Thallium complexes hydroxides

Scheme 20.15). One equivalent of hydroxide or alkoxide is necessary to replace the halogen on the palladium complex I and the second equivalent is essential to form the borate II, so that the allq l group becomes more nucleophilic. According to Kishi and coworkers,the advantage of using thallium(i) hydroxide over sodium hydroxide is that the first can form insoluble thallium halide (TlX) which contributes to enhance this step and to accelerate the coupling. 

Porphyrin, octaethyl-, thallium hydroxide complex cyclic voltammetry, 4, 399 <73JA5140)... 

When this coupling is extended to more complex substrates, the rate slows drastically and undesired by-products are formed, even when 1 equiv. of Pd(0) is used.5 Fortunately the rate is markedly affected by the choice of the base, being highest with thallium hydroxide. Under TlOH conditions the coupling to (E,Z)-and to (Z,Z)-dienes can be effected at 0° often within minutes. Under these improved conditions (Z)-l and (Z)-2 couple to form (Z,Z)-3 in 73% yield, and (E)-1 and (Z)-2 couple to give (E,Z)-3 in 94% yield. 

The thallium salt 180 which can be prepared in nearly quantitative yield by treatment of dihydropentalene with thallium sulfate in aqueous sodium hydroxide solution, can be directly transformed into dianion 179 as well as the complexes 181 and 182 si)... 

Thallium (Tl, at. mass 204.37) occurs in its compounds in the I and III oxidation states. Thallium(I) compounds are the more stable. Thallium(I) forms sparingly soluble compounds, white TlCl, yellow Til, and black TI2S, as well as thiosulphate and ammine complexes of low stability. Colourless Tl ions can exist only in strongly aeidic media since the brown hydroxide, Tl(OH)3, which has no amphoteric properties, is precipitated at pH values as low as 0.3. Thallium(ni) yields halide-, oxalate-, and tartrate complexes. T1(I) is oxidized to Tl(ni) only by powerful oxidants, e.g., Mn04 , aqueous Cl2, and aqueous Br2. 

An example of separation of overlapping waves is the analysis of mixtures of lead(II) and thallium(I). A mixture of these two ions in neutral media gives a wave that cannot be resolved into the individual waves of Pb and Tl the half-wave potentials differ by only about 60 mV. When excess sodium hydroxide is added, the wave for thalUum(I) remains at virtually the same potential as in neutral media (as thallium does not form hydroxo complexes), whereas the wave of lead(II) is shifted to more negative potential by about 300 mV, due to formation of plumbate (Fig. 

If solvent extraction is carried out in the presence of cyanide, the zinc group of metals (Zn, Cd, Hg) is complexed and they will not extract. Addition of citrate complexes the elements of the ammonia group (Fe, Al, etc.) so that their hydroxides will not precipitate. The precipitation of the alkaline earth phosphates can be prevented by the addition of hexametaphosphate (Jl). Under these conditions, Bi(III), TI(I), and Sn(II) interfere in alkaline solution. The bismuth can be removed by preextraction at pH 3. Alternatively, if a positive lead test is found, bismuth could be ruled out or confirmed by back-extracting at pH 3. If bismuth is present, it will remain in the organic layer while lead will go into the aqueous phase. Extraction of thallium can be prevented by extracting the lead at pH 6.0-6.4 with chloroform. Or the thallium can be back-extracted at this pH this requires much closer control of the pH. The oxidation of dithizone by air is catalyzed by the presence of significant amounts of manganese (II). 

The kinetics in the basic media are summarised in the table. Since the rate is not affected by the buffer under due conditions, the reaction mechanism seems to involve essentially that of hydroxo complexes except for thallium, and the attack of hydroxide ions upon the complex appears to play an important role. The fact that the rate of the indium complex is proportional to the square of the hydroxide ion concentration tells that indium is the most inert among the three. Such an inertness of indium complexes may be reflected in the small value of its apparent dissociation constant of the coordinated water molecule, K. ... 

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