Vanadium-based salts

The understanding of direct-initation mechanisms. In this context, tire use of metal salts of strong acids has opened a new area of fundamental studies. Indeed, we believe that the chemical insertion of the olefin between the metal cation and the anion following its adsorption on the salt surface closely resembles recent mechanistic proposals put forward by Zambelli and collaborators to rationalise initiation in stereospecific polymerisation (propene with vanadium-based catalysts). We are inclined to conclude that the cationic nature of stereospecific polymerisations of the Ziegler-Natta type is supported by our findings , viz. electrophilic attack by... 

Vanadium-based complexes and salts have been used for oxidation either with oxygen in the presence of coreductants [7i], with peroxyacetic acid in acetonitrile [7j], or with HP/O2 combined oxidants [7k-mj. 

An important industrial process based on the above reactions is the air oxidation of cyclohexane to a mixture of cyclohexanol and cyclohexanone [73,74], which are intermediates in the manufacture of Nylon-66. In the DuPont process, the mixture is further oxidized with nitric acid in the presence of copper (II) and vanadium(V) salts as... 

The reaction of the vanadium salt with the aluminum alkyl leads to displacement of the vanadium ligands, with the formation of V-C bonds. As a consequence, the catalytic site is not sterically demanding. As mentioned above, vanadium-based catalysts behave as SSCs for olefin polymerization. Although the structure of their active catalytic sites is still unknown, the structures of polymers produced with vanadium systems are typical of those from SSCs. The majority of commercially available EP(D)M grades are from vanadium-based catalysts. ... 

Early catalysts for acrolein synthesis were based on cuprous oxide and other heavy metal oxides deposited on inert siHca or alumina supports (39). Later, catalysts more selective for the oxidation of propylene to acrolein and acrolein to acryHc acid were prepared from bismuth, cobalt, kon, nickel, tin salts, and molybdic, molybdic phosphoric, and molybdic siHcic acids. Preferred second-stage catalysts generally are complex oxides containing molybdenum and vanadium. Other components, such as tungsten, copper, tellurium, and arsenic oxides, have been incorporated to increase low temperature activity and productivity (39,45,46). 

Al—Ti Catalyst for cis-l,4-PoIyisoprene. Of the many catalysts that polymerize isoprene, four have attained commercial importance. One is a coordination catalyst based on an aluminum alkyl and a vanadium salt which produces /n j -l,4-polyisoprene. A second is a lithium alkyl which produces 90% i7j -l,4-polyisoprene. Very high (99%) i7j -l,4-polyisoprene is produced with coordination catalysts consisting of a combination of titanium tetrachloride, TiCl, plus a trialkyl aluminum, R Al, or a combination of TiCl with an alane (aluminum hydride derivative) (86—88). 

Metal-induced reductive dimerization of carbonyl compounds is a useful synthetic method for the formation of vicinally functionalized carbon-carbon bonds. For stoichiometric reductive dimerizations, low-valent metals such as aluminum amalgam, titanium, vanadium, zinc, and samarium have been employed. Alternatively, ternary systems consisting of catalytic amounts of a metal salt or metal complex, a chlorosilane, and a stoichiometric co-reductant provide a catalytic method for the formation of pinacols based on reversible redox couples.2 The homocoupling of aldehydes is effected by vanadium or titanium catalysts in the presence of Me3SiCl and Zn or A1 to give the 1,2-diol derivatives high selectivity for the /-isomer is observed in the case of secondary aliphatic or aromatic aldehydes. 

Although some [V(dtc)4] complexes have been isolated,671 oxovanadium(IV) compounds are usually obtained by the direct reaction of oxovanadium(IV) salts with dtc bases. Several [V(dtc)4] complexes have also been prepared by insertion of CS2 into V—N bonds of vanadium tetraamides (equation 47).419,672... 

These dyes were very popular initially until the mid-1900s and are still commonly applied. Aniline black, discovered by J. Lightfoot (1863), is the oldest known oxidation dye. The polymeric dye is obtained by impregnating the hair with aniline hydrochloride and oxidizing with sodium chlorate in the presence of copper and/ or vanadium salt as catalyst at pH 1-2. Aniline black, C.I. Oxidation Base 1, 50440 [13007-86-8] (1) has a polymeric structure. 

No carbonyl cations of vanadium with a-donor ligands have been reported. When Lewis bases react with vanadium hexacarbonyl, either a substituted derivative or a hexacarbonylvanadate salt is obtained. The latter is formed by disproportionation, which also produces a carbonyl-free cation. 

To overcome the problems encountered in the homogeneous Wacker oxidation of higher alkenes several attempts have been undertaken to develop a gas-phase version of the process. The first heterogeneous catalysts were prepared by the deposition of palladium chloride and copper chloride on support materials, such as zeolite Y [2,3] or active carbon [4]. However, these catalysts all suffered from rapid deactivation. Other authors applied other redox components such as vanadium pentoxide [5,6] or p-benzoquinone [7]. The best results have been achieved with catalysts based on palladium salts deposited on a monolayer of vanadium oxide spread out over a high surface area support material, such as y-alumina [8]. Van der Heide showed that with catalysts consisting of H2PdCU deposited on a monolayer vanadium oxide supported on y-alumina, ethene as well as 1-butene and styrene... 

Also, coordination compounds and metal carbonyls are able to undergo a PET, resulting in initiating radicals [63]. Recently investigated examples are iron chloride based ammonium salts [149], vanadium(V) organo-metallic complexes [150], and metal sulfoxide complexes [151]. However, the polymerization efficiency of some systems is only low due to redox reactions between the central metal ion and the growing polymer radical, and the low quantum yields of PET. 

Cerium dioxide is preferred over other oxides because platinum is expensive and vanadium and iron oxides are poisons for FCC catalysts. Usually an aqueous solution of a cerium salt is used to impregnate a spinel base which is then calcined to obtain the Ce02 active form. We have found that a 10 to 12% Ce02 is sufficient for effective S02 oxidation(1). 

The manufacture of phthalic anhydride (world installed capacity ca. 4.4 Mt/a) has several points of similarity to that of maleic anhydride in that there are two alternative feedstocks and a large amount of heat is released. The first process, introduced by BASF at the end of 19 century, was based on the liquid phase oxidation of naphthalene catalyzed by mercury salts. It was later replaced by the cleaner gas phase process, carried out over vanadium and molybdenum oxides. Naphthalene was supplied by coal tar distillation and was used exclusively until the end of 1950s when u-xylene, of petrochemical origin, became an abundantly available feedstock (Equation 36). A few production units however can use either feedstock, taking advantage of price fluctuations in coke plants (naphthalene) and in refineries (u-xylene). 

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