Catalytic hydrogenation electroreduction

Naphthaleneamine. 1-Naphthylamine or a-naphth5iamine/7i5 -i2- can be made from 1-nitronaphthalene by reduction with iron—dilute HCl, or by catalytic hydrogenation it is purified by distillation and the content of 2-naphthylamine can be reduced as low as 8—10 ppm. Electroreduction of 1-nitronaphthalene to 1-naphthylamine using titania—titanium composite electrode has been described (43). Photoinduced reduction of 1-nitronaphthalene on semiconductor (eg, anatase) particles produces 1-naphthylamine in 77% yield (44). 1-Naphthylamine/7J4-J2-. can also be prepared by treating 1-naphthol with NH in the presence of a catalyst at elevated temperature. The sanitary working conditions are improved by gas-phase reaction at... 

The most important factor in electrolytic reduction (electroreduction) is the nature of the metal used as a cathode. Metals of low overvoltage - platinum (0.005-0.09 V), palladium, nickel and iron - give generally similar results of reduction as does catalytic hydrogenation [727]. Cathodes made of metals of high overvoltage such as copper (0.23 V), cadmium (0.48 V), lead (0.64 V), zinc (0.70 V) or mercury (0.78 V) produce similar results to those of dissolving metal reductions. 

The pyridine ring is easily reduced in the form of its quaternary salts to give hexahydro derivatives by catalytic hydrogenation [446], and to tetrahydro and hexahydro derivatives by reduction with alane aluminum hydride) [447], sodium aluminum hydride [448], sodium bis 2-methoxyethoxy)aluminum hydride [448], sodium borohydride [447], potassium borohydride [449], sodium in ethanol [444, 450], and formic acid [318]. Reductions with hydrides give predominantly 1,2,5,6-tetrahydro derivatives while electroreduction and reduction with formic acid give more hexahydro derivatives [451,452]. 

Phthalazine and its homologs and derivatives are easily hydrogenolyzed. Electroreduction in alkaline medium gave 1,2-dihydrophthalazines [495], while in acidic media [495] and on catalytic hydrogenation [496], the ring was cleaved to yield o-xylene-a,a -diamine. 

Bipyridine is likewise reduced to 4,4 -bipiperidine by sodium and amyl alcohol and by catalytic hydrogenation. " 2,2 -Dimethyl-4,4 -bipyridine is reduced to 2,2 -dimethyl-4,4 -bipiperidine. Electrochemical reduction of 4,4 -bipyridine affords 4,4 -bipiperidine and some partly reduced 4,4 -bipyridines. Further work on the electroreduction of 4,4 -bipyridine has been reported. Reduction of 4,4 -bipyridine by tin and hydrochloric acid " or by controlled catalytic hydrogenation - gives l,2,3,4,5,6-hexahydro-4,4 -bipyridine. 4,4 -Bipyridine is reduced to its 1,4-dihydro derivative by bisdihydropyridyl metal complexes and to its radical anion by alkali metals and related processes. " " The ionization constant of the radical anion has been determined. ... 

Electroreduction of pyridazines in the presence of acetic anhydride gives the acylated open-chain diamines (cf. 117 -> 222). In aqueous solution a 1,2-dihydropyridazine is formed, which decomposes to nitrogen and an unsaturated hydrazino-aldehyde that polymerizes. Allylic bromi-nation of l,2-dicarbomethoxy-l,2,3,6-tetrahydropyridazine followed by de-hydrobromination gives l,2-dicarbomethoxy-l,2-dihydropyridazine. Catalytic hydrogenation gives the hexahydro compound." ... 

Electroreduction of nitro compounds is of considerable importance for electroorganic synthesis. Interesting catalytic effects were reported for the reduction of aromatic nitro compounds on Pt. Figure 11 shows that Ph, Tl, and Bi adlayers shift the half-wave potential positively by 100 to 300 mV. The catalytic effect was attributed to a change in the mechanism of the reduction of the nitro group from a catalytic hydrogenation on bare Pt to an electron-transfer mechanism on Pt/Mad, that is, a direct electron exchange between the nitro compound and the adatom-covered electrode surface, namely. 

