Vanadium trichloride catalyst

Vandenberg (77) has found that vinylethers are polymerized by combinations of vanadium tetrachloride and triethylaluminum. Vandenberg believed that the intermediate vanadium trichloride, produced by reduction of the vanadium tetrachloride, reacted with the triisobutyl-aluminum-tetrahydrofuran complex to produce the modified Friedel-Crafts catalysts that converted the vinylether to isotactic polymer. 

Natta (119) has made an excellent summary of the catalysts which produced various structures of polybutadiene. The more acidic vanadium and titanium trichloride catalysts produced large amounts of trans 1.4-polymer. Less acidic titanium iodide, cobalt, and nickel catalysts produced high amounts of cis 1.4 structure (Table 9). 

For instance, in the field of elastomers, alkyllithium catalyst systems are used commercially for producing butadiene homopolymers and copolymers and, to a somewhat lesser extent, polyisoprene. Another class of important, industrial polymerization systems consists of those catalyzed by alkylaluminum compounds and various compounds of transition metals used as cocatalysts. The symposium papers reported several variations of these polymerization systems in which cocatalysts are titanium halides for isoprene or propylene and cobalt salts for butadiene. The stereospecificity and mechanism of polymerization with these monomers were compared using the above cocatalysts as well as vanadium trichloride. Also included is the application of Ziegler-Natta catalysts to the rather novel polymerization of 1,3-pentadiene to polymeric cis-1,4 stereoisomers which have potential interest as elastomers. 

Lithium hydride, prepared by hydrogenolysis of /-butyllithium under pressure, was observed to reduce aldehydes and cyclohexanones to the corresponding alcohols in the presence of transition metal halides.An equimolar quantity of vanadium trichloride was found to be the most effective catalyst, but the identity of the active reducing species was not established. 

When using, however, two-component catalysts alcohols also react with inactive metal-polymer (aluminium-polymer) bonds which are formed in the chain transfer reactions with a cocatalyst. It is expedient to use the alcohol method only for catalytic systems and polymerization conditions for which the number of inactive metal-polymer bonds is low. Such a case is the polymerization of 4-methyl-1-pentene on vanadium trichloride activated with various organoaluminium compounds. For this system the influence of catalyst composition and polymerization conditions on Cp and kp was determined by quenching the polymerization with tritiated alcohol. 

The catalysts are usually prepared in hydrocarbon solvents, essentially in the absence of air or moisture and are mixtures of ill-defined composition. In many instances dark-coloured precipitates are formed of variable stoichiometry containing complexes of the organo-metal compound with the transition metal in a lower valence state. Natta [5] showed that pure lower valence transition metal compounds, such as titanium or vanadium trichloride, when treated with organo-metal compounds were effective catalysts, and were particularly suitable for the preparation of crystalline high melting point polyolefins. The close identity of these two classes of catalyst has led to their description as... 

Ferric chloride hexahydrate Iron pentacarbonyl Palladium diacetate Phosphotungstic acid Vanadium pentoxide catalyst, organic synthesis Boron tribromide Boron trichloride Boron trifluoride Cobalt Mercury acetate (ic) Trimethylsilyl trifluoromethane sulfonate Zinc acetate... 

Many ot-olefins were polymerized by the Ziegler-Natta catalysts to yield high polymers and many such polymers were found to be stereospecific and crystalline. Polymerizations of a-olefins of the general structure of CH2 = CH — (CH2) — R, where x is 0-3 and R denotes CH3, CH-(CH3)2, C(CH3)3, or CsHs, can be catalyzed by vanadium trichloride/triethyl aluminum [80]. The conversions are fairly high, though higher crystallinity can be obtained with titanium-based catalysts [81]. Addition of Lewis bases, such as ( 4119)20, (C4H9)3N, or ( 4119)3 , to the catalyst system further increases crystallinity [82]. 

