Chemistry of crown ethers XIX. Functionalized crown ethers for the solubilization of barium sulfate

The use of seawater as injection fluid in oil‐producing formations often leads to blocking of the wells as a result of barium sulfate‐scale formation. Macrocyclic complexants specifically designed to solubilize barium sulfate efficiently into water have been synthesized and their BaSO4‐solubilizing capacities have been determined. The stability of barium complexes of macrocyclic polyethers can be greatly increased by the introduction of flexible side‐chains containing anionic groups. Most of the newly synthesized complexants, based mainly on diaza‐18‐crown‐6, give very stable complexes. However, many of them are extremely insoluble in water. Only bis(carboxymethyl)diaza‐18‐crown‐6, bis(phosphonomethyl)diaza‐18‐crown‐6 and, to a lesser extent, bis‐(dicarboxymethyl)diaza‐18‐crown‐6 and bis[(hydroxyphosphinyl)methyl]diaza‐18‐crown‐6 are efficient solubilizers of BaSO4 in water.