Process for preparing carboxyl-containing organic phosphorus compounds

Carboxyl-containing organic phosphorus compounds of the general formula I where the substituents are as defined in Claim 1, are obtained by reacting in a first stage phosphines with alpha , beta -unsaturated carboxylic acid in the presence of aqueous hydrochloric acid, admixing in a second stage the resulting phosphonium chlorides without interim isolation with an oxidising agent, and isolating the resulting compounds of the general formula I from the oxidation product. The main advantages of the process of the invention over the known processes are for example that relatively readily obtainable starting materials can be used, that the reaction involved is a 1-pot reaction where there is no need to isolate intermediates, and that the process leads in a simple manner and good yield to readily isolable and uniform end products of high purity.