Intercalation and interlayer amidation properties of n-alkylmonoamines for γ-zirconium (2-carboxyethyl)phosphonate phosphate

Abstract

The uptake of n-alkylmonoamines C _n H _2n+1 NH ₂ (n = 2–10) by γ-zirconium (2-carboxyethyl)phosphonate phosphate, ZrPO ₄ (H ₂ PO ₄ ) _0.36 (HO ₃ PCH ₂ CH ₂ CO ₂ H-2) _0.64 ·2.3H ₂ O, derived from γ-zirconium phosphate has been studied at 25 °C. The alkylamines with n 4 form an intercalated phase in which the amine molecules are arranged as a bilayer with their axes perpendicular to the inorganic layers, whereas the shorter-chain amines cannot be stably held in the interlayer space. The amine uptake increases with increasing carbon number until it reaches a constant value of 0.32 mol per formula weight for the amines with n 6. The amine uptake and IR data indicate that the ammoniated guest molecules replace primarily the protons of the interlayer carboxyl groups. On heating at 220 °C, the ionically bonded CO ₂ ^- NH ₃ ⁺ group in the ammonium-exchanged solids is thermally condensed into the amide CONH form without any significant release of the amine guest.