Regioselective conversions of H4pdta (1,2-propanediaminetetraacetic acid) and H4eed3a to their triacetates on peroxotitanates

Abstract

1,2-Propanediaminetetraacetic acid (H₄pdta = C₁₁H₁₈O₈N₂) is degraded selectively to 1-methyl-1,2-propanediaminetriacetic acid (H₃pd3a = C₉H₁₆O₆N₂) with a yield of 75% at room temperature, while N-(2-hydroxyethyl) ethylenediaminetriacetic acid (H₄eed3a = C₁₀H₁₈O₇N₂) is converted with difficulty to ethylenediaminetriacetic acid (H₃ed3a = C₈H₁₄O₆N₂) on peroxotitanates(IV), showing the influence of the uncoordinated leaving group. Various species in the reaction sequence are isolated and fully characterized, including (NH₄)[Ti(O₂)(Hpdta)]·H₂O (1), (NH₄)₃[Ti(O₂)(pdta)H(pdta)(O₂)Ti]·7H₂O (2), (NH₄)[Ti(O₂)(pd3a)]·H₂O (3) and (NH₄)[Ti(O₂)(Heed3a)]·H₂O (5). Peroxo dimer 2 forms a strong intramolecular hydrogen bond [2.451(3) Å] as an intermediate in the peroxo Ti-pdta system, which results in the absence of a fully deprotonated species of peroxo pdta titanate. A catalytic reaction of the peroxo titanate (NH₄)₃[Ti(O₂)(pdta)H(pdta)(O₂)Ti]·7H₂O (2) for the conversion of pyridine to pyridine N-oxide shows 94% conversion at 80 °C.