Gas phase equilibrium between acetaldehyde and paraldehyde, thermodynamic values for the trimerisation of acetaldehyde and the polymerisability of paraldehyde

Abstract

Equilibrium constants for reaction (1) 3CH₃CHO(g)⇌(CH₃CHO)₃(g)(1) have been measured in the temperature range 19 to 40°C. The results can be expressed by eqn (2). log(K_p/m⁴ kN^–2)=(6.97 ± 0.09)10³K/T–(27.90 ± 0.30)(2) The standard enthalpy and standard entropy changes at 25°C for the trimerisation of liquid acetaldehyde to form liquid paraldehyde are ΔH^°₂₉₈=–98.1 kJ (mol paraldehyde)^–1 and ΔS^°₂₉₈=–299.5 J K^–1(mol paraldehyde)^–1. Liquid paraldehyde is shown to be thermodynamically unpolymerisable.