Enhancer Formic acid

Another important difference in the poison formation reaction is observed when studying this reaction on Pt(lll) electrodes covered with different adatoms. On Pt(lll) electrodes covered with bismuth, the formation of CO ceased at relatively high coverages only when isolated Pt sites were found on the surface [Herrero et al., 1993]. For formic acid, the formation takes place only at defects thus, small bismuth coverages are able to stop poison formation [Herrero et al., 1993 Macia et al., 1999]. Thus, an ideal Pt(lll) electrode would form CO from methanol but not from formic acid. This important difference indicates that the mechanism proposed in (6.17) is not vahd. It should be noted that the most difhcult step in the oxidation mechanism of methanol is probably the addition of the oxygen atom required to yield CO2. In the case of formic acid, this step is not necessary, since the molecule has already two oxygen atoms. For that reason, the adatoms that enhance formic acid oxidation, such as bismuth or palladium, do not show any catalytic effect for methanol oxidation. 

The most widely studied conducting polymer support is polyaniline (PANl), which has been shown to decrease the poisoning of Pt by COads [88]. Gharibi et al. have recently explored the factors responsible for the enhanced formic acid oxidation activity of Pt supported on a carbon/PANI composite [89]. They concluded that improvements in both electron and proton conductivities, as well as the increased methanol diffusion coefficient and decreased catalyst poisoning, could be involved. A carbon nanotubes/PANI composite [90], poly(o-methoxyaniline) [91], and polyindole [92] have recently been reported as effective supports for formic acid oxidation at Pt nanoparticles, while polycarbazole [93] has also been used to support PtRu nanoparticles. 

Kim B-J, Kwon K, Rhee CK, Han J, Lim T-H (2008) Modification of Pt nanoelectrodes dispersed on carbon support using irreversible adsorption of Bi to enhance formic acid oxidation. Electrochim Acta 53 7744—7750... 

Bauskar A, Rice CA (2013) Bi modified Pt/C for enhanced formic acid electro-oxidation. Electrochim Acta 93 152-157... 

Moreover, there is some indication in the literature that the purity of formic acid might play a role in affecting the order of stability among Pd, Pt, and PdPt. The long-term activity of Pd improved with enhanced formic acid purification [176]. This effect has not yet been thoroughly validated. 

Zeng J, Sun S, Zhong J, Li X, Wang R, Wu L, Wang L, Fan Y (2015) Pd nanoparticles supported on copper phthalocyanine functionalized carbon nanotubes for enhanced formic acid electrooxidation. J Hydrogen Energy in press... 

When the reaction was followed in an nmr probe, the appearance and disappearance of two intermediates 66 and 67 was observed along with the buildup of product 65. The rate of reaction of 64 at 75° in formic acid, k = 3xl0" sec, is six times faster than the rate of the corresponding saturated system, 2,2-dimethyl-1-pentyl tosylate, k = 5xl0" sec, under identical conditions. If the inductive rate retarding effect of the triple bond is taken into account, then the calculated rate enhancement resulting from triple-bond participation in the solvolysis of 64 is about 3000(81). The... 

GL 2] [R 5] [P 3] By addition of formic acid, the polarity of the solvent can be enhanced, which is known to favor the electrophilic pathway. Using formic acid/ acetonitrile mixtures, conversions of44-77% and yields of 60-78% were obtained for different contents of the solvents and different flow rates [16]. The performance in pure acetonitrile was much lower (conversion, 15% yield, 71%) and was accompanied by fouling of the micro device due to insufficient liquid reactant solubility. 

Beltramo G, Shubina TE, Koper MTM. 2005. Oxidation of formic acid and carbon monoxide on gold electrodes studied by surface-enhanced Raman spectroscopy and DFT. ChemPhysChem 6 2597-2606. 

SamjeskeG, Miki A, YeS, Yamakata A,Mukouyama Y, Okamoto H, OsawaM. 2005. Potential oscillations in galvanostatic electrooxidation of formic acid on platinum A time-resolved surface-enhanced infrared study. J Phys Chem B 109 23509-23516. 

Samjeske G, Miki A, Ye S, Osawa M. 2006. Mechanistic study of electrocatal3dic oxidation of formic acid at platinum in acidic solution by time-resolved surface-enhanced infrared absorption spectroscopy. J Phys Chem B 110 16559-16566. 

The methylation of secondary amines works better than for primary amines because there is no competition between the formation of mono- or dimethylated products. The best results for the microwave-enhanced conditions were obtained when the molar ratios of substrate/formaldehyde/formic acid were 1 1 1, so that the amount of radioactive waste produced is minimal. The reaction can be carried out in neat form if the substrate is reasonably miscible with formic acid/aldehyde or in DM SO solution if not. Again the reaction is rapid - it is complete within 2 min at 120 W microwave irradiation compared to longer than 4 h under reflux. The reaction mechanism and source of label is ascertained by alternatively labeling the formaldehyde and formic acid with deuterium. The results indicate that formaldehyde contri-... 

Water has been shown to enhance the activity of ruthenium and rhodium catalysts in both the TEAF and potassium formate systems [34, 36, 52]. The aqueous systems enable much simpler control of pH this is important, as Xiao has found that a low pH markedly slows the reaction [52]. The pH at which this occurs corresponds with the pKa of formic acid (i.e., 3.7), implying that the formate anion is required for complexation with the catalyst. Xiao has proposed two possible catalytic cycles - one that provides poor ee-values at low pH as a result of ligand decomplexation, and another that gives high ee-values at high pH. 

The PO mode is a specific elution condition in HPLC enantiomer separation, which has received remarkable popularity especially for macrocyclic antibiotics CSPs and cyclodextrin-based CSPs. It is also applicable and often preferred over RP and NP modes for the separation of chiral acids on the cinchonan carbamate-type CSPs. The beneficial characteristics of the PO mode may arise from (i) the offset of nonspecific hydrophobic interactions, (ii) the faster elution speed, (iii) sometimes enhanced enan-tioselectivities, (iv) favorable peak shapes due to improved diffusive mass transfer in the intraparticulate pores, and last but not least, (v) less stress to the column, which may extend the column lifetime. Hence, it is rational to start separation attempts with such elution conditions. Typical eluents are composed of methanol, acetonitrile (ACN), or methanol-acetonitrile mixtures and to account for the ion-exchange retention mechanism the addition of a competitor acid that acts also as counterion (e.g., 0.5-2% glacial acetic acid or 0.1% formic acid) is required. A good choice for initial tests turned out to be a mobile phase being composed of methanol-glacial acetic acid-ammonium acetate (98 2 0.5 v/v/w). 

Kitamoto, T., Ogomori, K., Tateishi, J., and Prusiner, S. (1987) Formic acid pretreatment enhances immunostaining of cerebral and systemic amyloids. Lab. Invest. 57, 230-236. 

Moore DF, Bentley AM, Dawling S et al Folinic acid and enhanced renal elimination in formic acid intoxication. Clin Toxicol 32 199-204, 1994... 

All patients with methanol toxicity should be given folic acid 50 milligrams intravenously every 4 hours to increase the metabolism of formic acid. In ethylene glycol ingestion, folate, thiamine and pyri-doxine should all be administered, to enhance the metabolism of the poison to non-toxic products, and minimize oxalic acid production. Calcium supplements are required for symptomatic hypocalcaemia. 

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