The highly reactive chloroacyl(diphenyl)phosphane oxides RC(O)-P(O)Ph2 (2a-d, g) [R = HCCl2 (a), CCl3 (b), CH3CHCl (c), CH3CCl2 (d), ClCH2CH2 (e), CH3CHClCH2 (f), ClCH2(CH2)2 (g)] are obtained by oxidation of the thermally labile chloroacyl(diphenyl)- phosphanes RC(O)-PPh2 (1a-d, g) with molecular oxygen in ether at low temperatures. While hydrolysis leads to a complete decomposition of 2a-d, g, the oxidation of 1a, c, e-g with oxygen in the presence of HP(O)Ph2 yields the diphosphorylated alcohols RC[P(O)Ph2]2OH (3a, c, e-g). 3e, f can be interpreted as trapping products of the not isolable oxides 2e, f. In tetrachloroethene a partial transformation of 3a into the phosphinate RC[P(O)Ph2][OP(O)Ph2]H can be observed which can be followed 31P{1H}-NMR spectroscopically. In solution the alcohols 3c, e-g decompose to give HP(O)Ph2 and the corresponding phosphane oxides 2c, e-g.