Synthesis and properties of complexes of lead(II), cadmium(II), and zinc(II) with N-phosphonomethylglycine

摘要

Sparingly water soluble complexes of lead(II), cadmium(II), and zinc(II) with N-phosphonomethylglycine (glyphosate, NPMG) of the general formulae C3H6O5NPPb, C3H6O5NPCd . 2H(2)O, and C3H6O5NPZn were synthesized. The complexes were also precipited from a dilute Roundup solution, and their solubility in water was determined. Thermal, diffractometric, and IR spectrophotometric analyses were carried out. It was found that the metal is bonded to glyphosate through the oxygen atoms of the carboxylic and phosphonate groups; metal-nitrogen binding is absent in the above compounds. Studying the complexing behaviour in solution by UV spectrophotometry pointed out that a complex of the composition Pb(II):NPMG = 1:1 with an absorption band at 232nm is formed. Its stability constant as determined by Job's method is logK = 5.9 +/- 0.1. Using potentiometric techniques, the dissociation constant of N-phosphonomethylglycine and the stability constants of its complexes with cadmium (II) and zinc (II) were determined. [References: 23]