about 2 0 ml solvent per g 5 acetamido n n u2032 bis 2 3 dihydroxypropyl 2 4 6 triiodo isophthalamide in the presence of about 0 30 to about 0 36 mole equivalents of epichlorohydrin and wherein the reaction solution has a ph value of about 11 5 to about 12 2 the process according to the present invention is carried out with a concentration of about 0 8 to about 2 0 ml solvent per g compound a more preferably about 0 8 to about 1 0 and most preferably about 0 80 to about 0 85 the temperature during the dimerisation should be in the range of about 10 to about 20 u00b0 c with about 10 u00b0 c being most preferred the temperature can be constant throughout the dimerisation or varied within the specified range preferably the temperature is lowered throughout the dimerisation the dimerisation agent used in the present invention is epichlorohydrin which is added in about 0 3 to about 0 36 mole equivalents the ph value in the reaction solution is about 11 5 to about 12 2 the ph value can preferably be varied throughout the dimerisation having a higher value at the start of the dimerisation than at the.