Blueprint for a modern sustainable phosphorus chemistry

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The current depletion of available primary phosphorus resources is extremely worrying, which is why the EU has included phosphate rock and elemental phosphorus in the list of critical raw materials. So far, the value chain from phosphate ores to basic chemicals does not correspond to the guiding principle of "green chemistry". In addition, the problem of phosphorus recovery through suitable large-scale recycling processes to recover valuable phosphorus compounds will become drastically more acute in the future. For these reasons, the development of new and innovative chemical methods in the value chain of the important element phosphorus is urgently needed. In our blueprint for a modern sustainable phosphorus chemistry, we investigate systematic as well as atom and energy efficient ways to deoxygenate phosphoric acid and recycled phosphate resources (struvite from sewage sludge, LiFePO4 from cathode material). The advantage of our approach is the avoidance of the very energy-intensive conversion of phosphate to white phosphorus (reduction of P(V) to P(0)) and reoxidation/chlorination to the currently most important phosphorus intermediates PCl3, OPCl3 and P4O10 (oxidation of P(0) to P(III) or P(V)). Our goal here is the direct conversion of phosphates (PO43-) or other P(V) reagents to P1 building blocks, allowing "redox neutral" synthesis of a variety of valuable P(V) compounds, thus providing direct access to a wide range of platform chemicals. Furthermore, starting from these P(V) compounds, we will develop electrochemical reduction processes to P(III) compounds (e.g. phosphanes). The conversion of phosphate resources with suitable anhydrides (e.g., Tf2O) in the presence of a base (e.g., LN) will provide P1 building blocks, including those of the type (LN)2PO2[OTf], which can be converted "redox neutrally" to phosphorus (V) platform chemicals. A challenging extension of this approach is the synthesis of various PF6 salts, very important for battery electrolytes, starting from the highly problematic depleted compound UF6. With this exploratory project, we will combine new approaches in sustainable phosphorus chemistry with alternative synthetic routes for the disposal of depleted uranium hexafluoride (UF6), thus contributing overall to one of the most pressing problems of modern chemistry - the sustainable management of non-renewable and/or critical resources and risk mitigation of hazardous waste.