Enhanced formation of formate by freezing in solutions of hydrated formaldehyde-metal-hydrogen peroxide

Abstract

We detected the formation of formate (HCOOH/HCOO -) in solutions containing hydrated formaldehyde (CH 2 (OH) 2 ), HOOH, and Fe(III) or Cu(II). Formate formation increased significantly (ca. 5 times) when the solution underwent freezing and thawing. Although the reaction mechanisms are not clearly understood, we believe that the concentration effect of freezing enhanced the catalytic reactions between HOOH and Fe(III) or Cu(II) and the reduction of transition metals, i.e., Fe(III) to Fe(II) and Cu(II) to Cu(I). The concentration effect also enhanced reactions between Fe(II) and HOOH or Cu(I) and HOOH, which generated OH radical ("freeze-Fenton reaction"). We suspect that hydroxyl radical formed by the freeze-Fenton reaction probably oxidized CH 2 (OH) 2 and resulted in the formation of formate. Samples of identical compositions kept in the refrigerator did not form any formate except for the CH 2 (OH) 2 -Fe(III)-HOOH solution that formed a small amount of formate. Our study of the effects of pH on the CH 2 (OH) 2 -Fe(III)-HOOH solution (pHs between 1.5-5.0) showed that formate formation was the highest at pH = 4.0, indicating that the speciation of Fe(III) affected the formation of formate. Concentration-dependent experiments demonstrated that Fe is probably the limiting agent under typical environmental conditions.

Does Aqueous‐Phase Oxidation of HCHO Opens a Pathway to Formic Acids in Atmosphere?

“…The results showed that formic acid was the only significant product of the aqueous oxidation [11]. Arakaki et al [12] have detected the formation of formic acid in solutions containing hydrated HCHO (aq) (CH 2 (OH) 2 ), HOOH, and Fe(III) or Cu(II). These experiments suggest that formic acid was a product of the oxidation of HCHO (aq) in aqueous solutions in experimental condition.…”

Advances in Cryochemistry: Mechanisms, Reactions and Applications

“…Compared with reactions in solution, the rate of certain reactions may show interesting phenomena in frozen systems where solvent crystallization produces liquid-to-solid transitions [ 20 , 21 , 22 , 23 ]. What kinds of engine devices exist in the frozen system and how do they drive the acceleration of reactions?…”

Cyanide Formation in Freezer Stored Foods: Freezing of a Glycine and Nitrite Mixture

“…In particular, these effects are further suppressed under freezing conditions. However, some reactions are accelerated under freezing conditions. − Reactions in ice are mainly explained by the freeze-concentration effect, which is generally experienced to be very sweet in partially frozen fruit juice destined for human consumption.. When an aqueous solution is frozen, the solutes in the aqueous solution are rejected by the ice crystals and are concentrated around each small ice crystal.…”