Preparation of isocyanates and/or derivatives thereof

A process for the preparation of isocyanates and/or the corresponding carbamates containing at least one group having a structure selected from the group consisting of --N.dbd.C.dbd.O and ##STR13## wherein A represents a group OB or NR.sup.1 R.sup.2 wherein B represents an alkyl or aryl group which may or may not be substituted with one or more halogen atoms, alkyl or alkoxy groups and R.sup.1 and R.sup.2 which may be the same or different each represent a hydrogen atom or an alky or aryl group which may or may not be substituted with one or more halogen atoms, alkyl or alkoxy groups, which comprises oxidatively converting in a reaction zone as feed a compound selected from alkyl, aryl, alkaryl and aralkyl oxamic acids, salts thereof and oxanilides according to the general formula ##STR14## wherein Q represents a group selected from an alkyl group and an aryl group, which group may contain one or more substituents selected from a halogen atom or an alkyl or alkoxy group, a group ##STR15## wherein X represents a group OY or ##STR16## wherein Y represents a hydrogen atom, a metal ion or a group NR.sup.3 R.sup.4 R.sup.5 R.sup.6 wherein each of R.sup.3, R.sup.4, R.sup.5 and R.sup.6 which may be the same or different, represent a hydrogen atom, an alkyl group having up to 8 carbon atoms, or an (alk)aryl group which may be substituted by one or more lower alkyl groups and Z represents an alkyl group or an aryl group which may be substituted by one or more substituents, or a group ##STR17## wherein R.sup.7 and R.sup.8 which may be the same or different each represent a hydrogen or halogen atom or an alkyl or alkoxy group, a group ##STR18## wherein X is as defined hereinbefore or a group ##STR19## wherein R.sup.9 and R.sup.10 which may be the same or different each represent a hydrogen atom or an alkyl group;

• and separating the conversion products from said reaction zone.