Formation of Hemiformals in Aqueous Formaldehyde Solution Containing Methanol

Abstract

Formaldehyde exists as an equilibrium mixture of lower polyoxymethylene glycols in aqueoussolution or as an equilibrium mixture of lower polyhemiformals in methanol solution. Formation of hemiformals in aqueous formaldehyde solution containing methanol was studied byeans of infrared and near infrared spectroscopy. The attachment, Hitachi Model ATR-2, which has a prism KRS-5, was used for observing attenuated total reflection, i. e., ATR spectra.
The weak band at 1190 cm-i was assigned to CHs rocking vibration of end methyl greups of lower polyhemiformals. The absorptions of the end methyl groups of all seven model compounds eccurred in the range 1200. v1180 cm-i.
The band at 1190 cmwwi did not appear in the spectrum of aqueous formaldehyde solution, but it appeared when methanol was added to the solution.
Furthermore, it was found that the calculated relative number of moles of bound water, which was consumed to form lower polyoxymethylene glycols, was almost equal to the sum of the relative number of moles of bound water and that of moles of the added methanol, when less than 11e/o of methanol was added to aqueous formaldehyde solution.
It seemed that formation of hemiformals occured easily in aqueous acid or alkaline formaldehyde solution when methanol was added to it.