Abstract: Aromatic phosphorus-chlorine compounds, especially diphenylphosphinyl chloride (C.sub.6 H.sub.5).sub.2 P(O)Cl, phenylphosphonyl dichloride C.sub.6 H.sub.5 P(O)Cl.sub.2, dichlorophenylphosphine C.sub.6 H.sub.5 PCl.sub.2 and chlorodiphenylphosphine (C.sub.6 H.sub.5).sub.2 PCl, and the corresponding sulfur analogs, are obtained by reaction of aromatic phosphorus compounds, which contain oxygen or sulfur, of the formula I ##STR1## in which X=O or S, and m=1, 2 or 3, with phosphorus-chlorine compounds of the formula II(C.sub.6 H.sub.5).sub.3-n P Cl.sub.n (II)in which n=1, 2 or 3, at temperatures between about 330.degree. and 700.degree. C. Preferred starting materials are triphenylphosphine oxide (C.sub.6 H.sub.5).sub.3 PO and phosphorus trichloride PCl.sub.3.The reaction products are mainly intermediates in a variety of special areas, such as the pharmaceuticals, plant-protection, dye and polymer sectors.