Acetaldehyde trimerisation

Trimerisation of acetaldehyde to form paraldehyde has been closely studied in the presence of zeolites [169]. 2a,4a,6P-Trimethyl-l,3,5-triox-ane was synthesised at 15°C under a nitrogen atmosphere using partly protonated ZSM-5, while the presence of CuZSM-5 promoted the formation of 2a,4a,6a-trimethyl-l,3,5-trioxane. Yields of up to 94% were reported. 

KSF montmorillonite catalyses the benzodioxepination of carbonyl compounds to the corresponding l,5-dihydro-3H-2,4-benzodioxepines. This reaction is useful for the protection of ketones (e.g. equation 4.47) [170]. 

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Hendra and Loader (48) demonstrated that acetaldehyde trimerises on the surface to paraldehyde. 

Sequential aldol trimerisation of acetaldehyde catalysed by aldolases followed by enzymic addition of pyruvic acid has afforded the tetradeoxy-nonulopyrano-sonic acid 26, and the preparation of some 3-deoxy-octulosonic acids and 3-deoxy-heptulosonic acids is discussed in Chapter 2. 

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