Electron transfer agents

Most metal carbonyls are synthesized in nonaqueous media. Reactive metals, such as sodium (85), magnesium (105), zinc (106), and aluminum (107,108), are usually used as reducing agents. Solvents that stabilize low oxidation states of metals and act as electron-transfer agents are commonly employed. These include diethyl ether, tetrahydrofiiran, and 2-methoxyethyl ether (diglyme). 

Butyroin has been prepared by reductive condensation of ethyl butyrate with sodium in xylene, or with sodium in the presence of chloro-trimethylsilane. and by reduction of 4,5-octanedlone with sodium l-benzyl-3-carbamoyl-l,4-dihydropyridine-4-sulfinate in the presence of magnesium chloride or with thiophenol in the presence of iron polyphthalocyanine as electron transfer agent.This acyloin has also been obtained by oxidation of (E)-4-octene with potassium permanganate and by reaction of... 

The second step involves the transfer of electrons from the reduced [FMNHg] to a series of Fe-S proteins, including both 2Fe-2S and 4Fe-4S clusters (see Figures 20.8 and 20.16). The unique redox properties of the flavin group of FMN are probably important here. NADH is a two-electron donor, whereas the Fe-S proteins are one-electron transfer agents. The flavin of FMN has three redox states—the oxidized, semiquinone, and reduced states. It can act as either a one-electron or a two-electron transfer agent and may serve as a critical link between NADH and the Fe-S proteins. 

Cytochrome c oxidase contains two heme centers (cytochromes a and %) as well as two copper atoms (Figure 21.17). The copper sites, Cu and Cug, are associated with cytochromes a and respectively. The copper sites participate in electron transfer by cycling between the reduced (cuprous) Cu state and the oxidized (cupric) Cu state. (Remember, the cytochromes and copper sites are one-electron transfer agents.) Reduction of one oxygen molecule requires passage of four electrons through these carriers—one at a time (Figure... 

Mr 220-250 kDa. Figure 1 shows an overall electron transfer pathway for the nitrogenases where the Fe proteins act as very specific, essential electron donors to the larger proteins. This is not the only role for the Fe proteins (see Section IV,C) and their role in the mechanism is almost certainly more complex than that of a simple electron transfer agent (see below. Section V). Electron transfer from the Fe protein to... 

Deinococcus radiodurans strain Rl Anaerobic cultures grown with lactate could reduce chromate, although reduction was increased by the presence of electron transfer to AQDS. Reduction of U(VI) and Tc(VII) could also be accomplished in the presence of the electron transfer agent (Fredrickson et al. 2000). 

All of the following ejqperiments were conducted with the photocatalyst and electron transfer agent in the reactor. 

The reduction of tetrazolium salts by NADH is greatly accelerated by electron transfer agents (ETAs) such as phenazine methosulfate (PMS 233) or its derivatives.451-454 Other classes of ETAs such as quinones.455,456 ferricinium,457 phenothiazine,458 the viologens,459 acridiniums,460 and phe-nazinium or quinoxalinium salts461 as well as the enzyme diaphorase462 have been used. 

Morozov and co-workers electrochemically demonstrated the pyridazine ring fragmentation induced by electron transfer agents. This reaction proceeded by elimination of chloride ions, cleavage of the pyridazine ring, and the formation of phthalonitrile 202 from 201 <00MC34>. 

The synthetic importance of non-nucleophilic strong bases such as lithium diisopro-pylamide (LDA) is well known but its synthesis involves the use of a transient butyl lithium species. In order to shorten the preparation and make it economically valuable for larger scale experiments an alternate method of synthesis has been developed which also involves a reaction cascade (Scheme 3.14) [92]. The direct reaction of lithium with diisopropylamine does not occur, even with sonication. An electron transfer agent is necessary, and one of the best in this case is isoprene. Styrene is used in the commercial preparation of LDA, but it is inconvenient in that it is transformed to ethylbenzene which is not easily removed. It can also lead to undesired reactions in the presence of some substrates. The advantages of isoprene are essentially that it is a lighter compound (R.M.M. = 68 instead of 104 for styrene) and it is transformed to the less reactive 2-methylbutene, an easily eliminated volatile compound. In the absence of ultrasound, attempts to use this electron carrier proved to be unsatisfactory. In this preparation lithium containing 2 % sodium is necessary, as pure lithium reacts much more slowly. 

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