Electrochemically induced chemical

Fig. 6.5 Schematic illustration of CdS film growth by electrochemically induced chemical deposition (EICD) method. 71...

Electrochemically Induced Chemical Deposition (EICD) of CdS Thin Films... 

Tan SLJ, Webster RD (2012) Electrochemically induced chemically reversible proton-coupled electron transfer reactions of riboflavin (Vitamin B2). J Am Chem Soc 134(13) 5954-5964... 

II. Ease of electrical connection Here the main problem is that of efficient electrical current collection, ideally with only two electrical leads entering the reactor and without an excessive number of interconnects, as in fuel cells. This is because the competitor of an electrochemically promoted chemical reactor is not a fuel cell but a classical chemical reactor. The main breakthrough here is the recent discovery of bipolar or wireless NEMCA,8 11 i.e. electrochemical promotion induced on catalyst films deposited on a solid electrolyte but not directly connected to an electronic conductor (wire). 

Yamaguchi K, Yoshida T, Sugiura T, Minoura H (1998) A Novel approach for CdS thin-film deposition electrochemically induced atom-by-atom growth of CdS thin films from acidic chemical bath. J Phys Chem B 102 9677-9686... 

Principles and Characteristics Contrary to poten-tiometric methods that operate under null conditions, other electrochemical methods impose an external energy source on the sample to induce chemical reactions that would not otherwise occur spontaneously. It is thus possible to analyse ions and organic compounds that can either be reduced or oxidised electrochemi-cally. Polarography, which is a division of voltammetry, involves partial electrolysis of the analyte at the working electrode. 

Opening and shortening of the tubes is a sought-after event for certain applications and can be induced ad hoc by different techniques such as ball milling, mechanical cutting, electrochemically and chemically. The open tips can be closed again if required [14]. 

The use of controlled potential electrolysis of fullerenes has thus far been used as a synthetic tool in two general ways. One method has involved the preparation of fullerene derivatives from the reaction of electrochemically generated anions of the pristine cages with electrophiles. The second method has involved an electrochemically induced retro-synthetic reaction of fullerene derivatives, which results in a number of different products, some of which have not been achieved by chemical synthesis. Both methods are described in the following, but special... 

Yamagnchi et al. described an interesting extension of the CD process for CdS ns-ing a parallel electrochemical step [66]. They termed this process electrochemi-cally induced chemical deposition. It is based on electroreduction of protons in so-Intion, which resnlts in an increase in pH locally at the electrode. They nsed thioacetamide as a snlphnr sonrce. In the acid solutions in which the deposition is carried ont (pH between 1.6 and 4.6), no film deposition of CdS occurs (although it does precipitate in the solntion) in the absence of the electrochemical proton re-dnction. In the presence of proton rednction, CdS films were formed. These films... 

Methyl viologen (/V, /V - d i m e t h I -4,4 - b i p r i d i n i u m dication, MV2+ ) can function as an electron acceptor.34 When MV2+ is linked to electron donor, photoinduced electron transfer would occur. For example, within molecule 24 the 3MLCT excited state of [Ru(bpy)3]2+ is quenched by MV2+ through oxidative electron transfer process. The excited state of [Ru(bpy)3]2 + can also be quenched by MV" + and MV°. The transient absorption spectroscopic investigations show that the quenching of the excited state of [Ru(bpy)3]2+ by MV + and MV° is due to the reductive electron transfer process. Thus, the direction of the photoinduced electron transfer within molecule 24 is dependent on the redox state of MV2 +, which can be switched by redox reactions induced chemically or electrochemically. This demonstrates the potential of molecule 24 as a redox switchable photodiode.35... 

Cleavage of a C—S bond in the initially formed anion radical has been shown to be the first chemical step in the electrochemically induced rearrangement of 5,5-diarylbenzene-1,2-dicarbothioates to 3,3-bis(arylthio)phthalides in dimethylformamide. The reaction can be effected with 0.1 F/mol and is considered a kind of internal SRN1 reaction (Praefke et al. 1980). 

