Thallium -carboxylates

The thallium benzoate and thallium 2-oxocarboxylates are available via the reaction of thallium acetate with benzoic acid or the 2-oxocarboxylic acids, due to the lower values of these acids (benzoic acid 4.22, benzoylformic acid 1.2, 2-oxoglutaric acid 31/5.14, pyruvic acid 2.49) compared to acetic acid (4.76) (167). The free acetic acid is distilled off with water as an azeotrope and the thallium carboxylates are obtained in high purity. 

Several other metal salts have been proposed to react with acid halides to give acid anhydrides in good yield. Thus, thallium carboxylates in etheral suspension may be treated with acid halides to lead to acid anhydrides in high yield. The method has the advantage that thallium chloride can be separated by filtration and the product is isolated after evaporation of the solvent. Another synthetic possibility exists in the desulfurization of thioesters with mercury(II) carboxylates. Mercuiy(II) carboxylates can also be reacted with triethyl phosphite or tri-n-butylphosphine to provide acid anhydrides in yields of 60-80%. Another possibility is offered by the reaction of 1 mol of iV,Af-dicyclohexylthiourea and 2 mol of silver or mercury(II) carboxylates. Mixed carboxylatocarbamato anhydrides follow from the room temperature reaction of iV, -dialkylcarbamato metal derivatives with acid chlorides. Either Na, Cu", Ti" or V" are employed. ... 

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. 

Fig. S.6. Trandtion temperatures of thallium carboxylates. Numteis at the various pcmts indicate transiticm entropies in J/(K mol). Numbers in parenthesis indicate a further low tempouture jdiase of the givm entropoy of transition. Drawn after Ref.

Soap-like molecules are examples of condis crystals of small molecules. This is illusU ated on the case of the homologous series of thallium carboxylates, TK, in Fig. 5.147. These soaps are amphiphilic molecules and form lamellar, smectic liquid crystals without the help of a mesogen by ordering on both sides of the interface between the polar and nonpolar parts of the nanophase-separated molecules. The only regular increases of entropy with chain-length n occur, when adding all transition... 

Hg(C H2 +iCOO)2] for /i=7-17, are not mesogenic, while thallium carboxylates [T1(C H2 +iCOO)2] gave stable lamellar phases with branched alkyl chains [37]. 

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