Another Unprecedented Wieland Mechanism Confirmed: Hydrogen Formation from Hydrogen Peroxide, Formaldehyde, and Sodium Hydroxide

摘要

In 1923, Wieland and Wingler reported that in the molecular hydrogen producing reaction of hydrogen peroxide with formaldehyde in basic solution, free hydrogen atoms (H-.) are not involved. They postulated that bis(hydroxymethyl)peroxide, HOCH2OOCH2OH, is the intermediate, which decomposes to yield H-2 and formate, proposing a mechanism that would nowadays be considered as a concerted process. Since then, several other (conflicting) mechanisms have been suggested. Our NMR and Raman spectroscopic and kinetic studies, particularly the determination of the deuterium kinetic isotope effect (DKIE), now confirm that in this base-dependent reaction, both H atoms of H-2 derive from the CH2 hydrogen atoms of formaldehyde, and not from the OH groups of HOCH2OOCH2OH or from water. Quantum-chemical CBS-QB3 and W1BD computations show that H-2 release proceeds through a concerted process, which is strongly accelerated by double deprotonation of HOCH2OOCH2OH, thereby ruling out a free radical pathway.