Quinquevalent phosphorus acids

This chapter shows, as in previous years, the most important achievements of the 2020 year in the area of organo-phosphorus compounds containing: three P–O bonds (section: phosphoric acids and their derivatives), two P–O and one P–C bonds (section: phosphonic acids and their derivatives) as well as one P–O and two P–C bonds (section: phosphinic acids and their derivatives), in addition to the phosphoryl group P═O. Each of the main sections covers “synthesis and reactions” including pure synthesis without applications, “synthesis and biological applications” and “synthesis and miscellaneous applications” including synthesis directed towards non-biological applications. At the end of each subsection, the corresponding achievements are shown for hetero-analogues in which phosphorus–oxygen bonds have been replaced by phosphorus–heteroatom P–X and/or P═Y bonds (X, Y = N, S or Se). The subsection on quinquevalent phosphorus acids and their derivatives as catalysts has been placed, as usual, at the end of the entire chapter, after a review of all three main groups of compounds. In this year, the area devoted to phosphoric and phosphonic acids and their derivatives dominated traditionally over a smaller section of phosphinic acids and their derivatives, and all sections remained in a ratio 1 : 2 : 0.5, respectively.