H₂O₂ Generation by Decamethylferrocene at a Liquid|Liquid Interface

Abstract

Die Erzeugung von Wasserstoffperoxid an einer Flüssig‐flüssig‐Grenzfläche verläuft mit einer Ausbeute von 20 % bezogen auf die Konzentration des Reduktionsmittels Decamethylferrocen (gelbe Struktur; siehe Bild). Zur Umwandlung von O2 in H2O2 führt die Flüssig‐flüssig‐Grenzfläche Elektronen aus dem Reduktionsmittel und Protonen aus der wässrigen Phase zu. Das H2O2 wird im Verlauf der Reaktion in die wässrige Phase extrahiert. DCE = 1,2‐Dichlorethan.

Proton Pump for O2 Reduction Catalyzed by 5,10,15,20‐Tetraphenylporphyrinatocobalt(II)

“…This current response arises from proton transfer followed by O 2 reduction by DMFc, as previously reported. [28] This reaction produces decamethylferrocenium (DMFc + ) in DCE, whose transfer across the water j DCE interface resulted in a current wave at the negative potential (…”

“…Therefore, they can be [14,15] Shake flask experiments: [CoA C H T U N G T R E N N U N G (tpp)] catalyzed O 2 reductions by Fc, DFc and DMFc at a water j DCE interface at which the polarization was chemically controlled by a common ion, so called shake flask experiments, were performed as reported previously. [28] Dissolving lithium tetrakis(pentafluorophenyl)borate (LiTPFB, 5 mm) and HCl (10 mm) in water and BTPPATPFB (5 mm) in DCE (water/ DCE = 1:1 in volume), the Galvani potential difference across the interface is fixed by the common ion TPFB À at a potential greater than 0.59 V. [28,32] At this potential, proton initially present in water will partition into DCE, leading finally to a distribution of proton in two phases according to the Nernst equation. If only [CoA C H T U N G T R E N N U N G (tpp)] is present in DCE, a Soret band (l max = 427 nm) and a Q band (l max = 540 nm) are observed after the shake flask experiment, which demonstrates a bathochromic shift relative to those of a fresh [Co-A C H T U N G T R E N N U N G (tpp)] solution at 410 nm and 526 nm, as shown in Figure 3.…”

“…The detection of I 3 À confirms the production of H 2 O 2 in the shake flask experiment, since H 2 O 2 is a strong oxidant that can oxidize I À to I 3 À . [15,28] One more point should be mentioned is that in the shake flask experiments, the Q band of [CoA C H T U N G T R E N N U N G (tpp)] (l max = 526 nm) was observed for all three ferrocene compounds, whereas that of [Co DMFc, DFc and Fc, could be effectively catalyzed by [Co-A C H T U N G T R E N N U N G (tpp)]. This is in agreement with a conclusion that made previously that monomeric cobalt porphyrins only catalyze two-electron reduction of O 2 .…”

“…Recently, O 2 reduction by decamethylferrocene (DMFc) at a polarized water j 1,2-dichloroethane (DCE) interface, also called the interface between two immiscible electrolyte solutions (ITIES), has been reported. [23,[28][29][30][31] In this case, one reactant, namely protons, is located in the aqueous phase, whereas the second one, namely the electron donor, is located in the organic phase. We have shown that in this biphasic system the ORR probably proceeds through a proton transfer from water to DCE followed by O 2 reduction by DMFc in DCE.…”

“…We have shown that in this biphasic system the ORR probably proceeds through a proton transfer from water to DCE followed by O 2 reduction by DMFc in DCE. [28] The H 2 O 2 formed is then extracted to the adjacent water phase immediately after its formation in DCE. The oxidation of DMFc to DMFc + has also been confirmed by UV-visible spectrophotometric and electrochemical measurements.…”