Hydrogen catalytic evolution

In contrast, sulphoxides appear to possess a more classical behaviour in electrochemistry, due to their intermediate oxidation state which allows, in most of the cases, their reduction to sulphides but also their oxidation to sulphones with no cleavage process. Moreover, the increase of the sulphur atom basicity may also produce catalytic hydrogen evolution in acidic solution. 

The Co(II) -phenylthiourea-borax buffer system has been studied applying CSV at HMDE [69]. An irreversible peak observed at —1.5 V was attributed to the catalytic hydrogen evolution. The first reduction step, combined with the adsorptive accumulation of herbicide metribuzin at mercury electrode, has been used for its determination by adsorptive stripping voltammetry [70]. 

Lund reported the major product of the reduction of 2- and 4-acid 56 to be the aldehydes 41 and 42, respectively94 a recent report confirmed these results in the case of 2-(56).95 Somewhat contrary to these citations, Brown et al. indicated that the 2-aldehyde (41) was formed in low yield and that with acetate buffer the major product was carbinol 29.96 When rotating disc electrodes were used, the reduction products of 2- and 4-(56) were the aldehydes, but 3-(56) gave only catalytic hydrogen evolution.97... 

Kaur-Ghumaan S, Schwartz L, Lomoth R, Stein M, Ott S. Catalytic hydrogen evolution from mononuclear iron(II) carbonyl complexes as minimal functional models of the [FeFe] hydrogenase active site. Angew Chem Int Ed. 2010 49(43) 8033-6. 

Of some relevance to this review is adenine, which is a component of nucleic acids, and of key nucleotide coenzymes like NAD". This base, and its nucleosides and nucleotides 35>, exhibit a single reduction wave, with about the same total current as the parent purine, of the magnitude expected for a 4e process15,153). On controlled-potential electrolysis, however, it undergoes a 6e reduction to give the same product as does purine in its overall 4e reduction 15,35,36 153), as shown in Scheme 25. The reduction of adenine is accompanied by catalytic hydrogen evolution, so that it is not possible to determine directly the number of electrons involved. 

Catalytic hydrogen wave - catalytic hydrogen evolution... 

Attempts to support models of the catalytic activity and the operative mechanism with results of theoretical considerations have been reported for the oxygen reduction [iii] and hydrogen oxidation [iv]. Electrocatalytic electrodes are indispensable parts of fuel cells [v]. A great variety of electrocatalytic electrodes has been developed for analytical applications [vi]. See also electro catalysis, catalytic current, -> catalytic hydrogen evolution, catalymetry. 

See also - bifunctional mediator, - biofuel cells, -> catalytic current, - catalytic hydrogen evolution, - dye cell, -> enzyme electrodes, -> ferrocene, - glucose sensor, -> indirect and direct electrolysis, and - surface-modified electrodes. 

Pyridine is not polarographically reducible in aqueous media in MeCN catalytic hydrogen evolution is the main reaction of protonated pyridine at the cathode [224]. Pyridine can, however, be reduced to piperidine at a lead cathode in 10% H2SO4 [225] the yield is very dependent on the purity of the lead and other components. Side products are a,a, a,y-, and y,)/-dipiperidyl. Pyridine may be reduced to a dimer in liquid ammonia [226]. In MeCN pyridine is reduced in a two-electron wave dihydropyridine and cyanomethylated tetra-hydropyridine are formed, the latter by attack of (CH2CN) on the dihydropyridine [227]. Electrochemical synthesis involving pyridine and its derivatives has been reviewed [Ic]. 

Roy S, Mazinani SKS, Groy TL, Gan L, Tarakeshwar P, Mujica V, Jones AK (2014) Catalytic hydrogen evolution by Fe(II) carbonyls featuring a dithiolate and a chelating phosphine. Inorg Chem 53(17) 8919-8929. doi 10.1021/ic5012988... 

The potentiostatically accumulated species is determined voltammetrically by reduction or oxidation of the central atom or of the ligand of the metal chelate complex or via catalytic hydrogen evolution. Adsorbed organic molecules can be determined in an analogous way by the oxidation or reduction of their electroactive functional groups. 

An example of the first kind is the behaviour of A -3-ketosteroids.< ) The protonized forms of these substances are reduced in well developed waves usually between pH 4 and 7. At lower pH-values the wave is obscured by catalytic hydrogen evolution. Moreover, the well developed waves of the unprotonized form are observed in OT n lithium hydroxide containing 50 per cent ethanol. Between pH 8 and 10 two waves are observed, which are interesting from the theoretical point of view, but not very suitable for analytical purposes. 

Mairanovskii defended his Ph.D. thesis in 1953. The new theory of catalytic hydrogen evolution (B and DH are the catalyst and proton dmior) was a part of that thesis ... 

See also -> catalytic current, -> catalytic hydrogen evolution, electrocatalysis. 

Figure 5. (a) Probable scheme of the catalytic hydrogen evolution in the Brdicka reaction, (b) Real voltammograms of 20 fmol metallothionein (red line) and the Brdicka s solution as a supporting electrolyte containing 1 mM Co(NH3)5Cl3 and 1 M NH3(aq ) + NH4CI, pH 9.6 (black line). Parameters of DPV method were as follows initial potential -0.35 V, end potential -1.8 V, modulation time 0.057 s, time interval 0.2 s, step potential 1.05 mV/s, modulation amplitude 250 mV, time of accumulation of MT 120 s, Eads = 0 V. All measurements were carried at temperature of 5 °C. 

With some tetrazolium salts Jambor discovered anomalies which he attributed to adsorption prewaves and catalytic hydrogen evolution waves [170]. 

Like catalytic hydrogen evolution, catalytic proton transfer may have surface or volume characteristics, i.e., the transfer may occur onto a compound adsorbed at the electrode or onto a depolarizer in the vicinity of the electrode. If small amounts of the strongly adsorbed polyvinyl alcohol are added to the solution, at the moment when the electrode surface is completely covered with this compound the surface kinetic reduction current of protonated propiophenone decreases almost to zero (Curves 1, Fig. 27). If pyridine catalyst is added to the solution, reduction current for the protonated propiophenone is also observed on the completely covered electrode surface (Curves 2-4, Fig. 27), and even a considerable increase in the... 

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