Sidestepping white phosphorus

Making phosphorus-containing compounds is not something to be undertaken lightly. Typically, phosphate is reduced to white phosphorus—a pyrophoric and toxic allotrope of the element—which is then reacted with chlorine gas to produce phosphorus trichloride—a base reagent for making phosphorus-containing compounds. Despite the dangerous reagents, this route is used to mass-produce compounds such as the herbicide glyphosate and the battery electrolyte lithium hexafluorophosphate. Now, MIT chemists Michael B. Geeson and Christopher C. Cummins report an alternative route to organophosphorus compounds and other phosphorus-containing chemicals that avoids using white phosphorus as an intermediate (Science 2018, DOI: 10.1126/science.aar6620). The reaction begins with dehydration of phosphoric acid by sodium chloride to produce trimetaphosphate. The MIT chemists then reduce the trimetaphosphate with trichlorosilane—a chemical made in large amounts for the semiconductor industry—to produce the previously unknown bis(trichlorosilyl)phosphide anion. This anion reacts with various compounds to produce organophosphorus compounds (example shown), phosphine gas, and the hexafluorophosphate