A process for the preparation of a phosphorus complex corresponding to the following general formula:
wherein R represents optionally substituted aryl, wherein the substitution may comprise at least one selected from nitro, chloro, fluoro, alkyl, fluoro-alkyl and alkoxy, or optionally substituted alkyl; characterised in that it comprises reacting phosphorus pentachloride and a phosphonic dichloride corresponding to the following general formula:
    RPOCl₂
wherein R is as defined above; in the presence of an inert solvent boiling at a temperature of from 120 to 150°C, which is capable of co-distilling a phosphorus oxychloride reaction product, and co-distilling a phosphorus oxychloride reaction product, the molar ratio of phosphorus pentachloride:phosphonic dichloride being from 0.1:1 to 10:1 is disclosed.
There is further disclosed a process for chlorinating compounds containing a carbon atom bonded to a hetero-atom selected from oxygen, nitrogen and sulfur which comprises contacting the carbon hetero-atom containing compound with a chloro phosphorus complex corresponding to the following general formula:
wherein R represents optionally substituted aryl or optionally substituted alkyl, so that the hetero-atom is replaced by at least one chlorine atom; the reaction may be extended to compounds containing the carbon to chlorine bond alpha to a carbon atom having at least one hydrogen atom, it may be further dehydrochlorinated by either heating to a temperature of from 50 to 300°C or by reaction with a selected base.