[WP = white phosphorus ; RP = red phosphorus ; ARP = activated red phosphorus]

A YT channel, Extraction & Ire has a video from two years ago (2018) on converting WP to RP by keeping the former in sunlight for several days. Chloroform was chosen as solvent to dissolve WP in a glass vial. The solution had gone from deep orange to red on slight when kept in sunlight for 5 days. After 5 days, the solution was tested with sodium hydroxide solution to confirm that if it is RP (RP doesn't react with $\ce{NaOH}$, WP does). On dumping it to the $\ce{NaOH}$ solution, it immediately started reacting (phosphine was evolving which had a dreadful smell). After 15 minutes on adding, the orange-red color vanished, that means all of the phosphorus has reacted. Some white crystals formed in the solution which is presumed to be sodium formate ($\ce{HCOONa}$) from the chloroform (isn't it soluble in water?).

$$\ce{P4_{(?)} + 3NaOH + 3H2O -> PH3 ^ + 3NaH2PO2} \\ \ce{2NaH2PO2 -> PH3 ^ + Na2HPO4} \\ \ce{CHCl3 + 4NaOH -> HCOONa (\downarrow ?) + 3NaCl + 2H2O}$$

So, the conversion failed. He apparently named the species "ARP". He made the following conclusion:

\begin{array}{c|c|c|c} \mathbf{~} & \mathbf{WP} & \mathbf{RP} & \mathbf{ARP} \\\hline \text{color} & \text{white} & \text{red} & \text{red}\\ \text{soluble in chloroform} & \text{Yes} & \text{No} & \text{No}\\ \text{Reactive towards NaOH} & \text{Yes} & \text{No} & \text{Yes}\end{array}

So, apparently WP converted to an unknown species(allotrope?) which was assumed to be ARP. We actually don't know its composition nor we can find any convincing literature. Google didn't give any relevant hits except two papers:

  1. Sukhov, Boris & Malysheva, S. & Kuimov, Vladimir & Smetannikov, Yu & Tarasova, N. & Lupanov, A. & Gusarova, N. & Trofimov, BA. (2004). Reaction of Activated Red Phosphorus with Allyl Bromide under Phase-Transfer Catalysis. Russian Journal of General Chemistry - RUSS J GEN CHEM. 74. 1128-1129. 10.1023/B:RUGC.0000045878.42411.31 (it says it is polymerized organophosphorus chains)
  2. Nucleophilic Activation of Red Phosphorus for Controlled Synthesis of Polyphosphides, Minyoung Jo, Alina Dragulescu-Andrasi, L. Zane Miller, Chongin Pak, and Michael Shatruk,Inorganic Chemistry 2020 59 (8), 5483-5489 DOI: 10.1021/acs.inorgchem.0c00108 (it says it is series of polyphosphides)


  1. What is ARP? What is the actual composition of ARP?
  2. Is it a different allotrope of phosphorus?

The 2020 paper says "RP is readily activated by refluxing it with different potassium alkoxide to give soluble polyphosphide ions". Polyphosphides is known and has been studied a lot (first paper I could find dates way back in 1967). So, what does "readily activation of red phosphorus" mean in this context? Could it mean ARP?

  • $\begingroup$ Another fancier allotrope of P is black phosphorous. Since nitrogen and P are of the same group, scientists have been able to make black nitrogen as well. There is a violet allotrope of P as well. $\endgroup$
    – AChem
    Sep 28, 2020 at 6:18
  • $\begingroup$ @M.Farooq Yes indeed, all those allotropes were discovered way back (violet - 1865, black -1914). Also, this question discusses about allotropes of grp 15 elements: chemistry.stackexchange.com/questions/28124/… $\endgroup$ Sep 28, 2020 at 6:51
  • $\begingroup$ Black nitrogen: sciencealert.com/… ... phys.org/news/… ... newatlas.com/materials/black-nitrogen-allotrope-periodic-table $\endgroup$ Sep 28, 2020 at 7:06
  • 1
    $\begingroup$ Well if ARP is "a series of polyphosphide ions and polymerized organophosphorus chains" it isn't an allotrope of phosphorous $\endgroup$
    – Ian Bush
    Sep 28, 2020 at 7:49
  • 3
    $\begingroup$ I can't answer that. But I will comment that the complex allotropy of phosphorous always amazes me, particular in the bizarre set of experimental conditions required to make this subtly different allotrope from that one. I mean recrystallise from molten lead - why did Hittorf think of that? So maybe these guys were simply the first to "wake up this morning, got the dissolve it in chloroform and irradiate for 5 days blues" As for the composition, well from what you have presented that looks like an active research question. $\endgroup$
    – Ian Bush
    Sep 28, 2020 at 9:29


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