Formaldehyde, formation

Mechanistic aspects of the action of folate-requiring enzymes involve one-carbon unit transfer at the oxidation level of formaldehyde, formate and methyl (78ACR314, 8OMI2I6OO) and are exemplified in pyrimidine and purine biosynthesis. A more complex mechanism has to be suggested for the methyl transfer from 5-methyl-THF (322) to homocysteine, since this transmethylation reaction is cobalamine-dependent to form methionine in E. coli. 

Interaction of formaldehyde with 2,4-dinitrophenylhydrazine in acid media causes 2,4-dinitrophenylhydrazone (DNPhydrazone) formaldehyde formation. Gas-chromatographic analysis of 2,4-DNP-hydrazone formaldehyde toluene extract with an electron holding detector makes it possible to detect it at the level of 0,001 mg/dm. Phenol is detected in the form of tribromphenol yield, the hexane extract of which undergoes chromatography with an electron holding detector which provides the level of phenol detection of 0.001 mg/dm (the limit of quantitative detection). 

The selectivity of formaldehyde formation and conversion of methanol at 650 K is shown in Fig.5. The yield of formaldehyde was shown in Fig.6. 

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. 

Figure 13.7 (Continued) (b) Solid line, m/z = 44 ion current transients gray line, potential-step oxidation of pre-adsorbed CO derived upon CH3OH adsorption at 0.16 V, in CHsOH-free H2SO4 solution, (c) m/z = 60 ion current transients, (d) Current efficiency transients for CO2 formation (dashed line), formic acid formation (dash-dotted line), and formaldehyde formation (dotted line).

The current efficiencies for the different reaction products CO2, formaldehyde, and formic acid obtained upon potential-step methanol oxidation are plotted in Fig. 13.7d. The CO2 current efficiency (solid line) is characterized by an initial spike of up to about 70% directly after the potential step, followed by a rapid decay to about 54%, where it remains for the rest of the measurement. The initial spike appearing in the calculated current efficiency for CO2 formation can be at least partly explained by a similar artifact as discussed for formaldehyde oxidation before, caused by the fact that oxidation of the pre-formed COacurrent efficiency. The current efficiency for formic acid oxidation steps to a value of about 10% at the initial period of the measurement, and then decreases gradually to about 5% at the end of the measurement. Finally, the current efficiency for formaldehyde formation, which was not measured directly, but calculated from the difference between total faradaic current and partial reaction currents for CO2 and formic acid formation, shows an apparently slower increase during the initial phase and then remains about constant (final value about 40%). The imitial increase is at least partly caused by the same artifact as discussed above for CO2 formation, only in the opposite sense. 

The reaction sequence of formaldehyde formation and subsequent COad formation can proceed either as sequential reactions of adsorbed species, or it can involve formation and desorption of formaldehyde into the electrol5d e and subsequent re-adsorption and further decomposition of formaldehyde to COad. Considering the significant transport and catalyst loading effects discussed above, it is clear that desorption and subsequent re-adsorption plus dehydrogenation of formaldehyde will play an important role also for COad formation, although a direct reaction of adsorbed RIad species can not be ruled out. 

Islam M, Basnayake R, Korzeniewski C. 2007. A study of formaldehyde formation during methanol oxidation over PtRu hulk alloys and nanometer scale catalyst. J Electroanal Chem599 31-40. 

Brononol (2-Bromo-2-nitropropane-1,3-diol) in combination with methyl and propyl paraben. The paper generated by the Danish group (ref. 5 Knoll BASF publication) shows that the mechanism of action of Bronopol is independent of formaldehyde formation. The inclusion of Tetrasodium EDTA at about 0.02% to remove ions in the water or extracts and carefully excluding any tertiary amines such as triethanolamine to counteract the fears of the marketers with reference to possible nitrosamine formation and release of formaldehyde. The pH used is usually at 6 and below. 

Methanol still proceeds through an initial C H bond scission, but reacts with water before the OH bond breaks. Alternatively, formaldehyde formation likely occurs along the same pathway as CO formation. This is true if HCO is an intermediate in the decomposition pathway. Furthermore, the lack of a kinetic isotope effect for CH3OD indicates that formaldehyde is not the product of an initial O-H scission.94 Because formaldehyde and formic acid are not the thermodynamically favored products of methanol oxidation, they must be the result of kinetic limitations preventing the full oxidation to C02, analogous to the production of H202 for the reduction of oxygen (see next section). 

Ci compounds (reduced single carbon compounds) include methane, formaldehyde, formate, methanol, and methylamine. Source After Levellle, R. J., and S. K. Juniper (2003) Biogeochemistry of Marine Systems, Blackwell Publications, pp. 238-292. 

Fig. 13. Accelerated kinetics of formaldehyde formation observed in the presence of His-2D compared the free hemin in 100 mM Tris-HCl buffer (pH 7.4) with 15% (v/v) TPE (119). Reproduced with permission of The Royal Society of Chemistry.

Thereafter, the propagation reactions proceed controlling the overall chemistry. Recent models include more than 160 radical reactions (37), of which those accounting for formaldehyde formation are ... 

Reaction with formaldehyde (formation of phenol-formaldehyde... 

Harris and Egerton (25) reported that formaldehyde added to a 1 to 1 mixture of oxygen and propane at 300° to 340° C. increased the induction period. Satterfield and Wilson (51) ascribe formaldehyde formation in propane oxidation above 370° C. to CH3 + 02 — CH20 -f OH. 

This circumstance indicates that cross recombination by reaction (5.23) is the main means of formaldehyde formation. Other alternative pathways of formaldehyde formation were also considered ... 

Based on the suggested mechanism of formaldehyde formation, the following scheme of kinetic equations which adequately describe the experimental data (Figure 5.1) was suggested [36, 37] ... 

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