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

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, HOCH2 OOCH2 OH, is the intermediate, which decomposes to yield H2 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 H2 derive from the CH2 hydrogen atoms of formaldehyde, and not from the OH groups of HOCH2 OOCH2 OH or from water. Quantum-chemical CBS-QB3 and W1BD computations show that H2 release proceeds through a concerted process, which is strongly accelerated by double deprotonation of HOCH2 OOCH2 OH, thereby ruling out a free radical pathway.