Formic acid reduction

The desired pyridylamine was obtained in 69 % overall yield by monomethylation of 2-(aminomethyl)pyridine following a literature procedure (Scheme 4.14). First amine 4.48 was converted into formamide 4.49, through reaction with the in situ prepared mixed anhydride of acetic acid and formic acid. Reduction of 4.49 with borane dimethyl sulfide complex produced diamine 4.50. This compound could be used successfully in the Mannich reaction with 4.39, affording crude 4.51 in 92 % yield (Scheme 4.15). Analogous to 4.44, 4.51 also coordinates to copper(II) in water, as indicated by a shift of the UV-absorption maximum from 296 nm to 308 nm. 

The formic acid reduction has great stereospecificity. Reduction of (-)-zl -dehydrosparteine (159) and (—)-.d "-didehydrosparteine affords (—)-sparteine (160) and (—)-(x-isosparteine, respectively (252). 

Reduction of carbon dioxide takes place at various metal electrodes. The main products are formic acid in aqueous solutions and oxalate, CO, and formic acid in nonaqueous solutions. An indium electrode is the most potential saving for C02 reduction. Due to the difference in optimum conditions between those for C02 reduction to formic acid and those for formic acid reduction to further reduced products, direct reduction of C02 in aqueous solutions without a catalyst to highly reduced products seems to be difficult at metal electrodes. However, catalytic effects of metal electrodes themselves have recently become more clear for example, on Cu, methane was detected, while on Ag and Au, CO was produced effectively in aqueous solutions. Furthermore, at a Mo electrode, methanol was obtained. The power efficiency is, however, still low at any electrode. 

Neto and co-workers examined the ex situ Pt L3 EXAFS for a series of PtRu catalyst powders in air of varying nominal composition from 90 10 through to 60 40 atom %. The catalysts were prepared using a formic acid reduction method developed by the authors which resulted in very poorly alloyed particles, even after heat treatment to 300 °C under a hydrogen atmosphere. Unfortunately, the authors were not able to obtain Ru K edge data to identify the local structure of the Ru in their catalysts. 

The mechanism of formic acid reduction has been investigated in the reactions of deuterium-labeled formic acid (DCOOH, HCOOD, DCOOD) with quinolizidine200 (Scheme 134). 

In contrast to aluminum hydride reductions (see Section II, B, 4), no ring openings have been observed in reductions of quaternary pyridinium salts by means of sodium borohydride. Whenever possible, both isomeric tetrahydropyridines are formed, as it may be seen from the following examples (aluminum hydride, electrolytic, and formic acid reductions are included for comparison). 

Formic acid reduction and O, other methods. b Salts a, picrate and 6, hydrobromide of a dibromide. 

Aqua ions are known but not very stable. Substitution of Pt in aqueous solution is sometimes zero-order in the added ligand, L, or can have both L-dependent and L-independent contributions to the rate, probably because intermediate formation of an unstable aqua complex is the rate-determining step for the L-independent pathway. A large number of O-donors, particularly anionic ones, give stable complexes, for example, carbonate, acetate, oxalate, acetylacetonate, and alkoxide. Tetrameric platinum(II) acetate is formed by formic acid reduction of Pt solutions in acetic acid. It does not appear to be a very useful synthetic precursor for Pt chemistry. The acetylacetonate [Pt(acac)2] is monomeric and square planar. 

CO2 reduction proceeds readily to formic acid on most metal electrodes, and formic acid reduction proceeds most rapidly on electrodes with high hydrogen overvoltage such as lead, tin, and indium this appears to be related to the stability of intermediates (22, 23). 

C in aprotic solvents such as acetone or, more smoothly, in -PrOH, with 80% yield to 1,3,7-octatrienes (1). The presence of COj greatly enhances the catalytic activity of [Pd(PR3) ] (n = 2-4) and causes isomerization of 1 to 2,4,6-octatrienes. In formic acid, reductive dimerization proceeds and, depending on catalyst and cocatalyst, either... 

Formic acid has been used in a variety of rather specific reductions. Heating triphenylcarbinol (580) in formic acid, for example, led to triphenylmethane (581). 92 most common application of formic acid reduction involves enamines, presumably via conversion to an iminium salt, which is the actual species reduced... 

Dimerization of alkylallene 160 proceeded regioseleetively at each C-2 carbon, and the cross-conjugated triene 161 was obtained in high yield using P(< -Tol)3 as a ligand and p-nitrophenol as an additive [53]. In the presenee of formic acid, reductive dimerization at C-2 carbons occurred to give the conjugated dienes 164 and 165. The dimerization is explained by the formation of the palladacycle 163, formed by oxidative cyclization, as an intermediate [54]. 

Regarding the co-catalytic role of Sn for methanol oxidation, on the other hand, the experimental evidence is less conclusive compared to the case of CO oxidation. Colmati et al. prepared PtSn/C catalyst formulations (9 1 and 3 1 atomic ratio) using formic acid reduction and compared the activity with commercial (E-TEK Inc.) Pt/C and PtSn (3 1)/C, including DMFC foel cell experiments [79]. Unfortunately, no comparison with PtRu was presented. Employing 0.4 mg cm anode catalyst load and 3 atm O2 pressure, the maximum fuel cell power output at 343 K was obtained with PtSn (3 1) produced by the formic acid method, 400 mW... 

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