Abstract: An improved process is described for obtaining triazacyclononanes, esepcially 1,4,7-trimethyl-1,4,7-triazacyclononame. The first step involves reacting diethylenetriamine (DET) with a sulfonylation agent to form a sulfonamidated DET, in an aqueous medium with an inorganic base. In a second step, but preferably within the same reactor vessel without isolating intermediates, the sulfonamidated DET aqueous mixture is contacted with an aprotic organic solvent in the presence of a cyclizing unit such as ethylene glycol ditosylate or ethylene dibromide, thereby resulting in a cyclized sulfonamidated triamine compound. Thereafter the protecting groups are removed and the amine is alkylated, preferably within a single reaction vessel without isolation of intermediates.