| Abstract: | This article describes the equilibrium cyclotrimerization of β-methoxypropionaldehyde (MPA), 4,7-dioxaoctanal (DOA), and n-octanal (OA) initiated by boron trifluoride etherate in toluene at a temperature range of ?10 to 25°C. The enthalpy and entropy changes corresponding to the conversion of 1 mole of the monomers to 1/3 mole of their cyclic trimers in toluene solution, at the initial monomer concentration of 1 mole/liter, were evaluated as follows: ΔHss = ?5.9 ± 0.3 kcal/mole and ΔSss = ?19.1 ± 1.3 cal/mole deg for the MPA system; ΔHss = ?7.4 ± 0.4 kcal/mole and ΔSss = ?24.1 ± 1.7 cal/mole deg for the DOA system; ΔHss = ?6.1 ± 0.4 kcal/mole and ΔSss = ?21.2 ± 1.5 cal/mole deg for the OA system. The comparison of these values with those in their polymerization indicates that the cyclotrimerization of aldehydes is thermodynamically of greater advantage than their polymerization. The effects of long and polar substituents are discussed from the view-point of the intermolecular interactions by the polar groups in monomers and their cyclic trimers. |
