Formation of cyclic oligomers in concentrated aqueous solutions of formaldehyde

An MNDO calculation gave the formation enthalpies of the components of equi librium mixtures in concentrated aqueous acid solutions of formaldehyde. Th e results of this study suggest that intramolecular cyclization of linear o ligomers with greater than or equal to 5 and greater than or equal to 9 CH2 O units, respectively, is the most plausible mechanism of formation of cycl ic oligomers of formaldehyde - trioxane and tetraoxane. Ring protonation by the hydroxonium ion with ring opening is the most energetically favorable route of cyclic acetal decomposition.