Hydrogen sulfide electron-transfer reactions with

Apparently the alkoxy radical, R O , abstracts a hydrogen from the substrate, H, and the resulting radical, R" , is oxidized by Cu " (one-electron transfer) to form a carbonium ion that reacts with the carboxylate ion, RCO - The overall process is a chain reaction in which copper ion cycles between + 1 and +2 oxidation states. Suitable substrates include olefins, alcohols, mercaptans, ethers, dienes, sulfides, amines, amides, and various active methylene compounds (44). This reaction can also be used with tert-huty peroxycarbamates to introduce carbamoyloxy groups to these substrates (243). 

Since LAW and H2LAW are present at much lower concentrations than hydrogen sulfide, the redox potential, (pH) of the system is essentially determined by Eq. 21 with [H2S]T = 5x 10 3M. Hence, in analogy to a pH buffer for proton-transfer reactions, the H2S/S(s) couple is used as a redox buffer for electron transfer. 

In this case, a plot of log krcl versus h(W) for a series of substituted nitrobenzenes should yield a straight line with a slope of (1/0.059), which as is shown in Figure 9, is actually found for the compounds listed in Table 7. Hence, for the reduction of neutral substituted nitrobenzenes in homogeneous aqueous hydrogen sulfide solution with lawson as electron-transfer mediator, the relative reaction rate of a given compound may be predicted from its one-electron reduction potential. Similar results have been obtained for the same set of compounds with another quinone (i.e., 5-hydroxynaphthoquinone (reaction 10 in Table 5) see Schwarzenbach et al. (in press b). 

Reduced ferredoxin reacts with proteins that participate in the dissimilatory reduction of sulfate to sulfide oxidized ferredoxin reacts with pyruvate dehydrogenase that catalyzes the conversion of pyruvate to acetyl CoA (phosphoroclastic reaction). In sulfate reduction, molecular hydrogen is the electron source, and in the phosphoroclastic reaction, protons are the terminal electron acceptor and hydrogenase mediates electron transfer between cytochrome c3 and protons or molecular hydrogen. 

Direct pyrolysis in the ion source of a mass spectrometer (DPy-MS) operating both in electron impact and chemical ionisation modes was used in these studies. Flash Py-GC-MS was also used in the case of polythiomethylene to confirm the DPy-MS results. The overall evidence indicated that the primary thermal decomposition of these polymers yielded a wide range of cyclic sulfides by an intramolecular exchange process. A 3-CH hydrogen transfer reaction, occurring in parallel with the former process, produced primary pyrolysis compounds with SH end-groups. 

By the reaction of iodine and small amounts of liquid ammonia at -75° a black brown solid is formed. A tensimetric deammonation shows that this solid is an addition compound of iodine and ammonia with 2 moles of ammonia per mole of iodine. Further deammonation effects formation of a compound Ij.NH finally, I remains. Ammonolysis of iodine takes place only to a small extent. These brown addition compounds of iodine correspond to the well known brown addition compounds of iodine and ether, alcohol, pyridine or liquid hydrogen sulfide respectively and are looked upon as charge-transfer complexes with iodine as electron acceptor and the solvents as electron donors. This view was proved by the measurement of the charge transfer band of iodine-ammonia in heptane at 229 m i (2). 

This first example is relevant for environments where reduced sulfur species (e.g., HS") are present (e.g., produced by microbial sulfate reduction). As already mentioned above, in the presence of hydrogen sulfide, dissolved natural organic matter (NOM) constituents may act as electron transfer mediators for NAC reduction (Figure 4). Such NOM constituents most probably include hydroquinone structures (11,60,64), and sulfur derivatives that result from addition reactions of quinone type structures with hydrogen sulfide (54). Dunnivant et al. (11) found that pseudo-first-order reduction rate constants, kobs (Figure 4), determined for a series of substituted nitrobenzenes and nitrophenols were proportional to NOM concentrations. For a given compound and at given conditions (T, pH, [H2S]tot), they calculated a carbon-normalized second-order rate constant, k oM... 

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