By Cathodic Reduction of

Hexaorganodistannanes can also be prepared by electrochemical reduction of triorgano-tin salts, particularly the formates, in an undivided cell consisting simply of a beaker with a stainless steel cathode and carbon anode (equation 18-28).31 

In a related reaction, hexakis(2-cyanoethyl)distannane, (NCCH2CH2)3SnSn(CH2CH2CN)3, can be prepared in 50% yield by the electrolysis of an aqueous alkaline solution of acrylonitrile with a sheet tin cathode and platinum gauze anode.32,33 

The emphasis of most other electrochemical studies, however, has been on the formation of polystannanes, (R.2Sn) , from difunctional compounds R3SnX2 (see below). 

Examples of acyclic and cyclic oligostannanes are given in Table 18-1 some di- and tri-stannaferrocenophanes are described in Section 9.3.4 

Homolysis of the SnSn bond can be induced by irradiation with UV light, and the quantum yield can be increased by adding di-t-butyl peroxide or a ketone, when stannyl radicals are also produced by the Sh2 reaction of the t-butoxyl radical (equations 18-35 and 18-36) or ketone triplet (equation 18-37), respectively, at tin.45-46 

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Ethyl radicals can be produced in various ways for instance, by cathodic reduction of ethyl bromide ... 

Analysis by cathodic reduction of triphenyltin acetate in pesticide preparations131 and in samples from marine sources132 can reach detection limits of 1CT8 M to 2.5 x 10 9 M,... 

The fact that most pulp and paper applications use dilute solutions of hydrogen peroxide in alkali has kindled interest in the electrosynthesis of alkaline peroxide solutions by cathodic reduction of oxygen. 

It can be pointed out that results are not reproducible, depending on the quality of the cobalt salt used and particularly of the ZnBr2. This last species should be produced preferably by cathodic reduction of 1,2-dibromoethane combined with the anodic oxidation of a zinc anode according to Scheme 5 (see Section . ). 

The indirect electrochemical reduction of alkyl halides is also possible by use of nickel(I) complexes which may be obtained by cathodic reduction of square planar Ni(n)-complexes of macrocyclic tetradentate ligands (Table 7, No. 10, 11) 2 4-248) Comparable to the Co(I)- and Ni(O)-complexes, the Ni(I)-species reacts with the alkyl halide unter oxidative addition to form an organo nickel(III) compound. The stability of the new nickel-carbon bond dominates the overall behavior of the system. If the stability is low, the alkyl group is lost in form of the radical and the original Ni(II)-complex is regenerated. A large number of regenerative cycles is the result. 

R NCIO system also makes the medium acidic, however the strength of the EGA is much weaker than that of a CH Clj—LiClO system due to neutralization of EGA with trialkyl amine produced by cathodic reduction of the ammonium cation Therefore, an EGA-catalyzed reaction can be performed even in a CH Cl — —R NCIO or MeCN—R NCIO system when a divided cell is employed. Presumably, amines generated in the cathode compartment diffuse slowly into the anode compartment where the EGA reaction occurs. 

The formation of TAA-metals by cathodic reduction of TAA+ cations at several solid electrodes has recently been reported n. These coloured materials were observed at Hg, Pb, Sn, Bi and Sb cathodes, while Pt and Cr were unreactive. They all act as reducing agents and seem to incorporate both TAA+ and metal atoms (from the cathode) into their structure. They behave similarly and are probably related to the compounds resulting from the reduction of TAA+ at graphite cathodes 2). The best known and most extensively studied TAA-metals are those generated at mercury cathodes. They are also the likely catalysts for the organic electroreductions described below. Because TAA-mercury may be pervasively involved in the preparative reductions which are the topic of this review, the next few paragraphs provide information about their composition and evidence for their involvement as catalysts. 