SECM employs an UME probe (tip) to induce chemical changes and collect electrochemical information while approaching or scanning the surface of interest (substrate). The substrate may also be biased and serve as the second working electrode. The nature of the tip and the way it interacts with the substrate determine what information can be obtained in an SECM experiment. Many different types of UMEs have been fabricated, for example, microband electrodes, cylindrical electrodes, microrings, disk-shaped, and hemispherical electrodes [10, 11]. For reasons discussed below, the disk geometry is preferred... 

Halary-Wagner, E., Wagner, F. and Hoffmann, P. (2004). Titanium dioxide thin-film deposition on polymer substrate by light induced chemical vapor deposition. J. Electrochem. Soc. 151(9), C571-C576. 

The mass transfer and chemical reaction between a single microdroplet and the surrounding solution phase can be induced by the laser and microcapillary manipulation and microelectrochemistry system. An example of the electrochemically induced mass transfer across a single microdroplet/solution interface is shown in Figure 9.3. If... 

An interesting example of sullur-bridged systems is shown in equation (27). The disulftir-bridged dianion does not contain a metal bond. Chemical or electrochemical oxidation generates the neutral species that does have a metal metal bond. This process of electrochemically induced changes in bond order will be discussed below for porphyrin complexes as well. 

Radical ions are created in solution by chemically or electrochemically induced electron transfer to or from a conjugated ir-system. Even if these ions are thermodynamically stable they are only of limited persistence since they are susceptible to reactions with electrophiles and nucleophiles or undergo other processes like dimerization or electron-transfer induced bond cleavage [9, 10]. Pairs of radical anions and radical cations can also be formed by electron transfer between neutral donors and acceptors either in the ground state or upon photochemical excitation [11, 12]. 

The catalytic substitution reactions of metal carbonyl clusters, including [M3(CO)i2] (M = Fe, Ru, or Os), [Ru4H4(CO)i2], [Rh6(CO)i6], and [Co3(CO)9(/it-CCl)], with isocyanides or Group V-donor ligands may be induced by either electrochemical or chemical (benzophenone ketyl) reduction. The most favorable conditions for efficient substitution include (1) the formation of a radical anion with a significant lifetime and (2) the use of a ligand which is not reduced by [Ph2CO], and which is less of a tt acid than CO (166). 

These cyclizations both involve the reductive intramolecular addition of an electron deficient alkene function to an aldehyde carbonyl function, and both are effected in ca 90 % yields. The mechanism of this latter type of electrochemically induced cyclizations of carbon-carbon double bonds to carbonyl double bonds have been studied rather extensively, with especial attention to the fundamental mechanistic question of whether the cyclization step involves an anion radical, radical, or anionic mechanism [122]. The latter two mechanisms would involve the protonation of the initially formed anion radical intermediate to form a radical, which could then cyclize or, alternatively, be further reduced to an anion, which could then cyclize. Extensive and elegant electrochemical and chemical studies have led to the formulation of these reactions as involving anionic cyclization (Scheme 74). 

Figure 30. An example of externally induced ring rotation in a [2]catenane [92]. The motion could be triggered either electrochemically or chemically.

Of these three systems, Cu.31 is the most promising compound in relation with electrochemically induced molecular motions, due to the perfect chemical reversibility of the processes. Interestingly, the rates of the movements in rotaxane Cu.31 are very different from those measured for the related catenane Cu.25 (see Section 8.5) [95-97]. The conversion Cu"(4) to Cu"(5) is faster in Cu.31 than in Cu.25. This difference could reflect a greater ability of Cu (4j in Cu.31 to interact with solvent molecules or anions, the copper(ll) center being perhaps loosely bound to a fifth ligand which would thus stabilize intermediate states on the way to Cu"(5). 

---