Preparation by Electrolytic Reduction

Although it is relatively easy to electrolyze metal tetrahydroborates (23, 275), a suitable electrolyte 

---

Europium(TTI) salts are typical lanthanide derivatives. Europium(ll) salts are pale yellow in colour and are strong reducing agents but stable in water. EuX2 are prepared from EuX -hEu (X=C1, Br, I) or EuFa + Ca EuCl2 forms a dihydrale. EUSO4 is prepared by electrolytic reduction of Eu(III) in sulphuric acid. Eu(II) is probably the most stable +2 stale of the lanthanides... 

Aldehydes are more generally prepared by electrolytic reduction of amides, the reduction of carboxylic adds being possible only when they are activated by a strongly electron-withdrawing group (58). 

The coordination chemistry in this oxidation state is essentially confined to the ions Sm", Eu and Yb . These are the only ones with an aqueous chemistry and their solutions may be prepared by electrolytic reduction of the Ln " solutions or, in the case of Eu", by reduction with amalgamated Zn. These solutions are blood-red for Sm", colourless or pale greenish-yellow for Eu" and yellow for Yb", and presumably contain the aquo ions. All are rapidly oxidized by air, and Sm" and Yb" are also oxidized by water itself although aqueous Eu" is relatively stable, especially in the dark. 

When equimolar quantities of 80a and its dication 110 are combined in acetonitrile, single electron transfer occurs and the coproportionation product was obtained (95TL2741).Tliis deeply red-colored, air-sensitive radical cation 111 showed a strong ESR signal (g = 2.0034). On the other hand, the excellent electron donor 80a could be prepared by electrolytic reduction starting from 110. It was necessary to carry out the reduction with scrupulous exclusion of oxygen. Tlius, the electrolysis of 110 at -1.10 V initially gave rise to an intense red color, which was presumably due to the formation of 111. Upon further reduction, the red color faded and the tetraaza-fulvalene 80a was isolated at a 62% yield (Scheme 45). 

I, 4-benzoquinone.4 Other methods that have been employed include the oxidation of naphthalene with hydrogen peroxide,5 the oxidation of 1,4-naphthalenediamine 6 and naphthylamine sulfonic acid 7 and the oxidation of 4-amino-1-naphthol prepared by electrolytic reduction of 1-nitronaphthalene.8... 

Nitroso compounds are usually not obtained directly but rather by reoxidation of hydroxylamino compounds or amines. Hydroxylamino compounds are prepared by electrolytic reduction using a lead anode and a copper cathode [573], by zinc in an aqueous solution of ammonium chloride [574 or by aluminum amalgam [147], generally in good yields. 

Hydroxylamine hydrochloride is prepared by electrolytic reduction of ammonium chloride. 

In 1969, Elschenbroich and Cais reported the ESR spectra of several ferrocenyl anion radicals, including benzoyl, p-tolyl, p-carbomethoxy-benzoyl, p-nitrophenyl, p-cyanophenyl, and nitroferrocene, prepared by electrolytic reduction in either acetonitrile or DMF (5S). In general, the ferrocenyl group destabilizes the anion radicals compared to a phenyl substituent. When both groups are present, delocalization of the unpaired electron into the phenyl substituent is more extensive, and the ESR spectra resemble, for the most part, anion radicals of substituted aromatics. There is small spin density in the ferrocenyl moiety, which appears as small hyperfine couplings for the cyclopentadienyl protons ortho to the point of substitution (38). 

Paramagnetic NbIV octacyanide anions have been isolated as alkali metal or tetraalkylam-monium salts. K4[Nb(CN)8] has been obtained in low yield by air- or hydrogen-peroxide-oxidation of K5[Nb(CN)8] prepared by electrolytic reduction of NbCl5 in an MeOH-KCN medium.536 K4[Nb(CN)8j 2H20 disproportionated photolytically to restore the Nbm derivative. The [Nb(CN)8]4 anion is dodecahedral in the solid all Nb—C distances are equal... 

