The present invention primarily relates to a process for producing methyldichlorophosphane (MDP) by reaction of methane with PCl.sub.3 (phosphorus trichloride) in the presence of a catalytically active amount of a compound of formula SO.sub.xCl.sub.2, wherein the index x may take the value 1 (SOCl.sub.2, thionyl chloride) or 2 (SO.sub.2Cl.sub.2, sulphuryl chloride). The present invention further relates to particular mixtures that are particularly suitable for producing methyldichlorophosphane (MDP) in the context of the process according to the invention/that are formed when carrying out a process according to the invention.