ON THE THERMOCHEMISTRY OF INTERCALATION OF N-ALKYLAMINES INTO ALPHA-TITANIUM HYDROGENPHOSPHATE

Lamellar alpha-titanium hydrogenphosphate (alpha-TiP) suspended in water or 1,2-dichloroethane (dce) intercalates approximately 7.70 meq g 1 of n-alkylamines (C1-C4), as determined by potentiometry and thermogravimetry. The thermal decomposition of the intercalates takes place in three stages: dehydration, removal of amines, and condensation of the hydrogenphosphate to pyrophosphate. The increase in the alpha-TiP interlayer distance (7.56 X 10(2) pm) during the intercalation was followed by x-ray powder diffraction. The standard enthalpy (DELTA-r(H)m-degrees) involved in the overall reaction O3PO-H + RNH2 --> O3P-O +H-3NR, which was determined by reaction-dissolution calorimetry, correlates linearly with the number of carbons in the alkyl chain and with the interlamellar distance. An intercalation mechanism is proposed, starting from the amine protonation by POH groups and its insertion between the sheets. An increase in enthalpy of -2.67 and +2.56 kJ mol-1 or -1.24 and +1.20 kJ mol 1/10(2) pm for each CH2 group of the n-alkyl chain in dce and water, respectively, for this series of amines is prosposed.