THE OXIDATION OF FORMIC ALDEHYDE BY HYDROGEN PEROXIDE.¹

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

“…As expected, the ground state of the monoanion HP À (4/4a)i ss trongly hydrogen-bonded in an intramolecular fashion (DH HB À12 kcal mol À1 ;s ee 18/18 a,T able S21), again stabilizing an unfavourable conformation for concerted H 2 release.The related transition state (5/5a)isslightly lower in energy than that of H2P (2/2a), but both agree well with the experiments in water [8] (see Figure S30). Interestingly, TS 6/6a for decomposition to (initially) HCOOH and HOCH 2 O À now involves a1 ,2-CH 2 hydrogen shift to the adjacent peroxide oxygen atom.…”

“…Reaction (1), first reported in 1898, [7] has been the subject of considerable mechanistic speculation, both before and after Wielandsp roposal as shown in Figure 1, but much of the speculation has ignored or overlooked established facts. Thereaction has three times been reported to follow secondorder kinetics.I nt he first of these studies, [8] thee ffect of added base (essential if the reaction is to proceed at an oticeable rate at or below 25 8 8C) was already recognized, but the evolved gas was assumed to be O 2 !The second study [9] explicitly incorporated base into ap roposed mechanism. Unfortunately,i tw as concluded that the H 2 came from the two HO groups,a ccording to 2 CCH(OH)O À !2HCOO À + H 2 ,d espite an earlier study [10] in D 2 Oi nw hich the evolved hydrogen was converted into water, the density of which indicated that it was H 2 O.…”

Ein weiterer “unerhörter” Wieland‐Mechanismus bestätigt: Wasserstoffbildung aus Wasserstoffperoxid, Formaldehyd und Natriumhydroxid

“…Ordnung folge. In der ersten dieser Studien wurde der Effekt zugesetzter Base (notwendig für eine merkliche Geschwindigkeit bei und unter 25 °C) erkannt, doch das freigesetzte Gas wurde als O 2 angesehen! Die zweite Arbeit bezog Base explizit in den vorgeschlagenen Mechanismus ein, doch wurde unglücklicherweise gefolgert, dass das H 2 von den beiden OH‐Gruppen stamme, d. h. 2 .…”

“…18 / 18 a in Tabelle S21) und stabilisiert dadurch wiederum eine ungünstige Konformation für die H 2 ‐Abspaltung. Der zugehörige ÜZ 5 / 5 a liegt energetisch etwas niedriger als der von H2P ( 2 / 2 a ); beide stimmen gut mit den experimentellen Daten in Wasser überein (siehe Abbildung S30). Der ÜZ 6 / 6 a für den Zerfall in (anfänglich) HCOOH und HOCH 2 O − steht nun für eine 1,2‐CH 2 ‐Wasserstoffverschiebung zum benachbarten Peroxid‐Sauerstoffatom.…”

Biocatalysis and Biomass Conversion in Alternative Reaction Media

“…Enzymes functiono ptimally in water,w hich is generally perceived as an advantage but can be as erious shortcoming if the organic substrate is only sparingly soluble in water.H ence, the longstanding interesti nn onaqueous enzymology.A lthought here weree arlier reports of the use of enzymes in organic media, [4] it was the seminal paper by Zaks and Klibanov in 1984, [5] describing enzymatic catalysis at 100 8Ci no rganic media, that heraldedt he era of "nonaqueous enzymology". [6] They observed that many enzymes were actually more thermally stable in organic solvents, such as toluene, than in water, leadingt ot he realization that biocatalysis had am uch broader scope than was previously thought possible.…”