otherwise herein the use and administration of the x ray contrast media of this invention is fully conventional and analogous e g to that of the conventional x ray contrast agent metrizamide iopamidol diatrizoate iohexol the present invention furthermore concerns a process for the preparation of compounds of formula i comprising conventionally n alkylating a compound of formula ii in the 5 position str3 wherein r 39 is the same as r defined above but free hydroxy groups present in the molecule can be in the blocked form using a compound of formula iii str4 wherein a and b combined represent the oxygen atom of an oxido ring or a is a chlorine sulfate or c 1 2 alkyl sulfate phenyl or tosyl sulfate and optionally subsequently liberating blocked hydroxy groups the n alkylation of the 5 acylamino group according to this invention is conducted by means of methods known to those skilled in the art thus the compounds of formula ii can be reacted for example in a suitable solvent such as methanol ethanol or 1 2 propanediol in the presence of an alkali metal alcoholate or alkali metal amide with the compound of formula iii for example with chloroethanol or ethylene oxide at a temperature of from room temperature to 80 u00b0 c preferably 20 u00b0 60 u00b0 c the alkylation can also be conducted by using the compound ii with intermediarily blocked hydroxy groups in this case the conventional blocking of the hydroxy groups in the form of a ketal acetal ortho ester or triphenylmethyl ether either has taken place as early as during the production of the.