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Materials

Unstable allotropes stored safely in carbon

Activated carbon enables white phosphorus and yellow arsenic to be stored and shipped with minimal decomposition

by Bethany Halford
February 5, 2018 | APPEARED IN VOLUME 96, ISSUE 6

Credit: Courtesy of Manfred Scheer
White phosphorus bursts into flame when exposed to air but is stable when encapsulated in activated carbon (front left). Yellow arsenic is also stable when stored in activated carbon (front right).

Although the elemental allotropes white phosphorus (P4) and yellow arsenic (As4) have the potential to be useful reagents, these compounds aren’t commonly used by chemists because of their notorious instability. White phosphorus will burst into flame when exposed to air and is subject to strict shipping regulations. Light-sensitive yellow arsenic turns to gray arsenic so quickly that solutions of the element must be used in complete darkness. Chemists have been working to create materials in which these allotropes can be stored stably, but their success has been limited. Now, University of Regensburg’s Manfred Scheer and colleagues have found that the pores within activated carbon work well at storing both white phosphorus and yellow arsenic. What’s more, the elements can be released from the activated carbon into solution, where they can subsequently be used as reagents (Nat. Commun. 2018, DOI: 10.1038/s41467-017-02735-2). Scheer’s group prepares the material by adsorbing a solution of P4 or As4 in tetrahydrofuran onto activated carbon with a defined pore size and distribution. After centrifugation, decanting, and drying, the resulting black powder can be stored on a benchtop and exposed to light and air with only minimal decomposition (Scheer’s group recommends, instead, storing the arsenic-filled carbon carefully in a closed container because of its unknown toxicity). The researchers note that this opens new avenues for reactions with white phosphorus and yellow arsenic, as well as for activated carbon as a storage material for unstable chemicals.

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