Thallation Thallium acetate

Mercuration-Thallation. Mercuric acetate and thallium ttifluoroacetate react with benzene to yield phenyHnercuric acetate [62-38-4] or phenylthaHic ttifluoroacetate. The arylthalHum compounds can be converted iato phenols, nitriles, or aryl iodides (31). 

Ethylbenzene, Thallium triacetate Ucmura, S. et al., Bull. Chem. Soc., Japan., 1971, 44, 2571 Application of a published method of thallation to ethylbenzene caused a violent explosion. A reaction mixture of thallium triacetate, acetic acid, perchloric acid and ethylbenzene was stirred at 65°C for 5 h, then filtered from thallous salts. Vacuum evaporation of the filtrate at 60°C gave a pasty residue which exploded. This preparation of ethylphenylthallic acetate perchlorate monohydrate had been done twice previously and uneventfully, as had been analogous preparations involving thallation of benzene, toluene, three isomeric xylenes and anisole in a total of 150 runs, where excessive evaporation had been avoided. 

Lithiation and mercuration are directed by the oxygen atom and occur at the 4-position, but thallation, achieved by treatment of dibenzofuran with thallium(III) isobutyrate at 110°C, affords the 2-thallium di(isobutyrate), which may be converted to the 2-iodo compound by reaction with iodine. Mercuration is achieved by treatment of dibenzofuran with mercuryfll) acetate at 150°C, and the resultant 4-mercuric acetate (56%) may also be converted to the iodo compound. ... 

Thallium (III) Compounds. Thallium (ITT) derivatives have been used extensively as oxidants in oiganic synthesis. In particular, thallic acetate and trifluoroacetate are extremely effective as electrophiles in oxythallation and thallation reactions. For example, ketones can be prepared from terminal acetylenes by means of Tl(OOCCH3)3 in acetic acid (oxythallation) (30) ... 

Thallation of l-methoxyindole-3-carbaldehyde with thallium trisfluo-roacetate followed by treatment with potassium iodide gave the 4-iodo derivative in 91% yield, and this has been converted into many other 1-methoxyindole derivatives (86CPB677). When the thallated indole reacted with methyl acrylate in the presence of a catalytic quantity of pal-ladium(ll) acetate, 47% of the product was the 4-derivative 160, but 11% of the 5-isomer was also formed (86CPB4116). 

The carboxylates of indium and thallium are obtained by dissolving the oxides in acid. Acetate and trifluoroacetate salts are used extensively as reagents in organic synthesis. Certain other thallium compounds have been used also. The trifluoroacetate, T1(02CCF3)3, will directly thallate aromatic compounds to give arylthal-lium species, for example, C6H5T1(02CCF3)2 (cf. aromatic mercuration, Section 15-15) and oxidize arenes to biaryls. 

Although thallium(III) acetate fails to react with aromatic compounds under mild conditions, thallium (III) trifluoroacetate will effect rapid electrophilic thallation of a wide range of aromatic substances (40, 168, 169, 170, 203) according to the general reaction [Eq. (11)]. These reactions are very rapid and are usually completed in a few minutes at room temperature for activated aromatic nuclei, to give stable colorless solids that generally crystallize from solution. The orientation of thallation in such reactions may be influenced by temperature [Eq. (13)], or by the substituents on the aromatic nucleus. 

When -phenylethyl alcohol, C6H5CH2CH2OH, is treated with thallium trifluoro-acetate followed by potassium iodide, there is obtained predominantly one aryl iodide, the particular isomer depending upon the conditions of thallation (a) 25°, ortho (b) 75°, meta (c) prior conversion to the ester, QH5CH2CH2OCOCH3, then 25°, para. Suggest an explanation for each case of regiospecificity. 

Thallium carboxylates, particularly the acetate and trifluoroacetate, which can be obtained by dissolution of the oxide in the acid, are extensively used in organic chemistry.14 Both Tl metal and Tl1 salts such as the acetylaceton-ate also have specific uses. One example is the use of thallium(m) acetate in controlled bromination of organic substances such as anisole. The trifluoroacetate will directly thallate (cf. aromatic mercuration, Section 18-9) aromatic compounds to give aryl thallium ditrifluoroacetates, e.g., C6H5Tl(OOCCF3)2. It also acts as an oxidant, inter alia converting para-substituted phenols into p-quinones. 

Thallation of thiophens in the 2-position with thallium(m) trifluoro-acetate in trifluoroacetic acid is complete within a few minutes at room temperature. The thallium derivative reacts in situ with aqueous potassium iodide solution to give a convenient and high-yield synthesis of iodo-thiophens. A mixture of thallium(m) acetate has been shown to be a mild and efficient reagent for electrophilic aromatic bromination. Thiophen yields 2-bromothiophen in 82% yield and very little dibromothiophen. 3-Methylthiophen appears to be selectively brominated in the 2-position and 2-methylthiophen in the 5-position in 70—75% yield. The direct thiocyanation of thiophen and some alkylthiophens with thiocyanogen under various conditions using a variety of Friedel-Crafts catalysts has... 

---