5,6-Di:hydro-6-thioxo-1,3,5- thiadiazine-4-one derivs. - prepd. by reaction of carbonyl di:isothiocyanate with hydroxy, mercapto or amino cpds

New 1,2,5-thiadiazine derivs. are cpds. of formula (I). (where R1 is H, open-chain or cyclic alkyl, aralkyl or aryl; and X is O, S or NR2, R2 being H, open-chain or cyclic alkyl, aralkyl or aryl). Prodn. of (I) comprises reaction of SCN-CO-NSC with R1-XH. The reaction is carried out in the presence of an inert solvent at ca 0-30 deg.C. (I) are useful as pharmaceuticals, microbicides, fungicides andinsecticides. They are also useful as reactive intermediates in particular, cpds. (I) in which R1 is alkyl, aralkyl or aryl or, when X is NR2, also H may be used for the preparation of carbonyl-thiocarbonyl-amine cpds. of the formula A-CO-NH-SC-B (where A is -Y-R4 or -NH-Y-R6; Y is O, S or NR5; R4 is alkyl, aralkyl or aryl or, when Y is NR5, also H; R5 is H; alkyl, aralkyl or aryl; R6 is aryl; B is XR3; R3 is alkyl, aralkyl or aryl or, when X is NR2, also H; R2 is H, alkyl, aralkyl or aryl; or A and B are each morpholino, piperidino, piperazino or thiomorpholino; or A and B together represent a group -NR8-CS-NH- in which R8 is aralkyl or aryl), which in turn are useful as pharmaceuticals, microbicides, fungicides, insecticides and starting materials for polymers.