Collect. Czech. Chem. Commun. 1986, 51, 1819-1833

A quantum-chemical study of dehydration of ortho forms of formaldehyde and formic acid

Jaroslav Leška, Eugen Németh and Dušan Loos

Department of Organic Chemistry, Comenius University, Mlynská dolina 2, 842 15 Bratislava


Gas-phase dehydration of methanediol (I) and methanetriol (II) has been studied by the MINDO/3 method with full optimization of the reaction paths. The intramolecular dehydration goes via high barriers (I 257.4, II 193.3 kJ mol-1). The acid-catalyzed dehydration involving protonation at oxygen atom of I goes via a considerably lower barrier (63.3 kJ mol-1), whereas protonation at oxygen atom of II results in practically spontaneous dehydration (0.4 kJ mol-1), which is the reason for the formic acid not being hydrated in water. Deprotonation of the protonated formaldehyde (II) and protonated formic acid (IV) is connected with high barriers (429.1 and 523.0 kJ mol-1, resp.). The deprotonation by a water molecule added to III and IV involves substantially lower barriers (53.9 and 96.3 kJ mol-1, resp.).