Formic acid, from hydrogenation

Apart from the Meerwin-Ponndorf-Verley (MPV) reaction,16 18catalytic asymmetric transfer hydrogenation has remained quite primitive,111,112 with successful examples of reduction of activated olefins, using alcohols or formic acid as hydrogen source, being reported only recently.113,114... 

Gordon used a household microwave oven for the transfer hydrogenation of benz-aldehyde with (carbonyl)-chlorohydridotris-(triphenylphosphine)ruthenium(II) as catalyst and formic acid as hydrogen donor (Eq. 11.43) [61]. An improvement in the average catalytic activity from 280 to 6700 turnovers h-1 was achieved when the traditional reflux conditions were replaced by microwave heating. 

As shown in Figure 1, the next step in the catalytic cycle of carbon dioxide hydrogenation is either reductive elimination of formic acid from the transition-metal formate hydride complex or CT-bond metathesis between the transition-metal formate complex and dihydrogen molecule. In this section, we will discuss the reductive elimination process. Activation barriers and reaction energies for different reactions of this type are collected in Table 3. 

Formic acid from any of these sources is obtained in the concentrated state by decomposing plumbic formate with sulphuretted hydrogen, and a nrarda rectifying the amd over plumbic fonuato —... 

This is the only MMDA analogue that has been explored as an N-methyl derivative. A more highly substituted analogue has also been made, the N-methyl derivative of DMMDA. Isoapiole (see its preparation under DMMDA) was oxidized with formic acid and hydrogen peroxide to the ketone (2,5-dimethoxy-3,4-methylenedioxyphenylacetone, a solid with a mp of 75-76 °C from methanol) which was reductively aminated with methylamine and amalgamated aluminum to give 2,5-dimethoxy-N-methyl-3,4-methylenedioxyamphetamine hydrobromide... 

Cleavage of the bis(methylsulfanyl)methylene group is achieved either with performic acid (generated in situ from formic acid and hydrogen peroxide) or with 0.5 M aqueous HCI in THF (Scheme 69).t A conversion of this protection group into the Z group is possible in a one-pot reaction with the sodium salt of benzyl alcohol in anhyd THF at 30 °C for 6 hours... 

The catalytic addition of hydrogen on COj presents also an important starting point for the utilization of CO2 as a couple of technical important basic chemicals can be produced on this way (Scheme 7). The formation of formic acid from carbon dioxide and dihydrogen is an exothermic but strongly endergonic process under standard conditions. 

In spite of the elimination of formic acid in a couple of steps changing the oxidation number of the rhodium metal center from -nl to -i-3 and vice versa, the reaction could take place by an alternative mechanistic pathway via cr-meta-thesis between the coordinated formate unit and the nonclassical bound hydrogen molecule [48, 49]. Initial rate measurements of a complex of the type 13 show that kinetic data are consistent with a mechanism involving a rate-limiting product formation by liberation of formic acid from an intermediate that is formed via two reversible reactions of the actual catalytically active species, first with CO2 and then with H2. The calculations provide a theoretical analysis of the full catalytic cycle of CO2 hydrogenation. From these results s-bond metathesis seems to be an alternative low-energy pathway to a classical oxidative addition/reductive elimination sequence for the reaction of the formate intermediate with dihydrogen [48 a]. 

The above examples demonstrate that there are several efficient ways to hydrogenate C02 in the presence of amines or other bases either in aqueous or in nonaqueous solutions. However, the separation of free formic acid from the reaction mixtures is a challenge4—ingenious approaches are also found in the patent literature.50,51 In any case, the catalyst must be removed from the reaction mixtures since it... 

