Activated Thallium

After reaction, the activity of a 25.0-mL water sample is 745 counts per minute (cpm), caused by the presence of Tl+-204 ions. The activity of Tl-204 is 5.53 X 105 cpm per gram of thallium metal. Assuming that 02 is the limiting reactant in the above equation, calculate its concentration in moles per liter. 

In the phosphor-photoelectric detector used as just described, the x-ray quanta strike the phosphor at a rate so great that the quanta of visible light are never resolved they are integrated into a beam of visible light the intensity of which is measured by the multiplier phototube. In the scintillation counters usual in analytical chemistry, on the other hand, individual x-ray quanta can be absorbed by a single crystal highly transparent to light (for example, an alkali halide crystal with thallium as activator), and the resultant visible scintillations can produce an output pulse of electrons from the multiplier phototube. The pulses can be counted as were the pulses-from the proportional counter. 

The reaction between acyl halides and alcohols or phenols is the best general method for the preparation of carboxylic esters. It is believed to proceed by a 8 2 mechanism. As with 10-8, the mechanism can be S l or tetrahedral. Pyridine catalyzes the reaction by the nucleophilic catalysis route (see 10-9). The reaction is of wide scope, and many functional groups do not interfere. A base is frequently added to combine with the HX formed. When aqueous alkali is used, this is called the Schotten-Baumann procedure, but pyridine is also frequently used. Both R and R may be primary, secondary, or tertiary alkyl or aryl. Enolic esters can also be prepared by this method, though C-acylation competes in these cases. In difficult cases, especially with hindered acids or tertiary R, the alkoxide can be used instead of the alcohol. Activated alumina has also been used as a catalyst, for tertiary R. Thallium salts of phenols give very high yields of phenolic esters. Phase-transfer catalysis has been used for hindered phenols. Zinc has been used to couple... 

The reactions of TTN with a variety of unsaturated systems have been studied systematically during the last two years, and the results obtained clearly establish the synthetic utility of the reagent as a specific oxidant. Attempts were made in 1966 by Uemura et al. 162) to oxidize a,)8-unsatur-ated carbonyl compounds with thallium(III) acetate, but were unsuccessful. In 1970, however, Ollis and his co-workers 121-123) reported that prolonged treatment of highly activated chalcones (Scheme 20) with thal-... 

The classical view of the lone pair is that, after mixing of the s and p orbitals on the heavy metal cation, the lone pair occupies an inert orbital in the ligand sphere [6]. This pair of electrons is considered chemically inert but stereochemi-cally active [7]. However, this implies that the lone pair would always and in any (chemical) environment be stereochemically active, which is not the case. For example, TIF [8] adopts a structure, which can be considered as a NaCl type of structure which is distorted by a stereochemically active lone pair on thallium. In contrast TlCl [9] and TlBr [10] adopt the undistorted CsCl type of structure at ambient temperature, and at lower temperatures the (again undistorted) NaCl type of structure. The structure of PbO [11] is clearly characterized by the stereochemically active lone pair. In all the other 1 1 compounds of lead with... 

The repulsion of the thallium and oxygen lone pairs lead to a distortion of the Tl-6s lone pair, which is no longer totally spherical as one would intuitively expect for an s orbital. The thallium contributions involved in the anti-bonding combination are indeed of 97.7% s-, 1.8% p- and 0.5% d-character. Thus, a much less than expected p-character is found for the thallium orbital, which shows that extensive s-p mixing or hybridization is not essential for the lone pair to become stereochemically active. 

Scintillation counters are constructed by coupling a suitable scintillation phosphor to a light-sensitive photomultiplier tube. Figure 25 illustrates an example of a scintillation counter using a thallium-activated sodium iodide crystal. 

Berndt et al. [740] have shown that traces of bismuth, cadmium, copper, cobalt, indium, nickel, lead, thallium, and zinc could be separated from samples of seawater, mineral water, and drinking water by complexation with the ammonium salt of pyrrolidine- 1-dithiocarboxylic acid, followed by filtration through a filter covered with a layer of active carbon. Sample volumes could range from 100 ml to 10 litres. The elements were dissolved in nitric acid and then determined by atomic absorption or inductively coupled plasma optical emission spectrometry. 

Haapakka and Kankare have studied this phenomenon and used it to determine various analytes that are active at the electrode surface [44-46], Some metal ions have been shown to catalyze ECL at oxide-covered aluminum electrodes during the reduction of hydrogen peroxide in particular. These include mercu-ry(I), mercury(II), copper(II), silver , and thallium , the latter determined to a detection limit of <10 10 M. The emission is enhanced by organic compounds that are themselves fluorescent or that form fluorescent chelates with the aluminum ion. Both salicylic acid and micelle solubilized polyaromatic hydrocarbons have been determined in this way to a limit of detection in the order of 10 8M. 

