Compounds of Thallium

Intermetallic compounds with gallium are used as semiconductors. Indium is used to coat other metals to protect against corrosion, especially in engine bearings it is also a constituent of low-metal alloys used in safety sprinklers. The toxicity of thallium compounds has limited the use of the metal, but it does find use as a constituent of high-endurance alloys for bearings. 

The relative toxicities of thallium compounds depend on their solubHities and valence states. Soluble univalent thallium compounds, eg, thaHous sulfate, acetate, and carbonate, are especiaHy toxic. They are rapidly and completely absorbed from the gastrointestinal tract, skin peritoneal cavity, and sites of subcutaneous and intramuscular injection. Tb allium is also rapidly absorbed from the mucous membranes of the respiratory tract, mouth, and lungs foHowing inhalation of soluble thallium salts. Insoluble compounds, eg, thaHous sulfide and iodide, are poorly absorbed by any route and are less toxic. 

Eor laboratory use, cyclopentadienylthalLium [34822-90-7] reacts cleanly with TiX compounds, where X is halogens (258—264). The cost and toxicity of thallium compounds ate drawbacks to large-scale use. However, Cp2Pb may, in certain cases, be useful (see Lead compounds Thallium and thallium compounds) (265). 

For both classes of compounds, the chemistry of the group 13 trivalent and monovalent complexes proceeds similarly for Al, Ga, and In, and so these complexes will be treated together. Much of the chemistry of thallium compounds tends to be unique and will largely be handled separately. 

CAUTTON Thallium salts are very toxic when inhaled, ingested, or absorbed through the skin. Appropriate safety precautions and procedures should be taken when handling and disposing of thallium compounds. 

Effect of Thallium on Plants and Animals. On January 29, 1863, R. C. Bottger announced that he had detected spectroscopic traces of thallium in wine, chicory, tobacco, sugar beet, and beech wood, and had concluded that it must be widely diffused in the vegetable kingdom (47, 73). Because of the toxicity of thallium compounds, they are sometimes added in small concentrations to the soil of rodent-infested fields. Too high a concentration of thallium inhibits germination, growth rate, and chlorophyll formation in the crops, especially in rainy weather (78). 

As with indium, the literature contains a number of surveys of the general inorganic1 and organometallic chemistry of thallium,273 and the reviews of this element already cited are also concerned with the adducts of the halides and pseudohalides,5 and with other aspects of the coordination chemistry.6 A monograph by Lee provides a most useful treatment of the literature up to 1970.274 The application of thallium compounds in organic synthesis has been discussed.275 276... 

The anodic crystallization of thallium oxide (TI2O3) has been investigated fo over a century, and has also attracted attention during the recent decade [332], owinj to prospects for the wide use of thallium oxide films [333-336] having varie composition, structure, and texture. In the case of thallium compound synthesis because of the environmental aspects of this problem the development of low temperature electrochemical methods is of special importance. 

The earliest ° T1 NMR solid state studies were of the common thallium salts in both the solid phase and the melt, and of thallium silicate, borate and chalcogenide glasses. The ° T1 NMR literature up to 1988 has been extensively reviewed by Hinton et al. (1988). The chemical shift data for a number of thallium compounds are presented in Table 9.11. In view of the large CSA values which can occur in T1 compounds, distortion of the lineshapes can occur by loss of signal during the probe deadtime. Some of the earlier ° T1 NMR data may be corrupted in this way, and should be treated with caution. 

The chemistry of thallium has also been studied for its potential contribution to environmental pollution. Even though the annual world production of thallium is probably negligible in this respect (- 1000 times less than mercury, and —1,000,000 times less than lead), the element is released to the environment mainly through coal-burning power plants (33b). Therefore, it has been considered important to follow thallium s further fate in the natural environment, and a large number of thallium compounds have been characterized with this motivation (46-48). 

Another type of thallium compounds which have potential applications in converting light into electrochemical energy are the hi- or oligometallics of the type shown in Fig. 19. Similar compounds, such as (CN)5-Fe -(/u-CN)-Pt (NH3)4-(/L-NC)-Fe -(CN)5, have recently been shown to undergo redox reaction when irradiated by visible light (356). Research in this field has been active during the last few years, and... 