In cathodic reductive processes, the cathode of electrolysis provide an electron source for the reduction of organic compounds. Generally the rate of reduction increases with the acidity of the medium. Electroreduction of unsaturated compounds in water or aqueous-organic mixtures give reduced products — this process is equivalent to catalytic hydrogenation. 

D-Mannitol has been synthesized by several methods. The commercial methods have been the electroreduction and more recently catalytic reduction of D-glucose, under more or less alkaline conditions sorbitol is formed simultaneously. Depending on the alkalinity, over 20 % of the glucose can be converted to D-mannitol in this manner. Catalytic hydrogenation of invert sugar to give a similar mixture of D-mannitol and sorbitol would appear to be a method capable of commercial exploitation. 

Figure 9 The increase in the catalytic hydrogen peroxide electroreduction current upon adding the soybean peroxidase-labeled target in microelectrodes loaded with different amounts of the probe oligonucleotide. The probe was deposited for (a) 1 minute, (b) 2.5 minutes, (c) 5 minutes, and (d) 10 minutes.

The thermodynamic stability of CO2 requires high energy substances or electroreductive processes for its transformation into valuable chemicals in which the carbon atom has a lower oxidation state than 4 [1, 3, 4, 197]. Catalytic hydrogenation of CO2 has been acknowledged as one of the major potential steps for CO2 valorization to fuels, or other products (e.g., HCOOH, methanol, H2CO, and C1+) which are considered to be potential hydrogen carriers or useful chemicals or fuels [1, 198]. 

The water-soluble Fe porphyrin, 3Na+ [Fe(III)(TPPS)] -12H20 [H2TPPS4- = tetra-anionic form of meso-tetrakis(7r-sulfonatophenyl)porphine], has recently been shown to be an effective catalyst for the electroreduction of nitrite to ammonia [419]. The Fe meso-tetrakis(A -methyl-4-pyridyl) porphyrin and/or the Fe meso-tetrakis (jr -sulfophenyl) porphyrin complex shows a catalytic activity for the reduction of dioxygen in aqueous solutions, leading to hydrogen peroxide [420]. 

Phthalimide was hydrogenated catalytically at 60-80° over palladium on barium sulfate in acetic acid containing an equimolar quantity of sulfuric or perchloric acid to phthalimidine [7729]. The same compound was produced in 76-80% yield by hydrogenation over nickel at 200° and 200-250 atm [43 and in 75% yield over copper chromite at 250° and 190 atm [7730]. Reduction with lithium aluminum hydride, on the other hand, reduced both carbonyls and gave isoindoline (yield 5%) [7730], also obtained by electroreduction on a lead cathode in sulfuric acid (yield 72%) [7730]. 

For these low-temperature fuel cells, the development of catalytic materials is essential to activate the electrochemical reactions involved. This concerns the electro-oxidation of the fuel (reformate hydrogen containing some traces of CO, which acts as a poisoning species for the anode catalyst methanol and ethanol, which have a relatively low reactivity at low temperatures) and the electroreduction of the oxidant (oxygen), which is still a source of high energy losses (up to 30-40%) due to the low reactivity of oxygen at the best platinum-based electrocatalysts. 

Moreover, the conductivity, and hence the catalytic decomposition of hydrogen peroxide, has been observed to influence the stability of the oxygen electrode. The stability of phthalocyanine catalysts is a decisive factor for the practical applicability of organic catalysts in fuel cells operating in an acid medium. This is therefore a very important observation. The observed disturbance of the delocalization of the n electrons (rubiconjugation) in Fe-polyphthalocyanines, in addition to the correlation between conductivity on the one hand, and electrocatalysis and catalytic decomposition of hydrogen peroxide on the other, leads to a special model of the electroreduction of oxygen on phthalocyanines. The model... 

Some Ni(II) complexes show catalytic activity for the electrocatalytic reduction of C02 in water, where an intermediate formation of Ni(I) species has been proposed. To obtain a useful electrocatalyst in the electroreduction of C02, the selectivity of the process is highly important. As many electrochemical systems available for reducing C02 require the presence of water, the reduction of molecular hydrogen is always a competing reaction that needs to be avoided. 

---