Cerium-based reagent

A review has focused on differentiation between polar and SET mechanisms through kinetic analysis.82 hi two separate reviews, the effects of solute-solvent interactions on electron-transfer reactions have been described.83,84 A review of the behaviour of radical cations in liquid hydrocarbons has given particular emphasis to those with high mobility.85 A paper presents selected studies in the formation of radicals by oxidation with manganese- or cerium-based reagents and then- application to C—C bond formation by SET processes.86... 

Titanium- and cerium-based reagents have been used to prepare binaphthol structures [95, 96]. Jiang showed that treatment of 2-naphthol (68a) with cerium(IV) ammonium nitrate (CAN) leads to the biaryl product 69a in yields of around 90 % (Scheme 32). Crosscoupling of differently substituted naphthols can be accomplished using the same reagents, albeit in lower yields. 

Alternatively, Pb(OAc)4 or (NH4)2Ce(N03)6 are reagents known for generating alkoxyl radicals from alcohols. " However, exposure of alcohol 22 to the lead-based reagent resulted in the formation of aldehyde 15 among other unidentified products, while the cerium-based reagent led to decomposition of the starting materials. 

To determine of Ce(IV) in acid soluble single crystals, a simple and sensitive method is proposed. The method is based on the reaction of tropeoline 00 oxidation by cerium(IV) in sulfuric acid solution with subsequent measurement of the light absorption decrease of the solution. The influence of the reagent concentration on the analysis precision is studied. The procedure for Ce(IV) determination in ammonium dihydrophosphate doped by cerium is elaborated. The minimal determined concentration of cerium equal to 0.04 p.g/ml is lower than that of analogous methods by a factor of several dozens. The relative standard deviation does not exceed 0.1. 

Redox titrants (mainly in acetic acid) are bromine, iodine monochloride, chlorine dioxide, iodine (for Karl Fischer reagent based on a methanolic solution of iodine and S02 with pyridine, and the alternatives, methyl-Cellosolve instead of methanol, or sodium acetate instead of pyridine (see pp. 204-205), and other oxidants, mostly compounds of metals of high valency such as potassium permanganate, chromic acid, lead(IV) or mercury(II) acetate or cerium(IV) salts reductants include sodium dithionate, pyrocatechol and oxalic acid, and compounds of metals at low valency such as iron(II) perchlorate, tin(II) chloride, vanadyl acetate, arsenic(IV) or titanium(III) chloride and chromium(II) chloride. 

Reductions of cyclic enediones by NaBH4 in the presence of CeCl3 are controlled by accessibility for complexation by the Lewis acid and therefore more regioselective than those conducted without complexation.239 This combination of reagents in MeOH has been used for the selective reduction of a decalin-based ketone from the more hindered, equatorial face of the molecule.240 Use of 1.4 equiv. of NaBH4 and 1.1 equiv. of CeCl3 at high dilution (0.005 m) and low temperature (—95 °C) led to a 95 5 ratio of the axial to equatorial alcohol (compared with a 20 80 ratio in the absence of cerium). 

Compared to iron(III), copper(ll), and especially manganese(III) and cerium(IV) other metals have found less application for the oxidative generation of radicals [1]. An exception is cobalt(III)-mediated radical reactions, based on the pioneering work of Iqbal et ah, which was recently reviewed [20] (see also Volume 1, Chapter 1.8). Some examples of oxidative couplings of silyl enol ethers 44 in the presence of silver(I) oxide were developed [21]. However, there is no advantage over copper(II)-mediated radical reactions, since the reagent is more expensive and the 1,4-diketones 45 are isolated in only moderate yield (Scheme 15). 

The coulometry methods based on the physical law which sets the link between the weights of turned electricity and quantity of spent electricity. In many cases the electro generated coulometrical titrate enters in the oxidation process with organic substratum on the mechanism of reaction with the electron carriers. The most effective carriers ate the variable valence metals ions and its components oxidants—chrome (VI), manganese (III), cobalt (III), cerium (IV), vanadium (V), copper (II) deoxidants—cobalt (II), chrome (II), vanadium (HI), titanium (III), iron (II), copper (I), tin (II). The wide area of practical use of the halide ions (chloride-, bromide-, iodide-ions) highlights them apart Ifom a number of reagents—electron carriers. Halide—ions are... 

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