Oxidation of formaldehyde

Typical non-enolising aldehydes are formaldehyde and benzaldehyde, which are oxidised by Co(III) Ce(IV) perchlorate and sulphate , and Mn(III) . The main kinetic features and the primary kinetic isotope effects are the same as for the analogous cyclohexanol oxidations (section 4.3.5) and it is highly probable that the same general mechanism operates. kif olko20 for Co(III) oxidation of formaldehyde is 1.81 (ref. 141), a value in agreement with the observed acid-retardation, i.e. not in accordance with abstraction of a hydroxylic hydrogen atom from H2C(OH)2-The V(V) perchlorate oxidations of formaldehyde and chloral hydrate display an unusual rate expression, viz. 

The oxidation of formaldehyde by V(V) has an isotope effect of ca 4.5 which accords with the depicted C-H cleavage. ... 

The ferricyanide oxidation of formaldehyde is also base-catalysed , the rate law being... 

It was found by Chatterji and Mukherjee that the rate law for the oxidation of formaldehyde indicated that the chromic acid was esterified by the aldehyde hydrate formed, although they did not succeed in isolating the ester.The hypothesis of ester formation seems to be supported by the experience that the rate of reaction is increased by addition of pyridine. 

The iji vitro experiments, using the S-9 fraction from livers of uninduced Fisher 344 rats, was complicated by the fact that it became apparent that formaldehyde production was a poor measure of the extent of metabolism. The reason for that was that the S-9 fraction apparently catalyzed the oxidation of formaldehyde to formate. Consequently, determination of formaldehyde in an S-9 catalyzed reaction consistently gave low values of nitrosamine metabolism. Many workers use semicarbazide to suppress formaldehyde loss. We found, however, that semicarbazide is not a neutral bystander. 

Nakabayashi, S., Yagi, 1., Sugiyama, N., Tamura, K. and Uosaki, K. (1997) Reaction pathway of four-electron oxidation of formaldehyde on platinum electrode as observed by in situ optical spectroscopy. Surf. Sci., 386, 82-88. 

Shropshire JA. 1965. The catalysis of the electrochemical oxidation of formaldehyde and methanol by molybdates. J Electrochem Soc 112 465-469. 

Similarly, the m/z = 60 ion current signal was converted into the partial current for methanol oxidation to formic acid in a four-electron reaction (dash-dotted line in Fig. 13.3c for calibration, see Section 13.2). The resulting partial current of methanol oxidation to formic acid does not exceed about 10% of the methanol oxidation current. Obviously, the sum of both partial currents of methanol oxidation to CO2 and formic acid also does not reach the measured faradaic current. Their difference is plotted in Fig. 13.3c as a dotted line, after the PtO formation/reduction currents and pseudoca-pacitive contributions, as evident in the base CV of a Pt/Vulcan electrode (dotted line in Fig. 13.1a), were subtracted as well. Apparently, a signihcant fraction of the faradaic current is used for the formation of another methanol oxidation product, other than CO2 and formic acid. Since formaldehyde formation has been shown in methanol oxidation at ambient temperatures as well, parallel to CO2 and formic acid formation [Ota et al., 1984 Iwasita and Vielstich, 1986 Korzeniewski and ChUders, 1998 ChUders et al., 1999], we attribute this current difference to the partial current of methanol oxidation to formaldehyde. (Note that direct detection of formaldehyde by DBMS is not possible under these conditions, owing to its low volatility and interference with methanol-related mass peaks, as discussed previously [Jusys et al., 2003]). Assuming that formaldehyde is the only other methanol oxidation product in addition to CO2 and formic acid, we can quantitatively determine the partial currents of all three major products during methanol oxidation, which are otherwise not accessible. Similarly, subtraction of the partial current for formaldehyde oxidation to CO2 from the measured faradaic current for formaldehyde oxidation yields an additional current, which corresponds to the partial oxidation of formaldehyde to formic acid. The characteristics of the different Ci oxidation reactions are presented in more detail in the following sections. 

The partial faradaic current for formaldehyde oxidation to CO2, calculated from the m/z = 44 ion current, is plotted as a dashed hne in Fig. 13.3b (upper panel). Complete oxidation of formaldehyde to CO2 contributes only one-third (positive-going scan) or one-quarter (negative-going scan) of the corresponding faradaic current peaks (sohd hne in the upper panel of Fig. 13.3b). The difference between the measured net current and the calculated faradaic current, which is plotted as a dotted line in Fig. 13.3b (upper panel), reflects the partial current for incomplete formaldehyde oxidation to... 

