Disclosed is a process for making a thiophosphine compound of formula (I): ##STR00001## wherein X represents SH or ##STR00002## with R.sub.1 being H or --CH.sub.3, R and R' represent, independently from each other, an alkyl radical, an alkoxy radical, an aryl radical or a phenyl radical which may be substituted with one or more alkyl and/or alkoxy groups, n is an integer from 0 to 4, n' is an integer from 0 to 5, x is an integer from 0 to 2, y is an integer from 1 to 5 with the proviso that y+n is an integer from 1 to 5, wherein y =1, X is in para position with regard to phosphorus and represents SH.