The natural products gutta-percha and balata consist of tra w-l,4-polyisoprene. With the aid of vanadium trichloride and triethylalumium, tra w-l,4-polyisoprene can be produced with 98% trans-, A enchainments [133,258]. The optimal Al/V ratio is the range of 5 to 7. The activity can be increased by the addition of small amounts of ether, heterogenerization on supports (kaolin, Ti02), or blending with titanium(III) chloride or titanium alcoholates [259-261]. Further catalysts featuring lower activity, however, are allylnickel iodide, trisallylchormium on silica, or complexes of neodymium [262 265]. 

The use of an optically active catalyst is illustrated by the polymerization of rra s-l,3-pentadiene in the presence of a Ziegler-Natta catalyst of vanadium trichloride and optically active triisoamylaluminium although the monomer is not itself optically active an optically active transA, 4-polymer is produced ... 

Substantially trafi5-1,4-polyisoprenes have been obtained with several catalyst combinations of which an excellent example is that obtained from an aluminium trialkyl (e.g. A1(/-C4H9)3) with vanadium trichloride. The products have a trans- content in the range 99-100%. The addition of a titanium compound of the type Ti(OR)4 is reported to improve the efficiency and increase the polymerization rate. Such a material may be considered as a synthetic gutta percha. 

The most widely used transition metal salts have been the relatively cheap titanium or vanadium halides, reduced with aluminum alkyls. In Ziegler s work, titanium tetrachloride was reduced to brown yS-titanium trichloride, which was able to polymerize ethylene. However, when yS-titanium trichloride catalyst was used in the polymerization of propylene, the product contained a high proportion of the gum like atactic polymer, which was not viable for commercial use. In contrast, Natta, in his work on the polymerization of propylene and other a-olefins, showed that violet a-titanium trichloride could polymerize propylene to the useful, crystalline, isotactic polymer. Nevertheless, a relatively large quantity of atactic polypropylene still had to be separated from the commercial isotactic product. 

Karapinka, Smith, Carrick (79) studied the use of methyltitanium trichloride as a catalyst for polyethylene. Alone it was inactive for the polymerization of polyethylene. It required the predecomposition to titanium trichloride at 120° or the addition of titanium trichloride to produce an active catalyst. Vanadium tetrachloride also produced an active catalyst. Aluminum bromide failed to activate the catalyst, whereas trialkylaluminum which reacts to produce alkylaluminum chlorides was effective. 

The use of certain vanadium compounds as catalysts has been increasing. Vanadium oxy trichloride is a catalyst in making ediylene-propylene rubber. Ammonium metavanadate and vanadium pentoxide aie used as oxidation catalysts, particularly in the production of polyamides, such as nylon, in the manufacture of H>S04 by the contact process, in the production of phdialic and maleic anhydrides, and in numerous other oxidation reactions, such as alcohol to acetaldehyde, anthracene to anthraquinone, sugar to oxalic acid, and diphenylamine to carbazole. Vanadium compounds have been used for many years 111 die ceramics field for enamels and glazes. Colors are produced by various combinations of vanadium oxide and silica, zirconia, zinc, lead, tin, selenium, and cadmium. Vanadium intermediate compounds also are used in the making of aniline Mack used by the dye industry... 

Several alkyl and aryl azides have been reduced to the corresponding amines in good yield by tin(II) chloride at room temperature the less reactive azides require a catalytic amount of aluminum trichloride to be added. Aqueous vanadium(ll) chloride is a useful reducing agent for aryl azides heteroaryl and arenesulfonyl azides have been reduced with aqueous titanium(lll) chloride and with a molybde-num(III) catalyst generated from molybdenum(V) chloride and zinc. ... 

Transition metal catalysts not only increase the reaction rate but may also affect the outcome of the oxidation, especially the stereochemistry of the products. Whereas hydrogen peroxide alone in acetonitrile oxidizes alkenes to epoxides [729], osmic acid catalyzes syn hydroxylation [736], and tungstic acid catalyzes anti hydroxylation [737]. The most frequently used catalysts are titanium trichloride [732], vanadium pentoxide [733,134], sodium vanadate [735], selenium dioxide [725], chromium trioxide [134], ammonium molybdate [736], tungsten trioxide [737], tungstic acid [737],... 

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