Shatruk group
 
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