Dithiol-phosphoric acid esters

Novel compounds of the general formula (RS)2P(O)OC2H5 where R is a n-propyl or isopropyl radical are prepared by reacting C2H5O-P(O)(Hal)2, where Hal is a halogen atom, preferably Cl or Br, with n- or isopropylmercaptan in the presence of an acid-binding agent, or with the corresponding alkali metal or ammonium mercaptide. The reaction is preferably carried out in the presence of solvents or diluents, e.g. optionally chlorinated hydrocarbons, ethers, ketones or nitriles, at a temperature between -20 DEG C. and the boiling point of the reaction mixture. Atmospheric pressure is usually employed, but increased pressure may be used. The O-ethylphosphoric acid ester dihalide starting materials may be prepared by reacting phosphorus oxyhalides with ethanol, preferably without the use of an acid-acceptor. The compounds have nematocidal activity.ALSO:Nematocidal compositions contain a compound of the formula (RS)2P(O)OC2H5 where R is n-propyl or isopropyl ralical, in admixture with a solid or liquid diluent or carrier. They may be formulated as solutions, emulsifiable concentrates, emulsions, suspensions, spray powders, pastes, soluble powders, dusts and granules. The active compounds or formulations containing them may be used to combat nematodes by applying them to a nematode habitat, e.g. soil, by e.g. pouring, spraying, scattering, vapourising, or soil injection.