Figure 13.4 Current efficiency plots for the potentiodynamic electro-oxidation of formaldehyde (a) and methanol (h positive-going scan c negative-going scan) on a Pt/Vulcan thin-fihn electrode (data from Fig. 13.3a, h) dashed lines, current efficiency for CO2 formation dash-dotted fines, current efficiency for HCOOH formation dotted fines, current efficiency for HCHO formation.

Figure 13.6 Potential-step electro-oxidation of formaldehyde on a Pt/Vulcan thin-film electrode (7 p,gpt cm, geometric area 0.28 cm ) in 0.5 M H2SO4 solution containing 0.1 M HCHO upon stepping the potential from 0.16 to 0.6 V (electrolyte flow rate 5 pL at room temperature). (a) Solid line, faradaic current transients dashed line, partial current for HCHO oxidation to CO2 dotted line, difference between the net faradaic current and that for CO2 formation, (b) Solid line, m/z = 44 ion current transients gray line potential-step oxidation of pre-adsorbed CO derived upon HCHO adsorption at 0.16 V, in HCHO-free sulfuric acid solution, (c) Current efficiency transients for CO2 formation (dashed line) and formic acid formation (dotted line).

OH/oxide species. At potentials anodic of 1 V, incomplete oxidation of formaldehyde to formic acid is activated, while methanol oxidation is almost completely hindered. This reflects an easier oxidation of the C-H group in the aldehyde than in the alcohol. For the negative-going scan, where the COadouble-peak stmcture in the current efficiency. 

Beltowska-Brzezinska M, Heitbaum J. 1985. On the anodic oxidation of formaldehyde on Pt, An and Pt/Au-alloy electrodes in alkaline solution. J Electroanal Chem 183 167-181. 

Chen Y-X, Heinen M, Jusys Z, Behm RJ. Dissociative adsorption and oxidation of formaldehyde on a Pt film electrode under controlled mass-transport conditions, an in-situ spectro-electrochemical flow-cell study. To he published. 

Loucka T, Weber J. 1968. Adsorption and oxidation of formaldehyde at the platinum electrode in acid solutions. J Electroanal Chem 21 329-344. 

Miki A, Ye S, Sensaki T, Osawa M. 2004. Surface-enhanced infrared study of catal)4ic electio-oxidation of formaldehyde, methyl formate, and dimethoxymethane on platinum electrodes in acidic solution. J Flectroanal Chem 563 23-31. 

Mishina F, Karantonis A, Yu Q-K, Nakabayashi S. 2002. Optical second harmoitic generation during the electrocatalytic oxidation of formaldehyde on Pt(lll) Potentiostatic regime versus galvanostatic potential oscillations. J Phys Chem B 106 10199-10204. 

Samjeske G, Miki A, Osawa M. 2007. Electrocatalytic oxidation of formaldehyde on platinum under galvanostatic and potential sweep conditions studied by time-resolved surface-enhanced infrared spectroscopy. J Phys Chem 111 15074-15083. 

Sidheswatan P, Lai H. 1971. A study of intermediates adsorbed on platinized platinum during the anodic oxidation of formaldehyde. J Electroanal Chem 34 173-183. 

Spasojevic MD, Adzic RR, Despic AR. 1980. Electrocatalysis on surfaces modified by foreign metal adatoms Oxidation of formaldehyde on platinum. J Electroanal Chem 109 261-269. 

Stadler R, Jusys Z, Baltmschat H. 2002. Hydrogen evolution during the oxidation of formaldehyde on Au The influence of single crystal structure and Tl-upd. Electrochim Acta 47 4485-4500. 

Aerobic oxidation of formaldehyde in water under mild conditions (20-40 °C, 1 atm of air or 02) in the presence of Ce-substituted POMs affords formic acid with high selectivity. 