Little is known so far about the alkylation of thallium compounds with trialkyl alanes, although it has been reported that thallium trichloride gives good yields of dialkyl thallium chlorides with various trialkyl alanes (268). 

Preliminary studies have also been carried out on solutions of thallium compounds (see Table XIII). In every case studied, the enhancement was positive for both thallus and thallic compounds. However it was found that for thallus compounds the presence of free radical greatly broadened the n.m.r. signal, and that the observed enhancements were much larger than for thallic compounds. A similar explanation to that suggested for phosphorus has been used to explain this behaviour. In the thallus compounds the electron spin density from the free radical can be transmitted to the nucleus via the lone pair of electrons in the 65 orbital. In thallic compounds this lone pair is no longer available, and the unpaired electron density is then assumed to be transmitted via an indirect mechanism. 

There is little doubt that semi-synthetic and biological strategies towards estrone are highly attractive. The toxicity of thallium compounds and the use of lead tetraacetate represent drawbacks in the chemical procedures compared with biological approaches. The availability of microbiological methods for transforming cholesterol (and sitosterol) into androstanes enhances the latter methodology (ref. 118). 

Gerber GB and Leonard A (1997) Mutagenicity, carcinogenicity and teratogenicity of thallium compounds. Mutat Res 387 47—53... 

Normally, ambient air contains < 1 ng T1 per m (Ewers 1988). The range of thallium concentrations in sea water (in the form of n ions) has been reported to be relatively constant at 0.01 to 0.016 pgL , and in non-polluted river water this is 0.01 to 1 pgL (Kaplan and Mattigod 1998). The lowest environmental concentrations were found by Cheam (2001) in arctic snow and ice (< 0.05 to 8.4 ng L ). The high water solubility of thallium compounds may result in the local contamination of river and ground water by mining, smelting, and cement works wastewater (Fbrstner and Wittmann 1979, Cheam 2001). 

Although the chemistry of thallium compounds bears some resemblance to that of alkali metal analogs, thallium bis(trimethylsilyl)amide was only structurally characterized <1994JOM167>. Lappert and co-workers have reported on the reactions of the corresponding sodium and thallium amides MN(SiMe3)2 with 1,3,5-triazine, and the structures of the novel products, 1,3,5,7-tetraazaheptatrienylsodium 20 and -thallium 21 (Equation 2). 

Method L is conducted with thallium hydroxide as the base and Pd(PPh3)4 as catalyst under very mild reaction conditions to afford a wide variety of biaryls, including highly encumbered, in fair yields [16]. The biaryl 189 was prepared from mesitylboronic acid (283) and iodobenzene in almost quantitative yield. Scheme 23. Whereas tri-ort/io-substituted biphenyls were obtained by this method in respective yields, synthesis of tetra-ort/io-substituted analogues failed [16], Among base-sensitive groups, only an ester function has survived thallium hydroxide-mediated reactions at room temperature. Concerning the extreme toxicity of thallium compounds, the method is applicable only in the small-scale labo-synthesis. 

Thallium is prepared from filter dust obtained after roasting of sulfide ores. The dust is dissolved in sulfuric acid. Then thallium co-precipitates with lead sulfate. The lead manufactured by reduction with coke contains thallium metal. Lead is first removed in two electrolytic processes, and in a second step thallium is precipitated on a steel cathode. As an alternative, thallium can be won from a sulfuric acid solution with an ion-exchange technique. The annual production of thallium compounds corresponds to 30 tonnes of thallium, but the production of the metal is not large - in the whole world less than 10 tonnes. 

In this chapter, we present the use of thallium compounds as catalysts in organic reactions. Both, homogenous and heterogeneous thallium-hased catalysis are covered with the most relevant applications. 

There are a few examples in the literature of the application of thallium(i) compounds as acid catalysts, thallium(i) acetate and thallium(i) carbonate were used to produce polyethylene terephthalate (PET) by initial transesterification of dimethyl terephthalate with ethylene glycol to form diethylene glycol terephthalate, which then polymerised to give a spinnable material (Scheme 20.21). According to the authors, the use of thallium compounds as catalyst improves the thermal stability and photochemical resistance of the formed polymer. 

The utilization of thallium compounds CpTl and (MeC5H4)Tl, which are more excessively handled and more stable than Cp2Hg, gives better results [18, 19]. 

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