Thallium , oxidation with

Thallium( ) oxide, TI2O. Black powder formed by heating TIOH, gives T1(I) salts with acids. 

Alkenes can also be oxidized with metallic acetates such as lead tetraacetate or thallium(III) acetate " to give bis-acetates of glycols. Oxidizing agents such as benzoquinone, Mn02, or 02, along with palladium acetate, have been used to convert conjugated dienes to l,4-diacetoxy-2-alkenes (1,4 addition). ... 

Hydrogen sulfide is rapidly oxidised, and may ignite in contact with a range of metal oxides, including barium peroxide, chromium trioxide, copper oxide, lead dioxide, manganese dioxide, nickel oxide, silver(I) oxide, silver(II) oxide, sodium peroxide, and thallium(III) oxide. In the presence of air, contact with mixtures of calcium oxide or barium oxide with mercury oxide or nickel oxide may cause vivid incandescence or explosion. 

Mixtures of the oxide with sulfur or antimony trisulfide explode on grinding in a mortar. Dry hydrogen sulfide ignites, and sometimes feebly explodes, over thallium oxide. 

In a new reaction of the pyrano[2,3-c]azepines 40 with hydrazine hydrate, the first derivatives of the pyridazino[4,3-c]azepine system 42 (for example R1 = R2 = Me) have been described (Scheme 10). The rearrangement probably involves initial ring opening to the intermediate 41. Aromatisation of this system was achieved by further oxidation with thallium (III) nitrate or copper(II) acetate . 

Biaryl phenol coupling.1 The natural dibenzylbutanolide lignans, prestegane A (la) and B (lb), are converted to the corresponding bisbenzocyclooctadiene lactones (2) by oxidation with Ru02 in TFA-TFAA in 80-85% yield. The usual reagent for this oxidation, thallium tris(trifluoroacetate), is less efficient (45-50% yields). 

Certain thallium salts, particularly T1(N03)3, effect oxidation with an accompanying rearrangement. Especially good yields are found when the thallium salt is supported on inert material. Two examples are given. Formulate a mechanistic rationalization. 

Thallium oxide also can he prepared hy thermal dissociation of thallium hydroxide, TlOH or thallium carbonate, TI2CO3. Thallium oxide dissolves in water forming thallous hydroxide, TlOH. It reacts with carbon dioxide to form thallous carbonate, TI2CO3. 

When burned in suitable pits, pyrite yields, among other products, sulfur dioxide, arseniouS and selenious adds, and the oxide of thallium, which are carried over into the first lead chamber, with the ferruginous dust. In this first chamber, espedally if it has no other communication with the following ones than the gas pipe, the oxide of thallium deposits and accumulates, and finally thallium sulfate, with sulfates of lead, iron, and other foreign substances coming fiom the pyrite. 

Oxidative cyclizations of cyclodipeptides incorporating tryptophan have also been reported (81TL5323). Thus, irradiation of the piperazinedione (39) in formic acid in the presence of a sensitizer such as proflavine or chloranil gave the hydroxypyrroloindole (40). Oxidation with thallium (III) trifluoroacetate gave the dimer (41) in 3% yield. 

Maritidine. It was observed that a variety of alkoxyl or silyloxy phenols 340 (Scheme 51), on oxidation with the non-toxic pheny 1 iodo-tos-trifluoroacetate, instead of customary heavy metal reagents such as trivalent thallium or pentavalent vanadium salts, in the weakly nucleophilic solvent, trifluoroethanol at low temperature, furnished consistently improved yields of cyclisation products 341 [89],... 

As already remarked, carbon monoxide has a similar reducing action on the oxides of the more easily reducible elements. The product in this case is the dioxide, C02, for example, Fe203+3C0 = 2Fe + 3C02- This action requires a red heat. Another reducing agent, applied by fusing the oxide with it, is potassium cyanide, KCN it is converted into the cyanate, KCNO. The metal thallium may be prepared by its help, T120 + KCN = 2TI + KCNO. As the cyanide is somewhat expensive, it is used only in special cases. 

Oxidative phenolic coupling.1 The vancomycin antibiotics are polypeptides with bridging diphenyl ether groups. Evans et al. have shown in model systems such as 1 that cyclization to o-halophenolic peptides (2) can be accomplished by oxidation with thallium(III) nitrate in THF-methanol or CH2Cl2-methanol followed by CrCl2 reduction of a para-quinol intermediate (a). In three cases the yield of cyclic products was 40-48%. 

Enhancement by strong acids such as TFA is a general feature of oxidations with metal acetates. Metal trifluoroacetates in TFA are much more powerful oxidants (electrophiles) than the corresponding acetates in acetic acid. Activation of the metal oxidant in TFA has been observed with co-balt(III)217 249,259,27S 276 manganese(III),237,275 lead(IV),277-281 thallium-(III),282-287 cerium(IV),288 289 and copper(II).290 Similarly, the electrophilic properties of copper(I)291 and mercury(II)292 acetates are strongly enhanced by replacement of acetate by trifluoroacetate. It has been proposed217,276 that the potent oxidizing properties of Co(III) trifluoroacetate are due to ionization to the cationic Co(III) species,... 

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