Mendeleev Commun., 2014, 24, 334–335 – 334 – © 2014 Mendeleev Communications. All rights reserved. Mendeleev Communications The phosphorous oxyacids are an important source for the produc- tion of pharmaceuticals, fertilizers, pesticides, herbicides, flame retardants, lubricants, etc. 1 Thus, new methods for the selective preparation of phosphorous compounds starting from elemental (white) phosphorus are of high practical interest. From synthetic viewpoint, reagents like phosphane (PH 3 ) and hypophosphorous (hypo) acid (H 3 PO 2 ) are of considerable importance. The phos- phane oxide H 3 PO is a highly reactive intermediate between a reduced form of phosphorus hydride and hypo acid. According to the electronic structure of H 3 PO, the oxygen atom carries a partial negative charge and phosphorus has a partial positive charge. 2 The high reactivity of this molecule is most likely due to its polarity, which converts phosphorus into an electrophile. The charge imbalance between the P and O atoms is considerable to make it unstable. 3 Note that this molecule can occur in its tautomeric form as phosphinous acid H 2 P(OH). 4 Previously, it was considered that the phosphane oxide mole- cule H 3 PO does not exist at room temperature. Some experi- mental observations of this molecule include the application of molecular beam sampling mass spectrometry 5 for monitoring the reaction of atomic oxygen with PH 3 in a discharge-flow system, IR spectroscopy of the photolysis products of the phosphane- ozone complex in a solid state, 6 the product of PH 3 oxidation by atomic oxygen in an argon matrix 7 and the microwave spec- trum detection of the radical H 2 PO 8 and the molecule H 3 PO. 9 The matrix isolation and theoretical study of the photochemical reaction of PH 3 with OVCl 3 and CrCl 2 O 2 were also described. 10 Recently, we found that this compound can be easily generated in solution by the mild electrochemical oxidation of phosphane PH 3 generated in situ from white phosphorus (P 4 ). 11 Phosphane oxide was characterized by NMR spectroscopy as free species in solution and in a coordinated form as a ligand in water-soluble ruthenium complexes. The phosphane oxide molecule in our former experiments was generated in a single electrochemical cell supplied with a sacrificial zinc anode. Here, we describe the effects of sacrificial anodes made from Al, Cd, Co, Mg, Ni, Nb, Sn and Zn on the electrochemical reduction of white phosphorus and generation of phosphane oxide. † The reduction of white phosphorus is irreversible and proceeds through radical anion formation: 12 P 4 + e ® P 4 ·– . The formed P 4 ·– radical anion initiates the polymerization of white phosphorus leading to polyphosphorus compounds. The derivatives containing the P–H bond are formed in the presence of active proton donors which can protonate phosphide anions initially produced in the electrochemical process. Thus, in protic media, all P–P bonds in white phosphorus tetrahedrons and formed polyphosphorus intermediates are sequentially opened and phos- phane PH 3 is formed as the main product of the electrochemical process: P 4 + 12 e + 12 H + ® 4 PH 3 . 13 From the viewpoint of electrochemical process efficiency, cathodes with high hydrogen overvoltage, like lead and mercury, have been used. 14,15 According to the cyclic voltammetry data, the electrochemi- cally produced phosphane PH 3 displays one irreversible peak of oxidation. 16,17 We were interested in the study of the products formed in the oxidation process and performed the electro- chemical oxidation of PH 3 on different metal anodes in order to generate phosphane oxide H 3 PO. Thus, we carried out the in situ generation of PH 3 in acidic ethanol–water mixtures in a single electrochemical cell supplied with sacrificial anodes of Al, Cd, Co, Mg, Ni, Nb, Sn or Zn at a constant current density of 5 mA cm –2 (10–20 V cell voltage). In case of niobium and tin electrodes displaying relatively high electric resistivity, 18 the current density was limited by 1–2 mA cm –2 at a cell voltage increased up to 40 V. The electrochemical reactions in the systems are shown in Scheme 1. Effect of a sacrificial anode material on the electrochemical generation of phosphane oxide (H 3 PO) Elena V. Gorbachuk, a,b Khasan R. Khayarov, a Oleg G. Sinyashin b and Dmitry G. Yakhvarov* a,b a A. M. Butlerov Institute of Chemistry, Kazan Federal University, 420008 Kazan, Russian Federation b A. E. Arbuzov Institute of Organic and Physical Chemistry, Kazan Scientific Center of the Russian Academy of Sciences, 420088 Kazan, Russian Federation. Fax: +7 843 273 2253; e-mail: yakhvar@iopc.ru 11.005 DOI: 10.1016/j.mencom.2014. The highest yields of phosphane oxide in the title process were obtained in electrochemical cells supplied with aluminium (49%), tin (36%) or zinc (67%) anodes. Cathode: P 4 + 12 H + + 12 e 4 PH 3 Anode: M 0 M n+ + n e 4 PH 3 + 4 H 2 O 4 H 3 PO + 8 H + + 8 e Summary: P 4 + 4 H 2 O + M 0 + 4 H + + 4 e 4 H 3 PO + M n+ + n e M = Sn, Zn (n = 2), Al (n = 3) Scheme 1 † For experimental details, see Online Supplementary Materials. 0 –80 –160 –240 –320 –400 –480 d/ppm PH 3 P 4 H 3 PO H 3 PO 2 3.5 –17.2 –240.5 –525.2 Al Sn 31 Figure 1 P NMR spectra of an acidic EtOH–H 2 O solution of P 4 after electrolysis (30 min) in an undivided electrochemical cell supplied with Al (top) and Sn (bottom) anodes.