Several NbIV alkoxo compounds have been obtained, by miscellaneous methods, but were often only poorly characterized. A series of salts containing the [NbCl5(OR)]2 anion (R = Me, Et, Pr ) has been prepared by electrolytic reduction of NbCl5 in saturated HC1-ROH solutions.7 A different experimental treatment of the initial electrolytic solution led to the diamagnetic [NbCl(OEt)3py]2, which was further converted to the extremely moisture-and oxidation-sensitive diamagnetic [Nb(OEt)4] (Scheme 5). 

Hypovanadous Chloride, vanadium dichloride, VC12.—Solutions of vanadium dichloride can be prepared by electrolytic reduction of higher chlorides,3 or by the addition of amalgamated zinc to a hydrochloric acid solution of vanadium pentoxide.4 The solution undergoes very rapid oxidation, hence the isolation of vanadium diehloride cannot... 

Reduction of add solutions of vanadium pentoxide to the tetravalent state also takes place with bismuth amalgam 5 magnesium gives the trivalent salts of vanadium, while by using zinc, zinc coated with cadmium, electrolytically deposited cadmium, or sodium amalgam in the absence of air, divalent vanadium salts are obtained in solution.7 Vanadous salts and hypovanadous salts are, however, much more conveniently prepared by electrolytic reduction of acid solutions of vanadium pentoxide in an atmosphere of carbon dioxide.8... 

A six-membered ring anion prepared by electrolytic reduction at —120 °C will rearrange spontaneously to a five-membered ring, even at low temperature and in a short period (half-life 5.3 min at -120 °C). 

Aqueous Solutions. The most stable of the ions, Eu2 +, can be readily made by reducing aqueous Eu3 1 solutions with Zn or Mg. The other ions require the use of sodium amalgam, but all three can be prepared by electrolytic reduction in aqueous solution or in halide melts.51... 

It can be seen that the activities of the amorphous alloys are lower than those of the polycrystalline catalysts. Formation of the corresponding diol was not observed on the amorphous catalysts, while the crystalline catalysts either produced the diol selectively, or a mixture of the diol and the hydroxy ketone was formed. The fundamental reason for the lower activity and higher selectivity of the amorphous alloys is their rather small surface area. Of the amorphous alloys studied, Ni-B and Ni-P alloy powders prepared by chemical reduction exhibited higher activities than those of Ni-P alloys prepared by electrolytic reduction or rapid quenching. This difference in activity can be attributed to an oxide layer covering the surface of m-P foils [Ij. It is necessary to point out, however, that the comparison of activities is based on unit catalyst weight. Obviously, this comparison does not take into account the real surface area of the nickel samples, nor active site densities. 

An unexpected transformation, the exclusive formation of ethyl 2,2,4-trimethyl-3-oxovalerate, taking place via ring scission with the participation of solvent ethanol, was observed on Ni-P foil prepared by electrolytic reduction. After preparation this foil was treated with sulfuric acid to dissolve the Cu plate used as substrate to deposit the amorphous Ni-P foil. We attribute this unusual transformation to acidic centres of the catalyst formed during the latter treatment. In an independent experiment, 1 was reacted without any catalyst in 1 M ethanolic hydrochloric acid at 398 K. The ring-opened ketoester was the only product formed, indicating that the transformation is an acid-catalysed process. The mechanism proposed to account for the selective ring-opening is to be seen in Fig. 2. 

Slow oxidation by water, rapid oxidation by air, to U . Prepared by electrolytic reduction (Hg cathode). 

Stable to water, rapid oxidation by air to Np. Prepared by electrolytic reduction (Hg cathode). Stable to water and air. Oxidizes by action of its own a-radiation to Pu . Prepared by reduction by SO2, Zn, U or H2(g) with Pi catalyst. 

Disproportionates to and U02. Most stable at pH 2.5. Prepared by electrolytic reduction of U02 " (Hg cathode) and by reduction of 002 by Zn(Hg) or H2(g). pH around 2.5 used. Stable. Disproportionates only at high acidities. Prepared by oxidation of lower oxidation states by CI2 or 0104" and by reduction of higher oxidation states by NH2NH2, NH2OH, HNO2, H2O2/HNO3, Sn + or SO2. 

Optically active arsines containing alkyl groups have recently been prepared by electrolytic reduction of optically active quaternary arsonium salts 450). The optically active arsine combines with sulfur in benzene to give the active arsine sulfide. 

---