Cathodic reduction 67) of 2,3-dihydrobenzofuran (5(5) was also achieved. The optimum conditions were 0.25 M (C4H9)4NBF4 in THF-4% H20 and a constant low current (4 mA cm-2). The reactant was consumed after transfer of charge equivalent to 3 F mol-1 and the product was the tetrahydrobenzofuran (57) in 59% yield. Tetra-hydrobenzofuran (57) could also be obtained directly by cathodic reduction of benzo-furan (55) when charge in excess of 2 F mol-1 was transferred. 

The reduction of compounds suitably substituted with reducible functional groups can be advantageously used for the preparation of heterocyclic ring systems 15 5 The guiding principle here is to form a nucleophilic center in the molecule by cathodic reduction of a functional group and then have this to react with an electrophilic center (which may also be formed in an electrochemical process or be present in the starting material) suitably positioned for ring closure. Thus, 2,2-dinitrobiphenyl can be reduced to benzo[c] cinnoline in acid solution ... 

Anions generated by cathodic reduction of carbonyl compounds, benzyl-chloride or activated double bonds can be trapped by addition to C02. With benzophenone the carbonate of benzilic acid was obtained (Eq. (134) ) 304 ... 

Tetralelluride anions were generated by cathodic reduction of tellurium at — 1.4 V in a cell consisting of a tellurium cathode and a platinum-net anode. AIM solution of dry sodium perchlorate in dimethylformamide served as the catholy te. The tetratelluride ions were then reacted with alkyl halides to yield the corresponding dialkyl ditellurium5. 

Ammonium Amalgam. The similarity of the ammonium ion to an alkali ion suggests that it might be possible to reduce ammonium ion to ammonium metal, NH. This has not been accomplished however, a solution of ammonium metal in mercury, ammonium amalgam, can be made by cathodic reduction of ammonium ion. 

Whereas the lithium aluminium hydride reduction of an optically active benzylphos-phonium salt in tetrahydrofuran leads to a racemic or highly racemized tertiary phosphine and toluene, the reduction of (—)-benzyl(n-butyl)methylphenylarsonium bromide (68) or (S)-(-(-)-benzylmethylphenyl(n-propyl)arsonium bromide, (S)-(-I-)-64, with this reagent affords (—)-n-butyImethylphenylarsine, ( —)-12, or (S)-(-l-)-methyl-phenyl(n-propyl)arsine, (S)-(-)-)-65, of similar optical purity to the products obtained by cathodic reduction of the respective arsonium compounds (Table 4) . Moreover,... 

The radical formed by cathodic reduction of 3,5-diaryl-1,2-dithiolium cations can undergo further reduction, giving a 1,3-diaryIpropane-1,3-dithionate anion, which can be oxidized back to the corresponding radical and then to the 1,2-dithiolium cation. 

Aldoximes may be transformed into nitriles via nitrile oxides, obtained by indirect anodic oxidation of the aldoxime in methanol, followed by cathodic reduction of the nitrile oxide [92]. 

This reaction has been employed for the synthesis of saturated and unsaturated amino acids by cathodic reduction of azidocinnamic esters [237]. Reduction of azides in DMF in the presence of acetic anhydride yields diacetylated amines [237]. Azide groups in activated methylene groups may, however, be reduced to azide ion and methyl compound [236]. 

Photovoltage spectra are measured at open circuit using chopped light of low intensity. It might appear that an advantage of photovoltage spectroscopy over photocurrent spectroscopy is that no photocorrosion occurs. However, this is not necessarily correct, because anodic photocorrosion in the illuminated areas may be balanced by cathodic reduction of solution species such as oxygen or protons. 

Recently, the benzoin condensation of aromatic or heteroaromatic aldehydes (in the absence of VOCs and bases) catalysed by NHCs, obtained by cathodic reduction of RTILs, has been reported. a-Hydroxyketones have been isolated in good to elevated yields, in short reaction time. No a-hydroxyketones have been obtained from linear or short-branched aldehydes instead aldol products and carbene-aldehyde adducts have been isolated in elevated yields (Scheme 16.22) [150,151]. 

Scheme 16.22 Benzoin condensation catalysed by NHCs obtained by cathodic reduction of RTILs (Reprinted from Ref. [151] with kind permission of Elsevier)...

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