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(Kp/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.