Aptotic Media

Olah, G. A., Laali, K. K., and Sandford, G. (1992a). Comparison of the nitration of poly-fluoronitrobenzenes by nitronium salts in superacidic and aptotic media Activation of the nitronium ion by protosolvation. Proc. Natl. Acad. Sci. U.S.A. 89, 6670-6672. 

The electrochemical reduction of 02 in aptotic media is dramatically changed by the presence of electroinactive metal cations.2 Figure 9.5 illustrates the effect of a fivefold excess of [Znu(0H2)6](C104)2, [Znn(dimethylurea)6] (C104)2, and [Znu(bpy)3](C104)2 on the cyclic voltammetry of 02 in DMF at a platinum electrode. Prior to each reductive scan the electrode has been repolished a second scan yields a much reduced peak current. In the presence of an excess concentration of Zn(II) cations the reduction of 02 is a totally irreversible process, and the electrodes (Pt, Au, and C) are passivated after the initial negative scan. 

Derivatives of Sn , Ti Cr , V , Cu, Sm are well-known as reductants [108, 109]. In particular, Kagan s reagent Sml2 reduces acyl chlorides to diketones, aldehydes, and ketones to pinacols in aptotic media and to alcohols in protic media [110], It has also been applied to many other organic reactions [110], Cr salts have been extensively used to reduce alkyl- and aryl halides [109]. These reduced metal complexes have been known as reductants of transition metal ions since Taube s pioneering work [108, 109]. 

This brief review is limited to consideration of platinum group metals in aqueous solutions. Thermodynamic approaches should work in other protic solvents. However these solvents are always of organic nature, and the experimental measurements of any thermodynamic quantities are complicated by irreversible dissociative adsorption of organic species. Another interesting field, still separated, is platinum electrochemistry in aptotic media. 

Kojima H, Bard AT (1975) An A.C. technique for determining the rates of rapid electrode reactions of aromatic compounds in aptotic media. J Electroanal Chem Interfacial Electrochem 63(2) 117-129. doi 10.1016/S0022-0728(75)80285-3... 

Vsndevan D, Wendt H. Electrorednction of oxygen in aptotic media. J Electroanal Chem 1995 392 69-74. 

Saha MS, Ohsaka T. Electrode kinetics of the 02/02-redox conple at Hg electrode in the presence of PVC in aptotic media. Electrochim Acta 2005 50 4746-51. 

Imino lactones, such as (22), can be reduced cleanly to the morpholinone (23) in an aptotic medium using diethyl malonate as a mild proton donor (equation 9). The electroreductive behavior of this class of activated imines is presently under study. 

The synthesis starts from anthranilic acid which is first diazotized and the selenium introduced by treatment of the diazonium salt with Li2Sc2, obtained from elemental lithium and selenium in an aptotic medium <1993LA1239> or better with Na2Se2, prepared in advance by the reaction of selenium powder, 100% hydrazine hydrate, and sodium... 

The extent to which rearrangement occurs depends on the structure of the cation and foe nature of the reaction medium. Capture of carbocations by nucleophiles is a process with a very low activation energy, so that only very fast rearrangements can occur in the presence of nucleophiles. Neopentyl systems, for example, often react to give r-pentyl products. This is very likely to occur under solvolytic conditions but can be avoided by adjusting reaction conditions to favor direct substitution, for example, by use of an aptotic dipolar solvent to enhance the reactivity of the nucleophile. In contrast, in nonnucleophilic media, in which fhe carbocations have a longer lifetime, several successive rearrangement steps may occur. This accounts for the fact that the most stable possible ion is usually the one observed in superacid systems. 

The significance of the medium for diis type of reaction accounts also for unsuccessful attempts to achieve Pd catalyzed cyclizations of various 2,7-octadienyl acetates in aptotic solvents. Nevertheless, Pd° catalyzed cyclization of 4-alkyl-4-hydroxy-2,7-octadienyl acetates such as (178), (181) and (184) were really accomplished in boiling acetonitrile. Some of these (presumably hydroxy assisted) ring closures led preferentially to products with cif-related hydroxy and vinyl groups, e.g. (179) and (182) (Scheme 38). 

Shukla SK, Murulana LC, Ebenso EE (2011) Inhibitive effect of imidazolium based aptotic ionic liquids on mild steel corrosion in hydrochloric acid medium. Int J Electrochem Sci 6 (9) 4286-4295... 

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