Thallium catalysts

The presence of thallium(0) led to an increase in activity and selectivity of metallic palladium catalysts supported on silica in aldose oxidation reactions. However, silica-supported thallium(0) had no activity by itself (entry 3). ° Similarly, the bimetallic catalyst platinum-thallium/ZSM-5, prepared by impregnation of thallium sulfate and chloroplatinic acid on Zeolite Socony Mobil-5 (ZSM-5), showed greater selectivity in propane aromatisation and almost the same catalytic activity as monometallic thallium/ZSM-5 (entry 4). Similar comparison of vanadium-caesium-copper and vanadium-caesium-copper-thallium catalysts supported on TiOa.SiC demonstrated that addition of thallium improved the catalytic activity in partial oxidation of p-tert-butyltoluene to p-tert-butyl-benzaldehyde (entry The application of solid-supported thallium-based catalysts in different processes includes (a) iron-thallium catalysts in carbon monoxide hydrogenations to form hydrocarbons and alcohols, and catalytic reforming of... 

R. Advani, Preparation of spinnable polyesters using thallium catalysts, US 3220982 A, 1965. 

M. A. Richard, F. J. Wright and J. C. Pirkle, Process for producing alcohols using iron-thallium catalysts, CA 1233833 Al, 1988. 

S. P. Current, Using heterogeneous palladium a(d thallium catalyst on carbon, US 4523029 A, 1985. 

Most synthetic camphor (43) is produced from camphene (13) made from a-piuene. The conversion to isobomyl acetate followed by saponification produces isobomeol (42) ia good yield. Although chemical oxidations of isobomeol with sulfuric/nitric acid mixtures, chromic acid, and others have been developed, catalytic dehydrogenation methods are more suitable on an iadustrial scale. A copper chromite catalyst is usually used to dehydrogenate isobomeol to camphor (171). Dehydrogenation has also been performed over catalysts such as ziac, iadium, gallium, and thallium (172). 

Thallium tris(3-mesitylpyrazol-l-yl)borate and [(j -cod)2RhCl] produce [(ry -TpORhfjj -cod)] (93IC3471). These complexes appeared to be good catalysts... 

The Teijin oxychlorination, on the other hand, is considered a modern version of the obsolete chlorohydrin process for the production of ethylene oxide. In this process, ethylene chlorohydrin is obtained by the catalytic reaction of ethylene with hydrochloric acid in presence of thallium(III) chloride catalyst ... 

Catalyst regeneration occurs by the reaction of thallium(I) chloride with copper(II) chloride in the presence of oxygen or air. The formed Cu(I) chloride is reoxidized by the action of oxygen in the presence of HCI ... 

Isobutylene oxide is produced in a way similar to propylene oxide and butylene oxide by a chlorohydrination route followed by reaction with Ca(OH)2. Direct catalytic liquid-phase oxidation using stoichiometric amounts of thallium acetate catalyst in aqueous acetic acid solution has been reported. An isobutylene oxide yield of 82% could be obtained. 

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... 

Colloids of more electronegative metals such as cadmium and thallium also act as catalysts for the reduction of water. In the colloidal solution of such a metal, an appreciable concentration of metal ions is present. The transferred electrons are first used to reduce the metal ions, thus bringing the Fermi potential of the colloidal particles to more negative values. After all the metal ions have been reduced, excess electrons are stored as in the case of silver. 

For practical applications it is important to minimize the production of the intermediate peroxide, and to ensure that the reaction goes all the way to water. Sometimes this can be ensured by the addition of a suitable catalyst. A case in point is oxygen reduction on gold from alkaline solutions. At low and intermediate overpotentials the reaction produces only peroxide in a two-electron process at high overpotentials the peroxide is reduced further to water. The addition of a small amount of Tl+ ions to the solution catalyzes the reaction at low overpotentials, and makes it proceed to water. Thallium forms a upd layer at these potentials it seems that a surface only partially covered with T1 is a good catalyst, but the details are not understood [3]. 

Friedel-Crafts reactions involving electrophilic substitution of aromatic compounds have been reported on solid base catalysts such as thallium oxide and MgO. The rates of benzylation of toluene by benzyl chloride over MgO nanocrystals were found to be of the order CP-MgO > CM-MgO > AP-MgO.56 An important observation in the study was that x-ray diffraction of the spent catalyst... 

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]. 

All these protocols allow us to form a new carbocycle in a bimolecular process. The cyclization involving two different molecules besides CO has been realized, involving carbapalladation of norbornene, migratory insertion of CO, and subsequent intramolecular Heck-like attack at thiophene residue. Thallium acetate is required as electrophilic co-catalyst (Scheme 18). ... 

The reaction of /V-pentenyl-2-iodoindole in the presence of a palladium-triphenylphosphine catalyst led to the formation of a mixture of isomeric products in good yield (4.8.), Addition of thallium(I) acetate favoured the formation of an exocyclic double bond, while in its absence the product containing the endocyclic olefin moiety is formed preferentially. The shortening of the A-alkenyl chain by one carbon leads to the selective formation of a five membered ring.9 Starting from indole-carboxamide derivatives both /3-. and carbolinones are available in intramolecular Heck coupling. 

Acyl cyanides1708 can be prepared by treatment of acyl halides with copper cyanide. The mechanism is not known and might be free-radical or nucleophilic substitution. The reaction has also been accomplished with thallium(I) cyanide,1709 with MejSiCN and an SnCl4 catalyst,1710 and with Bu3SnCN,1711 but these reagents are successful only when R = aryl or tertiary alkyl. KCN has also been used, along with ultrasound,1712 as has NaCN with phase transfer catalysts.1713 OS III, 119. 

Thallium zeolites, 4A and 13X. The catalyst is prepared from a mixture of T12C03 and the crushed molecular sieves in water at 45°, and then washed with acetone and dried at 190°. Co or Cd zeolites are prepared similarly with C0CO3 or CdC03.1... 

O-Glycosylation. Traditional glycosylation catalysts are silver or mercury salts. Recently silver zeolite2 has been recommended as the catalyst for preparation of 1,2-cw-glycosides. The thallium zeolite is useful when the glycosyl bromide is unstable in the presence of silver catalysts.1 Example ... 

ACTIVATOR. 1. A substance that renders a material or a system reactive commonly, a catalyst. 2. A special use of this term occurs in the flotation process, where an activator assists the action of the collector. 3. An impurity atom, present in a solid, that makes possible the effects of luminescence, or markedly increases their efficiency. Examples are copper in zinc sulfide, and thallium in potassium chloride. See also Enzyme. 

A tetracobalt anionic complex, viz. [In Co(CO)4 4] (27) (37,37a), has been briefly described together with the thallium analogue (28) (37a), both formed by addition of [Co(CO)4] to either 25 or 26. No structural details have been reported although the indium and thallium centers are presumably tetrahe-drally coordinated by the four cobalt atoms. Mention is also made (37a) of the facile heterolytic bond dissociation (In—Co or Tl—Co) observed in polar solvents. Little has been reported about the reactivity of these complexes, although a discussion on the use of 25 as a catalyst in the dimerization of norbornadiene has appeared (58). 

The Heck reaction has now been reviewed448,449. Evidence for the formation of zerova-lent palladium from (AcO Pd and Ph3P via a redox process has been provided450. This explains the origin of Pd(0) required for certain palladium-catalysed reactions in cases where Pd(II) is added to the reaction as the primary form of the Pd-catalyst. Thallium has been found to accelerate the Heck-type cyclization-carbonylation451. 

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