It is now well established that organometallic compounds are formed in the environment from mercury, arsenic, selenium, tellurium and tin and hence were also deduced on the basis of analytical evidence for lead, germanium, antimony and thallium. Biological methylation of tin has been demonstrated by the use of experimental organisms. Methylgermanium and methyllead were widely found in the environment but it is debatable whether germanium and lead are directly methylated by biological activity in natural environment. 

Thallium(i) salts have long been used in reactions with organic and organometallic halide complexes as a means of activating the halide by removal as insoluble T1X. However, the thallium ions proved not to be innocent bystanders, and numerous examples were reported in COMC (1995) where the metal-bound thallium complexes were formed. Deliberate reactions of thallium(i) and thallium(m) salts with metal carbonyl anions have yielded a variety of complexes of the form T1 MLJ3. In the past decade, new examples of metal carbonyl derivatives of thallium have been prepared (see Table 2). In addition, the propensity for Tl+ to form adducts with 16-electron noble metal complexes has been exploited. 

When dioxane is added to [Au(C6C1s)2T1]00 (Equation (108)),120 a simple dimer results in which the Au-Tl groups are connected via a dioxane bridge between the two thallium atoms 132.120 The thallium atom is coordinated in a 7r-fashion to the toluene which served as the solvent of the reaction. The Tl(i) ion does not exhibit a stereochemically active lone pair, and the blue luminescence was attributed to an Au Tl charge transfer transition. 

We will start by assuming that the activity coefficients of Tl" (a ,) and Tl " (aq) are the same, in which case activities and concentrations may be considered as being interchangable. If Eappiied = Eo,r> then from equation (6.2) we see that co/cr = 1. In other words, half of the thallium remains as Tl" while the other half has been converted to TP. The concentration profiles will follow the traces shown in Figure 6.4. 

The thallium trinitrate-mediated ring contraction of frani-decal-2-ones has opened up a new route to the hydrindane system, and fluorinative ring contraction of cyclic alkenes to afford difluorocycloalkanes has been induced by iodotoluene difluoride and EtsN-HF. A possible mechanism is shown in Scheme 78. The double bond of the cyclohexene ring is attacked by iodotoluene difluoride activated by HF from the axial direction, followed by the addition of a fluoride ion from the trans direction. Reductive elimination of iodotoluene from the resulting adduct, ring contraction and the addition of the fluoride ion to the carbocation stabilized by fluorine then take place to give the ring-contracted difluorinated product. 

Several mechanisms have been postulated to account for thallium s toxicity, including ligand formation with sulfhydryl groups of enzymes and transport proteins, inhibition of cellular respiration, interaction with riboflavin and riboflavin-based cofactors, alteration of the activity of K -dependent proteins, and disruption of intracellular calcium homeostasis. ... 

Dilsizian V, Perrone-Filardi P, Arrighi JA, Bacharach SL, Quyyumi AA, Freedman NM et al. Concordance and discordance between stress-redistribution-reinjection and rest-redistribution thallium imaging for assessing viable myocardium. Comparison with metabolic activity by positron emission tomography. Circulation 1993 88 941-952... 

Tamaki N, Yonekura Y, Yamashita K, Senda M, Saji H, Hashimoto T et al. Relation of left ventricular perfusion and wall motion with metabolic activity in persistent defects on thallium-201 tomography in healed myocardial infarction. Am J Cardiol 1988 62 202-208... 

Tamaki N, Ohtani H, Yamashita K, Magata Y, Yonekura Y, Nohara R et al. Metabohc activity in the areas of new fill-in after thallium-201 reinjection comparison with positron emission tomography using fluor-ine-18-deoxyglucose. J Nucl Med 1991 32 673-678... 

Karski and co-workers found that thallium acts also as a promoter and prevents the poisoning of the palladium particle with oxygen. Indeed, a bimetallic system which contained 5 wt% of Th led to 100% selectivity to gluconic acid at 95% conversion [117]. On their side, Boimeman et al. reported that charcoal-supported Pd-Pt catalysts prepared from a colloidal solution of Pd-Pt/NOct4Cl exhibit a superior activity and selectivity than industrial heterogeneous Pd-Pt-based catalysts [118]. 

It was originally stated that CaCOa activated with manganese cannot be excited by UV radiation, but CaCOa activated with lead, thallium or cerium and manganese shows an orange-red manganese luminescence under UV irradiation at room temperature (Bolden 1952). Nevertheless, in many minerals luminescence of Mn " " has been found with excitation spectra typical for this center without additional bands of Pb or Ce impurities. 

Rapid exchange of alkyl groups occurs in thallium(III) alkyls as demonstrated by the proton NMR study of Maher and Evans (81). At low temperatures ( —85°) the multiplet structure expected for proton-thallium coupling is superimposed on the proton spectra of thallium alkyls. On warming, the multiplets collapse. Analysis of this collapse region [Eq. (29)] yielded a value of 6 1 kcal mole-1 for the exchange-activation energy... 

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