Electrochemical iodination of N,N′-(2,3-dihydroxypropyl)-5-hydroxy-1,3-benzenedicarboxamide

A process for preparing N,N′-bis-[2,3-dihydroxypropyl]-5-(hydroxyacetyl) methylamino]-2,4,6-triiodo-1,3-benzenedicarboxamide (IV) comprising the steps of:

• a) dissolving N,N′-(2,3-dihydroxypropyl)-5-hydroxy-1,3-benzenedicarboxamide (II) in a reaction medium in the presence of molecular iodine (I2);
• b) iodinating said compound (II) with the molecular iodine (I2) to obtain N,N′-bis-(2,3-dihydroxypropyl)-5-hydroxy-2,4,6-triiodo-1,3-benzenedicarboxamide (I);
• c) isolating said compound (I);
• d) reacting said compound (I) with CICH2 (CO) NHCH3 to obtain the intermediate (III)
• e) subjecting said intermediate (III) to Smile's rearrangement in the presence of a base, so as to obtain N,N′-bis [2,3-dihydroxypropyl]-5-(hydroxyacetyl) methylamino]-2,4,6-triiodo-1,3-benzenedicarboxamide (IV)
• wherein the reaction medium of step a) is an aqueous solution, and the molecular iodine (I2) in step b) is in situ electrochemically generated from a source of iodide ions (I−) and wherein steps a) and b) are carried out in
• galvanostatic mode using an undivided electrolytic cell or
• in potentiostatic mode using an electrolytic cell formed by two-compartments divided by a porous septum or by a ionic exchange membrane.