Jessop and co-workers have pointed out that homogeneous catalysis in supercritical fluids can offer high rates, improved selectivity, and elimination of mass-transfer problems.169 They have used a ruthenium phosphine catalyst to reduce supercritical carbon dioxide to formic acid using hydrogen.170 The reaction might be used to recycle waste carbon dioxide from combustion. It also avoids the use of poisonous carbon monoxide to make formic acid and its derivatives. There is no need for the usual solvent for such a reaction, because the excess carbon dioxide is the solvent. If the reaction is run in the presence of dimethy-lamine, dimethylformamide is obtained with 100% selectivity at 92-94% conversion.171 In this example, the ruthenium phosphine catalyst was supported on silica. Asymmetric catalytic hydrogenation of dehydroaminoacid derivatives (8.16) can be performed in carbon dioxide using ruthenium chiral phosphine catalysts.172... 

Several patents describe the production of formic acid or formates by hydrogenation of C02, bicarbonates or carbonates [292,293], It is disclosed, that in water/2-propanol mixtures the yield of formic acid was a function of the molar composition of the solvent. While in water the yield was 13 %, it increased sharply to 54.5 % in 2-propanol/water 20/80, passed through a maximum at 60/40 (60.7 %) and fall back to 43.4 % in neat 2-propanol. In this particular case the reaction conditions were the following [ RuCl2(CO)2 n], NEt3, 80 °C, 27 bar C02, 54 bar H2. It seems that greater difficulties are in the separation of the product formic acid from the reaction mixture than in the chemistry of its production - ingenious approaches are also found in the patent literature [292,293],... 

My own experience with this reaction dates to the early 80s, when I decided to torment myself by trying it. Detailed cooking procedures using it can be found in Pikhal under MDMA. My experience with the KOH isomerization was that the conversion of safrole to isosaffole went cleanly at about 100% yield, as long as traces of moisture were excluded from the reaction. The conversion of isosafrole to methylenedioxy-phenylacetone is another matter. The yields are low, a lot of work is required because the formic acid and hydrogen peroxide must be removed from the reaction mixture under a vacuum before final treatment with sulfuric acid solution to yield the phenylacetone, and these vapors corrode the aspirator supplying the vacuum. This method stinks ... 

The results obtained in this work are related mainly with the high rates for the reduction process achieved with this kind of electrodes. With Co phthalocyanine electrodes the only significant products were CO and H2 and the results are highly dependent on the potential used for the electrolysis experiments. Other important factor described by the authors was the amounts of carbon monoxide and hydrogen produced from sample to sample, reflecting probably variations in the exact composition of different Co phthalocyanines electrodes. For Mn, Cu, and Zn impregnated electrodes both formic acid and hydrogen were produced. 

Virtually all materials extracted from plants and animals fall under the heading of organic compounds— that is, compounds that include some combination of carbon and hydrogen. In the chemist s quest for materials, plants and animals have always been exploited as much as the stones we have focused on so far. Extracts of herbs have been used for medicines and ethanol for mood control. Soaps and many dyes have their origins in plant and animal products, as do many acids, including acetic acid from sour wine, lactic acid from milk, citric acid from lemons, and formic acid from the dry distillation of ants (alchemists tended to throw anything in the pot that was not faster than they were). 

The mechanism of the last oxygenation and the A-ring aromatization remains controversial. If loss of formic acid from C-19 and the ip-hydrogen occurs early in this process, a second double bond would be introduced in the A-ring, and tautomerization of the 3-ketone would complete the aromatization reaction. Other proposals include a mechanism in which a ferric peroxide attacks the C-19 oxo-intermediate... 

Moret S, Dyson P, Laurenczy G (2014) Direct synthesis of formic acid from CO2 by hydrogenation in acidic media. Nat Commun 5 1-7... 

Pomelli et al. (156) reported a theoretical study using density functional methods to investigate how coordination of a CO2 molecule can assist in the release of formic acid from the catalyst complex in the last step of the catalytic cycle for the hydrogenation of CO2 with rhodium complexes. They find that the presence of a CO2 molecule in their active site model thermodynamically favors the formic acid dissociation from the complex and enhances the reaction rate. This may provide some additional explanation of the dramatic rate increases observed by Noyori and coworkers. 

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