Crystalline calcium phenylphosphonate—thermodynamic data on n-alkylmonoamine intercalations

Abstract

Lamellar crystalline calcium phenylphosphonate, as anhydrous Ca(HO 3PC 6H 5) 2 and hydrated Ca(HO 3PC 6H 5) 2·2H 2O compounds, were used as hosts for intercalation of polar n-alkylmonoamine molecules of the general formula CH 3(CH 2) n NH 2 ( n=0–4, 7) in water or 1,2-dichloroethane. An increase in the interlayer distance was observed. The exothermic enthalpic values for intercalation increased with the number of carbon atoms and with increasing concentration of the amines. The intercalation followed by a titration procedure in the solid/liquid interface with Ca(HO 3PC 6H 5) 2·2H 2O and Ca(HO 3PC 6H 5) 2 gave the enthalpy/number of carbons correlations: Δ int H=−(1.74±0.43)–(1.30±0.13) n c and Δ int H=−(4.15±0.15)–(1.07±0.03) n c, for water and 1,2-dichloroethane, respectively. A similar correlation Δ int H=−(4.27±0.80)–(1.85±0.21) n c was obtained in water by using the ampoule breaking procedure for Ca(HO 3PC 6H 5) 2·2H 2O. The increase in exothermic enthalpic values with the increase in n-aliphatic carbon atoms is more pronounced for the anhydrous compound and also when using the ampoule breaking procedure. The Gibbs free energies are negative. Positive entropic values favor intercalation in these systems.