Alkylthallium compounds

The level of soluble thallium present in the sea (e.g. Pacific Ocean, Atlantic Ocean, Irish Sea, Australian Coast) is between 9 and 16 ng/L (Matthews and Riley, 1970). This is remarkably lower than in fresh waters. In natural sea water (pH 8.1), the oxygen content is sufficient to oxidize Tl(l) to Tl(lll). because formation of chloro-complexes stabilizes the trivalent state. In the Pacific Ocean, 80% of the thallium was found to occur as Tl(lll), and only 20% as the sum of Tl(l) and alkylthallium compounds (Batley and Florence, 1975). As Tl(lll) is easily adsorbed and coprecipitated, it continuously moves down to the sediments. 

Monoalkylthallium(III) compounds are unstable (73, 79), and very few examples of this class have been isolated. A number of alkylthallium diacetates have been obtained either from oxythallation of olefins with thallium-(III) acetate (see below) or from exchange reactions such as that shown in Eq. (11) (74, 75). Only four alkylthallium dihalides have been isolated so far, namely a neopentylthallium dihalide (60) [Eq. (12)] and the isomeric 2-, 3-, and 4-pyridiomethylthallium dichlorides (20) [Eq. (13)]. Monoaryl-and monovinylthallium(III) derivatives are considerably more stable than... 

Monoalkylthallium(III) compounds can be prepared easily and rapidly by treatment of olefins with thallium(III) salts, i.e., oxythallation (66). In marked contrast to the analogous oxymercuration reaction (66), however, where treatment of olefins with mercury(II) salts results in formation of stable organomercurials, the monoalkylthallium(III) derivatives obtained from oxythallation are in the vast majority of cases spontaneously unstable, and cannot be isolated under the reaction conditions employed. Oxythallation adducts have been isolated on a number of occasions (61, 71,104,128), but the predominant reaction pathway which has been observed in oxythallation reactions is initial formation of an alkylthallium(III) derivative and subsequent rapid decomposition of this intermediate to give products derived by oxidation of the organic substrate and simultaneous reduction of the thallium from thallium(III) to thallium(I). The ease and rapidity with which these reactions occur have stimulated interest not only in the preparation and properties of monoalkylthallium(III) derivatives, but in the mechanism and stereochemistry of oxythallation, and in the development of specific synthetic organic transformations based on oxidation of unsaturated systems by thallium(III) salts. 

The utility of thallium(III) salts as oxidants for nonaromatic unsaturated systems is a consequence of the thermal and solvolytic instability of mono-alkylthallium(III) compounds, which in turn is apparently dependent on two major factors, namely, the nature of the associated anion and the structure of the alkyl group. Compounds in which the anion is a good bidentate ligand are moderately stable, for example, alkylthallium dicar-boxylates 74, 75) or bis dithiocarbamates (76). Alkylthallium dihalides, on the other hand, are extremely unstable and generally decompose instantly. Methylthallium diacetate, for example, can readily be prepared by the exchange reaction shown in Eq. (11) it is reasonably stable in the solid state, but decomposes slowly in solution and rapidly on being heated [Eq. (23)]. Treatment with chloride ion results in the immediate formation of methyl chloride and thallium(I) chloride [Eq. (24)] (55). These facts can be accommodated on the basis that the dicarboxylates are dimeric while the... 

Similarly to the reaction of arylthallium(III) compounds, the reaction of potassium iodide with (121), the product of oxythallation of alkenes, afforded the derived oxy-iodination product (123) in good yields through the alkylthallium diiodide intermediate (122). ... 

The formation of a carbon-carbon bond by reaction of alkylthallium(III) compounds has been described in the a-nitroalkylation of alkanes. The reaction of alkylthallium (129) with nitroalkane anions leads to the nitroalkyl derivatives (130). In this case, radical intermediates generated by electron transfer activation of the carbon-thallium bond are involved in a non-chain substitution process. 

Hydrodethallation of alkylthallium(iil) compounds using N-benzyl-1,4-dihydronicotinamide (BNAH) gives high yields of alkanes via an unusual homolysis of the thallium-carbon bond. On irradiation with light, BNAH also allows aliphatic nitro-groups of compounds containing cyano-, carboalkoxy-. 

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