Thermochimica Acta, Vol.400, No.1-2, 51-59, 2003
Crystalline calcium phenylphosphonate-thermodynamic data on N-alkylmonoamine intercalations
Lamellar crystalline calcium phenylphosphonate, as anhydrous Ca(HO3PC6H5)(2) and hydrated Ca(HO3PC6H5)(2).2H(2)O compounds, were used as hosts for intercalation of polar n-alkylmonoamine molecules of the general formula CH3(CH2)(n)NH2 (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(HO3PC6H5)(2).2H(2)O and Ca(HO3PC6H5)(2) gave the enthalpy/number of carbons correlations: Delta(int)H = -(1.74 +/- 0.43)-(1.30 +/- 0.13)n(c) and Delta(int)H = - (4.15 +/-0.15)-(1.07 +/- 0.03)n(c) for water and 1,2-dichloroethane, respectively. A similar correlation Delta(int)H = -(4.27 +/-0.80)-(1.85 +/- 0.21)n(c) was obtained in water by using the ampoule breaking procedure for Ca(HO3PC6H5)(2).2H(2)O. 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.