Thermochemical data for interaction of some primary amines with complexed mercury on mercapto-modified silica gel

Mercury chloride was complexed on functional SH groups attached to silica gel to yield the material Sil-S-Hg. Adsorption and thermochemical data for the interaction of some primary amines with the immobilized mercury(II) have been obtained from calorimetric measurements at 298.15 K, with the objective of charting the newly created acidic sites. By using calorimetric titrations with direct determination of reaction extension, values of maximum capacities of interaction (N), interaction enthalpies at different coverage of the surface (Delta(int(i))H(m)) and the molar enthalpy of interaction for monolayer formation of the anchoring amines (Delta(mon)H(m)) were determined. It is shown that the values of the thermochemical parameters Delta(int(i))H(m) and Delta(mon)H(m) are in the sequence: Sil-S-Hg/C2H5NH2 > Sil-S-Hg/C4H9NH2 > Sil-S-Hg/CH3NH2 > Sil-S-Hg/C3H7NH2, and are correlated with the order of the basicity constants of the amines. The general tendency found earlier for the energy distribution of the adsorption sites on the heterogeneous surface has been confirmed. (C) 2002 Elsevier Science B.V. All rights reserved.