The development of catalysts for the oxidation of organic compounds by air under ambient conditions is of both academic and practical importance (1). Formaldehyde is an important intermediate in synthetic chemistry as well as one of the major pollutants in the human environment (2). While high temperature (> 120 °C) catalytic oxidations are well known (3), low temperature aerobic oxidations under mild conditions have yet to be reported. Polyoxometalates (POMs) are attractive oxidation catalysts because these extensively modifiable metal oxide-like structures have high thermal and hydrolytic stability, tunable acid and redox properties, solubility in various media, etc. (4). Moreover, they can be deposited on fabrics and porous materials to render these materials catalytically decontaminating (5). Here we report the aerobic oxidation of formaldehyde in water under mild conditions (20-40 °C, 1 atm of air or 02) in the presence of Ce-substituted POMs (Ce-POMs). 

It is noteworthy that Na24Hi 6SiWnCe039 and Na3PWiiCe039 were practically inactive compared to NaH3SiWnCe039 (Table 1), indicating that the number of protons in the Ce-POM is a crucial factor in catalytic activity. The stoichiometric oxidation of formaldehyde with Ce(IV) in aqueous acid solutions was reported in the early 1970 s (10). We have found that Ce(S04)2 shows considerable catalytic activity in aerobic formaldehyde oxidation however, it requires the use of a large excess of H2S04 (Table 1). 

Table 2 Aerobic oxidation of formaldehyde in water in the presence of l. a...

CMD = carbon metabolism determined, i.e., energetically independent. a This range results from differences in possible energy gains derived from the oxidation of formaldehyde. 

A continuous flow system utilising the oxidation of formaldehyde and gallic acid with alkaline hydrogen peroxide to produce a chemiluminescence was studied by Slawinska and Slawinski [ 137]. While the major peak of the chemiluminescence spectrum occurred at 635 nm, the photomultiplier used summed all of the available light between 560 and 850 nm. The intensity of the chemiluminescence was linearly proportional to formaldehyde concentration from 10 7 to 10 2 M, producing a detection limit of 1 xg/l. This method should be sensitive enough for use in seawater. 

Kinetic studies on the oxidation of glutamate by manganese(III) in aqueous sulfuric acid, acetic acid, and pyrophosphate suggest different mechanisms for each case. In all cases there is evidence for the involvement of free radicals and in the case of acetic acid and pyrophosphate media a chelated intermediate is postulated. Simultaneous Mn(III)/Mn(IV)-mediated reaction is observed in the oxidation of formaldehyde by... 

Cerium(IV) oxidations of organic substrates are often catalysed by transition metal ions. The oxidation of formaldehyde to formic acid by cerium(IV) has been shown to be catalysed by iridium(III). The observed kinetics can be explained in terms of an outer-sphere association of the oxidant, substrate, and catalyst in a pre-equilibrium, followed by electron transfer, to generate Ce "(S)Ir", where S is the hydrated form of formaldehyde H2C(OH)2- This is followed by electron transfer from S to Ir(IV) and loss of H+ to generate the H2C(0H)0 radical, which is then oxidized by Ce(IV) in a fast step to the products. Ir(III) catalyses the A -bromobenzamide oxidation of mandelic acid and A -bromosuccinimide oxidation of cycloheptanol in acidic solutions. ... 

The oxidation of formaldehyde by chlorite, C102, has been studied in aqueous solution.In the presence of excess chlorite, formaldehyde was oxidized to CO2, with CIO2 also being formed. This compound was also obtained as an oxidation product when HCHO was in excess, in which case the latter was oxidized only as far as formic acid. The first step of the reaction produces HOCl, which acts as an autocatalyst, catalysing the formation of CIO2 and the further oxidation of HCO2H to CO2. The build-up of CIO2 is due to the fact that HOCl reacts much more rapidly... 

Figure 8.4. Current-potential curves for the reduction of Cu ions and the oxidation of reducing agent Red, formaldehyde, combined into one graph (an Evans diagram). Solution for the Tafel line for the reduction of Cu ions O.IM CUSO4, 0.175M EDTA, pH 12.50, Egq (Cu/Cu ) = -0.47 V versus SCE for the oxidation of formaldehyde 0.05 M HCHO and 0.075 M EDTA, pH 12.50, (HCHO) = -1.0 V versus SCE temperature 25 0.5°C. (From Ref. 10, with permission from the American Electroplaters and Surface Finishers Society.)...

The most studied anodic partial reaction is the oxidation of formaldehyde. Red = H2CO. The overall reaction of the electrochemical oxidation of formaldehyde at the copper electrode in an alkaline solution proceeds as... 

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